Study of the effect of shade on Poplar height and diametric growth and pest abundance in Guilan province, Iran

Poplar plantation is of the main plantations in Guilan province. Shading caused by the adjacent trees is one of the effective environmental factors affecting the growth and development of poplar seedlings in nurseries, pest population densities and epidemics of pathogenic agents on poplar. During the years 2001-2002 a study was carried out to quantify the effect of shading on growth of poplar seedlings and population density and damage rate of two species of important poplar pests in Poplar Research Center of Safra-Basteh in Astane-Ashrafieh in Guilan province. Cuttings of the clone P. deltoides 69/55 were planted in this station in 9 rows (treatments) spaced differently from the adjacent shading trees, which were located in southern edge of the examining plot. There were 9 space intervals as treatment including 11, 12.6, 14.2, 15.8, 17.4, 19, 20.6, 22.2 and 23.8 meters apart from the shading trees. In the end of each year, heights of the seedlings and diameter of the stocks were measured and recorded. Population density of poplar mottled weevil, Clorophanus votuptificus and poplar defoliator wasp, Staurenematus compressicornis (important pests of poplar in this province) were counted weekly and were recorded for each treatment and replicates separately. Analysis of the data using MSTAT-C software showed that there is a significant difference between the treatments in terms of diametric growth and height. The more the distance of rows from shading trees, the more was their diameter and height. The treatments were in terms of the number of weevils significantly different (?=1%), so that the highest density of the weevil was on the treatments that were more in shade and the least number of weevils were recorded on the treatments 8 and 9 which had the most distant from shading trees. The behavior and reaction of the poplar defoliator wasp was completely different in terms of the population density of the defoliator wasp. There was a positive high correlation between height and diameter of the seedlings (r2=0.99) and a negative significant correlation was proved between the seedling heights with number of the weevils (r2=0.90). Correlation of the seedling heights with the number of the defoliator wasp was positive and significant (r2=0.73).