Growth Of Lodgepole Pine Research Articles

Impact of slash removal, drag scarification, and mounding on lodgepole pine cone distribution and seedling regeneration after cut-to-length harvesting on high elevation sites

Excessive slash loading could pose a problem for the regeneration of the serotinous lodgpole pine especially in forests at higher elevation where soil temperature is limiting. In the past, these forests have commonly been harvested using full-tree harvesting where trees are processed at roadside; however, recently cut-to-length harvesting has become a more frequent harvesting method. In cut-to-length harvesting the harvested trees are processed in the block, as a result slash accumulation is much higher on these cutblocks. In an experimental field trial, the cone distribution, natural lodgepole pine regeneration, and the growth and establishment of planted lodgepole pine were evaluated in response to slash load, drag scarification, and mounding after cut-to-length harvesting of high elevation lodgepole pine stands in the Rocky Mountains. Twelve sites were established, each contained six plots which were randomly assigned to six treatment combinations of two slash removal (slash and slash removed) and three mechanical soil preparation treatments (no soil preparation, drag scarifying, and mounding). The slash removal reduced slash volume by more than 50% but also reduced the number of lodgepole pine cones available for regeneration by over 33%. However, soil mechanical treatments offset this effect as fewer cones were necessary to achieve high natural pine regeneration densities. Drag scarification of plots resulted in 12 times the number of pine seedlings compared to the non-prepared plots. Although slash removal did not have an effect on the number of naturally regenerated lodgepole pine seedlings, it had a positive effect on their growth performance. Conversely, planted pine seedlings had lower mortality and better growth in soils that had been mechanically prepared and had the slash removed; however, the growth effects became only apparent 4 years after planting. While slash removal and mechanical soil preparation did increase soil temperatures; the slash removal treatment had a more transient effect on soil temperatures than soil preparation. Differences in soil temperature decreased over time which appeared to be mostly driven by a warming of the soils in the plots with no soil preparation, likely a result of the decomposition of the finer slash and feathermosses. Overall, it appears that surface disturbance on these high elevation sites had a far greater effect on lodgepole pine regeneration and growth than the increased accumulation of slash as a result of cut-to-length harvesting.

Lodgepole pine growth as a function of competition and canopy light environment within aspen dominated mixedwoods of central interior British Columbia

Three lodgepole pine and aspen mixedwood sites located in the central interior of British Columbia within the Sub Boreal Spruce (SBS) biogeoclimatic zone were chosen to study the neighbourhood aspen competition and canopy light environment of 14–19-year-old lodgepole pine. All three sites had previously been established as separate research trials designed to explore various silviculture options for controlling aspen competition (aspen brushing, herbicide, thinning and untreated areas). For each site, 33–36 pine trees were selected to represent the observed range of light regimes under the influence of various aspen competition levels. At each sample pine, competition and stand measurements were made and a series of vertical canopy light measurements from the top to the base of the live crown. After an evaluation of a variety of competition indices, the index DRD; sum of the ratio of each of the three nearest neighbour's DBH to the subject pine divided by their distance and, amount of available light at the top of the crown (DIFN t) were found as the best overall predictors of pine stem volume growth. A site specific exponential relationship of relative pine stem volume growth to DRD was found and minimum growth response competition thresholds were determined, which could provide useful targets where maximizing pine volume is intended. Evaluation of both linear and non-linear models of DIFN t versus height growth indicated the response to be linear across the observed range of available light. Implications for management are discussed.

Soil properties and lodgepole pine growth on forest landings rehabilitated by tillage and fertilizer application

Soils on forest landings are often degraded and unable to support optimal growth of planted conifers unless rehabilitation practices are applied. This study evaluated the effects of tillage and fertilization on soil properties and growth of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seedlings on rehabilitated forest landings in the central interior of British Columbia. Six study sites were rehabilitated in 1998 (but without topsoil replacement) and planted with lodgepole pine in 1999. Tillage treatments were: (i) no tillage; (ii) low intensity (one pass of an excavator and six-toothed rake, target clod size 8–10 cm); (iii) medium intensity (two passes, target clod size 4–7 cm); and, (iv) high intensity (three passes, target clod size 1–3 cm). Fertilizers were applied at the time of planting as slow-release formulations; treatments included: (i) no fertilizer; (ii) NPK-fertilizer; and, (iii) NPK + S-fertilizer. After 5 yr, soil mechanical resistance was higher on the untilled control than the tilled treatments. Neither tillage nor fertilization had any effects on soil chemical properties (total C and N, pH, cation exchange capacity, exchangeable cations). Tillage effects after one growing season were variable; however, after four or five growing seasons, the low-intensity tillage resulted in greater seedling height and diameter growth than the untilled control. After one growing season, fertilization increased seedling height and diameter growth relative to the untreated control, but after four or five growing seasons, fertilization had no effect on lodgepole pine growth. Our findings indicate that a single pass with the excavator and rake was the most suitable rehabilitation practice on these sites. Key words: Forest soil rehabilitation, landing and road rehabilitation, soil conservation, soil degradation, soil compaction, soil productivity

