Chemical and mechanical site preparation: effects onPinus contortagrowth, physiology, and microsite quality on grassy, steep forest sites in British Columbia

Abstract

Site preparation alleviates the effects of pinegrass (Calamagrostis rubescens Buckl.) interference on conifers in British Columbia, but little is known about interference mechanisms and appropriate site preparation methods for steep slopes. In this study, lodgepole pine (Pinus contorta Dougl. ex Loud.) was planted in pinegrass controls and small (90 × 90 cm) and large (180 × 90 cm) patches where (i) only pinegrass was removed using glyphosate or (ii) both pinegrass and the forest floor were removed using an excavator. Treatments were replicated three times in east-and west-facing clearcuts and effects were followed for 9 years. Two-year pine survival was 78% in the control and >97% in large patches. All patch treatments improved pine growth, but it was greatest in large chemical patches during the initial 6 years and in both large patch treatments thereafter. Removal of the forest floor reduced foliar and soil nutrients, increased bulk density and soil water availability, decreased porosity and aggregate stability, and reduced ectomycorrhizal diversity and richness. These changes were not observed in chemical patches. All patch treatments increased soil temperatures and reduced frost relative to controls, but more so in large patches. Pinegrass can suppress early pine performance, and large chemical patches that retain the forest floor are best for relieving the multiple environmental stressors.Résumé : La préparation de terrain réduit l'interférence causée par Calamagrostis rubescens Buckl. sur les conifères de la Colombie-Britannique, mais les mécanismes d'interférence et les méthodes de préparation de terrain appropriées pour les pentes fortes demeurent peu connus. Dans cette étude, des pins de Murray (Pinus contorta Dougl. ex Loud.) ont été plantés dans des parcelles témoins avec Calamagrostis, des petits placeaux (90 × 90 cm) et des grands placeaux (180 × 90 cm) où le Calamagrostis avait été éliminé (i) en utilisant le glyphosate seulement ou (ii) en enlevant aussi la couverture morte avec l'aide d'une excavatrice. Les traitements ont été répétés trois fois dans des coupes à blanc faisant face à l'est et à l'ouest et les effets ont été suivis durant 9 ans. La survie des pins après 2 ans était de 78 % dans les témoins et supérieure à 97 % dans les grands placeaux. Tous les traitements en placeaux ont amélioré la croissance du pin, mais l'effet le plus important a été observé dans les grands placeaux traités à l'herbicide au cours des six premières années, et dans les deux traitements en grands placeaux par la suite. L'élimination de la couverture morte a réduit la concentration en éléments nutritifs dans le sol et le feuillage, a augmenté la densité apparente et la disponibilité en eau du sol, a réduit la porosité et la stabilité des agrégats, et a réduit la diversité et la richesse des ectomycorrhizes. Ces changements n'ont pas été observés dans les placeaux traités à l'herbicide. Tous les traitements en placeaux ont augmenté la température du sol et réduit les gelées en comparaison avec les témoins, mais de...

Growth of Douglas-fir, lodgepole pine, and ponderosa pine seedlings underplanted in a partially-cut, dry Douglas-fir stand in south-central British Columbia

“…In adjacent large openings (> 0.1 ha in size with all trees removed) on the same site, Huggard et al (2005) similarly found that small patch site preparation was adequate for good survival. On another dry, cool IDF site that had been clearcut, Simard et al (2003) also found that lodgepole pine survival reached 80% in small (90 cm ϫ 90 cm) grass-free prepared patches, but that it reached 97% in larger (90 cm ϫ 180 cm) patches. Larger patches may be necessary to improve survival on clearcut sites where frost susceptibility (Fleming et al 1998) and pinegrass competition tend to be greater (Heineman et al 2003).…”

Long-term effects of timber harvesting on hemicellulolytic microbial populations in coniferous forest soils

“…Accordingly, previous studies have shown only small differences in the effects of OM1 versus OM2 on overall bacterial and fungal communities (Hartmann et al, 2012) and small or no differences in effects on soil chemistry and tree growth (Ponder et al, 2012). The OM3 treatment, involving removal of whole trees plus forest floor, is a very severe disturbance, which was previously found to impact the overall soil microbial community due to the loss of nutrients and habitat (Simard et al, 2003;Hartmann et al, 2012). This treatment eliminated all above-ground woody biomass and was expected to have an extreme effect on hemicellulolytic populations.…”

Mycorrhizal networks and complex systems: Contributions of soil ecology science to managing climate change effects in forested ecosystems

“…Indeed, the highgrading management approach, combined with summer drought (Hamman and Wang 2006), episodic seed dispersal (Klinka et al 2000) and gap-phase disturbance regime characteristic of interior Douglas-fir forests (Klenner et al 2008), have led to variable natural regeneration across the dry climatic zones of interior Douglas-fir (Newsome et al 1991;Stark et al 2006). To augment natural regeneration, seedlings are often planted, but even they suffer from high mortality due to drought, competition from pinegrass, summer frost, tramping by cattle (Simard et al 2003), and lack of mycorrhizae at the time of planting, due to high fertilization and irrigation regimes used in commercial nurseries (Berch et al 1999). In the dry forests that interface with the grassland, survival of planted interior Douglas-fir has averaged only 40%, and at higher, wetter elevations, survival is still less than 50% where pinegrass competition and cattle grazing are not carefully controlled (but approx.…”

“…However, colonization of non-local tree genotypes by weakly compatible local ectomycorrhizae may be an important barrier to seedling establishment and successful migration. Most temperate trees are colonized by host-specific and generalist fungal taxa, potentially forming mycorrhizal networks (Molina et al 1992;Simard et al 2002). However, research on arbuscular mycorrhizae suggests the symbiosis can range from mutualistic to parasitic depending on the specific pairings (Bever 2002;Klironomos et al 2003).…”