Abstract
Carbon emissions from afforestation and tending operations were studied in this work. Renewable resources from the operations were evaluated in terms of their potential as fuel. New planting operations were found to result in higher energy consumption, biomass, and emissions compared with the tending operations. The greenhouse gas emissions from new planting and afforestation operations for plantation were 405.0 kg CO2/ha, 50.1 g CH4/ha, and 27.1 g N2O/ha, whereas those from the tending operations were 277.7 kg CO2/ha, 36.3 g CH4/ha, and 19.0 g N2O/ha. The major components of the renewable resources from the afforestation and tending operations were C, O, and H, and the contents of N and S were lower than those specified in the regulations by the European Union for refuse-derived fuels. Therefore, the refuse-derived fuel prepared from the renewable resources of the afforestation and tending operations did not cause NOx or SOx pollution. This fuel resulted in zero CO2 emissions, and it could be used as an alternative fuel for small boilers in the future.
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Afforestation and Tending Operations Affecting the Carbon Footprint and Renewable Resources at an Artificial Forest in Taiwan
Fang-Chih Chang,a,* Chun-Han Ko,b and Ming-Jer Tsai a,b
Carbon emissions from afforestation and tending operations were studied in this work. Renewable resources from the operations were evaluated in terms of their potential as fuel. New planting operations were found to result in higher energy consumption, biomass, and emissions compared with the tending operations. The greenhouse gas emissions from new planting and afforestation operations for plantation were 405.0 kg CO2/ha, 50.1 g CH4/ha, and 27.1 g N2O/ha, whereas those from the tending operations were 277.7 kg CO2/ha, 36.3 g CH4/ha, and 19.0 g N2O/ha. The major components of the renewable resources from the afforestation and tending operations were C, O, and H, and the contents of N and S were lower than those specified in the regulations by the European Union for refuse-derived fuels. Therefore, the refuse-derived fuel prepared from the renewable resources of the afforestation and tending operations did not cause NOx or SOx pollution. This fuel resulted in zero CO2 emissions, and it could be used as an alternative fuel for small boilers in the future.
Keywords: Tending; Carbon footprint; Miscellaneous trees; Refuse-derived fuel; Resource recycling
Contact information: a: The Experimental Forest, College of Bio-Resources and Agriculture, National Taiwan University, Nan-Tou 55750, Taiwan; b: School of Forestry and Resource Conservation, National Taiwan University, Taiwan; *Corresponding author: d90541003@ntu.edu.tw
INTRODUCTION
The basic principle of sustainable forest management is to maintain the stability of a forest ecosystem and enable it to achieve multi-objective functions. In the context of silviculture strategies, this means the appropriate extension of a forest’s rotation period, with tending operations used as a supporting measure. Tending operations include the timely and appropriate thinning of forests to manage and regulate their density and structure, while pruning and vine removal simultaneously produce high-quality, large-diameter wood and conserves soil, water, and biological resources (Ishii et al. 2008). The implementation of forest tending operations is divided into non-logging artificial tending and logging-based tending. Non-logging artificial tending involves fertilizing, weeding, vine removal, and intertillage (soil scarifying during seedling growth) to facilitate growth, whereas logging-based tending involves cleaning-cutting (removal of unhealthy wood, stand density adjustment, quality improvement, and material improvement) and thinning (removal of unhealthy wood, stand density adjustment, quality improvement, and increasing income) (Putz et al. 2000; Bilic 2010). Thinning is a crucial mid- and late-stage tending measure in forest management (Yen 2015). Research has indicated that thinning can increase the growth space of forest trees, reduce the competition for forest nutrients, and promote the growth of forest trees (Batsaikhan et al. 2018). Stand thinning changes root density and activity; reduces canopy density, the leaf area index, the total photosynthesis system, and transpiration; increases pore density; and promotes direct light exposure during the day, and thereby increasing soil temperature (Tang et al. 2005; Campbell et al. 2009; Pang et al. 2013). Thinning can be divided into (1) qualitative thinning, which is further divided into low thinning, high thinning, mechanical thinning (spacing or row thinning), or selective thinning based on the canopy or stem level; and (2) quantitative thinning, whereby the quantity and quality of thinning are determined together with qualitative thinning, and the number of thinned trees is determined by the number of trees, the diameter at breast height, distance between trees, the tree height, and basal area. Numerous studies have focused on the effects of thinning operations on carbon conservation in soils, forest litter decomposition, the conversion of organic matter in soils, and soil respiration, all of which affect the carbon cycle of a forest ecosystem (Fernandez et al. 2012; Olajuyigbe et al. 2012; Smolander et al. 2013). However, these studies did not examine the carbon emissions caused by the afforestation and tending operations.
