_{1}

^{*}

Forty-three trees (23 Rhizophora mucronata and 20 Avicennia marina) were studied for the establishment of allometric relationships between the aboveground biomass “y” and the following dendrometric variables “x”: diameter at breast height DBH, (DBH)2 product Ht (where Ht is the total height), and the basal circumference Cb of the trees. The Log y = A Log [(DBH)2·Ht] + B equation gives a fairly satisfactory regression coefficient (R2 > 0.9) for the woody compartments. For A. marina, it is the equation Log y = A Log Cb + B that is the best correlated for the estimation of less woody compartments (R2 = 0.826 to 0.847). As for R. mucronata, these are much more related to DBH. For trees of 8 - 10 m height, the aboveground biomass of the delta is higher (171 t·ha-1 for R. mucronata) than that of Puerto Rico, but quite comparable to that of Australia (110 t·ha-1 for A. marina). The first tools for estimating aboveground biomass are given for these two characteristic species of the Indo-Pacific Region and East Africa. Because of the low values of the regression coefficients for some allometric relationships obtained, precautions should be taken in case of extrapolation.

Covering nearly 327,000 ha [

According to [

Very few reliable scientific data exist on Malagasy mangroves [

To compensate for these shortcomings, the present article tries to provide quantitative data on the aerial phytomass of the two species characteristic of the Mangoky Delta, namely Avicennia marina Vierh. (Avicenniaceae) and Rhizophora mucronata. It tries to establish allometric relationships between the aboveground biomass, the diameter at breast height, and the total height and basal circumference of trees. The mathematical models thus established will constitute specific tools for the practical estimation of the production potential in aboveground biomasses of the two Mangrove species of the Mangoky Delta―SW Madagascar.

Located on the South-West coast of Madagascar, the study area concerns the Mangoky Delta (

Forty-three trees (23 Rhizophora mucronata and 20 Avicennia marina) were selected and fell to the ground on October 2009. These operations were preceded by a floristic inventory of the trees, which was carried out in four 100 m linear transects (

After felling the trees, the following main dendrometric parameters were measured on the site itself:

- Height of the stem “Hf”;

- Height of the crown “Hh”;

- Total height of the tree “Ht = Hf + Hh”;

- Width of the crown “Lh”;

- Circumference of the stem at the base, on the ground “Cb”;

- Diameter of the tree at 1.30 m from the ground “DBH”.

The entire aerial part of each tree was weighed on site, distinguishing foliage, boughs (less than 2 cm in diameter), branches (woody part of more than 2 cm in diameter located above first branch) and the stem (woody part below the first branch). The weight of hard wood (whole stem and branches) was calculated.

5 cm < DBH < 10 cm | 10 cm < DBH < 15 cm | 15 cm < DBH < 20 cm | 20 cm < DBH < 25 cm | TOTAL | |
---|---|---|---|---|---|

Avicennia marina | 5 | 5 | 5 | 5 | 20 |

Rhizophora mucronata | 5 | 5 | 8 | 5 | 23 |

TOTAL | 10 | 10 | 13 | 10 | 43 |

The aerial roots of Rhizophora mucronata were also weighed. The fruits and the flowers, not very abundant on the felled trees, were not taken into account. For each tree and for each compartment, samples were taken, weighed and placed in an oven (105˚C) during 72 hours, and this, in order to deduce the weight of dry phytomass.

The modeling of the dry biomass of felled trees was carried out from the logarithmic equation:

or whether:

where y represents dry biomass, x a variable defined from the measured dimensions of the tree such as DBH, (DBH)^{2}∙Ht and Cb.

The linearity of established logarithmic regressions was verified from the correlation coefficient R^{2}, which is considered significant from 0.9.

At least 6 species of Mangrove are present in the studied delta: Avicennia marina, Xylocarpus granatum Koen. (Meliaceae), Ceriops tagal C. B. Rob. (Rhizophoraceae), Rhizophora mucronata, Bruguiera gymnorhiza, and Sonneratia alba. The average height of trees varies from 8.3 to 9.2 m, respectively for the facies with A. marina and R. mucronata. Their average diameter is 14 cm (with a minimum of 6.37 cm and a maximum of 23.57 cm) for the first and 15 cm (with a minimum of 6.05 cm and a maximum of 21.34 cm) for the second.

