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Wind disturbance in northern hardwood forests of the US North Central Great Lakes region creates heterogeneously distributed structural attributes such as downed woody debris (DWD) and canopy openings across temporal and spatial scales. The decomposition of DWD contributes to greenhouse gas (GHG) fluxes, provides habitat, and potentially influences soil biogeochemistry. We assessed the effects of DWD addition on soil GHG fluxes in the decade after experimental manipulation of downed woody amounts and canopy openings in a maturing second-growth deciduous forest to (1) determine the spatial relationship between DWD proximity and soil GHG fluxes (CO2, CH4, N2O); (2) evaluate the relationship of decay class, canopy condition and environmental variables to wood decomposition and soil fluxes; and (3) use the fine scale surface patterns to estimate carbon emissions from the ground layer stratum. Our results revealed the shifting influence of individual pieces of DWD on soil microbial activity with advancing wood decay and depending on canopy condition. Modeled daily soil CO2 fluxes increased near moderately and highly decayed DWD in open canopy compared to control soils but decreased near highly decayed wood in closed canopy. Despite high variability and low CH4 (mean: − 0.02 ± 0.01 mg m−2 s−1) and N2O (mean: − 0.0007 ± 0.0008 mg m−2 s−1) soil fluxes, higher uptake in closed canopy paralleled the patterns of CO2 efflux. Our findings indicated that northern hardwood forests have the potential to be important CO2 and trace gas sinks, especially under intact canopy, but that widespread reductions in DWD in secondary forests of the region likely altered potential GHG soil uptake.

Corn (Zea mays L.) residues and perennial C4 grasses are two Midwest bioenergy feedstock candidates due to their compatibility with agricultural infrastructure and potential for ecosystem service delivery. We validated the ecosystem process model AGRO-BGC by comparing model estimates with empirical observations from corn and perennial C4 grass systems across Wisconsin and Illinois under no-tillage, nitrogen fertilized, and unfertilized management. Validation parameters included soil organic carbon (SOC), total soil nitrogen (N) to 1.2 m, aboveground net primary productivity (ANPP), net ecosystem productivity (NEP), and leaf area index (LAI). We parameterized AGRO-BGC to represent ecophysiological characteristics of corn and perennial prairie grasses, and constructed scenarios to represent corresponding edaphic, climate, and management conditions. Unfertilized annual model estimates had normalized mean average errors relative to field measurements of 0.3, 23, and 4 t ha−1 for ANPP, SOC, and N, respectively. Fertilized simulations erred from observations by 0.6, 29, 5 t ha−1 for ANPP, SOC, and N, respectively. We also estimated long-term implications of varying residue removal rates on SOC. Model estimates compared to field data tested the hypothesis that long-term increased residue removal decreases SOC. Field observations showed 0.17, 0.09, and a −0.17 t C ha−1 yr−1 change for control, harvest, and bare grass residue removal treatments, respectively. Simulated SOC loss was greatest for the most intensive residue removal scenarios (−0.48 and −0.68 t C ha−1 yr−1 for corn and grass, respectively), compared to no-harvest scenarios that increased SOC by 0.05 t C ha−1 yr−1 for both corn and grass. AGRO-BGC estimated a 0.07 t C ha−1 yr−1 loss under corn residue harvest, while estimating 0.09 t C ha−1 yr−1 loss for grass. Results suggest long-term increased corn and grass residue harvest (beyond grain) for biofuel feedstock will decrease SOC and soil productivity by approximately 15% in corn and 21% in grass systems over 47 years.

Forest harvesting and the associated loss of nutrients and carbon has the potential to negatively affect the soil microbial community, which plays a significant role in the health and productivity of the forest ecosystem. We used an experiment to evaluate the effects of group selection using whole-tree harvesting on the soil microbial community in a second growth northern hardwood forest dominated by sugar maple (Acer saccharum Marsh.) in northern Wisconsin, USA. We compared the response of the soil microbial community in 200 m2 and 380 m2 harvested gaps to unharvested controls during the spring and summer in the first two years post-harvest, and continued to monitor changes in the soil microbial communities and microenvironment in 380 m2 gaps in years four, five, and seven post-harvest. Changes in community size and composition were assessed using phospholipid fatty acid (PLFA) analysis. We found that the abundance of arbuscular mycorrhizal fungi initially decreased following harvest, while abundance of anaerobic and gram positive bacteria, and the cyclo/pre-cyclo microbial stress ratio increased; responses that can be linked to microclimatic variability and resource accessibility. Neither actinomycete bacteria nor saprotrophic fungi exhibited an initial response to harvest, but in later years, we observed a decrease in actinomycetes and an increase in fungal abundance, suggesting a competitive interaction between the two main complex carbon-utilizing microbial groups. Canopy gap size had a minimal effect on the soil microbial community, resulting in a higher microbial stress ratio in 200 m2 gaps. The microbial community exhibited seasonal and yearly fluctuation, which reinforces the need for repeated sampling over multiple seasons to correctly interpret management effects. Despite the large amount of seasonal and yearly variability, we began to see signs of recovery in the soil microbial community between two and four years post-harvest. We conclude that group selection accomplished via whole-tree harvesting of this size and scale does not result in long-term effects on the soil microbial community in this temperate northern hardwood forest.

Larches (Larix spp.), deciduous conifers, oc- cur in the northern hemisphere in cold-temperate and boreal climates - an environment normally thought to favor evergreen tree species. We compare foliar carbon isotope discrimination (D), instantaneous water use ef- ficiency, total foliar nitrogen concentration, and specific leaf area (for a subset of sites) between Larix spp. and co-occurring evergreen conifers at 20 sites throughout the natural range of larches. Except for Larix occiden- talis in the xeric Intermountain West, USA, D is signif- icantly (P < 0.05) greater for larches than co-occurring evergreen conifers at 77% of the sites, suggesting that larches use water less eAciently. At elevations greater than 3000 m, the D of Larix spp. and co-occurring co- nifers converge, suggesting that water is not the limiting resource. Foliar nitrogen concentration and specific leaf area are two ecophysiological characteristics that are positively correlated with high photosynthetic capacity. Foliar nitrogen concentration is significantly greater for larches than evergreen conifers at 88% of the sites and specific leaf area is approximately three times greater for larches than co-occurring conifers. Future studies should examine the potential eAect that global warming may have on the distribution of larch forests because the water use eAciency of larches is commonly less than co- occurring evergreen conifers and the boreal and high- latitude environments are likely to experience the greatest climate warming.

Structural heterogeneity has become a goal of contemporary forest management, yet the effect of incorporating variable sized canopy openings characteristic of older forests on ecosystem services is still largely unknown. Single-tree selection silviculture reduces tree species diversity, and group-selection harvests often produce inconsistent results in maintaining the proportion of species with low or intermediate shade tolerance. It is unclear how much variability is related to inherent growth rate differences among shade tolerance classes, asymmetric competition, sprouting behavior, herbivory, and other factors. We conducted an experiment to control several of these factors. The northern hardwood study area in north-central Wisconsin included 15 replicates of each of 3 sizes of experimental gaps (50 m 2

Pine and oak are common tree species in the Vila Real district, northern Portugal, a region where forests are an important land use (38%). The net primary production (NPP) of these forests is not well known. The objective of this study was to quantify the aboveground biomass and aboveground NPP (ANPP) of pine ( Pinus pinaster Aiton), pyrenean oak ( Quercus pyrenaica Willd.) and mixed pine–oak forests in the Vila Real district and to evaluate the relationships between ANPP and their stand characteristics. To achieve this objective, 15 stands of pine, 15 stands of oak and 9 stands of mixed pine–oak were studied between 2008 and 2011. ANPP average (and range) of pine, oak and mixed stands were 7.9 (2.9–15.1), 7.3 (3.0–12.1), and 12.1 (6.5–17.2) Mg ha −1 yr −1 , respectively. An analysis of covariance (ANCOVA), to reduce the within-groups variability and detect the differences between the stand compositions, was performed. In this analysis, we rejected the null hypothesis that the composition stands had the same mean among ANPP. Mixed stands had a significantly higher mean ANPP than pine or oak. Also, we verified that in pine, the greater distribution of biomass was on the stem (4.0 ± 0.7 Mg ha −1 yr −1 , 50% of the total productivity) component where carbon sequestration is retained longer, whereas in oak and mixed stands the foliage was the component with the greater distribution of biomass (4.0 and 6.0 Mg ha −1 yr −1 , respectively). Aboveground biomass was significantly different among the three stands types and averaged 83.4, 61.4 and 110.5 Mg ha −1 for pine, oak and mixed stands, respectively. Regression models performed showed that there was a strong relationship between aboveground biomass and basal area in all stands. This study concludes that the production efficiency, defined as stem productivity/leaf area index, was significantly different in mixed stands. Pine had the greatest production efficiency in all stand types and, in mixed stands, had 85% of the total production efficiency.

