Disentangling the relative influence of background versus disturbance related mortality on forest demography is crucial for understanding long‐term dynamics and predicting the influence of global ...change on forests. Quantifying the rates and drivers of tree demography requires direct observations of tree populations over multiple decades, yet such studies are rare in old‐growth forest, particularly in the temperate zone of Europe. We use multi‐decade (1980–2020) monitoring of permanent plots, including observations of mode of mortality and disturbance events, to quantify rates and drivers of tree demography across a network of old‐growth remnants in temperate mountain forests of Slovenia. Annual rates of mortality and recruitment varied markedly among sites and over time; census intervals that captured intermediate severity canopy disturbances caused subtle peaks in annual mortality (e.g., >2%/year), while rates of background mortality in non‐disturbed intervals averaged about 1%/year. Roughly half of the trees died from modes of mortality associated with disturbance (i.e., uprooting or snapped‐alive). Results of a Bayesian multilevel model indicate that beech (Fagus sylvatica) had a higher likelihood of disturbance related mortality compared to fir (Abies alba), which mainly died standing, and there was a notable increase in the odds of disturbance mortality with increasing diameter for all species. Annual recruitment rates were consistently low at sites (<0.5%) that lacked evidence of disturbance, but often exceeded 3% on sites with higher levels of past canopy mortality. Recruitment was dominated by beech on sites with more diffuse background mortality, while the less shade tolerant maple (Acer pseudoplatanus) recruited following known disturbance events. Our study highlights the important role of stand‐scale, partial canopy disturbance for long‐term forest demography. These results suggest that subtle climate‐driven changes in the regime of intermediate severity disturbances could have an important influence on future forest dynamics and warrant attention.
We use multi‐decade monitoring of permanent plots to quantify rates and drivers of tree demography across a network of old‐growth remnants in temperate mountain forests. Annual rates of mortality and recruitment varied markedly among sites and over time, and roughly half of all trees died from disturbance related mortality. Our study highlights the important role of stand‐scale, intermediate severity disturbance for long‐term forest demography.
Mixed species forests are presently on the advance and widely held to provide many ecosystem functions and services better than pure stands. Recent studies well explored species mixing effects at the ...individual tree or stand level. However, the link between individual and stand level which is represented by the size-structure dynamics of stands, is still hardly understood.Aim of this study: The objective was to analyse how species mixing modifies the size-structure dynamics of mixed compared with pure forest stands. Area of the study: the study was carried out in Southern Germany.Material and Methods: We selected 11long-term experiments comprising 129 plots of un-thinned or just lightly thinned pure and mixed stands of European beech (Fagus sylvatica L.) and analysed their size structure dynamics.Main Results: Based on the Gini coefficient, skewness and kurtosis we show how mixing with Norway spruce (Picea abies L. Karst) and sessile oak (Quercus petraea (Matt.) Liebl.) modifies the size-structure dynamics of European beech. The size distribution of beech in mixture mostly lags behind the pure stand, is more size-asymmetric, and the mortality shifts from the smaller diameter classes further to the taller trees than in pure stands.Research highlights: The revealed changes of the size-structure dynamics of beech in mixed versus pure stands result from a modification of both growth partitioning and self-thinning. We draw conclusions of the reduced size growth and size equality of beech in mixed versus pure stands for forest management planning and perspectives for forest research.Keywords: species selection effect; true mixing effect; morphological plasticity; size-distribution; growth partitioning between trees; mode of mortality; European beech (Fagus sylvatica L.); Norway spruce (Picea abies L. Karst); sessile oak (Quercus petraea (Matt.) Liebl.).
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