جستجوی مقالات مرتبط با کلیدواژه « stand density » در نشریات گروه « کشاورزی »

In this study we assessed the role of plantation spacing on the quantitative and qualitative characteristics of black poplar (Populous nigra L.) in three stands at 1/5×1, 1/5×irregular (0.44-1) and 3×1-meter planting intervals in the campus of Urmia University. The diameter at breast height (dbh) along with qualitative characteristics, including tree forking and vitality, crown and/or stem breakage and tree leaning of all individuals, were assessed in an area of 2500 m2 in each stand. To calculate form factor (F), 30 stems were chosen randomly in each stand (90 in total) and felled at 10-15 cm above ground. The diameter of all cut trees was measured at intervals of 0.1, 0.3, 0.5, 0.7 and 0.9 of tree length. A growth-ring disk (cross-section) was obtained from the stump of each tree to study the relationships between annual rings and plantation spacing. Furthermore, the standing volume of each stand was calculated using Huber, Hohenadel and simple (F=0.5) formulas. Results showed that the maximum dbh and height growth occurred in 1x3 m and 1x1/5 m planting intervals, respectively (α=5%). Also, the minimum mean volume was recorded for 1/5×irregular spacing. No significant differences were obtained for the amount of standing volume/ha using the three methods. Based on our results, the highest incidence of stem breakage and nearly 50% of tilted trees were observed in 1/5×1 m spacing.

The aim of the study was to investigate the effects of tree mortality on structural characteristics of an oak stand named Shalam Forest, with 670 ha area, located 10 km south east Ilam city of I.R. Iran. The structural characteristics consisted of stand density, basal area, canopy cover density, species composition, silvicultural form and distribution pattern of dead trees density and basal area and different diameter classes. The studied area was divided to 20 homogeneous topographical units in which three circular plots with 1000m2 area were located to measure diameter at breast height (dbh), minimum and maximum diameter of tree's crown, percentage of dried crown, trees origin and silvicultural form of each species separately and record the data. The results showed that the trees and shrubs density was reduced at 15.7%, in which 97.65% belonged to Quercus brantii. Basal area reduced at 14.23%, in which 95.29% belonged to Q. brantii. Mortality was found at most of the diameter classes, but the greatest amount was found at 10 to 25 cm classes and the maximum rate was found at 5, 60 and 75 cm classes. In addition, the maximum reduction rate of basal area was found at 25 to 45 cm classes. Although density of the most trees and shrubs species reduced and their mixture percentage changed, but the species composition was almost stable. Crown density reduction was about 12.88%. Tree mortality at coppice forest type was more than the standard type, but mortality rate at standard forest was more than the coppice one. DCA analysis defined the sample plots distribution according to their circumstances and situation and showed that there is a relationship between tree decline and dbh variable. Overall, tree mortality at the studied area caused great changes in stand structure of Q. brantii, for instance different tree characteristics changed, particularly dbh, which separated tree population before and after their mortality. The results might be used for conservational and protectional management of the dried and declined forest of Zagros region of I.R. Iran.