Vegetation Characteristics Of Degraded Forest And Ecological Restoration In Daqingshan, Guangxi

The study area (106°39′～106°59′E, 21°57′～22°19′N) is located on the south-eastern border in the Guangxi Zhuang Autonomic Region, China. This region belongs to the south-eastern edge of the sub-tropical monsoon climate area. It borders on the north tropical zone in the humid and semi-humid area. Resources such as sunlight, heat, and water are abundant. There are vegetation and climate characteristics between tropical and subtropical in this area , but it was not typical relativing to one of two climate zone.Because of the overcharged population, land use change made the large area natural forest be destructed and distribute fragmentedly, replacing with mass pure coniferous leaved forest.This statement has resulted in worse sequel ,such as productivity decreasing , biodiversity declining ,land degenerating ,ecosystem service such as water and soil conservation,carbon sink etc.declining,we study on the population relation,vegetation structure ,biodiversity, succession sere,carbon sink,soil chemical and physical characteristics of degred forest, in order to proffer academic reference on the semi-natural vegetation restoration and ecological function enhancement. Primary research content and conclusion are as follows:(1)Cunninghamia lanceolata is the main timber tree in the low subtropical area. Because of the simple stand structure and the traditional management focusing only on wood production, the potential consequences of biodiversity loss for ecosystem function and services have received considerable attention in recent years. It is necessary to change stand structure and species composition of Chinese fir plantation in order to increase its species diversity and ecosystem services. The understorey woody plant was beneficial to maintaining site productivity, species diversity and stability of community. Study on the species richeness,interspecific association and correlation could direct the sound practice of vegetation restoration.There were 71 species in shrub layer in Cunninghamia lanceolata plantation after natural succession.The species richness and diversity have increased with slight anthropogenic disturbance. The status and function of understorey woody species were judged by analysis of important Value. Ficus hispida, Cudrania tricuspidata ,Mallotus apelta, Millettia semicastrata etc. were the constructive species; Periploca forrestii,Alangium chinese,Pueraria thunbergiana,Mallotus barbatus etc. were the subdominant species, Clerodendron cytophyllum, Maesa japonica ,Randia spinosa,Litsea cubeba etc. are the companion species ; Viburnum dilatatum, Cayratia japonica ,Rubus palmatus etc. are the rare species. X² statistics and r test were used for testing significance of interspecific association and correlation among 25 main understorey woody plants selecting from the woody population.The results clearly shew their interspecific relationships and their differences in resource utilization. Species-pairs of positive association were in the majority. The most species have accommodated the shady habitat.There was a positive correlation between the important value of species and the interspecific association. The higher important value of the species was, the more close and significant interspecific association was. Based on analytical results of interspecific association and correlation ,25 woody plants in shrub layer could be divided into 4 ecological species groups:â… .Ficus hispida+Antidesma bunius+Mallotus barbatus+ Ficus cunia+Saurauia tristyla +Mallotus philippinensis+Maesa japonica+Ficus hirta+Alchornea rugosa+Ficus fulva+Mallotus apelta ;â…¡. Cudrania tricuspidata+Schefflera octophylla ;â…¢. Cunninghamia lanceolata+ Clerodendron cytophyllum+ Millettia semicastrata+ Randia spinosa+ Litsea cubeba+ Litsea pungens;â…£.Ardisia japonica+Psychotria rubra+Vitex quinata+Cephalanthusoccidentalis+Pithecellobium lucidum+Mycetia sinensis.If species groupâ…¢orâ…¡was advantaged species in shrub layer, the community would change from coniferous forest to sparse evergreen broad-leaved forest; For groupâ…£, the community would be relatively stable; For groupâ… , the coniferous forest would be mixed coniferous-broad leaved forest. The analyse of shrub eigenvalue and classification of ecological species groups would provide a theoretical basis on judging its ecological function,especially water and soil conservation, adjusting the stand structure of plantation and directing the suitable natural vegetation type through the close–natural restoration process. (2)A study on the natural understorey vegetation in artificial masson pine replanted after Chinese fir being cutting down for 13 years indicated that there were 100 species of undergrowth vegetation .There were 74 species of shrub or small arbor, appropriating 74.0 percent of total species,,belonging 41 faculties and 63 categories;the amount of herbs was 26 ,belonging 14 faculties and 23 categories.The