Responses of deciduous forest trees to severe drought in Central Europe

Abstract

In 2003, Central Europe experienced the warmest summer on record combined with unusually low precipitation. We studied plant water relations and phenology in a 100-year- old mixed deciduous forest on a slope (no ground water table) near Basel using the Swiss Canopy Crane (SCC). The drought lasted from early June to mid September. We studied five deciduous tree species; half of the individuals were exposed to elevated CO(2) concentration ([CO(2)]) (530 ppm) using a free-air, atmospheric CO(2)-enrichment system. In late July, after the first eight weeks of drought, mean predawn leaf water potential about 30 m above ground was -0.9 MPa across all trees, dropping to a mean of -1.5 MPa in mid-August when the top 1 m of the soil profile had no plant accessible moisture. Mean stomatal conductance and rates of maximum net photosynthesis decreased considerably in mid-August across all species. However, daily peak values of sap flow remained surprisingly constant over the whole period in Quercus petraea (Matt.) Liebl., and decreased to only about half of the early summer maxima in Fagus sylvatica L. and Carpinus betulus L. (stomatal down- regulation of flux). Although we detected no differences in most parameters between CO(2)-treated and control trees, predawn leaf water potential tended to be less negative in trees exposed to elevated [CO(2)]. Leaf longevity was greater in 2003 compared with the previous years, but the seasonal increase in stem basal area reached only about 75% of that in previous years. Our data suggest that the investigated tree species, particularly Q. petraea, did not experience severe water stress. However, an increased frequency of such exceptionally dry summers may have a more serious impact than a single event and would give Q. petraea a competitive advantage in the long run.

Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

“…Besides, drought-induced mortality has been repeatedly observed in Scots pine stand from Mediterranean [28] and Central Europe populations [4]. On the contrary, Q. petraea was less affected than other coexisting species by the extreme 2003 summer drought in Central Europe [26].…”

“…To convert P. sylvestris projected leaf area to half-total leaf area we multiplied the former by a coefficient of 1.35 [40]. Given that the main purpose of our study was to identify the different responses to varying environmental conditions of pines and oaks, we normalised sap flow per unit leaf area at midday (Q L, md ) with respect to its maximum value [26]. Relative sap flow at midday was then related to vapour pressure deficit (D), net radiation (R n ) and soil moisture deficit S MD, calculated from maximum and minimum values of soil moisture (θ max , θ min ) [18]:…”

“…Indeed, there is increasing evidence that extreme drought episodes affect Scots pine particularly [28], while deciduous oaks like for instance Quercus petraea (Matt.) Liebl., seem unaffected [26].…”

Leaf water status and stem xylem flux in relation to soil drought in five temperate broad-leaved tree species with contrasting water use strategies

“…represent species with a contrasting distribution range in Europe and, thus, putatively differing in drought avoidance and tolerance strategies (Marigo et al, 2000;Bolte et al, 2007;Ellenberg and Leuschner, 2009). Except for beech, data on the drought response of the important Central European tree species is scarce (Aranda et al, 2005;Bréda et al, 2006;Cochard et al, 1996;Leuzinger et al, 2005;Magnani and Borguetti, 1995;Marek et al, 1989;Nardini and Salleo, 2000).…”

Climate risks and their impact on agriculture and forests in Switzerland

“…Liebl. ), did not experience severe water stress at this site in 2003 (Leuzinger et al 2005). Although mean stomatal conductance and rates of maximum net photosynthesis decreased considerably in mid-August across all species, daily peak values of sap flow remained surprisingly constant in oak over the whole period, and it decreased to only about half of the early summer maxima in beech and European hornbeam (Carpinus betulus L).…”