39 results on '"Smithsonian ForestGEO"'
Search Results
2. Predicting snag fall in an old-growth forest after fire.
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Becker, Kendall M. L. and Lutz, James A.
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FOREST fires ,FOREST succession ,FIRE management ,FOREST density ,BARK beetles ,FUELWOOD ,TREE mortality - Abstract
Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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- 2023
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3. Large-diameter trees buffer monsoonal changes to tree biomass over two decades.
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Ku, Chen-Chia, Tang, Jianwu, Chao, Wei-Chun, Chao, Kuo-Jung, Song, Guo-Zhang Michael, Lin, Huan-Yu, and Lutz, James A.
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CARBON sequestration in forests ,BIOMASS ,TREE mortality ,FOREST density ,FOREST biomass ,TREES - Abstract
Forest carbon storage inherently depends on the frequency and severity of characteristic disturbances and long-term changes in climate. The tropical forest of Lanjenchi, Taiwan is affected by the northeast monsoon wind, resulting in a varying vegetation structure depending on wind exposure. However, the northeast monsoon winds have been decreasing due to the climate change. We used four censuses over 22 years (1997, 2005, 2013, and 2019) to examine how tree density and aboveground biomass change under different levels of wind stress. We assessed tree density, aboveground biomass, aboveground woody productivity, and aboveground woody mortality from trees with diameter at breast height (DBH) ≥ 1 cm across 5.28 ha subdivided into 10 × 10 m quadrats. We tested for differences in tree density and aboveground biomass among three habitat types (windward, intermediate, and leeward), among small-diameter (1 cm ≤ DBH < 10 cm), medium-diameter (10 cm ≤ DBH < 17.2 cm) and large-diameter trees (DBH ≥ 17.2 cm). The 49,481 trees (density 9,272 ± 3612 trees ha
−1 ) of 140 species held 129.37 ± 51.95 Mg ha−1 of aboveground biomass. From 1997 to 2019, tree density decreased and aboveground biomass was stable in the whole forest. However, changes in density and aboveground biomass were apparent among different habitat types and among different diameter classes. Specifically, in the windward habitat, aboveground biomass of small-diameter trees declined over time (from 35.34 Mg ha−1 to 26.29 Mg ha−1 ), and that of large-diameter trees increased (from 48.62 Mg ha−1 to 57.78 Mg ha−1 ). In the leeward habitat, large-diameter trees exhibited both high biomass productivity (1.04 Mg ha−1 year−1 ) and mortality (1.43 Mg ha−1 year−1 ). Although the overall state of the forest appears to possess multi-decadal stability, differences in dynamics among diameter classes and habitats may lead to forest changes if trees in those habitats continue to respond differentially to shifting magnitudes of monsoon wind speed. [ABSTRACT FROM AUTHOR]- Published
- 2023
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4. Large-diameter trees and deadwood correspond with belowground ectomycorrhizal fungal richness
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Joseph D. Birch, James A. Lutz, Soren Struckman, Jessica R. Miesel, and Justine Karst
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Belowground ecology ,Ectomycorrhizal fungi ,Pinus flexilis ,Pinus longaeva ,Saprotrophic fungi ,Smithsonian ForestGEO ,Ecology ,QH540-549.5 - Abstract
Abstract Background Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure; (ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood; and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, deadwood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomycorrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and distance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi.
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- 2023
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5. Large-diameter trees and deadwood correspond with belowground ectomycorrhizal fungal richness.
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Birch, Joseph D., Lutz, James A., Struckman, Soren, Miesel, Jessica R., and Karst, Justine
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FUNGAL communities ,FOREST dynamics ,ENDANGERED species ,NATIONAL monuments ,ECTOMYCORRHIZAL fungi ,TREES - Abstract
Background: Large-diameter trees have an outsized influence on aboveground forest dynamics, composition, and structure. Although their influence on aboveground processes is well studied, their role in shaping belowground fungal communities is largely unknown. We sought to test if (i) fungal community spatial structure matched aboveground forest structure; (ii) fungal functional guilds exhibited differential associations to aboveground trees, snags, and deadwood; and (iii) that large-diameter trees and snags have a larger influence on fungal community richness than smaller-diameter trees. We used MiSeq sequencing of fungal communities collected from soils in a spatially intensive survey in a portion of Cedar Breaks National Monument, Utah, USA. We used random forest models to explore the spatial structure of fungal communities as they relate to explicitly mapped trees and deadwood distributed across 1.15 ha of a 15.32-ha mapped subalpine forest. Results: We found 6,177 fungal amplicon sequence variants across 117 sequenced samples. Tree diameter, deadwood presence, and tree species identity explained more than twice as much variation (38.7% vs. 10.4%) for ectomycorrhizal composition and diversity than for the total or saprotrophic fungal communities. Species identity and distance to the nearest large-diameter tree (≥ 40.2 cm) were better predictors of fungal richness than were the identity and distance to the nearest tree. Soil nutrients, topography, and tree species differentially influenced the composition and diversity of each fungal guild. Locally rare tree species had an outsized influence on fungal community richness. Conclusions: These results highlight that fungal guilds are differentially associated with the location, size, and species of aboveground trees. Large-diameter trees are implicated as drivers of belowground fungal diversity, particularly for ectomycorrhizal fungi. [ABSTRACT FROM AUTHOR]
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- 2023
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6. Climate warming may weaken stabilizing mechanisms in old forests.
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Germain, Sara J. and Lutz, James A.
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OLD growth forests , *COEXISTENCE of species , *PLANT competition , *NUMBERS of species , *FOREST biodiversity , *COMPETITION (Biology) , *TREE mortality , *TEMPERATE forests - Abstract
Plant competition may intensify with climate warming, but whether this will occur equally for conspecific and heterospecific competition remains unknown. Competitive shifts have the potential to instigate community change because the relative strengths of conspecific and heterospecific negative density dependence mediate the stabilizing mechanisms underpinning species coexistence. We examined a mature temperate forest to assess both direct and indirect climate effects at multiple scales: individual species, interspecies relationships, and community stability mechanisms. Our coupled approach (1) quantified tree mortality risk dependence on the interactive effects of competition, climatic water deficit, snowpack, and soil moisture for 28,913 trees over 8 years (3149 mortalities), then (2) used a climate‐projection ensemble to forecast changes in conspecific and heterospecific competition from 2020 to 2100. We predict that projected climate warming will destabilize the foundational forest community by increasing the strength of heterospecific competition at a greater rate and to a greater degree than conspecific competition for four of five abundant tree species, particularly on dry microsites. Modeling showed that these findings were most pronounced after the year 2038, at which point snowpacks were projected to be too small to ameliorate the effects of drought on competitive interactions. Our finding that heterospecific competition is more sensitive than conspecific competition to climate warming may indicate the impending loss of ecosystem functioning. We join the growing body of work showing a predominance of indirect drought effects, yet coupled climate models still fail to consider how changing community dynamics may impact forest cover and, in turn, disrupt forest–climate carbon feedbacks. Ecosystems sharing characteristics with our example forest—those with low species richness and therefore a limited biodiversity insurance effect—may be similarly vulnerable to climate‐mediated destabilization. In such communities, increased heterospecific competition among even a small number of species can more easily destabilize communities without recourse from redundant species. This study of an overlooked but vital mechanism of community change can be adapted by research in a range of ecosystems to improve the understanding of climate change consequences. [ABSTRACT FROM AUTHOR]
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- 2022
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7. Large‐diameter trees affect snow duration in post‐fire old‐growth forests.
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Teich, Michaela, Becker, Kendall M. L., Raleigh, Mark S., and Lutz, James A.
