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1.
Several heavy wet snowfalls occurred during 2007-2009 across a broad-scale thinning and fertilization experiment to bring overstocked juvenile lodgepole pine (Pinus contorta var. latifolia) in the foothills of Alberta, Canada into an intensive management regime. We examined the bending and breakage of trees in relation to thinning and fertilization and used a multimodel information-theoretic approach to model stand and tree level predictors of snow damage. Fertilized stands suffered the greatest amount of snow damage, and this was most noteworthy when stands were also thinned; here 22% (17% broken stems) of trees were damaged compared to 8% (4% broken stems) in the thinned and unfertilized stands. At the stand level, needle weight and crown cover were reliable predictors of snow damage. At the tree level, separate models were developed for each combination of thinning and fertilization. All models used total tree volume; usually the smaller trees in the stands were more susceptible to damage but in the thinned and fertilized stands larger but slender trees with large asymmetrical crowns tended to be damaged. Also, trees with lower total stem volume were more susceptible to damage. Only in the thinned and fertilized stands were variables related to crown shape and asymmetry important predictors of snow damage. We conclude that snow damage is an important agent for self-thinning in unthinned stands and fertilization tends to exacerbate damage because of increase in foliage size. In areas with regular occurrence of heavy snow, we do not recommend fertilization at the same time as thinning, as the larger and more economically important trees in the stand are at risk.  相似文献   

2.
Total foliage dry mass and leaf area at the canopy hierarchical level of needle, shoot, branch and crown were measured in 48 trees harvested from a 14-year-old loblolly pine (Pinus taeda L.) plantation, six growing seasons after thinning and fertilization treatments.

In the unthinned treatment, upper crown needles were heavier and had more leaf area than lower crown needles. Branch- and crown-level leaf area of the thinned trees increased 91 and 109%, respectively, and whole-crown foliage biomass doubled. The increased crown leaf area was a result of more live branches and foliated shoots and larger branch sizes in the thinned treatment. Branch leaf area increased with increasing crown depth from the top to the mid-crown and decreased towards the base of the crown. Thinning stimulated foliage growth chiefly in the lower crown. At the same crown depth in the lower crown, branch leaf area was greater in the thinned treatment than in the unthinned treatment. Maximum leaf area per branch was located nearly 3–4 m below the top of the crown in the unthinned treatment and 4–5 m in the thinned treatment. Leaf area of the thinned-treatment trees increased 70% in the upper crown and 130% in the lower crown. Fertilization enhanced needle size and leaf area in the upper crown, but had no effect on leaf area and other variables at the shoot, branch and crown level. We conclude that the thinning-induced increase in light penetration within the canopy leads to increased branch size and crown leaf area. However, the branch and crown attributes have little response to fertilization and its interaction with thinning.  相似文献   


3.
Physiological parameters were measured under natural light conditions and needle orientation from towers and walkways erected in the canopy of a loblolly pine (Pinus taeda L.) plantation. Four silvicultural treatments were randomly assigned to the twelve plots in the fall of 1988. Plots were thinned to a density of 731 trees per hectare or left unthinned, at a density of 2990 trees per hectare. The plots were left unfertilized or fertilized with 744 kg/ha of diammonium triple superphosphate was applied. During the fifth growing season (1993) following thinning and fertilization, needle level physiology was not different with respect to the thinning treatment for fertilized or unfertilized plots. In contrast, upper crown levels within the fertilized and unfertilized plots had significantly higher light levels and photosynthetic rates than lower crown foliage. Light levels were greater in the thinned, fertilized plots than in the unthinned, fertilized plots. In contrast, no effect of thinning on canopy light levels was found in the unfertilized plots. Within crown variation in photosynthesis was strongly dependent on canopy light levels. A strong interaction of canopy level with thinning was apparent for net photosynthesis. Loblolly pine, being a shade intolerant species, showed only small physiological differences between needles from different parts of the crown. Because of the variability found in this study, more extensive sampling is needed to correctly describe the physiology of a forest canopy with adequate precision.  相似文献   

4.
Midcanopy layers are essential structures in “old-growth” forests on the Olympic Peninsula. Little is known about which stand and tree factors influence the ability of midcanopy trees in young-growth forests to respond to release; however, this information is important to managers interested in accelerating development of late-successional structural characteristics. We examined basal area growth response of midcanopy trees following variable-density thinning in an effort to determine the effect of thinning and local environment on the release of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata ex. D. Don) on the Olympic Peninsula in western Washington. Release was measured as the difference between average annual basal area growth over the 5-year prior to thinning and the 3-to-6 year period following thinning. Results indicate that while growth rates were similar prior to thinning (5.4 cm2 year−1in both thinned and unthinned patches) midcanopy trees retained in a uniformly thinned matrix grew significantly more (8.0 cm2 year−1) than those in unthinned patches (5.4 cm2 year−1) for western hemlock and for western redcedar. Crown fullness and crown crowding affected the release of western hemlock in the thinned matrix. Initial tree size, relative age, local crowding and measures of crown size and vigor affected the release of western redcedar in the thinned matrix. Our results indicate that midcanopy western hemlock and western redcedar retain the ability to respond rapidly with increased growth when overstory competition is reduced and the magnitude of response is related to neighborhood variables (intracohort competition, overstory competition, and tree vigor), thus suggest that variable-density thinning can be an effective tool to create variability in the growth of midcanopy trees in young-growth stands. We expect that this rapid response will produce even greater variability over time.  相似文献   

