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Fig. 1. Location of the four forest areas and study plots in the Taita Hills, Kenya (maps drawn by Mika Siljander, Dept. of Geosciences and Geography, University of Helsinki).

Table 1. Characteristics of the four forest areas and number of study plots.
Characteristic Forest area
  Ngangao Chawia Irizi Mbololo
Latitude (S) 03°21′55″ 03°28′48″ 03°19′40″ 03°18′15″
Longitude (E) 38°20′33″ 38°20′31″ 38°20′45″ 38°29′45″
Elevation (m a.s.l.) 1700–1952 1470–1600 1640–1705 1000–1779
Slope (%) 6–27 1–13 3–25 4–44
Area (ha) 206 111 47 185
MAT (°C) a) 17.8 18.9 18.5 18.6
MAP (mm) b) 1773 c) 1285 c) 1450 1716 c)
No. of plots d) 9 (2, 3, 2, 2) 6 (2, 2, 2, -) 9 (-, 1, 4, 4) 14 (4, 4, 2, 4)
a) Mean annual temperature, New LocClim (see text) values.
b) Mean annual precipitation, New LocClim (see text) values.
c) Value includes occult precipitation (+ 20% of annual precipitation).
d) Values in parentheses are the number of plots by forest type: Indigenous, Cypress, Eucalyptus, Pine.
Table 2. Stand and soil characteristics of study plots (stand by forest type and soil by layer) for the four study areas in the Taita Hills. View in new window/tab.
Table 3. Mean (± standard deviation) carbon densities (Mg C ha–1) in tree biomass and soil of the four forest types in the Taita Hills. Within each carbon stock, forest type mean values followed by different letters indicate a significant difference (Tukey’s test, p < 0.05).
Stock Indigenous
(n = 8)
Cypress
(n = 10)
Eucalyptus
(n = 10)
Pine
(n = 10)
Tree biomass C
Aboveground 360 ± 148.1a 158 ± 66.6b 221 ± 143.2ab 195 ± 87.8b
Belowground 90 ± 37.0a 39 ± 17.8b 72 ± 46.0ab 47 ± 21.0b
Total 450 ± 185.1a 197 ± 84.3b 292 ± 189.5ab 242 ± 108.8b
SOC
0–20 cm 146 ± 27.6a 115 ± 23.3ab 94 ± 33.7bc 78 ± 31.2c
20–50 cm 158 ± 35.9a 137 ± 27.8ab 116 ± 45.1ab 91 ± 43.5b
0–50 cm 305 ± 58.1a 252 ± 48.0ab 209 ± 77.4bc 168 ± 72.5c
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Fig. 2. Relationship between plot soil organic carbon (SOC, 0–50 cm) and total biomass carbon densities for each of the four forest types. Lines are linear regression lines.

Table 4. Correlations (Spearman) between plot mean carbon densities (Mg ha–1) for tree biomass (total) and soil (0–50 cm) and various climate and site variables by forest type. Values in bold denote significant correlation coefficients (p < 0.05).
  Forest type n MAP a) MAT a) PET b) AET c) Elevation Slope Clay d) PAWC e)
Biomass (total) Indigenous 8 –0.24 0.28 0.14 0.33 –0.36 –0.02 0.40 –0.49
Cypress 10 –0.35 –0.25 0.02 0.44 0.19 –0.38 0.16 –0.19
Eucalyptus 10 –0.07 0.48 –0.25 0.52 –0.49 0.05 0.42 0.22
Pine 10 0.10 0.52 –0.03 0.84 –0.53 0.48 –0.09 0.14
Soil (0–50 cm) Indigenous 8 0.52 –0.30 –0.36 0.24 0.62 0.10 –0.83 0.00
Cypress 10 0.55 –0.55 –0.56 –0.31 0.58 –0.44 –0.52 –0.49
Eucalyptus 10 0.41 0.22 –0.64 0.15 –0.31 –0.03 –0.02 –0.04
Pine 10 0.68 –0.34 –0.67 –0.32 0.67 0.35 –0.31 –0.45
a) Mean annual precipitation (including 20% cloud precipitation, except for Irizi) and mean annual temperature.
b) Mean annual potential (Jensen-Haise alfalfa reference crop) evapotranspiration.
c) Mean annual actual evapotranspiration.
d) Clay (<0.002 mm) content (%) of 0–50 cm soil layer.
e) Plant available water capacity (mm) of 0–50 cm soil layer calculated using method of Saxton et al. (1986).