Maggengo meadow patches enclosed by forests in the Italian Alps: evidence of landscape legacy on plant diversity

The maggenghi are mid slope meadows typical of all the southern and of great parts of the northern European Alps, for centuries managed with traditional and low intensity techniques. Usually, they are scattered patches in surrounding forests. The spontaneous expansion of trees and shrubs, favored by the recent decline of mountain agriculture, lead the maggengo patches patterns and shapes to change. Our objective was to analyze the effect of this change on current plant diversity of the remnant patches, as the adaptive response could be slow and possibly related more to historical than to current landscape patterns. We analyzed the trend of the size, shape, elongation, fractal dimension and connectivity of maggengo patches of a Central-Eastern Italian Alpine district, in four time steps, from 1973 to 2006, and in 1859, when mountain agriculture was still widespread. Then, we studied the relationships between those landscape metrics and two current patch-level plant diversity measures: interior species richness and species density. Aerial photographs were used to investigate that trend, while a historical cadastral map was used to assess the landscape metrics in 1859. As expected, in the last 30 years, the total size of maggenghi has been reduced by 57% while their shapes have been progressively simplified. Interior species richness was positively related to size, both in 2006 and over the past 30 years, but not to any 1859 measures. Conversely, species density was positively correlated only with 1859 size, shape index and connectivity. We conclude that the historical shape, size and connectivity are some of the key variables affecting the plant species density of maggengo patches, but not of their interior plant species richness.