Canopy gaps and coarse woody debris are two forest structural features that are more abundant in old-growth forests than in second-growth, even-aged stands. These features directly influence the carbon balance of the ecosystem, yet few studies have quantified their interactive effects. We experimentally manipulated the forest structure of a second-growth northern hardwood forest in north-central Wisconsin (USA) and measured the shift of C between pools of the ecosystem components. Here, we question the longevity of the changes to the aboveground pools and address their implications for total ecosystem C (TEC) and net ecosystem production (NEP) at both the gap and stand scale. At the scale of the gap, the harvest and removal of trees significantly reduced NEP (−3.2 to −3.5 Mg C ha−1 for gaps vs 2.2 to 2.5 Mg C ha−1 for reference conditions), but did not alter heterotrophic respiration. The addition of woody debris without harvest significantly increased heterotrophic respiration, decreasing soil C storage of the gap area (−0.5 to −1.1 Mg C ha−1). The combined treatment of gap creation and woody debris addition made the gap area a significant C source to the atmosphere for the 3 years of the study (−4.9 to −5.1 Mg C ha−1). We also estimated how these structural features would affect C dynamics at a broader scale. The conversion of 10% of the stand canopy to gap conditions caused only a brief decrease in the stand NEP with the C balance returning to reference conditions by the third year following tree harvest. The woody debris additions caused an increase in both TEC and heterotrophic respiration. When combined the addition of canopy gaps and woody debris caused plots to initially become significant C sources, relative to undisturbed locations that were consistently accumulating C, with an annual NEP ranging from 2.1 to 2.8 Mg C ha−1 y−1. Understanding the effects of these structural features on forest C dynamics is highly relevant as the maturing forests of the region transition to more structurally complex forests and the demand for managing ecosystems for long-term C sequestration increases.

The leaf area index (LAI) and fraction of photosynthetically active radiation (FPAR) absorbed by the vegetation are key biophysical measures of canopy foliage area and light harvesting potential. Accurately quantifying these properties is important for characterizing the dynamics of mass and energy exchanges between vegetation and the atmosphere. The overall objective of this research was to validate the spatial and temporal performance of the MODIS LAI/FPAR products for a boreal forest landscape in northern Manitoba, Canada. We examined both the MODIS collection 4 (C4) and updated collection 5 (C5) versions over a multiyear period (2004 to 2006) and spatially across seven different-aged forests originating from wildfire and ranging in age from 1- to 154-years-old. We made optical measurements of LAI and FPAR, which were empirically scaled to high-resolution imagery (ASTER; 15–30 m pixel size) to derive detailed reference LAI and FPAR maps. These maps were then aggregated to MODIS resolution (i.e. 1 km) for comparison. We characterized the temporal accuracy of the MODIS products using repeat measurements of LAI and FPAR, and through comparisons with continuously operating measurements of canopy light interception. MODIS captured the general phenological trajectory of these aggrading forests, however the MODIS LAI and FPAR products overestimated and underestimated the LAI and FPAR for the youngest and oldest sites, respectively. In addition, MODIS displayed larger seasonal variation in LAI and FPAR compared to field measurements for the needle-leaf evergreen dominated sites. The peak growing season difference between MODIS and spatially aggregated ASTER reference values of LAI and FPAR decreased significantly by 69% and 55%, respectively, for the updated C5 versus the previous C4 LAI/FPAR products. The overall uncertainty (i.e. RMSE) in the MODIS LAI retrievals decreased from 1.6 (C4) to 0.63 m2 m− 2 (C5) and from 0.20 (C4) to 0.07 (C5) for FPAR. The incorporation of understory vegetation into the validation of the MODIS products yielded significantly higher agreement between observed and MODIS values, likely due to the relatively open canopy architecture and abundant understory found within boreal forests.

The objective of this study was to use an ecosystem process model, Biome-BGC, to explore the effects of different harvest scenarios on major components of the carbon budget of 205,000 km2 of temperate forest in the Upper Midwest region of the U.S. We simulated seven harvest scenarios varying the (i) amount of harvest residue retained, (ii) total harvest area, and (iii) harvest type (clear-cut and selective) to assess the potential impacts on net biome production (NBP), net primary production (NPP), and total vegetation carbon. NBP was positive (C sink) in year 1 (2004) and generally decreased over the 50-year simulation period. More intensive management scenarios, those with a high percentage of clear-cut or a doubling of harvest area, decreased average NBP by a maximum of 58% and vegetation C by a maximum of 29% compared to the current harvest regime (base scenario), while less intensive harvest scenarios (low clear-cut or low area harvested) increased NBP. Yearly mean NPP changed less than 3% under the different scenarios. Vegetation carbon increased in all scenarios by at least 12%, except the two most intensive harvest scenarios, where vegetation carbon decreased by more than 8%. Varying the amount of harvest residue retention had a more profound effect on NBP than on vegetation C. Removing additional residue resulted in greater NBP over the 50-year period compared to the base simulation. Results from the seven model simulations suggest that managing for carbon storage and carbon sequestration are not mutually exclusive in Midwest forests.

Forests of the Midwestern United States are an important source of fiber for the wood and paper products industries. Scientists, land managers, and policy makers are interested in using woody biomass and/or harvest residue for biofuel feedstocks. However, the effects of increased biomass removal for biofuel production on forest production and forest system carbon balance remain uncertain. We modeled the carbon (C) cycle of the forest system by dividing it into two distinct components: (1) biological (net ecosystem production, net primary production, autotrophic and heterotrophic respiration, vegetation, and soil C content) and (2) industrial (harvest operations and transportation, production, use, and disposal of major wood products including biofuel and associated C emissions). We modeled available woody biomass feedstock and whole-system carbon balance of 220 000 km2 of temperate forests in the Upper Midwest, USA by coupling an ecosystem process model to a collection of greenhouse gas life-cycle inventory models and simulating seven forest harvest scenarios in the biological ecosystem and three biofuel production scenarios in the industrial system for 50 years. The forest system was a carbon sink (118 g C m−2 yr−1) under current management practices and forest product production rates. However, the system became a C source when harvest area was doubled and biofuel production replaced traditional forest products. Total carbon stores in the vegetation and soil increased by 5–10% under low-intensity management scenarios and current management, but decreased up to 3% under high-intensity harvest regimes. Increasing harvest residue removal during harvest had more modest effects on forest system C balance and total biomass removal than increasing the rate of clear-cut harvests or area harvested. Net forest system C balance was significantly, and negatively correlated (R2 = 0.67) with biomass harvested, illustrating the trade-offs between increased C uptake by forests and utilization of woody biomass for biofuel feedstock.

Coarse woody debris (CWD) and canopy gaps are thought to be important structural components that influence forest ecosystem processes, yet few studies have assessed whether these features interact to influence decay dynamics, and we know of none that does so under controlled experimental canopy gap conditions. By manipulating forest structure to create canopy openings, we tested whether canopy gaps, through their influence on microclimate, affect the respiration rate of CWD in a mature second- growth northern hardwood forest of Wisconsin, USA. We sought to determine the relative contribution of moisture or temperature as predictors of respiration, and to provide estimates of the annual C emission from CWD in these treatments. Differences in the surface temperature of CWD were apparent immedi- ately following gap treatments, with debris in gaps staying significantly warmer than beneath undis- turbed canopy. Coarse woody debris moisture content differed more between gaps and undisturbed canopy in the second post-treatment year due to higher insolation and temperature in gaps relative to undisturbed canopy. The gap treatment increased respiration rates and altered the relationship with CWD temperature and moisture in complex ways. The impacts of gap creation on C fluxes from CWD depended on the range of temperature and moisture being examined. The interaction of the temperature and moisture of the debris in combination with the decay class explained 60% of the observed variation in CWD respiration beneath undisturbed canopies. In gaps, only 23% of the variation of flux could be explained by environmental variables. Annual C fluxes were 128.2 g C kg � 1

