Correlation Studies Of Spruce Needle Castwith Forestland Factors And Stand Structure

As an important afforestation tree in China,spruce playsa great role in economy and ecology.Spruce Needle Cast caused by Lophodermium piceae?Fuckel?V.Hohnis a common disease in spruce plantations and usually resulted in fallen needles,especially in the young-age spruce plantations.Our research group has been devoted to the study of this disease in western Sichuan including the pathogen,pathogenetic mechanism and physiological response of spruce to pathogenic infection,etc.But it's still hard to control it.Although some chemical treatments were adopted,there are still some problems need to be solved.Some studies indicated that the stand structure is one of the significant influence factors in the occurrence and development of the disease,but no report indicated the relationship to the Spruce Needle Cast.And this is the main purpose of this paper.We chose Baishahe Forest Farm located in Tianquan county of Sichuan as test plot,in which 40standard sample plots were set up,and forestland factors?tree age,canopy density,slope aspect,density,slope gradient and altitude?,stand structure?tree species,chest diameter,tree height and spatial structure indexes?and the disease index were investigated.The correlation between the disease index and forestland factors,composition structure of tree species,distributions structure of chest diameter and stand spatial structure?uniform angle,mingling degree and neighbourhood comparison?was performed.The relationships between Spruce Needle Cast and forestland factors and stand structure were analyzed,and a theoretical reference to the ecological regulation of the disease was provided.The main results are as follows:?1?The correlationbetween Spruce Needle Cast and forestland factors was studied,and a predictive model for the disease index was established.According to the analysis of partial correlation coefficient,the contributed degree of each index to Spruce Needle Cast was spruce age?X₁?,canopy density?X₂?,slope aspect?X₃?,density?X₄?,slope gradient?X₅?and altitude?X₆?in order.The model showed an extremely significant level and reached certain credibility,showed as follows.Y_i?Disease index?=71.063X₁₁+55.757X₁₂+35.716X₁₃+12.106X₂₂+19.750X₂₃+14.778X₃₂+7.068X₃₃-16.519X₄₂-14.004X₄₃+2.747X₅₂-3.432X₅₃-5.666X₆₂-10.143X₆₃.R=0.822(>R_0.01=0.618).?2?The correlation between Spruce Needle Cast and composition structure of tree species was estimated.The results showed that shannon-wiener index had a significantly negative correlation with the incidence and the disease index?r₁=-0.677,P<0.01;r₂=-0.856,P<0.01?;The Pielou index was negatively correlated with the incidence and the disease index,but not significantly?r₁=-0.118,P>0.01;r₂=-0.110,P>0.01?;The Margalef significantly negatively correlated with the incidence and the disease index?r₁=-0.663,P<0.01;r₂=-0.822,P<0.01?.Based on the analyses,this disease may be under control through planting mixed forestation.?3?The correlation study betweenSpruce Needle Cast and distributions structure of chest diameter indicated that the average chest diameter of the trees with the highest infection grade?D3?,the average chest diameter of the trees with the lowest infection grade?D4?,location parameter?a?,shape parameter?c?were significantly negatively correlated with the disease index,and D4>a>c>D3.Another four indexes,the average chest diameter for all trees?D0?,average chest diameter of affected trees?D1?,average chest diameter of uninfected trees?D2?,and scaling parameter?b?,showed no significant correlation with the disease index.The average chest diameter of the trees with the lowest infection grade?D4?was most closely related to the diseaseindex,and has a significantly negative correlation with the diseaseindex,which indicated that the smaller chest diameter of lowlyinfected-grade spruce,the greater probability to resultin serious disease.Therefore,it is recommended that when carrying out forest managements,thinning the small chest diameter spruce,especially the diseased small chest diameter spruce could limit the development of this disease.?4?The effect of stand space structure on Spruce Needle Cast.The uniform angle was negatively correlated with the disease index,but not significantly?r=-0.081,P=0.894>0.05?;Mingling degree significantly negatively correlated with the disease index?r=-0.991,P=0.008<0.01?;The neighborhood comparison of chest diameter and tree height significantly negative correlated with the disease index?r1=-0.994,P<0.01;r2=-0.990,P<0.01?.To reduce the disease index of Spruce Needle Cast,the mingling degree and the neighborhood comparison should be adjusted rather than the uniform angle.Accor ding to the analysis,when planting mixed forests,the mingling degree is better to set up to 0.5-0.75.In addition,small plants should be planted to increase neighborhood comparison because of the spruce's slow growth.