Assessing the impacts of agricultural intensification on biodiversity: a British perspective

Abstract

Agricultural intensification is best considered as the level of human appropriation of terrestrial net primary production. The global value is set to increase from 30%, increasing pressures on biodiversity. The pressures can be classified in terms of spatial scale, i.e. land cover, landscape management and crop management. Different lowland agricultural landscapes in Great Britain show differences among these pressures when habitat diversity and nutrient surplus are used as indicators. Eutrophication of plants was correlated to N surplus, and species richness of plants correlated with broad habitat diversity. Bird species diversity only correlated with habitat diversity when the diversity of different agricultural habitats was taken into account. The pressures of agricultural change may be reduced by minimizing loss of large habitats, minimizing permanent loss of agricultural land, maintaining habitat diversity in agricultural landscapes in order to provide ecosystem services, and minimizing pollution from nutrients and pesticides from the crops themselves. While these pressures could potentially be quantified using an internationally consistent set of indicators, their impacts would need to be assessed using a much larger number of locally applicable biodiversity indicators.

Figure 1

A conceptual model of how agricultural systems can be described according to three dimensions of agricultural intensification, of large-scale land use, of landscape structure and diversity, and the management of crops and livestock at the field scale. It is possible to place any agricultural system within these dimensions for both the pressures on biodiversity and, separately, for the biodiversity states themselves, by using indicators for each dimension. These might include, for pressures, loss of natural habitat to agriculture, losses of landscape diversity and increases in fertilizers and pesticides. For biodiversity states, potential indicators might include populations of species associated with natural habitats, species diversity in agricultural habitats and the trait composition of within-field plant populations. See text for details.

Figure 2

The six environmental zones of GB. These group lands on the basis of climate, topography and geology (Firbank et al. 2003b). In this paper, we only consider the agricultural lowlands of England, Wales and Scotland, i.e. zones 1, 2 and 4.

Figure 3

Relationships between indicators of landscape diversity—(a,c) the Shannon diversity index of broad habitats only and (b,d) the Shannon diversity of broad habitats, subdividing agricultural broad habitats into main land cover types—and biodiversity ((a,b) species richness of plants on sample plots located in fields and unenclosed land, (c,d) species richness of breeding birds as sampled within transects) for the three environmental zones of lowland GB (black circles, zone 1; open diamonds, zone 2; and crosses, zone 4), as recorded within sample 1 km squares.

Figure 4

Relationships between indicators of intensity of crop management and nutrient inputs (a) N surplus and (b) atmospheric N deposition against Ellenberg N, meaned across all sample plots within the 1 km square for the three environmental zones of lowland GB (black circles, zone 1; open diamonds, zone 2; and crosses, zone 4).

Figure 5

Characterizing 1 km squares of lowland GB in terms of landscape structure (as indicated by the Shannon diversity of broad habitats) and crop management intensity (as indicated by N surplus; black circles, zone 1; open diamonds, zone 2; and crosses, zone 4).

Figure 6

Characterizing 1 km squares of lowland GB in terms of biodiversity indicators of landscape structure. (a) Plant species richness per 1 km square and (b) species richness of breeding birds per 1 km square and crop management (mean Ellenberg N score; black circles, zone 1; open diamonds, zone 2; and crosses, zone 4).