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: 1.87). 06/2010; 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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    ABSTRACT: Context: Growth partitioning among trees in forest stands is pivotal to silviculture, making it crucial to understand its control by factors such as stand development, stand density, or thinning. Since growth partitioning primarily depends on the partitioning of environmental resources among individuals, climatic change further calls for extending this framework to explicit climatic factors. Recent debate on adapting management to such changes also requires larger density gradients to be encompassed. Methods: We primarily aimed to investigate the effects of stand density and climatic factors on growth partitioning, in even-aged stands of sessile oak and Douglas-fir, two species currently managed under contrasted silvicultural regimes. We used two original permanent plot networks designed to explore effects of large density gradients, from open-grown to self-thinning situations. Growth partitioning was assessed on basal area growth, using both the growth dominance index, and the within-stand size-growth relationship. Their dependence on stand density, age, thinning, and climatic predictors was modeled statistically. A one-at-a-time sensitivity analysis of these models was performed to evaluate the magnitude of the effect of each predictor on growth partitioning. Simulations of the effect of extreme climatic conditions on stand growth, and on dominant, intermediate and close-to-suppressed trees growth were also performed. Results: For both species, stand density was found to strongly increase growth partitioning toward the biggest trees. Stand growth in sessile oak was reduced by high summer soil water deficit, with a particularly severe growth reduction for suppressed trees, suggesting asymmetric belowground competition for water in this species. In Douglas-fir, a stand growth reduction was found for high summer temperatures, with an increase in growth dominance that suggested a higher temperature-driven stress for suppressed trees. In addition, age slightly increased/decreased growth dominance in sessile oak/Douglas-fir, respectively. Conclusions: Growth dominance and size-growth relationships offered complementary insight into growth partitioning. Stand density appears to be the major driver of growth partitioning. Climatic factors were also shown to significantly affect growth partitioning, with species differences, in addition to stand density and ageing. These results suggest to maintain stands at medium density levels to reduce rotation length and minimize risk of exposure to extreme climatic events.
    Forest Ecology and Management 12/2014; 334:358–368. DOI:10.1016/j.foreco.2014.09.020 · 2.67 Impact Factor
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    ABSTRACT: Study 1 In most dendroecological studies, climate–growth relationships are established for trees growing on pure stands. However, response to climate may be affected by inter-species interactions and local constraints which begs the question of the effect of mixture on tree growth response under various ecological conditions. To assess these effects, climate–growth relationships of pure Abies alba stands were compared to those of three different mixtures: Abies alba with Fagus sylvatica, with Picea abies and with both species. 151 stands (456 Abies alba) were sampled in the Vosges mountains in north-eastern France under three contrasted climates, from low-altitude and dry conditions (mean precipitation in July < 85 mm and altitude < 600 m) to high-altitude and humid conditions (P July > 115 mm and alt. > 900 m). Soil water holding capacity and fertility, tree-size and age, stand basal area have been carefully controlled to avoid any interaction with the expected effect of mixture. The climate-growth relationships were evaluated from 12 Abies alba chronologies (4 mixtures x 3 conditions) through extreme growth years and response function analyses. Late previous summer conditions and current summer soil water deficit and temperature played a major role for Abies alba growth. Results showed greater sensitivity to (i) temperature at high elevation, and (ii) summer drought at low altitude and under dry conditions. Mixture (i) allowed to maintain a higher level of growth of Abies alba during extreme climatic events and (ii) reduced Abies alba response to summer drought especially under the driest contexts. Different facilitation processes may explain admixture effects such as changes in rooting depth, water input by stemflow and rainfall interception. This differentiated functioning of mixed forests highlights their importance for adapting forest management to climate change. Study 2 The aim of the study was to assess the effects of competition at both stand and tree levels on climate tree-growth relationships of 414 Abies alba and 243 Fagus sylvatica trees growing in 2 contrasting ecological conditions (north- and south-facing) under mountainous continental climate (mean altitude: 886 m). Stand level competition was considered through three Stand Basal Area (SBA) modalities (Low: 32 m²/ha, Medium: 41 and High: 49) while tree level competition was assessed through three Social Statuses (SST, Dominant, Codominant and Suppressed trees). A strong specific response to climate was pointed out with different key periods; growth of Abies being mainly driven by previous and current late summer temperatures, while that of Fagus was controlled by April and June ones. No obvious difference between facing sides was evidenced. Competition at stand level prevailed on competition at tree level. In Low and Medium SBA, trees exhibited similar responses to climate whatever their social statuses. On the opposite, sensitivity to summer drought increased with dominancy in high SBA. Inter-specific differences and consequences for forest management are discussed.
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    ABSTRACT: Combining national forest inventory (NFI) data with digital site maps of high resolution enables spatially explicit predictions of site productivity. The aim of this study is to explore the possibilities and limitations of this database to analyze the environmental dependency of height-growth of Norway spruce and to predict site index (SI) on a scale that is relevant for local forest management. The study region is the German federal state of Bavaria. The exploratory methods comprise significance tests and hypervolume-analysis. SI is modeled with a Generalized Additive Model (GAM). In a second step the residuals are modeled using Boosted Regression Trees (BRT). The interaction between temperature regime and water supply strongly determined height growth. At sites with very similar temperature regime and water supply, greater heights were reached if the depth gradient of base saturation was favorable. Statistical model criteria (Double Penalty Selection, AIC) preferred composite variables for water supply and the supply of basic cations. The ability to predict SI on a local scale was limited due to the difficulty to integrate soil variables into the model.
    Forests 11/2014; 2014(5(11)):2626-2646. DOI:10.3390/f5112626 · 1.14 Impact Factor

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Jochen Dieler