Soil disturbance and five-year tree growth in a montane alternative silvicultural systems (MASS) trial

Abstract

Ground-based forestry practices can negatively affect soil productivity by altering the physical, chemical, and biological properties of soil. The effect of soil disturbance on soil properties and tree growth was evaluated following single-pass hydraulic excavator and multiple-pass combined excavator and flexible track grapple skidder forwarding in four silvicultural systems treatments: Clearcut (CC), Green Tree Retention (GT), Patch Cut (PC), and Uniform Shelterwood (SW). The effectiveness of an excavator soil-rehabilitation technique (tilling) in decompacting skidtrails (i.e., reducing soil bulk density) and nutrient availability was also evaluated. Western hemlock (Tsuga heterophylla (Raf.) Sarg.) and amabilis fir (Abies amabilis Dougl. Ex. Forbes) seedlings were planted on undisturbed plots, within tracks and between tracks of skidtrails, and in rehabilitated trails within the four harvesting treatments in the spring of 1994. Seedling growth was measured after five growing seasons, and nutrient concentrations of current-year foliage were determined at the end of the fourth growing season. Seedling survival and growth was generally reduced by soil disturbances associated with skidtrails. Effects of disturbance on physical properties of soil (e.g., compaction, puddling) and disruption of drainage were the most likely causes. Nutrient deficiencies do not appear to be a factor. Nonetheless, nitrogen concentrations were lower in current-year foliage taken from rehabilitation treatments than from either undisturbed or skidtrail treatments. Effectiveness of soil rehabilitation varied. In well-drained deeper soils, tilling reduced soil bulk density to levels below those of undisturbed soils and, in the short-term (five years), improved tree growth. In wetter conditions, rehabilitation treatment decreased survival and growth of both species. Thus specific rehabilitation (tilling) prescriptions should not be universally applied across a landscape.Key words: Abies amabilis, Tsuga heterophylla, foliar analysis, soil bulk density, soil compaction, soil rehabilitation Les pratiques forestières sur le terrain peuvent altérer de façon négative la productivité pédologique en modifiant les propriétés physiques, chimiques et biologiques du sol. L'effet de la perturbation du sol sur les propriétés pédologiques et la croissance des arbres ont été éval-ués suite à un passage d'une excavatrice hydraulique et de plusieurs passages combinés de l'excavatrice et d'une débardeuse à grappin sur chenilles flexibles dans le cadre de quatre traitements sylvicoles : coupe à blanc (CC), rétention d'arbres verts (GT), coupe par trouée (PC) et coupes progressives uniformes (SW). L'efficacité d'une technique de réhabilitation des sols au moyen d'une excavatrice (labourage) pour décompacter les sentiers de débardage (c'est-à-dire, réduire la densité globale du sol) et la disponibilité des élé-ments nutritifs ont été évaluées. Les semis de pruche de l'Ouest (Tsuga heterophylla (Raf.) Sarg.) et de sapin amabilis (Abies amabilis Dougl. Ex. Forbes) ...

Post-harvest nitrogen cycling in clearcut and alternative silvicultural systems in a montane forest in coastal British Columbia

“…Any increases in seedling foliar N concentrations after clearcutting appear to last for up to four years after harvesting ( Fig. 8; Koppenaal and Hawkins 2000, Hawkins and Moran 2003, Maynard and Senyk 2004, which is fairly consistent with our results for N mineralization and availability in the soil. Changes in foliar N concentrations up to six years after harvesting suggest a possible response to a small assart effect that lasted from two to four years after harvesting.…”

“…Foliar N concentrations at the time of planting were 2.15% and 1.99% for western hemlock and amabilis fir, respectively. Additional data for naturally-regenerated seedlings at two and five years (Koppenaal and Hawkins 2000;see Table 2 for statistical differences at two years) and planted seedlings at four years (Maynard and Senyk 2004;undisturbed microsites) are included as single points, represented by smaller symbols. Horizontal line at 1.15% indicates deficiency level for true fir (Powers 1983), and line at 1.45% indicates adequate level for western hemlock (Ballard and Carter 1986).…”

“…Nitrogen losses from the rooting zone in leaching and harvested logs can also be placed in context by comparing leaching losses with N reserves in the soil (i.e., soil N capital). At MASS, the soil N capital (to 30 cm depth in mineral soil) that presumably has accumulated since the end of glaciation (~ 10 000 years ago) is estimated to be ~ 11 400 kg ha -1 (Senyk et al 1995, Maynard andSenyk 2004). Past catastrophic events that would have led to the natural loss of forests would have also caused some leaching losses, and any fires (rare in this ecosystem) would have volatilized some N. Even with natural N losses over the past 10 000 years, the net N accretion rate in the soil is therefore about 1 kg ha -1 yr -1 when estimated over millennia from present soil capital.…”

Impact of mechanized logging on compaction status of sandy forest soils

“…Greacen and Sands (1980) and Heilman (1981) reported that the elongation rate and penetration of primary roots are reduced when soil is compacted, inducing a lower uptake of nutrients and water (Kozlowski, 1999;Jordan et al, 2003). Compaction consequently leads to reduced tree growth (Gebauer and Martinková, 2005) and a higher tree seedling mortality (Brais, 2001;Stone and Kabzems, 2002;Maynard and Senyk, 2004). However, these effects are different depending on soil type, water regime and tree species (Jones, 1983;Gomez et al, 2002;Heninger et al, 2002).…”

Stumping trials in British Columbia — organic matter removal and compaction effects on tree growth from seedlings to midrotation stands

“…In the 1980s, total N concentration was determined by an automated semi-micro Kjeldhal method (McKeague 1978), whereas the 15-year resampling measurements were measured using a LECO N analyzer (LECO Corporation) (Maynard and Senyk 2004).…”