5.
We studied the combined effects of thinning on stand structure, growth, and fire risk for a Scots pine thinning trial in northern Spain 4 years following treatment. The thinning treatments were: no thinning, heavy thinning (32–46% of basal area removed) and very heavy thinning (51–57% of basal area removed). Thinning was achieved via a combination of systematic and selective methods by removing every seventh row of trees and then by cutting suppressed and subdominant trees in the remaining rows (i.e., thinning from below). Four years after thinning, mean values and probability density distributions of stand structural indices showed that the heavier the thinning, the stronger the tendency towards random tree spatial positions. Height and diameter differentiation were initially low for these plantations and decreased after the 4-year period in both control and thinned plots. Mark variograms indicated low spatial autocorrelation in tree diameters at short distances. Diameter increment was significantly correlated with the inter-tree competition indices, and also with the mean directional stand structural index. Two mixed models were proposed for estimating diameter increment using a spatial index based on basal area of larger trees (BALMOD) in one model versus spatial competition index by Bella in the other model. As well, a model to estimate canopy bulk density (CBD) was developed, as this variable is important for fire risk assessment. Both heavy and very heavy thinning resulted in a decrease of crown fire risk over no thinning, because of the reduction in CBD. However, thinning had no effect on the height to crown base and thus on the flame length for torching. Overall, although thinning did not increase size differentiation between trees in the short term, the increase in diameter increment following thinning and the reduction of crown fire risks support the use of thinning. Also, thinning is a necessary first step towards converting Scots pine plantations to more natural mixed broadleaved woodlands. In particular, the very heavy thinning treatment could be considered a first step towards conversion of overstocked stands.  相似文献   

6.
Development of understory vegetation has been influenced by the many densely stocked second-growth forest stands in North America, which have an extended stem exclusion successional stage. Understory composition and structure is important for ecosystem functioning, while also having social and economic value through the harvest of certain herb and shrub species. The potential for co-management of young and mature, managed and unmanaged stands for timber and non-timber forest products (NTFPs) was assessed in two separate replicated experiments. Experiment A examined pole-sized lodgepole pine (Pinus contorta) stands that had been pre-commercially thinned (PCT) to target densities of 250, 500, 1000, and 2000 stems/ha. Half of each of these four thinning units was repeatedly fertilized, resulting in eight experimental units. Experiment B examined six different stand types: young plantations, pole-sized lodgepole pine stands either PCT, PCT plus repeated fertilization, or unthinned, mature, and old growth. Fifty-four herb and shrub species were identified as potential NTFPs, with the responses of individual species, as well as mean total herb, shrub, berry-producing and overall total NTFPs being assessed. In Experiment A, mean total abundance (crown volume index) of NTFPs, as well as mean total herb NTFPs were significantly greater in fertilized than in unfertilized stands. Thinning treatments did not significantly affect NTFP volume, however, fertilization treatments produced five significant responses by individual species (Achillea millefolium, Epilobium angustifolium, Taraxacum officinale, Arctostaphylos uva-ursi, Rubus idaeus). In Experiment B, four of the six species responses that were significant had greater abundance in young, managed stands (young plantation, thinned, or thinned-fertilized) than in the unmanaged stands. Mean total NTFP volume and mean total herb NTFP volume also followed this pattern. A. uva-ursi, E. angustifolium, Lonicera involucrata, Sorbus sitchensis and Thalictrum occidentale all had significantly higher abundance in young, managed stands than in all other treatments. Results suggest that co-management for timber and NTFPs is possible in this ecosystem, with further research needed to evaluate livelihood values of these crops.  相似文献   

7.
Two levels each of thinning and fertilization were applied to a 7-year-old loblolly pine (Pinus taeda L.) plantation on a nitrogen- and phosphorus-deficient West Gulf Coastal Plain site in Louisiana. Levels of thinning were no thinning, or thinning applied 7 and 14 years after stand initiation. Levels of fertilization were no fertilization or broadcast fertilization with diammonium phosphate at age 7 years plus refertilization with urea, monocalcium phosphate, and potash at age 14 years. Long-term measurements of climate, stand development and productivity, projected leaf area index, and foliar nutrition were initiated at age 11 years. We found that by age 17 years, thinning increased mean live-crown length from 4.2 to 7.8 m, and mean tree diameter from 15.0 to 21.8 cm compared to the unthinned treatment. After rethinning at age 14 years, stand basal area increased 1.2 and 19.2% between ages 15 and 17 years on the unthinned and thinned plots, respectively. Refertilization at age 14 years reestablished foliar N, P and K sufficiency, which increased leaf area index from 4.2 to 6.0 m2 m−2 on the unthinned plots and from 3.2 to 3.8 m2 m−2 on the thinned plots, and subsequently, increased gross stand biomass from 114 to 141 Mg ha−1 on the unthinned plots and from 78 to 95 Mg ha−1 on the thinned plots by age 17 years. Leaf area was an important factor controlling loblolly pine productivity. At our study site, however, competition for light and water and nutrition-limited foliage growth influenced the variability and scope of this relationship. Our results suggest that a positive and linear relationship between leaf area and loblolly pine productivity does not universally occur on loblolly pine sites.  相似文献   

