Studies On The Light Characteristics Of Plant Communities In Some Beijing Greenbelt

In urban green space, light is not only one of the major factors which influence the structure of plant communities, but also affects people's action and feelings. This study selected 25 different plant communities to analyse changes of light intensity and ultraviolet radiation intensity. Then we can find out the change rules of iluminous environment in urban Greenbelt. This will provide Theoretical basis in building more reasonable and comfortable plant communities in the future.The results showed as follows:1. The daily changes of light intensity and ultraviolet radiation (UV) intensity are similar in different layers of communities and out communities. They both present the single-peak trends. The minimum of light intensity is 624.36 lx, the maximum of light intensity is 9381.46 lx. The minimum of UV intensity is 624.36μW/cm2, the maximum of UV intensity is 9381.46μW/cm2.2. In the open spaces, light intensity and UV intensity are always smaller in summer than that in autumn.But in communities, light intensity and UV intensity are only smaller in summer than that in autumn when it is dawn and dusk.3. In summer, different species have different light shading rates and different UV shadding rates. The minimum of light shading rates is 74.83% (Ginkgo biloba), the maximum is 96.20% (Platanus occidentalis).The light shading rates from large to small are Platanus occidentalis> Koelreuteria paniculata>Sophora japonica>Juglans regia>Eucommia ulmoides>Syringa pekinensis>Populus tomentosa>Fraxinus pennsylvanica>Malus spectabilis+ Morus alba> Acer truncatum> Robinia pseudoacacia> Prunus persica'Duplex'> Tilia mongolica> Liriodendron chinense>Paulownia tomentosa>Platycladus orientalis>Pinus tabulaeformis> Catalpa bungei>Salix matsudana'Pendula'> Ginkgo biloba.The minimum of UV shading rates is 68.20%(Ginkgo biloba), the maximum is 98.85% (Koelreuteria paniculata).The UV shading rates from large to small are Koelreuteria paniculata >Fraxinus pennsylvanica>Acer truncatum>Syringa pekinensis>Tilia mongolica>Eucommia ulmoides>Sophora japonica>Juglans regia>Populus tomentosa>Platanus occidentalis> Liriodendron chinense> Malus spectabilis> Platycladus orientalis> Pinus tabulaeformis> Catalpa bungei>Paulownia tomentosa>Salix matsudana'Pendula'> Robinia pseudoacacia> Ginkgo biloba. 4. The light Coefficient of variation (CV) and UV CV can well reflect the degree of homogeneity. The degree of homogeneity will decrease with the increase of light CV and UV CV. The light CV of different species from large to small are Populus tomentosa>Platycladus orientalis>Paulownia tomentosa>Tilia mongolica>Catalpa bungei>Pinus tabulaeformis> Robinia pseudoacacia>Sophora japonica>Ginkgo biloba>Salix matsudana'Pendula'; the UV CV of different species from large to small are Tilia mongolica>Acer truncatum> Paulownia tomentosa> Juglans regia>Platycladus orientalis>Pinus tabulaeformis>Ginkgo biloba>Salix matsudana'Pendula'.5. The light intensity has significant correlation with the UV intensity in communities. The shading rate is related to the diameter at breast height (DBH) and height under branch markedly. The shading rates have nothing to do with the canopy density among different species.