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POST-fire forests ,SNOW accumulation ,TREE mortality ,TREES ,SOLAR radiation ,CHESTNUT - Abstract
Snow duration in post‐fire forests is influenced by neighbourhoods of trees, snags, and deadwood. We used annually resolved, spatially explicit tree and tree mortality data collected in an old‐growth, mixed‐conifer forest in the Sierra Nevada, California, that burned at low to moderate severity to calculate 10 tree neighbourhood metrics for neighbourhoods up to 40 m from snow depth and snow disappearance sampling points. We developed two linear mixed models, predicting snow disappearance timing as a function of tree neighbourhood, litter density, and simulated incoming solar radiation, and two multiple regression models explaining variation in snow depth as a function of tree neighbourhood. Higher densities of post‐fire large‐diameter snags within 10 m of a sampling point were related to higher snow depth (indicating reduced snow interception). Higher densities of large‐diameter trees within 5 m and larger amounts of litter were associated with shorter snow duration (indicating increased longwave radiation emittance and accelerated snow albedo decay). However, live trees with diameters >60 cm within 10 m of a snow disappearance sampling point were associated with a longer‐lasting spring snowpack. This suggests that, despite the local effects of canopy interception and emitted longwave radiation from boles of large trees, shading from their canopies may prolong snow duration over a larger area. Therefore, conservation of widely spaced, large‐diameter trees is important in old‐growth forests because they are resistant to fire and can enhance the seasonal duration of snowmelt. [ABSTRACT FROM AUTHOR]
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- 2022
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8. Large-diameter trees dominate snag and surface biomass following reintroduced fire
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James A. Lutz, Soren Struckman, Tucker J. Furniss, C. Alina Cansler, Sara J. Germain, Larissa L. Yocom, Darren J. McAvoy, Crystal A. Kolden, Alistair M. S. Smith, Mark E. Swanson, and Andrew J. Larson
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California Rim Fire ,Fuel reduction ,Sierra Nevada mixed-conifer ,Smithsonian ForestGEO ,Yosemite Forest Dynamics Plot ,Yosemite National Park ,Ecology ,QH540-549.5 - Abstract
Abstract The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics, including reducing tree density and decreasing levels of woody biomass on the forest floor. However, reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass, with potential impacts to fuel accumulation, carbon sequestration, subsequent fire severity, and forest management. In this study, we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation, carbon sequestration, and subsequent fire severity potential. Beginning pre-fire, and continuing 6 years post-fire, we tracked all live, dead, and fallen trees ≥ 1 cm in diameter and mapped all pieces of deadwood (downed woody debris) originating from tree boles ≥ 10 cm diameter and ≥ 1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada, California, USA. We also tracked surface fuels along 2240 m of planar transects pre-fire, immediately post-fire, and 6 years post-fire. Six years after moderate-severity fire, deadwood ≥ 10 cm diameter was 73 Mg ha−1, comprised of 32 Mg ha−1 that persisted through fire and 41 Mg ha−1 of newly fallen wood (compared to 72 Mg ha−1 pre-fire). Woody surface fuel loading was spatially heterogeneous, with mass varying almost four orders of magnitude at the scale of 20 m × 20 m quadrats (minimum, 0.1 Mg ha−1; mean, 73 Mg ha−1; maximum, 497 Mg ha−1). Wood from large-diameter trees (≥ 60 cm diameter) comprised 57% of surface fuel in 2019, but was 75% of snag biomass, indicating high contributions to current and future fuel loading. Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels ≥ 10 cm diameter within 6 years. Repeated fires are needed to reduce surface fuel loading.
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- 2020
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9. Climate extremes may be more important than climate means when predicting species range shifts.
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Germain, Sara J. and Lutz, James A.
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CLIMATE extremes ,CLIMATE change ,CLIMATOLOGY ,SPECIES distribution ,SURVIVAL analysis (Biometry) - Abstract
It is well known that temperatures across the globe are rising, but climatic conditions are becoming more variable as well. Forecasts of species range shifts, however, often focus on average climatic changes while ignoring increasing climatic variability. In particular, many species distribution models use space-for-time substitution, which focuses exclusively on the effect of average climatic conditions on the target species across a geographic range, and is blind to the possibility of range-wide population collapse with increasing drought frequency, drought severity, or climate effects on other co-occurring species. Relegated to assessments of broad demographic patterns that ignore underlying biological responses to increasing climatic variability, this prevalent method of distribution forecasting may systematically underpredict climate change impacts. We compare six models of survival and abundance of a subcanopy tree species, Taxus brevifolia, over 40 years of past climate change to disentangle multiple sources of uncertainty: model formulation, scale of climate effect, and level of biological organization. We show that drought extremes increased Taxus individual- and population-scale mortality across a wide geographic climate gradient, precluding detection of a monotonic relationship with average climate. Individual-scale climatic extremes models derived from longitudinal data had the highest predictive accuracy (82%), whereas mean climate models had the lowest accuracy (< 65%). Our results highlight that conclusions drawn from forecasts of average warming alone likely underpredict climate change impacts by ignoring indicators of range-wide population declines for species sensitive to increasing climatic variability. [ABSTRACT FROM AUTHOR]
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- 2020
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10. Wildfire and drought moderate the spatial elements of tree mortality.
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Furniss, Tucker J., Larson, Andrew J., Kane, Van R., and Lutz, James A.
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TREE mortality ,FOREST declines ,DROUGHT management ,DROUGHTS ,WILDFIRES ,FIRE management ,FOREST dynamics ,BARK beetles - Abstract
Background tree mortality is a complex process that requires large sample sizes and long timescales to disentangle the suite of ecological factors that collectively contribute to tree stress, decline, and eventual mortality. Tree mortality associated with acute disturbance events, in contrast, is conspicuous and frequently studied, but there remains a lack of research regarding the role of background mortality processes in mediating the severity and delayed effects of disturbance. We conducted an empirical study by measuring the rates, causes, and spatial pattern of mortality annually among 32,989 individual trees within a large forest demography plot in the Sierra Nevada. We characterized the relationships between background mortality, compound disturbances (fire and drought), and forest spatial structure, and we integrated our findings with a synthesis of the existing literature from around the world to develop a conceptual framework describing the spatio‐temporal signatures of background and disturbance‐related tree mortality. The interactive effects of fire, drought, and background mortality processes altered the rate, spatial structuring, and ecological consequences of mortality. Before fire, spatially non‐random mortality was only evident among small (1 < cm DBH ≤ 10)‐ and medium (10 < cm DBH ≤ 60)‐diameter classes; mortality rates were low (1.7% per yr), and mortality was density‐dependent among small‐diameter trees. Direct fire damage caused the greatest number of moralities (70% of stems ≥1 cm DBH), but the more enduring effects of this disturbance on the demography and spatial pattern of large‐diameter trees occurred during the post‐fire mortality regime. The combined effects of disturbance and biotic mortality agents provoked density‐dependent mortality among large‐diameter (≥60 cm DBH) trees, eliciting a distinct post‐disturbance mortality regime that did not resemble the pattern of either pre‐fire mortality or direct fire effects. The disproportionate ecological significance of the largest trees renders this mortality regime acutely consequential to the long‐term structure and function of forests. [ABSTRACT FROM AUTHOR]
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- 2020
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11. Large-diameter trees dominate snag and surface biomass following reintroduced fire.
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Lutz, James A., Struckman, Soren, Furniss, Tucker J., Cansler, C. Alina, Germain, Sara J., Yocom, Larissa L., McAvoy, Darren J., Kolden, Crystal A., Smith, Alistair M. S., Swanson, Mark E., and Larson, Andrew J.
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WILDLIFE reintroduction ,COARSE woody debris ,FOREST dynamics ,TREE mortality ,FOREST management ,FOREST density ,FOREST biomass - Abstract
The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics, including reducing tree density and decreasing levels of woody biomass on the forest floor. However, reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass, with potential impacts to fuel accumulation, carbon sequestration, subsequent fire severity, and forest management. In this study, we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation, carbon sequestration, and subsequent fire severity potential. Beginning pre-fire, and continuing 6 years post-fire, we tracked all live, dead, and fallen trees ≥ 1 cm in diameter and mapped all pieces of deadwood (downed woody debris) originating from tree boles ≥ 10 cm diameter and ≥ 1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada, California, USA. We also tracked surface fuels along 2240 m of planar transects pre-fire, immediately post-fire, and 6 years post-fire. Six years after moderate-severity fire, deadwood ≥ 10 cm diameter was 73 Mg ha
−1 , comprised of 32 Mg ha−1 that persisted through fire and 41 Mg ha−1 of newly fallen wood (compared to 72 Mg ha−1 pre-fire). Woody surface fuel loading was spatially heterogeneous, with mass varying almost four orders of magnitude at the scale of 20 m × 20 m quadrats (minimum, 0.1 Mg ha−1 ; mean, 73 Mg ha−1 ; maximum, 497 Mg ha−1 ). Wood from large-diameter trees (≥ 60 cm diameter) comprised 57% of surface fuel in 2019, but was 75% of snag biomass, indicating high contributions to current and future fuel loading. Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels ≥ 10 cm diameter within 6 years. Repeated fires are needed to reduce surface fuel loading. [ABSTRACT FROM AUTHOR]- Published
- 2020
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12. Burn weather and three-dimensional fuel structure determine post-fire tree mortality.
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Jeronimo, Sean M. A., Lutz, James A., R. Kane, Van, Larson, Andrew J., and Franklin, Jerry F.
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TREE mortality ,POST-fire forests ,FUEL ,ECOLOGICAL resilience ,WEATHER ,BIOLOGICAL dressings - Abstract
Context: Post-fire tree mortality is a spatially structured process driven by interacting factors across multiple scales. However, empirical models of fire-caused tree mortality are generally not spatially explicit, do not differentiate among scales, and do not differentiate immediate from delayed mortality. Objectives: We aimed to quantify cross-scale linkages between forest structure—including spatial patterns of trees—and the progression of mortality 1–4 years post-fire in terms of rates, causes, and underlying demography. Methods: We used data from a long-term study site in the Sierra Nevada, California to build a post-fire tree mortality model predicted by lidar-measured estimates of structure. We calculated structural metrics at scales from individual trees to 90 × 90 m neighborhoods and combined them with metrics for topography, site water balance, and burn weather to predict immediate and delayed post-fire tree mortality. Results: Mortality rates decreased while average diameter of newly killed trees increased each year post-fire. Burn weather predictors as well as interactive terms across scales improved model fit and parsimony. Including landscape-scale information improved finer-scale predictions but not vice versa. The amount of fuel, fuel configuration, and burning conditions predicted total mortality at broader scales while tree group-scale fuel connectivity, tree species fire tolerance, and local stresses predicted the fine-scale distribution, timing, and agents of mortality. Conclusions: Landscape-scale conditions provide the template upon which finer-scale variation in post-fire tree mortality is arranged. Post-fire forest structure is associated with the etiologies of different mortality agents, and so landscape-level heterogeneity is a key part of ecosystem stability and resilience. [ABSTRACT FROM AUTHOR]
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- 2020
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13. Patterns of nitrogen‐fixing tree abundance in forests across Asia and America.