According to the results of the fourth forest resource investigation, the total forest area in Taiwan is up to 2.197 million ha, and the forest coverage rate is 60.71%. Taiwan only has a timber self-sufficiency rate of 1%, and is thus greatly dependent on imports from other timber-producing countries. Therefore, the Forestry Bureau has initiated the “Strategic Planning of Forestry Economic Revitalization” to raise the self-sufficiency rate of domestic materials to 3%. The bureau has also implemented plans that reward nationwide afforestation and plain area afforestation sites, providing circular economic utilization of all timber through forestry management approaches such as thinning or selective thinning. The development results of artificial afforestation by Taiwan’s forestry industry have gradually matured, with the volume of artificial forest reserves being approximately 47.67 million m3. Thinning operations in forest tending operations can promote forest renewal and establish the value of sustainability using domestic timber resources. By extending the rotation period of forest trees, the volume of timber accumulation and carbon sequestration of forest stands can be increased with appropriate timber and land use. The management model of artificial forests adopts a low-frequency human intervention approach that adjusts forest structure and density, increases species richness, and improves forest stand productivity and biodiversity through mid- and late-stage tending operations such as pruning and thinning. A rich amount of wood resources can be produced from thinning during mid- and late-stage tending operations, and the effective use of such wood resources from thinning can help improve the low domestic self-sufficiency ratio of timber of less than 1%. Additionally, because thinned forests mostly comprise medium- and small-diameter trees, which consist of a relatively high proportion of juvenile trees that are lightweight, soft, and contain numerous nodes, they are subjected to greater restrictions in terms of processing and utilization. Thinned wood, like ordinary wood, possesses natural and variable textures and colors and can adjust to humidity, absorb ultraviolet rays, insulate, and absorb sound. Therefore, innovatively using thinned wood from domestic afforestation can help utilize forest resources and produce high-quality forests. The active promotion of domestic wood and bamboo products by Wang (2015) is in line with the definition of “domestic production and the sales of timber products,” which promotes the local production and consumption of regional raw materials, thereby reducing CO2 emissions because the products have a shorter distance to travel. Therefore, improving the utilization of thinned wood from domestic afforestation is currently a focus of development that conforms to green and environmentally friendly appeals.
Afforestation and tending also produces forestry waste from weeding, vine removal, pruning, and trimming, as well as waste from thinning and processing, all of which are mostly abandoned onsite. Numerous studies have demonstrated that forestry waste is an exceptional biomass and can be used as biofuel (Solino et al. 2009; Akyuz and Balaban 2011; Chen et al. 2011; Tarelho et al. 2011), bioethanol (Regalbuto 2011; Dodic et al. 2012; Ko et al. 2012a), biodiesel (Dodic et al. 2012; Ko et al. 2012b; Prakash et al. 2013), functional carbon materials (Sevilla et al. 2011), and xylose (Ko et al. 2013).
As of March 31, 2018, the number of motor vehicles registered in Taiwan totaled 21,746,355, comprising 7,970,145 and 13,776,210 registered cars and motorcycles, respectively. The lubricating oil in the engines of these vehicles needs to be regularly replaced. The proper use of this waste oil, its conversion into renewable energy, the improvement of its recycling potential, and the creation of circular economic value have become crucial environmental topics.
