High-velocity upward shifts in vegetation are ubiquitous in mountains of western North America

Abstract

The velocity of climate change and its subsequent impact on vegetation has been well characterized at high elevations and latitudes, including the Arctic. But whether species and ecosystems are keeping pace with the velocity of temperature change is not as well documented. Some evidence indicates that species are less able to keep pace with the velocity of climate change along elevational gradients than latitudinal ones. If substantiated this finding could warrant reconsideration of a current cornerstone of conservation planning. Here we use 27 years of high-resolution satellite data to quantify changes in vegetation cover across elevation within nine mountain ranges in western North America, spanning tropical Mexico to subarctic Canada and from coastal California to interior deserts. Across these ranges we show a uniform pattern at the highest elevations in each range, where increases in vegetation have occurred ubiquitously over the past three decades. At these highest elevations, the realized velocity of vegetation varies among mountain ranges from 19.8–112.8 m · decade-1 (mean = 67.3 m · decade-1). This is equivalent, with respect to gradients in temperature, to a 14.4–104.3 km · decade-1 poleward shift (mean = 56.1 km · decade-1). This realized velocity is 4.4 times larger than previously reported for plants, and is among the fastest rates predicted for the velocity of climate change. However, in three of the five mountain ranges with long-term climate data, realized velocities fail to keep pace with changes in temperature, a finding with important implications for conservation of biological diversity.

Change in Dominant Plant Functional Types: Transitions from Forests to Shrublands or Grasslands in the Western U.S due to Warming, Droughts, and Fire

“…Upslope movement in vegetation has also been observed over the past few decades at the highest elevations and across mountain ranges in the western U.S., being primarily driven by persistent droughts and increasing temperatures 27 . In cases where vegetation shifts are not keeping pace with the changing climate, the habitat range for some species declines, putting some species at increased risk of extinction 27 . Our model shows that boreal and temperate coniferous forests' mean elevation will shift upslope by approximately 300 and 50 meters respectively, by the end of the century (Appendix A).…”

Future transition from forests to shrublands and grasslands in the western United States is expected to reduce carbon storage

“…The Las Conchas fire study in New Mexico illustrates this trend, where initial burns led to transitions from forests to savannas and shrublands 29,36 , which then showed greater fire resistance. Additionally, persistent droughts and rising temperatures are driving vegetation upslope across western United States mountain ranges 37 . This lag in vegetation adaptation to climate change reduces habitats and increases extinction risks for certain species.…”

Climate change disrupts the seasonal coupling of plant and soil microbial nutrient cycling in an alpine ecosystem

“…Alpine ecosystems are experiencing numerous direct and indirect climate change impacts, which include huge reductions in snow cover and widespread shifts in vegetation, respectively (Beniston et al., 2018; He et al., 2023). Reduced snow cover and shifts in vegetation are among the most pronounced and globally widespread signals of climate change in alpine ecosystems (Gobiet et al., 2014; Kellner et al., 2023; Notarnicola, 2020; Pepin et al., 2022; Steinbauer et al., 2018; Zong et al., 2022), yet how they interactively modify key nutrient cycles is poorly understood (Classen et al., 2015), with the vast majority of studies focussing on single global change factors (Rillig et al., 2019). Interactive effects of global change factors can be additive or non‐additive.…”