Meteorological response analysis of the nondestructive tree ring characteristics of poplar plantation

A poplar is one of the most important tree species in the northern temperate regions. There is the great difference in the growth state of poplar with different planting density and its response mechanism to climate factors. Tree ting characteristics (TRC) and tree measurement factors can provide the scientific basis for the sustainable management of forestry and the decision-making on countermeasures against meteorological change. This study aimed to clarify the response mechanism of poplar with the different planting densities to climatic factors using non-destructive measurement technology. A systematic analysis was implemented on the tree growth and response to meteorological factors under specific climatic conditions in the northern Jiangsu Plain. The research object was taken as the multi-density poplar plantation in the Chen Wei Forest field of Suqian City, Jiangsu Province, China. Resistograph resistance instrument was used to non-destructively measure the tree ring characteristics of 224 standard trees in four planting plots of poplar plantation. Six parameters were obtained, including ring width (RW), early wood width (EW), late wood width (LW), ring density (RD), early wood density (ED), and late wood density (LD). Five types of models were used to fit the growth model of ring width. Principal component analysis (PCA) was used to cluster the ring characteristics of four planting configurations. Pearson correlation analysis was used to investigate the correlation between annual meteorological factors and tree ring metrology characteristics under different planting configurations. The results show that: 1) There was the significant influence in the tree measurement factors. The stand density increased with the decrease of row spacing. The form factors and form quotients of chest height gradually increased, and the stem shape was straight and full. 2) The logistic model was better fitted the radial growth of poplar with four planting configurations. The R² values reached above 0.94 for all models, indicating the better prediction on the growth of tree rings. 3) The principal component analysis showed that the trees with the same planting density but different planting configurations (3m×8m and 5m×5m, 4.5m×8m and 6m×6m) were clustered into the same category, where the contribution rate of tree-ring density and width factor were 49.1% and 28.9%, respectively. 4) Poplars with the similar planting density showed the similar responses to meteorological factors. By contrast, the poplars with the high planting density (400 plants /hm²) were more sensitive to air temperature than those with the low planting density (278 plants /hm²); 5) There were significant differences in the response of radial growth of standing trees to climate factors under the four planting configurations. The growth of ring width was depended on the wind speed YS, indicating a significant positive correlation (the correlation of early wood width EW reached 0.85 in the planting area with configuration of 6m×6m). There was a negative correlation between the ring density and the annual meteorological factors, among which the average annual relative humidity YRH showed a significant correlation in the four planting configurations, and the maximum was −0.82 in the 3m×8m planting configuration. 6) The seasonal response was found in the monthly meteorological factors. In spring, the temperature factor was negatively correlated with the ring characteristics, while the precipitation factor was negatively correlated with ring density, and the humidity factor was positively correlated with ring width. The correlation between wind speed and ring characteristics was the greatest, especially in spring, with the sparse planting configuration, the correlation between wind speed and ring characteristics increased gradually. Nondestructive measurement of tree ring characteristics can provide the radial data of tree-ring of multi-density poplar plantation. The ring width and ring density index of the poplar plantation shared a strong correlation with the meteorological factors under different afforestation densities in the study area. The finding can provide the great potential to reveal the effect of meteorological change on the growth and development of plantation.