The Dynamics Of Picea Crassifolia Radial Growth During Growing Season And Its Relationship With Environmental Factors On The Northern Slope Of The Central Qilian Mountains

Picea crassifolia was a special tree species in Qilian mountainous area,which played an important role in maintaining biodiversity and soil and water conservation.Its growth status had a very important influence on the understanding of the ecological hydrological processes in Qilian mountainous area.In recent years,the research on the radial growth of P.crassifolia was focused on the inter-annual variation,while the role of growth within the year was ignored.Therefore,the experiment was carried out in Pailugou small watershed on the northern slope of the Central Qilian Mountains.At the altitude of 2500-3300 m,the growth of P.crassifolia was continuously monitored by the growth scale,and the environmental factors were monitored simultaneously.In this paper,the annual growth of P.crassifolia was summarized,and the relationship between the radial growth rate and tree size,community structure and environmental factors of P.crassifolia was analyzed.The purpose of this study was to understand the growth mechanism of trees in arid areas,and to provide a basis for the scientific prediction of forest resources dynamics and future development trends,as well as to provide support for the establishment of distributed eco-hydrological models in the Heihe River Basin.The main conclusions of this study were as follows:(1)The growth period of P.crassifolia85% of P.crassifolia began the radial growth in the end of May to early June and stopped it at the end of September,and with the increase of altitude,the growth period of P.crassifolia was prolonged,the growth period of low altitude(2500-2700 m)was 146 days,and middle altitude(2900 m)and high altitude(3100-3300 m)was 152 days.(2)The change of radial growth rate of P.crassifoliaThe radial growth rate of P.crassifolia was mainly affected by tree size,altitude and season.The growth of big trees was faster than that of middle trees and small trees.The average growth rate was 6.9 ?m·d-1,1.3 times of that of middle trees,and 5 times of small trees.The average radial growth rate of P.crassifolia varied with an “unimodal” trend along with an altitudinal increasing,and reached a peak of 9.65 ?m·d-1 at the altitude of 2900 m.It was 1.67-6.2 times of that of the altitude of 2500-3300 m.The seasonal distribution of the radial growth rate of P.Crassifolia was summer > autumn > spring.In summer(June-August),the average growth rate of P.crassifolia was 6.12 ?m·d-1,which was about 7 times that of spring(May)and 1.1 times that of autumn(September).(3)The change of annual total radial growth of P.crassifolia forestThe annual BAI growth of P.crassifolia forest was 1835.2 cm2·hm-2 in study area.The annual total radial growth of P.crassifolia was mainly affected by tree size,altitude and year.The contribution rate of the Middle-sized trees to the total growth of the forest was 45%,which was the most.And the total growth of BAI was 177.4 cm2·hm-2,which was 4 times of the Big Trees and 1.2 times of the Saplings.With the increase of altitude,the total growth of BAI of P.crassifolia showed a single peak,with a peak at an altitude of 2900 m.The total average growth of BAI was 1129.2 cm2·hm-2,and the contribution rate to the total growth of the forest was 61.5%,which was 4.6-14.3 times of other elevation.In 2016,the total growth of BAI was 2319.0 cm2·hm-2,which was 1.7 times that of P.crassifolia in 2015.(4)The effects on radial growth of P.crassifolia by environmental factorsComprehensive analysis showed that temperature was the dominant factor affecting the radial growth of P.Crassifolia.Among the factors,the radial growth of P.Crassifolia of the elevation of 2500-2700 m was mainly affected by soil temperature,daily mean temperature and maximum temperature.The radial growth of P.Crassifolia of the elevation of 2900-3300 m was mainly affected by ?0? accumulated temperature.Moisture was the second factor affecting the radial growth of P.Crassifolia.The radial accumulated growth of P.Crassifolia was positively correlated with rainfall,but the correlation was not significant.The correlation of radial accumulated growth of P.Crassifolia and soil moisture content was correlated with soil level.The radial accumulated growth of P.Crassifolia of the elevation of 2500m-3100 m showed correlated relationship with soil moisture content of 20-60 cm,the correlation coefficient was 0.225-0.832.The radial accumulated growth of P.Crassifolia of the elevation of 3300 m showed negatively correlated with soil moisture content of 20-40 cm,but the correlation was not significant.