Discuss how carbon storage differs among hardwood vs conifer stands in soils and

Question

Discuss how carbon storage differs among hardwood vs conifer stands in soils and above ground biomass. Suggest an experiment to test hypotheses related to the mechanism which you are proposing which may be the cause for the differences in carbon pools across each forest type. Discuss how carbon storage differs among hardwood vs conifer stands in soils and above ground biomass. Suggest an experiment to test hypotheses related to the mechanism which you are proposing which may be the cause for the differences in carbon pools across each forest type.

Explanation / Answer

Carbon dioxide (CO2) is the most important anthropogenic greenhouse gas that plays the greatest role in global warming (Li et al., 2014). Human activities for reducing atmospheric CO2 were started when the effects of global warming were specified. After ratification of the Kyoto Protocol, two different actions have been taken for reducing CO2 emissions: reducing human activities related to greenhouse gas emission; creating and improving carbon sinks in the biosphere by tree plantation (Bipal and Mrinmo, 2010; Aguirre-Salado et al., 2014). Trees play an important role in reducing CO2 by absorbing and accumulating it in their leaves, branches, stems and roots as biomass (McPherson and Simpson, 1999). Biomass has been widely used for carbon cycle studies because it is an important indicator of vegetation growth and dynamic (Yan et al., 2013). Establishing tree plantations in the vicinity of industrial areas is one of the mandatory Iranian environmental laws (Abdinezhad, 2012). Reforestation and afforestation projects have been in operation annually in Iran after the Clean Development Mechanism projects evolved since 1990.  Many of these plantations are watered by industrial waste water due to the shortage of the clean water in the area. Forest managers are interested in increasing the productivity of the planted forests and the timber production which accordingly can increase the carbon sequestration rates (Lemus and Lal, 2005; Woodbury et al., 2007). The simplest way to achieve this goal is to select proper species for plantation. To understand the effects of the different tree species on forest carbon storage and to determine the most appropriate reforestation species and forest management strategies (Zheng et al., 2008), it is necessary to examine the differences of carbon pools among the different plantations (Kaul et al., 2010). During the last century, selected deciduous and coniferous species have been planted in different areas in Iran. However, no enough information is available for managers on how to select the proper species with high carbon storage capacities under certain climatic conditions. In this research, we aimed to compare the carbon storage potential in the above- and below-ground parts of the four 17- year old monoculture plantations of the deciduous, mulberry (Morus alba L.) and black locust (Robinia pseudoacacia L.), and the coniferous, Eldar pine (Pinus eldarica Medw.) and Arizona cypress (Cupressus arizonica Greene). To our knowledge, the potential of carbon storage of coniferous and deciduous species has been examined in numerous studies, but not much on the amount of carbon stored in the above- and below-ground tree parts, particularly in arid areas.

Plantations can play a significant role in reducing atmospheric carbon dioxide. In this study, we compared the carbon storage among the four plantations at different soil depths, at the forest floor, as well as between the above- and below-ground tree components. The results of the study showed that the carbon storage potential for coniferous plantations was higher than that for the deciduous and Eldar pine had the highest carbon storage rate. In plantation management plans the potential for carbon dioxide fixation of trees should be considered. For the purpose of sequestrating atmospheric carbon dioxide by planting trees in areas with low rainfall, especially when waste water for irrigation is available, we recommend to plant Eldar pines. It is important to consider different carbon storage patterns among the plantations. Some species store more carbon in soil while the others store more carbon in their living tissues. Each species, due to characteristics of physiology, phenology and morphology, may need to be managed in different ways. Species selection can affect many aspects of ecosystem functions and services to fulfill multiple goals and purposes. Therefore carbon storage potential should not be the only criterion for the selection.

Methods

1 Tree biomass measurement In order to measure biomass of the four species, we randomly selected 12 plots in each stand (48 plots in total). The standing tree variables including diameter at breast height (DBH), crown width (CW) and total height (TH) were measured for EP and AC. But for M and BL, DBH were not measured because the trees were multi-stemmed under breast height and DBH was not a representative variable for tree dimension. The trees were stratified into 5 strata based on the range of DBH and TH. In each stratum, 3 individuals were selected randomly and were cut down (15 individuals for each species). The entire size range of each species was represented accordingly. After cutting down the trees, the above-ground parts of the trees were separated as stem, stem bark, branch, twig (diameter at the base <1 cm) and foliage to measure the above-ground biomass. The total fresh weight of each part was measured in situ. Then, 5 trees from each species were selected and their roots were completely dug out by a mechanical shovel to determine the below-ground biomass. The weight of roots with diameters >2 mm was measured. The entire tissue samples were collected from each part of the trees and representative subsamples were removed using chainsaw and branch clipper to determine water content. All tissues were dried to constant weight at 80°C. The percentage of carbon in all samples was determined using combustion method.

2 Forest floor and soil carbon pool In each plot, we established two 4.0 m×4.2 m (16.8 m2 ) subplots and measured the forest floor litter and understory vegetation by collecting the litter and clipping the vegetation. The collected materials were combined and weighed in situ. Then a subsample was taken and transported to the laboratory and dried at 80°C. Combustion method was used for determining carbon concentrations of different tissues (TSI Incorporated, 2004). In each stand, three plots were selected randomly and a combined soil sample was selected in each plot (totally 12 soil samples). The soil samples were collected down to the depth of 45 cm (0–15, 15– 30 and 30–45 cm). Furthermore, in fallow fields adjacent to each stand, three soil samples were randomly collected as the control treatment. All soil samples were air-dried and sieved (2 mm) prior to determining the total organic carbon by using the Walkley-Black method (Schumacher, 2002). Bulk density was determined for each sample using clod method (Prihar and Hundal, 1971).

3 Calculation of carbon storage and statistical analyses We used regression analysis based on power function to determine the allometric relationship of biomass for different tree components and standing tree variables (Verwijst and Telenius, 1999). The independent variable for AC and EP was diameter at breast height and the total height for M and BL. Then, we applied the derived allometric equations to estimate biomass of standing trees in the plots to upscale biomass and carbon at per stand level. The normality of the data was explored by the Kolmogorov-Smironov test. One-way analysis of variances (ANOVA) was used to test the significant differences in carbon concentration, biomass and carbon pools among the four plantations. Once a significant difference was detected, Tukey’s various range test was applied to examine the difference between the averages of the treatments at the significance level of P<0.05.

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