The maintenance of natural biodiversity and the production of mature pine sawtimber are two of the objectives of the management plan for longleaf pines (Pinus palustris) in the Apalachicola National Forest (ANF) in northern Florida. These management goals are constrained by the USFWS recovery plan for the red-cockaded woodpecker (Picoides borealis), which sets target limits for the size structure of stands and limits the removal of old trees. One issue that is not addressed in either the forest management plan or the red-cockaded woodpecker recovery plan is that, for such a system to be sustainable, stands of timber must have some balance among their age cohorts. For the last several decades, silvicultural treatments in this forest have consisted primarily of periodically thinning stands of mature timber to maintain a basal area of about 13 m²/ha. The 1999 management plan, which is currently in effect, calls for some shelterwood cuts and some uneven-aged management. The issues here are whether these modifications will be sufficient to sustain the full biodiversity of the forest and whether the maximal production of sawtimber will be compromised.

Results/Conclusions

Upon examining the size structure of a random sample of longleaf pine sawtimber stands in the ANF and determining the age structure of trees in 4 selected stands, we found that size and age structure exhibited bimodality, a phenomenon probably caused by past harvests when small and medium sized trees were removed. Using a sample of 222 increment cores taken from 17 stands, we show that the prediction of diameter at breast height from age at the time of coring has a sigmoidal pattern which shifts by site and presumably past management. Although competition theory predicts that the growth rate of a tree should increase after thinning, and open grown trees clearly have the highest rates of areal increment inside bark, the growth of individual trees is often negatively effected by thinning. Even if past harvest does not involve high grading, inadvertent selection of the fastest growing trees in small and medium size classes in a multi-aged stand means that over time, periodically harvested stands are left with slow growing genotypes. The objective of management should be to promote the development of balanced multi-aged stands of sawtimber with enough prescribed burning to maintain biodiversity and natural regeneration.