Influences of fire–vegetation feedbacks and post‐fire recovery rates on forest landscape vulnerability to altered fire regimes

Abstract

1. In the context of ongoing climatic warming, forest landscapes face increasing risk of conversion to non-forest vegetation through alteration of their fire regimes and their post-fire recovery dynamics. However, this pressure could be amplified or dampened, depending on how fire-driven changes to vegetation feed back to alter the extent or behaviour of subsequent fires. 2.Here we develop a mathematical model to formalize understanding of how firevegetation feedbacks and the time to forest recovery following high-severity (i.e. stand-replacing) fire affect the extent and stability of forest cover across landscapes facing altered fire regimes. We evaluate responses to increasing burn rates while varying the direction (negative vs. positive) of fire-vegetation feedbacks under a continuum of values for feedback strength and post-fire recovery time. In doing so, we determine how interactions among these variables produce thresholds and tipping points in landscape responses to changing fire regimes.3. Where the early-seral vegetation was less fire-prone than older forests, negative feedbacks limited the reductions in forest cover in response to higher fire frequency or slower forest recovery. By contrast, positive feedbacks (more flammable early-seral vegetation) produced a tipping point beyond which increases in burn rates or a slowing of forest recovery drove extensive forest loss.4. With negative feedbacks, the rates of forest loss and expansion in response to variation in fire frequency were similar. However, where feedbacks were positive, the conversion from predominantly forested to non-forested conditions in response to increasing fire frequency was faster than the re-expansion of forest cover following a return to the initial burn rate. Strengthening the positive feedbacks increased this asymmetry. 5.Synthesis. Our analyses elucidate how fire-vegetation feedbacks and post-fire recovery rates interact to affect the trajectories and rates of landscape response to altered fire regimes. We illustrate the vulnerability of ecosystems with positive firevegetation feedbacks to climate change-driven increases in fire activity, especially 1926 | Journal of Ecology TEPLEY ET aL.

Increased aridity drives post‐fire recovery of Mediterranean forests towards open shrublands

“…This model finding is potentially general and may be relevant at broader spatial scales and/or in other fire ecosystems, as fire-driven vegetation feedbacks have been reported across the world (Dantas et al, 2016;Tepley et al, 2018;Abis & Brovkin, 2019). This model finding is potentially general and may be relevant at broader spatial scales and/or in other fire ecosystems, as fire-driven vegetation feedbacks have been reported across the world (Dantas et al, 2016;Tepley et al, 2018;Abis & Brovkin, 2019).…”

“…of land use). This is expected in systems where flammability declines during succession (Kitzberger et al, 2012), and it follows from the interaction between decreased post-fire oak recovery rates and the positive feedback driven by the high shrubland flammability and fast recolonization after fires (similar to the scenario shown by Tepley et al, 2018, for temperate forests). However, direct observations also show that fires can transform pine forests into oak forests if the latter are present in the understory (Retana et al, 2002;Torres et al, 2016;Vayreda et al, 2016;Mart ın-Alc on & Coll, 2016).…”

“…Seeder shrubs are in general less vulnerable to aridity than resprouter species Saura-Mas et al, 2009;Pausas et al, 2016). The combination of these direct and indirect effects can have a dramatic impact on species composition and ecosystem functions (Pratt et al, 2014;Enright et al, 2015), and theoretically they may influence the vulnerability of a landscape to fire (Tepley et al, 2018). Because primary productivity in the region is generally moderate to high (Moreno et al, 2013), droughts increase the probability of fire (Turco et al, 2012;Bedia et al, 2014;Karavani et al, 2018), thus influencing species community composition also indirectly.…”

Consequences of climatic thresholds for projecting fire activity and ecological change

“…Furthermore, changes in one explanatory variable may affect changes in another. For example, increased precipitation can offset the influence of warming temperatures on fuel moisture (Flannigan et al, ), vegetation can mediate the direct influence of climate on fire (Higuera et al, ; Tepley et al, ) or humans can alter fire regimes through management or altering ignition patterns (Balch et al, ). Thus, it is crucial to understand how thresholds may occur in a multivariate setting under such interactions.…”

Climate change likely to reshape vegetation in North America's largest protected areas

“…Such fire-induced changes may have a greater impact on vegetation than the direct effects of climate change (Bond & Keeley, 2005). Such climate-mediated increases in disturbance have the potential to exceed the ecological resilience of forests, inducing broad-scale die-off (Allen et al, 2010), and shifts to non-forest ecosystems as tipping points are crossed (Batllori et al, 2018;Davis et al, 2019;Reyer et al, 2015;Stevens-Rumann et al, 2018;Tepley et al, 2018). In northern latitudes, thawing of the permafrost layer may trigger ground surface subsidence, killing trees (via waterlogging), and collapsing permafrost plateaus (Baltzer, Veness, Chasmer, Sniderhan, & Quinton, 2014).…”