Abstract
The Caspian forests of Iran were monitored and evaluated for forest natural regeneration after logging activities for more than a decade. This large area has a substantial ecological, environmental and socio-economic importance. Ground based skidding is the most common logging method in these forests and soil compaction is the most critical consequence of this method. One of the current main topics and important emerging issue in forest research of the last decade are discussed in this study. Soil compaction has major influences on growth and/or mortality rates of forest seedlings. This study has lasted for over ten years so as to have a clear overview related to forest natural regeneration after logging activities. We monitored and evaluated physical soil properties (bulk density, penetration resistance and total porosity) and their effects on maple and beech seedlings on 10-year-old skid trails in the Iranian Caspian forests. Results obtained from evaluating the impact of skid trails within the aforementioned three soil physical parameters were significant; bulk density increased by 12.6% on log skidded routes (between two skidder tires on skid trail) and 36.1% on tire tracks, compared to non-skid trails (1.19 g/cm3), penetration resistance increased by 68% on log skidded routes and 220% on tire tracks, compared to non-skid trails (0.25 MPa), total porosity decreased by 12.8% on log skidded routes and 30.9% on tire tracks, compared to non-skid trails (54%). Among the morphological parameters, lateral root length (LRL) and root penetration depth (RPD) showed the highest decrease at soil compaction compared to the control (decrease in LRL: 60% in maple and 44% in beech; decrease in RPD: 56% in both maple and beech); the main response of growth parameters to soil compaction was found in roots (decrease in dry mass of 36% both in maple and beech); architectural parameters were also influenced by soil compaction, and the response of both seedling species was more evident in the ratio of main root to stem length (RRS) (reduction in RRS 42% in maple, 33% in beech); the ratio of RPD to main root length (RPL) also showed a great reduction (reduction in RPL 20% in maple 33% in beech). Physical soil properties, changes in other environmental properties of skid trails, created differences in beech and maple seedling growth between the skid trails and non-skid trails. This was closely related to the physiological characteristics of the two species studied. Beech seedlings reacted well to a moderate uncovering but they needed little disturbed soil, even if there was a very mixed bedding. Maple seedlings reacted better than beech seedlings to the uncovering and soil disturbance. The effects of the skid trail on morphology, growth and architecture of maple seedlings in the Hyrcanian beech forests showed that the maple, as a seedling, is a suitable species for maintaining the physical properties of skid trails after logging operations in the beech stands in the Caspian forests of Iran.
Highlights
The use of heavy machinery for logging operations has increased in world forests due to their high productivity rate during last decades [1,2]
The United States Department of Agriculture (USDA) Forest Service has cited a critical level of forest soil disturbance at 20% of the total logging area, including roads, skid trails and landings; and compaction standard states that bulk density cannot increase more than 15% from its natural level in the top 20 cm of soil
Ten years later the larger number of tractor passes increased bulk density from 12.6% to 36.1% and penetration resistance from 68.0% to 220.0%, while porosity declined from 12.8% to 30.9% in winching corridors and tire track (Table 1)
Summary
The use of heavy machinery for logging operations has increased in world forests due to their high productivity rate during last decades [1,2]. Extensive damage to the soil potentially creates a serious threat to the soil ecosystem [3,4]. The United States Department of Agriculture (USDA) Forest Service has cited a critical level of forest soil disturbance at 20% of the total logging area, including roads, skid trails and landings; and compaction standard states that bulk density cannot increase more than 15% from its natural (undisturbed) level in the top 20 cm of soil. Critical level of soil disturbance can be determined based on the weather conditions, vegetation, topographic and habitat characteristics of each forest area [5]. Logging operations cause some degree of soil disturbance [5]
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