The total above ground biomass varies between 9 and 235 kg per tree for Avicennia marina. It is from 11 to 360 kg for Rhizophora mucronata. The arithmetic averages obtained are respectively around 110 kg and 173 kg per tree for both species (

Tree N˚ | DBH (cm) | Hf (cm) | Hh (cm) | Ht (m) | Lh (cm) | Cb (cm) | Stem (kg) | Branches (kg) | Hard wood (kg) | Boughs (kg) | Leaves (kg) | Total (kg) |
---|---|---|---|---|---|---|---|---|---|---|---|---|

38 | 6.37 | 90 | 420 | 5.10 | 400.00 | 25.00 | 2.90 | 4.74 | 7.64 | 0.58 | 0.83 | 9.05 |

39 | 6.69 | 180 | 400 | 5.80 | 300.00 | 30.00 | 6.44 | 4.43 | 10.87 | 1.46 | 1.65 | 13.98 |

27 | 7.32 | 200 | 400 | 6.00 | 400.00 | 39.00 | 7.73 | 6.01 | 13.74 | 1.75 | 2.27 | 17.76 |

36 | 7.64 | 110 | 540 | 6.50 | 160.00 | 34.00 | 7.09 | 15.81 | 22.90 | 1.46 | 2.68 | 27.04 |

40 | 8.60 | 100 | 370 | 4.70 | 250.00 | 27.00 | 3.87 | 7.59 | 11.46 | 0.88 | 0.62 | 12.95 |

10 | 12.74 | 350 | 620 | 9.70 | 270.00 | 59.00 | 27.70 | 26.56 | 54.27 | 2.34 | 3.10 | 59.70 |

32 | 14.33 | 200 | 500 | 7.00 | 350.00 | 52.00 | 19.97 | 39.21 | 59.19 | 5.26 | 4.95 | 69.40 |

12 | 14.97 | 320 | 620 | 9.40 | 350.00 | 70.00 | 41.88 | 31.62 | 73.50 | 11.10 | 11.97 | 96.57 |

17 | 14.97 | 300 | 500 | 8.00 | 375.00 | 124.00 | 90.20 | 92.97 | 183.17 | 14.02 | 14.03 | 211.23 |

23 | 14.97 | 600 | 650 | 12.50 | 450.00 | 55.00 | 75.38 | 16.44 | 91.83 | 1.75 | 2.89 | 96.47 |

35 | 15.29 | 210 | 500 | 7.10 | 400.00 | 72.00 | 31.57 | 49.33 | 80.90 | 4.09 | 4.54 | 89.53 |

31 | 16.24 | 250 | 550 | 8.00 | 450.00 | 58.00 | 30.93 | 46.17 | 77.10 | 4.67 | 5.37 | 87.14 |

16 | 16.88 | 290 | 390 | 6.80 | 500.00 | 100.00 | 51.54 | 56.92 | 108.47 | 12.27 | 11.97 | 132.70 |

30 | 16.88 | 200 | 600 | 8.00 | 400.00 | 63.00 | 32.21 | 36.68 | 68.90 | 3.80 | 3.71 | 76.41 |

34 | 18.15 | 150 | 600 | 7.50 | 450.00 | 50.00 | 39.95 | 84.12 | 124.07 | 6.43 | 7.02 | 137.51 |

11 | 20.38 | 350 | 700 | 10.50 | 550.00 | 80.00 | 74.09 | 69.57 | 143.67 | 8.76 | 9.08 | 161.51 |

13 | 20.70 | 320 | 700 | 10.20 | 620.00 | 123.00 | 96.64 | 98.03 | 194.68 | 15.19 | 23.53 | 233.39 |

26 | 21.34 | 310 | 1000 | 13.10 | 520.00 | 90.00 | 70.87 | 139.15 | 210.02 | 4.67 | 6.60 | 221.29 |

