Search

Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of changing climate and wildfire activity influenced conifer regeneration after 334 wildfires, using a dataset of postfire conifer regeneration from 10,230 field plots. Our findings highlight declining regeneration capacity across the West over the past four decades for the eight dominant conifer species studied. Postfire regeneration is sensitive to high-severity fire, which limits seed availability, and postfire climate, which influences seedling establishment. In the near-term, projected differences in recruitment probability between low- and high-severity fire scenarios were larger than projected climate change impacts for most species, suggesting that reductions in fire severity, and resultant impacts on seed availability, could partially offset expected climate-driven declines in postfire regeneration. Across 40 to 42% of the study area, we project postfire conifer regeneration to be likely following low-severity but not high-severity fire under future climate scenarios (2031 to 2050). However, increasingly warm, dry climate conditions are projected to eventually outweigh the influence of fire severity and seed availability. The percent of the study area considered unlikely to experience conifer regeneration, regardless of fire severity, increased from 5% in 1981 to 2000 to 26 to 31% by mid-century, highlighting a limited time window over which management actions that reduce fire severity may effectively support postfire conifer regeneration.

Mortality of tree species around the globe is increasingly driven by hotter drought and heat waves. Tree juveniles are at risk, as well as adults, and this will have a negative effect on forest dynamics and structure under climate change. Novel management options are urgently needed to reduce this mortality and positively affect forest dynamics and structure. Potential drought-ameliorating soil amendments such as nanochitosan - a biopolymer upcycled from byproducts of the seafood industry - may provide an additional set of useful tools for reducing juvenile mortality during hotter droughts. Nanochitosan promotes water and nutrient absorption in plants but has not been tested in the context of drought and heat stress. We evaluated factors affecting mortality risk and rate for dryland Pinus edulis juveniles (2-3 years old) in a growth chamber using a factorial experiment that included ambient and +4°C warmer base temperatures, with and without a 10 day +8°C heat wave, and with and without a nanochitosan soil amendment. The nanochitosan treatment reduced the relative risk of mortality, emphasizing a protective function of this soil amendment, reducing the relative risk of mortality by 37%. Importantly, the protective effects of nanochitosan soil amendment in delaying tree mortality under hotter drought and heat waves provides a new, potentially positive management treatment for tree juveniles trying to survive in the climate of the Anthropocene. [ABSTRACT FROM AUTHOR]

Context: The concept of the fire regime is central to understanding and managing fire-prone ecosystems globally, and information on past regimes can provide useful insights into species disturbance adaptations. Although observations from satellite imagery or palaeoecological proxy data can provide direct evidence of past, pre-colonial fire regimes, they may be limited in temporal or spatial resolution and are not available for all ecosystems. However, fire-related plant-trait and demographic data offer an alternative approach to understand species–fire regime associations at the ecosystem scale. Aims: We aimed to quantify the life-history strategies and associated fire regimes for six co-occurring shrub and tree species from fire-prone, Mediterranean-climate Banksia Woodlands in south-western Australia. Methods: We collected static demographic data on size structure, seedling recruitment, and plant mortality across sites of varying time since last fire. We combined demographic data with key fire-related species traits to define plant life-history strategies. We then compared observed life histories with a priori expectations for surface, stand-replacing, and mixed-severity fire-regime types to infer historical fire-regime associations. Key results: Fire-killed shrubs and weakly serotinous trees had abundant post-fire seedling recruitment, but also developed multi-cohort populations during fire-free periods via inter-fire seedling recruitment. Resprouting shrubs had little seedling recruitment at any time, even following fire, and showed no signs of decline in the long absence of fire, likely owing to their very long lifespans. Conclusions: The variation in life-history strategies for these six co-occurring species is consistent with known ecological strategies to cope with high variation in fire intervals in a mixed-severity fire regime. Whereas resprouting and strong post-fire seedling recruitment indicate a tolerance of shorter fire intervals, inter-fire recruitment and weak serotiny are interpreted as a bet-hedging strategy to cope with occasional long fire-free periods that may otherwise exceed adult and seed-bank lifespans. Implications: Our findings suggested that Banksia Woodlands have evolved with highly variable fire intervals in a mixed-severity fire regime. Further investigations of species adaptations to varying fire size and patchiness can help extend our understanding of fire-regime tolerances. Information on past fire regimes can provide useful insights into species disturbance adaptations. To test the idea that contemporary demographic parameters provide a signature of past fire regimes, we assessed fire-related plant life-history strategies by using static demographic data collected along a 1–35-year fire-age chronosequence for species with a variety of traits. Species displayed a collection of life-history strategies associated with a historical mixed-severity fire regime, including adaptations for short and long fire intervals, interacting with varying fire severity. Photograph by Russell Miller. [ABSTRACT FROM AUTHOR]

Context: Extinction debt, the time-delayed species loss response to fragmentation associated with habitat clearance, is a conservation concern for management of biological diversity globally. Extinction debt is well defined but difficult to measure owing to the long-term data needed to measure species loss, particularly for communities of long-lived species. Aims: We aimed to estimate extinction debt for two adjacent threatened communities with contrasting soil fertility in south-western Australia: banksia and tuart woodlands. Further, we assessed what species functional traits are associated with extinction risk. Methods: Using contemporary (2016) and historical (1992) data on vegetation richness, and patch characteristics dating back to the time of European colonisation (1829), we examined 60 woodland patches using three methods to detect and quantify extinction debt. Key results: We found evidence of extinction debt in banksia woodland, but not in tuart woodland. We estimated the extinction debt for banksia woodlands as a future average loss of 28% or ~13 species per patch. Conclusions: Our study demonstrated a delay of species loss consistent with extinction debt in one of two vegetation communities. Despite sharing species and traits, these vegetation communities have responded differently to landscape change over the same timescale and within the same landscape. Implications: Understanding how vegetation communities, and functional trait types, respond to time-delayed impacts helps land managers to prioritise intervention efforts to pre-empt species decline and extinction through species conservation, and ecological restoration of remnant vegetation patches. Time-delayed species loss in response to fragmentation associated with habitat clearance, is a conservation concern for management of biological diversity in the world's fragmented landscapes. We found evidence of future species loss in some of the study communities. Banksia woodlands had 28% average loss (13 species per patch). Understanding how different community types respond to time-delayed impacts helps land managers to prioritise intervention efforts to pre-empt species decline and eventual extinction through conservation, management and restoration of remnant vegetation patches. BT22134_toc.jpg [ABSTRACT FROM AUTHOR]

