Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.     

Height development of Betula pubescens following precommercial thinning by breaking or cutting the treetops in different seasons

Topping, i.e. cutting or breaking the treetops of secondary stems, may be an attractive alternative to traditional precommercial thinning. The survival and height development of downy birch (Betula pubescens Ehrh.) after topping were examined over three growing seasons in two dense, naturally regenerated stands, 3.1–3.5 m high, in northern Sweden. The topping was performed in experiments with a two-factor randomized complete block design, as follows. Three treatments were applied to individual secondary stems (top-breaking at half the sample tree mean height, top-cutting at half the sample tree mean height, and traditional cutting just above ground) at each of three times: winter, spring and summer (in frozen, dormant and growing conditions, respectively). A control (no treatment) was also included. The survival rate was lowest for traditionally cut stems and for stems cut in growing conditions. Height development after three growing seasons was significantly affected by time of treatment, the height growth being lowest after treatment in growing conditions, but not by treatment. Height growth of control stems was not significantly different from height growth in any combination of treatment and time of treatment, after three growing seasons. However, control stems had the greatest leading shoot length in the third growing season.     

Stand dynamics and tree quality response to precommercial thinning in a northern hardwood forest of the Acadian forest region: 23 years of intermediate results

In the late 1980s, large forest companies began precommercial thinning (PCT) operations in young northern hardwood cutovers in New Brunswick, Canada. To provide supporting growth and yield information, an industrial experiment was established at residual stand densities of 1300, 1600, 1900, and 2200?stems?ha^?1. Stand responses were examined for measurements recorded at 0 (1987), 5 (1992), 10 (1997), 16 (2003), and 23 (2010) years after establishment. Average diameter at breast height, quadratic mean diameter, stand basal area, and stand total volume growth increased as stem density decreased from PCT. There were significant linear differences for many of these variables between treatments and time periods (year). No significant differences were detected in tree height between treatments. In 2010, the four PCT thinning treatments did not exhibit any differences in potential sawlogs at 2.4?m (8?ft) and 3.6?m (12?ft) lengths. Significant differences were observed for 4.9?m (16?ft) sawlogs that were produced at the least dense spacing (1300?stems?ha^?1). Results from this study and recommendations from the European literature suggest that value-added timber products may be produced from more intense PCT treatments than are currently being practiced on sites dominated by yellow birch (Betula alleghaniensis Britt.).     

Effect of cleaning methods in mixed pine–deciduous stands on moose damage to Scots pines in southern Finland

Abstract

The effect of different cleaning treatments on moose (Alces alces L.) damage to Scots pines (Pinus sylvestris L.) was examined using a generalized linear mixed model (GLMM) with a binomial response (logit-link function). The treatments were the following: no cleaning, point-cleaning of broadleaves (mainly birch, Betula pendula Roth and B. pubescens Ehrh.) within a radius of 1 m from the pine, point-cleaning delayed 2 years, topping of competing broadleaves (main stem cut at a height of 1.3 m) and total cleaning of broadleaves. A randomized complete block design with three replicates was established in three planted pine stands (mean height of pines 1.5 m). Measurements taken four growing seasons later (mean height of pines 3.5 m) showed that all cleaning treatments reduced moose damage, although the difference was not significant (p=0.078) in the case of topping. The proportion of damaged pines was predicted as a function of the characteristics of pines and broadleaves in two untreated, planted pine stands with a height of 3 m. Within these untreated stands the number of damaged pines increased in plots with a higher number of broadleaves and taller broadleaves. In conclusion, the results show that on relatively fertile growing sites of pine cleaning treatments reduced moose damage on pine. It is recommended that cleaning is performed before broadleaved trees occur as overgrowth above pines.     

Timing and intensity of precommercial thinning in Pinus sylvestris stands

The effects of timing and intensity of precommercial thinning were studied in three Scots pine artificially regenerated stands on Vaccinium forest sites in southern Finland. A two-level factorial design (3×3) was used in each stand: thinning at dominant height of 3, 6 and 9 m to 1000, 1600 and 2200 stems ha^?1. The effects of the treatments were analysed after a period of 23–25 yrs when the dominant height was 14–15 m. Early thinning resulted in the highest standing volume and amount of merchantable wood, and also in slightly accelerated height development. Thinning to 1000 stems ha^?1 caused a considerable production loss, but there were no differences between the densities of 1600 and 2200 stems ha^?1. Branches became thicker after early thinning, but the differences between the treatments were negligible for crop trees. Crown ratio was lowest as the result of early or moderate thinning (2200 stems ha^?1).     