15 | 21.97 | 310 | 750 | 10.60 | 550.00 | 85.00 | 103.08 | 104.99 | 208.08 | 13.44 | 13.62 | 235.13 |

18 | 23.57 | 370 | 600 | 9.70 | 550.00 | 97.00 | 96.64 | 88.55 | 185.19 | 13.44 | 11.14 | 209.77 |

Tree N˚ | DBH (cm) | Hf (cm) | Hh (cm) | Ht (m) | Lh (cm) | Cb (cm) | Stem (kg) | Branches (kg) | Hard wood (kg) | Boughs (kg) | Leaves (kg) | Roots (kg) | Total (kg) |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|

37 | 6.05 | 120 | 350 | 4.70 | 250.00 | 25.00 | 3.39 | 4.11 | 7.50 | 1.42 | 1.70 | 0.60 | 11.23 |

7 | 6.69 | 260 | 140 | 4.00 | 160.00 | 24.00 | 8.15 | 6.32 | 14.47 | 0.47 | 0.85 | 6.03 | 21.82 |

41 | 6.69 | 180 | 330 | 5.10 | 230.00 | 31.00 | 6.11 | 8.22 | 14.33 | 1.66 | 4.68 | 6.03 | 26.69 |

6 | 7.64 | 470 | 250 | 7.20 | 250.00 | 29.00 | 15.62 | 6.32 | 21.93 | 1.19 | 1.06 | 6.03 | 30.21 |

14 | 8.92 | 340 | 340 | 6.80 | 300.00 | 28.00 | 15.62 | 10.11 | 25.73 | 2.37 | 2.55 | 14.46 | 45.12 |

1 | 10.19 | 440 | 600 | 10.40 | 450.00 | 33.00 | 30.21 | 13.90 | 44.12 | 3.09 | 4.89 | 12.96 | 65.05 |

3 | 10.19 | 600 | 450 | 10.50 | 400.00 | 40.00 | 42.77 | 18.33 | 61.10 | 2.85 | 2.55 | 15.07 | 81.57 |

2 | 10.51 | 550 | 400 | 9.50 | 400.00 | 36.00 | 32.59 | 7.90 | 40.49 | 1.66 | 1.91 | 9.04 | 53.10 |

8 | 12.10 | 580 | 450 | 10.30 | 280.00 | 48.00 | 51.60 | 30.97 | 82.56 | 4.75 | 5.32 | 16.87 | 109.50 |

4 | 14.97 | 550 | 450 | 10.00 | 550.00 | 47.00 | 69.93 | 42.34 | 112.27 | 10.45 | 9.36 | 43.39 | 175.47 |

22 | 15.29 | 420 | 600 | 10.20 | 450.00 | 57.00 | 64.50 | 56.88 | 121.37 | 6.65 | 8.08 | 66.29 | 202.39 |

24 | 15.29 | 700 | 550 | 12.50 | 400.00 | 55.00 | 90.98 | 41.08 | 132.05 | 5.22 | 7.66 | 66.89 | 211.83 |

9 | 15.92 | 320 | 400 | 7.20 | 550.00 | 52.00 | 46.85 | 74.57 | 121.42 | 13.77 | 14.47 | 43.39 | 193.04 |

21 | 17.20 | 480 | 550 | 10.30 | 400.00 | 59.00 | 75.36 | 48.03 | 123.39 | 4.27 | 10.21 | 90.39 | 228.27 |

5 | 18.15 | 570 | 400 | 9.70 | 500.00 | 65.00 | 101.84 | 31.60 | 133.44 | 8.07 | 6.38 | 42.18 | 190.07 |

20 | 18.15 | 800 | 450 | 12.50 | 450.00 | 66.00 | 152.08 | 22.12 | 174.20 | 2.85 | 5.11 | 75.33 | 257.48 |

28 | 18.79 | 550 | 550 | 11.00 | 550.00 | 64.00 | 135.78 | 82.15 | 217.94 | 5.70 | 9.79 | 113.29 | 346.72 |

