Mixed herbivore grazing on a lowland heath system: quantifying the collective impacts for conservation management

Abstract

Degradation of terrestrial habitats with high conservation value has resulted in strategic efforts to cease or reverse their declines. Broad habitat management can restore ecological processes and large herbivores can provide ecological function in some terrestrial systems. Following years of decline and fragmentation, owing to factors such as cessation of traditional practices, lowland heathland has become an internationally important habitat with strategic protection. Free-ranging grazing aims to assist in mitigating such losses to habitat and vegetation communities, but quantifying the grazing regime and its associated impacts is necessary to ensure protection of these vulnerable systems. Reviews of herbivore impacts on lowland heath provide detailed evaluations and recognise the absence of experimental assessments and baseline monitoring.

This research aimed to assess ecological activity and impacts (herbage removal, trampling and dunging) of horses and cattle on a lowland heath system to determine their influence on changing vegetation and to inform grazing management. This mixed regime is commonly adopted for restoration of semi-natural habitats but a failure to understand the separate vegetation impacts can be detrimental for the system as a whole.
Behavioural activity was quantified using scan-sampling assessing spatial and temporal variation in behaviour, habitat selection and niche overlap, spatial occupancy and diet. A factorial design was set up to quantify the impacts of herbage removal, trampling and dunging to vegetation separately. Assessments vegetation community composition and architecture in treatment and control areas were undertaken. Analyses incorporated non-parametric and general linear models.

Animals utilised their environments in different ways, varying for feeding and showed high habitat selectivity, based on physiology and foraging strategy primarily. Herbage removal strongly influenced vegetation architecture and heterogeneity owing to selection for graminoids and the plants’ competitive traits; effects on other plants were not as well defined due to minimal abundance. Trampling modified the vegetation structure due to reduced canopy density maintaining colonising gaps, but increased graminaceous cover and showed a capacity for lateral expansion. Dunging regime was highly influential for enhancing plant architecture and modified vegetation composition based on nutrient availability and competition. Worming regime was influential on architectural parameters and may be due to retarded dung degradation; further research is required.

The findings contributed knowledge to lowland heath grazing management, validating the use of mixed regimes at low densities, for generating vegetation heterogeneity, for the control of dominating plants and for understanding the impacts of different animal-management practices. Expanding the reach of this research to comparable systems is necessary to develop the knowledge of grazing-management impacts. The work addressed an absence of experimental evaluation on these systems and also illustrated the importance of separately quantifying the impacts of large herbivores.

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ORCID for P.E. Osborne: orcid.org/0000-0001-8919-5710

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