Precommercial thinning of beech (Fagus sylvatica L.): Early effects of stump height on growth and natural pruning of potential crop trees

Abstract

This paper reports the early effects of stump height on the growth and natural pruning of potential crop trees after precommercial thinning of a young stand of naturally regenerated beech (Fagus sylvatica L.) in Denmark. The experiment comprises five treatments based on combinations of three grades of precommercial thinning and three stump heights. Treatments include the unthinned control, thinning only of whips and wolf trees (using low stumps), and thinning for potential crop trees using low, medium or high stumps. All treatments were replicated three times. Stump heights averaged 10, 90 or 230 cm, respectively. Pretreatment stem number (live trees) varied from 17,500 to 41,000 ha^?1. In the potential crop tree treatment, post-treatment stem number ranged from 4750 to 9500 ha^?1. Following two growth seasons, the quantity of stump regrowth increased with increasing stump height, the rate of stump regrowth increased with increasing stump height, the diameter growth of potential crop trees increased with decreasing stump height, the increase in stand height did not depend on stump height or post-treatment stem number, and the natural pruning of potential crop trees increased with increasing stump height. It remains to be seen whether these trends hold in the long run, and whether additional economic return from the increase in wood quality with increasing stump height compensates for the reduction in diameter growth.     

Effects of thinning paper birch on conifer productivity and understory plant diversity

Naturally regenerated paper birch (Betula papyrifera Marsh.) is commonly removed from juvenile interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) plantations in southern interior British Columbia, Canada, to increase conifer productivity and create a free-growing stand; however, this practice is expensive and contentious because of possible negative ecological impacts. One solution is to retain an optimal density of birch where growth gains of understory Douglas-fir are balanced against losses to Armillaria ostoyae (Romagn.) Herink and understory plant species diversity. We sought to find this optimal density by comparing four evenly applied birch density reduction treatments (0, 400, 1111, and 4444 retained birch stems ha^?1) and an unthinned control (>7300 retained birch stems ha^?1). The mortality rate of Douglas-fir due to Armillaria root disease increased non-significantly with thinning intensity. Mean diameter increment of surviving Douglas-fir improved the most where birch was completely removed, with little variation among intermediate thinning treatments. Height growth was unaffected by the thinning treatments. Diversity of cryptogams was significantly greater in the control than where all birch was removed. We suggest that the treatment with 4444 retained birch stems ha^?1 provides the best balance for improving Douglas-fir growth while minimizing risk of increased Armillaria root disease and reduced understory plant diversity in young mixed stands.     

Pre-commercial thinning,birch admixture and sprout management in planted Norway spruce stands in South Sweden

Early management of the regenerated seedlings shapes the future stand properties. To address these issues, pre-commercial thinning (PCT) and control treatments were applied to planted Norway spruce (Picea abies L. Karst) and naturally regenerated birch (Betula pendula Roth., Betula pubescens Ehrh.) stands in forest experiments in southern Sweden (lat. 56–57?N) containing 1.1–5.5?m tall saplings. The treatments were retention of 1000 or 2000?stems?ha^?1 of Norway spruce, with no birch or birch at 1000?stems?ha^?1. Treatments were replicated with and without annual removal of birch sprouts from stumps. The periodic annual increment (PAI) over five years was calculated for total stand volume and individual trees. The mean PAI of dominant trees was significantly higher both following all PCT treatments than controls, and following low rather than high-density PCT. Birch retention did not affect growth of the dominant trees but PAI was lower in plots with uncontrolled sprouting. The PAI of birch was significantly higher in low-density Norway spruce plots than in control plots and the high-density plots. The treatment response was significant even in stands with initial heights of only 1–2?m.     

