If the trees burn, is the forest lost? Past dynamics in temperate forests help inform management strategies

Abstract

Forest dynamics are driven by top-down changes in climate and bottom-up positive (destabilizing) and negative (stabilizing) biophysical feedbacks involving disturbance and biotic interactions. When positive feedbacks prevail, the resulting self-propagating changes can potentially shift the system into a new state, even in the absence of climate change. Conversely, negative feedbacks help maintain a dynamic equilibrium that allows communities to recover their pre-disturbance characteristics. We examine palaeoenvironmental records from temperate forests to assess the nature of long-term stability and regime shifts under a broader range of environmental forcings than can be observed at present. Forest histories from northwestern USA, Patagonia, Tasmania and New Zealand show long-term trajectories that were governed by (i) the biophysical template, (ii) characteristics of climate and disturbance, (iii) historical legacies that condition the ecological capacity to respond to subsequent disturbances, and (iv) thresholds that act as irreversible barriers. Attention only to current forest conditions overlooks the significance of history in creating path dependency, the importance of individual extreme events, and the inherent feedbacks that force an ecosystem into reorganization. A long-time perspective on ecological resilience helps guide conservation strategies that focus on environmental preservation as well as identify vulnerable species and ecosystems to future climate change. This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions’.

Emerging palaeoecological frameworks for elucidating plant dynamics in response to fire and other disturbance

“…Palaeorecords are a powerful tool for contextualizing these modern observations, with millennial-scale palaeofire records demonstrating that these modern events are unprecedented over thousands of years (Feurdean et al, 2020;Hu et al, 2010;Kelly et al, 2013). Moreover, the accumulation of palaeoecological records across major global biomes (e.g., Hessburg et al, 2019;Hu et al, 2015;Iglesias & Whitlock, 2020;Leys et al, 2018;Whitlock et al, 2007) has been instrumental in understanding the historical effect of fire in driving ecological dynamics and community-level shifts in vegetation across space and time (McLauchlan et al, 2020;Whitlock et al, 2010).…”

Policy persistence: REDD+ between stabilization and contestation

“…For instance, the El Nino-linked 2016 Amazon fires temporarily cast a shadow on REDD+ optimism, and the politically-charged 2019 Amazon fires have seen donor countries like Germany and Norway become resolute in pulling REDD+ funding from Brazil. While highly uncertain, as we are literally in uncharted territory, predictions are that the overall stability of many forest ecosystems across the planet will deteriorate as global warming progresses, thus confounding and circumscribing the notion that these ecosystems can be relied on as stable carbon stocks in proposed climate change 'solutions' (Aragão et al 2018;Iglesias and Whitlock 2020). The instability of forest carbon due to global warming itself thus constitutes a fundamental limit to the search for a global forest-based climate fix.…”

Climate change and ecosystems: threats, opportunities and solutions

“…Resilience in ecological communities requires longer-term perspectives to improve our understanding of community responses to change. Iglesias and Whitlock [8] use palaeoenvironmental records of pollen and charcoal from temperate forests in the Northern and Southern Hemispheres to consider the role of fire in changing forest tree species composition. They find that the resilience or vulnerability of forest species composition to changing fire regimes depends on a variety of local factors, including climate, soil conditions and historical legacies; in some cases, extreme events, combined with biophysical feedbacks, can cause ecosystems made up of long-lived species to completely shift in ecosystem composition in response to a single fire event.…”