Serotiny, Geography, and Fire in the Pine Barrens of New Jersey

Givnish, T.

This report analyzes the relation between seronity and fire frequency in upland forests of the central New Jersey Pine Barrens by constructing inferred fire frequency from an ordination of 168 vegetation samples and 14 tree species. Evidence from 274 vegetation samples of pitch pine in the central Pine Barrens of New Jersey suggests that local fire frequency plays a predominant role in setting local levels of serotiny, contrary to an earlier suggestion by Ledig and Fryer (1972). Data from transect studies show that gene flow from the Pine Plains, an area of fireswept pygmy forests with a high incidence of serotiny, is not important in setting the frequency of serotiny in other Barrens areas more than 3-5 km away. Significant differentiation occurs between frequently burnt upland sites and rarely burnt lowland sites less than 100 m apart. I analyze the relation between serotiny and fire frequency in upland forests by constructing an index of inferred fire frequency from an ordination of 168 vegetation samples and 14 tree species. Serotiny correlates in a highly significant manner with the inferred fire frequency. After using this relation to remove the effects of differential fire history across sites at various distances from the Plains, I found gene flow to have a significant effect on the frequency of serotiny only within 2.5-3.0 km of the Plains. These data are related to a model that predicts fire frequency should increase from the edge to the center of the Pine Barrens, based on the premise that the sands underlying the Barrens are the ultimate cause of frequent fires there. This model is validated by an analysis of the geographic distribution of oak- and pinedominated forests in the Pine Barrens, using the fact that arborescent oaks are less fire-tolerant than pitch pine. As expected, the inferred frequency of fires is greatest in the broadest gap between the firebreaks caused by large rivers and swamps in the Barrens. The Pine Plains occur in the largest area free of major barriers to fire. The rarity of serotiny on the northern Coastal Plain and in the hybrid zone between pitch pine and pond pine may also result from physiographic constraints on fire frequency, and appears to be a consequence of the low incidence of fires expected near the geographic limits of Coastal Plain soils.

Serotiny, Geography, and Fire in the Pine Barrens of New Jersey

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