Potential effects of climate change on the growth of lodgepole pine across diameter size classes and ecological regions

We examined 65 lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta using a dendrochronological approach in order to examine the relationships between climate and growth of lodgepole pine across elevational ecoregions and diameter size classes. The 4 elevational ecoregions sampled included the Boreal Highlands (BH: 13 sites); the Foothills (FH: 36 sites); a grouping of the montane and subalpine zones of the southern Rocky Mountains (RM: 12 sites); and the montane zone of the Cypress Hills (CH: 4 sites). The first diameter size class was comprised of the three largest (top) diameter trees at each site. The tree list of each plot was ranked, then divided into three groups of equal basal area and the tree at the midpoint of each group (small, medium, and large) was selected for the other three size classes. Annual growth in basal area of lodgepole pine was generally sensitive to heat and moisture stress in late summer of the previous year, the degree of winter harshness, and the timing of the start of the growing season. Growth was inhibited by low temperature in all winter months at the most northern BH sites which had the coldest winters, but this effect was interrupted in some of the midwinter months in the more southerly sites in the RM, and we postulated this was due to the damaging influences of Chinook winds. Interannual growth patterns were strongly correlated between top diameter trees and the other classes, and trees of all diameter classes generally responded to climate in the same way, which indicated that it is sufficient to sample only the largest diameter trees in a stand to provide insight into growth–climate relationships. The forecasted growth estimates indicate that future climate warming will negatively impact the productivity of lodgepole pine in the FH, the heart of lodgepole distribution and productivity in Alberta.

Influences of climate on the radial growth of lodgepole pine in Alberta

We examined a network of 17 lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) sites in Alberta in the cordilleran forests along the eastern slopes of the Rocky Mountains and in western Cypress Hills, using a dendrochronological approach to identify the principal climatic factors that have influenced the historical, regional-scale pattern of radial growth of lodgepole pine. Correlation and regression analysis of the regional growth–climate relationships showed that radial growth was negatively associated with late-summer temperatures, and positively related to the late-summer precipitation totals from the previous growth season. Radial growth also responded positively to winter and spring temperatures, and was negatively related to late winter–early spring precipitation. The results suggested that the lag in response to heat and moisture stress, cold and snowy winters, and the length of the current growing season are important determinants of the radial growth of lodgepole pine in Alberta.

Incorporation of topsoil and burn-pile debris substantially increases early growth of lodgepole pine on landings

Rehabilitation of skid trails, temporary roads, and log landings is required for many harvested sites in British Columbia; however, more information is needed regarding practical methods to return these access areas to productive forest. Lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seedlings (1 + 0) were planted into (i) fully rehabilitated landings (burn-pile debris and topsoil incorporated), (ii) tilled landings, and (iii) unprepared portions of the adjacent cutblock. After two seasons of growth in the field, seedlings planted on fully rehabilitated landings were 38% larger, more robust, and exhibited 44% greater absolute growth and 22% greater relative growth rates, than seedlings planted in the adjacent cutblock. Seedlings planted on tilled landings were 33% smaller, and exhibited absolute growth rates 38% less, and relative growth rates 18% less, than seedlings planted in the adjacent cutblock. Seedlings planted in the cutblock exhibited higher ectomycorrhizal colonization rates. Our results indicate that tillage alone was not sufficient to fully rehabilitate these landings, but that incorporation of recovered topsoil and burn-pile debris produced an excellent growth substrate. This method, using materials found on site, can prevent a significant loss of land regenerating to productive second-growth forest.

