Ecological Consequences of Root Grafting in Tabonuco (Dacryodes excelsa) Trees in the Luquillo Experimental Forest, Puerto Rico

Ecological Consequences of Root Grafting in Tabonuco (Dacryodes excelsa) Trees in the Luquillo Experimental Forest, Puerto Rico
Khadga Basnet, F. N. Scatena, Gene E. Likens and Ariel E. Lugo
Vol. 25, No. 1 (Mar., 1993), pp. 28-35

Root grafting was commonly found in tabonuco (Dacryodes excelsa Vahl), a dominant tree species of tabonuco forest in the subtropical wet forest of Puerto Rico. Over 60 percent of all stems and basal area of tabonuco occurred in unions, clumps of trees interconnected by root grafts. Self and intraspecific grafting were extensive, while interspecific grafting was not common in tabonuco trees. Seedlings and saplings did not show any grafting, probably because of their size or age. Grafted trees were taller and had a smaller crown/DBH ratio. Hurricane damage was significantly higher in isolated individual tabonuco trees than those in unions. Weak relationships between diameter class, area, and size of union, and inter-tree distances and the sum of the trunk circumferences of the two nearest neighbors suggested that a noncompetitive force such as root grafting was more important than competitive forces in maintaining the unions of tabonuco, and thus the forest community. A conceptual model of the costs and gains of tabonuco in unions is presented.

Hurricane Hugo: damage to a tropical rain forest in Puerto Rico

Hurricane Hugo: Damage to a Tropical Rain Forest in Puerto Rico
Khadga Basnet, Gene E. Likens, F. N. Scatena and Ariel E. Lugo
Journal of Tropical Ecology
Vol. 8, No. 1 (Feb., 1992), pp. 47-55

Hurricane Hugo of September 1989 caused severe damage to the rain forest in the north-rust corner of Puerto Rico. We assessed the severity of damage distributed in space, species, and size-classes of trees in the Bisley Watersheds of the Luquillo Experimental Forest. We analyzed pie- and post-hurricane data for vegetation from transects established in 1987 and 1988. The severity of damage was significantly greater in valleys than on ridges and slopes. All the species except Dacryodes excelsa, Sloanea berteriana, and Guarea guidonia showed 100% severe damage. Large trees (> 70 cm DBH) were highly susceptible to hurricane damage, but there was no clear pattern in the small size-classes. D. excelsa (tabonuco) was the most resistant to damage by the hurricane. Tabonuco which has extensive root-grafts and root anchorage to bedrock and subsurficial rocks, apparently can survive frequent hurricanes and continue as a dominant species in this montane tropical rain forest. The high frequency of hurricanes, which can override other ecological and topographic factors, may largely determine the overall spatial pattern of species in this rain forest.
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