Environmental characteristics of tropical cloud forests in the rainy season in Bawangling National Nature Reserve on Hainan Island, South China

doi:10.3724/SP.J.1258.2011.00137

Abstract

Abstract:

Aims Tropical cloud forest, a seldom-studied but important type of tropical forest vegetation, is usually distributed around mountaintops and is characterized by unusual environmental conditions that determine its unique biodiversity and ecosystem functioning. Our objective was to explore the characteristics of solar irradiance, air temperature, air relative humidity, soil conditions and topographic conditions during the rainy season in two tropical cloud forest communities: tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF).
Methods Based on surveyed environmental data of TMEF and TMDF in Bawangling National Natural Reserve in Hainan Island of South China, we assessed differences in environmental conditions between the two cloud forests, and examined correlations among the environmental conditions, using principal component analysis and Pearson’s correlation analysis.
Important findings Daily photosynthetically active radiation (PAR) showed a unimodal curve both in TMEF and TMDF, but PAR in TMEF was significantly lower than in TMDF. From May to October, mean daily air temperature differed significantly between TMEF and TMDF and showed a unimodal curve in the two forests, with average values of (21.76 ± 2.44) °C and (19.33 ± 1.03) °C, respectively. Additionally, mean daily relative humidity differed significantly between TMEF and TMDF and showed an inverse “S” curve; average values were (88.44 ± 2.90)% and (97.71 ± 0.80)%, respectively. TMEF had higher total nitrogen, total phosphorous, available nitrogen, organic matter, pH and soil thickness, but lower total potassium and available phosphorous than TMDF. Slope, cover of exposed rock and altitude were lower in TMEF than TMDF, and were significantly correlated with other ecological factors. Principal component analysis and Pearson’s correlation analysis indicated that air temperature, available phosphorous, total potassium, total nitrogen and the three topographic factors were predictors of distribution of these tropical cloud forests.

Key words: air temperature, photosynthetically active radiation, relative humidity, soil factor, topographic factor, tropical montane dwarf forest, tropical montane evergreen forest

LONG Wen-Xing, DING Yi, ZANG Run-Guo, YANG Min, CHEN Shao-Wei. Environmental characteristics of tropical cloud forests in the rainy season in Bawangling National Nature Reserve on Hainan Island, South China[J]. Chin J Plant Ecol, 2011, 35(2): 137-146.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2011.00137

https://www.plant-ecology.com/EN/Y2011/V35/I2/137

Figures/Tables 7

Table 1 Comparison of study sites between tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF) (mean ± SD)

研究样地 Study site	海拔 Altitude (m)	郁闭度 Canopy density	平均树高 Mean tree height (m)	植株密度 Stem density (stems·100 m^-2)	基面积 Basal area (m²·100 m^-2)	物种丰富度 Species richness
热带山地常绿林 TMEF	1 200 ± 4.34	>0.7	5.55 ± 0.59	52.2 ± 6.4	0.43 ± 0.16	18.6 ± 2.3
热带山顶矮林 TMDF	1 300 ± 8.52	0.5-0.7	4.01 ± 0.58	115.3 ± 24.5	0.25 ± 0.09	29.7 ± 1.5

Fig. 1 Comparisons in photosynthetically active radiation (PAR), mean daily air temperature and air relative humidity between tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF) (mean ± SE). A, Photosynthetically active radiation. B, Mean daily air temperature. C, Mean daily relative humidity. Different letters (a, b) indicate significant difference at p < 0.05.

Table 2 Comparison in soil factors between tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF) (mean ± SD)

土壤因子 Soil factor	植被类型 Forest type		土壤因子 Soil factor	植被类型 Forest type
土壤因子 Soil factor	热带山地常绿林 TMEF	热带山顶矮林 TMDF	土壤因子 Soil factor	热带山地常绿林 TMEF	热带山顶矮林 TMDF
全氮 Total nitrogen (g·kg^-1)	2.25 ± 0.59^a	1.15 ± 0.38^b	有效钾 Available potassium (mg·kg^-1)	21.97 ± 1.39^a	31.97 ± 13.79^a
全磷 Total phosphorous (g·kg^-1)	0.79 ± 0.14^a	0.49 ± 0.32^b	有机质 Organic matter (g·kg^-1)	64.87 ± 22.23^a	36.71 ± 12.99^b
全钾 Total potassium (g·kg^-1)	12.68 ± 1.67^b	65.31 ± 12.50^a	pH	4.44 ± 0.29^a	3.96 ± 0.19^b
速效氮 Available nitrogen (mg·kg^-1)	153.02 ± 28.10^a	84.50 ± 15.44^b	腐殖质厚度 Humus thickness (cm)	8.75 ± 0.67^a	9.15 ± 1.22^a
有效磷 Available phosphorous (mg·kg^-1)	11.00 ± 1.65^b	19.46 ± 4.25^a	土壤厚度 Soil thickness (cm)	65.35 ± 8.63^a	54.90 ± 8.55^b

