Tekstura drzewostanów naturalnych w polskich parkach narodowych na tle teorii dynamiki lasu

The aim of the study was to compare a patch-mosaic pattern in the old-growth forest stands developed in various climate and soil conditions occurring in different regions of Poland. Based on the assumption, that the patch-mosaic pattern in the forest reflect the dynamic processes taking place in it, and that each type of forest ecosystem is characterized by a specific regime of natural disturbances, the following hypotheses were formulated: (i) the patches with a complex structure in stands composed of latesuccessional, shade-tolerant tree species are more common than those composed of early-successional, light-demanding ones, (ii) the patch-mosaic pattern is more heterogeneous in optimal forest site conditions than in extreme ones, (iii) in similar site conditions differentiation of the stand structure in distinguished patches is determined by the successional status of the tree species forming a given patch, (iv) the successional trends leading to changes of species composition foster diversification of the patch structure, (v) differentiation of the stand structure is negatively related to their local basal area, especially in patches with a high level of its accumulation. Among the best-preserved old-growth forest remaining under strict protection in the Polish national parks, nineteen research plots of around 10 ha each were selected. In each plot, a grid (50 × 50 m) of circular sample subplots (with radius 12,62 m) was established. In the sample subplots, species and diameter at breast height of living trees (dbh ≥ 7 cm) were determined. Subsequently, for each sample subplot, several numerical indices were calculated: local basal area (G), dbh structure differentiation index (STR), climax index (CL) and successional index (MS). Statistical tests of Kruskal- Wallis, Levene and Generalized Additive Models (GAM) were used to verify the hypotheses. All examined forests were characterized by a large diversity of stand structure. A particularly high frequency of highly differentiated patches (STR > 0,6) was recorded in the alder swamp forest. The patch mosaic in the examined plots was different – apart from the stands with a strongly pronounced mosaic character (especially subalpine spruce forests), there were also stands with high spatial homogeneity (mainly fir forests). The stand structure in the distinguished patches was generally poorly related to the other studied features. Consequently, all hypotheses were rejected. These results indicate a very complex, mixed pattern of forest natural dynamics regardless of site conditions. In beech forests and lowland multi-species deciduous forests, small-scale disturbances of the gap dynamics type dominate, which are overlapped with less frequent medium-scale disturbances. In more difficult site conditions, large-scale catastrophic disturbances, which occasionally appear in communities formed under the influence of gap dynamics (mainly spruce forests) or cohort dynamics (mainly pine forests), gain importance.

A proposed microcosm for landscape ecology – beyond the binary to the patch-mosaic model

BackgroundMicrocosms such as pitcher plants, or patches of mosses on a rock surface, have been used worldwide to allow for manipulative experiments that test hypotheses for patterns observed at larger extents, such as dispersal or community assemblage. Such microcosms can also be applied to questions in landscape ecology, but are limited by their binary (patch/non-patch structure). Here we examine a more realistic model landscape system that shares the patch-mosaic structure common to kilometres-extent landscapes. This system of lichen thalli on tree trunks has been shown to have consistent spatial patterns across replicate microcosms, but only when sampling within a limited area. To be relevant for experimentation across scales, it is necessary to determine whether previously observed patterns are consistent when sampling across a broader region and when using different tree species. Here, we test for consistent landscape patch pattern in both maco- and micro-lichens across 21 balsam fir (Abies balsamea) and yellow birch (Betula alleghaniensis) trees.MethodsWe measured spatial pattern of lichen thalli along the trunks of two species of trees, at two spatial resolutions; trees within a single stand (∼100 × 50 m) and trees dispersed across a larger region (500 km2). We used a “lichen ladder” comprised of 5 10 × 10 cm sampling blocks to quantify number of species and individuals in a 50 cm section of the tree trunk. We tested for similar patterns along the trunk and between the north and south sides at both sampling intensities using perMANOVA.ResultsWe find that lichen patches on tree trunks can function as replicate microscoms for landscape ecology. Patterns of thalli along the trunks of trees and between the north and south aspects of the trunk are statistically significantly consistent, although there is variation between tree species, and groups of lichens included. Our microcosm could be used as a model system for landscape ecology research; but researchers should test for consistent patterns first.

Patch mosaic cyclic succession associated with the growth and senescence of an alpine shrub

Endogenously-induced cyclic vegetation change has been associated with the life cycle of shrub species, resulting in mosaic or linear patterning in vegetation. We investigated whether mosaic cyclic succession was taking place in Richea acerosa (Lindley) F.Muell. alpine heath on the Central Plateau of Tasmania, Australia by determining the variation in species composition associated with different growth characteristics of the shrub and by monitoring shrubs in plots over 11 years. Temperatures below and adjacent to shrubs were measured in clear sky conditions to determine if microclimatic variation was associated with structural and floristic variation. Species richness was higher outside than inside the shrubs, and was further depressed by an increasing proportion of dead material in the shrub. However, Poa saxicola R.Br. appeared to be protected by the prickly foliage of R. acerosa and also preferentially occurred among the mass of dead stems that characterised the centre of older plants. There was a strong floristic shift associated with the development of the shrub. The live cover of individual shrubs remained constant in all plots over the 11 years, while plots initially dominated by senescent plants contained young plants and vice-versa. The live part of the shrubs moderated temperatures. However, root competition and protection from grazing seem likely to have made a major contribution to the shifting conditions associated with the mosaic cyclic succession.

Grazing and the absence of fire promote the dominance of an unpalatable shrub in a patch mosaic cyclic successional system

We experimentally determined how an apparently unpalatable and fire-sensitive shrub, Richea acerosa (Lindley) F.Muell., responded to the single and interactive effects of grazing and burning over 3–24 years at two subalpine sites in Tasmania. At the Middlesex Plains site, a low-intensity burn killed most individuals of the species 3 years after fire and fencing. At the Lake Botsford site, total grazing exclusion for 24 years resulted in a strong reduction of the number of small shrubs of the species, and in a lower proportion of dead material in plants of any given size. An open shrub layer results from the absence of R. acerosa seedlings in the open centres of senescing plants and their preferential location along the margins of the foliage of mature and senescing plants. Thus, the persistence of R. acerosa appears to require an absence of frequent fire and the presence of sufficient grazing pressure from vertebrate herbivores to produce lawn between shrubs. Richea acerosa is, thus, an unpalatable shrub that depends on grazing.