Partitioning the soil surface CO{sub 2} flux (R{sub S}) flux is an important step in understanding ecosystem-level carbon cycling, given that R{sub S} is poorly constrained and its source components may have different responses to climate change. Trenched plots are a classic method of separating the R{sub S} source fluxes, but labor-intensive and may cause considerable disturbance to the soil environment. This study tested if various methods of plant suppression in trenched plots affected R{sub S} fluxes, quantified the R{sub S} response to soil temperature and moisture changes, and estimated the heterotrophic contribution to R{sub S}. It was performed in a boreal black spruce (Picea mariana) plantation, using a complete randomized design, during the 2007 growing season (May-November). Trenched plots had significantly lower R{sub S} than control plots, with differences appearing {approx}100 days after trenching; spatial variability doubled after trenching but then declined throughout the experiment. Most trenching treatments had significantly lower (by {approx}0.5 {mu}mol m{sup -2} s{sup -1}) R{sub S} than the controls, and there was no significant difference in R{sub S} among the various trenching treatments. Soil temperature at 2 cm explained more R{sub S} variability than did 10-cm temperature or soil moisture. Temperature sensitivity (Q10) declined inmore » the control plots from {approx}2.6 (at 5 C) to {approx}1.6 (at 15 C); trenched plots values were higher, from 3.1 at 5 C to 1.9 at 15 C. We estimated R{sub S} for the study period to be 241 {+-} 40 g C m{sup -2}, with roots contributing 64% of R{sub S} after accounting for fine root decay, and 293 g C m{sup -2} for the entire year. These findings suggest that laborious hand weeding of vegetation may be usefully replaced by other methods, easing future studies of this large and poorly-understood carbon flux.« less

The purpose of this study was to quantify the effects of climate change (in the form of elevated air and soil temperatures) on transpiration and sap flux rates of black spruce ( Picea mariana (Mill.) BSP). Five treatments were established in northern Manitoba, Canada, with the experimental design consisting of heated and control blocks. Air and soil temperatures were maintained approximately 5 °C above control temperatures using greenhouse chambers. Two of the chambers also included controls to maintain ambient vapor pressure difference (VPD). Sap flux (JS), was not significantly different among treatments in the May or July time periods. However, JS was significantly greater for heated VPD controlled trees than for trees in all other treatments when averaged over the entire study period. JS was positively correlated to photosynthetic photon flux density for all trees. Lower photosynthetic photon flux density in chamber treatments resulted in the creation of models used to estimate JS and canopy transpiration (EC) values that were used in the analysis. Average daily and cumulative growing season EC values were significantly greater for the heated VPD controlled treatments than for other treatments. The results from this study suggest that EC of boreal black spruce will increase if VPD remains unchanged while air temperatures increase.

The effects of changing climate and disturbance on forest water cycling are not well understood. In particular bryophytes contribute significantly to forest evapotranspiration (ET) in poorly-drained boreal forests, but few studies have directly measured this flux and how it changes with stand age and soil drainage. We used large chambers to measure bryophyte evaporation (E) in Canadian Picea mariana forests of varying ages and soil drainages, as well under controlled laboratory conditions, and modeled daily E using site-specific meteorological data to drive a Penman-Monteith-based model. Field measurements of E averaged 0.37 mm day-1, and ranged from 0.03 (Pleurozium schreberii in a 77-year-old dry stand) to 1.43 mm day-1 (Sphagnum riparium in a 43-year-old bog). canopy resistance ranged from ~0 (at 25 °C, some values were

Restoring structural features of old-growth forests, such as increased canopy gap sizes and coarse woody debris, is a common management goal for second-growth, even-aged stands. We experimentally manipulated forest structure by creating variable-size canopy gaps in a second-growth northern hardwood forest in north-central Wisconsin following two growing seasons of pre-treatment monitoring. The objectives of this study were to quantify the influence of canopy gaps of different sizes (50-380 m 2 ) on aboveground biomass and productivity of each vegetation stratum two growing seasons following treatment. Two years after treatment, ground layer biomass in canopy openings increased significantly relative to surrounding undisturbed transition zones. The response of ground layer biomass was greatest in the large versus the me- dium and small gaps. Sapling aboveground net primary productivity was significantly greater in undisturbed transition zones than within gaps across gap sizes following the second post-treatment growing season. Annual stem diameter incre- ment was greatest for trees along gap borders and was correlated with crown class, percentage of crown perimeter ex- posed, gap area, and shade tolerance. Total aboveground net primary productivity was significantly lower in the gap addition plots the first year but by the second post-treatment growing season no longer differed from that in the control plots. Resume´ : La restauration des attributs structuraux des vieilles forets, tels que des trouees de plus grande taille dans la ca- nopee et davantage de gros debris ligneux, est une pratique d'amenagement usuelle dans les peuplements equiennes de se- conde venue. Nous avons modifieexperimentalement la structure forestiere en creant des trouees de taille variable dans la canopee d'une foret de feuillus nordiques de seconde venue etablie dans le centre-nord du Wisconsin. Ce travail a etepre ´- ceded'un suivi pretraitement pendant deux saisons de croissance. Les objectifs de cette etude etaient de quantifier l'in- fluence des trouees de taille variable (de 50 a 380 m 2 ) dans la canopee sur la biomasse aerienne et la productivitede

We used the ecosystem process model Biome-BGC to simulate the effects of harvest and residue removal management scenarios on soil carbon (C), available soil nitrogen (N), net primary production (NPP), and net ecosystem production (NEP) in jack pine (Pinus banksiana Lamb.) and sugar maple (Acer saccharum Marsh) ecosystems in northern Wisconsin, USA. To assess harvest effects, we simulated short (50-year) and long (100-year) harvest intervals, high (clear-cut) and low (selective) harvest intensities, and three levels of residue retention (15%, 25%, and 35%) over a 500-year period. The model simulation of NPP, soil C accumulation, and NEP agreed reasonably well with biometric and eddy-covariance measurements of these two ecosystems. The more intensive (50-year rotation clear-cuts with low residue retention) harvest scenarios tended to have the greatest NEP (420 and 678 t C ha−1 for the 500-year interval for jack pine and sugar maple, respectively). All the harvest scenarios decreased mineral soil C and available mineral soil N content relative to the no-harvest scenario for jack pine and sugar maple. The rate of change in mineral soil C decreased the greatest in the most intensive biomass removal scenarios (−0.012 and −0.072 t C ha−1 yr−1 relative to no-harvest for jack pine and sugar maple, respectively) and the smallest decrease was observed in the least intensive biomass removal scenarios (−0.002 and −0.009 t C ha−1 yr−1 relative to no-harvest for jack pine and sugar maple, respectively). The more intensive biomass removal harvest scenarios in sugar maple significantly decreased peak productivity (NPP) in the simulation period.

Soil surface CO2 flux (Sflux) is the second largest terrestrial ecosystem carbon flux, and may be affected by forest harvest. The effects of clearcutting on Sflux have been studied, but little is known about the effect of alternative harvesting methods such as selective tree harvest on Sflux. We measured Sflux before and after (i) the creation of forest canopy gaps (simulating group tree selection harvests) and (ii) mechanized winter harvest but no tree removal (simulating ground disturbance associated with logging). The experiment was carried out in a sugar maple dominated forest in the Flambeau River State Forest, Wisconsin. Pre-treatment measurements of soil moisture, temperature and Sflux were measured throughout the growing season of 2006. In January-February 2007, a harvester created the canopy gaps (200-380 m 2 ). The mechanization treatment consisted of the harvester traveling through the plots for a similar amount of time as the gap plots, but no trees were cut. Soil moisture and temperature and Sflux were measured throughout the growing season for 1 year prior to harvest and for 2 years after harvest. Soil moisture and temperature were significantly greater in the gap than mechanized and control treatments. Instantaneous Sflux was positively correlated to soil moisture and soil temperature at 2 and 10 cm, but temperature at 10 cm was the single best predictor. Annual Sflux was not significantly different among treatments prior to winter 2007 harvest, and was not significantly different among treatments after harvest. Annual (+1 std. err.) Sflux averaged 967 + 72, 1011 + 72, and 1012 + 72 g C m � 2 year � 1 in the control, mechanized and gap treatments, respectively, for the 2-year

Bryophytes are the dominant ground cover vegetation layer in many boreal forests and in some of these forests the net primary production of bryophytes exceeds the overstory. Therefore it is necessary to quantify their spatial coverage and species composition in boreal forests to improve boreal forest carbon budget estimates. We present results from a small exploratory test using airborne lidar and multispectral remote sensing data to estimate the percentage of ground cover for mosses in a boreal black spruce forest in Manitoba, Canada. Multiple linear regression was used to fit models that combined spectral reflectance data from CASI and indices computed from the SLICER canopy height profile. Three models explained 63–79% of the measured variation of feathermoss cover while three models explained 69–92% of the measured variation of sphagnum cover. Root mean square errors ranged from 3–15% when predicting feathermoss, sphagnum, and total moss ground cover. The results from this case study warrant further testing for a wider range of boreal forest types and geographic regions.

