فهرست مطالب saeed rahbari sisakht

The aim of this research was to assess the effect and range of each forest road geometric plans on biodiversity and composition of plants on its two sides. To this end, to study the biodiversity of species of lateral stands and the effects of environmental variables in the situation of establishment of plant species at different distances of the road, the comparison of Shannon biodiversity Index (H), Menhinick species richness and Smith-Wilson’s index of evenness, detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used respectively, according to its geometric plans. Results of the comparison between biodiversity indexes showed that in both sides of the straight road to switch back, Shannon index and Menhinik richness increased, while Smith-Wilson evenness had an inverse trend. The results of DCA and CCA analysis showed that the distribution of demanding species was positively correlated with increasing light intensity and temperature on the road verge. The effect of the road on these species was up to a depth of 10 meters from its edge as well. Shade tolerant species were more in-depth of forest than the road.

Forest roads are the most important infrastructure to access and apply the forest management activities, which they can impose a significant impact on adjacent stands. The objective of this study was to investigate the effect of the forest road geometric plan (switchback, curve, and straight road) on some chemical and biochemical indicators of soil in adjacent stands for forest road planning. Considering three different road geometric plans, from the edge of the road up to 100 meters toward the forest interior, the rate of organic carbon, nitrogen, and dehydrogenase and urease enzymes activity in forest soil at the depth of 0-10 and 10-20 cm in two forest types was measured. Data were analyzed by using t-test, ANOVA, and broken-line regression model. The results of ANOVA showed significant effect of forest type and geometric plans of the road on measured variables. In addition, results indicated that by increasing the depth of soil, the impact of the road on some measured indicators was not significant. The results of broken line regression model showed that the lowest range of road effect was related to the straight road (13 m) and its highest range was related to switchback road (42 m). Results of this study can provide guidelines for forest road planners and evaluators to design the road effect buffer at the stage of forest roads network planning and to minimize the effect of forest road on its adjacent stands.

Gaps created by falling trees (tree-fall gaps) are a natural disturbance in forest ecosystems. Understanding scale, pattern and the effect of gaps on regeneration is important to current and future forest management. The aim of this study was to determine the size, shape and the spatial pattern of tree-fall gaps and of associated regeneration. This study was carried out in three parcels (No.15, 18 and 19) of second District Shastkalateh forest in northern Iran. The size, location and regeneration of all tree-fall gaps were measured in these parcels. One way ANOVA was used to compare gap features and regeneration and Spearman’s rank correlation coefficient was used to test the relationship between gap size and regeneration density. The results showed that the total area of gaps created by tree-fall in three parcels was 13.72 ha, or 7.4% of the total area, and on average there were 1.06 gaps per hectare. Gap size ranged from 49 m2 to 1827m2, with mean gap size being 658.2m2. Most (69.2%) gaps were 200 m2 to 1000 m2. Results of spatial pattern analysis showed both uniform and irregular shapes for gaps in three parcels. ANOVA analysis showed a statistically significant difference between gap size and regeneration density and the Spearman rank correlation showed a direct relationship between gap size and the number of seedlings. These results provide information to enable forests to be managed according to ecological principles.

The FAO Penman - Monteith (F-P-M) method is now broadly accepted as the standard for estimating the reference evapotranspiration (ET0). The method is also now used for evaluating the temperature-based [Blaney-Criddle (B-C) and Hargreaves-Samani (H-S)] and radiation-based [Jensen-Haise (J-H) and Turc (Tc)] methods. The objective was to compare the ET0 estimated by the B-C، H-S، J-H، Tc methods with that estimated by the F-P-M method in a semiarid climate using the meteorological data recorded in Hashem-Abad Agro-Meteorological Station، Gorgan. The mean value of ET0 was 3. 13 mm. day-1 using the F-P-M method. At daily scale، Tc method showed the lowest RMSE (Root Mean Square Error)، 0. 98 mm. day-1. At monthly scale، in compare to the other methods، the RMSE values by Tc method were lower in April as well as from September to March، averaged 0. 06 mm. day-1 with the percentage error of 3%. During the summer season، July and August، however، B-C method suggested the lowest RMSE value than those of the others (RMSE 0. 32 mm. day-1 with the percentage error of 6%). The H-S method behaves the best for monthly estimation (RMSE 0. 42 mm. day-1، the percentage error of 7%) during May to June. The F-P-M method for estimating ET0 requires data often not recording in the meteorological stations; hence ET0 should be estimated using the proposed simpler methods in compare to the F-P-M. The adaptation of the methods to different climates should be essentially tested by the standard F-P-M method.

Forest roads are known as the most important factor of sediment production in forest ecosystems. Because of the importance of this issue، several models developed based on empirical relationships to estimate sediment yield. In this study، the amount of annual sediment yield derived from a forest road network was estimated as tons per year using CULSED model in ArcGIS. Base spatial layers such as: topography، stream، roads، and culverts were used in this model. Additional data such as the bed rock، vegetation، average precipitation، road age، the amount of traffic، road surface and road gradient were used in the model. First، digital databases were developed and the model was run. Then places with high rates of sediment yield were specified and some culverts were designed in appropriate places to decrease the amount of sediment production. The results showed that the amount of sediment with regards to existing 38 culverts was 13. 2 tons per year. Adding 16 proposed culverts in the areas with high sediment production resulted in 36% decrease in sediment yield. So، given the importance of reducing sedimentation from roads in the forest، this tool can be used before road construction to find optimal number and location of culverts by engineers. However، due to lack of available data and a native model، some uncertainty will be encountered that should be considered.