Abstract:
Contrary to general belief, planted and naturalized stands of introduced species facilitate the recovery of natural
evergreen forests and their diversity. Forest rehabilitation actions are often performed at great cost: mature forest
species are planted, while species with adaptations to recover effectively and quickly after severe disturbance are
ignored; or stands are cleared of invasive alien species before native tree species are planted. By contrast, cost-effective
commercial plantation forestry systems generally use fast-growing pioneer tree species introduced from other natural
forest regions. Such planted tree stands often facilitate the recovery of shade-tolerant native forest species. This paper
provides a brief overview of disturbance-recovery processes at landscape level, and how pioneer stands of both native
and introduced tree species develop from monocultures to diverse mature forest communities. It uses one example of a
study of how natural forest species from small forest patches of 3 ha in total invaded a 90-ha stand of the invasive Black
wattle, Acacia mearnsii, over a distance of 3.1 ha at Swellendam near Cape Town, South Africa. The study recorded 329
forest species clusters across the wattle stand: more large clusters closer to and more smaller clusters further away from
natural forest patches. The 28 recorded forest species (of potentially 40 species in the surrounding forest patches)
included 79% tree and 21% shrub species. Colonizing forest species had mostly larger fleshy fruit and softer small seeds,
and were dispersed by mostly birds and primate species. Maturing forest trees within developing clusters in the wattle
stand became a source for forest regeneration away from the clusters, showing different expansion patterns. Four sets of
fenced-unfenced plots in the wattle stand showed the impact of browsing by livestock, antelope, rodents and insects on
the successful establishment of regenerating forest species, and the dramatic effect of excluding browsing. The results
support the approach to rather selectively manipulate than clear invader plant stands in the natural forest environment.
This approach invests in the natural succession process rather than planting. It protects developing seedlings against
browsing by stacking invader plant debris around them, rather than protecting them by means of costly fencing. This
forest recovery process through nurse stands of invasive species can be managed, with additional benefits: Indigenous
tree species provide for better streambank stability; and the practice provides for local job creation over a 10-year period
for harvesting poles and firewood from the manipulative conversion process.
