Original Article

Assemblage composition of ants (Hymenoptera: Formicidae) affected by tree diversity and density in native timber tree plantations on former tropical pasture

Riedel, J., Dorn, S. & Mody, K.

Abstract: Afforestation of degraded tropical pastures with native timber trees may enhance biological diversity and provide goods and services to local communities. We tested the hypothesis that afforestation schemes affect ant diversity differentially, depending on tree stand diversity. We quantified structure and composition of arboreal ant assemblages on the native timber tree Tabebuia rosea (Bignoniaceae) in experimental plantations on former pasture in Central America to assess the effects of (1) tree stand diversity in an afforestation system with T. rosea planted in a three species mixture or in monoculture and of (2) a combination of T. rosea with companion trees in a silvopastoral system, with T. rosea being surrounded by either Guazuma ulmifolia (Malvaceae) or Gliricidia sepium (Fabaceae). We sampled 22 and 28 ant species in the pasture afforestation and in the silvopastoral system, respectively, with Ectatomma ruidum (Roger, 1860), Camponotus lindigi Mayr, 1870, and Solenopsis geminata (Fabricius, 1804) being the dominant species. In the pasture afforestation system, the three species tree mixture surpassed the Tabebuia rosea monoculture in ant diversity, as expressed by species richness, Ice (incidence based estimator of species richness), and Simpson index. Branch sampling did not indicate any difference in ant density among the planting schemes, but activity at baits was significantly higher in the monoculture than in the mixture. In the silvopastoral system, companion trees supported ant diversity on the central T. rosea tree, as species richness and ant activity at baits were significantly higher on the central tree surrounded by companion trees than on solitary T. rosea trees. Furthermore, Ice of T. rosea trees accompanied by Gliricidia sepium was significantly higher than Ice of solitary trees. The highest species similarity was found for T. rosea trees surrounded by the different companion tree species, whereas ant assemblages of T. rosea trees in monoculture were most dissimilar to all other planting schemes. Our study demonstrates that while newly established plantations of native timber trees on former pasture might host moderately diverse ant assemblages, wellconceived diversification-afforestation schemes are promising for enhancement of ant diversity.