The dependency of the size-growth relationship of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in forest stands on long-term site conditions, drought events, and ozone stress

Trees (Impact Factor: 1.93). 25(3):355-369. DOI: 10.1007/s00468-010-0510-1

ABSTRACT Against a backdrop of increasing climate change, the effects of site conditions, drought events and ozone stress on the size-growth
relationship in Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) stands are analyzed. The size-growth relationship is represented by a straight line defined by intercept and slope
of a simple linear equation with stem diameter at height 1.30m as independent variable and annual stem diameter increment
at height 1.30 as dependent variable. On the basis of 64 long-term experimental plots dating back to 1871 and representing
an ecological gradient from fertile to poor sites, it is shown that poorer sites exhibit shallower slopes of the linear size-growth
relationships than fertile sites. Annual measurements of the size-growth relationship, including the extremely dry years of
1976 and 2003, also showed that lower stand growth rates result in shallower size-growth relationship slopes. By comparing
stands with and without experimental twice-ambient ozone exposure between 2000 and 2007, it was found that ozone stress can
significantly reduce the slope of the size-growth relationship. This indicates that limiting site condition, whether acute
or chronic in nature, distinctly reduces the superiority of tall trees, and that a lower degree of resource limitation increases
the steepness of the size-growth relationship. The causes for this behavior and the consequences for stand dynamics, silvicultural
treatment and prognostication by models are discussed.

KeywordsSize-asymmetric growth–Diameter increment–Competition–Resource partitioning–Limitation–Allocation principle–Stand structure

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