Marginal effects of rural roads and irrigation canals on woody and non-woody species composition

Across the northern rural regions of Iran, gardens and farmlands are being fragmented into smaller and smaller patches by rural roads network with significant edge effects on plant species composition and abundance. In this study, the presence of different plant species was recorded in ninety 1´1 m plots on nine 100 m transects at the edge of terrene rural roads with irrigation canal and without irrigation canal. Thirty seven plant species were identified in the 9 transects surveyed. Twenty six (70.3%) of those species occurred near the irrigation canal (Transects 2 and 3). Rubus hyrcanus Juz (more than 80% in visually) were observed on transect 3 of the roadside with irrigation canal because of the availability of light and high soil moisture. Ulmus carpinifolia Borkh., Quercus castaneifolia C. A. Mey., Pterocarya fraxinifolia (Lam.) Spach., Parrotia persica C.A.M., Zelkova carpinifolia (pall.) Dipp. and Albizia julibrissin (Willd) Benth were the unique species that were found close to the irrigation canal especially on transect 2. These species are the final survivors of Hyrcanian forests in rural area that were protected from human damages. Plant species richness at the edge of rural road with irrigation canal (37 species) was more than the edge of rural road without irrigation canal (17 species), but the cover value was similar to each other. Punica granatum L. was the most frequent species (more than 80%) on both side of rural road (transect 2 and 3) without irrigation canal.Key words: Edge, Iran, irrigation canal, plant composition, rural road

The effect of terrain factors on landslide features along forest road

The objective of this study was to investigate the effects of physiographic features such as slope, altitude, aspect and soil on landslides dimensions and distribution in Pahnehkola forest, north of Iran. 30 landslides were selected for detailed observation, with their occurrences recorded by global positioning system (GPS) along the surveyed forest road. Then, landslides were mapped in Arc view and subsequently digitized into a geographic information system (GIS). Results indicate that the landslide area at a distance of 80 to 100 m from road edge was significantly more than that of other distances. The landslide dimensions increased with increasing slope angle. The mean of landslide area and mean of landslide volume on the Northwest aspect was significantly more than that on other aspects (P<0.01). The mean of landslide dimensions in altitude class of 400 to 650 m was significantly less than that in altitude class of 150 to 400 m (P<0.01). The mean of landslide dimensions increased significantly with increasing soil liquid and plastic limit. The logistic regression modeling indicate that independent variables including aspect, liquid limit, plastic limit and soil moisture, significantly influence the landslides area. The majority of landslides were situated along roads and on faults, and shallow landslides were more frequent along roads compared to those on faults.Key words: Landslide, forest road, physiographic features, GPS, Pahnehkola forest

Analyzing dynamic curve widening on forest roads

Forest roads require important design specifications to ensure all-season access for various vehicles. Long and heavy log trucks can face serious maneuvering problems on forest roads due to insufficient amount of area to the left for road widening on horizontal curves. In order to provide safe and continuous shipment and transportation, appropriate curve widening areas should be provided for long vehicles along horizontal curves. In this study, a statistical model was developed to provide curve-widening solutions for long trucks (e.g., those with 18 wheels) considering various curve radius and deflection angles. The dynamic curve widening feature of Plateia 2013 program was employed to calculate curve widening for the specified vehicle. During the solution process, nine different horizontal curve diameters from 10 to 50 m (by 5 m intervals) and 17 different deflection angles from 90A degrees to 170A degrees (by 5A degrees intervals) were evaluated to run horizontal curve-widening analysis. Using a multiple regression model, we made suitable predictions about curve widening. The curve-widening areas decrease as the horizontal curve radius increases, while increasing the deflection angle on horizontal curves increases curve widening areas. Clearly, the computer-based dynamic curve widening model developed in this study can be effectively used in determining optimum widening for horizontal curves by evaluating the number of alternatives that fit geometrical specifications and vehicle types