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Biomass of Rhizophora apiculata forest Dang Trung Tan Minh Hai Centre for Mangrove Forest Technique Application
I. Introduction Of the s...
Biomass of Rhizophora apiculata forest Dang Trung Tan Minh Hai Centre for Mangrove Forest Technique Application
I. Introduction Of the studies on mangrove forest. study on biomass is an important link due to its scientific and practical significance. According to Prof. B.F. Clough and K. Scott of Marine Science Institute. Australia. then “estimates in biomass and development rates constitute a basis for the estimation of total pure primary productivity in the ecological studies and the evaluation of benifits from forest economic products and for more perfect silvicultural methods”. Therefore many scientists at home and abroad have conducted research on this matter thereby different research methods have been applied. research results have been widely published providing a base for reference and comparison. Those are studies by Ong. 1985. Putz and Chan. 1986. B.F. Clough and K. Scott. 1989. abroad and Nguyen Quang Tri. 1986. Vien Ngoc Nam. Nguyen Son Thuy research on Rhizophora apiculata forest biomass in Can Gio. 1991. Nguyen Van Be – research on R. apiculata forest biomass in Ben Tre. 1999 in home country. Ca Mau is the province of largest area of R. apiculata in the whole country meanwhile research on R. apiculata forest biomass here so far has not really been adequate especially on R. apiculata forest plantation. That is why there must be an all-sided study. representative for the whole region on R. apiculata forest plantation.
II. Research methodology To estimate the R. apiculata forest plantation it must be first of all to formulate correlation equation between biomass and diameter of the forest tree. From this correlation equation forest biomass at each age class can be determined. With correlation equation between biomass and age of the forest we can estimate the forest biomass. Thus there are two methods.
1. Formulating correlation equation between diameter (DBH) and biomass Based on method by B.F. Clough and K. Scott i.e.: With real situation of existing forest ages in Ca Mau from 1 to 13. 22 and 34 we decided to choose the forest ages to gather the biomass 5. 13. 22 and 34. The number of trees that are cut down for collecting the biomass in each age class varies from 6 to 16 and total number of trees cut down for measurement and weighing is 105. A permanent sampling plot 100m2 to 1.500m2 is established for each age class. The plot area depends on the forest age and the variation coefficient of the trees. If the variation coefficient is too high a plot of larger area is established to ensure the allowed number of trees. Diameter measurement is conducted for all the trees in a plot and diameter are grouped into different diameter classes. From occurrence frequency of diameter groups. a number of trees are selected to be cut down to collect the biomass based on the ratio between the groups. Selected trees in a plot of a forest age class are cut down and devided into component parts: Leaves. branches. stem and aerial roots. Total fresh weight of each component part is determined right in the forest and the sub-samples of the component parts (0.5-1 kg each sub-sample) are brought to the laboratory where they are oven-dried to constant temperature of 800oC. Total dry weight of each component part is calculated from ratio between dry weight and fresh weight of corresponding sub-sample. As regards specific gravity of R. apiculata stem. it is usually determined from dry weight. length and average diameter of the section (0.51m) of the fresh stem. However in the field work there are some too big trees (nearly 30cm in diameter) that are hardly to be brought to the laboratory to dry in an oven. Therefore we do collect smaller samples determining fresh weight in the forest and bring them to the laboratory for volume measurement by displacement method (put the sample in the water. examining the different levels of the water) and then have the samples kiln dried. Specific gravity of the stem is then calculated. After determining the dry weight of each component part of the R. apiculata trees the samples of which have been collected. the formulation of correlation coefficient between diameter (DBH) and biomass is proceeded. The equation takes the form: Log biomass = A + B log DBH (1) This formula can be turned into: Biomass
= AP.DBH
(2)
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Where B has the same value in formula (1) and AP is Antilog of A in formula (1). 2. Method of estimating R. apiculata biomass: To determine rather accurately the R. apiculata forest biomass in the two provinces Ca Mau and Bac Lieu we have conducted the measurement and counting in 60 permanent sampling plots with all the forest ages existing in this region. The plots lie sparsely in the forest stand with different site types. at different tidal regimes but with the same initial planting density: 20.000 trees/ha; the forest has not yet been thinned and has been little interfered by human activities and natural forces. These permanent sampling plots all satisfy the required number of trees to be measured. depending the variation coefficient of each age class and sampling plot. The same as the case of selection of trees to collect biomass. each plot is from 100m2 to 1.500m2 in area with at least 3 replicates. Diameters breast high. D1.3. of all the trees are measured. With each and every plot after measurement of the diameter of all the trees in the plot and based on the established correlation equation between diameter and biomass. biomass is calculated for each plot and per ha. After obtaining the biomass of the plots in different forest ages. the correlation between the biomass and forest age is established.
