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Acer rubrum growth form changes in a subsiding coastal forest.
BATTAGLIA, LORETTA1, DENSLOW, JULIE2, 1 2
ABSTRACT- Subsidence and sea level rise are shifting hydrologic regimes in coastal forests fringing the Gulf of Mexico. Increased freshwater flooding in these deltaic systems eventually leads to regeneration failure of forest species and encroachment of marsh vegetation. Ability of some species to persist and vegetatively reproduce despite regeneration failure can delay transition to marsh. The role of vegetative reproduction in population dynamics of persistent species has received little attention. One example is Acer rubrum. There is evidence of sprouting in this species, particularly in frequently flooded areas. We examined the size class distribution, mortality, and sprouting patterns of A. rubrum in a five hectare plot spanning 1.3 meters in elevation in a coastal bottomland hardwood forest. All stems ≥ 2.5 cm dbh were mapped and measured in 1998; stem mortality was recorded in 2000. Sprouts per clump increased as elevation decreased. Larger trees and ones in the wetter end of the plot were more likely to be part of a clump. Mortality was highest in trees ≤ 10 cm dbh and in more flooded areas. Stem mortality, which ranged from 7 to 9%, did not differ significantly over clump sizes. There was no mortality of clumps with more than two stems. Low seedling recruitment, disproportionately high mortality of small saplings, and increased sprouting and persistence of large clumps indicate the possibility of regeneration failure and transition to vegetation reproduction.
KEY WORDS: wetland, subsidence, sprouting, flooding