| Biomass and productivity are the most basic indicators for measuring the structure and function of forest ecosystems.Exploring the system dynamics of forest biomass dynamics and the formation of forest productivity has important guiding significance on current issues such as how to maintain global carbon balance and guarantee the supply of human timber and its products.It has been a tedious and heavy work to measure the long-term pattern and dynamics of biomass and productivity in forest ecosystems.The rise of annual climatology and the gradual maturation of forest growth models have provided important support for forest biomass and productivity data.Pinus massoniana is a native tree species in China,which has the advantages of being resistant to plutonium and strong adaptability.It is the most widely distributed afforestation tree species in the humid subtropical regions of eastern China.On the basis of previous researches,this paper takes Pinus massoniana plantation distributed under the long-term strict protected area in Dinghushan National Nature Reserve of Guangdong as the research object,based on the investigation of the biomass of the sample plot.The tree-ring analysis method was used to calculate the long-term dynamics of the net productivity of the plantation forest from 1959 to2016,based on the monitoring data of long-term climatic factors,the correlation between climatic factors and the standard chronology representing the radial growth status of forest trees and the correlation between climatic factors and net productivity were constructed.Research indicates:?1?The annual average temperature?T?in the Dinghushan area had a significant increase?P<0.01?,but it was lower than the national average temperature rise level,the vapor pressure deficit?VPD?had a significant upward trend?P<0.01?.In terms of time series,there was no significant change in annual precipitation?P?and the climate moisture index?CMI??P>0.05?,and the total annual sunshine hours?R?,annual evaporation?E?,and annual average relative humidity?RH?all decreased significantly?P<0.01?.The trend of P,E and CMI were different from that of interannual trend.T,RH and VPD had the same monthly trend and interannual trend.The average maximum temperature in May,August,October months and the average minimum temperature in January to February,June to November months had a significant upward trend?P<0.01?,There was no significant trend of precipitation per month?P>0.05?.The evaporation in January and March to August of the region showed a significant downward trend?P<0.05?,there was an upward trend in October and November but not significant?P>0.05?,and VPD had a significant increase from month to month?P<0.05?.Among them,the rising trend from January to April was smaller than other months.?2?The exceptionally superior climatic conditions of the South Asian subtropics had resulted in a higher level of forest productivity.The total biomass of the tree layer of Pinus massoniana plantation in Dinghushan gradually increased from 5.58 t·hm-22 in 1959 to116.21 t·hm-22 in 2016.Between 1959 and 2016,the trend of annual changing in the biomass of various organs was basically the same.The distribution of total biomass in the tree layers showed that the ratio of total biomass to total biomass increased year by year,the proportion of tree trunk increased first and then decreased,and the ratio of total leaf biomass to total biomass decreased year by year.The average annual net productivity of Pinus massoniana plantation was 1.97 t·hm-2·a-1,the highest net productivity was 3.99 t·hm-2·a-1,and the maximum single tree net productivity was 32.78 kg·a-1.The change in net productivity of each organ was characterized by a greater increase in branch productivity than in leaves,and a net increase in leaf net productivity earlier than in other organs.The net productivity of each organ of Pinus massoniana has a tendency of“S”change year by year with the change of forest age.Climate productivity is an indicator used to describe the production potential of planted forests calculated from factors such as temperature and precipitation.Compared with most regions in China,the region had high potential for climate production.Affected by the density,the overall net productivity of the stand was not high,but the dominant tree maintained a high net productivity.Regional warming is evident in early spring and autumn and winter,and the threshold of annual average temperature difference is becoming smaller.The regional climate has a tendency of drought year after year,among which the dry season is even more drought.?3?The temperature in March was significantly positively correlated with the standard chronology of Pinus massoniana?P<0.05?.The temperature in March was the main climatic factor affecting the radial growth of Pinus massoniana.The regression analysis of climatic factors and net productivity showed that most of the variation in net productivity was caused by climatic factors.The formation of productivity depended on the demand and regulation of factors in different growth stages.The response of climatic factors to the net productivity of Pinus massoniana plantations differed at different times and scales.Average low temperature in February and The higher temperature and sunshine duration in October to November were conducive to the accumulation of biomass.The lower average minimum temperature and sunshine hours in August were more conducive to the accumulation of biomass of Pinus massoniana.At the same time,the higher net relative productivity of relative humidity and evaporation in August would be greater.The climatic conditions of the previous year also had an impact on the accumulation of biomass in the year,and the response of the net productivity of forest lands to the climatic conditions in different months was different.The temperature in early spring and late autumn in the region is an important factor in regulating the growth cycle of Pinus massoniana,and having higher heat level is an important factor that is higher than the net productivity of artificial forest in other regions.From March to June,the higher CMI was beneficial to the accumulation of net productivity in the Pinus massoniana forest,and the CMI in June had a significant positive correlation with the net productivity?P<0.05?,which was the key factor for the relatively high net productivity of the stand. |
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