Contrasting patterns in pine forest ecosystems

Forests and woodlands dominated by pines (Pinus spp.) occur naturally over an unusually broad range of environmental conditions in the northern hemisphere and now they are widely planted south of the equator. Some pine species occur in savannas that are characterized by surface fires every 10 years or less, while others form dense forests that are burned at intervals of 100-300 years. Contrasting disturbance, temperature and precipitation regimes have led to great diversity in the morphological and physiological adaptations of the numerous pine species, but most appear to be tolerant of low nutrient availability. Plant uptake and microbial immobilization lead to an accumulation of nitrogen that is derived primarily from atmospheric deposition rather than nitrogen fixation, with the largest amount of nitrogen stored in the soil organic matter. Available data suggest that annual net primary productivity ranges from about 200-1800 g C m~, with a large portion of the photosynthate allocated annually to the production of fine roots. Following disturbances, more photosynthesis occurs in the understory and there is the potential for increased water outflow and nitrogen leaching until pre-disturbance levels of leaf area are restored.