Ground-dwelling arthropod assemblages of partially improved heathlands according to the species of grazer and grazing regime

Rocío Rosa García,Rafael Celaya,Urcesino García,Koldo Osoro

doi:10.14411/eje.2011.014

Abstract

The creation of improved areas is one way of increasing the productivity of livestock on Cantabrian heathland (NW Spain), a habitat that is frequently located in less favourable mountainous areas where the development of sustainable husbandry is limited. The effect of this on the biodiversity of heathland is unclear and likely to depend on several factors, such as the grazing regime. In order to clarify this situation, the effects of type of vegetation, species of grazer and grazing regime on the composition of the ground-dwelling arthropod fauna of partially improved heathland were determined. The effects of grazing by cattle or sheep and two grazing regimes (cattle or sheep, or both of them together with goats) were studied in eight plots (two replicates per treatment). Each plot included two types of vegetation, gorse (Ulex gallii)-dominated shrubland and improved grassland (Lolium perenne-Trifolium repens). Arthropods were surveyed using pitfall traps. Overall, the composition of the arthropod fauna did not differ between plots grazed by different species of grazer or using different grazing regimes but was significantly associated with the type of vegetation. Most of the opilionids and several carabids clearly preferred shrubland, while lycosids and various carabids were mainly associated with grassland. While the species of grazer affected the faunal composition of grassland, grazing regime was more important in shrubland. Arthropod responses to the grazing treatments were determined by the grazing behaviour of the large herbivores and the habitat requirements of each arthropod taxon. The great structural heterogeneity of the vegetation and the more microhabitats in shrubland grazed by mixed flocks was mainly a result of the goats preferring to browse on the woody vegetation in these areas. The grazing by either sheep or cattle had less of an affect on the fauna of shrubland than grassland.

Highlights

Rural Europe is characterized by a great diversity of cultural landscapes of high nature-conservation value, shaped by traditional land-use systems (Bignal, 1998; Ostermann, 1998), which support high levels of biodiversity
The SIMPER analysis indicated that the main differences in the composition in the fauna caught in the different types of vegetation were attributed to a set of species that were more abundant in gorse-dominated shrubland, such as the harvestmen Nemastoma hankiewiczii (Kulczynski, 1909) (11.8%), Homalenotus quadridentatus (Cuvier, 1795) (8.8%), Sabacon franzi Roewer, 1953 (8.5%) and Odiellus spinosus (Bosc, 1792) (6.4%), the ground beetles Carabus macrocephalus Dejean, 1826 (6.7%) and Steropus gallega (Fairmaire, 1859) (5.4%), and the wolf spider Pardosa nigriceps (Thorell, 1856) (6.6%)
Certain species seemed to be associated with either sheep or cattle, most of the fauna was not associated with a particular species of grazer in shrubland, whereas clear associations with cattle [e.g. Pardosa monticola (Clerck, 1758) and Calathus spp.] or sheep grazed sites [e.g. P. pullata and Trochosa terricola (Thorell, 1856)] were recorded in grassland (Fig. 2)

Summary

Introduction

Rural Europe is characterized by a great diversity of cultural landscapes of high nature-conservation value, shaped by traditional land-use systems (Bignal, 1998; Ostermann, 1998), which support high levels of biodiversity. Cantabrian heathland cover a wide area in the northern Iberian Peninsula, accounting for 21% of the area of Asturias (Álvarez et al, 2004) and are frequently less-favoured areas traditionally used to graze livestock. The sustainability of such systems is constrained by the low nutritive value of the woody vegetation of heathland (Osoro et al, 2007) the partial transformation of heathland into improved pasture is one way of improving the socio-economic situation in these areas (Sineiro et al, 1984). Information on the cascading effects on the local fauna is clearly lacking, even though it is known that the transformation of native systems into pasture or cropping land may result in considerable changes in the arthropod communities (Decaens et al, 2004), which might differ depending on the species of grazer (Dennis et al, 1997; Rosa García et al, 2010) or grazing regime (Dennis, 2003; Dennis et al, 2008)

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