Modelling the distribution pattern of soil organic carbon in protected and grazed areas of mangrove forests (Avicennia marina)

Figures & data

Table 1. Coordinates for selected Avicennia marina mangrove locations on the southern coast of Saudi Arabia, Red Sea

Location	Coordinates	Grazed/Protected
1	18° 03 01.54 N, 41° 37 56.09 E	Protected
2	18° 02 05.22 N, 41° 38 33.30 E	Protected
3	17° 59 51.11 N, 41° 40 20.69 E	Protected
4	17° 59 35.20 N, 41° 38 48.59 E	Protected
5	17° 48 27.37 N, 41° 51 56.81 E	Grazed
6	17° 48 23.83 N, 41° 53 28.73 E	Grazed
7	17° 48 03.43 N, 41° 53 11.91 E	Grazed
8	17° 47 30.79 N, 41° 53 19.30 E	Grazed
9	17° 09 20.80 N, 42° 25 10.32 E	Grazed
10	17° 10 46.26 N, 42° 21 59.85 E	Grazed
11	17° 04 56.23 N, 42° 25 54.02 E	Grazed
12	17° 00 10.95 N, 42° 33 07.13 E	Grazed

Figure 1. Curve-fitting models for volumetric SOC density (kg C/m³) as a function of soil profile (m) in protected and grazed Avicennia marina mangrove locations. F_Location = 106.9***; F_Depth = 9.7***; F_{Location × Depth} = 4.5***; F-values represent a two-way repeated measures ANOVA results; ***: p < 0.001.

Figure 2. Curve-fitting models for cumulative SOC stock (kg C/m²) as a function of soil profile (m) in protected and grazed Avicennia marina mangrove locations. F_Location = 123.5***; F_Depth = 751.5***; F_{Location × Depth} = 87.9***; F-values represent a two-way repeated measures ANOVA results; ***: p < 0.001.

Table 2. Statistical summary of soil bulk density (g/cm³) at different depth intervals in protected and grazed Avicennia marina mangrove locations

Soil depth (cm)	Protected				Grazed
	Mean (n = 20)	Min	Max	CV (%)	Mean (n = 20)	Min	Max	CV (%)
0–5	0.93	0.23	1.56	44.4	1.09	0.75	1.61	22.2
5.1–10	1.15	0.62	1.62	31.0	1.19	0.89	1.72	18.1
10.1–15	1.21	0.72	1.66	27.2	1.27	1.03	1.79	16.7
15.1–20	1.30	0.72	1.69	25.2	1.32	1.03	1.80	17.2
20.1–25	1.39	1.03	1.81	15.8	1.40	0.74	1.82	23.4
25.1–30	1.42	1.05	1.83	15.3	1.45	0.86	1.83	21.7
30.1–35	1.47	1.23	1.85	14.0	1.54	1.05	1.87	18.1
35.1–40	1.51	1.24	1.94	14.1	1.59	1.18	1.89	14.8
40.1–45	1.54	1.25	1.94	14.3	1.67	1.29	1.91	10.0
45.1–50	1.59	1.28	2.02	14.5	1.77	1.32	1.98	10.7
50.1–55	1.64	1.32	2.08	15.3	1.84	1.35	2.15	11.4
55.1–60	1.69	1.40	2.26	15.9	1.95	1.73	2.53	13.2
60.1–65	1.79	1.42	2.40	15.0	2.03	1.73	2.50	13.1
65.1–70	1.85	1.47	2.59	15.5	2.19	1.73	2.74	14.2
70.1–75	1.90	1.52	2.80	17.0	2.27	1.73	3.03	16.3
FLocation = 21.7***, FDepth = 189.4***, FLocation × Depth = 2.8**

Min: Minimum; Max: Maximum; CV: Coefficient of variation; F-values represent a two-way repeated measures ANOVA; **: p < 0.01; ***: p < 0.001.

Table 3. Statistical summary of soil organic carbon contents (g C/kg) at different depth intervals in protected and grazed Avicennia marina mangrove locations