The boreal forest is predicted to experience the greatest warming of any forest biome during the next 50-100 years, but the effects of warming on vegetation phenology are not well known. The objectives of this study were to (1) examine the effects of whole ecosystem warming on bud burst and annual shoot growth of black spruce trees in northern Manitoba, Canada and (2) correlate bud burst to cumulative degree-days (CDD). The experimental design was a complete randomized block design that consisted of four replicated blocks. Each replicate block contained four treatments: soil warming only (heated outside, HO), soil and air warming (heated inside, HI), control outside (no chamber, no heating, CO), and inside a chamber maintained at ambient conditions (no soil or air warming, control inside, CI). Bud burst was measured during the first and second years of the experiment, starting in 2004, and annual shoot growth was measured for the first 3 years (2004-2006) of the study. On average, shoot bud burst occurred 11 and 9 days earlier in 2004 and 2005, respectively, for HI than for other treatments. However, mean CDD required for bud burst for HI was within the standard deviation of CO for both years. In year 1 of the treatments, shoot bud burst occurred earlier for HI than other treatments (CI, CO, HO), but final shoot length of HI trees was less than in CO trees. In the second year of warming, final shoot length was not different for HI than CO. By the third year of warming final shoot length was significantly greater for HI than all other treatments. Empirical results from this study suggest that soil and air warming causes an earlier bud burst for all years of observation and greater shoot lengths by the third season of warming. A longer growing season and greater annual shoot growth should increase carbon uptake by boreal black spruce trees in a warmer climate.

Changes in fire regimes are driving the carbon balance of much of the North American boreal forest, but few studies have examined fire-driven changes in evapotranspiration (ET) at a regional scale. This study used a version of the Biome-BGC process model with dynamic and competing vegetation types, and explicit spatial representation of a large (106 km2) region, to simulate the effects of wildfire on ET and its components from 1948 to 2005 by comparing the fire dynamics of the 1948-1967 period with those of 1968-2005. Simulated ET averaged, over the entire temporal and spatial modeling domain, 323 mm yr-1; simulation results indicated that changes in fire in recent decades decreased regional ET by 1.4% over the entire simulation, and by 3.9% in the last ten years (1996-2005). Conifers dominated the transpiration (EC) flux (120 mm yr-1) but decreased by 18% relative to deciduous broadleaf trees in the last part of the 20th century, when increased fire resulted in increased soil evaporation, lower canopy evaporation, lower EC and a younger and more deciduous forest. Well- and poorly-drained areas had similar rates of evaporation from the canopy and soil, but EC was twice as high in the well-drained areas. Mosses comprised amore » significant part of the evaporative flux to the atmosphere (22 mm yr-1). Modeled annual ET was correlated with net primary production, but not with temperature or precipitation; ET and its components were consistent with previous field and modeling studies. Wildfire is thus driving significant changes in hydrological processes, changes that may control the future carbon balance of the boreal forest.« less

This research quantified the canopy phenology, growing season and inter-annual dynamics of the overstory and understory vegetation in a boreal wildfire chronosequence in northern Manitoba, Canada. Optical measurements of the canopy radiation regime were made in the 2004–2006 growing seasons to evaluate the spatial and temporal variation in the effective leaf area index (Le) and fraction of intercepted photosynthetic active radiation (FIPAR) of the canopy.

Recent studies of vegetation phenology of northern forests using satellite data suggest that the observed earlier spring increase and peak amplitude of the normalized difference vegetation index (NDVI) are a result of climate warming. In addition to undergoing an increase in temperature, the northern forests of Canada have also seen a dramatic increase in area burned by wildfire over the same time period. Using the Canadian Large Fire Database, we analyzed the impact fire had on the phenological dates derived from fitting a logistical model to yearly data from 2004 for several different subsets of both AVHRR-NDVI and MODIS LAI in wildfire dominated terrestrial ecozones. Fire had a significant but complex effect on estimated phenology dates. The most recently burned areas (1994–2003) had later green-up dates in two ecozones for AVHRR data and all ecozones for MODIS. However, older forested (not burned during 1980–2003) had estimated green-up dates 1 to 9 days earlier than the entire forested area in the MODIS LAI data. These data corroborate studies in Canada and demonstrate that fire history is influencing boreal forest phenology and growing season LAI.

Non-native plant species pose a serious ecological and economic threat to managed and natural ecosystems; therefore, there is a great need to identify sources for the introduction of non-native species and develop management plans to reduce or eliminate their introduction. Horses have been suggested to be an important source for the introduction of non-native plant species along trails, but the conclusions were based on anecdotal evidence. In this study, horse hay, manure, and hoof debris samples were collected from 12 to 24 horses at five endurance ride events in North Carolina, Kentucky, Illinois, Wisconsin, and Michigan. One sub-sample of each material from each horse was sown in pots and grown under ideal conditions to determine if horse hay, manure, and hoof debris samples contained seeds from non-native species. A second sub-sample of each material from each horse was placed back on their respective trail to determine what plants would germinate and establish on the trail. Vegetation surveys were also conducted along 50 m transects perpendicular to horse and hiking (horses not permitted) trails at three of the five sites to compare species composition of native and non-native plant species. On average, non-native plant species germinated in 5.2% of the hay samples in the pots, but non-native species did not germinate from the manure or hoof debris samples. Only 3 of the 288 (≈1% of total samples) hay, manure, and hoof debris plots established on horse trails at the five sites contained plants, all of which were native plants, at the end of the first growing season and no plants were observed at the end of the second growing season. Non-native species composition and percent of total plants species did not differ significantly (p = 0.56) between horse and non-horse trails, and non-native plant species were only found within 2 m of the trail. The results of this and another study [Campbell, J.E., Gibson, D.J., 2001. The effect of seeds of exotic species transported vie horse dung on vegetation along trail corridors. Plant Ecology 157, 23–35] demonstrate that horse hay and manure does contain seeds of non-native plant species, but native and non-native plant species rarely become established on horse trails because of the harsh environmental conditions. Management and policy implication of this study are discussed.

We re-visited a seven-stand boreal chronosequence west of Thompson, Manitoba, Canada, in which coarse woody debris (CWD) and its instantaneous decomposition were measured in 2000. New CWD measurements were performed in 2007, and tree inventories updated to provide mortality and snag failure data. These data were used to model CWD changes, compare methods of estimating decomposition, and infer possible fragmentation rates. Measured CWD was between 9.7 (in both the 77- and 43-year-old stands) and 80.4 (in the 18-year-old stand) Mg ha−1 in 2007. Spatial variability was high; at most stands CWD levels had not changed significantly from 2000 to 2007. Tree mortality was a significant flux only in older stands, whereas snag fall rate varied by an order of magnitude, from 2.9% y−1 (0.2 Mg ha−1 y−1) in the 9-year-old stand to 9.8% y−1 (2.3 Mg ha−1 y−1) in the 12-year-old stand. A one-pool model based on these inputs underestimated actual 2000–2007 CWD decomposition in the younger stands, suggesting that fragmentation could be an important part of the carbon flux exiting the CWD pool. We compared three independent measures of annual decomposition (k): direct measurements of CWD respiration, rates based on the 7-year re-sampling effort described here, and rates inferred from the chronosequence design itself. Mean k values arrived at via these techniques were 0.06 ± 0.03, 0.05 ± 0.04, and 0.05 ± 0.05 y−1, respectively. The four-pool model suggested that the transition rate between decay classes was 0.14–0.19 y−1; the model was most sensitive to initial CWD values. Although the computed k values implied a problem with chronosequence site selection for at least one site, the overall CWD trend was consistent with a larger number of sites surveyed in the region.

