| With the exception of a few intensive forests,the growth of most forests is highly dependent on external conditions,among which climatic conditions are the most important factor.The area of Mount Tai is located in the middle of Shandong Province,and water resource is relatively scarce.In recent years,extreme climatic events such as drought in spring or summer in Shandong occurred more and more frequently.The shortage of water resources is an important factor that restricts the forest quality improvement,and it is also the main difficulty of plantation management in this area.The principle of ecological water balance should be followed in the process of stand construction and management.There is a certain demand for water in different stands,and precipitation is the direct source of water for stand growth.Therefore,it is of great theoretical and practical significance to explore the corresponding characteristics and correlation of different stands to precipitation,build and manage the stand reasonably according to the local precipitation conditions,and improve and give full play to the productive potential of the stand.Most of the existing research results are based on the relationship between forest growth and long-term precipitation,such as year,month,etc.The annual rainfall and monthly rainfall are traditionally commonly used rainfall metering indexes,but these two indexes reflect the rainfall sum in a long period of time.However,actually,the growth of trees requires a certain amount of water(mainly from precipitation),and the demand for water is constant,stable and uniform.Therefore,on the basis of annual and monthly precipitation,this study attempts to explore the comparison and analysis of short-term precipitation such as 5-day precipitation,ten-day precipitation and forest water demand in the corresponding period to construct the evaluation index of precipitation suitability.In order to reflect the uniformity and sustainability of precipitation,and then analyze the influence and correlation of its changes on the growth of trees,and compare it with the suitability index constructed by monthly precipitation and annual precipitation.The superiority of precipitation suitability index based on shorter precipitation is analyzed.In this study,three typical artificial forest species,Quercus acutissima,Robinia pseudoacacia and Pinus densiflora,were selected as the research objects,taking the typicalmountainous area of Shandong-Taishan area as the research area by means of tree-ring climatology.In the same altitude range,the growth cone samples of the three tree species were collected,and the standard chronology of DBH growth of three tree species was established.Based on the meteorological data of 1976~2016a,the suitability function model of the difference between the theoretical water demand of Quercus acutissima,Robinia pseudoacacia and Pinus densiflora and the actual precipitation conditions was established to evaluate the influence of the precipitation in 5 days,10 days or months during 1976~2016a.Finally,the correlation analysis was made between the standard chronology of three tree species and the suitability of precipitation in 5 days,10 days,months,and interannual precipitation,and the correlation of actual annual precipitation and annual distribution on the DBH growth of three tree species during 1976~2016a were analyzed.The main findings are as follows:(1)The interannual water demand of Quercus acutissima,Robinia pseudoacacia,and Pinus densiflora was 445.1~596.2mm,420.5~577.5mm,489.1~817.1mm respectively,which was lower than actual annual precipitation during 1976~2016a.In the years with less or more precipitation,the precipitation suitability of the three species was low and the tree ring growth in the corresponding year was lower than the expected value.Therefore,too much or too little precipitation,as well as nonuniform distribution of rainfall in the year could not meet the water requirement of Quercus acutissima,Robinia pseudoacacia,and Pinus densiflora.On the contrary,in 2008 a and 2014 a,the short-term(5 days,10 days)precipitation suitability of three tree species was relatively high,and the tree-ring growth of three tree species was higher than expected value,which indicated that the precipitation of 2008 a and 2014 a was suitable for the growth of Quercus acutissima,Robinia pseudoacacia,and Pinus densiflora.(2)At the same altitude,the short-term precipitation suitability values of Quercus acutissima,Robinia pseudoacacia and Pinus densiflora were significantly correlated with the tree-ring width of three tree species.The correlation between tree-ring width index of three tree species and monthly precipitation suitability or annual precipitation suitability was not significant.Compared with long-term precipitation(monthly precipitation,annual precipitation),the growth of three tree species is more susceptible to short-term(5 days,10days)precipitation changes.Therefore,the suitability index constructed by short-term precipitation can better reflect the rainfall conditions.(3)In the same altitude range,the correlation between the tree-ring width index of three tree specie and the short-term(5 days,ten days)precipitation suitability is different.The tree-ring width index of Robinia pseudoacacia has a significant positive correlation with theshort-term precipitation suitability,while the tree-ring width index of Quercus acutissima and Pinus densiflora has a significant positive correlation with the short-term precipitation suitability.It means that the DBH growth of Robinia pseudoacacia was more susceptible to the short-term change(5 days,10 days)of precipitation than that of Quercus acutissima and Pinus densiflora.Therefore,short-term water control should be strengthened in the plantation management of Quercus acutissima,Robinia pseudoacacia,and Pinus densiflora in order to improve the ability of tree species to cope with extreme climatic events and to reduce the cost risk of forest management.This study attempts to evaluate the difference between theoretical water demand and actual precipitation in three species of Quercus acutissima,Robinia pseudoacacia,and Pinus densiflora by means of precipitation suitability evaluation model,and uses correlation analysis to study the relationship between the DBH growth of three tree species and the variation of precipitation suitability in different periods.The evaluation model of precipitation suitability is reasonable and operable,which provides a new idea for the study of the relationship between stand growth and climate factors,and has practical reference value. |
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