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Menge, Duncan N. L., Chisholm, Ryan A., Davies, Stuart J., Abu Salim, Kamariah, Allen, David, Alvarez, Mauricio, Bourg, Norm, Brockelman, Warren Y., Bunyavejchewin, Sarayudh, Butt, Nathalie, Cao, Min, Chanthorn, Wirong, Chao, Wei‐Chun, Clay, Keith, Condit, Richard, Cordell, Susan, Silva, João Batista, Dattaraja, H. S., Andrade, Ana Cristina Segalin, and Oliveira, Alexandre A.
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NITROGEN fixation , *TROPICAL forests , *ASIAN Americans , *TEMPERATE forests , *TREES , *BASAL area (Forestry) - Abstract
Symbiotic nitrogen (N)‐fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N‐fixing trees are well characterised in the Americas, but less well outside the Americas.Here, we characterised the abundance of N‐fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N‐fixing trees was correlated with mean annual temperature and precipitation.Outside the tropics, N‐fixing trees were consistently rare in the forest plots we examined. Within the tropics, N‐fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N‐fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N‐fixing tree abundance between the Asian and American tropics.Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N‐fixing trees. By analysing a large dataset of ~4 million trees, we found that N‐fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N‐fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N‐fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought. [ABSTRACT FROM AUTHOR]
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- 2019
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14. Determinants of spatial patterns of canopy tree species in a tropical evergreen forest in Gabon.
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Engone Obiang, Nestor Laurier, Kenfack, David, Picard, Nicolas, Lutz, James A., Bissiengou, Pulchérie, Memiaghe, Hervé R., Alonso, Alfonso, and Nakashizuka, Tohru
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TROPICAL forests , *SEED treatment , *FOREST density , *POISSON processes , *SPECIES , *SEED dispersal , *SPECIES distribution , *YOUNG adults - Abstract
Questions: We examined the spatial patterns of dominant canopy species in a tropical forest to investigate: (a) what is the niche occupancy of canopy species with respect to topographic gradients; (b) what are the dominant ecological processes that explain their distribution; (c) what are the interactions among the most prevalent canopy species; and (d) what are the interactions between canopy species adults and juveniles trees? Location: Rabi permanent CTFS‐ForestGEO plot, Gabon. Methods: We selected the four most abundant canopy species and one timber species. We used Berman's test to determine the effect of three topographic variables on the distribution of each species and univariate analysis to model the spatial pattern of each species using either an inhomogeneous Poisson process or an inhomogeneous Cox process. We also used a bivariate form of the pair correlation function (PCF) to determine the spatial interaction between species and the correlation among conspecific adult and juvenile trees. Results: Four of the five species had aggregated spatial patterns while Lophira alata showed spatial randomness. Most of the variance in the local tree density was explained by within‐population dispersal processes rather than environmental factors. Bivariate PCF tests showed significant segregation between species associations. Two species exhibited aggregation at small distances between young and adult trees, while others showed either complete spatial randomness at small inter‐tree distances or segregation at large distances. Conclusions: This study showed that the spatial pattern in the majority of canopy species was aggregation. Seed dispersal limitation mainly explained the observed aggregation pattern. Habitat filtering, as evidenced by the influence of topographic variables on niche occupancy, marginally, yet significantly, explained this pattern. The different spatial patterns of the principal species permit their coexistence. Spatial segregation among adult and juvenile trees reveals a strong pattern of either species‐specific seed predation or pathogens. [ABSTRACT FROM AUTHOR]
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- 2019
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15. The importance of small fire refugia in the central Sierra Nevada, California, USA.
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Blomdahl, Erika M., Kolden, Crystal A., Meddens, Arjan J.H., and Lutz, James A.
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FOREST fires ,TREE mortality ,FOREST management ,POST-fire forests ,RANDOM forest algorithms - Abstract
Graphical abstract Highlights • Small (1 m
2 ≤ area ≤ 900 m2 ) unburned patches occupied 5% of the area burned. • Areas with all fire severity classifications contained small unburned patches. • Tree survival was higher when trees were rooted in an unburned patch. • Small tree survival was higher towards the interior of unburned patches. Abstract Fire refugia – the unburned areas within fire perimeters – are important to the survival of many taxa through fire events and the revegetation of post-fire landscapes. Previous work has shown that species use and benefit from small-scale fire refugia (1–1000 m2 ), but our understanding of where and how fire refugia form is largely limited to the scale of remotely sensed data (i.e., 900 m2 Landsat pixels). To examine the causes and consequences of small fire refugia, we field-mapped all unburned patches ≥1 m2 within a contiguous 25.6 ha forest plot that burned at generally low-to-moderate severity in the 2013 Yosemite Rim Fire, California, USA. Within the Yosemite Forest Dynamics Plot (YFDP), there were 685 unburned patches ≥1 m2 , covering a total unburned area of 12,597 m2 (4.9%). Small refugia occurred in all fire severity classifications. Random forest models showed that the proportion of unburned area of 100 m2 grid cells corresponded to pre-fire density and basal area of trees, distance to the nearest stream, and immediate fire mortality, but the relationships were complex and model accuracy was variable. From a pre-fire population of 34,061 total trees ≥1 cm diameter at breast height (1.37 m; DBH) within the plot (1330 trees ha−1 ), trees of all five of the most common species and those DBH < 30 cm had higher immediate survival rates if their boles were wholly or partially within an unburned patch (P ≤ 0.001). Trees 1 cm ≤ DBH < 10 cm that survived were located closer to the center of the unburned patch than the edge (mean 1.1 m versus 0.6 m; ANOVA; P ≤ 0.001). Four-year survival rates for trees 1 cm ≤ DBH < 10 cm were 58.8% within small refugia and 2.7% in burned areas (P ≤ 0.001). Species richness and the Shannon Diversity Index were associated with unburned quadrats in NMDS ordinations 3 years post-fire. Burn heterogeneity in mixed-conifer forests likely exists at all scales and small refugia contribute to diversity of forest species and structures. Thus, managers may wish to consider scales from 1-m2 to the landscape when designing fuel reduction prescriptions. The partial predictability of refugia location suggests that further work may lead to predictive models of refugial presence that have considerable potential to preserve ecological function or human habitation in fire-frequent forests. [ABSTRACT FROM AUTHOR]- Published
- 2019
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16. Multi-scale assessment of post-fire tree mortality models.
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Furniss, Tucker J., Larson, Andrew J., Kane, Van R., and Lutz, James A.
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TREE mortality ,FOREST fires ,GYMNOSPERMS - Abstract
Post-fire tree mortality models are vital tools used by forest land managers to predict fire effects, estimate delayed mortality and develop management prescriptions. We evaluated the performance of mortality models within the First Order Fire Effects Model (FOFEM) software, and compared their performance to locally-parameterised models based on five different forms. We evaluated all models at the individual tree and stand levels with a dataset comprising 34 174 trees from a mixed-conifer forest in the Sierra Nevada, California that burned in the 2013 Rim Fire. We compared stand-level accuracy across a range of spatial scales, and we used point pattern analysis to test the accuracy with which mortality models predict post-fire tree spatial pattern. FOFEM under-predicted mortality for the three conifers, possibly because of the timing of the Rim Fire during a severe multi-year drought. Locally-parameterised models based on crown scorch were most accurate in predicting individual tree mortality, but tree diameter-based models were more accurate at the stand level for Abies concolor and large-diameter Pinus lambertiana , the most abundant trees in this forest. Stand-level accuracy was reduced by spatially correlated error at small spatial scales, but stabilised at scales ≥1 ha. The predictive error of FOFEM generated inaccurate predictions of post-fire spatial pattern at small scales, and this error could be reduced by improving FOFEM model accuracy for small trees. We conducted an evaluation of post-fire tree mortality models with the largest sample to date, and we summarised model accuracy at multiple scales. We found that First Order Fire Effects Models generally had high accuracy for gymnosperms, but accuracy was poor for angiosperms. Fire-related mortality was elevated because of severe multi-year drought, and we provide new mortality models with improved accuracy for fires that occur during drought. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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17. Differences in regeneration niche mediate how disturbance severity and microclimate affect forest species composition.
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Becker, Kendall M.L. and Lutz, James A.