A common hypothesis for northern ecosystems is that low soil temperatures inhibit plant productivity. To address this hypothesis, we reviewed how separate components of ecosystem carbon (C) cycling varied along a soil temperature gradient for nine welldrained, relatively productive boreal black spruce (Picea mariana Mill. [B.S.P.]) forests in Alaska, USA, and Saskatchewan and Manitoba, Canada. Annual soil temperature [expressed as soil summed degree days (SDD)] was positively correlated with aboveground net primary productivity (ANPP), while negatively correlated with total belowground carbon flux (TBCF). The partitioning of C to ANPP at the expense of root processes represented a nearly 1:1 tradeoff across the soil temperature gradient, which implied that the amount of C cycling through these black spruce ecosystems was relatively insensitive to variation in SDD. Moreover, the rate at which C accumulated in the ecosystem since the last stand replacing fire was unrelated to SDD, but SDD was positively correlated to the ratio of spruce-biomass:forest-floor-mass. Thus, plant partitioning of C and the distribution of ecosystem C were apparently affected by soil temperature, although across regions, precipitation co-varied with soil temperature. These two factors likely correlated with one another because of precipitation’s influence on soil heat balance, suggesting that a soil temperature‐precipitation interaction could be responsible for the shifts in C allocation. Nonetheless, our results highlight that for this boreal ecosystem, ANPP and TBCF can be negatively correlated. In tropical and temperate forests, TBCF and ANPP have been reported as positively correlated, and our results may reflect the unique interactions between soil temperature, forest floor accumulation, rooting depth, and nutrient availability that characterize the black spruce forest type.

Soil surface carbon dioxide (CO 2 ) flux (Rs) was measured for 2 years at the Boreal Soil and Air Warming Experiment site near Thompson, MB, Canada. The experimental design was a complete random block design that consisted of four replicate blocks, with each block containing a 15 m x 15 m control and heated plot. Black spruce [Picea mariana (Mill.) BSP] was the overstory species and Epilobium angustifolium was the dominant understory. Soil temperature was maintained (∼ 5 °C) above the control soil temperature using electric cables inside water filled polyethylene tubing for each heated plot. Air inside a 7.3-m-diameter chamber, centered in the soil warming plot, contained approximately nine black spruce trees was heated ∼ 5 °C above control ambient air temperature allowing for the testing of soil-only warming and soil + air warming. Soil surface CO 2 flux (Rs) was positively correlated (P

This study analyzed the spatial dependencies of soil moisture and temperature in a six-stand chronosequence of boreal black spruce (Picea mariana (Mill.) BSP) stands. Spatial variability of soil temperature (TSOIL) was evaluated twice during the growing season using four transects in each stand, employing a cyclic sampling design with measurements spaced 2–92 m apart. Soil moisture (θg) was measured on one occasion. A spherical model was used to analyze the geostatistical correlation structure; θg and TSOIL at the 7- and 21-year-old stands did not exhibit stable ranges or sills. The fits with stable ranges and sills modeled the spatial patterns in the older stands reasonably well, although unexplained variability was high. Calculated ranges varied from 3 to 150 m for these stands, lengths probably related to structural characteristics influential in local-scale energy transfer. Transect-to-transect variability was significant and typically 5%–15% of the mean for TSOIL and 10%–70% for θg. TSOIL and θg were negatively correlated for most stands and depths, with TSOIL dropping 0.5–0.9 °C for every 1% rise in θg. The results reported here provide initial data to assess the spatial variability of TSOIL and θg in a variety of boreal forest stand ages.

Climate change is predicted to alter the canopy phenology of temperate and boreal forests, which will affect carbon, water, and energy budgets. Therefore, there is a great need to evaluate remotely sensed products for their potential to accurately capture canopy dynamics. The objective of this study was to compare several products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) to field measurements of fraction photosynthetically active radiation (FPAR) and plant area index (PAI) for a deciduous broadleaf forest in northern Wisconsin in 2002. MODIS products captured the general phenological development of the canopy although MODIS products overestimated the leaf area during the overstory leaf out period. Field data suggest that the period from budburst to canopy maturity, or maximum PAI, occurred in 10 to 12 days while MODIS products predicted onset of greenness and maturity from 1 to 21 days and 0 to 19 days earlier than that from field observations, respectively. Temporal compositing of MODIS data and understory development are likely key factors explaining differences with field data. Maximum PAI estimates differed only by 7% between field derived and MODIS-based estimates of LAI. Implications for ecosystem modeling of carbon and water exchange and future research needs are discussed.

Global maps of land cover and leaf area index (LAI) derived from the Moderate Resolution Imaging Spectrometer (MODIS) reflectance data are an important resource in studies of global change, but errors in these must be characterized and well understood. Product validation requires careful scaling from ground and related measurements to a grain commensurate with MODIS products. We present an updated BigFoot project protocol for developing 25-m validation data layers over 49-km2 study areas. Results from comparisons of MODIS and BigFoot land cover and LAI products at nine contrasting sites are reported. In terms of proportional coverage, MODIS and BigFoot land cover were in close agreement at six sites. The largest differences were at low tree cover evergreen needleleaf sites and at an Arctic tundra site where the MODIS product overestimated woody cover proportions. At low leaf biomass sites there was reasonable agreement between MODIS and BigFoot LAI products, but there was not a particular MODIS LAI algorithm pathway that consistently compared most favorably. At high leaf biomass sites, MODIS LAI was generally overpredicted by a significant amount. For evergreen needleleaf sites, LAI seasonality was exaggerated by MODIS. Our results suggest incremental improvement from Collection 3 to Collection 4 MODIS products, with some remaining problems that need to be addressed

Global products of vegetation green Leaf Area Index (LAI) and Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) are being operationally produced from Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODIS) at 1-km resolution and eight-day frequency. This paper summarizes the experience of several collaborating investigators on validation of MODIS LAI products and demonstrates the close connection between product validation and algorithm refinement activities. The validation of moderate resolution LAI products includes three steps: 1) field sampling representative of LAI spatial distribution and dynamic range within each major land cover type at the validation site; 2) development of a transfer function between field LAI measurements and high resolution satellite data to generate a reference LAI map over an extended area; and 3) comparison of MODIS LAI with aggregated reference LAI map at patch (multipixel) scale in view of geo-location and pixel shift uncertainties. The MODIS LAI validation experiences, summarized here, suggest three key factors that influence the accuracy of LAI retrievals: 1) uncertainties in input land cover data, 2) uncertainties in input surface reflectances, and 3) uncertainties from the model used to build the look-up tables accompanying the algorithm. This strategy of validation efforts guiding algorithm refinements has led to progressively more accurate LAI products from the MODIS sensors aboard NASA's Terra and Aqua platforms

This study examined the nitrogen (N) dynamics of a black spruce (Picea mariana (Mill.) BSP)-dominated chronosequence in Manitoba, Canada. The seven sites studied each contained separate well- and poorly drained stands, originated from stand-killing wildfires, and were between 3 and 151 years old. Our goals were to (i) measure total N concentration ([N]) of all biomass components and major soil horizons; (ii) compare N content and select vegetation N cycle processes among the stands; and (iii) examine relationships between ecosystem C and N cycling for these stands. Vegetation [N] varied significantly by tissue type, species, soil drainage, and stand age; woody debris [N] increased with decay state and decreased with debris size. Soil [N] declined with horizon depth but did not vary with stand age. Total (live + dead) biomass N content ranged from 18.4 to 99.7 g N m−2 in the well-drained stands and 37.8–154.6 g N m−2 in the poorly drained stands. Mean soil N content (380.6 g N m−2) was unaffected by stand age. Annual vegetation N requirement (5.9 and 8.4 g N m−2 yr−1 in the middle-aged well- and poorly drained stands, respectively) was dominated by trees and fine roots in the well-drained stands, and bryophytes in the poorly drained stands. Fraction N retranslocated was significantly higher in deciduous than evergreen tree species, and in older than younger stands. Nitrogen use efficiency (NUE) was significantly lower in bryophytes than in trees, and in deciduous than in evergreen trees. Tree NUE increased with stand age, but overall stand NUE was roughly constant (∼ ∼150 g g−1 N) across the entire chronosequence.

