Indigenous forests do not operate in isolation and are teeming with life, including insects that have colonised almost every space. But accessing forest canopies and studying insect biodiversity is not easy – data in this field remains scant.
Researchers from the University of Stellenbosch are trying to narrow the knowledge gap in South Africa’s indigenous forests.
Just before sunrise, they release a column of fog into tree. As the fog slowly rises in the morning air and envelops the tree, large sails underneath the tree capture insects and spiders displaced by the fog.
“Data suggests estimates of the arthropod diversity at more than 3 000 species in the forest canopy,” says Rudi Swart, PhD candidate in Conservation Ecology at the University of Stellenbosch. “This is probably an underestimation as we include only eight species of tree in a forest complex with approximately 470 plant species.”
These include assegai (Curtisia dentata), real yellowwood (Podocarpus latifolius), ironwood (Olea capensis macrocarpa), Cape beech (Rapanea melanophloeos), hard pear (Olinia ventosa), red alder (Cunonia capensis), white alder (Platylophus trifoliatus) and candlewood (Pterocelastrus tricuspidatus).
The study took place at five nature reserves and forests within Afromontane forest regions, namely Oubos in the Riviersonderend Mountains, Grootvadersbosch near Heidelberg, Kleinbos near Friemersheim, Woodville near Sedgefield and Witelsbos near Storms River.
Data indicates the assegai tree has the biggest species diversity, with more than 600 arthropod species found in its canopies.
While Swart’s research is ongoing, there have already been some interesting results. Despite similar dominant tree species found in all the different study areas, each forest hosts species unique to its locality.
“Oubos has the most unique community of insects,” he says. “It is the furthest west and isolated from the other forests by a gap between the Langeberge and Riviersonderend Mountains.”
Swart says there is an excessive number of insect species shared among the patches, even though these forests are not connected. “This fits with the understanding that these forests were once connected.” Swart also noticed that certain insect species prefer certain trees. “Should one tree species be lost from a forest, it will be to the detriment of many host-specific insect species,” he says.
Written by René de Klerk
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