Authors:G. Koncz, P. Török, M. Papp, G. Matus, and B. Tóthmérész
Intensification of land use in the last few decades resulted in an increased rate of fragmentation of natural forest habitats. With decreased patch size but increased total borderline length the influence of the surroundings also increased. The extent of influence is especially crucial where the forest stands are adjacent to agricultural lands. We studied the vegetation (cover) and seed bank (soil samples, seedling emergence) along adjacent stands of an abandoned vineyard and edge and interior of an oak forest community (Quercetum petraeae-cerris) widespread in Central-Europe, using five transects (16 m2 plots along each transect). We asked the following questions: (i) How do vegetation and seed bank composition differ between the vineyard and forest interior and (ii) which weeds are able to penetrate into the forest herbaceous understorey vegetation and seed banks from the vineyard? In total, 15 phanaerophytes and 147 herbs were detected. Negatively associated with canopy shading, herb cover proved the lowest in the forest inferior. Few weeds and other ruderals recorded in vineyard penetrated into the forest interior. Mean seed density decreased one order of magnitude from the vineyard to the forest interior (from 20,831 to 2,159 seed/m2). The seed banks of the abandoned vineyard and edge and forest interior were dominated by ruderals, but decreasing proportion of weeds was detected from the vineyard to the forest interior. Characteristic forest herbs possessed at most sparse seed banks. Our results suggest that high canopy cover mitigates the negative impact of surrounding weedy vegetation on the forest herb layer. Therefore, the effect of surroundings is detectable mostly in the seed banks. We can assume that the formation of an increased ruderal herb cover can be foreseen if canopy opens, because the local propagule sources of forest species are missing from vegetation and soil seed banks.
Authors:R. Ádám, P. Ódor, A. Bidló, L. Somay, and J. Bölöni
Dry oak forests have one of the richest understory vegetation in Europe, but the environmental drivers of this community have been scarcely revealed. In this study, we assessed whether the amount of light, soil pH or stand heterogeneity affect primarily the species composition of this community. We investigaed 332 sampling plots in 40-165 year old managed and abandoned Quercus cerris and Q. petraea dominated forests in North Hungary. Presence-absence data of herbaceous species and seedlings of woody species were recorded in 28 subplots within each sampling plot. Stand structure, canopy openness and soil pH were also measured in each plot. The relationships between stand characteristics and the species assemblage were explored by redundancy analysis, while the individual responses of species and species groups were studied by generalized linear mixed models. Multivariate methods and individual species response analyses provided similar results, the amount of light and soil pH were equally important variables (both of them explained 2.8% of species variance), while stand heterogeneity had a bit lower, albeit still significant role in determining understory species composition (1.9% of species variance explained). Seedlings of woody species preferred shaded (half-shaded) conditions, while many herbaceous species were positively related to light. The effect of the three explanatory variables was hard to separate, since they influenced each other as well. Sessile oak seedlings and herbs typical of dry forests, forest edges, grasslands and acidic soil habitats preferred light rich habitats with homogeneous stand structure and low soil pH. Mesic forest herbs and seedlings of other woody species were related to relatively high soil pH, heterogeneous stand structure and closed canopy. These two understory types were clearly separated regarding composition. This study emphasizes the importance of heterogenous light conditions and mosaic, diverse forest structure (presence of homogeneous and heterogeneous forest patches) during forest management for the maintenance of understory biodiversity.
Different types of forest use significantly changed the structure and species composition of European temperate forests. Herbaceous species and seedlings are important parts of the forest ecosystem, thus it is necessary to understand the effects of stand characteristics on the species composition of the understory. In our study we assessed the main factors that affect the species composition of herb and tree seedling assemblages in Quercus petraea and Q. cerris dominated stands (age 50–150 years) in the Bükk Mountains, Hungary. The relationship between the studied assemblages and explanatory variables (tree species composition, stand structure, canopy closure and topography) were explored by Redundancy Analysis (RDA). The occurrence of herbaceous species was affected by canopy closure, stand structure (mean DBH and DBHcv of trees), topography and the density and diversity of shrub layers. Oak forest species were associated with more open stands with sparsely distributed large trees, while mesic forest species were positively associated with heterogeneous stand structure, low shrub density, and western exposure. Seedlings of trees and shrubs showed a dispersal limited phenomenon. The composition of seedlings was significantly influenced by the mean DBH of trees, the structural heterogeneity of the overstory, the tree species diversity and the density of shrub layers. However the seedlings of both dominant oak species required the same stand structure, sessile oak was able to regenerate almost exclusively in those stands where it was dominant in the overstory, which is significant for the management of the species. Generally, forest management affects species composition and structure of the overstory, accordingly it had direct and indirect effects on the understory community as well.
Authors:G. Koncz, Mária Papp, P. Török, Zs. Kotroczó, Zs. Krakomperger, G. Matus, and B. Tóthmérész
We studied the potential role of seed bank in the dynamics of the understorey in a turkey oak-sessile oak forest (Querceteum petraeae-cerris) in Hungary. We used long-term records of the herb layer (1973–2006) and the seed bank composition of 2006 to assess the role of seed bank in the regeneration of herb layer. The total cover of herb layer decreased from 22% (1973) to 6% (1988), and remained low (<10%) till 2006; coinciding with the increasing cover of secondary canopy dominated by Acer campestre. We found a low density seed bank (ca. 1300 seeds/m2). Altogether 33 species were germinated from the soil samples. A few generalist weed species composed the majority of seed bank. It was possible to assign a seed bank type for 19 species; 14 species out of 19 was long-term persistent. We found that the characteristic perennial forest herbs and grasses had only sparse seed bank. The Jaccard similarity between vegetation and seed bank was low (<30%). Our results suggest that the continuous establishment of forest herbs are not based on local persistent seed bank; it should be based on vegetative spreading and/or seed rain.
., Burke, D. A., Elliott, K. A. and Holmes, S. B. (2008): Effects of single-tree and group selection harvesting on the diversity and abundance of spring forestherbs in deciduous forests in southwestern Ontario. —
Forest Ecol. Management 255