A warming world will cause the snow in Australia’s alpine regions to melt much earlier than in previous decades; a potentially devastating situation for many alpine plants that rely on the protection and insulation that snow offers for their survival. Without snow in early spring, alpine plants may be subjected to severe frosts at a time when they are most physiologically active; rapidly growing and preparing for the short growing season ahead.
But how early would the snow need to melt for it to be notably earlier than what plants might experience anyway due to inter-annual variability in snowmelt date, and subsequently cause frost damage and affect plant growth? In recent months, I’ve been testing these questions in two ways: 1) by examining the freezing resistance of alpine shrub foliage that is exposed to frost early, compared with foliage that is protected under snow for almost two weeks longer; and 2) by contributing to an global effort to understand the interacting effects of exposure to frost and drought on plant growth.
So what’s going on?
1) Overall, shrub foliage that is exposed early, i.e., the upper branches that poke through the snow in spring, are no more or less resistant to freezing than the foliage which is lower down on the shrub, buried in snow and exposed about 14 days later. This was an unexpected finding, as plants generally ‘frost-harden’ over time, but obviously not markedly in these species at the start of the growing season. As the growing season progressed, the freezing resistance of all four shrub species in this study did improve over time; with some of the species tested being able to withstand -10 to -21°C. Since air temperatures never reached below -9 °C during the period of study (and temperatures never really get much colder than that in the Snowy Mountains anyway), it appears that these shrub species may not be affected by frosts as the snow melts.
The full story is here:
Venn SE and Green K (2018) Evergreen alpine shrubs have high freezing resistance in spring, irrespective of snowmelt timing and exposure to frost: an investigation from the Snowy Mountains, Australia. Plant Ecology 219:209-216. DOI 10.1007/s11258-017-0789-8
What else is going on?
2) In a global study across 13 sites, co-ordinated by Hugh Henry at Western University, Canada and within the framework of the International Drought Experiment and DroughtNet, we investigated the interaction between and imposed drought treatment (by using rainout shelters), and snow removal (by digging). Among sites, we observed a negative correlation between the snow removal effect on minimum soil temperature and plant growth (measured the following growing season by means of biomass production). Only three sites exhibited a significant rainout shelter effect on plant productivity, and there was actually no significant interaction between snow removal and imposed drought on plant growth. However, these two factors did exhibit significant effects simultaneously for a single site. The local Bogong High Plains site showed no real trends. So overall, our results reveal that reduced snowfall, when it decreases minimum soil temperatures, can be an important component of the total effect of reduced precipitation on plant productivity.
The full story is here:
Henry HA, Abedi M, Alados CL, Beard KH, Fraser LH, Jentsch A, Kreyling J, Kulmatiski A, Lamb EG, Sun W, Lreyling J, Kulmatiski A, Lamb E, Sun W, Vankoughnett MR, Venn SE, Werner C, Beil I, Blindow I, Dahlke S, Dubbert M, Effinger A, Garris HW, Gartzia M, Gebauer T, Arfin Khan MAS, Malyshev AV, Morgan JW, Nock C, Paulson JP, Pueyo Y, Stover HJ, Yang X (2018) Increased Soil Frost Versus Summer Drought as Drivers of Plant Biomass Responses to Reduced Precipitation: Results from a Globally Coordinated Field Experiment. Ecosystems Accepted 4 February 2018. https://doi.org/10.1007/s10021-018-0231-7 in press
Perhaps the future interactions between snow cover, frost exposure and drought won’t be as devastating to alpine plant life as anticipated? Or, it might take several consecutive poor snow seasons for the conditions to be well outside of the background inter-annual variability for the plants to notice sufficiently and respond.
In the meantime, it appears Australian alpine plants are reasonably well equipped to take on the challenges of short and sporadic exposure and frosts and drought.