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DROUGHTS ,FOREST dynamics ,TREE mortality ,SPECIES ,FOREST fires ,SOIL mineralogy ,FIR ,SEEDLINGS ,CLIMATE change - Abstract
• Disturbance severity and snow duration have species-specific effects on seedlings. • Lower substrate burn severity disadvantaged Abies concolor seedlings. • Earlier snowmelt in the germination year decreased Abies concolor survival. • Post-fire compositional shifts toward drought-tolerant Pinus species are possible. Climate change is altering forest composition through species-specific responses to fire and drought. Future forest composition will depend on how the different regeneration niches of co-occurring species align with current environmental conditions, especially after fire, which can promote germination by exposing mineral soil. Few studies, however, have examined the effects of disturbance severity and microclimate on post-fire regeneration to define and compare the regeneration niches of co-occurring tree species. We used seven years of annual demography and microenvironment data from a 25.6-ha fully censused, stem-mapped forest dynamics plot in California, USA, to examine how disturbance severity, snow duration, and temperature extremes affect the survival of Abies concolor and Pinus lambertiana seedlings that germinated naturally after a low- to moderate-severity fire. We defined disturbance severity at the microsite level, based on characteristics of the substrate, and at the neighborhood level, based on tree mortality. Both disturbance severity and snow duration had species-specific effects on seedling survival, but these differed by life stage. During the germination year, later snow disappearance was associated with a 0.5 increase in survival probability for A. concolor but hardly affected P. lambertiana ; in contrast, higher neighborhood disturbance severity increased survival of both species. After the germination year, higher substrate burn severity was associated with a 0.8 increase in survival probability for A. concolor but hardly affected P. lambertiana ; higher neighborhood disturbance severity and later snow disappearance increased annual survival of both species, but maximum summer temperature had minimal effect. Overall, available seed, higher substrate burn severity, higher neighborhood disturbance severity, and later snow disappearance promoted natural regeneration. However, lower substrate burn severity and earlier snow disappearance in the germination year disadvantaged A. concolor seedlings, increasing the relative abundance of P. lambertiana seedlings compared to the local tree population. Our results indicate that natural post-fire compositional shifts toward drought-tolerant Pinus species–and away from less drought-tolerant Abies species–are possible in the Sierra Nevada, with potential benefits for forest persistence under climate change. Broadly, we show that species differences in regeneration niches shape how disturbance severity and microclimate affect forest species composition. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
18. Old-Growth Forest Dynamics After Fire and Drought in the Sierra Nevada, California, USA
- Author
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Becker, Kendall M.L.
- Subjects
Pinus contorta ,regeneration niche ,Abies concolor ,low‐severity fire ,Calocedrus decurrens ,snag persistence ,post‐fire seedlings ,Pinus jeffreyi ,Smithsonian ForestGEO ,old‐growth forest ,Yosemite National Park ,Pinus ponderosa ,post‐fire growth ,snag dynamics ,Abies magnifica ,moderate‐severity fire ,snag fall ,Yosemite Forest Dynamics Plot ,Pinus lambertiana ,Sequoia & Kings Canyon National Park ,growth rate ,Rim fire ,prescribed fire ,Environmental Sciences - Abstract
Understanding forest ecosystems is important because forests cover approximately one-third of Earth’s land area, store half of Earth’s carbon, shelter half of Earth’s species, and absorb a quarter of new anthropogenic carbon emissions, slowing climate change. This dissertation provides insight into future forest habitat, fuels, species composition, and structure by investigating what happens to snags, seedlings, and trees in an old-growth forest after a low- to moderate-severity fire. Chapter II explores how low- to moderate-severity fire changes snag fall rates. Predicting how long snags will remain standing after fire is essential for managing habitat, understanding chemical cycling in forests, and modeling forest succession and fuels. Pre-fire snags––which tend to be preferred habitat because they include more large-diameter snags in advanced stages of decay––were at least twice as likely to fall as new snags within 3–5 years after fire. Pre-existing snags were most likely to persist five years after fire if they were > 50 cm in diameter, > 20 m tall, and charred on the trunk to heights above 3.7 m. Chapter III examines the effects of fire severity and microclimate on conifer regeneration after fire. Available seed, lower burn severity on the forest floor, more fire-caused tree mortality, and earlier snowmelt during the germination year gave Pinus lambertiana seedlings an advantage over Abies concolor seedlings, suggesting that lower-severity fire could naturally shift forest species composition toward Pinus species, which are more resistant to fire and drought. Chapter IV investigates the effects of lower-severity fire on tree growth by analyzing the tree-ring widths of seven mixed-conifer species throughout the Sierra Nevada. Post-fire growth patterns were not substantially different from growth fluctuations at adjacent unburned plots, suggesting that reintroducing lower-severity fire to forests where fire has been excluded over the last century will not prevent surviving trees from attaining pre-fire growth rates within five years after fire. Chapter V focuses on recruitment of large-diameter trees after fire, analyzing how local post-fire mortality within tree neighborhoods impacts post-fire radial growth of surviving trees. Cause of mortality influenced the relationship between neighborhood change and the growth of surviving trees, and this relationship was different for A. concolor compared to P. lambertiana, suggesting that species differences in cause of mortality could affect the species composition of future large-diameter tree populations. These findings demonstrate that low- to moderate-severity fire can promote Pinus seedlings and trees, exemplifying the concept that ecosystems shift toward species composition and structure that maximize resilience to challenging climate and disturbance regimes. This research was possible because of the existence of a long-term, spatially explicit, observational old-growth forest dataset with annual resolution.
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- 2022
19. Soil Enzyme Activity and Soil Nutrients Jointly Influence Post-Fire Habitat Models in Mixed-Conifer Forests of Yosemite National Park, USA
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Jelveh Tamjidi and James A. Lutz
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dispersal limitation ,habitat filtering ,soil enzymes ,Smithsonian ForestGEO ,species–habitat association ,Yosemite Forest Dynamics Plot ,Physics ,QC1-999 - Abstract
Disentangling the relative importance of habitat filtering and dispersal limitations at local scales (2) in shaping species composition remains an important question in community ecology. Previous studies have examined the relative importance of these mechanisms using topography and selected soil properties. We examined both topography and edaphic properties from 160 locations in the recently burned 25.6 ha Yosemite Forest Dynamics Plot (YFDP) in Yosemite National Park, California, USA. In addition to eight soil chemical properties, we included phosphatases and urease enzymes in a definition of habitat niches, primarily because of their rapid changes with fire (compared to soil nutrients) and also their role in ecosystem function. We applied environmental variables to the distributions of 11 species. More species–habitat associations were defined by soil properties (54.5%) than topographically-defined habitat (45.4%). We also examined the relative importance of spatial and environmental factors in species assemblage. Proportions explained by spatial and environmental factors differed among species and demographic metrics (stem abundance, basal area increment, mortality, and recruitment). Spatial factors explained more variation than environmental factors in stem abundance, mortality, and recruitment. The contributions of urease and acid phosphatase to habitat definition were significant for species abundance and basal area increment. These results emphasize that a more complete understanding of niche parameters is needed beyond simple topographic factors to explain species habitat preference. The stronger contribution of spatial factors suggests that dispersal limitation and unmeasured environmental variables have high explanatory power for species assemblage in this coniferous forest.
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- 2020
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20. Hidden Mechanisms of Climate Impacts in Western Forests: Integrating Theory and Observation for Climate Adaptation
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Germain, Sara J.
- Subjects
plant-soil feedbacks ,longitudinal data ,Ecology and Evolutionary Biology ,coexistence ,population decline ,Life Sciences ,multitrophic interactions ,drought ,permanent sample plots ,Utah Forest Dynamics Plot ,Smithsonian ForestGEO ,facilitation ,stabilization ,climate change ,Yosemite Forest Dynamics Plot ,bark beetles ,mycorrhizae ,competition ,associational resistance ,fire ,biodiversity ,Wind River Forest Dynamics Plot - Abstract
Fire, insects, and disease are necessary components of forest ecosystems. Yet, climate change is intensifying these tree stressors and creating new interactions that threaten forest survival. This dissertation combined field observations with statistical predictions of changing disturbances in western forests to identify 1) how conventional models may underestimate future forest loss, and 2) how positive relationships between trees may be exploited by managers to prevent forest loss. In Chapter II, I tested whether increasingly extreme weather with climate change increases Pacific yew extinction risk. I found that conventional modeling methods underestimated local extinction risk because trees were adapted to a range in average conditions, but had limited tolerance of extreme drought. In Chapter III, I predicted whether future climate change will alter the strength of competition between species (heterospecifics) versus within species (conspecifics). I found that heterospecific competition is more sensitive to drought than conspecific competition, leading to higher tree mortality during drought than is currently expected. In Chapter IV, I looked at sugar pine tree rings to measure how pines respond to three centuries of fire exclusion, drought, fire, and a bark beetle outbreak. I found that fire suppression led to higher competitive stress, which decreased pines’ resilience to fire, and consequently, decreased pines’ survival during a subsequent bark beetle outbreak. Woody species diversity, however, was able to increase pine survival following fire and bark beetles by allowing higher pine growth and defenses. In Chapter V, I tested whether beneficial relationships between trees and mutualistic fungi could help trees survive across regional differences in climate, environmental conditions, and disturbances. I found that woody species diversity increased large-diameter tree resistance to insects and disease, but only if those species shared a mycorrhizal network. Large trees comprising 17 common western species across three canonical forest types showed this pattern –– despite residing in different topographic positions and climatological contexts. I identified how biodiversity can increase forest resistance and resilience to disturbances, but also found climate change to be weakening the processes responsible for maintaining biodiversity. Managers must take a more active approach to cultivating and preserving forest tree biodiversity to ensure forests are able to continue provisioning essential services, such as carbon storage, in the future. These four long-term studies of spatially explicit, cause-specific tree mortality provided useful insights into tree survival and forest change that will improve vegetation model accuracy and inform management of mature forests in western North America.
