Climate extremes may be more important than climate means when predicting species range shifts
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Climate extremes may be more important than climate means when predicting species range shifts Sara J. Germain 1
& James A. Lutz
1
Received: 14 October 2019 / Accepted: 11 September 2020/ # Springer Nature B.V. 2020
Abstract
It is well known that temperatures across the globe are rising, but climatic conditions are becoming more variable as well. Forecasts of species range shifts, however, often focus on average climatic changes while ignoring increasing climatic variability. In particular, many species distribution models use space-for-time substitution, which focuses exclusively on the effect of average climatic conditions on the target species across a geographic range, and is blind to the possibility of range-wide population collapse with increasing drought frequency, drought severity, or climate effects on other co-occurring species. Relegated to assessments of broad demographic patterns that ignore underlying biological responses to increasing climatic variability, this prevalent method of distribution forecasting may systematically underpredict climate change impacts. We compare six models of survival and abundance of a subcanopy tree species, Taxus brevifolia, over 40 years of past climate change to disentangle multiple sources of uncertainty: model formulation, scale of climate effect, and level of biological organization. We show that drought extremes increased Taxus individual- and population-scale mortality across a wide geographic climate gradient, precluding detection of a monotonic relationship with average climate. Individual-scale climatic extremes models derived from longitudinal data had the highest predictive accuracy (82%), whereas mean climate models had the lowest accuracy (< 65%). Our results highlight that conclusions drawn from forecasts of average warming alone likely underpredict climate change impacts by ignoring indicators of range-wide population declines for species sensitive to increasing climatic variability. Keywords Longitudinal data . Permanent sample plots . Population decline . Smithsonian ForestGEO . Taxus brevifolia . Wind River Forest Dynamics Plot (WFDP)
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10584-02002868-2) contains supplementary material, which is available to authorized users.
* Sara J. Germain [email protected]
1
Department of Wildland Resources, Utah State University, Logan, UT 84321, USA
Climatic Change
1 Introduction Predicting species range shifts is a central aim of climate impacts research (Parmesan and Yohe 2003), both to identify conservation priorities (VanDerWal et al. 2013, Urban 2015) and to inform coupled global climate models (Stark et al. 2016, Fisher et al. 2018). Changing forest distributions are a particularly large source of uncertainty when predicting future climate (Purves and Pacala 2008) due to the prominent role of forest biomes in regulating global carbon and hydrological cycles (Snyder et al. 2004, Adams et al. 2010), in tandem with the complex biotic and abiotic pr
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