The Eastern Cape harbours 46% of South Africa’s limited remaining natural forest cover, including many of the country’s most threatened forest types, and forms part of the Maputaland-Pondoland-Albany Hotspot for biodiversity.
In a study published in the journal Forest Ecology and Management last week, PhD student Jessica Leaver and fellow researchers investigated the impact of timber, pole and bark harvesting on bird diversity in five Eastern Cape forests: Mqaba, Manubi, Ntlaboya, Gomo and Pirie.
They focused on the number of ecological roles filled by birds within the forests, of which there were 64 bird species.
The study showed insect-eating birds such as the Southern black flycatcher, the Blue-mantled crested flycatcher, and the African dusky flycatcher could be negatively affected, as more sunlight penetrated the canopy due to more trees dying and there could be fewer insects on the forest floor.
Three species of seed-eaters, the Forest canary, the Green twinspot and the Lemon dove, were also negatively affected by bark harvesting.
Again the study showed more sunlight penetrating the canopy cover led to more foliage plants and less grass on the forest floor, thereby reducing the availability of seeds.
Pole harvesting, i.e. the selective removal of sub-canopy trees, also negatively affected forest specialist species, such as the Dark-backed weaver, the Grey cuckooshrike, the Olive bushshrike, the Yellow-streaked greenbul and the Yellow-throated woodland warbler - forest birds which are mostly found in the tree canopy.
Conversely, generalist species such as the Cape white-eye and the Black-headed oriole were found to be positively affected by pole harvesting.
Generalist species were more easily able to take advantage of habitat changes.
Professor Michael Cherry, a behavioural ecologist from the Department of Botany and Zoology at Stellenbosch University and co-author, said the persistence of bird diversity was critical for the functioning and regeneration of these forest systems, some of them at least five million years old.
“It now seems likely that habitat degradation arising from informal harvesting is negatively affecting the number of ecological roles filled by forest birds in this region, and contributing to their decline,” Cherry said.