III. Research results 1. Result of formulation of correlation equation between diameter and biomass With data on diameter and dry weight of the component parts stem. branches. leaves. roots and total dry weight obtained from 105 R. apiculata trees as mentioned above and through calculation. the following correlation equations are obtained: -Correlation equation between biomass and DBH: Y = 0.1709 x 2.5627 with R2 =0.9928; -Correlation equation between root biomass and DBH: Y = 0.17090026 x 3.1356 with R2 =0.9647; -Correlation equation between leaf biomass and DBH: Y = 0.0348 x 1.8706 with R2 =0.9128; -Correlation equation between stem biomass and DBH: Y = 0.1347 x 2.547 with R2 =0.9947; -Correlation equation between branch biomass and DBH: Y = 0.6177 x 2.645 with R2 =0.9306; (According to formula 2: Biomass = Ap.DBHBB) Where Y = biomass Ap = Antilog of A X is D1.3 (DBH) B is constant From these equation we can establish the relation of various component parts of R. apiculata with diameter class (DBH). See Table 1 Table 1. Correlation between dry biomass of various component parts of R. apiculata and diameter (DBH). DBH (cm) 1
Total dry weight (kg) 0.17
Total stem dry Total branch dry Total leaves dry weight (kg) weight (kg) weight (kg) 0.13 0.02 0.03
Total root dry weight (kg) 0.00
2
1.01
0.79
0.11
0.13
0.02
3
2.85
2.21
0.32
0.27
0.08
4
5.97
4.60
0.67
0.47
0.20
5
10.57
8.12
1.21
0.71
0.40
6
16.86
12.92
1.95
0.99
0.72
7
25.03
19.14
2.92
1.33
1.16
8
35.24
26.89
4.15
1.70
1.76
9
47.66
36.29
5.65
2.12
2.55
10
62.44
47.46
7.46
2.58
3.55
11
79.71
60.51
9.57
3.09
4.79
12
99.62
75.52
12.03
3.63
6.29
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13 14
122.31 147.89
92.59 111.83
14.84 18.03
4.22 4.85
8.09 10.20
15
176.49
133.31
21.61
5.52
12.67
16
208.23
157.13
25.60
6.22
15.51
17
243.23
183.37
30.01
6.97
18.76
18
281.60
212.10
34.87
7.76
22.44
19
323.45
243.42
40.18
8.58
26.58
20
368.89
277.39
45.98
9.45
31.22
21
418.02
314.09
52.26
10.35
36.39
22
470.94
353.60
59.04
11.29
42.10
23
527.77
395.99
66.35
12.27
48.40
24
588.59
441.33
74.19
13.29
55.30
25
653.50
489.69
82.58
14.34
62.86
26
722.59
541.13
91.53
15.43
71.08
27
795.97
595.73
101.06
16.56
80.01
28
873.72
653.55
111.18
17.73
89.68
29
955.94
714.65
121.91
18.93
100.11
30
1042.70
779.10
133.25
20.17
111.34
31
1134.11
846.97
145.23
21.44
123.39
32
1230.24
918.30
157.85
22.76
136.31
33
1331.18
993.17
171.12
24.11
150.31
34
1437.02
1071.63
185.07
25.49
164.85
35
1547.84
1153.74
199.70
26.91
180.53
2. Research results on correlation between biomass of R. apiculata forest and forest age in Ca Mau province. To formulate the correlation equation between biomass of R. apiculata forest and forest age in Ca Mau province we carried out the counting and measurement is all the 64 permanent sampling plots at different age classes in Ca Mau including ages: 4. 5. 6. 7. 8. 9. 10. 11. 12. 22 and 34. In these permanent sampling plots measurement of diameter was done with all the trees. From diameter of each tree by application of correlation equation between diameter and biomass. biomass is calculated for each tree and each permanent sampling plot and then biomass per hectare. From the obtained data on forest age and total dry weight we have formulated 2 correlation equations as follows (exponent and log equations):