Field performance of conifer and hardwood species 5 years after nursery inoculation in the Canadian Prairie Provinces

The field performance of conifer and hardwood species inoculated with different inoculation treatments was evaluated 5 or 3 years after outplanting in the field trials established in the Canadian Prairie Provinces. In conifer trials, the growth of white spruce, black spruce, lodgepole pine, and larch seedlings observed on different sites varied greatly to different inoculation treatments depending on plant and fungal species involved. Five years after outplanting, most of the introduced fungi were replaced by several indigenous ectomycorrhizal fungal species except for Laccaria bicolor strain. Survival rates of most of the inoculated seedlings were not significantly different from control seedlings naturally colonized by other resident fungi. In hardwood trial, the effects of nursery inoculation of different poplar clones, aspen and balsam poplar were very limited. Growth and survival data were combined into seedling volume and plot volume index (PVI) for measurement of total growth response of seedlings. Our results demonstrated that certain inoculated plant-fungus combinations have played a positive role during the initial establishment of these seedlings in the field, which was reflected on significantly greater stem volume and PVI compared to non-inoculated control seedlings. The results from this study provided useful information on field evaluation for potential benefits of mycorrhizal inoculation in nursery.

Effects of 12 years of repeated fertilization on the foliar nutrition and growth of young lodgepole pine in the central interior of British Columbia

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.

Evaluation of competitive effects of green alder, willow and other tall shrubs on white spruce and lodgepole pine in Northern Alberta

In boreal forests of western Canada, lodgepole pine ( Pinus contorta Dougl. ex. Loud.) and white spruce ( Picea glauca (Moench) Voss) often grow together with numerous tall shrubs such as green alder ( Alnus crispa (Ait.) Pursh) and little-tree willow (Salix spp .). In an area south of Grande Prairie, Alberta, Canada, we examined the effects of shrubs, herbs and other trees on nutrient and light availability and growth of white spruce and lodgepole pine. For white spruce the best competition measure (tested against volume increments of the past 3 years) was visually estimated % ground cover times the height of the competitor (VCHT) with light (DIFN) ranking in third place. For lodgepole pine, DIFN was the best competition measure for predicting volume increment and the best competition index was again VCHT. Taller conifers had a stronger competitive effect than tall shrubs, with their effect on white spruce being larger than that on lodgepole pine. Comparison of the effects of alder and willow indicates that both species are having negative effects on growth of pine and spruce on these sites with green alder having a stronger influence on spruce than pine due to the smaller size of the spruce. Herbaceous cover was having more effect on white spruce than lodgepole pine and may be related to both their height and differences in rooting depth. The results did not show any significant relationship ( p > 0.05) between nitrogen availability and cover of alder and willow and between conifer foliar nutrient concentrations and cover of alder and willow. Our study suggests that the current Alberta regeneration standards may be overestimating the effect that competing vegetation has on conifer growth since significant growth reduction occurs only at high shrub densities.

Forest soil rehabilitation with tillage and wood waste enhances seedling establishment but not height after 8 years

We evaluated soil conditions of rehabilitated log landings in the Interior Douglas-fir biogeoclimatic zone of British Columbia during the first 3 years after treatment and the growth of lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) on these log landings over 8 years. Rehabilitation treatments included combinations of tillage and the addition of either stockpiled topsoil or one of three organic amendments: hog fuel, sort-yard waste, and a wood waste – biosolids compost. The woody amendments were either applied as a surface mulch or incorporated into the soil after tillage. Tillage and addition of wood waste reduced soil bulk density and increased carbon content. Daytime soil temperatures in summer were lower under a hog fuel mulch than for the other treatments. The plots receiving hog fuel also had higher soil moisture content. One year after treatment, soil mechanical resistance for untreated soils, and those that were simply tilled, exceeded 2500 kPa for much of the growing season. Plots receiving wood waste had lower mechanical resistance. Use of wood waste in rehabilitation improved soil conditions and contributed to improved survival rates for planted lodgepole pine seedlings. Height growth after 8 years was not significantly affected by the treatments.

