Ground-layer vegetation of cleared woodlands (pastures) has lower biodiversity and different invertebrate assemblages to remnant woodlands in grazed landscapes of eastern Australia

Abstract

Introduction: Clearing of woodlands is used by graziers to promote pasture production, even though understanding of impacts of clearing on native fauna is lacking. Aim/Methods: To evaluate impacts of clearing on biodiversity by comparing invertebrates associated with ground-layer vegetation in pastures to that of nearby uncleared woodlands. Two replicates of cleared woodlands (pastures) were compared with two woodlands at each of four locations. The adjacent riparian forest to each pasture and woodland site provided a geographic control, making four habitats. Invertebrates of ground-layer vegetation were sampled using three suction subsamples of 1m2 at each site. Results: Pastures had significantly lower order richness, herbivores, pollinators and macroinvertebrates (food for birds) than the woodlands, whereas the riparian forests closely resembled each other in all metrics. Invertebrate assemblages of pastures also differed from those of the woodlands, groundcover and leaf-litter correlating strongest with invertebrate composition. Discussion: Findings of this study contrasted with another in recently cleared woodlands where few differences were observed. Our study differed in the much longer period since clearing (> 20 years cf. 5 years) and the dominance by introduced grasses (> 40% cover in pastures cf. <15% in woodlands) rather than native grasses. Implications for insect conservation: Pastoralists have the capacity to improve outcomes for invertebrate biodiversity by maintaining groundcover above 80%, by encouraging native pastures over introduced species such as Buffel Grass and by retaining native woodlands. Biodiverse invertebrates benefit graziers by contributing to soil health, food webs that support pest control, pollination, herbivory of weeds and sustainable grass production.