Many grasslands are fire-driven grazing systems, but the potential to manipulate fire management to maintain or enhance provisioning services while also increasing other ecosystem services is only partially understood. Research has shown that mimicking the fire-grazing interaction with patch-burn-grazing (PBG) benefits biodiversity, enhances soil nitrogen, and can reduce invasive plants. However, little work has been done on how PBG affects ecosystem services in subtropical grasslands. The objective of this study was to determine how PBG affected forage production (ANPP) and plant diversity from subtropical grasslands. This is part of a larger study to examine how PBG affects greenhouse gas regulation and water use efficiency of subtropical grasslands.
A randomized block design experiment was established in 2017 with 16 pastures (16 ha each) in two different pasture-types (intensively-managed (IM) vs. semi-natural (SN)) at Archbold Biological Station’s Buck Island Ranch in FL, USA. In 2017, eight pastures were completely burned (“full-burned”: FB). The remaining eight pastures were partially burned (“patch burn grazing”: PBG); only one-third of the pasture was burned in 2017 (the other two-thirds will be burned in subsequent years). Statistical comparisons are between PBG pastures (average of burned and unburned sectors) and FB pastures, or within PBG comparing burned and unburned sectors.
Results/Conclusions
Plant species richness (SR) and diversity (H’) were greater (F (1,14) =10.07, p<0.007) in SN pastures (SR: 36.2±10, H’: 20±7.2) compared to IM pastures (SR: 21.2±8.9, H’:9.9±5.1) but did not differ among burn treatments (FB vs. PBG) the first year after fire treatments. Within PBG pastures, burned sectors had higher SR and H’ compared to unburned sectors, but only for SN pastures (Burned: SR=29±12, Unburned: SR=19.8±7.7; F(1,3)=16.2,p=0.03). ANPP did not differ among burn treatments, however, when comparing burned to unburned areas within PBG pastures, unburned plots had marginally significantly lower ANPP in both pasture types (F(1,10)=3.31, p=0.09). In both pasture-types, percent of live biomass was greater in FB pastures (F(1,6)=8.4, p=0.03).
In summary, in the first year after experimental burns, burning resulted in greater plant diversity in SN pastures and ANPP was higher in burned patches in both pastures types. The proportion of live biomass was greater in FB pastures due to a greater area burned and this likely influences the carbon sink strength of pastures. It is expected that as time-since-fire increases in FB pastures, structure and function of grasslands will diverge among FB and PBG treatments.