Changes in soil properties, tree growth, and nutrition over a period of 10 years after stump removal and scarification on moderately coarse soils in interior British Columbia

Silvicultural site preparation treatments that involve severe soil and forest floor disturbance may, in the long-term, reduce soil productivity and negate the initial increased forest productivity obtained by controlling root diseases or vegetation. The effect of a range of stump removal treatments on selected soil chemical and physical properties, and growth of planted lodgepole pine ( Pinus contorta) and hybrid spruce ( Picea glauca (Moench) Voss × Picea engelmanii Parry), was examined at three sites in the Interior Cedar–Hemlock (ICH) zone of British Columbia. Changes in forest floor and mineral soil chemistry and bulk density were measured 1 year after treatment and again 9 years later. Tree growth and foliar nutrient status of planted seedlings were measured 3, 5 and 10 years after planting. Forest floor mass and depth were altered by treatment, and decreased significantly between years 1 and 10. Mineral soil bulk density was greater in all stump-removal treatments than in the non-stumped treatment in year 1; however, 10 years after treatment, bulk densities had decreased and no treatment effects were apparent. Changes in forest floor chemistry that were measured in year 1 had largely disappeared by year 10. Mineral soil chemical concentrations were not affected by treatment at any time, except for a significant increase in carbon (C) concentration between years 1 and 10. Lodgepole pine height and diameter were increased over the measurement period by the most intense, scarified treatment, whereas spruce growth was largely unaffected by stump removal treatment. Both tree growth and soil measurements suggest that, on the moderately coarse soils within the climatic regime of the present study, soil limits to tree growth have not been exceeded.

Effects of feathermoss removal, thinning and fertilization on lodgepole pine growth, soil microclimate and stand nitrogen dynamics

The influence of a continuous feathermoss layer (dominated by Pleurozium schreberi) on soil temperature, soil water potential and tree growth was assessed in a 5-year study. The feathermoss layer was manually removed from 900 m 2 plots in lodgepole pine ( Pinus contorta) stands of northwestern Alberta. The interception and retention of nutrients by moss was estimated in N fertilization treatments with and without moss removal. As well, the potential for intraspecific competition to affect nutrient dynamics was assessed through a thinning treatment. Removal of the moss layer increased soil temperatures in summer and increased the period when soil was frost free, but the plots without moss had soil temperature as low as −13 °C in one winter period with little snow cover. Moss removal did not significantly affect N concentrations of the tree foliage but did reduce needle weight. Thinning had little effect on the rate of diameter growth after the first 3 years, but produced a significant increase in growth by year 4. Fertilization had a consistently positive effect on radial stem increments and N content of foliage, regardless of the presence of moss on the plot. Overall, the intraspecific competition between trees was apparently greater than interspecific competition between moss and trees.

Growth-climate Relations of Lodgepole Pine in the North Cascades National Park, Washington

Information about the sensitivity of lodgepole pine to climate will allow forest managers to maximize growth, better understand how carbon sequestration changes over time, and better model and predict future ecosystem responses to climate change. We examined the effects of climatic variability during the 20th century on the growth of lodgepole pine along an elevation gradient in the North Cascades National Park, Washington. Multivariate analysis and correlation analysis were used to simplify growth patterns and identify climate-growth relations. Mid-elevation chronologies correlated negatively with growing season maximum temperature and positively with growing season precipitation. By contrast, high-elevation chronologies correlated positively with annual temperatures and winter Pacific Decadal Oscillation index. Projected increases in summer temperatures will likely cause greater soil moisture stress in many forested ecosystems and the potential of extended summer drought periods over decades may significantly alter spatial patterns of productivity, thus impacting carbon storage. The productivity of lodgepole pine likely will decrease at sites with shallow, excessively drained soils, south and west facing aspects, and steep slopes, but increase at high-elevation sites.

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

The effects of partial cutting on seedling growth of three conifer species were studied at a very dry, hot interior Douglas-fir site near Kamloops, British Columbia. Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.), and ponderosa pine (Pinus ponderosa Dougl. ex. P. & C. Laws.) seedlings were planted in mechanically prepared 50 cm × 50 cm patches under different canopy conditions created by harvesting 60% of the original stand volume. The prepared areas were selected to represent canopy closures from open to closed, slopes from 0 to 60%, and all aspects. After six years, survival of Douglas-fir, lodgepole pine and ponderosa pine was 78%, 76% and 70%, respectively. Light level had a strong influence on survival and condition. Growth of all species increased linearly with light, and was greatest for lodgepole pine, followed by ponderosa pine and Douglas-fir. Multiple regression analysis showed that six-year seedling size was most significantly affected by total light, and only occasionally by aspect, slope, or crown closure. The best models explained 53%, 47% and 42% of the variation in diameter of lodgepole pine, ponderosa pine, and Douglas-fir, respectively. Natural abundance 13C was positively correlated with light and soil moisture availability, reflecting higher photosynthetic capacity of all species in the wetter, open canopy conditions. Patterns in isotopic discrimination also indicated greater water use efficiency of Douglas-fir and ponderosa pine than lodgepole pine under low light conditions. Underplanting stands thinned to a basal area of less than 15m2 per ha offers a solution to regeneration difficulties on hot, dry Interior Douglas-fir sites. Key words: partial cutting, Douglas-fir, lodgepole pine, ponderosa pine, light, soil moisture, 13C, growth, survival, Opax Mountain Silvicultural Systems Project

