Soil properties and forest productivity can be affected by heavy equipment used for harvest and site preparation but these impacts vary greatly with site conditions and operational practices. We assessed the effects of ground‐based logging on soil physical properties and subsequent Douglas‐fir [Pseudotsuga menziesii (Mirb) Franco] growth on a highly productive site receiving vegetation control in coastal Washington. We also tested the effectiveness of tillage in maintaining or enhancing site productivity. On average, about half of the area of ground‐based harvested plots was affected by vehicular traffic. Sixty‐three percent of the trees were planted on microsites with some degree of soil disturbance. Soil bulk density at the 0‐ to 30‐cm depth increased from 0.63 to 0.82 Mg m−3 in the most compacted portions of traffic lanes. The area‐weighted increase in soil bulk density in the 0‐ to 30‐cm depth was 27%. Soil strength in traffic lanes increased at all depths < 55 cm but never exceeded 1300 kPa. Tillage to the 60‐cm depth returned the soil to its initial strength condition. Volumetric soil water content in compacted traffic lanes was greater than that in noncompacted soil. Total soil porosity decreased 10 to 13% with compaction, while available water holding capacity increased. In compacted soil, macropore space was reduced 40 to 52%. The study revealed no detrimental effects on tree height and diameter from soil compaction at age 4. At stand age 3, a tree volume index was actually greater for trees planted on traffic lanes than for those on non‐disturbed soil.

Abstract:We (i) quantified effects of skidder yarding on soil properties and seedling growth in a portion of western Oregon, (ii) determined if tilling skid trails improved tree growth, and (iii) compared results with those from an earlier investigation in coastal Washington. Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were hand planted at eight recent clearcuts in skid ruts in either nontilled or tilled trails, in adjacent soil berms, and in adjacent logged-only portions. Four and 5 years after skidding, rut depths averaged 15 cm below the original soil surface; mean fine-soil bulk density (0-30 cm depth) below ruts of nontilled trails exceeded that on logged-only portions by 14%. Height growth on nontilled trails averaged 24% less than on logged-only portions in year 4 after planting and decreased to 6% less in year 7. For years 8-10, mean height growth was similar for all treatments. Reduced height growth lasted for about 7 years compared with 2 years for coastal Washington. Ten years after planting, trees in skid-trail ruts averaged 10% shorter with 29% less volume than those on logged-only portions. Tillage improved height and volume growth to equal that on logged-only portions. Generalizations about negative effects of skid trails on tree growth have limited geographic scope. R~sum~ : Nous avons (i) mesur6 les effets du d6bardage par t616ph6rage sur les propri6t6s du sol et la croissance de jeunes arbres dans une partie de l'ouest de l'Oregon, (ii) d6termin6 si le fait de labourer 16g~rement le sol dans les ornitres am~liore la croissance des arbres et (iii) compar6 nos r6sultats avec une exp6rience prdc6dente r6alis6e dans la r6gion c6ti6re de l'6tat de Washington. Des semis de douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco) ont 6t6 plant6s manuellement sur le site de huit coupes ~ blanc r6centes, dans des ornibres labour6es ou non, dans les talus adjacents et dans des coupes adjacentes. Quatre et 5 ans apr~s le d6bardage, la profondeur des orni~res atteignait en moyenne 15 cm sous la surface initiale du sol; la densit6 moyenne du sol (0 ~t 30 cm de profondeur) sous les orni~res non labour6es 6tait 14% plus 61ev6e que celle des zones qui avaient seulement 6t6 coup6es. La croissance en hauteur des arbres dans les orni~res non labour6es 6tait, en moyenne, inf6rieure de 24% ~t celle observ6e dans les zones qui avaient seulement 6t6 coup6es 4 ans apr~s la plantation et la diff6rence n'6tait plus que de 6% inf6rieur apr~s 7 ans. Entre la huiti~me et la dixibme ann6e, la croissance moyenne en hauteur des arbres 6tait similaire pour tousles traitements. La rdduction de croissance a dur6 environ 7 ans comparativement ~t seulement 2 ans dans la r6gion c6tibre de l'6tat de Washington. Dix ans apr~s la plantation, les arbres qui avaient pouss6 dans les ornibres 6taient 10% plus petits et avaient un volume inf6rieur de 29% aux arbres dans les zones qui avaient seulement 6t6 coup6es. Le labourage a amdlior6 la croissance en hauteur et en volume des arbres au point d'6galer celle dans les zon...

Carbon and nutrients in the forest floor and mineral soil were measured to determine amounts and variation among eighteen 0.081‐ha plots in a Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] plantation growing with volunteer red alder (Alnus rubra Bong.). Ten years earlier, the preceding mature conifer stand was clearcut and nearly all logging slash and forest floor were consumed by slash fire. Forest floor mass in the 9‐yr‐old plantation averaged 9.86 Mg ha‐1, with 3.71 Mg C, 98.0 kg N, 10.6 kg P, and 8.4 kg S ha‐1. Mineral soil to 1‐m depth averaged 176 Mg C, 8330 kg N, 3340 kg P, and 605 kg S ha‐1 in the <2‐mm fraction. The 2‐ to <6‐mm soil fraction averaged an additional 100 Mg C, 4480 kg N, and 1700 kg P ha‐1. Net mineralizable N as NH4 (anaerobic N mineralization index) totaled 99 kg N ha‐1 in the top 45 cm of the mineral soil and 62 kg N ha‐1 in the 45‐ to 100‐cm depth. Density fractionation showed that the light fraction (<1.65 Mg m‐3) was only 13.4% of the fine soil mass of the 0‐ to 15‐cm depth, yet contained about 40% of the total C and N capital in the <2‐mm size fraction. The substantial amounts of C and nutrients in this low‐bulk density soil (<2‐mm fraction, 0.30 Mg m‐3) indicate a fertile soil despite large previous losses of organic matter and N from the site.

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