Variation in flowering patterns and flowering phenology in alpine cushion plants in response to microclimate

Abstract

Alpine environments are of global importance due to their distinct environments, small geographic range, and fragmented distribution. Alpine landscapes are characterized by high topographic heterogeneity and consequently contain a wide a range of microclimates. Microclimates are localized climatic zones defined by variations in aspect, wind exposure, and solar radiation. Cold and windy alpine conditions have led to the evolution of distinct plan life forms that are compact and have low stature, one of which are cushion plants. Flowering phenology is the timing of seasonal flowering events and is crucial for the reproductive success of a plant species as it determines the temporal overlap with pollinator species. Continental-wide changes in flowering phenology correlates well with recent climate change and have been reported for a large number of species and regions. However, there is little research quantifying phenological response to fine-scale topographical heterogeneity. The aim of this study is to quantify the impact of microclimatic variation on the flowering patterns and flowering phenology of two alpine cushion plant species, Dracophyllum muscoides (Ericaceae) and Phyllachne colensoi (Stylidiaceae). The study was conducted at two sites on the Rock and Pillar Range, South Island, New Zealand at 1300 m a.s.l. during one growing season. Cameras were placed at five plots at opposing north and south- facing aspects and recorded flowering phenology and summer frost events throughout the growing season. Patch size, flowering probability, and flower abundance were measured using image analysis and manual flower counting. Temperature and soil moisture were also recorded at sixteen plots at each aspect. North-aspects were 2.3°C warmer on average on both sites at ground level, had 8.7% fewer recorded frost events, and had 5.5% lower soil moisture. P. colensoi patches were 38% less likely to flower on the north aspect on one site and north aspect patches were smaller for both species. First flowering date was advanced on the north aspect for both D. muscoides (7.3 days) and P. colensoi (1.2 days). There was high intra-aspect variation in flowering phenology, suggesting that increasing temperatures and decreasing soil moisture under climate change conditions may not lead to a uniform phenological response amongst individuals even across small spatial scales. The implications for this research are that flowering patterns and phenology under climate change conditions can be forecasted using fine- spatial scales. Under a 2°C warming scenario it is expected that D. muscoides patches can be up to four times smaller in size and flower seven days earlier. P. colensoi patches are expected to be up to two times smaller, flower one day earlier, and have a 28% lower chance of flowering.