Rice yield of five farmland shelter-belt models on Chongming Island,Shanghai

Farmland shelter-belts are the main component of Chongming Islands shelter forest network. The objective of this study was to select the optimum farmland shelterbelt type by determining the optimal shelter forest porosity. After choosing the main shelter forest models（Taxodium ascendens forest，mixed Metasequoia glyptostroboides（water fir）-Cryptomeria fortunei forest，M. glyptostroboides forest，Populus spp. （poplar） forest，and C. fortunei forest） and surveying the community structure，rice yield and 1 000-grain weight were determined for each shelter forest. Results showed that at different distances within the same sample plot，forest protection significantly improved rice yield and 1 000-grain weight；leaf area index also improved. Among the different models，yield increase was in the order T. ascendens＞the mixed forest of M. glyptostroboides and C. fortunei＞M. glyptostroboides＞Populus spp.＞C. fortunei. The range of shelter forest porosity was 0.31 - 0.39，and the most effective protective distance was 5H（fivefold height of the tree）－10H. In addition，the mixed forest was better than the monotypic forest with the mixed forest of M. glyptostroboides and C. fortunei being the optimal shelterbelt model. ［Ch，3 fig. 3 tab. 21 ref.］