Leaf Expansion Dynamic Of Woody Species From Evergreen Broad-Leaved Forests In Tiantong, Zhejiang

Leaf expansion dynamic refers to the process of the increase in the number and area of new leaves. Leaf expansion process and environmental changes in coordination due to long-term evolution and adaptation, and thus it makes plant species maximize resources utilization, and causes each species to form a specific pattern of leaf expansion. Therefore, leaf expansion dynamic research can reflect the life history strategy of each species to a great extent.Evergreen broad-leaved forests widely distribute in the subtropical region of China. So far, there have been just few reports concerning the leaf expansion dynamic in this region, especially at the community level. So20woody species were sampled from evergreen broad-leaved forests, which was located in Tiantong National Forest Park, Zhejiang Province. Based on field observation from2010to2011, their leaf number dynamic, individual leaf area, total leaf area of individuals and communities were measured and analyzed at the level of individual, life form, and plant community. Meanwhile, the reasons for differences in leaf expansion were also discussed to explain the coexistence of different species on a community scale. The main results were as follows:(1) On the whole, most evergreen broad-leaved species(include8species of canopy trees,6species of sun-growing shrubs and6species of shade-tolerant shrubs) began to leaf in middle and later April in Tiantong, Zhejiang Province, and reached the end of leaf emergence in early and middle May. The earlier the leaf began to emergence, the earlier the leaf ended the emergence. The later the leaf ended emergence, the longer the duration of leaf emergence lasted. There was no relationship between the beginning time and the duration of leaf emergence. For shrubs beginning time and ending time of leaf emergence were earlier compared with canopy trees, but there was no significant difference. Leaves emergence occurred earlier in shade-tolerant shrub than sun-growing shrubs, but there was no significant difference. The ending time of leaf emergence of shade-tolerant shrubs was later than of sun-growing shrubs, but there was no significant difference. According to the duration time, of leaf emergence those20species can be divided into flushing type(12species)and succeeding type(8species). In addition, according to the beginning time of leaf emergence, flushing type can be categorized into earlier-flushing (7species) and later-flushing(5species), succeeding type can be categorized into earlier-succeeding(5species) and later-succeeding(3species).(2) Overall, for most species the beginning time of leaf expansion was in the middle April, their peaking time of leaf expansion was in the middle and later April, and many species ended the process of leaf expansion in last10days of April, or early and middle May. This was very similar to the process of leaf emergence. The earlier the species began leaf expansion, the earlier their peaking time reached, and the relationship between the beginning time and peaking time of leaf expansion was positively correlated. The earlier the species began to leaf, the earlier the species ended the process. For shrubs the beginning time, the peaking time and the ending time of leaf expansion were earlier compared with canopy trees, but there was no significant difference between them. The relative growth rate of canopy trees was higher than of shrubs, but there were also no significant difference. For shade-tolerant shrubs, the beginning time and ending time of leaf expansion were earlier than for sun-growing shrubs, but there was no significant difference. The duration of leaf expansion of shade-tolerant shrubs lasted longer than sun-growing shrubs, and there were significant difference between them. The relative growth rate of sun-growing shrubs was higher than of shade-tolerant shrubs, and there were significant difference.(3) Null-model test results showed that:at the beginning time of leaf expansion, canopy trees and shrubs showed the aggregated distribution; however, at the peaking time of leaf expansion, canopy trees had the random distribution, while shrubs had the aggregated distribution.(4) The beginning time, the peaking time and ending time of leaf expansion of Schima superba forest were earlier than Castanopsis fargesii forest, and the relative growth rate of Schima superba forest was roughly twice as same as Castanopsis fargesii forest. The differences of the two communities in leaf expansion dynamic might be probably due to the characteristics of different species and forest stand conditions (including water).