The role of facilitation and competition in the development and resilience of aspen forests

Clair, Samuel B. St.; Cavard, Xavier; Bergeron, Yves

doi:10.1016/j.foreco.2013.02.026

Cited by 29 publications

(15 citation statements)

References 113 publications

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“…This fact may in part explain the observed fluctuations in regeneration density, shifts in species dominance, and the failure of some cohorts to persist (see St Clair et al. ). Cyclic wetting and drying and fluctuating temperatures are known inhibitors of early growth in aspen (McDonough ).…”

Section: Discussionmentioning

confidence: 97%

“…Regeneration following high-severity fires is free of competition from above-ground legacies but is more sensitive to environmental conditions. This fact may in part explain the observed fluctuations in regeneration density, shifts in species dominance, and the failure of some cohorts to persist (see St Clair et al 2013). Cyclic wetting and drying and fluctuating temperatures are known inhibitors of early growth in aspen (McDonough 1985).…”

Section: Discussionmentioning

confidence: 99%

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Is initial post‐disturbance regeneration indicative of longer‐term trajectories?

et al. 2017

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Abstract. The ability to estimate and model future vegetation dynamics is a central focus of contemporary ecology and is essential for understanding future ecological trajectories. It is therefore critical to understand when the influence of initial post-disturbance regeneration versus stochastic processes dominates long-term post-disturbance ecological processes. Often, conclusions about post-disturbance dynamics are based upon initial regeneration in the years immediately after disturbances. However, the degree to which initial post-disturbance regeneration indicates longer-term trends is likely to be contingent on the types, intensities, and combinations of disturbances, as well as pre-disturbance ecosystem structure and composition. Our relatively limited understanding of why initial post-disturbance regeneration is sometimes a poor predictor of future ecosystem trajectories represents a critical gap in post-disturbance ecological forecasting. We studied the composition and density of regeneration of tree species following wind blowdown in 1997, wildfire in 2002, and compounded disturbances by blowdown and wildfire in subalpine forests of Colorado. We examined regeneration of Picea engelmannii, Abies lasiocarpa, Pinus contorta, and Populus tremuloides in 180 permanent plots across 12 sites (classified by pre-disturbance age and composition) in 2003, 2010, and 2015. At sites that were blown down but not burned, regeneration was dense and dominated by Picea and Abies. At these sites, regeneration observed from 2003 to 2005 (hereafter initial regeneration) was also highly predictive of regeneration 5-10 yr later. In contrast, at sites that were burned and sites that were blown down and burned, regeneration was less dense and dominated by a mix of species. At these sites, initial regeneration was a poor predictor of longer-term trends as species dominance and overall density fluctuated over the 13-yr period. These findings call into question our ability to confidently predict ecosystem trajectories based upon observations made in the years immediately after large, severe disturbances such as wildfires and compounded disturbances. As compounded disturbances become more common under climatically driven changes in disturbance regimes, post-disturbance ecosystem trajectories may become increasingly stochastic and unpredictable.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Is initial post‐disturbance regeneration indicative of longer‐term trajectories?

et al. 2017

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“…Aspen and other post‐disturbance pioneering species play a fundamentally important role in facilitating the post‐disturbance re‐establishment of forest communities (St. Clair et al ), but intense browsing by ungulates can be detrimental to their establishment and recruitment (Baker et al ). Based on the results in this study, regeneration resilience to browse pressure may be increased with high burn severity conditions.…”

Section: Discussionmentioning

confidence: 99%

Fire severity alters plant regeneration patterns and defense against herbivores in mixed aspen forests

