Thermal properties and fauna on the bark of trees in two different African ecosystems

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Abstract
The thermal properties of 26 African tree species in two different ecosystems were studied using thermocouples. In a subtropical moist forest were three bark types of trees: species with thin and smooth bark types with low values of insulation across the bark; species with a more structured bark type and medium insulation values; and species with deep-fissured or scaly bark types and high insulation values. Only these latter trees are able to survive openings in the subtropical forest and stand alone on edges of forest gaps. In the savanna all tree species showed adaptations in the structure of their bark in different forms: many tree species shade their trunks. Some have low bark insulation and these are known to be sensitive to fires. Some tree species show high bark insulation and do not shade their trunks. Tree species with white bark avoid overheating of their surface by reflection of the radiation. The arthropod community living exclusively on the bark was investigated for the first time on South African trees, on ten tree species. In the two different ecosystems this habitat is occupied by different arthropod groups. In the subtropical forest Acari, Araneae, Opiliones, Isopoda, Myriopoda, Blattodea, Psocoptera, Heteroptera, Coleoptera, Formicidae, and Nematocera (Diptera) are the main arthropod groups living exclusively on the bark of trees. In the savanna Pseudoscorpiones, Araneae, Collembola, Blattodea, Psocoptera, Coleoptera, Neuroptera, Termites, Formicidae, Hymenoptera and Brachycera (Diptera) are the main arthropod groups living exclusively on the bark of trees. Within one ecosystem on one bark type the dominant species are similar; richly structured bark types have a richer fauna. In the forest, bark arthropod diversity is related to the bark structure of the constituent trees, and the arthropod communities on the bark would reflect changes in the structure of the forest. Forests comprising tree species with different bark types would have a richer total bark arthropod fauna. Specialists on richly structured bark types would die out if tree species composition were altered by man to give stands consisting only of tree species with smooth bark types. Bark arthropods in a subtropical moist forest have different proportions of herbivorous and fungivorous compared to carnivorous species than those on the bark of trees in a savanna.