ESTIMATING ABOVEGROUND BIOMASS AND CARBON SEQUESTRATION FOR NATURAL STANDS OF QUERCUS AEGILOPS. IN DUHOK PROVINCE

Assist. Prof. Prof. Assist. Prof. 1 Dept. of Forestry, Coll. of Agric., University of Duhok, Kurdistan Region, Iraq 2 Dept. of Economics,Coll. of Economics, University of Duhok, Kurdistan Region, Iraq 3 Dept. of Environ. Science, Faculty of Science,University of Zakho, Kurdistan Region, Iraq zeki.akrawee@uod.ac ABSTRACT The study was aimed to develop above ground biomass(AGB) and its component models for an individual tree and stand of Quercus aegilops The benefits of this study are to know the amount of forest biomass to help us to estimate the amount of the lost or emitted carbon during deforestation and will give a clear idea of the forest capacity in capturing and storing carbon C in the forest ecosystem.. The study was conducted in six locations in the northeastern Duhok province in Kurdistan region of Iraq. Twenty-one trees were selected according to their diameter classes and felled to measure fresh weight (FW) and dry weight (DW) from different organs, including (stem, branches, leaves, and whole tree). In addition to, all trees with diameter at breast height (D ≥5 cm) in 89 plots of 0.04 ha, each was measured. Allometric equations of individual trees were used for estimating AGB and its component depending on D only. The DW of AGB and its components were converted into C by multiplying it on a half. The AGB estimated for FW and DW of the entire study area are 157.5285, 115.1153 (Mg ha -1 ) respectively. The results showed that Csequestration in the stands for stems, branches, leaves and the whole tree are 146.005, 73.9333, 31.38121and 249.9924 Mg ha -1 respectively.


‫العراقية‬ ‫الزراعية‬ ‫العلوم‬ ‫مجلة‬
Forests are one of the most important natural resources of wood products. It provides direct and indirect benefits to human beings from economic and environmental aspects (1). Moreover, forests are a basin of carbon dioxide (CO 2 ) due to the photosynthesis process that performs by forests. This leads to reducing the amount of CO 2 from the atmosphere which ultimately diminishes the rate of global warming (15). Carbon is a major global concern Hassoon (6). For that reason, the process of storing carbon in the tree is directly related to its biomass.The AGB estimation becomes a basic necessity for forest management and evaluation (4). Consequently,several studies have been conducted to determine forest production and growth that are concerned with the quantitative output of trees biomass (2) Field-based estimation of biomass is generally performed with two different methods. They are destructive and non-destructive methods (16). The first method is usually achieved by dropping a tree and separating its parts (main stem, branches, leaves, and whole tree) after that, weigh each part separately. The nondestructive method is the most widely used in the estimating above/below-ground biomass also known as allometric equations (7). This procedure does not request to cut down the trees in the forest. Allometric equations are developed through making relationships between different parameters of trees as diameter at breast height, total tree height, tree form, crown diameter, etc.These variables can be used either individually or in combination with each other to estimate AGB. Most models for biomass estimation have been developed and used by the forestry or ecology community. These models normally divide aboveground components into main stem, branches, and leaves parresol (19). In Iraq, Mohammed (12) was the first researcher used allometric equations to estimate AGB of poplar trees in the warso village-Zakho district-governorate of Duhok northern Iraq. More recently, Khalaf (10) was published in his thesis, estimating AGB of Pinus brutiaTen. Performed for three areas (Acre, Atrush and Zaweta) located in Duhok governorate northern Iraq. However, so far there are no equations have been developed to estimate AGB of Quercus aegilopsin Kurdistan region of Iraq. This is the first attempt to develop allometric equations to estimate AGB and its component of oak.Therefore, this study was aimed to determineFW, DW and the amounts of carbonin individual tree and stand.

