In Sarawak, Malaysia, logging is conducted with a 25-year harvesting cycle; however, it remains largely unclear if this cycle length is sufficient for forest recovery. This study aims to investigate how the structure of logged forests recovered along the periods after logging. We conducted this study in the Anap-Muput Forest Management Unit (AMFMU), Sarawak. We first established permanent sample plots with different logging history; that is, from 5 years to more than 37 years after the most recent logging. Using the various sample plots, we assessed the stem density, basal area (BA), proportion of dipterocarps, growth and mortality. To compare the forest structure of the logged over forests with that of primary forests, we used our previous data of a primary forest in Batang Ai National Park. We found significant differences in the stem density, total BA, and the proportion of dipterocarp among the plots. Generally, the stem density and total BA increased with the period after logging and decreased with diameter at breast height (DBH) size classes, except of tree of ≥60 cm DBH in several plots. The growth rates and mortalities were higher in more recent logged forests. These results indicated that logged forest was recovering with periods after logging partly because of higher growth rate; however, even in a forest of 37 years after logging, the forest structure was not fully recovered compared to the primary forest. Thus, we concluded that a 25-year harvesting cycle in the selective logging system would not be sufficient for the AMFMU forest to recover. We further need other effective strategies with systematic monitoring.

Revealing the size-dependency of traits (physiological and morphological properties) not only provides insights into species’ life history strategies but also contributes to the accurate prediction of changes in tree- and forest-level growth and responses to environments. We investigated the size-dependency of 18 leaf, wood, and bark traits related to resource use strategies and wood quality, using twenty 23-year-old Falcataria falcata trees with variable sizes (14.6−53.0 cm and 9.4−21.9 m in diameter at breast height [DBH] and height, respectively) in Okinawa, Japan. The radial variation in the wood density from the pith was also investigated. No leaf traits were correlated with DBH and height, whereas several wood and bark traits changed significantly with size. Larger trees produced dense wood with high water content and thick inner and outer bark, possibly reflecting the greater mechanical loads at the stem and greater translocation of carbon from the larger canopy. The radial gradients in wood density were steeper for small-sized trees, suggesting that age partially controlled xylem formation. We also found that fast growth did not compromise stem stiffness. Our results reveal the size-dependency differ between leaf and stem traits, possibly reflecting their different functional requirements. The size-related changes in traits observed here will be utilized for model parameterizations to predict changes in growth, carbon stocks, responses to environments, and wood quality in F. falcata plantations during the stand development.

There is a widespread belief that organic matter decomposition in phosphorus (P)-poor tropical forests is limited by P shortage and stimulated by exogenous P addition. An incubation experiment was performed to test the effect of P addition on decomposition of litter layers taken from two tropical tree plantations. The result was compared with our earlier soil incubation experiment in the same region. Contrary to the traditional view, we found no significant effects of P addition on the litter layer decomposition, which was also in contrast with our previous soil incubation experiment that showed stimulatory effects of P addition on soil microbial respiration. The difference between our two experiments was attributed to the role of added P to release organic matter from the sorption sites on mineral soils, which made the adsorbed organic matter in soil accessible for microbes and easier to be decomposed. Overall, our incubation experiments did not support the P-limitation hypothesis: organic matter decomposition in P-poor tropical forests is limited by P shortage.