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Ben Thornes

Change in calcareous grasslands of Dorset

Tuesday 15th July 2014

The changing structure, composition and dynamics of Dorset’s calcareous grassland metacommunity over a 70-year interval.

Dorset’s calcareous grasslands are communities of high conservation value, and are often characterised by high plant species richness. These grasslands in general have experienced a major decline in area throughout Europe, principally from agricultural intensification. Although they have been the focus of extensive previous research, few attempts have been made to examine the long-term dynamics of multiple communities at the landscape scale.

To assess the long-term change in the structure and composition of Calcareous grassland metacommunities in Dorset, 88 extant sites first surveyed by Ronald Good in the 1930’s were resurveyed in 2009. The values of ??-, ?- and ??-diversity were compared between the two surveys, using a one-way analysis of similarity (ANOSIM) and non-metric multidimensional scaling. Elements of metacommunity structure (EMS) analysis were used to identify metacommunity structure, and changes in metacommunity composition were related to plant traits.

The subsequent analysis indicated that ??-diversity had increased over time, with the mean (�SD) species richness per site increasing from 29.31 � 7.65 in the 1930s to 40.18 � 16.41 in 2009. No change in ?-diversity was recorded. However, ??-diversity did increase, the total number of species rose from 219 in the 1930s to 280 in 2009. Results show that species composition has shifted over time; this is associated with a decline in ‘stress-tolerant’ species typical of species-rich calcareous grasslands, and an increase in species typical of mesotrophic grasslands. This shift has been associated with an increase in the mean Ellenberg N value, which would suggest that eutrophication has been a driver of floristic change.

Elements of the metacommunity structure analysis indicated that the structure of this grassland plant metacommunity was Clementsian at both survey times, which would indicate species sorting. The metacommunity structure was stable over time, despite changes in ??- and ??-diversity. Analysis of potential structuring mechanisms revealed the significant influence of elevation.

This investigation provides a rare example of an insight into the long-term dynamics of a plant metacommunity. The results indicate that substantial change has occurred in the composition of calcareous grasslands during this time, both at local and regional scales. The investigation provides evidence of the impact of environmental change on immigration and extinction processes operating in calcareous grasslands at different scales, and highlights the challenges evident for their future conservation.

Read the full article here.

Find out more about Professor Adrian Newton here.

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