tropical and subtropical elements were prominent.The species diversity and richness became decreasing after Masson Pine regenerating from Chinese fir.The analysis of important value shew that the main shrub species or small arbor were Tinomiscium tonkinensis,Mycetia longiflora,Evodia lepta,Paederia scandens,Mussaenda pubuscens,Actinodaphne pilosa,Quercus glauca ,etc. the main herb species were Cyrtococcum patens, Blechnum orientale, Dicranopteris dichotoma, Adiantum flabellulatum, Adiantum edgeworthii, Pteris semipinnata,etc. The biomass of vegetation distributing different position of slope was various, upside>downside>middle part. The niche characteristic of 18 main tree populations in shrub layer was measured,the results shew there was generally very significantly positive correlation between the niche breath and the important value of main woody population.The woody population whose important value higher than others were more adaptable to habitat and their niche breadth was larger than others.The niche overlap of six population counterpart was very large,such as Tinomiscium tonkinensis-Mycetia longiflora, Tinomiscium tonkinensis-Evodia lepta ,Mussaenda pubuscens-Maesa japonica, Quercus glauca-Aphananthe aspera, Actinodaphne pilosa -Saraca chinensis, Evodia lepta-Quercus glaucathese, these species could be the references on selecting and disposing the driving and key species during the natural restoration and reconstruction of the same stand. The niche overlap of major woody population counterpart was larger, which shew that the trend of sharing resource utilization was obvious.(3)The secondary regenerated evergreen broad-leaf forest was fragmentedly distributed after large-scale destruction of the virgin forests in subtropical area. Eco-reconstruction depended largely on the natural restoration capacity and regeneration process, which were rarely studied in Daqingshan, Guangxi. Population dynamics of secondary-growth natural forest over 26 years of successional process were studied for exploring the following questions: (a) What were the variation pattern of population character and interspecific correlation without human disturbance? (b) What was the zonal climax vegetation type?(c) How to restorate the degraded secondary forest effectively? The methodologies of population ecology were employed to measure and analyze the changes in intra-population structure and spatial distribution in terms of the population type, important value, niche breath and distribution pattern. The community investigation took place at the same site in 1980, and the historical data was used as the base of the analysis. The dominated heliophytes at the early successional stage had changed from intense contagious distribution into random distribution and their niche breaths had decreased accordingly. The mesophytes and shade-favorite tree species, however, had the reverse changes from random distribution into highly contagious distribution in concomitance with increasing niche breaths. The number of tree species had risen up from 32 to 65, of which 35 were the late-successional stage species and had rich species diversity.The analysis of niche overlap and interspecific association were made to ascertain the mutual adaptation and evolution of species relations.The results indicated that the values of niche overlap among the light favorite population,such as Castannopsis fleuryi, Aphanamixis grandifolia,etc. and others dropped generally,while the values of niche overlap of mesophytic population, such as Eurya nitida, Eberhardtia aurata, Schefflera octophylla, Knema guangxiensis etc,with others were increased slightly. At the same time, the values of niche overlap of the mesophytes partial to the shade habitats were also enhanced greatly and as the result these species have become dominant species, as the example of Beilschmiedia percoriacea, Adinandra millettii, Actinodaphne pilosa etc. The proportion of species pairs showing positive and negative associations interacted mostly intensively with decline for those species pairs of either no associations or negative associations and increase of the positive associations.The results of interspecific association analysis were consistent with that of niche overlap analysis, i.e., the species pairs with closely positive associations had large niche overlap, indicating that these species tended to utilize environmental resources homogenously. The study suggests that there have been occurring obvious species changes in community during natural restoration process especially for the individual quantities and distributions of many dominant species. All theses results indicated that current communities were developing into the status of increasing ecological stability, as the secondary communities were proceeding close to the zonal climax through the natural succession over 26 years.The study on the population dynamics of secondary-growth natural forest could direct the natural restoration of fragmented secondary forest effectively .