Abstract
A changing climate in the future with more severe drought events will affect the conditions for forest growth and vitality. Most knowledge on tree species response to drought is based on monocultures, even though many of the forests in the world consist of mixed stands. We aimed to investigate how trees respond to summer drought when grown in a three species mixture. For two subsequent summers canopy throughfall, and subsequently soil water potential, was reduced using sub-canopy roofs in monocultures and mixtures of Betula pendula, Alnus glutinosa and Fagus sylvatica,. The overyielding of the mixed stand was not affected by the drought using either above or below ground production, standing fine root biomass or soil respiration as parameters. However, Alnus glutinosa was the most negatively affected when growing in monoculture, whereas this species was less affected when growing in mixture. In contrast, Betula pendula was most negatively affected when growing in mixture. Fagus sylvatica was least affected by the drought and maintained growth over the two years. A water demanding species as Alnus glutinosa can perform well in a mixture during drought and not be outcompeted. This is opposite to what is assumed in most models of forest responses to climate change.
Highlights
Climate models suggest that extreme events of drought will increase in many parts of the world (IPCC 2014), which will affect production as well as health of terrestrial ecosystems
Understanding the strategies of individual species, in response to drought, and how they interact in mixed stands during drought, is essential when trying to model response to drought at an ecosystem level. We examined both the above and belowground responses of Silver birch (Betula pendula), European beech (Fagus sylvatica) and Common alder (Alnus glutinosa) to drought when grown as single species stands and as a mixture of the three species
The percentage of precipitation that was intercepted during the time the roofs were on was for Fagus sylvatica 52 %, Alnus glutinosa 46 %, Betula pendula 48 % and 55 % in the mixture
Summary
Climate models suggest that extreme events of drought will increase in many parts of the world (IPCC 2014), which will affect production as well as health of terrestrial ecosystems. How tree species grown in a mixture react to drought is less clear (DeClerck et al 2006; del Rio et al 2014; Pretzsch et al 2014; Zapater et al 2013). A changing climate in the future with more severe drought events will affect the conditions for forest growth and vitality. Most knowledge on tree species response to drought is based on monocultures, even though many of the forests in the world consist of mixed stands. We aimed to investigate how trees respond to summer drought when grown in a three species mixture
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