Stuy On Tree Species Space Structure Of Urban Eco-landscape Forest In Shenzhen

This paper analyzed Flora, community structure, plant diversity, species affinity, population distribution pattern, population niche and population dynamics of eco-landscape in Shenzhen, the results show that:(1) Natural secondary forest in Shenzhen is a typical subtropical monsoon evergreen broad-leaved forest, because the small area distribution, flora is not rich. There are 301 kinds of vascular plants (including exotic species, 10 species) in 29200m2 sample sites, which belong to 100 families, 209 genera. Fern has 22 species, belong to 13 families and 17 genera. Gymnosperm has 5 species, which belong to 3 genera and 3 families. Angiosperm has 274 species, which belong to 189 genera and 84 families. Natural secondary forest in Shenzhen flora contains most tropical family, genus and specie. The tropical species have a stronger impact to Shenzhen, reflecting seed plants have strong tropical property, while show some subtropical property and a little temperate element. Tropical distribution genera plants are dominant. East Asia and North America discontinuous distribution genera plants are also an important part of the overall flora. The flora in Shenzhen shows significant tropical property and also reflects the transition features from tropical to subtropical. By calculating the flora important value, we conclude that the characterization families of natural secondary forest in Shenzhen are Lauraceae, Myrsinaceae, Moraceae Theaceaae and Rutaceae, the dominant families are Myrsinaceae, Moraceae, Mimosaceae, Myrtaceae and Rutaceae.(2) The results show that there are 72 tree species in 1 hm2 permanent plots, which belong to 34 families and 57 genera including 6 large woody vines in the permanent plots. The dominant families are Lauraceae, Rubiaceae, Myrsinaceae, Celastraceae, Aquifoliaceae, Rutaceae, Theaceae, Myrtaceae; the dominant species are Machilus chekiangensis, Adina pilulifera, Machilus chinensi, Ardisia quinquegona, Psychotria asiatica, Euonymus nitidu, Ilex triflora, Zanthoxylum avicennae, Adinandra millettii, Syzygium hancei etc.. The near-natural secondary forest is made of single dominant species community Machilus chekiangensis. Machilus chekiangensis forms the canopy layer, of which the vertical spatial niche breadth value is the largest and the niche overlap value versus Adina pilulifera and versus Machilus chinensis is above 0.78. It is found that Machilus chekiangensis community has relatively rich species, of which species composition and structure is stable, and the main species has a relatively reasonable vertical spatial distribution pattern. It indicates that Machilus chekiangensis community is a climax community in the zonal vegetation of south sub-tropic evergreen forest, which appears in an extensive distribution in the low hills of Mt.Yangtai in Shenzhen.(3) Cluster analysis show that 15 1200m2 secondary forest in Shenzhen can be divided into 4 forms, i.e., Cryptocarya chinensis+Sterculia lanceolata+Sinosideroxylon wightianum community, Schefflera octophylla+Litsea rotundifolia+Castanopsis fissa community, Cunninghamia lanceolata+Aporosa dioica+Psychotria rubra community, Cinnamomum burmannii+Albizia falcataria+Alstonia scholaris community. Comparing with research made in the Baiyun Mt., Guangzhou and in Hong Kong, the species and the structure of secondary forest community are rather similar. It is also found that the percentage of trees with smaller diameter and the tree's height below 10m is much more in the existing secondary forest. All communities follows log-series distribution model. The biodiversity index of four kinds secondary forest vary insignificantly, in which the Schefflera octophylla+Litsea rotundifolia+Castanopsis fissa community has the highest species diversity, the mixed conifer Cinnamomum burmannii+Albizia falcataria+Alstonia scholaris community has the highest shrub species diversity.(4) 72 trees in 1hm2 natural secondary forests in Shenzhen show a general significant positive association, 61 pairs among 105 pairs of 15 dominant species are positive association, 44 pairs are negative association byχ~2 test, which proportion is 58% and 42%. The dominant aspect is positive association, which is the same with multi-species test. 37 pairs are significant association, 17 pairs are positive association. 28 pairs among 105 pairs of 15 dominant species are significant positive association, 5 pairs are positive association, which proportion is 31.4%, 21 pairs are negative association byχ~2 test, which proportion is 20%.(5) There are three positive association ecological species groups by combining species affinity and niche characteristics. The first ecological groups: Litsea rotundifolia, Zanthoxylum avicennae, Ilex asprella, Ilex triflora, Schefflera heptaphylla, Adinandra millettii, Machilus chekiangensis and Machilus chinensis; second ecological species groups: Ardisia quinquegona, Ficus fistulosa, Pavetta hongkongensis, Euonymus nitidus; third ecological species groups: Adina pilulifera, Syzygium hancei, Psychotria asiatica.(6) Studying on 1hm2 Machilus chekiangensis community show that two factors affect the species distribution pattern in different developmental stages, the first one is based on species'biological characteristics, and the second one is caused by the environmental conditions of intra-specific competition or inter-specific competition. In small diameter stage, the distribution pattern mainly be caused by the biological characteristics, and with the population growth, population is restricted by individual requirements from environmental conditions, result in high individual mortality. Because forest light transmission is poor, limiting the forest lower individual growth and development led to a sharp decline in population density. Finally the large diameter Machilus chekiangensis individuals'distribution pattern change, overall distribution pattern is random.(7) Machilus chekiangensis, Adina pilulifera, Ardisia quinquegona, Euonymus nitidus has higher niche breadth. They are the generalization species, widely distributed in the community. Ficus fistulosa, Litsea rotundifolia, Litsea rotundifolia has narrow niche breadth. They are specialized species distributed only in specific sections. The results show that the higher niche breadth species have higher niche overlap value with other species, average value is more than 0.5, conversely, narrow niche breadth species such as Ficus fistulosa, Schefflera heptaphylla, Adinandra millettii,etc. have low niche overlap value with other species, also not widely distributed, which average niche overlap values below 0.3 .(8) Instead of standing tree-level structure as age structure, we establish a static life table. The results show that Machilus chekiangensis population in ageⅠand ageⅢhas highest mortality rate, whose mortality rate is more than 57%. After ageⅣmortality rate and survivals tend to be stable. Machilus chekiangensis population survival curve belongs to Deevey-Ⅲtype. The overall performance of Machilus chekiangensis population is sharp drop in early phase, stable in late stage.