Microclimate characteristics of alpine bluff ecosystems of New Zealand's South Island, and implications for plant growth

Descriptions of alpine climate in areas of high solar radiation are increasing, but there is a paucity of microclimate data for shaded alpine rock bluff ecosystems. These shaded systems are important because they represent plant habitats that are subject to unique climate drivers within the alpine ecosystem, but which are poorly characterised globally. We describe microclimate characteristics, including photosynthetically active radiation (PAR), atmospheric vapour pressure deficit, and air (T_air) and soil temperature (T_soil) for three shaded alpine bluff sites at 1370–1800 m altitude on the South Island of New Zealand that support a diverse flora, including obligate shaded-bluff species of Pachycladon (Brassicaceae). Maximum instantaneous PAR at all study sites was generally < 100 µmol m^-2 s^-1, or approximately 5% of full sunlight. Monthly mean T_air at the lowest altitude site ranged between −1.1°C and +13.7°C and declined to between −4.2°C and +7.6°C at the highest altitude site. T_soil covaried with T_air, but with less extreme temperatures. The low-incident PAR of these bluff ecosystems suggests leaf temperatures at these sites are primarily regulated by air temperature and not by incident radiation. This study emphasises the need for information on the physiological response of these alpine plants to climate drivers, particularly in relationship to photosynthetic carbon uptake and respiratory carbon loss.