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- 2022
21. Global importance of large-diameter trees.
- Author
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Lutz, James A., Furniss, Tucker J., Johnson, Daniel J., Davies, Stuart J., Allen, David, Alonso, Alfonso, Anderson-Teixeira, Kristina J., Andrade, Ana, Baltzer, Jennifer, Becker, Kendall M. L., Blomdahl, Erika M., Bourg, Norman A., Bunyavejchewin, Sarayudh, Burslem, David F. R. P., Cansler, C. Alina, Cao, Ke, Cao, Min, Cárdenas, Dairon, Chang, Li-Wan, and Chao, Kuo-Jung
- Subjects
- *
SPECIES diversity , *FOREST density , *GLOBAL environmental change , *FOREST biomass , *FOREST conservation - Abstract
Aim: To examine the contribution of large-diameter trees to biomass, stand structure, and species richness across forest biomes. Location: Global. Time period: Early 21st century. Major taxa studied: Woody plants. Methods: We examined the contribution of large trees to forest density, richness and biomass using a global network of 48 large (from 2 to 60 ha) forest plots representing 5,601,473 stems across 9,298 species and 210 plant families. This contribution was assessed using three metrics: the largest 1% of trees ≥ 1 cm diameter at breast height (DBH), all trees ≥ 60 cm DBH, and those rank-ordered largest trees that cumulatively comprise 50% of forest biomass. Results: Averaged across these 48 forest plots, the largest 1% of trees ≥ 1 cm DBH comprised 50% of aboveground live biomass, with hectare-scale standard deviation of 26%. Trees ≥ 60 cm DBH comprised 41% of aboveground live tree biomass. The size of the largest trees correlated with total forest biomass (r2=.62, p<.001). Large-diameter trees in high biomass forests represented far fewer species relative to overall forest richness (r2=.45, p<.001). Forests with more diverse large-diameter tree communities were comprised of smaller trees (r2=.33, p<.001). Lower largediameter richness was associated with large-diameter trees being individuals of more common species (r2=.17, p5.002). The concentration of biomass in the largest 1% of trees declined with increasing absolute latitude (r2=.46, p<.001), as did forest density (r2=.31, p<.001). Forest structural complexity increased with increasing absolute latitude (r2=.26, p<.001). Main conclusions: Because large-diameter trees constitute roughly half of the mature forest biomass worldwide, their dynamics and sensitivities to environmental change represent potentially large controls on global forest carbon cycling. We recommend managing forests for conservation of existing large-diameter trees or those that can soon reach large diameters as a simple way to conserve and potentially enhance ecosystem services. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
22. Individual species–area relationships in temperate coniferous forests.
- Author
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Das, Adrian J., Larson, Andrew J., and Lutz, James A.
- Subjects
- *
REGRESSION analysis , *BIOMETRY , *CONIFEROUS forests , *ANALYSIS of variance , *BAYESIAN analysis - Abstract
Abstract: Questions: What drives individual species–area relationships in temperate coniferous forests? Location: Two 25.6‐ha forest plots on the Pacific Slope of North America, one in California, and one in Washington State. Methods: We mapped all trees ≥1 cm in diameter and examined tree species diversity of their local neighbourhoods by calculating the individual species–area relationship for each species and for each of three diameter classes (saplings, mature trees and large‐diameter trees). Results: In the California plot, small trees in four of the five major species occurred in neighbourhoods with higher levels of diversity than would be expected at random. In the Washington plot, small trees for four of five abundant species had neighbourhoods with lower than expected diversity at distances ≤5 m for small trees. However, at distances >5 m, all five species showed higher than expected diversity in their neighbourhoods. Larger trees at both plots tended to occur in neighbourhoods with lower than expected diversity, and no large‐diameter focal species had neighbourhoods with higher than expected diversity. Conclusion: Diversity and co‐existence in temperate conifer‐dominated forests do not appear to be the result of random processes. Competitive interactions appear to dominate for the largest trees of most species, resulting in neighbourhoods with lower diversity. For smaller trees, we suggest that a positive response to environmental heterogeneity is the likely driver of neighbourhoods with higher than expected diversity, although we cannot rule out the possibility that facilitation or conspecific negative density dependence (CNDD) also play a role. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
23. Spatial patterns of seedlings dominated by proximity to deadwood and adult trees for Pinus flexilis and Pinus longaeva.
- Author
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Birch, Joseph D. and Lutz, James A.
- Subjects
PINE ,TREES ,TREE seedlings ,SOIL mineralogy ,SPECIES distribution ,POTASSIUM ,SEEDLINGS - Abstract
• Seedlings were highly aggregated 0 – 2.5 m around deadwood and mature adult trees. • Distance to deadwood was the most influential factor for Pinus flexilis seedlings. • Distance to mature Pinus longaeva was highly influential for P. longaeva seedlings. • Mature trees had similar habitat requirements and spatial patterns as seedlings. The spatial patterns of trees are a defining feature of forests, yet because of the long lifespan of trees, the full origins of these spatial patterns remain unclear. We used 15.6 ha of a mapped forest plot to assess the local habitat characteristics and spatial structure of 1,550 naturally established seedlings and 1,955 adults of Pinus flexilis (limber pine) and Pinus longaeva (Great Basin bristlecone pine) in southern Utah, USA. For both species, proximity to deadwood (large end diameter ≥ 10 cm) and mature trees were key parameters of habitat, likely indicating abiotic or biotic facilitation. Both seedlings and mature trees were highly aggregated 0.0–2.5 m around large pieces of deadwood, which can persist in this ecosystem for centuries or millennia. Seedlings were most often located around deadwood 15–22 cm in diameter, though deadwood size had little influence on the distance at which seedlings established. Seedlings of both P. flexilis and P. longaeva were abundant near heterospecific adult Pinus. The elevational distribution of seedlings and adults of both species were not different, indicating a regeneration niche similar to the niche of mature trees and also that changing climate at this site has not yet affected species distributions. Low amounts of manganese and higher levels of pH and potassium in the mineral soil were associated with P. longaeva seedlings but were less important for P. flexilis. Edaphic patterns combined with the presence of deadwood define the overlap between seedling and mature species habitat and identify the key drivers influencing the spatial structure in this high-elevation, old-growth forest. Likely, persistence of these two Pinus species as well as regeneration or site colonization is more favorable in the presence of large deadwood. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
24. Species Diversity Associated with Foundation Species in Temperate and Tropical Forests
- Author
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Aaron M. Ellison, Hannah L. Buckley, Bradley S. Case, Dairon Cardenas, Álvaro J. Duque, James A. Lutz, Jonathan A. Myers, David A. Orwig, and Jess K. Zimmerman
- Subjects
abundance ,Bray-Curtis ,codispersion analysis ,Smithsonian ForestGEO ,Shannon diversity ,Simpson diversity ,spatial analysis ,species richness ,Plant ecology ,QK900-989 - Abstract
Foundation species define and structure ecological communities but are difficult to identify before they are declining. Yet, their defining role in ecosystems suggests they should be a high priority for protection and management while they are still common and abundant. We used comparative analyses of six large forest dynamics plots spanning a temperate-to-tropical gradient in the Western Hemisphere to identify statistical “fingerprints„ of potential foundation species based on their size-frequency and abundance-diameter distributions, and their spatial association with five measures of diversity of associated woody plant species. Potential foundation species are outliers from the common “reverse-J„ size-frequency distribution, and have negative effects on alpha diversity and positive effects on beta diversity at most spatial lags and directions. Potential foundation species also are more likely in temperate forests, but foundational species groups may occur in tropical forests. As foundation species (or species groups) decline, associated landscape-scale (beta) diversity is likely to decline along with them. Preservation of this component of biodiversity may be the most important consequence of protecting foundation species while they are still common.
- Published
- 2019
- Full Text
- View/download PDF
25. Fire-caused mortality within tree neighborhoods increases growth of Pinus lambertiana more than growth of Abies concolor.
- Author
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Becker, Kendall M.L. and Lutz, James A.
