Composition and Dynamics of Hexapod Communities on Yushan Bamboo (Yushania niitakayamensis) in the Subtropical Montane Areas of Taiwan.

Plant communities that colonize high-elevation zones generally have short growing seasons which lead to specialized adaptations in such zones. In montane areas of Taiwan, Yushan bamboo (YB, Yushania niitakayamensis) is dominant at elevations ranging from 2500 to 3300 m and grows in a grassland-like open habitat. In this study, hexapods were collected from YB bimonthly between 2009 and 2012 by using a sweeping net. The composition of and several bioindices for the hexapods were determined, and multivariate analyses were conducted to explore the dynamics and seasonal distribution of the hexapods. A total of 32,000 individuals belonging to 11 orders and 113 families were collected, with adult individuals being collected more frequently in warmer seasons (from June to October). Of the sampled individuals, 90% belonged to the orders Collembola (42%), Hemiptera (35%), and Hymenoptera (13%). The number of individuals belonging to Hemiptera were stable in all seasons, and the number of hymenopteran wasps was influenced by temperature and exhibited a stable dynamic pattern. The number of individuals belonging to Collembola fluctuated dramatically. The multivariate analyses revealed that the collected hexapods could be divided into two major family groups according to survey season (i.e., summer and winter groups). Several families were collected only in summer, but a few were collected only in winter. Eigenvalues obtained from a principal component analysis revealed that the families Chironomidae, Delphacidae, Entomobryidae, Hypogastruridae, Sminthuridae, and Thripidae (all dominant) were the major contributors to the winter group. These families were abundant all year, although some were more abundant during winter. The three dominant orders Collembola, Hemiptera, and Hymenoptera, each of which has a distinct community structure and dynamic pattern, may have their own adaptive mechanisms in the subtropical regions of Taiwan. Hemiptera individuals, which feed on YB, were most abundant in the adult stage in summer and in the nymphal stage in winter. The abundance of parasitic hymenopteran wasps, which had stable dynamic patterns, was associated with that of their host insects and temperature. The drastic fluctuations in the abundance of Collembola may have been caused by abiotic factors, such as precipitation and microhabitat factors. The early onset of spring and the late onset of winter might also affect the dynamics of the studied hexapods.

Optimal Subdivision for Treatment and Management of Catastrophic Landslides in a Watershed Using Topographic Factors.

Recent extreme rainfall events led to many landslides due to climate changes in Taiwan. How to effectively promote post-disaster treatment and/or management works in a watershed/drainage basin is a crucial issue. Regarding the processes of watershed treatment and/or management works, disaster hotspot scanning and treatment priority setup should be carried out in advance. A scanning method using landslide ratio to determine the appropriate outlet of an interested watershed, and an optimal subdivision system with better homogeneity and accuracy in landslide ratio estimation were developed to help efficient executions of treatment and/or management works. Topography is a key factor affecting watershed landslide ratio. Considering the complexity and uncertainty of the natural phenomenon, multivariate analysis was applied to understand the relationship between topographic factors and landslide ratio in the interested watershed. The concept of species-area curve, which is usually adopted at on-site vegetation investigation to determinate the suitable quadrate size, was used to derive the optimal threshold in subdivisions. Results show that three main component axes including factors of scale, network and shape extracted from Digital Terrain Model coupled with areas of landslide can effectively explain the characteristics of landslide ratio in the interested watershed, and a relation curve obtained from the accuracy of landslide ratio classification and number of subdivisions could be established to derive optimal subdivision of the watershed. The subdivision method promoted in this study could be further used for priority rank and benefit assessment of landslide treatment in a watershed.

Empirical Model for Evaluating PM10 Concentration Caused by River Dust Episodes.

