Fire characteristics and environmental conditions shape plant communities via regeneration strategy

Abstract

© 2020 The Authors. Ecography published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos Climate change is altering disturbance regimes outside historical norms, which can impact biodiversity by selecting for plants with particular traits. The relative impact of disturbance characteristics on plant traits and community structure may be mediated by environmental gradients. We aimed to understand how wildfire impacted understory plant communities and plant regeneration strategies along gradients of environmental conditions and wildfire characteristics in boreal forests. We established 207 plots (60 m2) in recently burned stands and 133 plots in mature stands with no recent fire history in comparable gradients of stand type, site moisture (drainage) and soil organic layer (SOL) depth in two ecozones in Canada's Northwest Territories. At each plot, we recorded all vascular plant taxa in the understory and measured the regeneration strategy (seeder, resprouter, survivor) in burned plots, along with seedbed conditions (mineral soil and bryophyte cover). Dispersal, longevity and growth form traits were determined for each taxon. Fire characteristics measured included proportion of pre-fire SOL combusted (fire severity), date of burn (fire seasonality) and pre-fire stand age (time following fire). Results showed understory community composition was altered by fire. However, burned and mature stands had similar plant communities in wet sites with deep SOL. In the burned plots, regeneration strategies were determined by fire severity, drainage and pre- and post-fire SOL depth. Resprouters were more common in wet sites with deeper SOL and lower fire severity, while seeders were associated with drier sites with thinner SOL and greater fire severity. This led to drier burned stands being compositionally different from their mature counterparts and seedbed conditions were important. Our study highlights the importance of environment–wildfire interactions in shaping plant regeneration strategies and patterns of understory plant community structure across landscapes, and the overriding importance of SOL depth and site drainage in mediating fire severity, plant regeneration and community structure.

Disturbance interval modulates the starting point for vegetation succession

“…Earlier studies have found that resilience may vary with environmental conditions, for instance, with wet forests being more resilient than dry ones (e.g., Day et al. [2020]), but we are not aware of other studies that include a long time gradient to analyze resilience in relation to disturbance interval. To advance the understanding further, it is essential to explore if effects of disturbance interval are linear or nonlinear, for example, if there are time thresholds with disproportionately more late‐successional species.…”

Metacommunity resilience against simulated gradients of wildfire: disturbance intensity and species dispersal ability determine landscape recover capacity

“…A mechanistic understanding of the relationship between wildfires and system resilience is urgently required at a time where the intensity and area of this type of disturbance are already increasing above historical records around the globe (Pausas and Ribeiro 2013, Kovats et al 2014, Banks et al 2017, Young et al 2017, Turco et al 2018, Day et al 2020). Our study identified a gradual decline in resilience capacity with the increase in burned area but a sharp loss in resilience capacity when the fire affected more than half of the waterbodies (at approximately a 50% intensity).…”

“…Furthermore, it is expected that this change will interact with the dispersal ability of the considered species. However, the actual relationship between community resilience and disturbance size or intensity is not evident for temporary pond or other systems (Miller et al 2019, Crabot et al 2020, Day et al 2020. For example, it is not evident whether resilience will present gradual or sharp transitions along disturbance gradients (Scheffer 2009, Ratajczak et al 2018, at which level of disturbance size or intensity this transition could be expected (Moore 2018), what the strength of these disturbance properties could be as determinants of resilience (Seidl et al 2017), or how the differences in dispersal ability among taxa might determine future patterns (Sorensen and Shade 2020).…”

“…This change in wildfire dynamics is expected to impact ecosystem resilience (Wright and Bailey 1982, Christensen et al 1989, Prepas et al 2009, Chang et al 2013, Hegeman et al 2014, Miller et al 2019). However, we lack a deep understanding of the determinants of community resilience after wildfires, particularly regarding the role of landscape structure and metacommunity organization (Day et al 2020).…”

Rapid bird species recovery following high‐severity wildfire but in the absence of early successional specialists

“…For example, patterns of post‐fire recovery can be influenced by post‐fire climatic conditions which may promote or impair vegetation recovery (e.g. Day et al, 2020; Keeley & Pausas, 2019), with flow‐on effects on habitat suitability for animals (Regos et al, 2018; White et al, 2011).…”