For example, as the area of Tilled land increased the areas of most other land cover types declined (Table 6).
The first axis explained 30.9% of the variation in land cover and represents a gradient from landscapes dominated by Tilled land (i.e., arable cropping) to landscapes with a more equitable mixture of land cover types including Suburban, Urban, Managed grassland, Uough grassland, Woodland and Open water cover types (Fig.
The second axis, explaining 25.6% of variation, represents a gradient from landscapes characterised by these land cover types, and Tilled land, to landscapes with larger areas of Woodland and Managed grass (Fig.
The principal landscape gradient identified in Berkshire, Buckinghamshire and Oxfordshire reflected changes in the area of Tilled Land (arable) relative to the areas of other land cover types.
However, the most likely explanation for the observed decline in numbers of orthopteran species with increasing areas of Tilled land is that arable cropping is both directly, and indirectly, detrimental to the persistence of species at a landscape level.
The interpretation of the data is complicated because while the area of Managed grassland was not directly correlated with species richness (Table 5) it was correlated positively with the major axis derived from PCA (Table 7), and negatively with the area of Tilled land (Table 6).
All species became more frequent as the percentage of tilled land decreased along the principal gradient (Table 2).
While some of this "free construction" is attributed to the grass barriers, which slow wind erosion and trap soil particles much like they trap drifting snow, the majority of the effect is caused by farming activity and the resulting change in the way water moves across the tilled land