Soil moisture mediates alpine life form and community productivity responses to warming

Abstract

Climate change is expected to alter primary production and community composition in alpine ecosystems, but the direction and magnitude of change is debated. Warmer, wetter growing seasons may increase productivity; however, in the absence of additional precipitation, increased temperatures may decrease soil moisture, thereby diminishing any positive effect of warming. Since plant species show individual responses to environmental change, responses may depend on community composition and vary across life form or functional groups. We warmed an alpine plant community at Niwot Ridge, Colorado continuously for four years to test whether warming increases or decreases productivity of life form groups and the whole community. We provided supplemental water to a subset of plots to alleviate the drying effect of warming. We measured annual above-ground productivity and soil temperature and moisture, from which we calculated soil degree days and adequate soil moisture days. Using an information-theoretic approach, we observed that positive productivity responses to warming at the community level occur only when warming is combined with supplemental watering; otherwise we observed decreased productivity. Watering also increased community productivity in the absence of warming. Forbs accounted for the majority of the productivity at the site and drove the contingent community response to warming, while cushions drove the generally positive response to watering and graminoids muted the community response. Warming advanced snowmelt and increased soil degree days, while watering increased adequate soil moisture days. Heated and watered plots had more adequate soil moisture days than heated plots. Overall, measured changes in soil temperature and moisture in response to treatments were consistent with expected productivity responses. We found that available soil moisture largely determines the responses of this forbdominated alpine community to simulated climate warming.

Permafrost and drought regulate vulnerability of Tibetan Plateau grasslands to warming

“…, Winkler et al. ). Mean annual temperature, on the other hand, significantly affected relative changes in height under warming, and colder sites also experienced larger decreases in diversity.…”

Water as a resource, stress and disturbance shaping tundra vegetation

“…In light of rising temperatures, particularly in high‐altitude systems, vascular plant patterns are likely to become more dependent on hydrological conditions (Crimmins et al , Winkler et al ). Indeed, for high‐latitude vegetation, soil moisture may mediate the impacts of changing climatic conditions, including rising temperature and changing snow dynamics (Nabe‐Nielsen et al ).…”

“…The influence of soil moisture variation on vegetation patterns is a pronounced research gap in ecology, particularly at high‐elevations and ‐latitudes (Crimmins et al , le Roux et al , Silvertown et al ), where climate change has greatly impacted both the hydrosphere and cryosphere (Fountain et al , Bring et al ). These changes have implications for precipitation, evaporation and snow dynamics, all of which alter water conditions experienced by plants (Barichivich et al , Winkler et al ). Climate simulations project more rainfall in place of snowfall during winter, which combined with earlier snowmelt could lead to extreme drying late in summer and autumn (Bintanja and Andry , Kankaanpää et al ).…”

Treelines—Approaches at Different Scales

“…Thus, in the Colorado Front Range, the increase in droughts has led to high mortality in conifers in subalpine forests since the 1980s [108]. In the same place, artificial warming increases the productivity and competitive ability of plant communities in the alpine zone only if soil moisture is sufficient [109]. Long-lasting winter snowpack on the Sun-exposed leeside of local topography may prevent moisture stress until early summer, when moisture in the earlier snow-free sites is already exhausted [59,110].…”