The structure and regeneration of floodplain forests in southwestern Ohio

Background/Question/Methods Ohio floodplain forests often occur as narrow bands of vegetation varying in composition and structure from surrounding upland forests. In addition to providing a unique habitat they ameliorate the impact of surrounding land uses on waterways and aquatic organisms. For both reasons they are becoming of increased interest to land managers for conservation and restoration. We are studying two aspects of these forests: 1) their current structure and composition and 2) the initial pattern of stand development. We are using two sets of studies. First, we examined 63 20x25 m plots in existing floodplain forests along streams in six county parks in Montgomery and Greene counties, Ohio. We counted all stems >1 m high. Second, we quantified seedlings present in two floodplain areas that were released from farming about 5 yr prior to sampling and that are being allowed to develop into forest. Seedling composition was compared to the composition of trees surrounding the field.

Results/Conclusions

1) We found for 2103 stems in existing floodplain forests that 30% of the stems were 1 m high to <1 cm dbh, 33% were dbh 1-10 cm, 21% were dbh 10-25cm, 13% were dbh 25-40 cm, and 4% had dbh >40 cm. Average basal area was 21.8 m2/ha. Absolute frequency was high for Acer negundo (87%), Ulmus americana (59%), and Celtis occidentalis (52%). Relative density was highest for Acer negundo (23%), Aesculus glabra (15%), and Celtis occidentalis (13%). However, relative basal area was highest for Populus deltoides (21%), Platanus occidentalis (19%), Celtis occidentalis (13%), and Acer negundo (13%). Species varied in their regeneration, with some species well represented by small stems and others not. 2) Regeneration of species varied with field, even though the fields were adjacent to each other. They were released two years apart, however, so might have been affected by different annual patterns of weather or seed production. Seedlings in one field were dominated by Acer negundo (93%) and Acer saccharinum (4%) with 3.0 seedlings/m2 while the other field was dominated by Acer negundo (42%) and Populus deltoides (27%) with 1.4 stems/m2. The absence of Populus deltoides in the first field is puzzling because it was present as edge trees (8 trees, 5% of total). Regeneration in the second field varied with location, one side having much more Populus deltoides than the other. Experiments are being planned to examine the reasons for that difference.