Montane forest productivity across a semiarid climatic gradient.

Area of Science:

• Ecology
• Climate Science
• Forestry

Background:

• High-elevation montane forests are crucial carbon sinks in semiarid regions.
• These ecosystems face threats from climate change, affecting photosynthesis and growth.
• Low-elevation areas in semiarid climates are dry with low carbon density.

Purpose of the Study:

• To assess carbon sequestration in semiarid western US montane forests under projected warming and drying.
• To understand the seasonal drivers of gross primary productivity (GPP) in these forests.
• To identify key factors influencing annual GPP across different temperature and moisture regimes.

Main Methods:

• Utilized eddy covariance data from six evergreen conifer forest sites.
• Analyzed seasonal GPP patterns in relation to temperature, precipitation, snowmelt, and leaf area.
• Extrapolated findings within a framework of projected climate change scenarios.

Main Results:

• Colder sites showed a single summer GPP peak driven by snowmelt moisture.
• Warmer sites exhibited two GPP peaks, influenced by winter and summer precipitation, with transient winter dormancy.
• Leaf area index and moisture availability were the best predictors of annual GPP differences.
• Annual GPP was highest at the warmest site due to year-round photosynthetic activity.

Conclusions:

• Forest carbon sequestration is sensitive to reduced or delayed summer precipitation and snow drought.
• Warming has counteracting effects: positive in winter, negative in summer.
• Montane forest carbon sequestration is projected to remain stable long-term without severe disturbances, despite climate uncertainties.