Effects of Adult Tree Density and Fire on the Demography of Pregrass Stage Juvenile Longleaf Pine (Pinus Palustris Mill.)

Abstract

I Survival, growth (as measured by basal diameter) and density of a cohort ofjuvenile longleaf pines (> 1 year old, with secondary needles) were measured over a 4-year period to determine if density of adult conspecifics affects the demography and distribution of pregrass stage juveniles and if density of adults influences the effect of fire on juveniles. The pattern of mast years resulted in no competing juveniles less than 9 years of age. 2 Approximately 3000 juveniles were measured from 336 study plots placed in areas of low and high adult tree densities. Needle density was measured in each study plot prior to a prescribed burn conducted during the second year. Maximum fire temperatures were measured using temperature sensitive tablets. 3 Relationships among variables were quantified using path analysis. Path models were developed for independent and dependent variables before and after fire. 4 Survival, size and spatial distributions of pregrass stage longleaf pines were strongly affected by adult density, both in the absence and presence of fire. Juveniles in areas of low adult density were larger, and survival was higher. Aggregation of juveniles in areas of low adult densities was evident as early as the first year of growth and in the absence of fire. 5 Needle densities also affected juveniles in the absence of fire. Juveniles in areas of low needle litter accumulations were larger and had higher survival. Areas of low needle accumulations occurred in areas of low adult densities. 6 Fire markedly affected survival of juvenile longleaf pines. Only 21% of the initial cohort were alive one month after fire. Higher survival occurred in areas of low adult density, where juveniles were larger and needle density and fire temperatures were lower. Fire temperature was strongly related to needle density; hotter fire temperatures occurred in areas of greater needle density. Aggregation of juveniles was intensified after fire with higher densities of juveniles found in areas of low density of adults.