A mesoscale analysis of floristic patterns in the south-west Finnish Archipelago

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Abstract:

Abstract Aim

To identify the ecological gradients based on the flora on a mesoscale in an archipelago. To interpret the results of the ordination and the classification of a grid cell-based botanical data set, with several environmental and geographical attributes. To compare the mesoscale distribution patterns of vascular plants with patterns previously observed on an island scale, and to develop a floristic zonation of the study area. Location

The south-west Finnish Archipelago. Methods

Vascular plant species-lists from over 1500 localities were assigned to 5 × 5 km grid cells. The grid cell-based floristic data were subjected to both unconstrained [detrended correspondence analysis (DCA)] and constrained [detrended canonical correspondence analysis (DCCA)] gradient analyses. The results of DCA were interpreted with calculated weighted averages of Ellenberg's indicator values for vascular plants, the number of occurring taxa and indices for the strength of human influence and the occurrence of limestone. The results of DCCA were interpreted with geographical attributes of the grid cells and the occurrence of limestone. The grid cells were clustered using two-way indicator species analysis (twinspan). Results

Both the unconstrained and the constrained ordinations gave consistent and interpretable results. The main ecological gradient runs from the grid cells containing species-rich islands with high human impact to grid cells containing species-poor islands with low human impact. This gradient also represents the continuum from areas with large islands near the mainland, to the outermost areas at the edge of the open sea. The secondary gradient was shown to be a gradient of soil reaction.twinspangave a clustering primarily based on the location of the grid cells on an inner–outer archipelago gradient, but the occurrence of limestone also influenced the classification. The archipelago was divided into five non-homogeneous areas based on thetwinspanclusters. The detected gradients correspond well with the gradients detected in a similar island-level analysis. Main conclusions

The two major ecological gradients in the study area seem to be robust, which is indicated by the similar results obtained both on an island and on a mesoscale. A shift from local and regional processes to broader geographical gradients probably starts to occur at the applied scale. The distribution patterns are strongly affected by the inner–outer archipelago gradient and the occurrence of limestone.

Keywords: Archipelago; clustering; ecological gradients; mesoscale; ordination; vascular plants

Document Type: Research Article

DOI: http://dx.doi.org/10.1046/j.1365-2699.2003.00884.x

Affiliations: Section of Ecology, Department of Biology, University of Turku, Turku, Finland and

Publication date: July 1, 2003

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