PARENT SESSION
Oral Session #44: Disturbance ecology of forests: Animals, wind, gaps, edges. Presiding: S. Archer.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Hall of Ideas G.
Hurricane disturbance as an explanation for the unique structure of West Indian dry forest.
Van Bloem, Skip1 , Murphy, Peter1 , Lugo, Ariel2, 1 2
ABSTRACT- Dry forests of the West Indies have a short, shrubby physiognomy which differs from forests growing under similar climatic conditions in the mainland tropics. Many hypotheses attempt to explain these differences in forest structure, but our observations following Hurricane Georges point to hurricanes as an important factor. We measured stem damage and sprouting response of 2048 stems in Guánica Forest, Puerto Rico. Although 13% of stems were broken, tree mortality was less than 2%. Larger diameter stems were more likely to be broken than smaller stems and nearly half the broken stems resprouted within nine months. Surprisingly, sprouting occurred in over 32% of stems suffering only defoliation and in 29% of stems which appeared undamaged. The severity of defoliation did not appear to influence sprouting rates. The number of sprouts present on defoliated stems increased almost six-fold compared to pre-hurricane sprout rates. We suggest that severe shaking of a tree, even in the absence of stem breakage, elicits sprout growth which would explain the physiognomy of the West Indian dry forests. Disturbance by high winds can lead to a complex interaction of hormone growth regulators within trees that would regulate sprout growth and development. We conclude that hurricanes maintain dry forest structure in the West Indies directly by selectively damaging larger stems and indirectly through the induction of sprouting.
KEY WORDS: dry forest, hurricane, forest structure, sprouting