Fig. 2 Comparison in topographic conditions between tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF).A, Slope. B, Coverage of exposed rock. C, Altitude. Different letters (a, b) above the boxplot indicate significant difference at p < 0.05.

Fig. 3 Biplot of principal component analysis (PCA) showing changes in environmental variables across tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF).AK, available potassium; Alt, altitude; AN, available nitrogen; AP, available phosphorus; CER, coverage of exposed rock; HT, humus thickness; OM, organic matter; PAR, photosynthetically active radiation; RH, mean daily air relative humidity; Slo, slope gradient; ST, soil thickness; Tem, mean daily air temperature; TK, total potassium; TN, total nitrogen; TP, total phosphorus.

Table 3 The loadings and explained variance of environmental variables in the first two axes in principal component analysis (PCA)

环境变量 Environmental variables	PCA1	PCA2	PCA3	PCA4
海拔高度 Altitude (m)	0.86	0.23	-0.32	0.07
日平均空气相对湿度 Mean daily air relative humidity (%)	0.85	-0.10	-0.45	-0.01
日平均空气温度 Mean daily air temperature (℃)	-0.98	-0.07	-0.12	-0.004
坡度 Slope gradient (o)	0.90	-0.01	0.34	0.11
岩石裸露比例 Coverage of exposed rock (%)	0.92	-0.09	-0.28	0.06
土壤厚度 Soil thickness (cm)	-0.48	-0.58	0.34	0.23
腐殖质厚度 Humus thickness (cm)	0.53	0.56	0.46	0.17
光合有效辐射 Photosynthetically active radiation, PAR (μmol?m^-2?s^-1)	0.49	-0.76	-0.15	0.04
全氮 Total nitrogen (g?kg^-1)	-0.78	0.08	-0.27	0.25
全磷 Total phosphorus (g?kg^-1)	-0.42	0.53	-0.53	0.30
全钾 Total potassium (g?kg^-1)	0.87	0.16	0.34	0.001
速效氮 Available nitrogen (mg?kg^-1)	-0.45	-0.01	-0.15	-0.51
有效磷 Available phosphorus (mg?kg^-1)	0.90	-0.14	-0.33	-0.002
有效钾 Available potassium (mg?kg^-1)	0.61	-0.08	-0.16	0.11
有机质 Organic matter (g?kg^-1)	-0.65	-0.31	-0.07	0.43
pH	-0.75	0.24	-0.05	0.04
特征值 Eigenvalue	8.76	1.80	1.49	1.11
方差比例 Proportion of variance	0.547	0.113	0.090	0.070
累积方差比例 Proportion of cumulative variance	0.547	0.660	0.753	0.822

Fig. 4 Correlation among environmental conditions in both tropical montane evergreen forest (TMEF) and tropical montane dwarf forest (TMDF), indicating correlation coefficients of environmental factors and their significance. The figure was obtained with correlation analysis after combining environmental data of TMEF and TMDF.AK, available potassium (mg·kg-1); Alt, altitude (m); AN, available nitrogen (mg·kg-1); AP, available phosphorous (mg·kg-1); CER, coverage of exposed rock (%); HT, humus thickness (cm); OM, organic matter (g·kg-1); PAR, photosynthetically active radiation (μmol ? m-2 ? s-1); RH, mean daily air relative humidity (%); Slo, slope gradient (o); ST, soil thickness (cm); Tem, mean daily air temperature (℃); TK, total potassium (g·kg-1); TN, total nitrogen (g·kg-1); TP, total phosphorus (g·kg-1). *, p < 0.05; **, p < 0.01; ***, p < 0.001; figures without * indicate p > 0.05.

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