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Alpine summit vegetation, the highest point of species geographical distributions, is vulnerable to climate change (thermal niche contraction), and there is evidence of change in Northern Hemisphere summits. However, summits are experiencing multifaceted change due to warming and increasing fire frequency. Little is known about how these factors are affecting alpine summit vegetation. We used a revisitation approach to capture the long-term (eighteen years) dynamic changes in Australian alpine plant summit community patterns and to understand the mechanisms of change. We found that vegetation change was influenced by climate and moderated by site-specific factors. There was increased shrub cover over time; however, summit vegetation was largely stable unless disturbed. Fire-disturbed summits experienced higher instability in their vegetation cover over time. Linear mixed-effect models indicated that as time since fire increased and the growing degrees accumulated, there was a strong positive effect on forb and graminoid cover and a negative effect on shrub cover. Forb cover was higher at cooler, wetter, higher-elevation summits. These findings indicate the multifaceted nature of change that must be accounted for in alpine vegetation studies. We show that alpine summit vegetation will respond multidirectionally to a warming climate and changing fire regimes, with outcomes likely contingent on life history characteristics. [ABSTRACT FROM AUTHOR]

Changes to precipitation patterns and warming temperatures are predicted to reduce the water available to Australian alpine plants during the growing season. Soil water deficits are likely to co-occur with frost extremes that are common throughout the year and heatwaves which are increasing in severity with ongoing climate change. We aimed to determine whether co-occurring reductions in soil moisture would affect the capacity of alpine plants to tolerate temperature extremes. We used small rainout shelters to impose a drought treatment in situ in the alpine zone, which chronically reduced soil moisture in plots of alpine plant species including evergreen shrubs, graminoids and perennial forbs. We determined photosynthetic freezing tolerance and heat tolerance during the growing season across 2 years, and measured plant growth, in response to the drought treatment. Thermal tolerance was insensitive to chronically reduced soil moisture, and graminoids exhibited overall greater freezing and heat tolerance thresholds than other life forms. The drought treatment improved shrub growth, likely due to the amelioration of wind and the slightly warmer temperatures provided by the rainout shelters. We conclude that Australian alpine plants maintain high tolerances to both high- and low-temperature extremes during the growing season and are relatively robust to combined temperature extremes and reductions in near-surface soil moisture that are likely to occur with ongoing climate warming. [ABSTRACT FROM AUTHOR]

Alpine plants in Australia are increasingly exposed to more frequent drought and heatwaves, with significant consequences for physiological stress responses. Acclimation is a critical feature that allows plants to improve tolerance to environmental extremes by directly altering their physiology or morphology. Yet it is unclear how plant performance, tolerance, and recovery are affected when heat and water stress co-occur, and whether prior exposure affects responses to subsequent climate extremes. We grew a common alpine grass species under high or low watering treatments for three weeks before exposure to either none, one, or two heat stress events. We determined photosynthetic heat and freezing tolerance (LT50, mean temperature causing 50% irreversible damage to photosystem II) and growth. Physiological adjustments to low watering, including more negative water potentials and reduced growth, were also characterised by improved tolerance to high and low-temperature extremes. Shifts to higher heat tolerance were also evident with increasing exposure to heat stress events, though freezing tolerance was not affected. Acclimation effects were mostly short-term, however; prior exposure to heat and/or water stress had little to no effect on growth and thermal tolerance following the six-week recovery period. We conclude that rapid acclimation to water and heat stress that co-occur during summer enhances the capacity of alpine plants to tolerate increasingly frequent temperature extremes. [ABSTRACT FROM AUTHOR]

Conservation managers are under increasing pressure to make decisions about the allocation of finite resources to protect biodiversity under a changing climate. However, the impacts of climate and global change drivers on species are outpacing our capacity to collect the empirical data necessary to inform these decisions. This is particularly the case in the Australian Alps which have already undergone recent changes in climate and experienced more frequent large‐scale bushfires. In lieu of empirical data, we use a structured expert elicitation method (the IDEA protocol) to estimate the change in abundance and distribution of nine vegetation groups and 89 Australian alpine and subalpine species by the year 2050. Experts predicted that most alpine vegetation communities would decline in extent by 2050; only woodlands and heathlands are predicted to increase in extent. Predicted species‐level responses for alpine plants and animals were highly variable and uncertain. In general, alpine plants spanned the range of possible responses, with some expected to increase, decrease or not change in cover. By contrast, almost all animal species are predicted to decline or not change in abundance or elevation range; more species with water‐centric life‐cycles are expected to decline in abundance than other species. While long‐term ecological data will always be the gold standard for informing the future of biodiversity, the method and outcomes outlined here provide a pragmatic and coherent basis upon which to start informing conservation policy and management in the face of rapid change and a paucity of data. [ABSTRACT FROM AUTHOR]

We assessed the freezing resistance of leaves ex situ of 25 Australian alpine plant species. We compared the freezing resistance of forb, graminoid and shrub species from three alpine summits of different altitudes; from a low altitude site just above treeline, to a fully alpine tundra site. Foliar freezing resistance (LT50) in spring varied from −5.9°C to −18.7°C and standardized LT50 values within species were significantly related to site altitude. Additionally, when comparing all the species in the study, freezing resistance was significantly related to site; the LT50 of samples from a low-altitude summit (1696 m) were significantly lower than those of samples from mid- (1805 m) and high-altitude (1860 m) summits. The LT50 of juvenile foliage did not differ significantly from that of adult foliage. Shrubs were highly resistant to freezing. At the highest summit, we examined the course of seasonal freezing resistance from early summer to early autumn across three alpine plant communities that differed in the time of natural snowmelt; from sheltered (snowpatch) to exposed (open heath). No differences in freezing resistance over the growing season were detected for exposed or sheltered communities and there were no consistent trends indicating frost hardening over the growing season. Overall, the common Australian alpine species we investigated appear well adapted to freezing conditions throughout the snow-free growing season. We have no evidence to suggest that freezing temperatures soon after snowmelt in spring are especially damaging to the alpine plants at these summits. [ABSTRACT FROM AUTHOR]

The early life-history stages of plants, such as germination and seedling establishment, depend on favorable environmental conditions. Changes in the environment at high altitude and high latitude regions, as a consequence of climate change, will significantly affect these life stages and may have profound effects on species recruitment and survival. Here, we synthesize the current knowledge of climate change effects on treeline, tundra, and alpine plants' early life-history stages. We systematically searched the available literature on this subject up until February 2020 and recovered 835 potential articles that matched our search terms. From these, we found 39 studies that matched our selection criteria. We characterized the studies within our review and performed a qualitative and quantitative analysis of the extracted meta-data regarding the climatic effects likely to change in these regions, including projected warming, early snowmelt, changes in precipitation, nutrient availability and their effects on seed maturation, seed dormancy, germination, seedling emergence and seedling establishment. Although the studies showed high variability in their methods and studied species, the qualitative and quantitative analysis of the extracted data allowed us to detect existing patterns and knowledge gaps. For example, warming temperatures seemed to favor all studied life stages except seedling establishment, a decrease in precipitation had a strong negative effect on seed stages and, surprisingly, early snowmelt had a neutral effect on seed dormancy and germination but a positive effect on seedling establishment. For some of the studied life stages, data within the literature were too limited to identify a precise effect. There is still a need for investigations that increase our understanding of the climate change impacts on high altitude and high latitude plants' reproductive processes, as this is crucial for plant conservation and evidence-based management of these environments. Finally, we make recommendations for further research based on the identified knowledge gaps. [ABSTRACT FROM AUTHOR]