Shelterwood harvesting in root-disease infected stands - post-harvest soildisturbance and compaction

Soil disturbance and compaction are described for an integrated project, te sting the use of shelterwood harvesting and root removal treatments. Sites were winter harvested and assessed the following summer using criteria from the Forest Practices Code (FPC) of British Columbia. At two installations, pushover harvesting caused a significantly greater level of counted soil d isturbance and forest floor displacement than hand felling combined with gr ound skidding. Disturbance levels increased with basal area removal on push over harvested treatment units. The highest disturbance was on the clearcut -pushover treatment at the Golden site, where levels averaged 36% for both variables. Soil disturbance on the Nakusp site was lower for a number of re asons. Pushover harvesting at the Golden site also resulted in over 25% of the sample points becoming calcareous at the surface, due to exposure and d eposit of calcareous subsoil; as opposed to less than 5% on the hand felled treatment units. Pushover harvesting at Golden, compared to the Nakusp sit e, also yielded a greater proportion of the treatment units occupied by stu mp holes, because of larger tree size and finer soil textures. Soil compact ion significantly increased total bulk density at Golden and decreased tota l porosity and two measures of aeration porosity at both sites. Machine dis turbance not meeting the disturbance survey criteria of the FPC occupied up to 16% of treatment units at the Golden site. This uncounted disturbance w as not significantly different from countable compaction for five physical properties. Compaction impacts were usually significant, irrespective of th e harvesting method or basal area retention on a treatment unit. Aeration p orosities for some compacted samples were at or below 'critical' values of 15% on both sites. Tree growth at Golden is expected to be reduced because compaction has reduced aeration porosity and push felling exposed greater l evels of free lime. Site sensitivity guidelines for pushover harvesting are exceeded for the soil conditions at Golden. More recent harvesting on othe r sites has resulted in less disturbance than reported here. It appears tha t countable soil disturbance can be limited to 15% for pushover harvesting under operational conditions. (C) 2000 Elsevier Science B.V. All rights res erved.