Vegetational change was studied during 2010‐2015 in the coral-gravelly barrier spit that appeared in 2007 in association with the 2004 Indian Ocean Tsunami at Pakarang Cape, southwestern Thailand, related to topographical changes. No lichens, liverworts, or ferns were found during the study period, although lithophytic algae were widespread over the coral gravel. Several woody species, along with several creeping herbaceous species, colonized the area soon after appearance of the barrier spit. Coral gravel covering the ground surface prevented the sand movement, facilitating colonization by drifting seeds. In all, 37 species of vascular plants, comprising 21 woody and 16 herbaceous species, were recorded through 2015. Annual monitoring of the plant covered area, location, and height of all the trees taller than 20cm along with formation process of the barrier split using high-resolution GPS revealed that vegetation was affected strongly by topographical changes. In accordance with easterly movement of the barrier spit, vegetation largely disappeared in the western part, although it developed in the eastern part. Casuarina equisetifolia increased and grew significantly faster than other species, producing a thick forest in the stable central part of the barrier spit during the study period.
In the Southeast Asian tropics, the tree genus Macaranga includes many myrmecophytic species that associate with ‘plant-ants’ nesting in their domatia spaces. Plant-ants on Macaranga myrmecophytes protect their host-plants against herbivores. Because interspecific differences in ant defense intensities among Macaranga myrmecophytes affect the host-plant use by herbivorous insects, they need to be studied to better understand the ecology and evolution of herbivores on Macaranga myrmecophytes. In this study, to examine whether larvae of a lycaenid species, Arhopala major, which potentially feeds on some Macaranga myrmecophytes, can be used for a bioassay that assesses relative ant aggressiveness towards general herbivores on Macaranga plants, we experimentally introduced A. major larvae onto leaves of three Macaranga myrmecophytic species. We measured (1) the time required for the first touch by plant-ants on an introduced larva and (2) the number of plant-ant workers aggregating 3 min after the first touch. The order of three Macaranga species in ant defense intensity, as estimated by the two measurements, corresponded with the results of previous studies investigating the interspecific differences in ant defense intensities using ant-exclusion experiments. This suggests that the bioassay using A. major larvae is valid for the assessment of relative intensities of ant defenses on Macaranga species. As time and labor cost are low and standardization is easier, compared with the other methods, such as ant-exclusion experiments, the bioassay tested in this study is practical for assessing ant defense intensities on Macaranga plants.
The utilization of wood resources from unutilized fast-growing tree species found in secondary forests was investigated by studying the wood properties, including anatomical characteristics, of two Macaranga species-M. bancana and M. pearsonii-growing naturally in secondary forests in Central Kalimantan, Indonesia. Several wood properties related to pulp and paper quality were also evaluated, including the Runkel ratio, Luce＇s shape factor, flexibility coefficient, slenderness ratio, solid factor, and wall coverage ratio. The mean basic density of these two species ranged from 0.23 to 0.31g cm-1, while the mean values of vessel diameter, vessel element length, fiber diameter, fiber wall thickness, and fiber length ranged from 126 to 192μm, 0.88 to 1.19mm, 24.5 to 29.8μm, 0.99 to 1.14μm, and 1.42 to 1.69mm, respectively. The lignin content of M. bancana and M. pearsonii wood was 27.2 and 28.0%, respectively. Almost all wood properties related to pulp quality showed better values than those reported for Acacia and Eucalyptus species, although sheet density of paper might be lower due to higher solids factor and possibility of occurrence of vessel picking was probably higher due to longer vessel element length and larger vessel diameter. Based on the results, the wood from these two Macaranga species can be used as pulpwood.
Effects of phosphorus (P) addition on nitrous oxide (N2O) emissions from an Acacia mangium plantation soil was examined in relatively aerobic condition with carbon (C) and nitrogen (N) addition. We hypothesized that P addition reduced N2O emissions through stimulated microbial N immobilization and subsequent decrease in inorganic N resources for producing N2O. We prepared the following four experimental sets; high C (glucose 2000μg C g soil－1) and water-filled pore space (WFPS) 40% (H40), low C (glucose 100μg C g soil－1) and WFPS 40% (L40), high C and WFPS 60% (H60), and low C and WFPS 60% (L60). Nitrogen (NH4NO3, 20μg N g soil－1) was also added to all soils. We prepared P-added soils (Ca(H2PO4)2, 20μg P g soil－1) and non-added control to test the effects of P addition on N2O emissions. Contrary to our hypothesis, P addition did not reduce N2O emissions, although soil microbial N immobilization was stimulated by P addition in soils with low C addition. Stimulated total N cycling by P addition probably offset the decrease in soil inorganic N. Meanwhile P addition reduced soil microbial biomass N (MBN) content in H60, where N2O emissions increased significantly by P addition. It was possible that the microbial growth reached its peak and started dying more quickly in P-added soils in H60 due to the favorable condition for microbes (higher C and water content). Thus we concluded that (i) P addition did not necessarily stimulate soil microbial N immobilization, and (ii) N2O emissions might not decrease even if P addition stimulated soil microbial N immobilization.