(4)We studied the characteristics of species diversity of 8 forest community types, the results shew that the species of secondary forest was much more than that of artificial forest .Among the plantations,the species diversity of coniferous leaved forest was higher than that of the evergreen broad-leaf forest. The coniferous leaved forest tended to needle and broad leaved mixed forest, the species abundance of Chinese fir was higher than that of Pinus massoniana .The shrub species diversity index of native broad-leaved evergreen forests was in the following order: Tectona grandis> Erythrophleum fordii >Castanopsis hystrix>Michelia macclurel >Mytilaria laosensis ,that of herb species was : Erythrophleum fordii > Mytilaria laosensis> Tectona grandis> Castanopsis hystrix>Michelia macclurel . The understory species richness indexes(S) of two coniferous leaved forest were higher than other plantations; According to the various growth forms,shrub species abundance indexes of all forest were higher than that of herb species ,tree species of secondary forest was richer than that of shrub or herb species,the arbor species abundance indexes of all plantations was lower than other life form;The species Margalef indexes (Ma) and Gleason indexes(dGL) were intensive relative to richness indexes(S). The evenness indexes(J) shew complex orders, shrub species evenness indexes were lower in Castanopsis hystrix, Erythrophleum fordii and Mytilaria laosensis communities,although the shrub species was richer than herb species.J of other forest was relative to S;The Shannon-Wiener indexes(H/) of two coniferous leaved forest increased over 7～13a succession stages , after 13 years , the Shannon-Wiener indexes(H/) decreased contrarily;With the 14 years natural growth Pinus massoniana tree density increasing from 1350n·hm^-2 to 1800 n·hm^-2, undestory species diversity indexes increased .As the tree density increasing to 2100 n·hm-2, the species richness and diversity indexes decreased.The plant community with high species diversity had complex space and nutrition structure, stable productivity, relatively intensive capacity of self regulation and anti-interference and prominent ecosystem servise, so the species diversity characteristics of various plant communities could direct the goal and effect of natural vegetation restoration.(5)Soil chemical and physical properties were studied during the successional stages of typical forest community in Dangqingshan in Guangxi .The results shew that the difference of various forest was significant (p﹤0.05). After the original forest being cutting down, the soil degraded. Except for the total K,the nutrient content of natural forest was higher than that of all plantations ,in addition ,the soil physical capability was better, with higher soil saturated water capacity , total porosity and capillary porosity ,lower bulk density, so the secondary forest soil could saturate overmuch ground runoff and prenvent soil erosion effectively.In view of precipitous slope, intensive rainfall, thin soil and imestone terrain,if the soil was eroded , basement rock was easy bare ,vegetation was very difficult recovering , rocky desertification occurred on the lime rock in succession.So the secondary forest was very useful of soil erosion and rocky desertification prevention;The soil nutrient content of artificial vegetation fluctuated relativing to the abandoned land,the total N content increased after artificial reforestation, the soil P were rich in Tectona grandis, Michelia macclurel, Castanopsis hystrix,mixed forest of Chinese fir and Castanopsis hystrix.The soil nutrient contents of two coniferous leaved forest were lower than that of broad-leaved evergreen forest, after mixing with the evergreen broad leaved trees, the soil nutrient content increased .The soil chemical and physical traits developed during the succession from coniferous forest to coniferous broad leaved mixed forest.There were abundant K in the broadleaved forest soil.The total porosity of evergreen broad leaved forest were no significant (Pï¹¥0.05);With the natural succession (7a—13a—23a) of two coniferous forest types, the soil (0～20cm) organic matter ,total N, available N and soil CEC increasing ;Soil properties of Pinus massoniana was intensive related to the tree density.With the tree density increasing,total K accumulated .Contents of organic matter,total K and P were higher in the middle density forest soil with higher soil saturated water capacity, total porosity and capillary porosity,the superior function of keeping and storing water could prenvent the erosion of surface soil in middle density forest .Vegetation restoration was very significant of preventing water loss and soil erosion.