Biodiversity and the resistance of forest ecosystems to drought

The extreme events induced by climate change will have drastic consequences on forest functions and services and may bring about important drought-induced die-off events. It is known, however, that biodiversity can promote forest ecosystem performance and resistance to insect pests and diseases. Promoting higher tree species richness in temperate forests is also suggested to be an appropriate management practice to be considered in the context of increased drought frequency and intensity in the future. Indeed, interactions among species may lead to positive complementarity effects of resource acquisition and use and these mechanisms may result in greater resistance of diverse ecosystems to soil drought than pure ones.

To shed more light on the effects of biodiversity on the resistance of European forests to drought, we studied about 200 forest stands across Europe (Spain, Italy, Romania, Germany, Poland, Finland) with a variety of tree diversity levels (from monocultures to five species mixtures). For every region, we compared monocultures to mixed forests and looked at their respective capacity to resist to a major drought event.

We showed that mixed species forests are more resistant to drought stress than monocultures in some regions only: tree diversity may afford greater resistance to drought stress in drought-prone areas, i.e. in regions where the frequency and severity of drought during the growing season is high, whereas tree diversity may reduce resistance to drought in regions where drought events are unusual (e.g. boreal forests in Finland).

The generalization of forest management practices with mixed tree species thus does not necessarily provide better resistance of temperate forests to drought. Managing forest ecosystems for high tree species diversity alone does not necessarily ensure forest adaptability to possible future drought events. It might be of great importance to consider species identities and local climatic conditions, and not solely the degree of diversity in the mixtures, to obtain complementary use of resources and maintain ecosystem functions under drought stress.

The controversy surrounding the issues arises because it involves the convergence of three 'storms' 1) the global problem 2) its intergeneration dimension and 3) the inadequacies of the theoretical models ( Gardier SM 2011).
Biological diversity, or the shorter "biodiversity," means the diversity, or variety, of plants and animals and other living things in a particular area or region. It describes the variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part. Biodiversity includes diversity within species, between species, and between ecosystems. (MA, 2003)
The capacity of an ecosystem to withstand the impacts of drivers without displacement from its present state. ( MA 2003)
The unconsolidated mineral or organic material on the immediate surface of the earth that serves as the natural medium for the growth of land plant ( SAF dictionary, 2008).
A condition describes a requirement or requisite. wiki
A source or supply from which benefit is produced, typically of limited availability. In biology it means, substances or objects required by a biological organism for normal maintenance, growth, and reproduction. wiki
Grossiord - Drought Resistance and Tree Species diversity

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