33 | 19.75 | 210 | 550 | 7.60 | 600.00 | 65.00 | 43.45 | 119.44 | 162.89 | 14.72 | 18.72 | 75.93 | 272.26 |

25 | 20.38 | 640 | 470 | 11.10 | 450.00 | 66.00 | 127.64 | 60.04 | 187.67 | 8.07 | 9.79 | 66.29 | 271.82 |

19 | 20.70 | 550 | 700 | 12.50 | 450.00 | 63.00 | 116.77 | 88.47 | 205.25 | 6.65 | 11.49 | 90.39 | 313.78 |

42 | 20.70 | 210 | 550 | 7.60 | 600.00 | 65.00 | 42.77 | 119.44 | 162.21 | 14.72 | 18.72 | 38.57 | 234.22 |

29 | 21.34 | 670 | 500 | 11.70 | 550.00 | 73.00 | 175.84 | 69.52 | 245.36 | 7.12 | 9.79 | 97.62 | 359.89 |

43 | 21.34 | 400 | 550 | 9.50 | 500.00 | 72.00 | 112.70 | 86.58 | 199.28 | 13.77 | 15.74 | 42.79 | 271.58 |

With Avicennia marina, the Log y = A Log [(DBH)^{2}・Ht] + B equation has a correlation coefficient greater than 0.9 for the more woody compartments such as hardwood (R^{2} = 0.931) and the stem (R^{2} = 0.908). The use of the variable (DBH)^{2}. Ht is also quite satisfactory (R^{2} = 0.92) in the case of the total aboveground biomass (

This observation is verified in Rhizophora mucronata (^{2} value for the roots is less significant (0.839) under the formula Log y = A Log [(DBH)^{2}・Ht + B]. As for the total aboveground biomass, the coefficient remains the same (R^{2} = 0.959) as well as with Log y = A Log [(DBH)^{2}・Ht] + B and Log y = A Log DBH + B.

It is the Log y = A Log Cb + B equation that is the most correlated for the estimation of less woody compartments such as the leaves and boughs of A. marina, and this, despite the low value of R^{2} (respectively 0.847 and 0.826). It is the same for the branches where R^{2} = 0.876.

Despite the low value of R^{2} (0.734 to 0.865), it is with the DBH variable that we obtain the best correlation for estimating the weight of branches, leaves and boughs of R. mucronata. With a regression coefficient of 0.93 for both hard woods and total aboveground biomass, the use of basal circumference coefficient Cb is not as conclusive as the use of DBH or [(DBH)^{2}・Ht.

VARIABLE x | COMPARTMENT | A | B | R^{2} | n |
---|---|---|---|---|---|

DBH | Hard wood | 2.47 | −1.018 | 0.924 | 20 |

(DBH)^{2}・Ht | Hard wood | 0.967 | −1.284 | 0.931 | 20 |

Cb | Hard wood | 2.06 | −1.854 | 0.853 | 20 |

DBH | Branches | 2.441 | −1.276 | 0.876 | 20 |

(DBH)^{2}・Ht | Branches | 0.928 | −1.444 | 0.833 | 20 |

Cb | Branches | 1.999 | −2.046 | 0.78 | 20 |

DBH | Leaves | 1.89 | −1.481 | 0.674 | 20 |

(DBH)^{2}・Ht | Leaves | 0.73 | −1.658 | 0.661 | 20 |

Cb | Leaves | 1.838 | −2.699 | 0.847 | 20 |

DBH | Stem | 2.526 | −1.432 | 0.867 | 20 |

(DBH)^{2}・Ht | Stem | 1.008 | −1.770 | 0.908 | 20 |

Cb | Stem | 2.186 | −2.523 | 0.862 | 20 |

DBH | Boughs | 2.019 | −1.699 | 0.707 | 20 |

(DBH)^{2}・Ht | Boughs | 0.755 | −1.796 | 0.65 | 20 |

Cb | Boughs | 1.894 | −3.000 | 0.826 | 20 |

DBH | Total | 2.399 | −0.873 | 0.915 | 20 |

(DBH)^{2}・Ht | Total | 0.938 | −1.125 | 0.92 | 20 |

Cb | Total | 2.032 | −1.745 | 0.872 | 20 |

LEGEND: y = phytomass of dry matter in kg; DBH in cm; Ht in m; Cb in cm; R^{2}: regression coefficient of the equation Log y = A Log x + B, i.e. y = kx^{A} such that B = Log k; n = number of trees felled during sampling.

