Climate and Physical Factors
The climate of subalpine ecosystems is dominated by very long winters and short growing seasons of 6–9 weeks. Temperatures are cool even during the growing season and frost can occur 12 months of the year. Precipitation ranges from 750–1,250 millimetres (30–50 in) per year, which falls mostly as snow during the winter. Temperatures average -11.5 to 1.5 °C (11 to 35 °F) in January and 5.5 to 19.5 °C (42 to 67 °F) in July, with a mean annual temperature around 4 °C (39 °F). Snow depths often exceed 3 metres (10 ft), but average 2 metres (7 ft) by the end of March.
Winds can be high throughout the year and are a major factor limiting plant growth near the upper limit of the subalpine zone (tree line). Wind limits vegetative growth chiefly in two ways: by physically battering plants, including blowing snow and ice, and by increasing evapotranspiration in an environment that is already water-stressed.
Soils are thin, coarse and relatively nutrient-poor, owing to the unproductive climate and repeated glaciation events during the Pleistocene. Moisture retention is usually high, due to the presence of underlying granite bedrock, and soils often become waterlogged early in the growing season. However, because very little precipitation falls during the summer months, soils can dry quickly once snow melts and vegetative growth and reproduction is limited late in the growing season by drought.
Compared to subalpine zones in the Cascade Range, Sierran subalpine experiences less annual precipitation, with a longer drought period during the summer months, but similar temperature ranges throughout the year. Compared to Rocky Mountains subalpine zone, Sierran subalpine experiences a narrower (more mild) range of temperatures and higher annual precipitation, with more winter snow and less summer rain.
Read more about this topic: Sierra Nevada Subalpine Zone
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