Plant functional traits predict heterogeneous distributional shifts in response to climate change

Climate change is causing the rapid redistribution of vegetation as plant
species move to track their climatic optima. Despite a global trend of
upward movement in latitude and elevation, there is extensive
heterogeneity among species and locations, with few emerging
generalizations. Greater generalization may be achieved by considering
multidimensional changes in species’ distributions as well as
incorporating ecologically relevant functional traits into studies of
range shifts. To better understand how recent changes in climate are
influencing the elevational distribution of plant species and how species’
functional traits mediate distributional changes, we resampled a
2,438-meter elevation transect spanning a distance of 16 kilometers which
encompasses desert scrub, pinyon-juniper woodland, chaparral, and
coniferous forest plant communities. Over the last 42 years, total
perennial cover and species’ average cover increased at lower elevations
and decreased at higher elevations while the average elevational
leading-edge increased 116 m and the elevational rear edge decreased 84 m.
Notably, these changes were mediated by species’ functional traits, where
species exhibiting more conservative traits (lower SLA, greater δ13C,
larger seed mass) and taller height shifted upward in their leading-edge
range limit, average elevation, and trailing edge range limit, while
declining in abundance at the median and trailing edge of their range.
Species possessing more acquisitive traits (higher SLA, lower δ13C,
smaller seed mass) and shorter height shifted downward and increased in
abundance at their trailing edge, with increases in their total range
size. Our results provide clear evidence that heterogeneous range dynamics
under recent climate change can be generalized by considering ecologically
relevant plant functional traits, and how they respond to localized
climate exposure. Further, by documenting changes across a steep
ecological gradient comprising a large aridity gradient, we show divergent
patterns for plants occupying contrasting positions along the global
spectrum of plant form and function, which provides critical insight into
how trait-mediated changes under increasing aridity will impact ecosystem
functioning.