The effects of nitrogen and nitrogen + sulphur fertilization on the first-year fascicle weight and foliar nutrient status of immature, thinned lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) were evaluated at seven locations in the interior of British Columbia. The results indicate that sulphur deficiencies, either aggravated or induced by nitrogen fertilization, may limit the responsiveness of lodgepole pine to nitrogen additions. At four locations, combined sulphur and nitrogen additions improved the sulphur status of fertilized trees and significantly increased the weight of fascicles produced during the first year after treatment compared with that achieved with nitrogen alone. Ammonium sulphate was a superior sulphur source compared with elemental sulphur–sodium bentonite prills and also was readily taken up by trees. The oxidation of the elemental sulphur prills was apparently too slow to satisfy sulphur requirements in the first year. Increasing the sulphur application rate from 50 to 100 kg/ha generally gave only small improvements in first-year fascicle weight response despite a significant improvement in foliar sulphur concentration and content. The responsiveness to sulphur fertilization was not consistent across all sites. Further characterization of sites that are responsive and unresponsive to sulphur additions is needed to more accurately diagnose sulphur deficiencies and predict responsiveness to sulphur additions.

The effects of different regimes and frequencies of repeated fertilization (applied periodically and yearly) on the foliar nutrition and growth of young lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were investigated in central British Columbia. After 12 years, tree and stand growth responses indicated modest positive effects of two applications of nitrogen (N) and boron, with relatively large incremental gains to added sulphur and other nutrients (complete). Despite large increases in effective leaf area index and foliar N concentration relative to the control and periodic treatments, yearly applications of fertilizer were relatively ineffective in stimulating growth. When combined with frequent additions of other essential nutrients, annual fertilization with 50–100 kg N/ha over 12 years (825 kg N/ha in total) produced only slightly more “extra” wood than two applications of the multinutrient, complete fertilizer (400 kg N/ha in total) (19.4 m3/ha vs. 17.2 m3/ha, respectively). The most intensive fertilization treatment (1550 kg N/ha plus other nutrients over 12 years) produced shorter trees and less stand volume increment than periodic fertilization with the complete fertilizer. Treatment-induced changes in stand dynamics and growth allocation, disrupted foliar nutrient balance, and changes in soil biota and understory vegetation community structure may have negatively affected tree growth in intensively fertilized treatment plots.

A study was undertaken to investigate the effects of nitrogen and boron, applied singly and in combination, on the growth of young, thinned lodgepole pine in the interior of British Columbia. Results indicate that subacute boron deficiencies without visible growth disturbance symptoms, may reduce the nitrogen fertilization response potential of lodgepole pine. Combined nitrogen and boron application significantly improved the 3-year mean height and volume increment over that obtained with nitrogen alone. Relatively small boron additions (i.e., 1.5 and 3.0 kg boron•ha−1) to the soil surface elevated foliar boron concentrations and maintained them throughout the 3-year study period. No toxic effects of boron application on foliage were observed. Both 1st-year fascicle weight response and 2nd-year branch elongation proved to be reliable indicators of subsequent stem volume response. The slightly larger stem growth response obtained with a complete fertilizer treatment, when combined with needle weight and foliar analysis data, indicates that nitrogen and nitrogen plus boron treatments may have induced a marginal sulphur deficiency. Because boron deficiency symptoms can develop rapidly following an interruption in boron uptake, and because top dieback can have such an adverse effect on stem quality and value, it is recommended that boron be added to nitrogenous fertilizer when undertaking aerial fertilization projects in lodgepole pine forests where average foliar boron concentrations are below 15 ppm.

The effects of factorial combinations of post-thinning density and fertilization on the growth and development of young lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were investigated in central British Columbia. The effects of density and fertilization (repeated every 5 years) on tree height were small relative to the effects on stem radial growth. Tree radial growth increased with thinning intensity, whereas per-hectare growth was greatest at the highest residual density. Fertilizer effects varied across the range of residual densities tested. Tree and stand volume gains following fertilization were less, in both relative and absolute terms, at 600 trees/ha than at 1100 or 1600 trees/ha. Vigorous response of understory vegetation to nutrient additions (and strong competition for water and nutrients) may have reduced the effectiveness of fertilization on tree growth at 600 trees/ha relative to higher stand densities. Results indicate that the combined positive effects of thinning and fertilization on the growth of young lodgepole pine will accelerate stand development, thereby shortening technical rotation length. Results also indicate that significant growth gains following fertilization of thinned lodgepole pine will partially compensate for stand volume losses due to thinning. However, fertilization may be less effective at low stand densities, where negative effects of thinning on harvest volume are greatest.

This study was designed to test the hypothesis that large-scale pre-commercial thinning (PCT) to various stand densities, at ages 12-14 years, combined with repeated fertilization, would, over a 10-year treatment period, enhance productivity of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) crop trees. Study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had nine treatments: four pairs of stands thinned to densities of ~ 250 (very low), ~ 500 (low), ~ 1000 (medium) and ~ 2000 (high) stems ha − 1 , with one stand of each pair fertilized fi ve times at 2-year intervals, and an unthinned stand. The very low, low-and medium-density stands were also pruned to a 3-m lift 5 years after thinning. At the tree level, fertilization treatments signifi cantly increased diameter at breast height (DBH), basal area (BA) and volume growth and heavy PCT signifi cantly increased DBH and BA growth. Pruning may mitigate some of the negative stem form and wood quality attributes associated with fast-growing trees without adversely affecting stem growth. At the stand level, PCT to very low and low densities signifi cantly decreased the volume growth compared with high-density stands. The potential benefi cial impacts that PCT and repeated fertilization treatments have for mitigating timber supply shortfalls, as well as potentially minimizing crop tree losses due to mountain pine beetle (Dendroctonus ponderosae Hopk.), are also discussed.

