Slow community responses but rapid species responses 14 years after alpine turf transplantation among snow cover zones, south–central New Zealand

Abstract

Alpine ecosystems are particularly vulnerable to the impact of global climate change. Depth and duration of seasonal snow cover are major drivers of variation in alpine plant community composition, so a reduction in snow cover as a result of climate change would expose plants that are currently protected by snow in winter and spring to greater extremes of temperature and increased risk of frost damage. We reciprocally transplanted 64 intact 60 cm × 60 cm × 10 cm (minimum depth) turves of alpine vegetation among four topographic zones on the Rock and Pillar Range, south-central South Island, New Zealand to investigate how shifts along a snow cover gradient affected plant growth, survival and community composition. The four zones: late-melting snowbed and early-melting snowbed in depressions, moderately exposed leeward upper slopes dominated by herbfield, and extremely exposed summit plateau dominated by cushionfield, differed in winter and spring snow cover. As expected, the highest species losses occurred in turves transplanted to very different zones e.g. late snowbed to summit plateau and vice versa. However many snowbed species still survived on the summit plateau seven years following transplantation. The degree to which turves had been colonised after seven years was significantly related to transplant zone rather than turf origin or original species richness; turves transplanted to the most species-rich zones were affected most by colonisation. Measurements of leaf production over three years in three focal Celmisia species (Asteraceae), characteristic of the herbfield on leeward slopes, and early and late snowbeds, showed that the late snowbed specialist suffered significantly reduced growth when transplanted to more exposed sites, but its survival was more affected by invertebrate herbivory rather than the direct effects of exposure. The cosmopolitan focal lichen species Thamnolia vermicularis, monitored over 14 years, rapidly colonised turves transplanted to cushionfield on the exposed summit plateau, where this and other lichens are abundant, but equally rapidly declined in turves transplanted to snowbeds. These findings add to a growing body of evidence that biotic interactions and species-specific traits will be critical drivers of alpine vegetation change under future climate scenarios.