The impact of forest disturbance on Taxodium distichum forests, between 1964 and 1995, on the Lower Mississippi River Alluvial Plain, USA

Background/Question/Methods

Taxodium distichum (L.) Rich. (baldcypress) forests on the Lower Mississippi River Alluvial Plain (LMRAP) have been threatened by habitat loss and cutting over the last 125 years.  Nearer the Gulf Coast, land subsidence and saltwater intrusion are also problematic.  To evaluate these impacts, we used USDA Forest Service, Forest Inventory and Analysis (FIA) data to track change on permanent plots from the 1960’s to the 1990’s on the LMRAP of Arkansas, Louisiana, and Mississippi.  These permanent sample plots were placed on a 4.8 X 4.8 km square grid.

Results/Conclusions

The results showed that there were 3,104,987 ha (C.I. ±43,780) of forests in this area in the 1960’s but by the 1970’s 627,060 ha had been cleared.  By the 1990’s an additional 375,300 ha had been cleared.  Out of 1,332 forest plots measured in the 1960’s, we identified 308 plots where baldcypress was one of the four dominant trees in the overstory.  In the 1960’s, basal area of these stands averaged 21.9 m² ha^-1 (± 0.64, 1 SEM), density averaged 382 trees ha^-1 (± 13, 1 SEM), and the quadratic mean stand diameter (QMD) was 28.9 cm (±0.44, 1 SEM).  Between the 1970’s and 1990’s conversion to agriculture and cutting accounted for the majority of the 26 percent of plots that no longer qualified as the baldcypress type.  In the 1990’s, basal area on the remaining 227 plots averaged 27.1 m² ha^-1 (± 0.80, 1 SEM), density averaged 383 trees ha^-1 (± 14, 1 SEM), and QMD averaged 31.3 cm (± 0.54, 1 SEM).  The small increase in both basal area and QMD, with little change in density, indicates that many of the surviving stands have, at least in part, escaped major disturbance.  However, the habitat loss and stand conversions (primarily from cutting) that have taken place over the last 30 years overshadow the positive changes seen in the surviving stands.