Estimates of daily gross primary production (GPP) and annual net primary production (NPP) at the 1 km spatial resolution are now produced operationally for the global terrestrial surface using imagery from the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor. Ecosystem-level measurements of GPP at eddy covariance flux towers and plot-level measurements of NPP over the surrounding landscape offer opportunities for validating the MODIS NPP and GPP products, but these flux measurements must be scaled over areas on the order of 25 km 2 to make effective comparisons to the MODIS products. Here, we report results for such comparisons at 9 sites varying widely in biome type and land use. The sites included arctic tundra, boreal forest, temperate hardwood forest, temperate conifer forest, tropical rain forest, tallgrass prairie, desert grassland, and cropland. The ground-based NPP and GPP surfaces were generated by application of the Biome-BGC carbon cycle process model in a spatially-distributed mode. Model inputs of land cover and leaf area index were derived from Landsat data. The MODIS NPP and GPP products showed no overall bias. They tended to be overestimates at low productivity sites — often because of artificially high values of MODIS FPAR (fraction of photosynthetically active radiation absorbed by the canopy), a critical input to the MODIS GPP algorithm. In contrast, the MODIS products tended to be underestimates in high productivity sites — often a function of relatively low values for vegetation light use efficiency in the MODIS GPP algorithm. A global network of sites where both NPP and GPP are measured and scaled over the local landscape is needed to more comprehensively validate the MODIS NPP and GPP products and to potentially calibrate the MODIS NPP/GPP algorithm parameters.

Mixedwood forests are an ecologically and economically important ecosystem in the boreal forest of northern Canada. The objectives of this study were to (i) compare the age–height relationships for dominant tree species growing on two contrasting soil types and originating from different disturbances (logging versus wildfire), and (ii) determine the influence of competition on tree growth. Eight stands were selected that encompassed two age-classes replicated on two soil types (clay loam and sand) in a split-plot design. Four of the eight stands originated from logging (21–26 years old), and the four others originated from wildfires (80 years old). Nonlinear age–height analyses were used to compare annual height and radial increment growth of black spruce (Picea mariana (Mill.) BSP), jack pine (Pinus banksiana Lamb.), and trembling aspen (Populus tremuloides Michx.). Species, soil type, and size class explained significant amounts of the measured variation in the age–height models. Aspen, black spruce, and jack pine were 16%, 27%, and 19% taller, respectively, on clay soils than on sandy soils at the burned stand. Tree heights did not differ significantly among species or between soil types in logged stands. Diameter growth decreased as competition increased for black spruce and jack pine in the burned stands. The results for these three important boreal tree species are discussed in the context of sustainable forestry for boreal mixedwood forests.

Safe and economical disposal of paper mill sludge is a key consideration for forest products industry. A study was conducted to examine the effects of amendments of sludge and nutrients on soil surface CO2 flux (Rs) in northern hardwood forests and to quantify the relat among R5, soil temperature, and moisture in these stands. The experiment was a randomized complete block design that included sludge-amended, fertilized, and control treatments in sugar maple (Acer saccharum Marsh) dominated hardwood forests in the Upper Peninsula of Michigan, USA. Results showed that Rs was positively correlated to soil temperature (R2=0.80, p

Carbon budgets are developed to understand ecosystem dynamics and are increasingly being used to develop global change policy. Traditionally, forest carbon budgets have focused on the biological carbon cycle; however, it is important to include the industrial forest carbon cycle as well. The overall objective of this study was to quantify the major carbon fluxes associated with the production of Wisconsin's industrial roundwood, by using life cycle inventory (LCI) methodology to produce an industrial forest carbon budget. To achieve this objective we (1) developed carbon LCIs for the harvest process for three major forest ownerships (state, national, and private non-industrial), (2) developed carbon LCIs for a dimensional lumber and two oriented strand board (OSB) mills and (3) completed a scaled version of 1 and 2 to include more Wisconsin forestlands and to incorporate the other major processes within the industrial forest carbon cycle (e.g. primary mill, secondary mill, product use and product disposal processes of the industrial forest carbon cycle). The carbon budgets for the harvesting process of the Chequamegon-Nicolet National Forest (CNNF), the Northern Highland American Legion State Forest (NHAL), and the non-industrial private forests that participated in the managed forest laws of Wisconsin (MFL-NIPF) were 0.10, 0.18 and 0.11 tonnes C ha−1 year−1), respectively. The dimensional lumber and OSB products were both net carbon sources, and released 0.05–0.09 tonnes C/tonnes C processed). More carbon is sequestered than released within the industrial forest carbon cycle of Wisconsin's national (6 g C m−2 year−1), state (12 g C m−2 year−1) and non-industrial private forests (7 g C m−2 year−1). Using published net ecosystem production data we estimate that the net forest carbon cycle budget (sum of the biological and industrial C cycle, [Gower, S.T., 2003. Patterns and mechanisms of the forest carbon cycle. Ann. Rev. Environ. Resour. 28, 169–204]) for the CNNF ranges between −897 and 348 g C m−2 year−1. Life cycle inventories of wood and paper products should be clear and explicitly state what processes are included, so that results can be used by policy makers and future researchers.

Broadleaf forest is a major type of Earth's land cover with the highest observable vegetation density. Retrievals of biophysical parameters, such as leaf area index (LAI), of broadleaf forests at global scale constitute a major challenge to modern remote sensing techniques in view of low sensitivity (saturation) of surface reflectances to such parameters over dense vegetation. The goal of the performed research is to demonstrate physical principles of LAI retrievals over broadleaf forests with the Moderate Resolution Imaging Spectroradiometer (MODIS) LAI algorithm and to establish a basis for algorithm refinement. To sample natural variability in biophysical parameters of broadleaf forests, we selected MODIS data subsets covering deciduous broadleaf forests of the eastern part of North America and evergreen broadleaf forests of Amazonia. The analysis of an annual course of the Terra MODIS Collection 4 LAI product over broadleaf forests indicated a low portion of best quality main radiative transfer-based algorithm retrievals and dominance of low-reliable backup algorithm retrievals during the growing season. We found that this retrieval anomaly was due to an inconsistency between simulated and MODIS surface reflectances. LAI retrievals over dense vegetation are mostly performed over a compact location in the spectral space of saturated surface reflectances, which need to be accurately modeled. New simulations were performed with the stochastic radiative transfer model, which poses high numerical accuracy at the condition of saturation. Separate sets of parameters of the LAI algorithm were generated for deciduous and evergreen broadleaf forests to account for the differences in the corresponding surface reflectance properties. The optimized algorithm closely captures physics of seasonal variations in surface reflectances and delivers a majority of LAI retrievals during a phonological cycle, consistent with field measurements. The analysis of the optimized retrievals indicates that the precision of MODIS surface reflectances, the natural variability, and mixture of species set a limit to improvements of the accuracy of LAI retrievals over broadleaf forests. © 2005 IEEE.

The spatial and temporal dynamics of soil temperature (TSOIL) strongly influence a wide range of biotic and abiotic processes in boreal forests. Relatively few spatial and temporal TSOIL measurements have been made in these systems; in addition, not all ecosystem models take into account the effect of changing stand structure during stand development on TSOIL dynamics. The goals of this study were to measure TSOIL and its spatiotemporal variability in a boreal forest chronosequence, develop and test a computationally simple empirical model to predict TSOIL, and quantify the effects of different approaches to deriving TSOIL on simulated ecosystem processes. TSOIL was measured hourly at six depths (0‐100 cm) for 3‐4 years, and sampled in a spatial grid monthly during one growing season, in a black spruce (Picea mariana (Mill.) BSP)-dominated boreal forest chronosequence. We report annual and daily TSOIL patterns, air‐soil hystereses, and TSOIL changes at the freeze-thaw transition. An empirical model predicting TSOIL as of the weighted sum of past air temperatures generally accounted for 90‐95% of temporal TSOIL variability at shallow depths, and 77‐83% at 50‐100 cm. A variety of stand structural characteristics affected the model parameters, with leaf area index (LAI) usually the most significant. Spatial TSOIL correlation, measured at depths of 2 and 10 cm, was generally constant between 5 and 30 m. The new empirical model that accounts for changes in canopy structure greatly improved the prediction of TSOIL for stands with high LAI in the Biome-BGC process model; the broader implications of this change are discussed. This model has simple data requirements ‐ only air temperature and LAI ‐ although the parameters given here should only be used for boreal stands with similar soil types. # 2005 Elsevier B.V. All rights reserved.