Foliar Responses of Understorey Abies lasiocarpa to Different Degrees of Release Cutting in a Betula papyrifera and Conifer Mixed Species Stand

Foliar responses of subalpine fir [Abies lasiocarpa (Hook.) Nutt.] to thinning were studied in a 35-yr-old mixed stand of paper birch (Betula papyrifera Marsh.) and conifers. The stand regenerated naturally after a wildfire with a canopy dominated by paper birch (average height 9.8 m) and an understorey dominated by subalpine fir (average height 1.6 m). The stand was thinned to four densities of birch: 0, 600 and 1200 stems ha-¹ and control (unthinned at 2300-6400 stems ha-¹) in the autumn of 1995. The understorey conifers, mainly subalpine fir, were thinned to 1200 stems ha-¹. The study used a completely randomized split-plot design. Three sample trees were systematically selected from each treatment replicate and each tree stratum (upper, intermediate and lower understorey). One-year-old and older age class needles were collected from one south-facing branch within the fifth whorl from the tree top. Thinning of paper birch significantly (p <0.001) increased leaf area and dry weight per 100 needles for intermediate and short trees except in the 0 birch treatment. Understorey subalpine fir trees in 600 stems ha¹ birch (T3) had the largest leaf area and leaf dry weight per 100 1-yr-old needles. Specific leaf area (SLA) decreased from unthinned (T1) to 0 birch (T4). Lower understorey trees had the largest SLA. One-year-old needles had significantly higher N, P and K concentrations in all the thinning treatments. These responses are consistent with the shade tolerance of subalpine fir. The results suggest that when managing a paper birch-conifers mixed-wood forest it may be of benefit to understorey conifers to leave a birch canopy as a nursing crop.     

Functions for Biomass Estimation of Young Pinus sylvestris,Picea abies and Betula spp. from Stands in Northern Sweden with High Stand Densities

New silvicultural regimes with high within-stand competition require new functions for estimation of standing stock and growth of biomass components, since the allometry of trees is changed by light competition. This paper presents functions for estimation of the aboveground biomass dry weights for stem wood, stem bark, branches and leaves of young (diameter at breast height <10 cm) Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula pendula Roth. and Betula pubescens Ehrh.) trees growing in dense mixed stands. The functions were derived from a sample consisting of 84 Scots pine, 43 Norway spruce and 66 birch trees from six stands in northern Sweden with high stand densities (>10000 st ha^-1). The logarithmically transformed power function displayed a good ability to stabilize the variance of dry weights and showed a good fit to the material (0.37< R ² <0.99). A comparison with the most commonly used biomass functions in Sweden today showed that they overestimated the weight of stem wood and branches, while the weight of foliage was underestimated. The nature of these discrepancies suggested that the precision of biomass estimations might also be improved for young trees at wider spacing.     

Influence of early thinning in broadleaved stands on development of remaining stems

Abstract

Precommercial thinning studies were performed in eight hardwood stands in southern Sweden. Birch (Betula pendula Roth and B. pubescens Ehrh.) was the dominating tree species, but aspen (Populus tremula L.), black alder [Alnus glutinosa (L.) Gaertn.] and lime (Tilia cordata Mill.) were also present. Main stems were selected before thinning. Three treatments were applied in each stand: (1) no thinning (control), (2) standard thinning, and (3) strong thinning, i.e. leaving about two-thirds of the stem number of treatment 2. Each treatment was replicated three times on all sites. The development of the main stems were recorded during the five consecutive years. Breast height diameter and green crown size (length and width) developed significantly more slowly in the control treatment than in the thinned ones, whereas tree height development was little affected by treatment. Simulation of 10 years’ future growth from the time of the end of the study indicated that future diameter growth will be lower in initially non-thinned stands than in immediately thinned ones. The study results stress the importance for future growth of proper early silviculture in young broadleaved stands (i.e. early and high intensity thinning), a topic that has not been fully evaluated before.     

