Plant biomes demonstrate that landscape resilience today is the lowest it has been since end‐Pleistocene megafaunal extinctions

Abstract

Resilient landscapes have helped maintain terrestrial biodiversity during periods of climatic and environmental change. Identifying the tempo and mode of landscape transitions and the drivers of landscape resilience is critical to maintaining natural systems and preserving biodiversity given today's rapid climate and land use changes. However, resilient landscapes are difficult to recognize on short time scales, as perturbations are challenging to quantify and ecosystem transitions are rare. Here we analyze two components of North American landscape resilience over 20,000 years: residence time and recovery time. To evaluate landscape dynamics, we use plant biomes, preserved in the fossil pollen record, to examine how long a biome type persists at a given site (residence time) and how long it takes for the biome at that site to reestablish following a transition (recovery time). Biomes have a median residence time of only 230–460 years. Only 64% of biomes recover their original biome type, but recovery time is 140–290 years. Temperatures changing faster than 0.5°C per 500 years result in much reduced residence times. Following a transition, biodiverse biomes reestablish more quickly. Landscape resilience varies through time. Notably, short residence times and long recovery times directly preceded the end‐Pleistocene megafauna extinction, resulting in regional destabilization, and combining with more proximal human impacts to deliver a one‐two punch to megafauna species. Our work indicates that landscapes today are once again exhibiting low resilience, foreboding potential extinctions to come. Conservation strategies focused on improving both landscape and ecosystem resilience by increasing local connectivity and targeting regions with high richness and diverse landforms can mitigate these extinction risks.

Caught in a bottleneck: Habitat loss for woolly mammoths in central North America and the ice‐free corridor during the last deglaciation

“…Concurrently, in eastern North America, rates of habitat reorganization were high (Wang et al., 2020), and open conifer and mixed conifer–hardwood parklands were lost, replaced by a Holocene arrangement of grasslands and eastern mesic forests (Williams et al., 2004). These losses of Pleistocene open parklands may have reduced the habitat availability for megafaunal species (Blois & Hadly, 2009; Di Febbraro et al., 2017; Ficcarelli et al., 2003; Graham, 1986; Haynes, 2013), increased competition among megafauna species, and thus increased the extinction risk of the woolly mammoth.…”

“…This observed afforestation is partially attributable to rising temperatures (Fastovich et al., 2020) but may also indicate that woolly mammoths, as ecosystem engineers, played important roles in landscape transformation. These landscape transitions may also have acted as a positive feedback loop of habitat loss (Wang et al., 2020) that exacerbated the woolly mammoth population decline and extinction. A next step forward is to include megaherbivory in mechanistic dynamic vegetation models such as LPJ‐GUESS; such models are at the early stages of development (Pachzelt et al., 2013, 2015).…”

“…Barnosky et al., 2004; Surovell et al., 2016), with megafaunal species responding individualistically to the effects of climate change, habitat shifts, and growing human populations (Lorenzen et al., 2011). In temperate latitudes, regional habitat destabilization and rapid vegetation change during the last deglaciation may have contributed to the megafaunal extinctions in synergy with anthropogenic pressures (Blois & Hadly, 2009; Di Febbraro et al., 2017; Ficcarelli et al., 2003; Haynes, 2013; Mann et al., 2019; Nogués‐Bravo et al, 2010; Wang et al., 2020; Wroe et al., 2013). A key knowledge frontier is to better understand the particular interactions of climate, habitat, human pressures, and regional geography for each extinction.…”

Ecosystem integrity is neither real nor valuable

“…One study of lake‐sediment pollen cores corresponding to the last 20,000 years of North American ecological history showed that ecosystems persisted for an average of just 230–460 years before transitioning to another ecosystem type (Wang, Shipley, Lauer, Pineau, & McGuire, 2020). Sixty‐four percent of these systems eventually reverted to their previous ecosystem type, but the rest did not.…”

“…Sixty‐four percent of these systems eventually reverted to their previous ecosystem type, but the rest did not. In particular, Pleistocene megafaunal extinctions “led to rapid changes where plant communities transitioned through multiple alternative states rapidly” (Wang et al, 2020, p. 5,923).…”