Wan

Rhodes

Clair

2014

Oikos

Self Cite

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Fire and herbivory are primary disturbances that often overlap and strongly infl uence plant community development, but it is unclear how herbivory changes in relation to variability in burn severity. With climate change expected to alter fi re regimes globally there is a critical need to understand how heterogeneity in post-fi re habitat conditions modifi es plant -herbivore interactions. We examined herbivory patterns, growth responses and defense chemistry expression (phenolic glycoside, condensed tannins) of regenerating aspen Populus tremuloides that experienced variable burn severity in the 2010 Twitchell Canyon Fire, Utah, USA. Browse damage was approximately 60% lower in moderate and high burn severity plots compared to low severity and unburned plots. Aspen regeneration density was 2.3 and 3.1 fold greater in high and moderate severity burn plots than in low severity and unburned plots. High burn severity stimulated photosynthesis, vertical growth and biomass accumulation. Defense chemistry expression responded dynamically over time depending on burn severity. From June to August, phenolic glycoside concentrations showed no signifi cant change in unburned and low severity fi re conditions but increased 79% and 139% in moderate and high severity burn environments. By the end of summer, condensed tannins increased six-fold in high severity burn plots, with increases of 50% or less in the lower burn severity plots. Deer activity, as defi ned by pellet counts, was inversely related to fi re severity and positively related to browse damage. Elk and cattle activity showed no signifi cant relationship with browse activity. Greater light availability in higher severity burn environments appears to enhance tolerance and resistance of aspen against herbivory by increasing growth potential and defense chemistry expression of aspen. Th ese results suggest that burn severity infl uences plant -herbivore interactions through bottom -up and top -down mechanisms, and that higher fi re severity increases post-disturbance vegetation recruitment potential by increasing resilience to herbivory.

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“…; St. Clair et al. ). Acidity on the forest floor beneath some conifers increases the cation exchange capacity of the soil, promoting nutrient leaching (Augusto et al.…”

Section: Discussionmentioning

confidence: 99%

“…; St. Clair et al. ). These facilitation effects of trembling aspen could be site‐specific and depend on the proportion of trembling aspen, their position in the canopy and nutrient status of the site, which could explain why trembling aspen was only sometimes associated with higher productivity in certain assemblages (Legare et al.…”

Section: Discussionmentioning

confidence: 99%

Species composition determines resistance to drought in dry forests of the Great Lakes – St. Lawrence forest region of central Ontario

Arthur

Dech

2016

J Vegetation Science

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Question: Predicted changes in the frequency of short-term drought events raise concerns about potential effects of climate change on forest ecosystems. Few experiments have investigated the effects of tree species richness and composition in forest assemblages exposed to drought, and general conclusions for these systems are currently lacking. We tested the hypothesis that different species richness and composition affects community-level stability during a severe short-term drought event across a gradient of tree species assemblages typical of temperate forest ecosystems on dry substrates.Location: Great Lakes -St. Lawrence forest region, central Ontario, Canada. Methods:The study assemblages spanned a gradient of 15 different combinations of species richness and composition of four tree species. The drought occurred in 2005 and was characterized by high growing season temperature and low precipitation. Plots (n = 63) representing replicate assemblages were selected to collect increment cores (n = 1193) and examine growth responses to past drought at the community and population levels. Cross-dated tree ring measurements were used to reconstruct basal area increment (BAI) and calculate indices of resistance, resilience and productivity over the drought period. We used hierarchical analysis of variance models to estimate the effects of species richness and composition on drought responses. Results:We identified a significant effect of species composition on community-level resistance and productivity. White pine (Pinus strobus) abundance was associated with lower community resistance and white birch (Betula papyrifera) abundance with higher resistance. Assemblages with greater productivity were often characterized by the high abundance of trembling aspen (Populus tremuloides). There was no overall effect of the assemblage gradient on the population-level stability; however, red pine (Pinus resinosa) productivity was higher in combination with trembling aspen and white birch. Conclusion:Our study demonstrated that species richness had no effect on the community-level stability of growth during a drought in temperate forests on dry substrates. Instead, there were important compositional effects that determine some aspects of stability during drought events. If pine forests were managed to maintain a component of deciduous species, the capacity to dampen the community-level effects of more frequent drought would increase.

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The role of facilitation and competition in the development and resilience of aspen forests

Cited by 29 publications

References 113 publications

Is initial post‐disturbance regeneration indicative of longer‐term trajectories?

Is initial post‐disturbance regeneration indicative of longer‐term trajectories?

Fire severity alters plant regeneration patterns and defense against herbivores in mixed aspen forests

Species composition determines resistance to drought in dry forests of the Great Lakes – St. Lawrence forest region of central Ontario

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