Research On The Response Of Radial Growth To Thinning And Climatic Factors For Platycladus Orientalis Plantation In Beijing

Five sample plots of Platycladus orientalis plantation of different thinning intensities (14.7%, 16.7%,18.6%,24.5%,24.8%) were investigated in the Farm of Beijing Ming thirteen Tombs.27 Platycladus orientalis trees were selected by stem analysis and their DBH (diameter at breast height) disk of annual ring width were measured. Five competition indexes were associated with DBH, and the relative change in five competition indexes before and after cutting were used as a description for the change in space and related resource. In stand level, different thinning intensity affected the structure of forest stand, such as average diameter at breast height, stand per hectare accumulation, diameter, structure and the change of the intensity of competition. In individual tree level, the feature of radial growth release after thinning five years (2010-2014) was analyzed by the dendroecological method and multiple linear regression statistical modeling from the forest competition perspective. The relationship between radial growth characteristics of Platycladus orientalis and climate factors were analyzed with tree-ring method before cutting in 36 years (1974-2009) to explore the effect of climate change on radial growth of Platycladus orientalis. Climatic variables were monthly mean, maximum and minimum temperature and monthly total precipitation over the period from May in previous year to September in current year. The main conclusions were as follows:(1) For young stand of Platycladus orientalis, light thinning should be the main treatment. The volume cutting intensity should not be more than 20% and the cutting volume should be less than the periodic volume growth. Under the condition of the site in the research area, the stand density was adjusted to 2000 plants/hm2, average competition index (CI4r5) was around 7, stand volume per hectare was relatively high.(2) 5a moving average method was used to calculate the PGC (Percent Growth Change) in order to describe the size of tree growth release after cutting. According to the correlation coefficient R2 of the established regression equation between the PGC and CCI, the neighborhood interference radius of Platycladus orientalis was about 5 meters, which was determined by partition fitting method under the site condition. The relative change (CCI3, CCI4, CCI5) by the distance dependent competition indexes (CI3, CI4, CI5) was superior to the relative change (CCI1, CCI2) by the distance independent competition indexes (CI1, CI2). Among them, competition index change (CCI4) by the area of distance ratio (CI4) was the best index to describe the changes of the stand space and resources after cutting.(3) The multiple regression model was created by the independent variables of 5-meters neighborhood interference radius, CCI4,5, DBH of the object tree before the cutting and slope aspect. In the model, PGC was not significantly correlated with slope aspect (P=0.822). Growth release competition model 2 with the lowest AIC value was established by stepwise regression (PGC=40.840-109.392CCI4r5+5.926D,R2=0.527).This model explained 52.7% of the variation in PGC changes. The change in CCI4r5 was the most important factor affecting the PGC, which explained 45.8% of the variance in the tree growth reaction. PGC increased while CCI decreased, i.e. the radial growth after cutting increased while the growing space of trees was enlarged. The DBH tended to influence the tree growth response (P=0.06) and bigger trees had a larger growth release effect (maximum DBH was 11.9 cm in this paper). Radial growth was not significantly affected by slope aspect after cutting, since variable slope aspect was eliminated according to AIC in the process of modeling.(4) The correlation analysis indicated that radial growth of Platycladus orientalis was positively controlled by minimum temperature in previous May and June and current May, mean temperature in previous October and precipitation in current March and September. Both the correlation and response function showed that the radial growth was positive with spring precipitation (current March) significantly. Correlation coefficient and response coefficient were 0.62 and 0.43, respectively. The precipitation in spring (March) promoted the growth of Platycladus orientalis. The research on climate condition by the formation of characteristic tree-ring was conducted. This research found that the precipitation was the main factor affecting the growth of Platycladus orientalis, which means that the emergence of narrow tree-ring was due to few annual rainfalls. The characteristic wide tree-ring was heavier affected by winter and spring precipitation than that in growing season precipitation. The formation of characteristic tree-ring was not significantly affected by temperature.(5) One-way volume table (y=0.0003x2+0.0011x-0.0074, R2=0.9281) was created by the fitted polynomial equation regression in study area. Compared with one-way volume table in Beijing, the volume of Platycladus orientalis in study area was higher than that in Beijing under the same DBH. The corrected one-way volume table provided a reference for the calculation of individual Platycladus orientalis or stand volume.