VARIABLE x | COMPARTMENT | A | B | R^{2} | n |
---|---|---|---|---|---|

DBH | Hard wood | 2.382 | −0.799 | 0.962 | 23 |

(DBH)^{2}・Ht | Hard wood | 0.921 | −1.060 | 0.973 | 23 |

Cb | Hard wood | 2.679 | −2.699 | 0.934 | 23 |

DBH | Branches | 2.334 | −1.174 | 0.865 | 23 |

(DBH)^{2}・Ht | Branches | 0.851 | −1.268 | 0.777 | 23 |

Cb | Branches | 2.603 | −3.000 | 0.826 | 23 |

DBH | Leaves | 1.831 | −1.319 | 0.746 | 23 |

(DBH)^{2}・Ht | Leaves | 0.661 | −1.367 | 0.658 | 23 |

Cb | Leaves | 2.074 | −3.000 | 0.735 | 23 |

DBH | Stem | 2.334 | −0.987 | 0.834 | 23 |

(DBH)^{2}・Ht | Stem | 0.947 | −1.387 | 0.928 | 23 |

Cb | Stem | 2.633 | −3.000 | 0.815 | 23 |
---|---|---|---|---|---|

DBH | Roots | 2.779 | −1.721 | 0.828 | 23 |

(DBH)^{2}・Ht | Roots | 1.076 | −2.046 | 0.839 | 23 |

Cb | Roots | 3.084 | −3.699 | 0.782 | 23 |

DBH | Boughs | 1.872 | −1.481 | 0.734 | 23 |

(DBH)^{2}・Ht | Boughs | 0.682 | −1.553 | 0.659 | 23 |

Cb | Boughs | 2.081 | −3.000 | 0.697 | 23 |

DBH | Total | 2.373 | −0.606 | 0.959 | 23 |

(DBH)^{2}・Ht | Total | 0.913 | −0.851 | 0.959 | 23 |

Cb | Total | 2.668 | −2.398 | 0.930 | 23 |

LEGEND: y = phytomass of dry matter in kg; DBH in cm; Ht in m; Cb in cm; R^{2}: regression coefficient of the equation Log y = A Log x + B, i.e. y = kx^{A} such that B = Log k; n = number of trees felled during sampling.

The types of Equations (1) and (2) have been used by many authors to estimate aboveground biomass in Kenya [^{2}∙Ht to estimate it.

The present study tries to value the gains of the equations developed by these various authors by adapting them with the variables of the different compartments of a Mangoky Delta tree (

With 60 t・ha^{−1} of total aboveground biomass, (all species combined, average tree height = 5.83 m, mean DBH = 8 cm), the Mangoky Delta Mangrove is comparable to that of West Africa where [^{−1} at Saloum, for trees of 5.65 m high. It should be noted that in Puerto Rico, Mangrove yields 58 t・ha^{−1} year^{−1} of raw primary products and 9 t・ha^{−1} year^{−1} of net primary products [

As part of this study, where tree total heights were 8.3 m and 9.2 m, respectively for Rhizophora mucronata (DBH = 15 cm) and Avicennia marina (DBH = 14 cm), the respective total biomass values of 110 t・ha^{−1} and 171 t・ha^{−1} are important compared to the figures found by [^{−1} for R. mucronata. However, they are comparable to those measured in Australia where [^{−1} for trees of A. marina of 8.5 m high; and where [^{−1} for strata of 7 m. In the USA, [^{−1} for the species Rhizophora spp. of 9 m high. Those differences are surely linked to latitudinal and longitudinal variations of the studied ecosystems [^{−1} for the R. mucronata species in Sri Lanka (8˚2'S), compared to 452.02 t・ha^{−1} in Kenya (4˚25'S) according to [

The data on the share of the different compartments in the biomass constitution are comparable to the figures obtained by [

For Rhizophora, the expression of total aboveground biomass can be written in two forms:

Log y = 2.371 Log DBH − 0.606;

Log y = 0.913 Log [(DBH)^{2}・Ht] − 0.851.

