Nutrient dynamics of a Puerto Rican subtropical dry forest

The distribution of the nutrients N, P and K in soil and vegetation and their mobility through litterfall and decomposition in mature and successional stands of a subtropical dry forest were studied in Guánica, Puerto Rico. Soils of the Guánica forest have high total amounts of N (9100 kg/ha), P (1820 kg/ha), and K (7460 kg/ha). However, high extractable Ca (>4000 mg/g) and pH (> 7–8) may explain why only 1.3 and 25% of the total P and K, respectively, were extractable. Total ecosystem storage of N, P and K was 10,300, 1900 and 7700 kg/ha, respectively, of which vegetation stored only 10, 2 and 3%, respectively. Litterfall returned 26, 18 and 180% per year of the N, P and K stored in the ground litter compartment. Trees retranslocated about 30 and 65% of the N and P required to satisfy aboveground net primary production and immobilized P in dead roots. Slow leaf decomposition (7.3 yr for 95% decomposition) released K faster than mass, P as fast as mass, and ash and N slower than mass. The use efficiency of P by litterfall was high compared with other tropical forests, while that of N and K was similar to other tropical and temperate forests. Cutting and regrowth of vegetation resulted in differences in the nutrient concentration in litterfall and nutrient use efficiency of successional vegetation.