Measurement of harvested trees
Fieldwork was conducted for three months in 2016 (end of July untilthe ending of October). A total of 89 sample plots of 20 m×20 m were set up and covers an area of 3.56 ha. Plots were distributed in six locationswith different stand density. There were 17 plots in Bady, 19 plots in Rashaur, 12 plots in Banasur, 5 plots in Kamala, 17 plots in Barushka Sadeen and 19 plots in Bilijank.Within these plots, 1322 trees with D ≥ 5cm were measured using diameter tape. Randomly 208 trees were selected for analyzing data and used to estimate AGB with its components. Whereas the rest was used for the purpose of prediction.

Estimating AGB and its components
The first essential step of using the destructive method in the current study was tofelled down 21 trees from the stands with different D. The diameter at the stump d 0.3 m, diameters at breast height (D =1.30 m), diameter above breast height at one-meter intervals beginning at d 2.3 to d 6.3 , total tree height, crown diameter and crown height were measured directly in the field. This is implemented for the purpose of estimating FW, DW, moisture content, and the amount of carbon.The latitude, longitude, and altitude of trees were determined using a GPS device. Trees were sampled in 5 cm diameter classes, starting at 5 cm up to the maximum diameter found in the area. The main stem was cut into sections at one-metre intervals starting at d 0.3 m above the ground to the top of a tree that were weighed directly in the field. Cumulative weights of logs were added to obtain total FW of the main stem. From the large end of each log, a disc was cut to a thickness of 3-5 cm. These sub-samples were directly measured in the field.The crown length was divided into three equal sections: upper, middle and lower (9). Branches were cut into 1 m and then assembled and weighed directly in the field. Asub-sample of each section with a length of 20 cm was taken randomly (5), and then weighed using a scale with a precision of 0.05 g.The leaves were assembled and placed in plastic bags and weighed directly in the field. Randomlyone kg. of these leaves were taken and transferred to the laboratory for drying purposes.The total FW of each individual tree AGB was calculated as the sum of the weights of each tree component (17). Dryweight (DW): Sub-samples of each component of a tree dried at 105 ○ C ±2.

= * ( )
Where DWC is DW of each component of the tree, FWC is FW of eachcomponent of the tree, DWs is DW of each sub-sample, and FWs is the fresh weight of each subsample.The descriptive statistics of the data used for modeling are given in Table (1).

Estimation of AGB in Stand:
Estimating AGB in a stand, need to convert the weight of AGB in an individual tree and its component from Kg. to ton (Mg); then, convert it from ton to ton per hectare (Mg ha -1 ) using the following formula:

= ( )
Where: A is the areaMg ha -1 , and a is an area of our sample plot 400 m 2 Statistical Analysis Eight allometric regression equations were used including: linear, exponential, double reciprocal, logarithmic-X, multiplicative, square root-y, square root-X, and s-curve Table (4). Intricate models involving several variables were not considered to predict AGB because the additional variables increase multi-collinearity and reduce strengthening of the biomass equation (5). Also, transformed variables were not included in the dependent variable or returned to their original form Another important step in evaluating the equations was to perform a graphical analysis of the best-fit equation to assess the appearance of the fitted curves overlaid on the data set.

RESULTS AND DISCUSSION Trees distribution
Afterselecting 208 trees for data analyzing, the non-destructive method was used toestimate AGB and its component using allometric regression equations. Trees were classified into 8 diameter classes, starting from 5 cm to 45cm based on what has been found in the study area.The Dof trees classified and found that the majority of the trees are small in D classes. This is clearly shows in (Figure, 1)as 8.7% located between 5 and 9.9 cm, 15.4% located between 10 and 14.9 cm, and 19.2% between 15 and 19 cm. Medium trees in D classes with 16.8 % located from 20 to 24.9 and 13% located from 25 to 29.9 cm. Larger trees constitute a smaller percentage of tree composition, with 10% located within a range from 30 to 34.9 cm, 8.7% located with a range from 35 to 39.9 cm, and 8.2% located from 40 to 45 cm of the total number being measured.

