Reiichiro Ishii

Unmanned Aerial Survey of Fallen Trees in a Deciduous Broadleaved Forest in Eastern Japan

Since fallen trees are a key factor in biodiversity and biogeochemical cycling, information about their spatial distribution is of use in determining species distribution and nutrient and carbon cycling in forest ecosystems. Ground-based surveys are both time consuming and labour intensive. Remote-sensing technology can reduce these costs. Here, we used high-spatial-resolution aerial photographs (0.5–1.0 cm per pixel) taken from an unmanned aerial vehicle (UAV) to survey fallen trees in a deciduous broadleaved forest in eastern Japan. In nine sub-plots we found a total of 44 fallen trees by ground survey. From the aerial photographs, we identified 80% to 90% of fallen trees that were >30 cm in diameter or >10 m in length, but missed many that were narrower or shorter. This failure may be due to the similarity of fallen trees to trunks and branches of standing trees or masking by standing trees. Views of the same point from different angles may improve the detection rate because they would provide more opportunity to detect fallen trees hidden by standing trees. Our results suggest that UAV surveys will make it possible to monitor the spatial and temporal variations in forest structure and function at lower cost.

Linking Remote Sensing and In Situ Ecosystem/Biodiversity Observations by “Satellite Ecology”

Climate change and human activity (land use change and management) are the major drivers of changes in biodiversity, which ranges from the genetic composition of a given population to the structure and functions in an ecosystem and to the ecosystems in a landscape. The structural and functional diversity of an ecosystem on a landscape or regional scale could have a serious impact on the regional to global environmental sustainability and ecosystem services. Also, those ecosystem properties could have feedback effects on the population, individual, and genetic levels (e.g., Schulze and Mooney 1994). These cross-hierarchy consequences strongly suggest the need for understanding the relations between ecosystem properties and their internal and external drivers (Noss 1990; Scholes et al. 2008).

Isotopic composition of nitrogenous compounds with emphasis on anthropogenic loading in river ecosystems.

Nitrogenous compounds with high δ15N values were recently found in human-dominated small rivers in the Lake Biwa area. A detailed survey was performed to determine the distribution and variation of δ15N values in nitrogenous compounds in a representative small river (Hebisuna River) that flows into Lake Nishinoko, an inner bay of Lake Biwa. A high δ15N value was detected in the lower reaches of the river and the inner bay, most likely due to denitrification. These results strongly suggest that denitrification in small river systems such as the Hebisuna watershed has contributed to 15N enrichment in the Lake Biwa ecosystem during the past 40 years. We also observed a clear, stepwise, positive correlation between population density and δ15N values for particulate organic matter or sediments. These results demonstrate that δ15N POM and δ15N sediment are helpful indicators for assessing nitrogen loading from domestic sewage. Moreover, they will aid in the development of new concepts in the environmental capacity of river ecosystems and its relationship to redox conditions. Finally, our data suggest that a population density of 100–200 persons per km 2 is the upper limit for a watershed in which only simple conventional sewage treatment is in effect.

Development of a National Land-Use/Cover Dataset to Estimate Biodiversity and Ecosystem Services

Land-use/cover data are essential to estimate biodiversity and ecosystem services. Although many data and maps have been produced in Japan, there is significant variation in their characteristics, such as publication year, spatial resolution, and land-use/cover classification categories because the purposes of the data and maps differ (e.g., resource inventory). Unfortunately, little attention has so far been paid to biodiversity and ecosystem services, which require preparation of new land-use/cover data. First, we searched existing public national data in Japan published by government sectors and researchers and evaluated their characteristics. Second, we briefly reviewed user needs (e.g., temporal coverage, spatial resolution, and classification categories) to estimate biodiversity and ecosystem services. We then integrated the information, and we present herein a procedure to prepare a new national land-use/cover dataset from existing datasets to bridge the gaps between data producers and users by determining the temporal coverage needed to reveal historic change, determining the spatial resolution suitable for estimation, and setting classification categories needed for estimation. The resultant land-use/cover data could contribute significantly to research and management related to conservation of biodiversity and provision of ecosystem services.

Usability of noise-free daily satellite-observed green–red vegetation index values for monitoring ecosystem changes in Borneo

