جستجوی مقالات مرتبط با کلیدواژه « cluster sampling » در نشریات گروه « جنگلداری »

Forest health monitoring is essential to assess the changing state of forest resources and create awareness of forest health issues. This study was conducted to monitor forest health using two indicators of regeneration and deadwood in the Masouleh watershed,. To collect data in the study area, using Forest Health Monitoring method 5 clusters of plots including 20 plots in two different altitudes were considered. In each cluster, the regeneration status of species was determined based on the quality of seedlings and their division into two categories: healthy and unhealthy. The characteristics of the deadwood including diameter, and quality characteristics (species type, degree of decay) were measured and recorded. In the study area, 80% of the seedlings were healthy and 20% unhealthy. The results of the analysis of variance of the number of regenerations per hectare in the altitude classes showed that there is a significant difference between the number of healthy seedlings and unhealthy seedlings in the studied altitude classes. According to the results of the study, the volume of deadwood is 44 m3/ha, which is 34 and 10 m3/ha of down logs and standing deadwood, respectively. Analysis of variance showed that there was no significant difference between the volumes of deadwood per hectare in the two altitude classes in the study area. But there is a significant difference in the number of deadwood per hectare in the altitude classes. Study of the quality of deadwood showed that the highest percentage of deadwood belongs to the first-level decay (81%).

This study aimed to analyze tree diversity and tree crown and stem condition as two indicators of forest health in the Masouleh forest watershed, Guilan province. Field data collection was performed using cluster sampling based on Forest Health Monitoring (FHM) method. A total of 5 clusters including 20 subplots in the mixed beech (Fagus orientalis Lipsky.) forest stand were established. Within each cluster, quantitative and qualitative characteristics of existing trees such as diameter at breast height (dbh), total height, canopy diameter, density, and percentage of crown dieback and stem quality were studied and measured. To assess the tree species diversity, species biodiversity indices, richness and evenness were calculated in each cluster. Based on the results of the analysis of variance in 95% confidence level, there are no significant differences in the species diversity indices between the five different clusters (P>0.05). The highest and lowest value of the species diversity indices were measured in clusters 2 and 3, respectively. The largest change in the species diversity occurred at cluster 4. The results showed that all clusters in the study area had good status in terms of the species diversity indices. The amount of canopy drought in some species was proportional to the trend of canopy diameter changes and Buxus hyrcana Pojark. and Diospyros lotus L. species had the highest percentage of canopy drought (approximately 17%). Regarding the quality of stems, more than 80% of the trees in the forest stand have good quality. It is concluded that the health status of the studied ecosystem in terms of the level of tree diversity and tree crown and stem conditions is desirable.

The aim of the study was to identify the quantitative characteristics of wild pistachio forests of Fars province of Iran and their natural regeneration. For this reason, the cluster sampling method was applied which consisted of a 20×20 km network with nine sample plots, each of 2000 m² area with crucified pattern. The results showed that the natural regeneration was weak and the number of seedlings was 5.2/ha, the average crown cover was 171.25 m²/plot and 855 m²/ha or 8.5% of total forests area. The average of plots per cluster was 7.4 and the average of crown cover per cluster was 1256.1 m². Proportion of wild pistachio trees was 7.7%, consisting of 58.3% male individuals. Most of the stands were located in mountainous areas with steep slopes covered with rock materials or shallow soils. Application of rain-fed farming, tree cutting and over grazing were the main causes of forest degradation. Forest protection and reforestation with native shrubs including wild almond species might have positive effects on rehabilitation and improvement of wild pistachio natural regeneration.