Comparisons Of Species Diversity Of Intensive Green Roofs Between Honolulu, USA And Guangzhou, China

In the process of city with greening land area being reduced, roof greening as part of theupper space with a three dimensional greening, its role has been paid more and more attention.It is well documented that the environment on a green roof is considerably different fromterrene in terms of soil construction, temperature, atmosphere, wind and sunlight. However,due to the roof structure is on the top of buildings, the soil, temperature, wind, sunlight areentirely different from planting environment on ground. So Plants on green roofs arepurposefully selected to adapt to severe ecological and environmental conditions. Plants ingreen roofs should be strictly selected to fit the roof environment with temperature resistance,wind, drought, cold and harsh environment resistance. Roof greening form is divided intothree main types: green roof forms: extensive, semi intensive, intensive green roofs.The extensive green roofs, named open green roofs which is the most simple of threeforms has the following characteristics:(1) low maintenance;(2) less irrigation, using therainwater collecting irrigation;(3)using plants including moss, Crassulaceae plants andground cover plants greening and so on;(4) planting substrate thickness is3-8cm;(5)planting matrix weight is generally60-200kg/㎡;②semi intensive green roofs complexityis between extensive and intensive green roof and has following basic characteristics:(1) thetimely maintenance;(2)timing irrigation;(3) using plants including turfs and shrubs;(4)substrate thickness is at8-25cm;(5) weight is120-250kg/㎡;③intensive green roofsincluding plants and landscaping facilities, pavilions, terraces and open halls, sculpturefeatures such as the integration of the roof design, have the following basic characteristics:(1)fine maintenance;(2) frequent irrigation;(3) plant material including the lawn plants, lowshrubs, trees, etc.;(4) the minimum substrate thickness is12cm, typically substrate thicknesscan be above15to100cm;(5) the matrix weight is generally150-1000kg/㎡.Application ofplant species of intensive green roof in three forms is the most complex and can reflect thediversity of green roofs best.Guangzhou is located in low latitude and belongs to the subtropical monsoon climatezone with high temperature, high humidity, rainy summer, winter cold, dry and little rain. The average annual temperature is21.4℃-21.9℃, annual rainfall averages is1623.6-1899.8mm and annual precipitation is rich, and Chinese third rivers--the Zhujiang River isthrough the city, the wind speed. Honolulu is surrounded by the sea with strong wind from theocean and is located in the tropical area, so the climate (temperature and humidity) arerelatively mild. The temperature is rarely higher than32℃, and less than15℃is rarely. Twocities’temperature and humidity are similar with the river and ocean near the city, making thecities windy, picky for plants to resist wind.And the plant resources are mainly tropical andsubtropical plants. To sum up, the main factors of temperature, humidity, wind and plantselection are very similar so that we can compare the two cities’green roofs.Guangzhou, China and Honolulu, USAare two cities with a similar climate and geography.We randomly selected eight intensive green roofs in each city to investigate species diversity.The main results are as follows:Firstly, the survey of16roofs in two city, plant species are256kinds of plants,82families and170genera which includes roofs surveyed in Guangzhou have161kinds ofplants,76families and130genera; Roofs surveyed in Honolulu have152kinds of plants,49families and84genera. The plants in two cities have tropical and subtropical properties.Secondly, after the analysis and collection to the predominant family and the speciesthat are fit to grow, the conclusion can be drown that different types of greening roof-gardenis adaptive to different choices according to their standard. What is more, it is put forward thatChrysalidocarpuslutescens、Cordyline fruticosa (L.) A. Cheval and other species (totally70species) will be widely used to the greening of the roof-garden. As to the plant-furnishing, onone hand, the conclusion is that ‘Chrysalidocarpuslutescens、Plumeria rubra L. cv.Acutifolia+Liriope muscari+Wedelia chinensis+grass’totally10plant-furnishing patternthat have been used to the greening of the roof-garden nowadays. On the other hand, the newtypical Cantonese greening of the roof-garden pattern is put forward as‘Caryota ochlandra Hance、Plumeria rubra L. cv. Acutifolia+Cordyline fruticosa (L.) A.Cheval、Duranta repens、Ixora chinensis Lam+Liriope muscari’and so on（totally10species）Thirdly, a reference list of species used in green roofs was compiled from both cities for the entire study area. This reference list will be valuable for those creating green roofs incities with tropical and subtropical climates.