Establishment of pioneer seedling species on compacted skid tracks in a temperate Hyrcanian forest, northern Iran

The impacts of soil compaction along skid trails (haul roads) on the growth of seedlings were monitored during the first growing season in a mature deciduous stand in the Hyrcanian forests, northern Iran. Two native pioneer tree species, alder (Alnus subcordata C.A.M.) and maple (Acer velutinum Boiss.), were seeded within and beside the upslope and downslope tracks of two differently aligned skid trails: (1) flat skid trail (STF) and (2) skid trail with transversal (lateral) slope (STTS). Following a 5-month growth period, seedlings were measured for germination percentage, root length, above-ground stem height and root-to-stem ratio. Germination percentages of both species were unaffected by soil compaction, but mean root length of seedlings on control plots was significantly greater than those on plots disturbed by skidding operations. Seedlings developed longer roots in the track edge than the track centre positions although other growth parameters did not differ significantly. Seedling height was slightly greater on all tracks than on control plots, probably in response to increased light exposure of the seedlings after removal of overstorey along the skid trails. Maple and alder seedlings grown on undisturbed control areas with dense canopies generally produced deeper main roots and lower plant heights. Both species confirmed their value as pioneer trees in forest restoration by successfully establishing when seeded on disturbed and compacted ground.