Effects of forest roads on the growth of adjacent lodgepole pine trees

The effects of roads on growth of adjacent lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees were studied in an area near Williams Lake, British Columbia. Plots were established in a range of stand ages, site qualities, stand densities (stems/ha), stand basal areas (m2/ha), edge aspects, and adjacent road widths. Plots were divided into five zones beginning at the road edge: 0–5 m (zone 1), 5–10 m, 10–20 m, 20–30 m, and 30–40 m (zone 5) from the edge. When the 5 years prior to road establishment were used to scale growth rates, relative tree basal growth rates for zone 1 differed significantly from those for the other zones, with zone 1 rates being 32.1% higher, on average, for 3 to 15 years after the road opening was established. Fewer dead standing trees were found nearest the road edge. Tree bole shapes at breast height were not significantly different among zones, and no significant increases in average basal area per tree or in average height were found. On average, zone 1 had a 31.3% greater stand basal area than zone 5. For a 23.4 m wide road, the increased stand basal area translates to 3.13 m (2 × 31.3% × 5 m for zone 1), or 13.4% recovery of timber losses, if both sides of the road were similarly impacted. This estimate can be improved by using stand basal area to reduce variability.

Long-term responses of ecosystem components to stand thinning in young lodgepole pine forest: III. Growth of crop trees and coniferous stand structure

Enhanced growth of crop trees and development of late-seral structural characteristics in second-growth stands in temperate and boreal forest zones could be achieved by silvicultural practices such as pre-commercial thinning (PCT). This study was designed to test the hypotheses that large-scale stand thinning, at a 15-year period after PCT, would enhance: (i) productivity and structural features (crown volume, diameter, height, and volume growth of lodgepole pine ( Pinus contorta) crop trees); and (ii) coniferous stand structure (abundance, species diversity, and structural diversity of coniferous tree layers). Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of ∼500 stems/ha (low), ∼1000 stems/ha (medium), and ∼2000 stems/ha (high), with an unthinned young pine and old-growth pine stand for comparison. An overall analysis of tree growth in thinned stands, across these regional replicates, indicated that lodgepole pine grew significantly faster in mean diameter in the low- than either of the medium- or high-density stands. There was no difference in mean height growth among stand densities over the 15-year period since PCT. Mean tree volume increment was significantly higher in the low-density than in the high-density stands. Mean stand volume increment (m 3/ha) was similar in the medium-density (108.53) and high-density (132.51) stands, both of which were significantly higher than the low-density stands (72.88). Mean crown volume of crop trees was significantly greater in the low-density (52.8 m 3) and medium-density (42.9 m 3) stands than in the high-density (27.8 m 3), unthinned (11.7 m 3), or old-growth stands (30.9 m 3 pine only). This measure of crown size was similar among pine trees in the low-density, medium-density, and all conifers (43.2 m 3) in the old-growth stands. Other measurements of crown architecture followed this same pattern. Mean densities of understory trees were similar among stands for height classes up to 3 m. Mean species diversity and structural diversity of coniferous tree layers were highest in the low- and medium-density stands than in other treatment stands. Our results support the hypotheses that PCT enhances productivity (diameter and volume growth, but not height growth) and structural features (crown architecture) of young lodgepole pine, as well as diversity of coniferous tree layers in thinned stands. Accelerated development of some structural features of late-seral forest appeared in our young managed stands.