Ecosystem models are routinely used to estimate net primary production (NPP) from the stand to global scales. Complex ecosystem models, implemented at small scales (

We quantified the effect of stand age and tree species composition on canopy transpiration ( E C ) by analysing transpiration per unit leaf area ( E L ) and canopy stomatal conductance ( G S ) for boreal trees comprising a five stand wildfire chronosequence. A total of 196 sap flux sensors were used on 90 trees consisting of Betula papyrifera Marsh (paper birch; present in the youngest stand), Populus tremuloides Michx (quaking aspen), Pinus banksiana Lamb. (jack pine), and Picea mariana (Mill.) (black spruce). While fine roots were positively correlated with stand E C ; leaf area index, basal area, and sapwood area were not. Stands less than 70 years old were dominated by Populus tremuloides and Pinus banksiana and stands greater than 70 years old were composed almost entirely of Picea mariana. As Populus tremuloides and Pinus banksiana increased in size and age, they displayed an increasing sapwood to leaf area ratio ( A S : A L ), a constant minimum leaf water potential (Y L ), and a constant proportionality between G S at low vapour pressure deficit ( DjG Sref ) and the sensitivity of G S to D (‐d ). In contrast, A S : A L , minimum Y L , and the proportionally between ‐d and G Sref decreased with height and age in Picea mariana . A G S model that included the effects of D , A S : A L , tree height, and for Picea mariana an increasing soil to leaf water potential gradient with stand age, was able to capture the effects of contrasting hydraulic properties of Picea mariana , Populus tremuloides and Pinus banksiana during stand development after wildfire.

This study compared aspatial and spatial methods of using remote sensing and field data to predict maximum growing season leaf area index (LAI) maps in a boreal forest in Manitoba, Canada. The methods tested were orthogonal regression analysis (reduced major axis, RMA) and two geostatistical techniques: kriging with an external drift (KED) and sequential Gaussian conditional simulation (SGCS). Deterministic methods such as RMA and KED provide a single predicted map with either aspatial (e.g., standard error, in regression techniques) or limited spatial (e.g., KED variance) assessments of errors, respectively. In contrast, SGCS takes a probabilistic approach, where simulated values are conditional on the sample values and preserve the sample statistics. In this application, canonical indices were used to maximize the ability of Landsat ETM+ spectral data to account for LAI variability measured in the field through a spatially nested sampling design. As expected based on theory, SGCS did the best job preserving the distribution of measured LAI values. In terms of spatial pattern, SGCS preserved the anisotropy observed in semivariograms of measured LAI, while KED reduced anisotropy and lowered global variance (i.e., lower sill), also consistent with theory. The conditional variance of multiple SGCS realizations provided a useful visual and quantitative measure of spatial uncertainty. For applications requiring spatial prediction methods, we concluded KED is more useful if local accuracy is important, but SGCS is better for indicating global pattern. Predicting LAI from satellite data using geostatistical methods requires a distribution and density of primary, reference LAI measurements that are impractical to obtain. For regional NPP modeling with coarse resolution inputs, the aspatial RMA regression method is the most practical option.

Operational monitoring of global terrestrial gross primary production (GPP) and net primary production (NPP) is now underway using imagery from the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Evaluation of MODIS GPP and NPP products will require site-level studies across a range of biomes, with close attention to numerous scaling issues that must be addressed to link ground measurements to the satellite-based carbon flux estimates. Here, we report results of a study aimed at evaluating MODIS NPP/GPP products at six sites varying widely in climate, land use, and vegetation physiognomy. Comparisons were made for twenty-five 1km 2 cells at each site, with 8-day averages for GPP and an annual value for NPP. The validation data layers were made with a combination of ground measurements, relatively high resolution satellite data (Landsat Enhanced Thematic Mapper Plus at � 30m resolution), and process-based modeling. There was strong seasonality in the MODIS GPP at all sites, and mean NPP ranged from 80gCm � 2 yr � 1 at an arctic tundra site to 550gCm � 2 yr � 1 at a temperate deciduous forest site. There was not a consistent over- or underprediction of NPP across sites relative to the validation estimates. The closest agreements in NPP and GPP were at the temperate deciduous forest, arctic tundra, and boreal forest sites. There was moderate underestimation in the MODIS products at the agricultural field site, and strong overestimation at the desert grassland and at the dry coniferous forest sites. Analyses of specific inputs to the MODIS NPP/ GPP algorithm ‐ notably the fraction of photosynthetically active radiation absorbed by the vegetation canopy, the maximum light use efficiency (LUE), and the climate data ‐ revealed the causes of the over- and underestimates. Suggestions for algorithm improvement include selectively altering values for maximum LUE (based on observations at eddy covariance flux towers) and parameters regulating autotrophic respiration.

Light use efficiency (LUE) models are often used with remotely sensed data products to estimate net primary production (NPP) from local to global scales. However, data on the variability of the LUE coefficient, e, on the landscape are minimal and sometimes conflicting. The objectives of this study were to (1) quantify and compare the variability of LUE among five forest cover types: aspen, northern hardwoods, red pine, forested wetland, and upland conifer; and (2) quantify the variability of e between two years, 1999 and 2000, and relate differences to environmental conditions. The study site was in a northern temperate forest in Wisconsin, USA. Northern hardwood forests, primarily consisting of sugar maple, had the highest e each year followed by aspen, red pine, forested wetlands, and upland conifer. NPP was estimated using radial growth measurements and published allometric equations. Absorbed photosynthetically active radiation (APAR) was estimated optically using a Li-Cor Plant Canopy Analyzer. Growing season e of all forest cover types increased significantly from 0.42 in 1999 to 0.47 (gC MJ � 1 ) in 2000. Annual e of all forest cover types increased significantly from 0.33 in 1999 to 0.36 (gC MJ � 1 ) in 2000. Growing season and annual e differed significantly (pV0.001) among forest cover types for each year. Future research should consider variations in LUE among mixtures of many land cover types, especially forested wetlands. Results from this study show that LUE models should consider species-specific efficiency factors rather than biome-specific factors. Remote sensing-based land cover classifications should also reflect species differences for this area if the classification map is used in estimating NPP with an LUE model.

Soil surface CO2 flux (RS) is overwhelmingly the product of respiration by roots (autotrophic respiration, RA) and soil organisms (heterotrophic respiration, RH). Many studies have attempted to partition RS into these two components, with highly variable results. This study analyzes published data encompassing 54 forest sites and shows that RA and RH are each strongly (R 2 40.8) correlated to annual RS across a wide range of forest ecosystems. Monte Carlo simulation showed that these correlations were significantly stronger than any correlation introduced as an artefact of measurement method. Biome type, measurement method, mean annual temperature, soil drainage, and leaf habit were not significant. For sites with available data, there was a significant (R 2 50.56) correlation between total detritus input and RH, while RAwas unrelated to net primary production. We discuss why RA and RH might be related to each other on large scales, as both ultimately depend on forest carbon balance and photosynthate supply. Limited data suggest that these or similar relationships have broad applicability in other ecosystem types. Site-specific measurements are always more desirable than the application of inferred broad relationships, but belowground measurements are difficult and expensive, while measuring RS is straightforward and commonly done. Thus the relationships presented here provide a useful method that can help constrain estimates of terrestrial carbon budgets.

We calculated carbon budgets for a chronosequence of harvested jack pine (Pinus banksiana Lamb.) stands (0-, 5-, 10-, and � 29-year-old) and a � 79-year-old stand that originated after wildfire. We measured total ecosystem C content (TEC), above-, and belowground net primary productivity (NPP) for each stand. All values are reported in order for the 0-, 5-, 10-, 29-, and 79-year-old stands, respectively, for May 1999 through April 2000. Total annual NPP (NPPT) for the stands (MgCha � 1 yr � 1 � 1 SD) was 0.9 � 0.3, 1.3 � 0.1, 2.7 � 0.6, 3.5 � 0.3, and 1.7 � 0.4. We correlated periodic soil surface CO2 fluxes (RS) with soil temperature to model annual RS for the stands (MgCha � 1 yr � 1 � 1 SD) as 4.4 � 0.1, 2.4 � 0.0, 3.3 � 0.1, 5.7 � 0.3, and 3.2 � 0.2. We estimated net ecosystem productivity (NEP) as NPPT minus RH (where RH was calculated using a Monte Carlo approach as coarse woody debris respiration plus 30‐70% of total annual RS). Excluding C losses during wood processing, NEP (MgCha � 1 yr � 1 � 1 SD) for the stands was estimated to be � 1.9 � 0.7, � 0.4 � 0.6, 0.4 � 0.9, 0.4 � 1.0, and � 0.2 � 0.7 (negative values indicate net sources to the atmosphere.) We also calculated NEP values from the changes in TEC among stands. Only the 0-year-old stand showed significantly different NEP between the two methods, suggesting a possible mismatch for the chronosequence. The spatial and methodological uncertainties allow us to say little for certain except that the stand becomes a source of C to the atmosphere following logging.