The effects of heavy thinning on stem quality and timber properties of silver birch (Betula pendula Roth)

A study was carried out into the effects of heavy thinning onstem quality and timber properties of silver birch (Betula pendulaRoth). Comparisons were made with lightly thinned and unthinnedbirch stands. Birch stands from the UK were also compared withsimilarly managed stands from Germany and Denmark. In general,trees from lightly thinned and unthinned stands had similarcharacteristics. Heavy thinning enhanced diameter incrementthrough greater ring width in comparison with the other treatments.The timber properties of basic density, grain angle and shrinkagecoefficients in the radial, tangential and longitudinal directions,however, were largely unaffected. More and bigger branches andgreater stem taper were found on trees from heavily thinnedstands, but these stems still met the current Finnish veneerbirch quality and dimension standards. Comparisons between birchstands, managed by heavy and light thinning, from the UK andGermany and Denmark revealed no meaningful differences in timberproperties. The results suggest that veneer dimension and qualitylogs could be produced in the UK in rotations as short as 40years on good sites if heavy thinning is adopted.     

Dynamics of Crown Thinning and Mycobiota on Fallen Twigs of Mature Birches (Betula pendula) in Finland

The annual dynamics of birch crown thinning was studied by collecting fallen twigs monthly for two years. The detachment of birch twigs that had died during the summer was also followed. In addition, the fungi sporulating on the detached twigs were investigated by photomicroscopy to reveal morphological characters, and by DNA analyses to identify relationships between the fungi. The twigs that had died during the summer fell to the ground during the following winter and spring. Crown thinning, however, peaked in summer and early autumn. Altogether seven sporulating fungi were identified from the detached twigs. The most common fungus was Pleomassaria siparia (the teleomorph of both Prosthemium betulinum and P. asterosporum). The connection between crown thinning and fungi was not clear, but the results suggested that Pleomassaria siparia could be involved in the process.     

The effect of density after precommercial thinning on volume and structure in Pinus Sylvestris and Picea Abies stands

The interaction between stand density and dominant height and the development of volume, mean diameter, mortality and distribution of volume during a period from precommercial thinning to first commercial thinning was studied on permanent plots in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands in Sweden. The reciprocal equation of the yield density effect was used to level the volume yield. Higher density after precommercial thinning resulted in higher yield and smaller mean diameter. The mortality up to first thinning was low, but is also dependent on density after precommercial thinning. The positive skewness of the volume distribution was higher in denser stands.     

Early growth of planted yellow and paper birch and European birches in Vermont

Twelve native yellow birch (Betula alleghanensis Britt.) and paper birch (B. papyrifera Marsh.) sources and 9 European white birch (B. pendula Roth.) sources were planted on three sites in Vermont. Significant differences in growth were found among sources within two of the sites, and differences between sites were significant. Birch from Latvia appeard to be the best source on favorable sites attaining a total height of 5.18m, a total 6-year height increment of 4.29 m, and good stem form. Birches from Finland also showed good growth potential. Six yellow birch seed sources grew well on the best site and yellow birch ranks best there as a species group. European white birches do best as a group on the poor site. Silver birch (Betula pubescens Ehrh.) from Scotland grew poorest of the European birches.     

Variation in understory structure and plant species diversity influenced by silvicultural treatments among 21- to 26-year-old Picea glehnii plantations

We investigated effects of silvicultural treatments (planting and subsequent treatments) on understory structure and plant species diversity in managed Picea glehnii plantations (21–26 years old) in northern Japan. We evaluated the importance of each treatment (machinery site preparation, planting, weeding, and thinning) in 19 plantations, with considerable variation among treatments overall. The understory had 98 vascular plant species; the most dominant species was a dwarf bamboo Sasa senanensis, followed by tree species Abies sachalinensis and Betula ermanii. Multiple regression analyses showed that thinning negatively influenced plant species diversity. Planting density showed a strong positive correlation with density of seedlings (height <20 cm), but few independent variables were correlated with density of saplings (height ≥20 cm and diameter at breast height <1 cm). The negative effect of thinning and the positive effect of planting density seem to be related to the existence or reinitiation of dense cover of Sasa senanensis. We present possible mechanisms of response to treatments to generalize the results. We then suggest ways to improve current treatments to meet the goals of wood production and biodiversity conservation in the region.     

