Does grazing exclusion in Australia’s rangelands impact biomass and debris carbon stocks?

David Forrester; Jacqueline England; Ee Ling Ng; Melissa Piper; Ken Hodgkinson; Steven Bray; Stephen Roxburgh; Keryn Paul

Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

Does grazing exclusion in Australia’s rangelands impact biomass and debris carbon stocks?

David Forrester , Jacqueline England, Ee Ling Ng, Melissa Piper, Ken Hodgkinson, Steven Bray, Stephen Roxburgh, Keryn Paul

Abstract

Australia is dominated by 6 million km2 of rangelands that contribute significantly to the livestock industry and carbon (C) market, yet few studies have quantified the influence of grazing management on woody biomass and C stocks across these rangelands. Here we quantified stand-level C stocks (Mg C ha-1) in live aboveground biomass (AGB), live belowground biomass (BGB), standing dead mass, coarse woody debris (CWD) and litter of rangeland vegetation at 46 long-term (average 40 year) grazing trials comprising grazed control plots paired with exclosures protected from grazers. Four major woody vegetation types were considered: those dominated by Eucalyptus species, Acacia aneura, other Acacia species, and other species. Most C stocks (except litter-C) were highest in Eucalyptus dominated vegetation and lowest in the ‘other species’ types. There was high variability and few significant grazing effects on C stocks. There was a trend of higher AGB-C, BGB-C, woody basal area (m2 ha-1) and litter-C with grazing exclusion at sites with mean annual precipitation >300 mm, but the magnitude of increase was highly variable. The impact of the type of grazer was highly variable, though there was a trend of higher woody biomass C where rabbits and domestic livestock were excluded compared to exclusion of domestic livestock only. The relative effects of grazing declined as the woody basal area of grazed control plots increased. Our results show that although grazing exclusion can facilitate C stock accumulation in woody vegetation, it is difficult to predict when and where this may occur. To enable greater clarity, future studies may need to collect additional information, including data on soil water availability and current and historical grazing intensity.

RJ24028 Accepted 20 February 2025