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  • Author or Editor: S. Gärtner x
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Canopy gaps modify the environmental conditions available for plant growth in forests. Small canopy gaps are frequent in Nothofagus betuloides forests of Tierra del Fuego. Our objective was to study whether the forest floor vascular and non-vascular plant species composition and diversity are influenced by the occurrence of small-scale disturbances due to changes in the below-canopy solar radiation transmittances and forest floor heterogeneity (cover of litter, bare soil and fallen woody debris classed in three decay stages) in a N. betuloides forest located in south western Tierra del Fuego (53° 59t’S, 69°58′W). The vegetation was sampled in and around 13 canopy gaps (47 m2 on average). Following a light gradient, 65 plots (2 × 2 m) were established. The cover of all plant species was recorded using Londo’s scale. Species richness and total cover were calculated for each of the following taxonomical groups: spermatophyta (monocotyledons, dicotyledons), pteridophyta, bryophyta, marchantiophyta, anthocerotophyta and lichens. There were 63 species found on the forest floor. Marchantiophyta was the most diverse group with the highest species richness (6.6 species per plot). The vegetation on the forest floor was very homogeneous in species composition, richness and species diversity. The ordination analysis (NMS) showed that the community composition was weakly influenced by the patterns of below-canopy solar radiation transmittances and substrate heterogeneity. MRPP analysis of the community composition did not reveal differences in plant species assemblages between positions along transects running from areas beneath closed canopy to the open centres of canopy gaps. The marchantiophyte Chiloscyphus magellanicus was the only species which can be considered to be an indicator species; it was more likely to occur in gap centres (more open conditions). We conclude that these small canopy gaps do not very much modify the forest floor communities and the communities can be considered relatively stable.

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Today, native vegetation in the Valdivian Coastal Range (VCR) is restricted to areas where small-scale land use dominates resulting in a vegetation mosaic. This study (1) provides a description of the vegetation types (VT) within the vegetation mosaic, (2) identifies land use drivers that lead to either degradation or recovery processes and, (3) attempts to provide an explanation for the vegetation mosaic with a conceptual model. In two regions of the VCR we sampled 102 plots for composition of vegetation and indicators of livestock browsing, timber cutting and coppice forestry. We classified the vegetation using a flexible beta method and Bray-Curtis distance. Diagnostic species were identified by an extended indicator species analysis. The clustering results were visualized in NMDS and recursive partitioning was used to explain variations in the VTs as a function of the land use variables. Differentiating effects were tested using PERMANOVA and a conceptual model for the vegetation dynamics was developed from the results. Four VTs such as (1) extensively grazed non-native grasslands (EGN); (2), closed and semi-closed grazed Ugni and Berberis shrublands; (3) severely impacted evergreen forests; and (4) sparsely disturbed evergreen forests were recognized. The browsing indicators were important for differentiating the VTs. The EGN grasslands were differentiated by having more than 0.075 dung piles/m2. Areas with fewer dung piles but direct browsing effects had the greatest impact on vegetation. Forests were preserved when the mean browsing index was equal to or lower than 0.5. The cutting frequency was significant in determining overall floristic composition. We showed that shrublands and evergreen forests within the vegetation mosaic and the result of small-scale farming led to high native forest species richness. This makes the vegetation mosaic especially valuable in a landscape dominated by exotic tree monocultures.

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