Effects of roe deer browsing and site preparation on performance of planted broadleaved and conifer seedlings when using temporary fences

Abstract

The effects of fencing and site preparation on performance of birch (Betula pendula Roth), oak (Quercus robur L.), pine (Pinus sylvestris L.) and spruce [Picea abies (L.) Karst.] seedlings were studied over four growing seasons in southern Sweden. The experiment was composed of four browsing treatments, from which roe deer (Capreolus capreolus L.) were excluded for 0, 12, 24 or 42 months, and four soil treatments. Natural browsing was combined with artificial browsing (clipping). It was demonstrated that browsing by roe deer could be isolated from browsing by moose (Alces alces L.) by selective fencing. Except for birch, browsing had little effect on seedling survival. Browsing reduced height growth by more than 100% for oak and pine, and more than 60% of pine seedling developed multiple stems. Except for oak, site preparation increased seedling survival. Inverting site preparation, in combination with or without fertilization, produced positive growth responses in seedlings, whereas patch scarification did not. There was no interaction between browsing and soil treatments on seedling performance. It was concluded that long-term protection against browsing by roe deer is needed for oak and pine, whereas short-term fences might be used for birch, and that spruce is relatively unaffected by browsing.     

Functions for estimating belowground and whole tree biomass of birch in Norway

Obtaining accurate estimates of national belowground and whole tree biomass is important to better understand the global carbon cycle and to quantify biomass stocks and changes. However, the availability of individual tree belowground biomass functions is generally low due to the difficulty of extracting roots. Allometric birch (Betula pubescens Ehrh. and Betula pendula Roth) biomass functions were derived from 67 trees for belowground and whole tree biomass using diameter at breast height (dbh) and height as the independent variables. The sampled trees spanned a dbh range from 4.0 to 45.5?cm and the functions provided a good fit to the data (RMSE?=?14.2?kg for BG and 40.7?kg for whole tree with dbh as predictor). Belowground, total stem, live crown, and dead branch biomass comprised 29.2%, 52.2%, 18.1%, and 0.5% of the whole tree biomass, respectively. Observed root-to-shoot ratios were between 0.21 and 0.88 with a mean of 0.42. Comparisons with existing belowground birch biomass functions from Fennoscandia indicated considerable differences in estimates between existing functions. The derived data-set for belowground birch biomass is the largest in Fennoscandia and the developed functions are likely the best available for estimating national birch biomass stock and stock change in Norway.     

Stem Form and Taper Changes After Thinning and Nitrogen Fertilization in Picea abies and Pinus sylvestris Stands

Stem form and taper changes after thinning and thinning combined with N fertilization were studied in 23 Norway spruce [Picea abies (L.) Karst.] and 46 Scots pine (Pinus sylvestris L.) stands in Sweden observed for 5-28 yrs. Average taper was calculated for the stem section 1.3-6.0 m above ground level and as the ratio between the diameter at breast height and total tree height for periods of 5-10 yrs. At the start of the experiment, before the first thinning, the dominant height was 12-15 m. Once 65% of the basal area had been removed in a single thinning from below, the remaining trees showed a strong increase in taper compared with trees in unthinned stands. Stems in stands treated with heavily recurrent thinnings from below also increased in taper, although the increases were not always statistically significant. Trees in thinned, N-fertilized Scots pine stands in middle and northern Sweden developed a more pronounced taper compared with stems in equally thinned, unfertilized stands.     

Models for Assessing Timber Grade Distribution and Economic Value of Standing Birch Trees

In order to obtain a more precise prediction of the distribution of each timber grade or log grade with regard to the volume of birch (Betula pendula Roth., B. pubescens Ehrh.) in models for long-term planning, ordered probit models were developed. These models were developed by using data from three mixed birch and Norway spruce stands in Norway. The data consisted of 168 stems. In Norway, three ordinary birch saw log grades are commonly used, with pulpwood as a fourth grade. In this study, these four grades were applied in addition to waste timber, which was treated as a fifth grade. The developed models showed that the grade distribution of birch trees of mixed birch and spruce stands was highly correlated with tree height (p<0.01) and height to first visible dry branch (p=0.081). The statistical significance of both models was good (p<0.0001), as measured by log likelihood test statistics. Classifying the 168 stems by saw timber or pulpwood in butt log led to greatly improved estimates (p<0.01). The developed models would allow the incorporation of timber grade in stand simulators, enabling more precise predictions regarding the economic implications of alternative management strategies for birch trees.