Analysis Of The Microclimate Difference In Old-growth Forest And Secondary Forest Of Giant Pandas' Habitat

Giant panda(Ailuropoda melanoleuca)is a unique rare species in China,known as "national treasure" and "living fossil ",and is a precious natural heritage in the world.Nowadays,it has been the focus of research on whether the survival of giant pandas is affected by global climate change.The distribution and population changes of giant pandas in the historical period were mainly affected by geological changes and climate changes,etc.During the interglacial period,when the weather was warm and humid,the giant pandas spread north to higher latitudes,and the population size increased.During the glacial period,when the weather was cold and dry,the distribution area and the population size had shrunk too.Nowadays,the earth is experiencing global climate change,and many species have been confirmed to be affected by this.Our study is distinguished from previous studies which used macroclimate as research data.Macroclimate refers to the sum of climatic conditions in the geographical areas,whose climate data were generally obtained by weather stations,satellite detection,radar detection,etc.In order to explore whether the microhabitat of giant panda has a certain buffer effect on the climate,and whether the giant pandas will be affected by global climate change.Our study analyses the data from giant pandas' microhabitat and the microclimate include temperature,relative humidity,light intensity,etc.The study could provide a theoretical basis for the fine management of giant pandas' habitat in the future.In this study,we chose Li Ziping National Nature Reserve as our research site.Li Ziping National Nature Reserve is located in Xiaoxiangling Mountain,where the existing wild giant pandas are the least in the six major mountain.And it is an important part of the giant pandas' habitat in Xiaoxiangling.In this study,28 microhabitat samples were set up in old-growth forest and secondary forest in Liziping National Nature Reserve,and then we analyzed the data to compare the difference of vegetation structure between old-growth forest and secondary forest.The results showed that the vegetation structure in the old-growth forest was more complex,the trees were more dense: the DBH,height,quantity and canopy density of the trees in the old-growth forest were significantly larger than those in the secondary forest that the DBH(t =-8.346,P < 0.00),height(t =-8.021,P < 0.00),quantity(t =-10.333,P < 0.00)and canopy density(t =-25.453,P < 0.00).However,the coverage of bamboo was significantly lower than that in the secondary forest(t = 8.495,P < 0.00),which indicating that felling has a significant effect on forest structure.The tree canopy density and the number of perennial bamboo have the greatest contribution to distinguish the old-growth forest from the secondary forest,and the more suitable old-growth forest for the survival of giant pandas has greater canopy density and a more suitable number of perennial bamboo.In order to collect microclimate data,our study installed 14 data loggers(model: HOBO U12-012)in old-growth forest and secondary forest to record data such as temperature,relative humidity,illumination from April 2019 to October 2019.First,the multivariate analysis of variance found that the forest type had a significant effect on all variables except the highest relative humidity;the elevation had a significant effect on the average temperature,the lowest temperature,the highest temperature,the temperature range,the minimum relative humidity,the relative humidity range,the average illumination,the maximum illumination,the illuminance range;and the time had a significant effect on all variables.Secondly,the linear mixed model found that forest type and elevation had significant interaction effects on variables other than maximum temperature,average relative humidity and maximum relative humidity;forest type and time had significant interaction effects on mean temperature,minimum temperature,maximum illuminance,range of illuminance;elevation and time had significant interaction effects on mean temperature,minimum temperature,maximum temperature,minimum illuminance,maximum illuminance range of illuminance.The result show that the average and the highest temperature in the old-growth forest were significantly lower than that in secondary forest(t = 2.94,P < 0.00;t = 3.35,P < 0.00);and the lowest temperature was significantly higher than that in secondary forest(t =-6.37,P < 0.00).The average and the lowest temperature were higher from June to September,while the maximum temperatures were higher in April and August.The mean the lowest relative humidity in the old-growth forest were higher than that in secondary forest(t =-2.26,P < 0.02;t =-5.39,P < 0.00),and the higher values were observed from May to November.The mean and the maximum illuminance in old-growth forest were both significantly smaller than that in secondary forest(t = 13.16,P < 0.00;t = 12.96,P < 0.00),and from April to November,the illuminance in secondary forest was larger.The minimum illuminance in the old-growth forest was significantly larger than that in secondary forest.The average temperature,the lowest temperature,the highest temperature at the low elevation were significantly higher than those at the high elevation,while the temperature range at the middle elevation was the highest(F = 10.94,P < 0.00).Elevation only has a significant effect on the lowest relative humidity,range of relative humidity,the lowest relative humidity in the middle elevation is the smallest,while the range of relative humidity is the largest.The elevation significantly affected the mean illuminance,the minimum illuminance,the maximum illuminance,and the range of illuminance,in which the mean illuminance,the maximum illuminance,and the range of illuminance were all the largest at the medium elevation,while the minimum illuminance decreased significantly with elevation(F = 28.04,P < 0.00).The range of temperature,range of relative humidity and range of illuminance in theold-growth forest were all significantly lower than those in the secondary forest(t = 8.02,P < 0.00;t = 6.42,P < 0.00;t = 13.02,P < 0.00).From the whole April to October,the range of temperature,range of relative humidity and range of illuminance were all lower than those in the secondary forest.the minimum range of temperature,minimum range of relative humidity appeared in May,July,and September,while the minimum range of illuminance appeared from June to September.The results show that the microclimate such as temperature,humidity and light under the old-growth forest are more stable,the complex vegetation structure of the old-growth forest has a stronger buffering effect on the climate,and the forest cutting leads to the weakening of the buffer capacity of the secondary forest to climate change.In the context of global warming,it is of great significance to protect the forest environment – especially the old-growth forests –for the long-term survival of the giant panda populations in the future.