Around the estuary of the Zhuo-Shui River in Taiwan, the waters recede during the winter, causing an increase in bare land area and exposing a large amount of fine earth and sand particles that were deposited on the riverbed. Observations at the site revealed that when northeastern monsoons blow over bare land without vegetation or water cover, the fine particles are readily lifted by the wind, forming river dust, which greatly endangers the health of nearby residents. Therefore, determining which factors affect river dust and constructing a model to predict river dust concentration are extremely important in the research and development of a prototype warning system for areas at risk of river dust emissions. In this study, the region around the estuary of the Zhuo-Shui River (from the Zi-Qiang Bridge to the Xi-Bin Bridge) was selected as the research area. Data from a nearby air quality monitoring station were used to screen for days with river dust episodes. The relationships between PM10 concentration and meteorological factors or bare land area were analyzed at different temporal scales to explore the factors that affect river dust emissions. Study results showed that no single factor alone had adequate power to explain daily average or daily maximum PM10 concentration. Stepwise regression analysis of multiple factors showed that the model could not effectively predict daily average PM10 concentration, but daily maximum PM10 concentration could be predicted by a combination of wind velocity, temperature, and bare land area; the coefficient of determination for this model was 0.67. It was inferred that river dust episodes are caused by the combined effect of multiple factors. In addition, research data also showed a time lag effect between meteorological factors and hourly PM10 concentration. This characteristic was applied to the construction of a prediction model, and can be used in an early warning system for local residents.

Spatial variations of the aerosols in river-dust episodes in central Taiwan.

Daily and hourly average data of PM(10) from 17 air-quality monitoring stations distributed throughout four counties and along four rivers (the Ta-an River, the Tachia River, the Wu River and the Choshui River) in central Taiwan were collected from November 15 to 21, 2008. During this period, the wind speed and daily PM(10) concentrations increased drastically from the 17th to the 19th, and reached a maximum level on the 19th. Six air-quality monitoring stations (Dajia, Wurih, Siansi, Dungnan, Lunbei and Taisi) in the central Taiwan were selected for sampling fine (PM(2.5)) and coarse (PM(10-2.5)) aerosols samples during and after the river-dust episode. Most of the ratios of [crustal elements (Fe or Al)/reference elements (Cd or Mo)] for the samples obtained during episode are higher than those obtained after episode. The values of Fe(10-2.5)/Cd(10-2.5) and Fe(10-2.5)/Mo(10-2.5) were very high in Lubei, Taisi, and Dungnan stations where heavy aeolian river dust occurred. These data suggest that the ratios of Fe(10-2.5)/Cd(10-2.5) and Fe(10-2.5)/Mo(10-2.5) can be successfully used as indexes to evaluate the comparative degree of effect of aeolian river dust on the atmosphere of multiple stations.

Vegetation recovery patterns assessment at landslides caused by catastrophic earthquake: a case study in central Taiwan.

The catastrophic earthquake, 7.3 on the Richter scale, occurred on September 21, 1999 in Central Taiwan. Much of standing vegetation on slopes was eliminated and massive, scattered landslides were induced at the Jou-Jou Mountain area of the Wu-Chi basin in Nantou County. We evaluated three methods for assessing landslide hazard and vegetation recovery conditions. (1) Self-organizing map (SOM) neural network coupled with fuzzy technique was used to quickly extract the landslide. (2) The NDVI-based vegetation recovery index derived from multi-temporal SPOT satellite images was used to evaluate vegetation recovery rate in the denudation sites. (3) The spatial distribution index (SDI) based on land-cover topographic location was employed to analyze vegetation recovery patterns, including the invading, surviving and mixed patterns at the Jou-Jou Mountain area. On September 27, 1999, there were 849.20 ha of landslide area extracted using the self-organizing map and fuzzy technique combined model. After six years of natural vegetation succession, the landslide has gradually restored, and vegetation recovery rate reached up to 86%. On-site observation shows that many native pioneer plants have invaded onto the denudation sites even if disturbed by several typhoons. Two native surviving plants, Arundo formosana Hack and Pinus taiwanensis Hayata, play a vital role in natural vegetation succession in this area, especially for the sites on ridgeline and steep slopes.