| The Yangtai Mountain located at the northwest of Shenzhen City, where the forest coverage reached up to98%. It has abundant plant resources and landscape resources, and where the major vegetation was secondary south subtropical evergreen broad-leaved forest. The Machilus chekiangensis community was a typical zonal seasonal community of Yangtai Mountain. This paper explored its species composition, community structure and species diversity by field investigation and combined with remote sense inversing in this study. Therefor, the author put forward the suggestions for the optimized landscape configuration of tree species based on that. Then, we sampled six dominant tree to analyzed the hyperspectral reflectance characteristics of the color-plants and the target trees used the ASD handheld FliedSpec3spectrometer. Finaly, in order to determine the best viewing period of the community and find out driving factors on seasonal changes of community appearance, the paper analyzed correlation of trees seasonal color features with its year-cycle high spectral characteristicsand put forward suggestion on optimizing the Machilus chekiangensis community, in Yangtai Mountain.The research results showed as follow:(1)The Machilus chekiangensis community’s flora contained many tropical and subtropical plants, such as Rubiaceae, Lauraceae, Myrsinaceae, Euphorbiaceae, Rutaceae, Theaceae and so on. All that plant accounted for38.3%and33.3%of total species and the total genus respectively. This phenomenon reflected that the community had strong tropical and subtropical element, showing a transition property from tropical regions type to the subtropical type.Through the analysis species contained of three1200m2sample plots, showed that the important values of Machilus chekiangensis were22.21,22.83and27.75,thus it occupied obvious advantage position within the community. The vertical structure of community showed clear grass and shrub layers and abundant tree layer species. Machilus chekiangensis mainly dominated the first and second tree layers, respectively47%～58%and17%-30%. In the shrub layer, the main species were Machilus chekiangensis, Photinia beauverdiana, Geum aleppicum, Ardisia quinquegona, etc. The vines mainly were Smilax lanceaefolia, Millettia dielsiana, etc. Overall, the vertical spatial distribution was reasonable; the species composition was relatively variable, and community structure was stabable.(2)Combined with the hyperspectral characteristics of color-plants, the years cycle hyperspectral data of Machilus chekiangensis showed it has tree seasonal color period was divided to three period:bright yellow flower-stage, red-leaf and green-leaf stage. Its flower-stage was concentrated in the middle of February to early March, the duration was short. Its hyperspectral features of the green-stage was consistent with the green plants, at the550nm there were an obvious peak,then gradually reduced to a valley at690nm, continued up to750nm or so to the highest. The hyperspectral reflectance of flower-stage was bigger than leaf-stage overall, especially at the orange and red band (591-680nm).Taking reflectance value of the flower-stage and leaf-stage to curve fitting, the result showed exponential positive correlation and the determine coefficient was0.939.The hyperspectral curve trend of flower-stage was almost the same to the yellow-plant, rising sharply from490nm to550nm or so gradually leveling off, then appear "valley" at680nm. But due to the green-leaf background, the hyperspectral curve of flower-stage still had a peak at550nm, and the reflectance was below the yellow-plant as a whole, which showed the light absorption and utilization of the flower-stage was higher than the yellow-plant. Taking reflectance value of the flower-stage of Ficus microcabacv.GoldenLeave, Ligustrum vicaryi, Aucuba japonica var.variegata to curve fitting respectively, the result showed exponential positive correlation and the determine coefficients were0.8795,0.8805,0.8687.(3)The red-leaf period mainly concentrated in June to September, the most intense period was June and July. During this time, new leaves appeared bright red or slightly green, namely: turn-red stage and all-red stage. The reflectance curve of turn-red period had obviously peak and valley characteristics, appeared "green peak" at550nm, while during550-660nm band the reflectance increased, and then appeared "red valley" at680nm, arrived the maximum at 720nm. During the red-leaf period, the reflectance curve appeared "red peak" at630nm, and appeared "red valley" at680nm, then continued climbing to peak around720nm. In near infrared wave band (761-1100nm), the reflectance of turn-red and red-leaf period were lower than the green-leaf period, and the "red edge" also had a "blue shift" phenomenon. Taking reflectance value of the turn-red and red-leaf period to curve fitting with green-leaf period respectively, the result showed Logarithmic index correlation and the determine coefficient were0.95,0.9406.The hyperspectral curve characteristics of red-leaf period was almost same to the red-plant, while the reflectance value of turn-red and red-leaf period both lower than the red-plant during near infrared wave band (761-1100nm). Taking reflectance value of the red-leaf period to curve fitting with Syzygium rehderianum, Cordyline terminalis, Acalypha wilkesiana, Lorpetalum chindensevar respectively, the result showed linear correlation and the determine coefficient were0.9487,0.9468,0.9354,0.9244.(4) The analysis result of species composition, vertical structure and age structure indicated that Machilus chekiangensis, Geum aleppicum, Photinia beauverdiana, Liquidambar formosana, Meliosma rigida could formed stabable community structure, and had strong symbiotic. On the space, those species occupied different ecological niches, and formed rich-full and clear structure level. That kind of community had a high ornamental value, and could achieve well economic, ecological and landscape benefits. In the future transformation of ecological landscape forests, we could choose the configuration mode of taking Machilus chekiangensis as main-layer, while taking Geum aleppicum+Liquidambar formosana or Geum aleppicum+Sapium discolor as sub-layer tree, to build the seasonal-landscape variable, community hierarchy clear, community structure stable ecological forest.Compared the hyperspectral reflectance of the four directions (east, south, north, west) indicated that, during flower-period the east and south hyperspectral reflectance were higher than the west and north, and had a higher light utilization rate, a better color performance. The Machilus chekiangensis located in south and southeast slope showed a better seasonable color characteristic than the trees in north and west slope. In term of altitude, the flower period of the trees located on the first altitude class was slightly later than the trees on the second altitude class, due to the plashy environment of the first class could balance the temperature. The trees on third class performed best in the red-leaf period. So, we should choose high altitude and south or southeast slope area to plant Machilus chekiangensis as far as possible. |
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