Temporal dynamics in alpine snowpatch plants along a snowmelt gradient explained by functional traits and strategies

Abstract

Alpine snowpatches are characterised by persistent snow cover, short growing seasons and periglacial processes, which has resulted in highly specialised plant communities. Hence, these snowpatch communities are among the most threatened from climate change. However, temporal dynamics in snowpatch microclimate and plant composition are rarely explored, especially in the marginal alpine environments of Australia. Seven snowpatches were categorised into early, mid and late snowmelt zones based on growing season length, with soil temperatures recorded from 2003 to 2020 and plant composition surveyed in 84 1 m² quadrats in 2007, 2013 and 2020. Microclimate, species diversity, plant cover and composition, along with community trait-weighted means and plant strategies were assessed to understand snowpatch dynamics in response to climate change. We found that growing season length and temperatures have increased in late melt zones, while changes were less consistent in early and mid melt zones. There were few changes in species diversity, but increases in graminoids and declines in snowpatch specialists in mid and late melt zones. Community-weighted plant height, leaf area and leaf weight also increased, particularly in mid and late melt zones, while plant strategies shifted from compositions of ruderal-tolerant to stress-tolerant. Here, we show that snowpatch communities are rapidly changing in response to longer growing seasons and warmer temperatures, with the greatest changes occurring where snow persists the longest. The results highlight the climate-induced loss of de ning biotic and abiotic characteristics of snowpatches, as temporal convergence of compositions along snowmelt gradients threatens the novelty of snowpatch plant communities.

Early-melting snowpatch plant communities are transitioning into novel ecosystems

“…Hence, a novel plant community has emerged over time. By contrast, Verrall et al 23 found that biotic homogenisation was occurring in late-melting alpine snowpatches due to the increases in graminoids and declines in snowpatch specialists. They concluded that such changes were threatening the compositional distinctiveness of alpine snowpatches.…”

“…Earlier snowmelt may be reducing growing season soil moisture that typically comes from late-melting snow 12,44 , allowing expansion of dryland tussock grasses into areas where they were previously absent because of site wetness. Increases in tussock-forming grass species has been previously identi ed as a signal of change in late-lying snowpatches 23,29 , so their positive response in early-melting snowpatches over time are further con rmation of vegetation dynamics consistent with abiotic conditions now favouring species with different ecological strategies and/or traits to those in the past.…”

“…43 . There has been a signi cant decrease in both maximum snow depth, total snow accumulation 35 and snow persistence 23 . Indeed, the Australian snowpack is now at a 2000 year low 43 .…”

“…If the immigration of new species into snowpatches translates to the loss of snowpatch specialists due to competitive exclusion 22 , it may lead to their biotic homogenisation, with compositional similarity increasing over time 28 . Evidence for these types of change outcomes remain relatively scant (but see recent exceptions 22,23,29 ), as does the effect of environmental change on functional trait diversity, the measurable properties of plants (such as size, structure and biogeochemistry) that are intrinsically linked to the key functions of ecosystems 20 . In all likelihood, biotic differentiation is the rst outcome of climatic change for plant communities where immigrations outpace extinctions, with biotic homogenisation (and ecosystem collapse sensu Bergstrom et al 30 ) a longer-term response to altered abiotic drivers and a milieu of changed biotic factors which may be mediated by climate.…”

Early-melting snowpatch plant communities are transitioning into novel states

“…In areas with a short growing season, climatic warming can be expected to favor species that take advantage of the longer growing season; the arrival and expansion of grassland and heathland species from adjoining plant communities into snowpatches is a likely outcome 5 , 21 , 22 . This will have impacts on the structure, composition and ecological function of snowpatch communities 4 , but the mechanisms of change and outcomes for snowpatch communities remain poorly understood 23 – 25 . A re-assembly of the original community may result because of immigration of new species and the persistence of snowpatch species (e.g.…”