Comparison of Parametric and Nonparametric Methods for Estimating Size–Density Relationships in Old-Growth Japanese Cedar (Cryptomeria japonica D. Don) Plantations

Accurately quantifying the size–density relationships is important to predict stand development, estimate stand carrying capacity and prescribe silvicultural treatments. Parametric methods, such as segmented regression, were proposed to estimate the complicated trajectory of size–density relationships. However, applying nonparametric methods to assess stand development has not been explicitly examined. In this study, we compared parametric and nonparametric methods for estimating size–density relationships for Japanese cedar plantations in Taiwan. Specifically, we compared the efficacy of two segmented regression models with the penalized spline and random forest for regression methods. We also examined various stages in stand development for old-growth Japanese cedar stands. Data collected from 237 Japanese cedar permanent plots were used in model fitting and validation. Results indicated that the parametric and nonparametric methods used in this study can provide reliable estimates of the size–density relationship for Japanese cedar. Higher accuracy was achieved before the stands diverged from the self-thinning line. The penalized spline approach behaved consistently well regardless of datasets or stages in stand development, while the predictability of the random forest algorithm slightly decreased when the validation data was fitted. The results of this study provide insights on the use of methods to quantify the size–density relationships as well as enhance the understanding of long-term stand development

The Carbon Benefit of Thinned Wood for Bioenergy in Taiwan

Forest thinning is a way to make room for the growth of remaining trees, and the thinned wood can serve as a fuel for bioenergy in order to combat climate change. Using thinned wood for bioenergy can substitute for fossil fuel energy, resulting in potential carbon benefit. Since not all thinned wood can be transported out of the forest for processing, the extraction ratio (extraction volume/thinning volume) is an important variable for determining the net carbon benefit. This study investigated 52 forest-thinning sites in Taiwan. The extraction ratio was estimated to explore the benefit of thinned wood used as bioenergy. Cross analysis was adopted to find the relationships between site/species attributes and extraction ratio. The factors included age class, thinning method, land use classification, and species. Key variables included thinning volume, extraction volume, and extraction ratio. Statistical analysis was then applied to identify the significant differences. The analysis shows that the extraction ratio of thinned wood is 57.12%. The research outcomes could provide valuable information for green-energy policy making in Taiwan

The Carbon Benefit of Thinned Wood for Bioenergy in Taiwan

Forest thinning is a way to make room for the growth of remaining trees, and the thinned wood can serve as a fuel for bioenergy in order to combat climate change. Using thinned wood for bioenergy can substitute for fossil fuel energy, resulting in potential carbon benefit. Since not all thinned wood can be transported out of the forest for processing, the extraction ratio (extraction volume/thinning volume) is an important variable for determining the net carbon benefit. This study investigated 52 forest-thinning sites in Taiwan. The extraction ratio was estimated to explore the benefit of thinned wood used as bioenergy. Cross analysis was adopted to find the relationships between site/species attributes and extraction ratio. The factors included age class, thinning method, land use classification, and species. Key variables included thinning volume, extraction volume, and extraction ratio. Statistical analysis was then applied to identify the significant differences. The analysis shows that the extraction ratio of thinned wood is 57.12%. The research outcomes could provide valuable information for green-energy policy making in Taiwan

Numerical Ecology and Social Network Analysis of the Forest Community in the Lienhuachih Area of Taiwan

In this study, the integration of useful statistical methods from different disciplines for analyzing the forest community of the Lienhuachih area of central Taiwan was attempted. We employed a seriated heat map to confirm the presence of multiple community patterns in the area and used the gap statistics and a clustplot to confirm the number and structure of the patterns, respectively. A minimum spanning tree was used to display a succession series among the quadrats, and Renyi diversity was used to indicate the species composition of these patterns. The results confirmed the existence of six patterns with different biodiversity structures in which pattern C was the succession prototype of the local community patterns. Next, we used the patterns as nodes of a social network to perform bipartite network analysis. The results showed that a community network consisted of 108 taxa and six syntaxa. The syntaxa were highly vulnerable to extinction; therefore, the optimal conservation strategy for local species would be to first protect the syntaxa. The random forest method and bipartite modularity were used to analyze the dominant characteristic species of the six syntaxa. The results showed that these two methods are useful for detecting characteristic species of the syntaxa. Therefore, this study proposed a new nomenclature system, namely the Mathematic Code of Syntaxonomic Nomenclature, to support the results of numerical vegetation analysis. Finally, the potential for an apparently competitive network was examined, the role of an apparently competitive network in the local structuring community was explored, and six new associations in the Lienhuachih area were described