- Subjects
TREE mortality ,PINE ,FIR ,DEAD trees ,BARK beetles ,FOREST management - Abstract
• Density reduction from fire or mechanical damage increased post-fire growth rates. • Density reduction from bark beetle mortality did not affect post-fire growth rates. • Pinus had a stronger post-fire growth response to competitive release than Abies. • Mortality and diameter distribution, not growth, control composition of large trees. Global increases in large-tree mortality and multiple disturbances such as fire, drought, and pestilence increase the importance of understanding how large-tree growth responds to changes in competitive neighborhoods. We used 34,175 spatially mapped trees within 25.6 ha that burned at low to moderate severity in 2013 to investigate how changes to tree neighborhoods affected growth of 3,652 surviving trees of two species, Abies concolor (white fir) and Pinus lambertiana (sugar pine). Using diameter measurements taken in 2014 and 2019, we estimated post-fire radial growth of each surviving tree. We modeled annual basal area increment as a function of diameter and extracted residuals to yield relative growth rate (RGR). We used a multi-model approach and AIC to compare the species-specific effects on RGR of all post-fire tree mortality within a neighborhood radius versus mortality broken down by cause. To represent density reduction around each surviving tree, we computed crowding metrics for neighborhood radii up to 20 m for all tree mortality combined and for each mortality cause. The best-fit model included terms for density reduction within 10 m of the surviving tree due to 1) fire or mechanical damage and 2) bark beetle mortality, as well as their interactions with species and diameter. Density reduction due to fire or mechanical damage had a positive effect on RGR that was nearly twice as strong for P. lambertiana as A. concolor. Tree diameter interacted with density reduction for just P. lambertiana. Small-diameter (10-cm) P. lambertiana had a fourfold larger increase in basal area increment than large-diameter (60-cm) P. lambertiana as density reduction due to fire or mechanical damage ranged from 0 to 100 %. The strong growth response of medium-diameter P. lambertiana to density reductions could eventually increase the abundance of large-diameter (≥60 cm) P. lambertiana. In conjunction with mortality rates, which were lower for large-diameter P. lambertiana (0.97 %) than A. concolor (3.31 %), this could increase the relative abundance of large-diameter P. lambertiana from 51.2 % in 2020 to 62.6 % by 2050. Changes to competitive neighborhoods can have species-specific effects on large-tree growth, an important consideration for long-term management of fire-prone forests. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
26. Patterns of nitrogen‐fixing tree abundance in forests across Asia and America
- Author
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Renato Valencia, Duncan N. L. Menge, Guochun Shen, I. A. U. Nimal Gunatilleke, Keith Clay, Anuttara Nathalang, Rebecca Ostertag, Xiankun Li, Patrick A. Jansen, Mauricio Alvarez, Pagi S. Toko, Ana Andrade, Keping Ma, Stephen P. Hubbell, Christine Fletcher, Norm Bourg, Tomáš Vrška, Geoffrey G. Parker, Yide Li, Bin Wang, Li Zhu, Richard P. Phillips, Michael D. Morecroft, Luxiang Lin, Sean M. McMahon, João Batista da Silva, Stuart J. Davies, David Allen, Lee Sing Kong, William J. McShea, Weiguo Sang, Jan den Ouden, Sean C. Thomas, Sheng-Hsin Su, Billy C.H. Hau, Robert W. Howe, Jonathan Myers, Michael Drescher, James A. Lutz, Han Xu, Ankur Shringi, Daniel J. Johnson, Chang-Fu Hsieh, Min Cao, C. V. Savitri Gunatilleke, Alberto Vicentini, Lawren Sack, H. S. Suresh, Xihua Wang, Vojtech Novotny, Christian P. Giardina, George D. Weiblen, H. S. Dattaraja, Sandra L. Yap, Amy Wolf, Raman Sukumar, Tak Fung, Sylvester Tan, Nathalie Butt, Richard Condit, Warren Y. Brockelman, Sarayudh Bunyavejchewin, Yiching Lin, Yadvinder Malhi, Susan Cordell, I-Fang Sun, Faith Inman-Narahari, Shirong Liu, Fangliang He, Kassim Abd Rahman, Wei-Chun Chao, Jessica Shue, Martha Isabel Vallejo, Alexandre Adalardo de Oliveira, Kamariah Abu Salim, Jiangshan Lai, Ryan A. Chisholm, Chen-Chia Ku, Wirong Chanthorn, David A. Orwig, Andrew J. Larson, Perry S. Ong, Kamil Král, Xiangcheng Mi, and Shawn K. Y. Lum
- Subjects
0106 biological sciences ,Plant Science ,010603 evolutionary biology ,01 natural sciences ,Latitude ,Basal area ,forest ,Abundance (ecology) ,Bosecologie en Bosbeheer ,Ecosystem ,Precipitation ,Ecology, Evolution, Behavior and Systematics ,nutrient limitation ,Ecology ,Tropics ,legume ,PE&RC ,Smithsonian ForestGEO ,Forest Ecology and Forest Management ,symbiosis ,Fixation (population genetics) ,Geography ,nitrogen fixation ,Wildlife Ecology and Conservation ,Nitrogen fixation ,010606 plant biology & botany - Abstract
Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.
- Published
- 2019
27. The importance of small fire refugia in the central Sierra Nevada, California, USA
- Author
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Crystal A. Kolden, Arjan J. H. Meddens, Erika M. Blomdahl, James A. Lutz, and Elsevier
- Subjects
0106 biological sciences ,Population ,fire heterogeneity ,Management, Monitoring, Policy and Law ,010603 evolutionary biology ,01 natural sciences ,Yosemite National Park ,Basal area ,Common species ,Yosemite Forest Dynamics Plot ,Revegetation ,education ,Forest Sciences ,Nature and Landscape Conservation ,education.field_of_study ,Forest dynamics ,fire mortality ,Diameter at breast height ,Forestry ,Grid cell ,Smithsonian ForestGEO ,Forest Management ,fire severity ,Geography ,Taxon ,010606 plant biology & botany - Abstract
Fire refugia – the unburned areas within fire perimeters – are important to the survival of many taxa through fire events and the revegetation of post-fire landscapes. Previous work has shown that species use and benefit from small-scale fire refugia (1 m2 to 1000 m2), but our understanding of where and how fire refugia form is largely limited to the scale of remotely sensed data (i.e., 900 m2 Landsat pixels). To examine the causes and consequences of small fire refugia, we field-mapped all unburned patches ≥1 m2 within a contiguous 25.6 ha forest plot that burned at generally low-to-moderate severity in the 2013 Yosemite Rim Fire, California, USA. Within the Yosemite Forest Dynamics Plot (YFDP), there were 685 unburned patches ≥1 m2, covering a total unburned area of 12,597 m2 (4.9%). Small refugia occurred in all fire severity classifications. Random forest models showed that the proportion of unburned area of 100 m2 grid cells corresponded to pre-fire density and basal area of trees, distance to the nearest stream, and immediate fire mortality, but the relationships were complex and model accuracy was variable. From a pre-fire population of 34,061 total trees ≥1 cm diameter at breast height (1.37 m; DBH) within the plot (1,330 trees ha-1), trees of all five of the most common species and those DBH
- Published
- 2019
28. Large-diameter trees dominate snag and surface biomass following reintroduced fire
- Author
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Darren McAvoy, Andrew J. Larson, Larissa L. Yocom, Alistair M. S. Smith, Sara J. Germain, Tucker J. Furniss, Mark E. Swanson, C. Alina Cansler, Soren Struckman, Crystal A. Kolden, James A. Lutz, and SpringerOpen
- Subjects
0106 biological sciences ,Sierra Nevada mixed-conifer ,010504 meteorology & atmospheric sciences ,Forest management ,Carbon sequestration ,010603 evolutionary biology ,01 natural sciences ,Yosemite National Park ,Yosemite Forest Dynamics Plot ,lcsh:QH540-549.5 ,Fuel reduction ,Transect ,Forest Sciences ,0105 earth and related environmental sciences ,Forest floor ,Biomass (ecology) ,Ecology ,biology ,Forest dynamics ,Ecological Modeling ,Abies concolor ,Forestry ,Smithsonian ForestGEO ,biology.organism_classification ,Snag ,Environmental science ,lcsh:Ecology ,California Rim Fire - Abstract
The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics, including reducing tree density and decreasing levels of woody biomass on the forest floor. However, reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass, with potential impacts to fuel accumulation, carbon sequestration, subsequent fire severity, and forest management. In this study, we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation, carbon sequestration, and subsequent fire severity potential. Beginning pre-fire, and continuing 6 years post-fire, we tracked all live, dead, and fallen trees ≥ 1 cm in diameter and mapped all pieces of deadwood (downed woody debris) originating from tree boles ≥ 10 cm diameter and ≥ 1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada, California, USA. We also tracked surface fuels along 2240 m of planar transects pre-fire, immediately post-fire, and 6 years post-fire. Six years after moderate-severity fire, deadwood ≥ 10 cm diameter was 73 Mg ha−1, comprised of 32 Mg ha−1 that persisted through fire and 41 Mg ha−1 of newly fallen wood (compared to 72 Mg ha−1 pre-fire). Woody surface fuel loading was spatially heterogeneous, with mass varying almost four orders of magnitude at the scale of 20 m × 20 m quadrats (minimum, 0.1 Mg ha−1; mean, 73 Mg ha−1; maximum, 497 Mg ha−1). Wood from large-diameter trees (≥ 60 cm diameter) comprised 57% of surface fuel in 2019, but was 75% of snag biomass, indicating high contributions to current and future fuel loading. Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels ≥ 10 cm diameter within 6 years. Repeated fires are needed to reduce surface fuel loading.