Height growth of planted conifer seedlings in relation to solar radiation and position in Scots pine shelterwood

Seedlings of different provenances of Scots pine ( Pinus sylvestris L.), lodgepole pine ( Pinus contorta Dougl., var. latifolia Engelm.) and Norway spruce ( Picea abies (L.) Karst.) were planted in three Scots pine shelterwoods (125, 65 and 43 stems ha −1) and a clear-cut, all in northern Sweden. The sites were mounded and planting took place during 2 consecutive years (1988 and 1989). The solar radiation experienced by the individual seedlings was determined using a simulation model. Height development of the seedlings was examined during their first 6 years after planting. During the final 3 years of the study, height growth of Norway spruce was relatively poor, both in the shelterwoods and the clear-cut area. Height growth of lodgepole pine was significantly greater than that of Scots pine, both in the shelterwoods and the clear-cut. In contrast to Norway spruce, Scots pine and lodgepole pine displayed significantly greater height growth in the clear-cut than in the shelterwoods. For all three species in the shelterwoods, regression analyses showed that height growth was more strongly correlated with the distance to the nearest tree than with the amount of radiation reaching the ground, i.e. growth was reduced in the vicinity of shelter trees. Therefore, we conclude that the significant reduction in height growth of seedlings of Scots pine and lodgepole pine in Scots pine shelterwoods was partially caused by factors associated with the distance to the nearest shelter tree. Because the substrate was a nitrogen-poor sandy soil, we suggest that root competition for mineral nutrients, especially nitrogen, accounts for the reduction in height growth.

Soil Compaction and Forest Floor Removal Affect Early Growth and Physiology of Lodgepole Pine and Douglas-Fir in British Columbia

Abstract We investigated the effects of soil compaction and forest floor removal on growth and physiology of lodgepole pine (Pinus contorta ex Loud. var. latifolia Engelm.) and Douglas-fir (Pseudotsuga menziesii var. glauca [Baissn.] Franco) seedlings on a calcareous long-term soil productivity (LTSP) study site near Invermere, British Columbia. Treatments consisted of factorial combinations of soil compaction (noncompacted versus compacted) and forest floor removal (forest floor intact versus forest floor removed) as well as a remedial (rehabilitation) treatment of deep ripping following soil compaction. The experiment was not replicated at the treatment plot level, therefore no statistically based mean comparisons were made. After two growing seasons, we found that the two tree species responded differently to those treatments. Lodgepole pine height and diameter growth and unit needle-weight (dry mass per unit needle) averaged 25, 51, and 30% greater, respectively, in the rehabilitation than in the other treatments, whereas Douglas-fir responded to the rehabilitation treatment by increasing stem diameter growth by 27%, but not height growth (a change of 9%). Forest floor removal decreased height growth in lodgepole pine by 11%, but increased diameter growth in Douglas-fir by 15%. The decreases in growth for lodgepole pine in the forest floor removal treatments were accompanied by lower foliar N concentrations. Foliar N concentrations were positively correlated with rates of net photosynthesis (r = 0.69, P = 0.004) and height growth (r = 0.76, P = 0.004) in lodgepole pine, but not in Douglas-fir. Low N supply (as observed for lodgepole pine) and depletion of soil moisture as a result of forest floor removal likely played a role in shaping the growth and physiological responses of the trees in this study. FOR. SCI. 51(6):513–521.

Mechanical disturbance impacts on soil properties and lodgepole pine growth in British Columbia’s central interior

Forest landings are areas located adjacent to haul roads where harvested trees that were skidded from the cutblock are processed and loaded onto trucks. Soils on landings are often excessively compacted by heavy timber harvesting machinery and may take many years to recover from such disturbance. This study examined soil properties and tree growth on unrehabilitated landings (with and without natural regeneration) and adjacent naturally regenerated clearcuts in the central interior of British Columbia (BC), 23 yr after landing construction. Landings (both with and without natural regeneration) had less favorable conditions for tree growth than did clearcuts, including significantly greater surface soil bulk density and mechanical resistance (on some dates) and lower total porosity and concentrations of C and N. Landings without natural regeneration had the least favorable soil conditions, which may account for the lack of natural regeneration. Lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) growing on portions of the landings did not differ in height from those growing in adjacent clearcuts. Site index, as estimated using the growth intercept method, did not differ between naturally regenerated landings (21.7 m) and clearcuts (22.0 m), suggesting that the soils may be equally capable of supporting productive forests. Key words: Forest soil disturbance, soil mechanical resistance, soil productivity, soil water content, natural regeneration

Effects of post-thinning density and repeated fertilization on the growth and development of young lodgepole pine

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.