Fire, land use, and the long-term dynamics of a pitch pine woodland in coastal Maine, USA

Background Pitch pine is a globally rare tree species that occurs on xeric sites in the largely mesic landscape of eastern North America. Supporting a rich assemblage of rare species, pitch pine communities are undergoing succession to more mesophytic species in the absence of natural and anthropogenic disturbance. We examined the multi-millennial dynamics of pitch pine in relation to fire and land use across a local moisture gradient in southern coastal Maine, USA. Results Fossil pollen revealed that pitch pine has inhabited the study area for at least 9000 years. A positive correlation of pitch pine pollen with macroscopic charcoal (> 250 mu m) demonstrated the historical importance of fire for this species. Euro-American settlement profoundly altered the forest. The sediment record revealed a pulse of fire, settlement-associated weeds, and pitch pine establishment as intensive land use commenced, followed by a recent decline as forests regenerated after pasture abandonment and fire suppression. Tree age structures and current regeneration patterns revealed ongoing succession of pitch pine to more mesophytic species, such as red oak and red maple, except on the most xeric sites, where the species appears to be self-perpetuating. Conclusions The results support a conceptual model of varying pitch population dynamics across a xeric to mesic gradient. They also reveal current mesophication and contraction of pitch pine woodland, a pattern found across the species' range. If maintenance of large areas of pitch pine woodlands in the study area is an important management goal, then active management to reduce competing vegetation should be considered. If other goals, such as carbon sequestration or restoration of pre-colonial conditions, when pitch pine was apparently less abundant are paramount instead, then allowing natural succession to more mesic forest would make sense.