Exotic nurse trees foster regeneration of native Podocarpus in a mountain forest of Ethiopia
2 Departement of Biology, Addis Abeba University
O 1.9 in Ecosystem Function
15.04.2010, 11:15-11:30, H13
It is a widespread view that plantations of exotic tree species in the tropics are harmful to the environment and hamper the regeneration of a native forest. It is claimed that fast growing exotic trees, once established in a plantation may exert higher competitive strength than indigenous trees, or may inhibit their regeneration by allelopathy. The contrary was observed in a semi-dry montane forest area of the Ethiopian Rift valley (the Munessa forest) where remnants of a degraded natural forest and plantations of exotic species grow side by side. Higher germination success and advanced growth of indigenous tree species under the canopy of a plantation of exotic species than under the natural canopy was noticed. This different “nurse-tree-effect” of native versus exotic canopy trees was examined. Experimental trees were Podocarpus falcatus (Pf) as indigenous canopy and sapling (1.5 m) species, and Pinus patula (Pp) and Eucalyptus saligna (Es) as exotic canopy trees. Parameters were the sub-canopy microclimate, relative growth rates (RGR), photosynthesis, and WUE of the saplings. RGR was slightly (Es), and 4-times (Pp) higher in the plantations than under Pf, WUE was highest in the Pinus plantation (3.8), high also natural forest (3.2), but relatively low (2.6) under Es. Differences in the microclimate of the 3 stands were small except the daily light sums and the light flecks. The better nurse tree effect of the exotics is attributed to a more favourable light climate.
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