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Resultats del tractament per disminuir la competència de faig a la teixeda de la font del Vilar
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Results of the Treatment to Reduce the Competition of Beech in the Yew Forests at Font del Vilar (Montseny): The yew (Taxus baccata) is a special tree and the habitat of its populations is of community interest (9580*). In Montseny there are isolated specimens in several points of the massif or forming small stands, the most prominent of which are at Turó de l’Home and Font del Vilar in Pla de la Calma. In 2013, measures were taken to eliminate a good part of the competition of beeches with the yew population at Font del Vilar. In 2015 monitoring was begun in order to evaluate the conservation action by measuring the growth, regeneration and study of the floral composition of the forest. The results of this first period clearly demonstrate that yews have been favoured by logging as those that are in areas where competition has decreased grow more than those in dense areas. However, we still have to continue analysing their long-term evolution and the effects of treatment on regeneration.
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Forest succession depends strongly on the life history strategies of individual trees. An important strategic element is the ability to survive unfavourable environmental conditions that result in strongly reduced tree growth. In this study, we investigated whether the relationship between growth and mortality differs among tree species and site conditions. We analysed 10 329 trees of nine tree species (Picea abies, Taxus baccata, Fagus sylvatica, Tilia cordata, Carpinus betulus, Fraxinus excelsior, Quercus robur, Betula spp. and Alnus glutinosa) from unmanaged forests of Europe: the continental Białowieża forest (Poland) and several oceanically influenced Swiss forest reserves. For each species, we calculated a set of flexible logistic regression models with the explanatory variables growth (as measured by relative basal area increment), tree size and site. We selected the species-specific model with the highest goodness-of-fit and calculated its discriminatory power (area under the receiver operating characteristic curve, AUC) and calibration measures. Most models achieved at least a good discriminatory power (AUC>0.7) and the AUC ranged from 0.62 to 0.87; calibration curves did not indicate any overfitting. Almost all growth–mortality relationships differed among species and sites, i.e. there is no universal growth–mortality relationship. Some species such as F. excelsior showed reduced survival probabilities for both unfavourable and very good growth conditions. We conclude that the growth–mortality relationships presented here can contribute to the life-history classification of trees and that they should also help to improve projections of forest succession models.
The aim of the present work was a comparison of the age and spatial structure of two populations of Taxus baccata in the Kórnik Arboretum, formed spontaneously under different initial conditions. The first of them (plot one) comes from at least 11, while the second (plot two) from only two, potential mother tress at a distance up to about 100m. The influence of the local climate conditions on the seedlings was also analyzed.Age structure of the population formed from 11 mother trees was found to be typical for young, but developing populations of shade tolerant trees about 40 years after the first cohorts were founded. The youngest seedlings formed the most numerous age class, still without saplings. The class ranking next consisted of tree-like specimens of the highest age. Obviously, the population of the first plot was formed by only few cohorts of seeds, in period of about 20 years. Seedlings may have appeared every year, but most often nearly all of them died. The sub-population on the second plot, developed as offspring from only two close-by growing mother trees, was formed during much a longer period and is characterized by a different age structure. The oldest individuals are less numerous as those in sub-population one. There is also a number of saplings, which are still joining the main stand; such saplings were not found in the other sub-population. The spatial structure of two sub-populations is also different. The first of them, which comes from several mother trees, is characterized as rather uniform, while the second which can be traced back to two mother trees, shows a clump distribution of tree-like yews.The climate parameter limiting the number of surviving seedlings in particular years appears to be a minimal temperature below −7.5°C in November. Temperatures of winter and spring, as well as the drought/precipitation regime during the vegetation period do not restrict the survival rate of the seedlings.Obviously, the distribution of individuals of the ornithochoric species T. baccata is strongly determined by the availability of mother trees in a distance suitable to be bridged by birds. Long distances limit seed supply heavily and retard and prolong the period of colonization. As a consequence, dispersal distances influence strongly age and spatial structure of cohorts founded from isolated (groups of) mother trees.
- P A Thomas
- A Polwart
Thomas, P. A.; Polwart, A. (2003): «Taxus baccata L.». J Ecol, núm. 91;
p. 489-524.