African Journal of Biotechnology Vol. 6 (24), pp. 2810-2820, 17 December, 2007 Available online at http://www.academicjournals.org/AJB ISSN 1684–5315 © 2007 Academic Journals
Full Length Research Paper
Species composition, plant cover and diversity of recently reforested wild lands near Dabao Highway in Longitudinal Range-Gorge Region of Yunnan Province, China Dong, S. K.*, Cui, B. S., Yang, Z. F., Liu, S. L., Liu, J., Wang, J., Ding, Z. K., Gao, L. N. and Zhao, S. Q. Environmental School of Beijing Normal University, Beijing, 100875, China. Accepted 22 November, 2007
Deforestation, over-cultivation and rural growth have severely damaged native vegetation of woodlands along roadsides in the Longitudinal Range-Gorge Region of Yunnan Province. This study was conducted to evaluate the effect of different reforestation practices, which consisted of natural restoration or planting with tree seedlings that varied in species composition, coverage and diversity, on damaged roadside woodlands. Three randomly selected 10 m x 10 m plots in each reforestation practice were investigated. The results showed that the species composition, plant cover and species diversity of the planted communities varied with reforestation strategies and time since planting. A higher number of species, proportion of native species and woody plants, canopy cover and species diversity were found in naturally restored plots and in 3 - 4 year old plots that were planted with native plants. In the early stages of reforestation, herbs dominated the plant community in most plots, and woody plants became more important with time after reforestation. Preliminary results suggest that plant height can be used an auxiliary indicator of plant cover to assess ecosystem function status of the restoration project. Also, evenness may be easier to restore than species richness. Natural restoration or reforestation with native dominant plants is a good management strategy for vegetation restoration or improvement. Key words: Vegetative characteristics, plant community, restoration, Southwest China. INTRODUCTION Land degradation, due to the root causes of overpopulation, poverty and lack of enforceable policies and reasonable management measures, is a worldwide environmental problem limiting the sustainable development of global society (Sisk et al., 1994; McCracken and Abaza, 2001; Reynolds and Smith, 2002; World Bank, 2002). Degraded ecosystems, with damaged biotic components, have diminished control over resources such as soil nutrients and water resources (Davenport et al., 1998). Seriously damaged lands not only lose control over resources, but also lose the capacity for self-repair and are unable to prevent additional degradation (Whisenant, 1999). Thus, they are less resilient to addi-
*Corresponding author. E-mail:
[email protected].
tional stress or damage and provide fewer environmental services (Myers, 1996). As these degrading processes continue, a threshold can be crossed exceeding the ability for the ecosystem to recover and desertification results, a dynamic and self-perpetuating process (Tivy, 1990; Thurow, 1991). Since the early 1980s, China has achieved remarkable agricultural and rural growth with the de-collectivization of agriculture, which greatly reduced poverty but addressed many environmental problems such as resource loss and land degradation (Wang, 1999; Wang and Gao, 2001). The Longitudinal Range-Gorge Region of Yunnan Province, Southwest China is an example of a region which has been severely affected by agricultural decollectivization (Peng and Wang, 2005), especially in the sites along the roadsides (Wang and Shi, 2001; Zhao, 2006). With excessive biomass removal and continued
Dong et al.
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Table 1. Reforestation practices and sites description.
Reforest practices I
Plantings Eucalyptus maideni
Reforest year 2004
Distance to road (m)
Slope 12
Soil type clay
Soil moisture
300-500
Aspect S
35%
II
Pinus yunnanensis
2004
500-700
S
13
clay
30%
III
Alnus nepalensis and Pinus yunnanensis
2002
800-1000
S
12
clay
38%
IV
Pinus yunnanensis
2002
400-500
SE
11
clay
28%
V
Pinus yunnanensis
1999
600-800
SE
13
clay
32%
VI
Pinus yunnanensis
1994
150-200
SE
15
clay
35%
VII
None
2002
200-300
SE
10
clay
26%
VIII
None
2004
900-1000
SE
12
clay
25%
over-cultivation, plant populations changed, and biological diversity and productivity decreased. Continued reductions in plant productivity decreased litter and vegetative cover, which in turn increased erosion and desertification (He, 1991; Gao, 2003). Vegetation conservation and restoration in this region is becoming a significant regional and national concern (Liu et al., 2002). Presently, these lands are the focus of woodland forest restoration efforts by the local government (Liu, 2005). An increasingly common goal of ecosystem restoration is to restore the high levels of plant species, traits and functional groups similar to that found in remnant sites (Pywell et al., 2003; Smith et al., 2003). However, no sites remain that can serve as a reference woodland forest for restoration in this region due to severe disturbance from agricultural production and rural development activities in the past. Most of the degraded lands have been reforested recently under one of China’s National Ecological Construction Plans, “Returning Agricultural Land to Forest Land”, which was established in 1999. Given the importance of colonization on forest stand composition and species spatial patterns (Oliver and Larson, 1996), evaluation of early restoration efforts on marginal agricultural lands is critical to assess the value of reforestation efforts and to aid in the planning of future plantings (Kruse and Groninger, 2003). In this sense, this study was proposed to evaluate the early success of different reforestation efforts. Restoring community structure (e.g. species composi-tion and diversity) and ecosystem processes typically are listed as the two main objectives of restoration and vegetation improvement (Palmer et al., 1997; Lockwood and Pimm, 1999; Smith et al., 2000). Some researchers Bradshaw (1996), Hobbs and Norton (1996), and Martin et al. (2005) have proposed that the proportion of native species and plant diversity at all spatial scales are the criteria that should be used to evaluate the success of restoration efforts. We focus on these two criteria- the ratio of native plants in the species composition, and plant diversity at the site scale to