Valuation of Forest Ecosystem Services in Taiwan

Forest is the largest ecosystem in the land area of Taiwan. In the past, most of the studies on the evaluation of forest ecosystem services were regional, and therefore lacked national assessment. This study uses a market value method and a benefit transfer method to assess the value of the forest ecosystem services in Taiwan, and expounds the link between ecosystem services and the effectiveness of forestry management and conservation. Preliminarily, it is estimated that the total value of forest ecosystem services in 2016 was approximately NT $749,278 million (equal to approximately 47.6 billion U.S. dollars, PPP-corrected), accounting for 4.28% of the GDP in 2016. The quotation of unit price data has a huge impact on the final assessment results of forest ecosystem service value, and therefore it is necessary use it appropriately

Security Assessment of Taiwan Solid Wood Product Supply

Taiwan is highly dependent on imports of solid wood materials. In the past ten years (2009–2018), it imported raw materials for solid wood products from 117 countries. Therefore, the diversity of raw material sources is a serious concern. The purpose of this research is to evaluate the risks of solid wood product supplies. The dispersion and concentration of supply sources are the measures. The SWI and HHI models are used to calculate the six major imported solid wood products. The results show that from the beginning of 2009 to the end of 2018, wood chips and pellets with the highest average annual import quantity had the lowest average performance in SWI and with the highest average HHI value, which indicates that wood chips and pellets are the riskiest items among the 6 solid wood products. While the sawn wood has the highest average SWI value and the lowest HHI value, it offers the smallest supply risk

Valuation of Forest Ecosystem Services in Taiwan

Forest is the largest ecosystem in the land area of Taiwan. In the past, most of the studies on the evaluation of forest ecosystem services were regional, and therefore lacked national assessment. This study uses a market value method and a benefit transfer method to assess the value of the forest ecosystem services in Taiwan, and expounds the link between ecosystem services and the effectiveness of forestry management and conservation. Preliminarily, it is estimated that the total value of forest ecosystem services in 2016 was approximately NT $749,278 million (equal to approximately 47.6 billion U.S. dollars, PPP-corrected), accounting for 4.28% of the GDP in 2016. The quotation of unit price data has a huge impact on the final assessment results of forest ecosystem service value, and therefore it is necessary use it appropriately

Abiotic Factors and Yushania Influences on Abies Forest Composition in Taiwan

Abies kawakamii forests are generally distributed above 3,000 m in Taiwanese high mountains. The community data used in our analysis were derived from the database of the National Vegetation Diversity Inventory and Mapping Project of Taiwan (NVDIMP), and environmental data were obtained from the WorldClim and NVDIMP databases. We used non-metric multidimensional scaling (NMDS) to identify vegetation composition of Abies communities and the structural equation models (SEMs) were used to examine the complex relationships between environmental factors and vegetation composition. The results of ordination showed the most important factors determining species composition of Abies forests involved habitat rockiness, heat load index, warmth index and summer and winter. SEM results approved the warmth index and winter precipitation were the main drivers determining the latent variable—climate, which significantly affect the overstory composition of Abies communities. The relative frequency of Yushania niitakayamensis also had a minor effect on the overstory. However, the relative frequency of Yushania had strong and significant effects on the understory flora and it was also strongly correlated with rock ratio and winter precipitation. Moreover, the overstory displayed a negative but insignificant coefficient on the understory composition, and this might be attributed to the fragile and high heterogeneous habitat in Taiwanese high mountain areas