And
Y = 146469 Ln (X) –193837 with R2 = 0.9217 equation (1) Y = 352.01 x 2 + 23506 X – 61973 with R2 =0.9241–equation (2)
From equation (1) we construct correlation table between forest age and R. apiculata forest biomass in Ca Mau (Table 2). Table 2: Correlation between total biomass and forest age in Ca Mau
IV. Discussion and conclusions 1. As regards correlation equation between DBH and biomass: In the correlation equation formulated there is a very close correlation. generally with R2 > 0.9 in all component parts. In this report only with leaves the correlation is least close. R2 =0.9128 but still acceptible as according to Clough. leaf biomass changes in seasons and is also easily affected by strong winds. Moreover the ratio of leaf biomass is very low (lower than 10%) in the total above-ground biomass of R. apiculata > 10cm in diameter. Thus leaf biomass generally is not highly significant and it does not affect total above-ground biomass. There is not much difference between the correlation equation between diameter (DBH) and biomass given in this report with those by Clough. Ong. Putz and Chan. especially with trees of high diameter classes. But as compared with that by Vien Ngoc Nam formulated for R. apiculata in Can Gio-Ho Chi Minh City. it does differ greatly. May be it is due to the difference of the studied targets and research methodology. Total dry weight (kg) Species
DBH (cm)
Clough
Ong
Rhizophora apiculata
5 10 15 20 25 30
8 51 151 327 595 970
11 58 154 309 530
34
1358
Putz and Chan 10 56 156 321 562
Nam 14 53 116 221 309 437
Tan (This report) 10 62 176 368 653 1042
555
1437
2.Estimation of biomass of R. apiculata in Ca Mau In formulating table of correlation between total biomass and forest age in Ca Mau. permanent sampling plots were established with existing age classes: 4 to 12. 22 and 34. There is a lack of classes of forest age from 13 to 21 and from 23 to 33. Due to this reason the correlation equation is not yet complete. However this is a real fact and the above equation is temporarily accepted. It is found in correlation table that the oldest forest in Ca Mau now is 34 years with total dry weight of 32.7 m3/ha. Annual biomass increment is 9.500 kg/ha and at age 6 it is highest: 26.704 kg/ha. The increment decreases with increased age and at age 35 it attains only 4.245 kg/ha/year. Similarly. mean annual tree diameter increment of R. apiculata forest is 0.620 cm and that of age class 4 is 0.644 and it gradually decreases to 0.596 in 34-year old forest. References: 1. Clough and Scott. 1989: Allometric mangrove species.
relationship for estimating above-ground biomass in six
2. Dang Trung Tan. 1998: Report of research subject: “Study on growth and increment of Melaleuca leucadendron and Rhizophora apiculata in main site types in Minh Hai” 3. Dang Trung Tan. 1998: report on tidal submersion level on the development of forest. 4.FAO. 1994: mangrove forest management guidelines. 5. Thach Phu: Forest and fishery enterprise. Ben Tre province. Forest inventory and planning subInstitute. Report on R. apiculata forest increment survey. 6. Nguyen Hai Tuat: Agriculture Publishing House. 1992 Statistics in forestry. 7. Vien Ngoc Ham. Nguyen Son Thuy. 1994: R. apiculata forest biomass in Can gio.
