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

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 90 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 (...)