This study first investigated the carbon emissions from afforestation and tending operations to calculate the carbon sequestration of forests. Next, the waste from afforestation and tending operations (miscellaneous trees) was recycled to evaluate its potential for preparing refuse-derived fuels and its possible impact on the environment. Waste engine oil was used as an additive and mixed with miscellaneous wood and granulated to produce miscellaneous wood-derived biomass fuel.
EXPERIMENTAL
Investigating Afforestation and Tending Operations and Recycled Resources
This study investigated afforestation and tending operations (planting/tending) implemented in the artificial experimental forest at National Taiwan University (NTU). The geographical location and forest resource map of the NTU experimental forest are shown in Figs. 1 and 2, respectively. The artificial forest has reached the threshold for newly planted afforestation or mid- and late-stage tending operations. Afforestation and tending can improve poor forest physiognomy and the renewal of unsatisfactory forest stands, as well as improve biodiversity and forest ecosystems, thereby facilitating the absorption of CO2. In this study, each afforestation and tending treatment (planting/tending) was repeated thrice at six sampled areas (three for planting and three for tending). The size of each area was 0.1 ha (40-m-long, 25-m-wide). Additionally, the afforestation and mid- and late-stage tending areas and emissions also are calculation from 2008 to 2017 at the NTU experimental forest. The biomass of the weeds from the afforestation and tending operations, the amount of recycled resources produced by those operations, and the associated carbon footprint at each sampled area were surveyed. The initial period of afforestation and tending operations was conducted in this study (Table 1). During the first to third years, the newly planted forest required soil preparation, planting, tending, weeding, and replanting. Another 3-year tending operation involving tending and weeding, vine removal, and trimming was implemented at the afforestation site in the fourth to sixth years.
Carbon Footprint Calculation
The carbon emissions from the afforestation and tending operations in this study were calculated according to the emission coefficient by the Intergovernmental Panel on Climate Change (IPCC) and the Bureau of Energy. This involved multiplying the activity data of the emissions sources (fuel consumption, electricity consumption, water consumption, and amount of garbage) with the emissions coefficients (IPCC 2006). The emissions coefficients of CO2, CH4, and N2O were 2.26 kg/L, 8.16 × 10-4 kg/L, and 2.61 × 10-4 kg/L, respectively.
The distance between the tending site and the Wood Utilization and Practice Factory of the College of Bio-Resources and Agriculture at NTU were used for the transportation distance to calculate the resulting carbon emissions from the forest afforestation and tending processes, serving as a reference for calculating forest carbon sequestration. The data presented are means ± standard deviation. The existence of significant differences in newly planted group and tending group was tested using t-test. A p-value of 0.05 or less was defined as statistically significant.
Refuse-derived Fuel of Renewable Forestry Resources
The renewable forestry resources were exactly the same as the previous study (Lu et al. 2017). The renewable forestry resources were ground and sifted for their particles to pass through a 40-in mesh screen, after which they were mixed in proportion with waste engine oil to prepare 2 mm of miscellaneous wood-derived fuel.
The potential of the refuse-derived biofuel was evaluated by analyzing its calorific value, proximate components (water, ash, and combustibles [volatile and fixed carbon]), and element analysis (carbon, hydrogen, oxygen, nitrogen, sulfur, and chlorine). Its calorific value, combustion efficiency, and the emissions of NOx and SOx were then assessed to determine the optimal refuse-derived fuel. The proximate component analysis referenced the Chinese National Standards CNS 10821 (2012), CNS 10822 (2012), CNS 10823 (2012), and CNS 10824 (2012); the elemental analysis was based on NIEA R403.21C (2005), and the dry-basis calorific value was analyzed based on NIEA R214.01C (2005).
Table 1. Characteristics of Newly Planted Forest and the Tending Operation Site
