166 research outputs found
A novel empirical approach for determining the extension of forest development stages in temperate old-growth forests
No full textRegeneration Dynamics Following the Formation of Understory Gaps in a Slovakian Beech Virgin Forest
No full textThe frequency and size of canopy gaps largely determine light transmission to lower canopy strata, controlling structuring processes in the understory. However, quantitative data from temperate virgin forests on the structure of regeneration in gaps and its dynamics over time are scarce. We studied the structure and height growth of tree regeneration by means of sapling density, shoot length growth and cumulative biomass in 17 understory gaps (29 to 931 m2 in size) in a Slovakian beech (Fagus sylvatica L.) virgin forest, and compared the gaps with the regeneration under closed-canopy conditions. Spatial differences in regeneration structure and growth rate within a gap and in the gap periphery were analyzed for their dependence on the relative intensities of direct and diffuse radiation (high vs. low). We tested the hypotheses that (i) the density and cumulative biomass of saplings are higher in gaps than in closed-canopy patches, (ii) the position in a gap influences the density and height growth of saplings, and (iii) height growth of saplings increases with gap size. Sapling density and biomass were significantly higher in understory gaps than under closed canopy. Density of saplings was positively affected by comparatively high direct, but low diffuse radiation, resulting in pronounced spatial differences. In contrast, sapling shoot length growth was positively affected by higher levels of diffuse radiation and also depended on sapling size, while direct radiation intensity was not influential. Conclusively, in this forest, regeneration likely becomes suppressed after a short period by lateral canopy expansion in small gaps (<100 m2), resulting in a heterogeneous understory structure. In larger gaps (≥100 m2) saplings may be capable even at low plant densities to fill the gap, often forming a cohort-like regeneration layer. Thus, gaps of different sizes imprint on the resulting canopy structure in different ways, enhancing spatial heterogeneity
Classifying development stages of primeval European beech forests: is clustering a useful tool?
No full textAbstract Background Old-growth and primeval forests are passing through a natural development cycle with recurring stages of forest development. Several methods for assigning patches of different structure and size to forest development stages or phases do exist. All currently existing classification methods have in common that a priori assumptions about the characteristics of certain stand structural attributes such as deadwood amount are made. We tested the hypothesis that multivariate datasets of primeval beech forest stand structure possess an inherent, aggregated configuration of data points with individual clusters representing forest development stages. From two completely mapped primeval beech forests in Albania, seven ecologically important stand structural attributes characterizing stand density, regeneration, stem diameter variation and amount of deadwood are derived at 8216 and 9666 virtual sampling points (moving window, focal filtering). K-means clustering is used to detect clusters in the datasets (number of clusters (k) between 2 and 5). The quality of the single clustering solutions is analyzed with average silhouette width as a measure for clustering quality. In a sensitivity analysis, clustering is done with datasets of four different spatial scales of observation (200, 500, 1000 and 1500 m2, circular virtual plot area around sampling points) and with two different kernels (equal weighting of all objects within a plot vs. weighting by distance to the virtual plot center). Results The clustering solutions succeeded in detecting and mapping areas with homogeneous stand structure. The areas had extensions of more than 200 m2, but differences between clusters were very small with average silhouette widths of less than 0.28. The obtained datasets had a homogeneous configuration with only very weak trends for clustering. Conclusions Our results imply that forest development takes place on a continuous scale and that discrimination between development stages in primeval beech forests is splitting continuous datasets at selected thresholds. For the analysis of the forest development cycle, direct quantification of relevant structural features or processes might be more appropriate than classification. If, however, the study design demands classification, our results can justify the application of conventional forest development stage classification schemes rather than clustering
Biomass Stock and Productivity of Primeval and Production Beech Forests: Greater Canopy Structural Diversity Promotes Productivity
No full textOur knowledge of temperate broadleaf forest ecology is based mostly on the study of production forests, which lack the terminal stage of forest development and have a simpler stand structure than old-growth and primeval forests. How primeval and production forests differ in net primary production (NPP) is not well known. In three primeval and three nearby production forests of European beech (Fagus sylvatica) in the Slovakian Carpathians, we measured aboveground biomass stocks (live and dead), aboveground NPP (ANPP) and parameters characterizing canopy structural diversity (leaf area index and its spatial variation). Our study aims were (1) to explore the role of canopy structural diversity for ANPP and (2) to assess evidence of a productivity decline in the terminal stage. While aboveground live biomass stocks were on average 20% greater in the primeval forests (386 vs. 320 Mg ha−1; insignificant difference at two sites), deadwood mass stocks were on average four times larger than in the production forests (86 vs. 19 Mg ha−1). ANPP was similarly high in the primeval and production forests (10.0 vs. 9.9 Mg ha−1 y−1) and did not decrease towards the terminal stage. Production models indicate that, in the primeval forests, about 10% of ANPP (ca. 1 Mg ha−1 y−1) was generated by effects related to leaf area heterogeneity, evidencing a positive effect of structural diversity on forest productivity, even though species diversity was low. This study helps to better understand the impact of forest management on the productivity and carbon storage in temperate woodlands
Forest management impact on soil organic carbon: A paired-plot study in primeval and managed European beech forests
No full textCanopy gap dynamics and tree understory release in a virgin beech forest, Slovakian Carpathians
No full textRemyranina Schweitzer & Feldmann 2010, n. gen.