Soil depth (cm)	Protected				Grazed
	Mean (n = 20)	Min	Max	CV (%)	Mean (n = 20)	Min	Max	CV (%)
0–5	35.7	27.2	45.3	15.2	18.2	12.4	29.0	28.5
5.1–10	31.2	22.5	42.6	16.9	13.0	10.9	16.3	14.1
10.1–15	29.2	21.8	41.4	18.1	11.7	8.8	14.2	15.1
15.1–20	27.6	20.4	38.5	18.5	11.0	8.8	14.1	16.5
20.1–25	25.4	17.6	31.2	16.6	10.5	7.6	14.1	18.4
25.1–30	24.3	17.5	30.9	16.4	9.9	7.4	13.5	19.8
30.1–35	21.7	9.3	29.3	20.5	9.4	6.6	12.4	19.8
35.1–40	20.0	9.2	28.3	21.6	9.0	5.7	12.2	21.4
40.1–45	19.3	8.0	28.1	23.1	8.2	5.7	10.0	18.3
45.1–50	17.5	7.5	26.9	25.8	7.8	5.6	9.8	18.5
50.1–55	16.5	7.0	23.2	24.8	7.2	4.7	9.6	23.1
55.1–60	15.2	6.8	22.2	27.0	7.2	4.7	9.9	26.9
60.1–65	14.8	5.3	20.9	26.1	7.0	4.2	9.9	28.2
65.1–70	13.6	3.6	21.3	34.3	6.8	3.6	9.9	29.2
70.1–75	12.6	2.8	21.3	42.2	6.8	3.1	9.9	27.7
FLocation = 176.8***, FDepth = 141.2***, FLocation × Depth = 24.6***

Min: Minimum; Max: Maximum; CV: Coefficient of variation; F-values represent a two-way repeated measures ANOVA; ***: p < 0.001.

Table 4. Model parameters and fitting results for volumetric SOC density (kg C/m³) using three equations in in protected and grazed Avicennia marina mangrove locations

Location	Allometric	Exponential	Sigmoid
Protected	y = 35.6779–19.3453*x^1.5720	y = 0 + 37.8644*exp^–0.5606*x	y = 25.1029 + (9.9939)/(1 + (exp(–(^x − 0.4285)/–0.0707)))
	R^2 = 0.907202	R^2 = 0.859197	R^2 = 0.956681
Grazed	y = 14136.5683–14123.5954*x^0.0001	y = 14.0835 + 16.7278*exp^–23.3248*x	y = 14.0835 + (294992945.5508)/(1 + (exp(–(^x + 0.7154)/–0.0429)))
	R^2 = 0.589398	R^2 = 0.893894	R^2 = 0.893890

Table 5. Model parameters and fitting results for cumulative SOC stock (kg C/m²) using three equations in protected and grazed Avicennia marina mangrove locations

Location	Allometric	Exponential	Sigmoid
Protected	y = −1.5050 + 30.7391*x^0.7875	y = 55.9858–56.4005*exp^–0.7086*x	y = 45.4998 + (−165.1798)/(1 + (exp(–(^x + 0.8152)/–0.8520)))
	R^2 = 0.999611	R^2 = 0.999936	R^2 = 0.999942
Grazed	y = 0.1955 + 14.0673*x^0.9598	y = 138.2466 − 137.9659*exp^–0.1064*x	y = 0 + (12.4464)/(1 + (exp(–(^x − 0.4166)/0.1909)))
	R^2 = 0.999910	R^2 = 0.999876	R^2 = 0.993194

Figure 3. Volumetric densities of SOC in the upper 75 cm of soil, expressed as TCFs (0–10/0–75 cm), at both protected and grazed Avicennia marina mangrove locations. A t-test comparison was displayed on the graph; the middle line is the median; the top and bottom of the box are quantiles (Q1 and Q3); the error bar is the largest and smallest value; and the + is the mean.

Table 6. Assessment of validation indices for volumetric SOC density (kg C/m³) using three equations in protected and grazed Avicennia marina mangrove locations

Location	Equation	MNAE	MNB	Student’s t-test
				t-value	p
Protected (n = 25)	Allometric	0.121	0.053	1.025	0.308
	Exponential	0.187	−0.066	1.892	0.061
	Sigmoid	0.103	−0.043	0.959	0.339
Grazed (n = 25)	Allometric	0.304	−0.069	1.904	0.059
	Exponential	0.133	−0.057	1.678	0.096
	Sigmoid	0.172	−0.062	1.735	0.085

MNAE: mean normalized average error; MNB: mean normalized bias.

Table 7. Assessment of validation indices for cumulative SOC stock (kg C/m²) using three equations in protected and grazed Avicennia marina mangrove locations

Location	Equation	MNAE	MNB	Student’s t-test
				t-value	p
Protected (n = 25)	Allometric	0.059	0.020	0.638	0.525
	Exponential	0.016	0.004	0.149	0.882
	Sigmoid	0.015	−0.003	0.111	0.912
Grazed (n = 25)	Allometric	0.027	−0.004	0.158	0.875
	Exponential	0.030	−0.005	0.529	0.597
	Sigmoid	0.062	0.041	0.783	0.435

MNAE: mean normalized average error; MNB: mean normalized bias.

Photo A1. Depicts camels engaging in browsing activity on Avicennia marina within grazed mangrove locations.

Photo A2. Presents images illustrating the effects of camel grazing on Avicennia marina within grazed mangrove locations.

Data availability statement

The data supporting the findings of this study are available upon reasonable request.