Large-scale wildfires (~[10.sup.4]-[10.sup.6] ha) have the potential to eliminate seed sources over broad areas and thus may lead to qualitatively different regeneration dynamics than in small burns; however, regeneration after such events has received little study in temperate forests. Following a 200 000 ha mixed-severity wildfire in Oregon, USA, we quantified (1) conifer and broadleaf regeneration in stand-replacement patches 2 and 4 years postfire; and (2) the relative importance of isolation from seed sources (live trees) versus local site conditions in controlling regeneration. Patch-scale conifer regeneration density (72%-80% Douglas-fir (Pseudotsuga menziesii (Mirb). Franco)) varied widely, from 127 to 6494 stems x [ha.sup.-1]. Median densities were 1721 and 1603 stems x [ha.sup.-1] 2 and 4 years postfire, respectively, i.e., ~12 times prefire overstory densities (134 stems x [ha.sup.-1]). Because of the complex burn mosaic, ~58% of stand-replacement area was ≤ 200 m from a live-tree edge (seed source), and ~81% was ≤ 400 m. Median conifer density exceeded 1000 stems x [ha.sup.-1] out to a distance of 400 m from an edge before declining farther away. The strongest controls on regeneration were distance to live trees and soil parent material, with skeletal coarse-grained soils supporting lower densities (133 stems x [ha.sup.-1]) than fine-grained soils (729-1492 stems x [ha.sup.-1]). Other site factors (e.g., topography, broadleaf cover) had little association with conifer regeneration. The mixed-severity fire pattern strongly influenced the regeneration process by providing seed sources throughout much of the burned landscape. Les grands feux (~[10.sup.4] a [10.sup.6] ha) peuvent eliminer les sources de semences sur de vastes superficies et peuvent donc provoquer des dynamiques de regeneration qualitativement differentes de celles qui resultent des feux de moindre importance. Cependant, la regeneration qui s'etablit apres de tels evenements a fait l'objet de peu d'etudes dans les forets temperees. A la suite d'un feu de severite variable qui a brule une superficie de 200 000 ha en Oregon, aux E tats-Unis, nous avons quantifie : (1) la regeneration de coniferes et de feuillus etablie dans les parcelles de terrain ou le feu avait completement detruit la foret, deux et quatre ans apres le passage du feu et (2) l'importance relative de l'isolement par rapport aux sources de semences (arbres vivants) et des conditions locales de station pour l'etablissement de la regeneration. A l'echelle des parcelles, la densite de la regeneration de coniferes (composee de 72 a 80 % de douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco) etait tres variable, passant de 127 a 6494 semis x [ha.sup.-1]. Deux et quatre ans apres le passage du feu, la densite mediane etait respectivement de 1721 et 1603 semis x [ha.sup.-1], ce qui correspond a environ 12 fois la densite du couvert dominant avant le passage du feu (134 tiges x [ha.sup.-1]). A cause de la mosaique complexe du feu, environ 58 % de la superficie ou le feu avait completement detruit la foret etait situee a 200 m ou moins de la bordure d'une foret (source de semences) et 81% de cette superficie etait situee a 400 m ou moins. La densite mediane de coniferes etait superieure a 1000 semis x [ha.sup.-1] jusqu'a une distance de 400 m de la bordure d'une foret et diminuait par la suite. L'etablissement de la regeneration etait surtout influence par la distance des arbres vivants et par le materiau d'origine du sol. Les sols squelettiques a texture grossiere supportaient des densites moins elevees (133 semis x [ha.sup.-1]) que les sols a texture fine (729 a 1492 semis x [ha.sup.-1]). Les autres variables de la station (p. ex. la topographie et le couvert de feuillus) avaient peu d'impact sur l'etablissement de la regeneration de coniferes. La severite variable du feu a fortement influence l'etablissement de la regeneration en fournissant des sources de semences sur la majeure partie du territoire brule. [Traduit par la Redaction], Introduction In many temperate forests, fires generate and maintain ecosystem structure, in part, by regulating tree establishment (Agee 1993; Turner et al. 1997). Patterns of conifer regeneration after wildfire strongly [...]

We studied the pollination biology of 18 common insect-pollinated plant species on Kent Island, a boreal island in the Bay of Fundy, New Brunswick, Canada. Under natural conditions, fruit set was relatively high in most of the species studied [although it was very low ( Overall, our results demonstrate that for many insect-pollinated plant species on Kent Island, pollinators are likely to be limiting, autogamy is common and inbreeding depression is negligible. Although pollinator limitation and autogamy regularly occur in mainland habitats as well, a review of the literature suggests that they may be more common on islands such as Kent Island. If such island-mainland differences are general, they may arise because genotypes and species capable of self-fertilization are more likely than obligate outcrossers to colonize and become established in isolated habitats.