to evaluate the success of reforestation projects implemented in recent years along the roadside of the Dabao Highway, Longitudinal Range-Gorge Region of Yunan Province, China. The overall goal of this study was to evaluate the effect of different reforestation practices on woodlands damaged by agricultural production and rural development, which included natural restoration and planting with different tree seedlings at different times before this survey on species composition, cover and diversity. MATERIALS AND METHODS Study site The study site is situated beside the Laoying exit of Dabao Hingway, Longitudinal Range-Gorge Region of Yunan Province, China (N25º19', E99º12', 1836 m a.s.l.), a subtropical region, where reforestation projects were initiated in 1994 for restoring wildlands and the former evergreen woodland. Within the study site, there were 8 reforestation practices (RP) shown in Table 1. All RPs have been implemented on neighboring plots within the study site. Environmental characteristics of the plots of different RP, including location, aspect, slope, soil type and moisture, were recorded before the vegetation investigation (Table 1). Vegetation surveys were conducted in 2004 and 2005. Sampling methods Field investigations and sampling were conducted in October to November, when most of evergreen vegetation was still growing but past the rainy season. At the beginning of investigation, all plants species within each reforestation plot were identified and species composition (total number, life form, native plant ratio) were quantified. Species were classified into different functional groups based on their growth form: trees, shrubs and herbs (Polley et al., 2005). Quantitative characteristics of the vegetation including cover, height, number of individual species, functional groups and plant community were investigated in three 10 m x 10 m quadrats which were randomly placed in each RP plot. Simpson’s diversity index, Marglef’s richness index, and the Pielou evenness index were calculated following the formulas cited by Dong (1997).
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Statistical analysis Species composition, canopy cover, plant height, species diversity, richness and evenness of the plant communities and functional groups under each RP are presented as the means of three replicates. The effects of RP on vegetation characteristics were analyzed via ANOVA using a Generalized Liner Model of SPSS 10.0 (Huang et al., 2001).
RESULTS Species composition of plant communities There were a total of 69 species in the study site, with 4 exotic and 65 native species, 16 trees, 15 shrubs and 38 herb species (Table 2). In individual RP plots, there was a total of 1 species in RPI, 33 in RPII, 24 in RPIII, 15 in RPIV, 25 in RPV, 15 in RPVI, 33 in RPVII and 16 in RPVIII. The species compositions of plant communities in the different RP varied greatly (Table 3). The plant community of RPI consisted of one species, the exotic tree, Eucalyptus maideni, a commercial tree imported from Southeast Asia. The community in RPII had a high species number (33, ranked 2nd of all plots), a relatively high proportion of exotic plants (12.1%), and the same proportion of tree and shrub species (18.2%). In RPIII, there were 24 plant species, with 91.7% native and 8.3% exotic species, and most species were herbs (62.6%). In RPIV, there were only 15 species (3 trees, 6 shrubs and 6 herbs) but a high proportion of these were exotic species (13.3%). The plant community of RPV was composed of 25 species, 92.0% of which were native species, and 12% were trees, 40% shrubs and 48% herbs. The plant community in RPVI had the highest proportion of both native species (93.3%) and trees (33.3%) among all plots, although the total number of species (15) was comparatively low. The plant community in RPVII had 33 species, the highest number among all plots, and had similar proportions of trees and shrubs. The plant community of RPVIII had only 12 species with a very high proportion of herbs (69.2%). The results showed that the species composition varied with reforestation strategy and time. The RPI plots were replanted with E. maideni and produced a single-species community, as native plants can not co-exist with this fast-growing and shady tree. Plots of RPVI were replanted with the native trees, Pinus yunnanensis and Lyonia ovalifolia, and RPVII was naturally restored, both of which had more native species and trees in their species composition. Although the plot of RPIV was replanted with the native tree, P. yunnanensis, there was a low total number of species and a high proportion of exotic plants in the composition. In all replanted plots except RPI, the plant communities reached the highest number of species at the beginning of reforestation. In naturally restored plots, the highest species numbers were observed in the third or fourth growing year. A
greater proportion of herbs were found in the early years following restoration. The proportion of shrubs increased with time following restoration after 4 - 5 years. Vegetative characteristics of the plant communities Table 4 shows that the RPI plot had complete plant cover with plant heights of 4.83 m, indicating RPI had the highest (P
