skip to main content

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, December 13 until 2:00 AM ET on Saturday, December 14 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Predicting snag fall in an old-growth forest after fire
Abstract Background

Snags, standing dead trees, are becoming more abundant in forests as tree mortality rates continue to increase due to fire, drought, and bark beetles. Snags provide habitat for birds and small mammals, and when they fall to the ground, the resulting logs provide additional wildlife habitat and affect nutrient cycling, fuel loads, and fire behavior. Predicting how long snags will remain standing after fire is essential for managing habitat, understanding chemical cycling in forests, and modeling forest succession and fuels. Few studies, however, have quantified how fire changes snag fall dynamics.

 Results

We compared post-fire fall rates of snags that existed pre-fire (n= 2013) and snags created during or after the fire (n= 8222), using 3 years of pre-fire and 5 years of post-fire data from an annually monitored, 25.6-ha spatially explicit plot in an old-growthAbies concolor–Pinus lambertianaforest in the Sierra Nevada, CA, USA. The plot burned at low to moderate severity in the Rim Fire of 2013. We used random forest models to (1) identify predictors of post-fire snag fall for pre-existing and new snags and (2) assess the influence of spatial neighborhood and local fire severity on snag fall after fire. Fall rates of pre-existing snags increased 3 years after fire. Five years after fire, pre-existing snags were twice as likely to fall as new snags. Pre-existing snags were most likely to persist 5 years after fire if they were > 50 cm in diameter, > 20 m tall, and charred on the bole to heights above 3.7 m. New snags were also more likely to persist 5 years after fire if they were > 20 m tall. Spatial neighborhood (e.g., tree density) and local fire severity (e.g., fire-caused crown injury) within 15 m of each snag barely improved predictions of snag fall after fire.

 Conclusions

Land managers should expect fall rates of pre-existing snags to exceed fall rates of new snags within 5 years after fire, an important habitat consideration because pre-existing snags represent a wider range of size and decay classes.

  more » « less
PAR ID:
10475368
Author(s) / Creator(s):
;
Publisher / Repository:
Springer Science + Business Media
Date Published:
Journal Name:
Fire Ecology
Volume:
19
Issue:
1
ISSN:
1933-9747
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ( , Journal of Vegetation Science)
    Abstract Questions

    Anthropogenic climate change is causing increases in the severity of wildland fire in many parts of the world. At the same time, post‐fire succession is occurring under new, warmer temperatures that are projected to continue increasing. Despite this, the combined effects of uncharacteristically high burn severity and increased ambient temperature on post‐fire community composition remain poorly understood. We ask how post‐fire forest understorey community composition and species richness are influenced by (1) burn severity, (2) experimental warming, and (3) years since fire.

     Location

    Museum Fire Scar,Pinus ponderosaforest, Arizona, United States.

     Methods

    We established 120 1‐m2quadrats in unburned, low‐ and high‐severity locations nine months after a mixed‐severity fire. Half of the plots were subject to experimental warming via open‐top warming chambers that elevated daytime temperatures by 1.079°C, simulating near‐term anthropogenic warming. Plant composition data were collected annually for three years. Relationships between community composition, burn severity, and experimental warming were analyzed using repeated‐measures PERMANOVA and linear mixed‐effects models.

     Results

    Composition differed significantly according to burn severity, time since fire, and their interaction, while experimental warming did not significantly influence composition. Species richness significantly increased in burned areas compared to unburned control within two years of fire.

     Conclusions

    Our results suggest that near‐term temperature increases, driven by anthropogenic climate change, will have little effect on community composition relative to fire severity. High‐severity fire drove large, rapid changes in plant composition compared to unburned controls, favoring exotic annuals in a historically perennial‐dominated plant community.

     
    more » « less
  2. ; ; ; ; ; ( , Journal of Vegetation Science)
    Abstract Questions

    (a) How did seedling numbers and species composition change in the first year after a wildfire during drought, relative to pre‐fire variation? (b) Has the community returned to pre‐fire composition after five years? (c) Has the degree of dominance by exotic annual grasses changed? (d) Is there any evidence that drought conditions affected community cover, before or after fire?

     Location

    Exotic‐dominated annual grassland in southern California, USA.

     Methods

    We monitored community cover and native annual forb densities for four years before and four (cover) to five (densities) years after an unintentional fire (fall 2013) coinciding with the spring 2012–2019 California drought. We also measured seedling emergence both before and during the first year post‐fire. We assessed post‐fire changes in cover and density relative to pre‐fire variation, and tested correlations between community cover and annual rainfall measures.

     Results

    Seedling emergence declined strongly after fire for exotic grasses, but remained stable for exotic forbs. Seedling densities of the most common native forbs declined, but several previously‐rare natives increased. Community cover initially shifted towards the exotic forbsErodiumspp., then returned to higher exotic grass densities. Yet the previously dominantBromus diandrusdeclined steeply, even as other exotic grasses and some native forbs increased. Up to five years after fire, relative cover and abundance of the most common exotic and native species still differed from pre‐fire composition. Common species were uncorrelated with annual precipitation, but several may have responded to shorter growing seasons.