No full textGenus Remyranina n. gen. TYPE SPECIES. — Raninella ornata Remy, 1960. ETYMOLOGY. — Th e generic name combines the name of the author of the type species and prominent French paleontologist, Jean-Marcel Remy, and Ranina, the type genus of the family. OCCURRENCE. — Th e sole specimen was collected from probable Eocene rocks of Ivory Coast, Africa. DIAGNOSIS. — Small raninid with expanded, moderately broad fronto-orbital margin; ovoid, slightly longer than wide, with carapace ornamentation granular in anterior half and strongly terraced in posterior half. DESCRIPTION. — As for emended description of species. DISCUSSION Although the specimen referred to the new genus clearly allies it with the Ranininae, the combination of characters is unique and readily justifies creation of the new taxon. Th e genus to which it is most closely allied is Lophoranina Fabiani, 1910. Th ese two genera are the only ones in the Raninidae that are characterized by possession of a trifid rostrum and development of terraced ornamentation. However, Lophoranina tends to be widest near the front or at the level of the last anterolateral spine, whereas Remyranina n. gen. is broadest at the midlength, well posterior to the anterolateral spines. Furthermore, the anterolateral spines and the postorbital spines on Lophoranina are generally small, whereas those on Remyranina n. gen. are large. Finally, the terraced lines of Lophoranina extend nearly to the front of the carapace, well in advance of the branchiocardiac grooves, whereas those on Remyranina n. gen. are confined to the posterior half of the carapace. Th ere seems to be no other genus of raninids with which Remyranina n. gen. could be confused.Published as part of Schweitzer, Carrie E. & Feldmann, Rodney M., 2010, New fossil decapod crustaceans from the Remy Collection, Muséum national d'Histoire naturelle, Paris, pp. 399-415 in Geodiversitas 32 (3) on page 401, DOI: 10.5252/g2010n3a3, http://zenodo.org/record/468845
Quantifying old-growthness of lowland European beech forests by a multivariate indicator for forest structure
No full textStrongly Connected Steiner Subgraphs with small number of Steiner vertices
No full textTitle: Strongly Connected Steiner Subgraphs with Small Number of Steiner Vertices Author: Tamás Dávid Kemény Department: Department of Applied Mathematics Supervisor: Dr. Andreas Emil Feldmann, Department of Applied Mathematics Abstract: Two well-established methods of dealing with hard optimization problems have been to develop approximation and parameterized algorithms. Recent results have shown that for some problems, it is only by combining these two approaches, into so-called pa- rameterized approximation algorithms, that we are able to efficiently find solutions that are of reasonable quality. This is the viewpoint from which we study the problem known as the Strongly Connected Steiner Subgraph problem, where a set of terminal vertices of an edge-weighted directed graph needs to be strongly-connected in the cheapest way possible. Keywords: Strongly Connected Steiner Subgraphs, Parameterized Algorithms, Approxi- mation Algorithms, Bidirected Graphs ii
Silné souvislé Steinerovské podgrafy s malým počtem Steinerovských vrcholů
No full textTitle: Strongly Connected Steiner Subgraphs with Small Number of Steiner Vertices Author: Tamás Dávid Kemény Department: Department of Applied Mathematics Supervisor: Dr. Andreas Emil Feldmann, Department of Applied Mathematics Abstract: Two well-established methods of dealing with hard optimization problems have been to develop approximation and parameterized algorithms. Recent results have shown that for some problems, it is only by combining these two approaches, into so-called pa- rameterized approximation algorithms, that we are able to efficiently find solutions that are of reasonable quality. This is the viewpoint from which we study the problem known as the Strongly Connected Steiner Subgraph problem, where a set of terminal vertices of an edge-weighted directed graph needs to be strongly-connected in the cheapest way possible. Keywords: Strongly Connected Steiner Subgraphs, Parameterized Algorithms, Approxi- mation Algorithms, Bidirected Graphs iiiKatedra aplikované matematikyDepartment of Applied MathematicsFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
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