Resolving interannual climate sensitivity of tree growth and forest productivity by integrating tree-rings, leaf hydraulic traits, and forest census data
Abstract
The climate sensitivity of forest ecosystem woody productivity (ANPP_{woody}) will influence carbon cycle responses to future changes in climate. Here, to understand how tree growth and forest productivity respond to climate drivers including drought, we integrate forest census data from a 25.6-ha ForestGEO plot in Virginia (USA), tree-ring records for 14 species representing 97% of ANPP_{woody}, leaf hydraulic trait measurements, and microhabitat data. Across 109 years (1901-2009), radial growth of most species and ecosystem-level ANPP_{woody} responded negatively to warmer and drier growing season conditions, but the same conditions in May-July of the previous growing season were associated with increased growth. In recent decades (1980-2009), responses were on average weaker and more variable. Individual-level growth responses to three droughts (1964-66, 1977, 1999) were stronger among taller trees in dominant canopy positions, those in wetter microsites, and for more drought-sensitive species as assessed by leaf traits (turgor loss at less negative leaf water potential , greater shrinkage with leaf dehydration), with substantial variation in the best predictor variables across given droughts. Our results indicated that ANPP woody is primarily limited by current growing season moisture, with a complex climate sensitivity that likely reflects the use of stored carbohydrate reserves. We conclude that although US eastern deciduous forests currently display limited moisture sensitivity, their ANPP_{woody} may decline with reductions of growing season moisture under projected hotter and potentially drier conditions. When droughts occur, large dominant trees, drought sensitive species, and individuals in moist microhabitats are likely to be most strongly affected. These findings highlight the urgent necessity of integrating multiple data streams across time scales to resolve the climate sensitivity of forest productivity.