     Conclusions

    Immediate post‐fire conditions favoured exotic and native forbs over grasses, as predicted. Yet in contrast to many previous studies, the community did not return quickly to pre‐fire composition but showed persistent changes that favoured neither natives nor exotics. Our results suggest post‐fire recovery in this habitat may be contingent on abiotic conditions, with drought one potential explanation for changes.

     
    more » « less
  3. ; ; ; ; ( , Fire Ecology)
    Abstract Background

    Warmer climate conditions are altering fire regimes globally, eroding the capacity of forest ecosystems to resist and recover from natural disturbances like wildfire. Severe and rapidly repeated wildfires are promoting tree regeneration failure of obligate-seeders and/or fire-sensitive species in temperate forests of the Southern Hemisphere. We collected post-fire field data to evaluate whether forest structure and tree regeneration responses varied between two Andean forest study areas dominated by the threatened Gondwanan coniferAraucaria araucanaandNothofagusspecies (southern beeches) — one area burned once, the other reburned after 13 years.

     Results

    Tree mortality was high across species after a single high severity and/or repeated wildfire, although someA. araucanatrees were able to survive both events. Post-fire seedling regeneration ofA. araucanaandNothofagusspp. was poor in areas affected by severe wildfires, and the latter was absent from reburned plots. A key driver of this regeneration failure was increasing distance to live seed source trees, which was negatively correlated with these species’ post-fire seedling abundances. In contrast, species with the capacity to regenerate via resprouting (A. araucana, N. alpina, N. obliqua) did so after a single high severity fire; however, only a singleNothofagusspecies (N. alpina)resprouted abundantly after a reburn.

     Conclusions

    Our findings suggest that high severity and short-interval fires can drastically change the structure of and limit post-fire tree regeneration inAraucaria-Nothofagusforests, promoting alternative post-fire forest ecosystem trajectories. Resprouting species of theNothofagusgenus, especiallyN. alpina, exhibit the greatest resilience to these emerging fire patterns. These forests are currently facing an unprecedented climatic shift toward greater fire activity, where resprouting is the favored regeneration strategy. If the occurrence of severe and short-interval fires increases in the coming decades, as predicted, we expectAraucaria-Nothofagusforests to shift toward a drier, more flammable shrubland ecosystem state.

     
    more » « less
  4. ; ; ; ( , Canadian Journal of Forest Research)
    In Southeast Alaska, many stands of yellow-cedar (Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little; hereinafter “YC”) contain numerous standing, dead snags. Snag-age estimates based on tree morphology have been used to support the interpretation that a warming climate after ca. 1880 has triggered unprecedented YC dieback. Here, we present new estimates of YC snag longevity by cross-dating 61 snags with morphologies that suggest they stood dead for extended periods. All but four of these snags have lost their outermost rings to decay, so we estimate when they died using a new method based on wood-ablation rates measured in six living trees that display partial cambial dieback. The results indicate that ∼59% of YC snags that lost their branches to decay (Class 5 snags) have remained standing for >200 years, and some for as long as 450 years (snag longevity mean ± SD: 233 ± 92 years). These findings, along with supporting evidence from historical photos, dendrochronology, and snag-morphology surveys in the published literature suggest that episodes of YC dieback also occurred before 1880 and before significant anthropogenic warming began. The roles played by climate change in these earlier dieback events remain to be further explored. 
    more » « less
  5. ; ; ; ; ; ; ; ; ( , Ecology)
    Abstract

    Standing dead trees (snags) decompose more slowly than downed dead wood and provide critical habitat for many species. The rate at which snags fall therefore influences forest carbon dynamics and biodiversity. Fall rates correlate strongly with mean annual temperature, presumably because warmer climates facilitate faster wood decomposition and hence degradation of the structural stability of standing wood. These faster decomposition rates coincide with turnover from fungal‐dominated wood decomposer communities in cooler forests to codomination by fungi and termites in warmer regions. A key question for projecting forest dynamics is therefore whether temperature effects on wood decomposition arise primarily because warmer conditions facilitate faster decomposer metabolism, or are also influenced indirectly by belowground community turnover (e.g., termites exert additional influence beyond fungal‐plus‐bacterial mediated decomposition). To test between these possibilities, we simulate standing dead trees with untreated wooden posts and follow them in the field across 5 yr at 12 sites, before measuring buried, soil–air interface and aerial post sections to quantify wood decomposition and organism activities. High termite activities at the warmer sites are associated with rates of postfall that are three times higher than at the cooler sites. Termites primarily consume buried wood, with decomposition rates greatest where termite activities are highest. However, where higher microbial and termite activities co‐occur, they appear to compensate for one another first, and then to slow decomposition rates at their highest activities, suggestive of interference competition. If the range of microbial and termite codomination of wood decomposer communities expands under climate warming, our data suggest that expansion will accelerate snag fall with consequent effects on forest carbon cycling and biodiversity in forests previously dominated by microbial decomposers.

     
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email