Motivated by the increasing importance of hyperspectral remote sensing data, this study sought to determine whether current-generation narrow-band hyperspectral remote sensing data could better track vegetation leaf area index (LAI) than traditional broad-band multispectral data. The study takes advantage of a unique dataset, wherein field measurements of LAI were acquired at the same general time and grain size as both Landsat ETM+ and AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) imagery in four different biomes. Biome types sampled included row-crop agriculture, tallgrass prairie, mixed hardwood-conifer forest, and boreal conifer forest. The effects of bandwidth, band placement, and number of bands were isolated from radiometric quality by comparing regression models derived from individual AVIRIS channels with those derived from simulated ETM+ and MODIS channels using the AVIRIS data. Models with selected subsets of individual AVIRIS channels performed better to predict LAI than those based on the broadband datasets, although the potential to overfit models using the large number of available AVIRIS bands is a concern. Models based on actual ETM+ data were generally stronger than those based on simulated ETM+ data, suggesting that, for predicting LAI, ETM+ data suffer no penalty for having lower radiometric quality. NDVI was generally not sensitive to LAI at the four sites. Band placement of broad-band sensors (e.g., simulated ETM+ and MODIS) did not affect relationships with LAI, suggesting that there is no inherent advantage to MODIS spectral properties over those of ETM+ for estimating LAI. Spectral channels in the red-edge and shortwave-infrared regions were generally more important than those in the near-infrared for predicting LAI.

Net primary production (NPP) was measured in seven black spruce (Picea mariana (Mill.) BSP)-dominated sites comprising a boreal forest chronosequence near Thompson, Man., Canada. The sites burned between 1998 and 1850, and each contained separate well- and poorly drained stands. All components of NPP were measured, most for 3 consecutive years. Total NPP was low (50‐100gCm � 2 yr � 1 ) immediately after fire, highest 12‐20 years after fire (332 and 521gCm � 2 yr � 1 in the dry and wet stands, respectively) but 50% lower than this in the oldest stands. Tree NPP was highest 37 years after fire but 16‐ 39% lower in older stands, and was dominated by deciduous seedlings in the young stands and by black spruce trees (485%) in the older stands. The chronosequence was unreplicated but these results were consistent with 14 secondary sites sampled across the landscape. Bryophytes comprised a large percentage of aboveground NPP in the poorly drained stands, while belowground NPP was 0‐40% of total NPP. Interannual NPP variability was greater in the youngest stands, the poorly drained stands, and for understory and detritus production. Net ecosystem production (NEP), calculated using heterotrophic soil and woody debris respiration data from previous studies in this chronosequence, implied that the youngest stands were moderate C sources (roughly, 100gC m � 2 yr � 1 ), the middle-aged stands relatively strong sinks (100‐300gCm � 2 yr � 1 ), and the oldest stands about neutral with respect to the atmosphere. The ecosystem approach employed in this study provided realistic estimates of chronosequence NPP and NEP, demonstrated the profound impact of wildfire on forest‐atmosphere C exchange, and emphasized the need to account for soil drainage, bryophyte production, and species succession when modeling boreal forest C fluxes.

Accurate characterization of leaf area index (LAI) is required to quantify the exchange of energy, water, and carbon between terrestrial ecosystems and the atmosphere. The objective of this study was to use a cyclic sampling design to compare the spatial patterns of LAI of the dominant terrestrial ecosystems that comprised the area around the 447-m WLEF television tower, equipped with an eddy flux system, near Park Falls, Wisconsin, USA. A second objective was to compare the efficiency of cyclic, random, and uniform sampling designs in terms of the precision of spatial information derived per unit sampling effort. The vegetation surrounding the tower was comprised (more than 80%) of four major forest cover types: forested wetlands, upland aspen forests, upland northern hardwood forests, and upland pine forests, and a fifth, nonforested cover type, grass (open meadow). LAI differed significantly among the five cover types and averaged 3.45, 3.57, 3.82, 3.99, and 1.14 for northern hardwoods, aspen, forested wetlands, upland conifers, and grass, respectively. The cyclic sampling design maximized information about the variance of vegetation characteristics of the heterogeneous landscape and decreased by 60% the number of plots needed to obtain the same confidence interval width using a random sampling design. The range of spatial autocorrelation for LAI was 147 m, but it was decreased to 117 m when vegetation cover was included as a covariate. The cyclic sampling design has several important advantages over other sampling designs. The cyclic sampling design increased the sampling efficiency by optimizing the placement of plots so they were distributed more efficiently for geostatistical analyses such as semi-variograms, correlograms, and spatial regression and can incorporate covariates (for example, vegetation cover, soil properties, and so on) that may explain the sources of spatial patterns. The cyclic sampling design was used to derive a spatial map of LAI and the average LAI for the 3 × 2 km area centered on the flux tower was 3.51 ± 0.89 (with a minimum of 0 and a maximum of 6.35). Airborne and satellite reflectance data have also been used to characterize LAI, but in this region, and many other forests of the world, remotely sensed vegetation indexes saturate in forests with an LAI greater than 3–5. The cyclic sampling design also provides a general ecological sampling approach that can be used at multiple scales.

The Moderate Resolution Imaging Radiometer (MODIS) is the primary instrument in the NASA Earth Observing System for monitoring the seasonality of global terrestrial vegetation. Estimates of 8-day mean daily gross primary production (GPP) at the 1 km spatial resolution are now operationally produced by the MODIS Land Science Team for the global terrestrial surface using a production efficiency approach. In this study, the 2001 MODIS GPP product was compared with scaled GPP estimates (25 km 2 ) based on ground measurements at two forested sites. The ground-based GPP scaling approach relied on a carbon cycle process model run in a spatially distributed mode. Land cover classification and maximum annual leaf area index, as derived from Landsat ETM+ imagery, were used in model initiation. The model was driven by daily meteorological observations from an eddy covariance flux tower situated at the center of each site. Model simulated GPPs were corroborated with daily GPP estimates from the flux tower. At the hardwood forest site, the MODIS GPP phenology started earlier than was indicated by the scaled GPP, and the summertime GPP from MODIS was generally lower than the scaled GPP values. The fall-off in production at the end of the growing season was similar to the validation data. At the boreal forest site, the GPP phenologies generally agreed because both responded to the strong signal associated with minimum temperature. The midsummer MODIS GPP there was generally higher than the ground-based GPP. The differences between the MODIS GPP products and the ground-based GPPs were driven by differences in the timing of FPAR and the magnitude of light use efficiency as well as by differences in other inputs to the MODIS GPP algorithm—daily incident PAR, minimum temperature, and vapor pressure deficit. Ground-based scaling of GPP has the potential to improve the parameterization of light use efficiency in satellite-based GPP monitoring algorithms.

Forests are an important source for fiber and fuel for humans and contain the majority of the total terrestrial carbon (C). The amount of C stored in the vegetation and soil are strongly influenced by environmental constraints on annual C uptake and decomposition and time since disturbance. Increasing concentrations of atmospheric carbon dioxide (CO2), nitrogen deposition, and climate warming induced by greater greenhouse gas (GHG) concentrations in the atmosphere influence C accumulation rates of forests, but their effects will likely differ in direction and magnitude among forest ecosystems. The net interactive effect of global change on the forest C cycle is poorly understood. The growing demand for wood fiber and fuel by humans and the ongoing anthropogenic perturbations of the climate have changed the natural disturbance regimes (i.e., frequency and intensity); these changes influence the net exchange of CO2 between forests and the atmosphere. To date, the role of forest products in the global C cycle have largely been ignored, and important emissions associated with the production, transport, and utilization of the forest products have been excluded, leading to erroneous conclusions about net C storage in forest products.

Quantifying forest net primary production (NPP) is critical to understanding the global carbon cycle because forests are responsible for a large portion of the total terrestrial NPP. The objectives of this study were to measure above ground NPP (NPPA) for a land surface in northern Wisconsin, examine the spatial patterns of NPPA and its components, and correlate NPPA with vegetation cover types and leaf area index. Mean NPPA for aspen, hardwoods, mixed forest, upland conifers, nonforested wetlands, and forested wetlands was 7.8, 7.2, 5.7, 4.9, 5.0, and 4.5 t dry mass·ha–1·year–1, respectively. There were significant (p = 0.01) spatial patterns in wood, foliage, and understory NPP components and NPPA (p = 0.03) when the vegetation cover type was included in the model. The spatial range estimates for the three NPP components and NPPA differed significantly from each other, suggesting that different factors are influencing the components of NPP. NPPA was significantly correlated with leaf area index (p = 0.01) for the major vegetation cover types. The mean NPPA for the 3 km × 2 km site was 5.8 t dry mass·ha–1·year–1.