volume: 31, issue: 1
volume: 35, issue: 1
volume: 36, issue: 2
volume: 38, issue: 1
volume: 39, issue: 2
The objective of this study was to compare forest soil bulk density values obtained through
conventional sampling methods such as the volumetric ring (VR: diameter 5 cm, length 10 cm)
and paraffin sealed clod (PSC), with a variation of the VR, where rectangular boxes (RB) of
four different dimensions were used. Sampling transects were established on a machine operating
trail located in a beech (Fagus orientalis Lipsky) stand in Northern Iran. At each
transect, three soil samples were collected at three different locations. Samples from different
methods were spaced by a 50 cm distance to avoid direct interactions. The soil class of our
study area was Combisols according to the WRB classification with a clay texture. Soil bulk
density differed significantly between the three sampling methods. The lowest values were
obtained with the RB (average 1.25 g cm-3), followed by the VR (average 1.40 g cm-3), and
lastly the PSC (average 1.52 g cm-3). The values obtained with four variations of the RB
method ranged from 1.22 to 1.28 g cm-3 and were not found significantly different. When soil
bulk density was calculated after the removal of the weight and volume of roots included in
the samples, the values were determined to be higher than before but with the same range of
magnitude. The lowest coefficient of variation was found for RB4 (CV=2.3%), while the highest
values were observed for VR and RB1 (CV=5.7%).
volume: 40, issue:
Ground-based mechanized forest operations often lead to increased runoff and soil loss on unbound forest roads and machine operating trails, which in turn can impede the technical trafficability of machines and cause negative impacts on the environment. The aim of this study was to evaluate the effectiveness of three Best Management Practice (BMP) treatments used to control erosion occurring on machine operating trails. The treatments included water bar, water bar and hardwood brush (H-brush), and water bar and softwood brush (S-brush). For a more comprehensive assessment of both brush treatments, two levels of brush thickness were tested; 0.5 m and 1.0 m. Results indicate that the most effective BMP treatments were the water bar and softwood brush followed by the water bar and hardwood brush and finally the least effective was the water bar. The average runoff rates and soil loss from the machine operating trails with the water bar treatment (52.64 l per plot, 8.49 g m-2) were higher than runoff and soil loss at the trails protected with hardwood brush (23.75 l per plot, 4.5 g m-2), and the trails protected by the hardwood brush had higher runoff and soil loss compared to trails covered by softwood brush (15.83 l per plot, 2.98 g m-2). Furthermore, results of this study showed that regardless of the treatment, the amount of runoff and soil loss decreased consistently as the thickness of the brush mat increased. Overall, erosion control techniques similar to either H-brush or S-brush that provide direct soil coverage should be used for erosion control, and final selection should be based on costs, availability of material, or landowner objectives.
volume: 40, issue:
Effective skid-trail design requires a solid understanding of vehicle-soil interactions, yet virtually no data exist on the effects of harvest traffic on soils in the switchback curves common in mountainous terrain. We contrast for the first time the effect of skidding on dry bulk density, total porosity, macroporosity, and microporosity in the straight segments of the skid trail and in various positions within switchbacks of differing trail curvature (deflection angle) on different slope gradients. Treatment plots with three replications included combinations of two classes of curvature (narrow = high deflection angle, 60–70°; wide = low deflection angle, 110–130°) and two categories of slope gradient (gentle = ≤20%; steep = >20%). The Cambisol soil was sampled in control and trafficked areas both before and after three passes with a rubber-tired skidder. After only three passes, significant effects were seen for dry soil bulk density (+), total porosity (–), macroporosity (–), and microporosity (+), with steady trends from undisturbed controls to straight segments to wide curves to narrow curves. Soil damage increased gradually and consistently toward the apex of the curve, particularly in narrow curves on gentle slopes. Our results establish that curvature and switchback position are important factors affecting soil compaction in ground skidding. The strong observed effects of even low harvest traffic volume on soil physical properties in curves indicate that the degree of soil compaction in skid trails may be underestimated in areas with numerous switchbacks, the placement of which within a skid trail system may require careful consideration on mountainous terrain.