Figure 1. Distribution of trees by diameterclasses Fresh weight and dry weight (FW and DW)
After analyses AGB of a single tree and its components,using allometric equations. The D was used alone as an independent variable to estimate the FW and DW.From eight allometric regression equations that were used in this study,the best four of them were selected for each component to estimate FW and DW of AGB and its component depending on theirstatistical criteria. This is reported in Tables(3and 4).   Another important step in evaluating an equation of each component of the tree was to perform a graphical analysis. The best-fit equation was tested to check the performance, especially before putting it into widespread use or practice.Broadly, graphs display that there is a very strong relationship between independent variable as diameter and dependent variable as FW and DW of the tree and its component. Furthermore, graphs show that the data didn't aggregate at a given location from the regression line. Samples are distributed along the line or very close to the regression line (Figure, 2). This is evident when the predicted values correlate with the observed values of each equation.

Figure 2. A, B, C, D.Represent the relationship between FWS, FWB, FWL, FWT and (D) respectively, whilea, b, c, drepresent observedvs. predicted for selected equation. Also E, F, G, H represent the relationship between DWS, DWB, DWL and DWT and (D) respectively, while a, b, c, d represent observed vs. predicted for selected equation AGB of Individual tree
Many conducted biomass assessment studies in forestry were focused on AGB (11,21). This is due to the fact that AGB accounts for the majority of the total accumulated biomass in the forest ecosystem. This study also focuses on the assessment of AGB of natural oak located in Duhok province. FW and DW were extracted for each individual tree and its component in kg based on their diameter classes. The mid-point of each diameter class, compensate inthe equation that has been selected according to fit test statistic, FW and DW of each individual tree and its component was estimated as shows in (Table, 6). Consequently, the weight of AGB and its components can be estimated for all regions that are presented in the study area.It is also, noticed that the weight of the main stem of a tree is approximately twice the weight of branches, whether it is FW or DW. In contrast, weight of branches per tree is roughly double weight of leaves (Figure, 3).

Figure 3. FW and DW of AGB and its components for oak AGB of Stands
The weight of AGB and its components for each region(Mg ha -1 ) was estimated based on the total number of trees in that area (Table,  7). There is a clear difference in the number of plots taken from each region. The largest numbers of plots werelocated in the region of Rashaur and Bilijank as 19 plots in each region with diameter means 10.84 -11.62 cm respectively. While smallernumbers of plots werelocated in the Kamala region, 5 plots with diameter means10 cm. The main reason for the differences in the number of trees in each regionis due to the nature of tree distribution in those areas, as well as to the density of the number of trees in each plot. As a result, this leads to a different weight of each component of the tree. In addition, the differences in the average diameter of trees in each region have led to differences in the biological weight of trees and their components regardless of the number of trees in that area.

Carbon storage estimation
The amount of carbon in the stem, branches, leaves and whole tree was calculated by multiplying the DW of each component of an individual tree by 50% (Table 8) it represents carbon sequestered in the tree (14). In another word, it refers to the total amount of carbon that is captured from the atmosphere during photosynthesis, as well as the amount of carbon sequestered by the tree. The results in (Table, 8)reveal carbon content values for an individual tree, based on their diameter values. Also, shows that the amounts of carbon that stored in older trees are larger than younger trees and this was confirmed by West and Marland (22). The results in (Table, 9)show the weight of carbon stored in the stands (Mg ha -1 ) for each region. Moreover the weight of carbon stored in the main stem, branches, leaves and whole tree. It was found the largest amount of carbon stock was concentrated in the main stem of the tree and lowest in the branches and the very lowest in tree leaves. Most researchers confirmed that the main stem represents the largest amount of carbon of the total biomass of trees, ranging from 50 to 92% for different species of trees (3,13,20). The results of this study fall within the range of 58.10%. While the amount of carbon sequestration in the branches and leaves was29.42%, 12.49%respectively. There is a clear differencesamong diameter means from one region to another that led to a differenes in weight of carbon stock in the parts of the tree. Moreover, a differences in the number of trees and the number of plots taken from each region was also observed. The number of trees and their plots were converted into hectares for the purpose of determining the amount of carbon stored in these areas, depending on the difference in the average diameter of trees per region.The results showed that the total carbon weight in these areas was 249.