(6)Carbon accumulation and distribution of the 13 years old Pinus massoniana and Cunninghamia lanceolata mixed plantation in Daqingshan,Guangxi were studied with 3 sampling plots.The results shew that the carbon contents varied with tissues and tree species, but the total carbon contents of Pinus massoniana were higher than that of Cunninghamia lanceolata. The average tissue carbon contents of Pinus massoniana were: wood (58.6%) > root (56.3%) > branch (51.2%) > bark (49.8%) > leaf (46.8%). While Cunninghamia lanceolata were: bark (52.2%) > leaf (51.8%) > wood (50.2%) > root (47.5%) > branch (46.7%). The carbon contents of soil (in depth of 60cm) ranged from 1.45% to 1.84%, with an average of 1.70%. The carbon content was higher in the surface soil (0～20cm) than in the deep layer (below 20cm). The average carbon content percentage was greatest for trees (51.1%), followed by litters (48.3%), shrub (44.1%) and herb (33.0%). The biomass of trees in the three plots ranged from 85.35 t·hm-2 to 101.35 t·hm-2, with the average of 93.83 t·hm-2, in which 75.7%～82.6% was accounted for Pinus massoniana. The biomass of the understory was 2.1～3.95 t·hm-2, with an average of 2.72 t·hm-2, while the standing stock of ground litter was 5.49～7.91 t·hm-2, with an average of 6.75 t·hm-2.The carbon storage of the mixed plantation was greatest in soil layer (69.02%), so water and soil conservation was significant of the carbon sink in forest ecosystem,followed by vegetation (29.03%) and standing litter (1.82%). The carbon storage of tree layer occupied 28.36% of total ecosystem and 97.7% of vegetation layer. Of total carbon storage in tree layer, Pinus massoniana took up 65.39%. The tissue carbon storages were positively related to the amounts of their corresponding biomass. Trunk accumulated the highest carbon storage, comprising 53.23% of the overstorey trees in Pinus massoniana and 55.57% in Cunninghamia lanceolata, respectively. Root made up about 19.22% of total tree carbon. The annual net productivity of mixed plantation was 11.46 t·hm^-2·a^-1, sequestering carbon of 5.96 t·hm^-2·a^-1, which was equvalent to fixing CO2 of 21.88 t·hm^-2·a^-1 . It was indicated that plantation was an important sink of atmospheric CO2.(7)Carbon accumulation and distribution were studied in plantation of Chinese fir forest ecosystem in Daqingshan ,Guangxi.The results shew that the average carbon concentrations in all organs Was in the following order:leaf(51.05%)> bark(50.18%)> wood(48.51%)> root(47.65%)> branch(46.21%).The carbon concentrations of soil (to 60cm) ranged from 1.14% to 2.11% ,with an average of 1.66%.Carbon concentrations of surface soil(to 20cm) was higher than the other layer. The average carbon concentrations in different layers was in the order as: trees (49.7%)> shrub (43.75%) >standing litters (43.75%)>herb (40.78%). The carbon storage order forest ecosystem was soil layer>vegetation >standing litter. Of total average carbon, 23.82% was distributed by vegetation component, 74.27% by soil (60cm depth), only 1.86% by standing ground litter layer. The carbon storage of tree layer occupied 22.94% of total ecosystem and 96.07% of vegetation layer. The carbon storage in different organs was positively related to the biomass of corresponding organs. Trunk accumulated the highest carbon storage, comprising 58.40% of carbon storage in tree layer. Root made up 20.09% of total tree carbon.The annual net productivity of forest plantation was 10.10t·hm^-2·a^-1,stored carbon up to 4.67 t·hm^-2·a^-1,amounted CO2 to 17.13 t·hm^-2·a^-1 . Forest was a important sink of atmospheric CO2.Sum up, if reducing the anthropogenic disturbance during the natural vegetation restoration, the vegetation composition, structure, population relationship, carbon sink,soil chemical and physical characteristics developed evidently. With progressive succession, the forest community species richness and diversity increased gradually, interspecific association and correlation became intensive, soil chemical and physical capability had improved, forest community tended to stabile stages.On the other hand,as native vegetion converting into the various palantation,retrogressive succession occurred ,as a result,the species richness and diversity decreased reversely , the stand structure was simplified ,the ecosystem service function declined. Land use change was the main intrusive factors of the forest degradation in this study area .So we can reference to the old aged natural secondary forest, natural successional traits and population dynamics to accelerate the progressive succession in order to tend to the original plant community finally. The vegetation restoration aimed to enhance the productivity and ecosystem foundation completely, especially the water and soil conservation and carbon storage .With closing mountains to facilitate forestation,the secondary and coniferous leaved plantation developed gradually,the structure of community became complex and stable,so near-natural restoration of secondary and coniferous leaved plantation was feasible with abundant water and heat resources.While the ever green broad leaved plantation was difficult to cause progressive succession,the artificial reconstruction was necessary up to the stable and complex stand structure.