volume: 42, issue:
Forest operations often enhance runoff and soil loss in roads and skid trails, where cut slopes and fill slopes are the most important source of sediment. This study evaluated the effectiveness of four erosion control treatments applied to cut slope and fill slope segments of forest roads of different ages in the Hyrcanian forest in northern Iran. The treatment combinations, each replicated three times, included four classes of mulch cover (bare soil [BS], wood chips cover [WCH], sawdust cover [SC], and rice straw cover [RSC]), two levels of side slope (cut slope and fill slope), two levels of side slope gradient (20–25% and 40–45%), and three levels of road age (three, 10 and 20 years after construction). Mulch cover treatments significantly reduced average surface runoff volume and sediment yield compared to BS. Regardless of erosion control treatment, greater surface runoff volume and soil loss under natural rainfall occurred on steeper slope gradients in all road age classes and decreased with increasing road age on both slope gradients. On cut slopes, average runoff and soil loss from the plots covered with WCH (17.63 l per plot, 2.43 g m–2) was lower than from those covered with SC (22.81 l per plot, 3.50 g m–2), which was lower than from those covered with RSC (29.13 l per plot, 4.41 g m–2 and BS (34.61 l per plot, 4.94 g m–2). On fill slopes, average runoff and soil loss from the plots covered with WCH (14.13 l per plot, 1.99 g m–2) was lower than from plots covered with SC (20.01 l per plot, 3.23 g m–2), which was lower than from plots covered with RSC (24.52 l per plot, 4.06 g m–2) and BS (29.03 l per plot, 4.47 g m–2). Surface cover successfully controlled erosion losses following road construction, particularly on steep side slopes with high erosion potential.
volume: 42, issue:
Forest operations can lead to increased runoff and soil loss on roads and skid trails. Best management practices (BMPs) aim to minimize erosion and water quality problems, but the efficacies of various BMP options such as water bars are not well documented. The aim of this study was to evaluate the effects of different densities of water diversion structures (water bars) on runoff volume and soil loss on different skid trail gradients on two soils with different textures in the Shenrood forest, Guilan province, northern Iran. The treatments included combinations of four densities of water bars (1, 2, 3 or 6 water bars per 150 m length of skid trail section [overland trail]), on two levels of trail gradient (≤20% and >20%) and two soil textures (clay loam and silt loam). Average runoff volume and soil loss per m2 of skid trail surface area were significantly greater (P≤0.05) on silt loam than on clay loam textured soils, and on slope gradients >20% (23–28%) than on gradients ≤20% (5–13%). Average runoff volume increased, and average soil loss decreased significantly (P≤0.05) with increasing density of water bars on both gradients and on both soil textures. On both soil textures, the lowest surface runoff volumes were observed with one water bar and the greatest volumes with six water bars installed. In contrast, the smallest amount of soil loss on both soil textures was observed with six water bars, and the greatest soil loss when only one water bar was installed. The installation of additional water bars led to significant differences in both responses at each level of density and led to reductions in soil loss of 77%, 57% and 27% in the clay loam, and 79%, 60% and 30% in the silt loam soil compared to the single water bar treatment. The reduced soil loss per unit of surface runoff volume is likely due to the reduced velocity of surface water runoff in the skid trail. The greater density of water bars appears to effectively divert more but slower flowing water from the skid trail, leading to reduced soil loss. While additional water bars thus better meet the objective of BMPs to minimize soil loss, managers need to balance the cost of the construction of additional water bars against the ecological benefits of reduced soil loss. An investment into additional water bars may be worthwhile if the additional structures are able to divert surface runoff more effectively to nearby vegetation and reduce the input of soil from skid trails to streams, thereby preventing the loss of water quality of these streams.