Annual burning drives plant communities in remnant grassland ecological networks in an afforested landscape

Abstract

Landscape ecological networks (ENs) are used to mitigate the negative effects of commercial forestry plantations on the biodiversity of southern Afromontane grasslands. Annually-burned firebreaks are fundamental to plantation forestry management, as they protect timber compartments from runaway fires. Here, we investigated the effect of annual burning with different levels of domestic cattle grazing in ENs, and annual burning without domestic cattle grazing in the adjacent protected area (PA). Sampling was conducted on three firebreak types, as well as two natural control grasslands (in the EN and PA each). The first two types (PA firebreaks and peripheral EN firebreaks) were on either side of the PA/plantation fenceline. The third type, plantation EN firebreaks, had forestry compartments on two sides and heavy cattle grazing. Although plant species richness was not significantly affected, plant communities of annually-burned firebreaks differed compositionally from those in the reference grasslands in the EN and PA respectively. Furthermore, plant species turnover was lower in annually-burned firebreaks than in reference EN and PA grasslands. Comparisons among different annually-burned firebreak types showed no difference in plant species richness. However, species composition and turnover of plant communities in peripheral EN fenceline firebreaks were similar to those of PA fenceline firebreaks, but both differed from the plantation EN firebreaks. Plant communities of longer-rotation burned grassland in the EN and PA were similar in species richness, composition and turnover. Overall, these results indicate that annual burning of firebreaks leads to homogeneous plant communities but not necessarily a reduction in species richness. High levels of cattle grazing exacerbate the effect of annual burning, as in plantation EN firebreaks. We recommend that managers should control heavy cattle grazing in annually-burned areas to maintain the natural plant communities as much as possible, while at the same time protecting the plantation blocks from runaway fires through necessary annual burning of appropriate firebreaks.