We examined the usability of daily green–red vegetation index (GRVI) observations from the Terra and Aqua Moderate Resolution Imaging Spectroradiometer satellite on cloud-free days for monitoring ecosystem changes in Bornean tropical forests at a 500 m spatial resolution over 11 years (2003–2013). The number of observational days of cloud-free GRVI data in the southwest monsoon period (May–October; 1–5 days/month) was greater than that in the northeast monsoon period (November–April; 0–2 days/month). Spatial variation in the observation frequency was noticed, with Terra (morning) and Aqua (afternoon) data showing different geographic distribution patterns of cloud-free data. The observation frequency in the western Kalimantan mountains (Sarawak and Sabah) was 1–2 days/month greater than that in the eastern mountains (Kalimantan). The quality of cloud-free GRVI data was validated by using sky images taken at the same time as the satellite observations and canopy surface images in a tropical rainforest. In oil palm and acacia plantations and peatlands, which were mainly distributed in coastal regions of Sarawak and West and Central Kalimantan, the cloud-free daily GRVI value fell below zero owing to deforestation and forest degradation caused by forest fire and increased with replanting and vegetation recovery. These results indicate that daily cloud-free GRVI data from multiple satellites collected at different times of the day are required for accurate monitoring of intra- and interannual phenological variation and forest degradation attributed to changes in climatic conditions and deforestation caused by human activities in tropical ecosystems.

A Possible Future Picture of Mongolian Forest-Steppe Vegetation Under Climate Change and Increasing Livestock: Results from a New Vegetation Transition Model at the Topographic Scale

In the northern part of Mongolia, one can observe clearly slope aspect-dependent and discontinuous vegetation transitions between forest and steppe as a general spatial pattern. In this region, water availability and grazing pressure by livestock are considered to be the most important factors to determine the dominant vegetation type. Because no sound explanations have been made for the generation of this pattern at the topographic scale, we here develop a new model scheme of vegetation transition at the topographic scale (with resolution <100 m) to incorporate these different essential factors at the same time. By incorporating a positive feedback mechanism between vegetation biomass and soil water contents (i.e., biomass accumulation enhances water infiltration and water-holding capacity of soil, which in turn facilitates further plant biomass increase) enabled us to generate the conspicuous vegetation pattern from slight topographic heterogeneity in solar radiation depending on the slope aspect, which was supported by field observations. Based on the model with available parameters, we could further develop a numerical spatial model to predict the qualitative future vegetation under various scenarios with changing climate and livestock density. This model suggests that drastic vegetation degradation might occur locally where precipitation decrease and/or livestock increase exceed the critical points. It also shows how these two factors synergistically enhance the vegetation degradation. To consider ecosystem sustainability in Mongolia more practically, we need a new modeling framework to cover broader spatial scales.

Effects of remnant primary forests on ant and dung beetle species diversity in a secondary forest in Sarawak, Malaysia

Tropical landscape structures have been transformed into mosaic structures consisting of small patches of primary and secondary forests, and areas of other land use. Diversity of insect assemblages is often higher in primary forests than in surrounding secondary forests. However, little is known about how the primary forests affect diversity in surrounding secondary forests in a landscape. In Sarawak, Malaysia, the typical landscape in areas from which lowland tropical rainforests had originally spread consists mainly of primary and secondary forests, with small areas of cultivation. In this study, we examined how the proportion of remnant primary forests in a landscape affects species diversity and species composition of ants and dung beetles in Macaranga-dominated secondary forests. The proportions were quantified based on remote-sensing data at various spatial scales, ranging from 100- to 5,000-m radius from each of the target forests. We found that the proportions of remnant primary forests within a 100-m radius had a significant positive effect on ant species diversity, and those within 100-, 300-, and 500-m radii significantly affected species compositions. However, the proportions of remnant primary forests had no significant relationship with dung beetle diversity, while those within 100- and 1,000-m radii had significant effects on species composition. The different responses to the remnant primary forests are likely to be related to differences in the movement and dispersal traits between the two taxa.

Efficiency of multi-frequency, multi-polarized SAR data to monitor growth stages of oilpalm plants in Sarawak, Malaysia

Carbon rich tropical forests of Southeast Asia have increasingly become a target for the conversion to plantation area. Plantations are economically important for the local society because they provide incentives in a short period of time. Southeast Asia has a high rate of conversion of tropical forests to various types of plantation species such as oilpalm, rubber, acacia, cashew, teak, eucalyptus etc. Therefore, monitoring of carbon loss due to the conversion of forests to various plantation species has become crucial in the global carbon cycle. Information about the age or growth stages (juvenile, young, mature and old) of plantation species is a useful parameter to calculate carbon sequestration as well as for predicting yield and a range of management practices such as determining location for thinning, harvesting and replantation. This study focuses on the comparison and efficiency of multi-frequency, multi-polarized Synthetic Aperture Radar (SAR) data to monitor various growth stages of oilpalm plants in Sarawak, Malaysia based on backscattering and polarimetric decomposition techniques. Phased Array type L-band Synthetic Aperture Radar (PALSAR) data with dual and quad polarization, Radarsat-2 data with quad polarization and TerraSAR-X (TSX) data with HH polarization have been used in this investigation. Results show that, PALSAR data with HV polarization shows highest sensitivity with the oilpalm plants age as compared to other SAR data. TSX based texture information will also be utilized to find the important texture parameters to identify various growth stages of oilpalm plants.