- Published
- 2020
29. The Consequences of Environmental Properties and Tree Spatial Neighborhood on Post-Fire Structure of Forest in Yosemite National Park
- Author
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Tamjidi, Jelveh
- Subjects
biotic interactions ,habitat heterogeneity ,Dispersal limitation ,Yosemite Forest Dynamics Plot ,species coexistence ,large-diameter trees ,Ecology and Evolutionary Biology ,fungi ,spatial pattern ,species-habitat association ,habitat filtering ,soil enzymes ,Smithsonian ForestGEO - Abstract
Separating the contribution of habitat filtering and dispersal mechanisms in forming species distribution remains a challenge in community ecology. Despite the effect of environmental variables in structuring communities, only restricted numbers of them were considered as a habitat dissimilarity. In Chapter 2, I used topography and soil properties to define habitats within the Yosemite Forest Dynamics Plot (YFDP). The soil enzymes were added in soil samples due to their important role in releasing nutrients into the soil environment. The preference of eleven species to a specific habitat were examined. Also, the relative importance of habitat filtering and dispersal limitation were examined. I found that more species associated with habitats defined by soil properties compare to those associated with topographically defined habitat. In addition, the contribution of dispersal process was greater in explaining change in species composition. In Chapter 3, I studied the underlying processes in shaping four abundant species spatial arrangement in YFDP. I examined the effect of habitat heterogeneity, dispersal process, fire event, interaction of adults on juveniles, and negative density dependence (as a result of increasing density) in shaping species spatial distribution. My results suggest that dominant species spatial patterns are partially explained by topographic variables, dispersal limitation, biotic interactions, and fire history.
- Published
- 2020
- Full Text
- View/download PDF
30. Detecting Tree Mortality with Landsat-Derived Spectral Indices: Improving Ecological Accuracy by Examining Uncertainty
- Author
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James A. Lutz, Van R. Kane, Tucker J. Furniss, Andrew J. Larson, and Elsevier Inc.
- Subjects
Landsat 8 ,010504 meteorology & atmospheric sciences ,0208 environmental biotechnology ,Ecology and Evolutionary Biology ,Soil Science ,02 engineering and technology ,01 natural sciences ,Basal area ,Monitoring Trends in Burn Severity ,Yosemite Forest Dynamics Plot ,Statistics ,Range (statistics) ,Computers in Earth Sciences ,Categorical variable ,0105 earth and related environmental sciences ,Remote sensing ,Mortality rate ,Diameter at breast height ,Geology ,Smithsonian ForestGEO ,020801 environmental engineering ,Tree (data structure) ,fire severity ,Environmental science ,Metric (unit) ,Scale (map) ,differenced Normalized Burn Ratio - Abstract
Satellite-derived fire severity metrics are a foundational tool used to estimate fire effects at the landscape scale. Changes in surface characteristics permit reasonably accurate delineation between burned and unburned areas, but variability in severity within burned areas is much more challenging to detect. Previous studies have relied primarily on categorical data to calibrate severity indices in terms of classification accuracy, but this approach does not readily translate into an expected amount of error in terms of actual tree mortality. We addressed this issue by examining a dataset of 40,370 geolocated trees that burned in the 2013 California Rim Fire using 36 Landsat-derived burn severity indices. The differenced Normalized Burn Ratio (dNBR) performed reliably well, but the differenced SWIR:NIR ratio most accurately predicted percent basal area mortality and the differenced normalized vegetation index (dNDVI) most accurately predicted percent mortality of stems ≥10 cm diameter at breast height. Relativized versions of dNBR did not consistently improve accuracy; the relativized burn ratio (RBR) was generally equivalent to dNBR while RdNBR had consistently lower accuracy. There was a high degree of variability in observed tree mortality, especially at intermediate spectral index values. This translated into a considerable amount of uncertainty at the landscape scale, with an expected range in estimated percent basal area mortality greater than 37% for half of the area burned (>50,000 ha). In other words, a 37% range in predicted mortality rate was insufficient to capture the observed mortality rate for half of the area burned. Uncertainty was even greater for percent stem mortality, with half of the area burned exceeding a 46% range in predicted mortality rate. The high degree of uncertainty in tree mortality that we observed challenges the confidence with which Landsat-derived spectral indices have been used to measure fire effects, and this has broad implications for research and management related to post-fire landscape complexity, distribution of seed sources, or persistence of fire refugia. We suggest ways to account for uncertainty that will facilitate a more nuanced and ecologically-accurate interpretation of fire effects. This study makes three key contributions to the field of remote sensing of fire effects: 1) we conducted the most comprehensive comparison to date of all previously published severity indices using the largest contiguous set of georeferenced tree mortality field data and revealed that the accuracy of both absolute and relative spectral indices depends on the tree mortality metric of interest;2) we conducted this study in a single, large fire that enabled us to isolate variability due to intrinsic, within-landscape factors without the additional variance due to extrinsic factors associated with different biogeographies or climatic conditions; and 3) we identified the range in tree mortality that may be indistinguishable based on spectral indices derived from Landsat satellites, and we demonstrated how this variability translates into a considerable amount of uncertainty in fire effects at the landscape scale.
- Published
- 2019
31. Fuel dynamics after reintroduced fire in an old-growth Sierra Nevada mixed-conifer forest
- Author
-
Cansler, C. Alina, Swanson, Mark E., Furniss, Tucker J., Larson, Andrew J., and Lutz, James A.
- Published
- 2019
- Full Text
- View/download PDF
32. Data from: Patterns of nitrogen-fixing tree abundance in forests across Asia and America
- Author
-
Menge, Duncan N.L., Chisholm, Ryan A., Davies, Stuart J., Abu Salim, Kamariah, Allen, David, Alvarez, Mauricio, Bourg, Norm, Brockelman, Warren Y., Bunyavejchewin, Sarayudh, Butt, Nathalie, den Ouden, Jan, Jansen, Patrick, Menge, Duncan N.L., Chisholm, Ryan A., Davies, Stuart J., Abu Salim, Kamariah, Allen, David, Alvarez, Mauricio, Bourg, Norm, Brockelman, Warren Y., Bunyavejchewin, Sarayudh, Butt, Nathalie, den Ouden, Jan, and Jansen, Patrick
- Abstract
Symbiotic nitrogen (N)‐fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N‐fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N‐fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N‐fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N‐fixing trees were consistently rare in the forest plots we examined. Within the tropics, N‐fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N‐fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N‐fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N‐fixing trees. By analysing a large dataset of ~4 million trees, we found that N‐fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N‐fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N‐fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.
- Published
- 2019
33. Fuel Dynamics After Reintroduced Fire in an Old-Growth Sierra Nevada Mixed-Conifer Forest
- Author
-
Mark E. Swanson, James A. Lutz, C. Alina Cansler, Andrew J. Larson, Tucker J. Furniss, and SpringerOpen
- Subjects
Environmental Science (miscellaneous) ,Basal area ,fuel consumption ,Yosemite Forest Dynamics Plot ,Fire protection ,Pinus lambertiana ,fuel heterogeneity ,Ecology, Evolution, Behavior and Systematics ,Hydrology ,geography ,geography.geographical_feature_category ,biology ,Abies concolor ,coarse woody debris ,Diameter at breast height ,Forestry ,Old-growth forest ,biology.organism_classification ,Smithsonian ForestGEO ,Rim Fire ,sample size ,FOFEM ,Other Life Sciences ,Litter ,Fuel efficiency ,Environmental science ,Coarse woody debris - Abstract
Background: Surface fuel loadings are some of the most important factors contributing to fire intensity and fire spread. In old-growth forests where fire has been long excluded, surface fuel loadings can be high and can include woody debris ≥100 cm in diameter. We assessed surface fuel loadings in a long-unburned old-growth mixed-conifer forest in Yosemite National Park, California, USA, and assessed fuel consumption from a management-ignited fire set to control the progression of the 2013 Rim Fire. Specifically, we characterized the distribution and heterogeneity of pre-fire fuel loadings, both along transects and contained in duff mounds around large trees. We compared surface fuel consumption to that predicted by the standard First Order Fire Effects Model (FOFEM) based on pre-fire fuel loadings and fuel moistures. We also assessed the relationship between tree basal area—calculated for two different spatial neighborhood scales—and pre-fire fuel loadings. Results: Pre-fire total surface fuel loading averaged 192 Mg ha−1 and was reduced by 79% by the fire to 41 Mg ha−1 immediately after fire. Most fuel components were reduced by 87% to 90% by the fire, with the exception of coarse woody debris (CWD), which was reduced by 60%. Litter depth in duff mounds were within 1 SD of plot means, but duff biomass for the largest trees (>150 cm diameter at breast height [DBH]) exceeded plot background levels. Overstory basal area generally had significant positive relationships with pre-fire fuel loadings of litter, duff, 1-hour, and 10-hour fuels, but the strength of the relationships differed between overstory components (live, dead, all [live and dead], species), and negative relationships were observed between live Pinus lambertiana Douglas basal area and CWD. FOFEM over-predicted rotten CWD consumption and under-predicted duff consumption. Conclusions: Surface fuel loadings were characterized by heterogeneity and the presence of large pieces. This heterogeneity likely contributed to differential fire behavior at small scales and heterogeneity in the post-fire environment. The reductions in fuel loadings at our research site were in line with ecological restoration objectives; thus, ecologically restorative burning during fire suppression is possible.