In either equation, the regression coefficient remains the same (R^{2} = 0.959). The values of A and B presented in this study are substantially similar to those found by [

Regarding hardwood (=stem + branches), the most significant allometric relationships established in this study are:

Log y = 0.921 Log [(DBH)^{2}・Ht] − 1.060 for R. mucronata where R^{2} = 0.973;

Log y = 0.967 Log [(DBH)^{2}・Ht] − 1.284 for A. marina where R^{2} = 0.931.

Using the variable DBH, the relationship becomes less significant (R^{2} = 0.962 for R. mucronata and 0.924 for A. marina); the differences in value between [

Regarding the Avicennia marina species, the equation Log y = 2.47 Log DBH − 1.018 obtained in the Mangoky Delta is relatively similar to that established by [

The most significant allometric relationships found in the Mangoky Delta are:

Log y = 1.831 Log DBH − 1.319 for R. marina where R^{2} = 0.746;

Log y = 1.838 Log Cb − 2.699 for A. marina where R^{2} = 0.847.

The regression coefficient on R. marina obtained in the delta has a mean value compared to that found by [^{2} values remain insignificant for the Rizophora and Avicennia leaves. Constituting 2% to 10% of the total biomass, leaf weight is insignificant and variable (

The most significant allometric relationships found in the Mangoky Delta are:

Log y = 2.334 Log DBH − 1.174 for R. marina where R^{2} = 0.865;

Log y = 2.441 Log DBH − 1.276 for A. marina where R^{2} = 0.876.

The equation of [

It is with the variable (DBH)^{2}・Ht, more precisely with the allometric relationship Log y = 1.076 Log [(DBH)^{2}・Ht] − 2.046 (where R^{2} = 0.839) that the best correlation was found for the roots of R. mucronata of the study area.

Based on a destructive method experimented directly in situ, this study has an interest that lies in the availability of the first tools for estimating the aboveground biomass of R. mucronata and A. marina, two main Mangrove species of the Indo-Pacific Region and East Africa, including the Mangoky Delta. The first more targeted equations adapted to sub-regional contexts are now available to

Compartment | Based on this study, Mangoky Delta in Madagascar | According to [ | ||
---|---|---|---|---|

Rhizophora mucronata | Avicennia marina | Rhizophora mucronata | Ceriops tagal | |

Stem | 40 ± 12.4 | 40 ± 11.2 | 50.2 ± 16.3 | 27.0 ± 7.3 |

Branch > 2 cm | 26 ± 9.6 | 47 ± 11.6 | 9.7 ± 4.8 | 28.5 ± 6.9 |

Boughs < 2 cm | 4 ± 2.5 | 6 ± 2.5 | ||

Leaves | 6 ± 3.8 | 7 ± 3 | 15.2 ± 4.8 | 14.2 ± 6.7 |

Aerial roots | 24 ± 7.6 | 24.9 ± 15.4 | 30.3 ± 8.0 |

complement those already established at larger scales. However, given the lack of baseline data on the productivity of Malagasy Mangroves on the one hand, and because of the small values of the regression coefficients obtained on certain allometric relationships, precautions should be taken in case of extrapolation. It is therefore essential to multiply allometric studies and those on the productivity of Malagasy and East African Mangroves. In any case, the results of this paper can already serve as the first modeling tools for the two main and most widespread species in Madagascar, East Africa and the Indian Ocean.

The authors declare no conflicts of interest regarding the publication of this paper.

Rakotomavo, A. (2018) Aboveground Biomass Estimation of Avicennia marina (Forssk) Vierh. and Rhizophora mucronata Lam. in the Mangoky Delta, SW Madagascar. American Journal of Plant Sciences, 9, 1894-1910. https://doi.org/10.4236/ajps.2018.99137