抄録
The aggressive reproduction strategy of the naturalized shrub Piper aduncum L., introduced from humid Neotropical regions, was studied in Sumatra paying special attention to fruit production and leaf longevity. A single piper shrub produced inflorescences throughout the year and the annual production of a mature inflorescence was estimated at 7.8 ton ha-1 yr-1. It was also shown to consume 100 kg of nitrogen per hectare for annual fruit production on the basis of its crown projection area, while 60 % of nitrogen in leaves and branches was reabsorbed with senescence and death. Average leaf longevity was 158 ± 48 days with an average turnover rate of 2.5 ± 0.51 yr-1. This high turnover rate is considered advantageous for continuous fruit production from early growth stages through effective allocation and reabsorption of energy and nutrients. Next, a mathematical model for optimum leaf longevity was proposed taking into account the maintenance costs of a single branch. The model showed that the observed leaf longevity approximately satisfied the expected minimum maintenance cost of a mature branch. A short leaf life span could save stem and branch construction costs through effective leaf production with low biomass. Economical branch structures in terms of energy and nutrient use could allow allocation of more resources to fruit production. This prioritization of fruit production over construction of a durable stem and branches could be evaluated as an adaptive living strategy of this shrubby pioneer species. Based on the proposed model, the adaptive survival strategies of other species were discussed with special reference to the relationship between leaf longevity and branch structure.
