Youngwoo Nam

Hazard rating of coastal pine forests for a black pine bast scale using self-organizing map (SOM) and random forest approaches

This study examined the effects of environmental factors on the abundance of black pine bast scale (BPBS), Matsucoccus thunbergianae Miller and Park, in coastal disaster prevention pine forests. Geographical factors, soil conditions and forest stand conditions were measured to evaluate the hazard rating for the occurrence of BPBS at 35 plots in the coastal forest stands. A combination of a self-organizing map (SOM), which classified the samples according to their characteristics, and a random forest model, which predicted the probability of the BPBS occurrence from SOM results, were used to assess the hazard rating. Our results showed that climate, tree size, and tree health are major factors determining the abundance of BPBS. BPBS was more common in low latitude coastal forests, suggesting that warmer conditions were favorable to BPBS population buildup. Tree size also influenced the abundance of BPBS, which was higher in forests composed of larger trees (greater DBH). Finally, BPBS was also more abundant in areas with high soil salinity and clay-loam soil, and north-facing slopes where tree vigor was lower. These results can provide useful information for improved coastal pine forests management against BPBS.

An Empirical Predictive Model for the Spring Emergence of Thecodiplosis japonensis (Diptera: Cecidomyiidae): Model Construction and Validation on the Basis of 25 Years of Field Observation Data

ABSTRACT The reliability of the empirical phenology model proposed by Nam et al. (2013) was tested using spring emergence data of Thecodiplosis japonensis Uchida et Inouye (Diptera: Cecidomyiidae) from 1986 to 2011 in Yeongcheon, Korea. First, the lower developmental threshold temperature (LDT) was estimated using spring emergence of T. japonensis and field temperatures. Then a degree-day model to predict spring emergence of T. japonensis was constructed, based on LDTs estimated from field observations and laboratory temperature-dependent development data. Based on field observations, the estimated LDT value for postdiapause development of T. japonensis was 6.1°C, only 0.2°C higher than that estimated from laboratory data. The explanatory power of the empirical degree-day model constructed on the basis of LDT from field observations was 87.2%, similar to the 87.0% of a degree-day model based on laboratory data, suggesting that both models had similar explanatory power. Furthermore, the predictions of median date of emergence in both models were only five days earlier than the observed median date in 2011. These results show that the empirical phenology model based on field observations is a reliable method for predicting the phenology of insects.

A Model for Predicting Spring Emergence of Monochamus saltuarius (Coleoptera: Cerambycidae) from Korean white pine, Pinus koraiensis.

ABSTRACT Monochamus saltuarius Gebler is a vector that transmits the pine wood nematode, Bursaphelenchus xylophilus, to Korean white pine, Pinus koraiensis, in Korea. To reduce the damage caused by this nematode in pine forests, timely control measures are needed to suppress the cerambycid beetle population. This study sought to construct a forecasting model to predict beetle emergence based on spring temperature. Logs of Korean white pine were infested with M. saltuarius in 2009, and the infested logs were overwintered. In February 2010, infested logs were then moved into incubators held at constant temperature conditions of 16, 20, 23, 25, 27, 30 or 34°C until all adults had emerged. The developmental rate of the beetles was estimated by linear and nonlinear equations and a forecasting model for emergence of the beetle was constructed by pooling data based on normalized developmental rate. The lower threshold temperature for development was 8.3°C. The forecasting model relatively well predicted the emergence pattern of M. saltuarius collected from four areas in northern Republic of Korea. The median emergence dates predicted by the model were 2.2–5.9 d earlier than the observed median dates.

Density related plasticity in stand-level spatial distribution of the ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae)

We tested the hypothesis that the population density of ambrosia beetles at the stand level influences the spatial distribution of infested trees. We evaluated the spatial distribution of the ambrosia beetle, Platypus koryoensis (Murayama) in three oak forest stands that varied in beetle population density using a multi-year trapping survey. We used these data to inform a clustering analysis based on aggregation indices using the SADIE software. Four important findings emerged: (1) the spatial distribution pattern of P. koryoensis at the stand level changed as the population density of the beetle varied; (2) at low population densities, beetle distribution was contagious at the stand level; (3) as beetle population densities increased, the spatial distribution of infested trees became random, potentially due to beetle avoidance of mass attacked trees; and (4) at high beetle population densities, the spatial distribution of infested trees became contagious, possibly due to temporal changes in location of the attack epicenter within the stand. Our results support the hypothesis that beetle population density has consequences for the spatial distribution of infested trees at the within-stand scale. We conclude that the spatial distribution of infested trees is flexible in response to beetle population density, suggesting that beetle attack behaviors are mediated by one or more density-dependent effects.