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Active restoration of woody canopy dominants in degraded S outh A frican semi‐arid thicket is neither ecologically nor economically feasible
Author(s) -
Vyver Marius L.,
Cowling Richard M.,
Campbell Eileen E.,
Difford Mark
Publication year - 2012
Publication title -
applied vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.096
H-Index - 64
eISSN - 1654-109X
pISSN - 1402-2001
DOI - 10.1111/j.1654-109x.2011.01162.x
Subject(s) - canopy , sowing , shrub , monoculture , biology , thicket , arid , woody plant , agroforestry , agronomy , ecology , habitat
Question Will the planting of nursery‐propagated woody canopy species within severely degraded A rid S ubtropical T hicket once dominated by the succulent shrub P ortulacaria afra ( S pekboom) be an efficient restoration strategy to employ in addition to the current restoration protocol of planting a monoculture of P . afra truncheons? Location K rompoort, a farm located on the northern footslopes of the G root W interhoek mountains, near K irkwood, E astern C ape, S outh A frica. Methods We planted, in degraded, intact and three differently aged post‐restoration ( P . afra truncheons) sites, nursery‐propagated individuals of two woody canopy dominants ( P appea capensis and S earsia longispina ), and two inter‐canopy shrubs ( L ycium ferocissimum and R higozum obovatum ) in S ep 2008 (spring). The experiment was repeated again in M ay 2009 (autumn) and a succulent canopy species ( P . afra ) was added. We assessed restoration success in terms of the survival of planted individuals after 24 mo (spring planting) and 12 mo (autumn planting). The estimated cost of a restoration effort to establish two woody canopy dominant species with the large‐scale planting of P . afra was calculated and compared with that of the already established protocol of planting only P . afra truncheons. Results Survival after spring (24 mo) and autumn (12 mo) plantings of the two woody canopy species was less than 5% , whereas survival of L . ferocissimum was low (19%), R . obovatum good (70%) and P . afra excellent (100%). Contrary to expectations, survival was not related to a gradient of intactness encompassing degraded, restoration and intact treatments that are associated with increasing biomass and soil carbon. The costs of incorporating the four woody canopy species into the restoration programme's protocol were 2.4 times the costs of restoring with P . afra alone. Conclusions Planting propagules of canopy species other than P . afra is likely to render the programme economically unfeasible, depending on the price of carbon. We conclude that biodiversity goals for the restoration programme are better achieved via spontaneous recruitment of woody canopy and other species, even though this may take more than 40 yr post restoration.