Seeds were collected from three red maple swamps (wet sites) and three uplands (dry sites) near Ithaca, New York, and the resulting seedlings were used in flood tolerance studies to investigate if red maple's broad habitat range is due to ecotypic differentiation. One-year-old seedlings were flooded while still dormant (spring flooding study) and net photosynthesis, growth and chlorophyll levels were measured at 1 mo intervals for 3 mo. Flooding reduced net photosynthesis, growth and chlorophyll levels in seedlings from both sites, but survival of both wet and dry site seedlings was near 100%. After 1 mo of flooding net photosynthesis of wet and dry site seedlings were similar, but after 3 mo, flooded wet site seedlings had higher photosynthetic rates than did dry site seedlings. Control wet site seedlings were significantly larger than dry site seedlings and had significantly higher photosynthetic rates and chlorophyll levels. These differences suggest either genetic variation between seedlings from the two habitats in response to the growing conditions or the influence of seed size differences and confound the spring flooding study results. Flooded wet site seedlings had higher, final, net photosynthetic rates than did dry site seedlings, but the response to flooding was greater for wet site seedlings than it was for dry site seedlings.

In a second study (summer flooding study), 1-y-old seedlings in full leaf were flooded for 22 d and then drained to determine if recovery from flooding stress differed for wet and dry site seedlings. Again, flooding decreased net photosynthesis for seedlings from both habitats but, when the trees were drained, net photosynthesis for wet site seedlings recovered more quickly and to a higher level than it did for dry site seedlings. Flooding also caused a drop in chlorophyll levels for seedlings from both habitats, but chlorophyll levels of seedlings from neither habitat recovered when the seedlings were drained. There were no significant differences between wet site and dry site control seedlings for net photosynthesis; therefore, the quicker and larger recovery of photosynthetic potential in wet site seedlings in the summer flooding study suggests that ecotypic differentiation has occurred and that genetic differences, in part, account for red maple's occurrence on contrasting edaphic sites.