Four rates of N (0, 50, 100, and 150 kg·ha -1 ) with and without a fertilizer mix containing P, K, S, Ca, Mg, and micronutrients were applied to a stand of 8-year-old lodgepole pine (Pinus contorta var. latifolia Engelm.) in four applications during 7 years. Fourteen years after the first fertilization, mean tree basal area and volume were significantly increased in the treatments containing the two highest rates of N plus the fertilizer mix. Mean tree basal area was 38% greater and mean tree volume was 42% greater in the highest N (525 kg·ha -1 ) plus mix treatment than in the control treatment. Stand basal area increased 48% over the control in the highest N plus mix treatment. Mean tree basal area and volume were 27 and 25% greater than the control under the intermediate N rate (350 kg·ha -1 ) with mix, respectively. Height growth was not significantly increased by fertilization. Both higher rates of N (four applications of >100 kg·ha -1 ) and the fertilizer mix were required for significant growth responses to occur. Addition of N alone or mix alone had a negative effect on mean tree basal area and volume. Addition of higher N rates without the mix decreased foliar total S and SO 4 -S concentration and increased the N/S ratio. Addition of the higher rates of N without the mix aggravated slight K deficiencies. The responses to the higher N rates in combination with the fertilizer mix are mainly attributable to S.Résumé : Quatre taux de N (0, 50, 100 et 150 kg·ha -1 ) avec ou sans un mélange d'engrais contenant P, K, S, Ca, Mg et des micro-éléments ont été appliqués dans un peuplement de pin lodgepole (Pinus contorta var. latifolia Engelm.) quatre fois sur une période de sept ans. Quatorze ans après la première application, la surface terrière et le volume moyens étaient significativement plus élevés dans les traitements contenant les deux taux de N les plus élevés avec le mélange d'engrais. La surface terrière et le volume moyens des arbres étaient respectivement 38 et 42% plus élevés dans le traitement avec le plus haut taux de N (525 kg·ha -1 ) combiné au mélange d'engrais que dans le traitement té-moin. La surface terrière et le volume moyens des arbres étaient respectivement 27 et 25% plus élevés dans le traitement avec le taux intermédiaire de N (350 kg·ha -1 ) combiné au mélange de fertilisant que dans le traitement témoin. La fertilisation n'a pas significativement augmenté la croissance en hauteur. La croissance en hauteur n'a pas été significativement affectée par la fertilisation. Les deux plus hauts taux de N (quatre applications de plus 100 kg N·ha -1 ) combinés au mélange d'engrais étaient nécessaires pour obtenir une augmentation significative de croissance. L'ajout de N seul ou du mélange d'engrais seul avait un effet négatif sur la surface terrière et le volume moyens des arbres. L'ajout des plus hauts taux de N sans le mélange d'engrais a causé une diminution de la concentration de S total et de S sous forme de SO 4 et a augmenté le rapport N/S. L'ajout des plus hauts taux de N sans...

We studied elements of the soil biota in a 24-year-old lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stand in interior British Columbia 10 years after initiation of annual fertilizer treatments. The treatments included an unfertilized control, ON1 (650 kg nitrogen (N), 400 kg phosphorus (P), 400 kg potassium (K)), and ON2 (1350 kg N, 400 kg P, 400 kg K). In the forest floor, the C/N ratio was lower in ON1 and ON2 than in the unfertilized control, while available P and exchangeable magnesium were higher; NO3 was higher only in ON2. In the upper mineral soil, available P was higher in ON1 and ON2, while NO3 was higher only in ON2. In both the forest floor and upper mineral soil, microbial activity was higher in ON1 than in the unfertilized control or ON2. In the forest floor and mineral soil, Acari density, especially Oribatida and Prostigmata, was higher in ON2 than in ON1 and the unfertilized control. In contrast, Collembola density, especially Hypogastruridae, increased in ON2 relative to that in other treatments. ON2 had less lodgepole pine fine-root length, fewer ectomycorrhizal roots, fewer active fine roots, more nonmycorrhizal fine roots, and a different ectomycorrhizal community structure than ON1 and the unfertilized control. These dynamic changes to the soil biota appear to reflect changes to the plant community in response to fertilization.

The 9-year effects of nitrogen (N) and boron (B) fertilization on the growth and foliar B nutrition of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were evaluated in two different ecosystems in the interior of British Columbia. When added alone, B had no effect on basal area or height increment. However, combined applications of N and B were superior to N alone in stimulating height development at both study sites. At one site, fertilization with N, alone and in combination with sulphur (S), resulted in a significant amount of top dieback symptomatic of severe B deficiency. No visible deficiency symptoms were observed when B was combined with N or N + S. Boron fertilization significantly increased foliar B concentrations at both study sites, and higher foliar B levels were maintained throughout the 9-year study period. Results suggest that significant visible symptoms of B deficiency in lodgepole pine are unlikely to occur at foliar levels >6 mg/kg, although subacute B deficiency may suppress height development in the absence of deficiency symptoms. When combined with nitrogenous fertilizers, B applications of 1.5–3.0 kg/ha are likely sufficient to achieve, and maintain, favourable B status and healthy growth of trees over a prolonged period.