The impact of browsing-induced degradation on the reproduction of subtropical thicket canopy shrubs and trees

Sigwela A.M. ; Kerley G.I.H. ; Mills A.J. ; Cowling R.M. (2009)


The regeneration dynamics of South African subtropical thicket are poorly understood. This lack of knowledge hampers the development of appropriate restoration protocols in degraded landscapes. To address this we compared the magnitude of seed production and the frequency seedlings of canopy species in intact and browsing-degraded forms of Portulacaria afra-dominated thicket. Severe browsing had a negative impact on sexual reproduction of canopy species. Seed production for all species was lower in the degraded than the intact states of both vegetation types. In the case of seedlings, almost all individuals were associated with beneath-canopy microsites, irrespective of degradation status. Exceptions were P. afra, Putterlickia pyracantha and Grewia robusta. Of the 511 seedlings that we observed, 480 (94%) were found in the beneath-canopy microsite and 31 (6%) in the open. In both intact and degraded sites, there were significantly fewer seedlings (all species combined) in open microsites than would be expected on the basis of the aerial extent of this microsite. The results show firstly that preservation of remnant clumps of closed-canopy thicket in degraded landscapes is of paramount importance for restoration, and that for recruitment of a wide range of canopy species to occur outside of these remnant clumps, it is essential to restore closed-canopy conditions as speedily as possible. © 2008 Elsevier B.V. All rights reserved.

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