Water Shortage Affects the Water and Nitrogen Balance in Central European Beech Forests

Abstract

Whilst forest policy promotes cultivation and regeneration of beech dominated forest ecosystems, beech itself is a highly drought sensitive tree species likely to suffer from the climatic conditions prognosticated for the current century. Taking advantage of model ecosystems with cool-moist and warm-dry local climate, the latter assumed to be representative for future climatic conditions, the effects of climate and silvicultural treatment (different thinning regimes) on water status, nitrogen balance and growth parameters of adult beech trees and beech regeneration in the understorey were assessed. In addition, validation experiments with beech seedlings were carried out under controlled conditions, mainly in order to assess the effect of drought on the competitive abilities of beech. As measures of water availability xylem flow, shoot water potential, stomatal conductance as well as d 13 C and d 18 O in different tissues (leaves, phloem, wood) were analysed. For the assessment of nitrogen balance we determined the uptake of inorganic nitrogen by the roots as well as total N content and soluble N compounds in different tissues of adult and young trees. Retrospective and current analysis of d 13 C, growth and meteorological parameters revealed that beech growing under warm-dry climatic conditions were impaired in growth and water balance during periods with low rain-fall. Thinning affected water, N balance and growth mostly of young beech, but in a different way under different local climatic conditions. Under cool, moist conditions, representative for the current climatic and edaphic conditions in beech forests of Central Europe, thinning improves nutrient and water status consistent to published literature and long-term experience of forest practitioners. However, beech regeneration was impaired as a result of thinning at higher temperatures and under reduced water availability, as expected in future climate.

Drought in forest understory ecosystems – a novel rainfall reduction experiment

“…Conversely, the quick response of leaf stomatal conductance (g s ) confirms that control of the transpiration is a very sensitive and short-term response of plants to reduced water supply (cf. Gessler et al, 2004). The finding that g s was mainly reduced in July and only marginally significantly in September clearly reflects the fact that our rain reduction was not absolute but proportional.…”

Gap regeneration in near-natural European beech forest stands in Central Bohemia – the role of heterogeneity and micro-habitat factors

“…In gaps, moisture and nutrient status may be particularly favourable for drought sensitive European beech seedlings when young individuals compete with surrounding ground vegetation (Bolte et al 2007). Gessler et al 2004 showed that not only water shortage has a negative effect on European beech water budget but it also constrains its nitrogen supply. Light conditions may also positively influence the growth response of beech seedlings to soil fertility.…”

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…Other processes related to the short and long term acclimation of trees to drought need be better understood. Finally, nitrogen nutrition and cycling is likely to be modified by drought [48], and the impact of nutrient shortage under water deficit has to be quantified under various levels of site fertility and among drought tolerant, resistant or avoiding tree species.…”