Mini-Cockchafers reveal threatening fragmentation of South African Forests

The remains of South Africa’s indigenous forests hold a valuable and unique wildlife, fostered by long-term climatic stability and complex patterns of local climates. Researchers of the Zoological Research Museum Alexander Koenig – Leibniz-Institute for Biodiversity of animals (ZFMK, Bonn, Germany) now investigated their still debated natural extend at hand of forest-associated chafers. Models of the beetle’s potential distribution were calculated using data on their preferred climate and occurrence. In combination with genetic data, they indicated a threatening break-down of habitat connectivity which could be the case also for other forest species.

Logging of a timber plantation, now “biological deserts” and no replacement habitats for forest species.
Copyright: D. Ahrens, ZFMK, Bonn

However, the analyses also revealed areas that connect or that might connect today’s beetle populations most effectively. These areas should thus be considered for high priority conservation.

Indigenous forests rare

Natural indigenous forests are rarely found in South Africa. They only cover 0.6% of the countries area and only survived in protected gorges and on mountain slopes. Among others, this is due to fires which are utilised to retain farmland but also to preserve the likewise ecologically valuable grassland and the typical South African fynbos (“fine bush”) vegetation.

Despite their small extent these forests hold a rich flora and fauna, constituted of species that only occur there. This is also attributed to southern African climate which was relatively stable over long evolutionary time scales compared to other regions in the world. Also, a complex variety of small-scale local climates facilitated today’s biological diversity. Since this is true for forests as well as for other vegetation forms, there are ongoing debates on the natural extent of the threatened South African forest remains.

A study about forest-associated mini-cockchafers that was recently published by researchers at the Zoological Research Museum A. Koenig in the scientific journal Global Change Biology, now suggests a larger potential natural extent of indigenous forest than currently believed. Because beetles of the genus Pleophylla exclusively occur in forests and their larvae and adults are not restricted to specific plant species, their occurrence can be assumed representative for the forests distribution. Models based on currently known occurrences of the beetles and suitable climate showed that a much wider extent of forests would be possible and thus support previous similar findings of other researchers.

Forest size fluctuation natural

Projecting the models back to past climate revealed that South African forests naturally increased and decreased several times since the last glacial. Under certain conditions these fluctuations could even help to explain the enormous species richness found in South Africa, which might in some cases be the result of repeated isolation of populations.

High degree of fragmentation

However, the current minimum of forest cover is threatening, because human activities like fire and forestry impede the forest’s natural expansion. The high degree of fragmentation pushes many species to their maximum dispersal capacity, so that there are already isolated populations. This is confirmed by climate-model-based connectivity analyses as well as genetic data of the investigated beetles. Further diminution of forests or the eradication of stepping stone populations might thus lead to genetic impoverishment or extinction of many populations. The insights of the researchers from Bonn can be seen as a first step to a sustainable conservation of the threatened South African forest fauna in accordance with other valuable land forms, since they show concrete corridors that are well suited for efficient afforestation and high priority conservation of forest patches.

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