Study On Restoration Of Degraded Subtropical Evergreen Broad-leaved Forests In Gaoligong Mountains In Northwest Yunnan, China

East Asian evergreen broad-leaved forests are the most extensive subtropical forest in the world.At the same time,this forest type is highly deforested and fragmented due to human activities,particularly in China.The Gaoligong Mountains Reserve is a flagship protected area located within the Eastern Himalayan global biodiversity hotspot,providing huge ecosystem services,and is also an environmentally sensitive area in northwest Yunnan,China.Forest restoration is a cornerstone of global biodiversity conservation and sustainable development.The present study focused on forest restoration using a diversity of native tree species in the buffer zone of the reserve.We carried out a series of experiments to study the propagation requirements and selection techniques of indigenous subtropical tree species.To evaluate restoration success,we compared vegetation structure,species diversity,and ecosystem processes among restoration planting,monoculture plantations,natural regeneration and reference sites.This study aims to improve the knowledge of propagation techniques for various native subtropical tree species in nurseries and identify suitable species for restoration practices.Moreover,this research includes a comparative study to test the effects of different reforestation strategies on forest recovery.The study for the above mentioned purpose was divided into three interlinked case studies,brief description and the main results of each case study is below:1.Propagation of native tree speciesSuccessful propagation of native tree species is essential for improving ecological restoration.The seed germination and seedling growth performance of 21 tree species collected from the natural forest were tested in a nursery environment.Germination percentages ranged from 45%to 96%and were ?50%for 19 species out of 21 selected species.The median length of germination time ranged from 24 days for Padus wilsonii to 144 days for Ilex polyneura.Fifteen species can reach the transplant size(?15 cm in height)within 12 months of seed collection.For all of the 12 tested species,seed germination percentages after wet sand storage were higher than for dry storage.This case study contributes additional knowledge regarding the propagation techniques for various native subtropical tree species in nurseries for forest restoration.2.Selection of native tree speciesSuccessful selection of species adapted to local conditions requires specific knowledge which is often lacking,especially in developing countries.In order to scale up forest restoration,experimental data on the responses of native species to propagation and restoration treatments across a range of local conditions are required.This study evaluated the restoration potential of 34 native tree species was evaluated based on nursery research and field planting experiments at a highly degraded site.Forest ecological knowledge,traditional uses to community living nearby,and availability of seeds at the time of collection were the criteria of selection of species in the first phase of the study.This case study examined performance of germination rates of selected species as well as survival rates and growth over two years after planting.Of the 34 species examined,25 had a germination percentage greater than 50%.Survivorship ranged from 0 to 97%across species and was greater than 50%for 20 species.Mean monthly growth increments varied between species.Pioneer species(n=4)performed well,and mid-and late-successional species(n=14)performed reasonably well in this study.However,the remaining 16 mid-and late-successional species performed poorly.These results indicate that carefully selected mid-and late-successional species can be effectively incorporated into mixed species plantings.This finding can provide useful information for restoration planning,helping to identify suitable species and so enhance the biodiversity and resilience of restored forests.3.Evaluation of different reforestation approachesIn this study,we present the restoration program we have developed for buffer zone restoration over the past 10 years.The initial restoration was conducted with a combination of pioneer and later successional species(>20 species).Some reforestation projects using different methods have been carried out in this study site.However,the extent to which the various reforestation approaches restore structure,species diversity and ecological functions to degraded lands is still poorly understood.The types of reforestation studied were restoration planting,plantation monocultures of native species(Alnus nepalensis,Taiwania cryptomerioides),and natural regeneration.The reforestation sites were 500 m from the nearest natural forest.Field-based comparative experiments were designed to evaluate these reforestation efforts.The results showed that forest structure under restoration plantings were more complex than monoculture plantations,with a relatively complex vertical stratification.Restoration plantings had developed a structure relatively similar to natural forest.Compared to monocultures,restoration plantings with multiple tree species could get higher understory species diversity and strengthen resistance to invasion in restored communities.Monoculture plantations of native species were relatively simple in structure.The density of woody seedling regrowth under plantation of the broadleaf species(Alnus nepalensis)was higher than that under native coniferous plantation(Taiwania cryptomerioides).However,the degraded site was still dominated by undershrubs and grasses>30 years after abandonment.Hence,we recommend active restoration plantings should be implemented if the major objective is to restore high-diversity subtropical forest system.For the advantages of providing more reforestation options than monocultures and of ecological benefits,we suggest to select a variety of native tree species and develop mixed-species forest.This study will inform restoration programs in subtropical regions,helping to speed forest successional processes,and enhance the biodiversity and ecological value of restored ecosystems.