- Published
- 2019
34. Data from: Patterns of nitrogen-fixing tree abundance in forests across Asia and America
- Subjects
nutrient limitation ,nitrogen fixation ,Wildlife Ecology and Conservation ,Determinants of plant community diversity and structure ,Bosecologie en Bosbeheer ,Forest ,legume ,PE&RC ,Smithsonian ForestGEO ,Forest Ecology and Forest Management ,symbiosis - Abstract
Symbiotic nitrogen (N)‐fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N‐fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N‐fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N‐fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N‐fixing trees were consistently rare in the forest plots we examined. Within the tropics, N‐fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N‐fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N‐fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N‐fixing trees. By analysing a large dataset of ~4 million trees, we found that N‐fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N‐fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N‐fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.
- Published
- 2019
35. Species Diversity Associated with Foundation Species in Temperate and Tropical Forests
- Author
-
James A. Lutz, Hannah L. Buckley, Alvaro Duque, Jonathan Myers, Dairon Cárdenas, Aaron M. Ellison, Jess K. Zimmerman, David A. Orwig, Bradley S. Case, and MDPI
- Subjects
0106 biological sciences ,spatial analysis ,010504 meteorology & atmospheric sciences ,Simpson diversity ,Ecology and Evolutionary Biology ,Biodiversity ,Beta diversity ,010603 evolutionary biology ,01 natural sciences ,species richness ,0105 earth and related environmental sciences ,abundance ,codispersion analysis ,Forest dynamics ,Ecology ,Species diversity ,Forestry ,lcsh:QK900-989 ,Bray-Curtis ,Smithsonian ForestGEO ,Geography ,lcsh:Plant ecology ,Foundation species ,Alpha diversity ,Species richness ,Shannon diversity ,Temperate rainforest - Abstract
Foundation species define and structure ecological communities but are difficult to identify before they are declining. Yet, their defining role in ecosystems suggests they should be a high priority for protection and management while they are still common and abundant. We used comparative analyses of six large forest dynamics plots spanning a temperate-to-tropical gradient in the Western Hemisphere to identify statistical &ldquo, fingerprints&rdquo, of potential foundation species based on their size-frequency and abundance-diameter distributions, and their spatial association with five measures of diversity of associated woody plant species. Potential foundation species are outliers from the common &ldquo, reverse-J&rdquo, size-frequency distribution, and have negative effects on alpha diversity and positive effects on beta diversity at most spatial lags and directions. Potential foundation species also are more likely in temperate forests, but foundational species groups may occur in tropical forests. As foundation species (or species groups) decline, associated landscape-scale (beta) diversity is likely to decline along with them. Preservation of this component of biodiversity may be the most important consequence of protecting foundation species while they are still common.
- Published
- 2019
36. Detecting tree mortality with Landsat-derived spectral indices: Improving ecological accuracy by examining uncertainty.
- Author
-
Furniss, Tucker J., Kane, Van R., Larson, Andrew J., and Lutz, James A.
- Subjects
- *
LANDSAT satellites , *MORTALITY , *CATEGORIES (Mathematics) , *UNCERTAINTY , *RELATIVE medical risk , *REMOTE sensing - Abstract
Satellite-derived fire severity metrics are a foundational tool used to estimate fire effects at the landscape scale. Changes in surface characteristics permit reasonably accurate delineation between burned and unburned areas, but variability in severity within burned areas is much more challenging to detect. Previous studies have relied primarily on categorical data to calibrate severity indices in terms of classification accuracy, but this approach does not readily translate into an expected amount of error in terms of actual tree mortality. We addressed this issue by examining a dataset of 40,370 geolocated trees that burned in the 2013 California Rim Fire using 36 Landsat-derived burn severity indices. The differenced Normalized Burn Ratio (dNBR) performed reliably well, but the differenced SWIR:NIR ratio most accurately predicted percent basal area mortality and the differenced normalized vegetation index (dNDVI) most accurately predicted percent mortality of stems ≥10 cm diameter at breast height. Relativized versions of dNBR did not consistently improve accuracy; the relativized burn ratio (RBR) was generally equivalent to dNBR while RdNBR had consistently lower accuracy. There was a high degree of variability in observed tree mortality, especially at intermediate spectral index values. This translated into a considerable amount of uncertainty at the landscape scale, with an expected range in estimated percent basal area mortality greater than 37% for half of the area burned (>50,000 ha). In other words, a 37% range in predicted mortality rate was insufficient to capture the observed mortality rate for half of the area burned. Uncertainty was even greater for percent stem mortality, with half of the area burned exceeding a 46% range in predicted mortality rate. The high degree of uncertainty in tree mortality that we observed challenges the confidence with which Landsat-derived spectral indices have been used to measure fire effects, and this has broad implications for research and management related to post-fire landscape complexity, distribution of seed sources, or persistence of fire refugia. We suggest ways to account for uncertainty that will facilitate a more nuanced and ecologically-accurate interpretation of fire effects. This study makes three key contributions to the field of remote sensing of fire effects: 1) we conducted the most comprehensive comparison to date of all previously published severity indices using the largest contiguous set of georeferenced tree mortality field data and revealed that the accuracy of both absolute and relative spectral indices depends on the tree mortality metric of interest;2) we conducted this study in a single, large fire that enabled us to isolate variability due to intrinsic, within-landscape factors without the additional variance due to extrinsic factors associated with different biogeographies or climatic conditions; and 3) we identified the range in tree mortality that may be indistinguishable based on spectral indices derived from Landsat satellites, and we demonstrated how this variability translates into a considerable amount of uncertainty in fire effects at the landscape scale. Image 1 • Various spectral indices detect different aspects of fire-related tree mortality. • dNBR was not the best index, but it was well suited for general use. • Relativized versions of dNBR did not consistently improve performance. • Range in observed mortality was as high as ±40% around the predicted mean. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
37. Shrub Consumption and Immediate Changes in Shrub Community and Spatial Patterns by Reintroduced Fire in Yosemite National Park, California, USA; Supplemental Information
- Author
-
Lutz, J. A., Furniss, T. J., Germain, S. J., Becker, K. M. L., Blomdahl, E. M., Jeronimo, S. A., Cansler, C. A., Freund, J. A., Swanson, M. E., Larson, A. J., and Utah State University
- Subjects
Yosemite Forest Dynamics Plot ,Ecology and Evolutionary Biology ,Smithsonian ForestGEO ,Rim Fire ,Forest Sciences - Abstract
Fire behavior in the Yosemite Forest Dynamics Plot during the Rim Fire as captured by the USFS Fire Behavior Assessment Team and reported in Ewell, C., D.F. Smith, M. Hilden, S. Greene, D. Coultrap, K. Robinson, N. Vaillant, A. Reiner, T. Norman. 2015. 2013 Rim Fire Stanislaus National Forest and Yosemite National Park Fire Behavior Assessment Team Summary Report. Each video was started based on a thermocouple trigger when the fire reached it.
- Published
- 2016
38. Species Diversity Associated with Foundation Species in Temperate and Tropical Forests.
- Author
-
Ellison, Aaron M., Buckley, Hannah L., Case, Bradley S., Cardenas, Dairon, Duque, Álvaro J., Lutz, James A., Myers, Jonathan A., Orwig, David A., and Zimmerman, Jess K.
- Subjects
BIODIVERSITY ,TEMPERATE forests ,TROPICAL forests ,BIOTIC communities ,ECOSYSTEMS - Abstract
Foundation species define and structure ecological communities but are difficult to identify before they are declining. Yet, their defining role in ecosystems suggests they should be a high priority for protection and management while they are still common and abundant. We used comparative analyses of six large forest dynamics plots spanning a temperate-to-tropical gradient in the Western Hemisphere to identify statistical "fingerprints" of potential foundation species based on their size-frequency and abundance-diameter distributions, and their spatial association with five measures of diversity of associated woody plant species. Potential foundation species are outliers from the common "reverse-J" size-frequency distribution, and have negative effects on alpha diversity and positive effects on beta diversity at most spatial lags and directions. Potential foundation species also are more likely in temperate forests, but foundational species groups may occur in tropical forests. As foundation species (or species groups) decline, associated landscape-scale (beta) diversity is likely to decline along with them. Preservation of this component of biodiversity may be the most important consequence of protecting foundation species while they are still common. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
39. The Evolution of Long-Term Data for Forestry: Large Temperate Research Plots in an Era of Global Change
- Author
-
Lutz, James A.
- Published
- 2015
- Full Text
- View/download PDF
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