8.
We assessed the effects of thinning (0, 20 and 30 % extraction of basal area) and canopy type (pine–beech vs. pine plots, beech accounting for 12 % of total basal area) on radial growth of dominant and codominant Scots pine at inter-annual scale and on microclimatic conditions, radial growth and xylogenesis 9 years after thinning at intra-annual scale. Thinning weakly affected pine growth, which was enhanced 3 years after harvesting. Over time, a gradual reduction in pine growth in mixed canopy relative to pure canopy occurred only in unthinned plots apparently due to beech expansion. Indeed, 9 years after thinning, a higher seasonal radial increment and a greater number of tracheids were produced under pine canopy in the unthinned plots, whereas no differences between canopy types were observed in the thinned plots. Radial increment and tracheid production were mainly affected by tree water status (air and soil humidity, throughfall). The differences of tree water status caused by treatments, and plausibly disparities in tree size and tree-to-tree competition, were the main drivers explaining the patterns observed for radial increment and xylogenesis. Our results suggest that the negative effects of beech competition on Scots pine growth in similar mixed forest may be controlled to some extent by thinning.  相似文献   

9.
Using tree data from permanent sample plots and climate data from the ClimateWNA model, mixed-effects height to live crown (HTC) models were developed for three boreal tree species in Alberta, Canada: trembling aspen (Populus tremuloides Michx.), lodgepole pine (Pinus contorta var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss). Three model forms, the Wykoff model, a logistic model and an exponential model, were evaluated for each species. Tree height was the most significant predictor of HTC and was used in all models. In addition, we investigated the effects of competition and climatic variables on HTC modelling. Height–diameter ratio and either total stand basal area or basal area of coniferous trees were used as competition measures in the models. Different climate variables were evaluated, and spring degree-days below 0 °C, mean annual precipitation and summer heat–moisture index were incorporated into the aspen, lodgepole pine and white spruce models, respectively. Site index was only significant in lodgepole pine models. Residual variances were modelled as functions of tree height to account for heteroscedasticity still present in the mixed-effects models after the inclusion of random parameters. Based on model fitting and validation results as well as biological realism, the mixed-effects Wykoff models were the best for aspen and white spruce, and the mixed-effects logistic model was the best for lodgepole pine.  相似文献   

10.
We studied the effects of two types of selective thinning on beech stands formed by a shelterwood cut in 1910 — with lower number of crop trees and higher thinning intensity (T1) and higher number of crop trees with lower thinning intensity (T2). The stands were thinned in 1980, 1991 and 2001. Despite a lower stand density after thinning, the annual basal area increments of thinned stands in both thinning periods (1980–1991 and 1991–2002) were around 20% higher compared to those of the control (unthinned) stands. The mean annual basal area increment of dominant trees was 30–56% larger in the thinned plots compared to the control plots. Of 176 initial crop trees in the T1, 72% were chosen again during the last thinning. In the T2, 258 crop trees were chosen in the first thinning, and only 62% of these trees were chosen again during the last thinning. Only crown suppression and diameter classes of crop trees significantly influenced their basal area increment when diameter classes, crown size, crown suppression, and social status were tested. In the thinned stands, the dominant trees are more uniformly distributed if compared to the dominant trees in the control plots. Finally, the herbaceous cover and the species diversity were higher in the thinned plots.  相似文献   

11.
Thinning of Korean pine (Pinus koraiensis Sieb. et Zucc.) is used to facilitate timber and cone production. The present study in Northeast China investigated the effects of thinning intensity on individual tree growth, temporal variation in cone yield, and seed quality in Korean pine plantation. In 2005, five thinning intensity levels (none, extreme, heavy, moderate and light) were set in 15 permanent plots in a 32-year-old Korean pine plantation at Mengjiagang Forest Farm, Jiamusi City, Heilongjiang Province. We recorded tree growth and seed cone production from 2013 to 2016, i.e., from 8 to 11 years after thinning. Except for height growth, thinning increased tree growth (diameter at breast height and crown size) and improved cone yield. The extreme thinning treatment (to 300 trees per hectare) resulted in the largest tree diameter, tree volume, crown size and 4-year cone production per tree. The highest cone yield per tree in the mast year (2014) was observed when stands were thinned to 500 trees per hectare (heavy thinning). Although the best cone and seed quality and the largest cone and seed mass per tree were recorded in the heavily thinned stand, no significant differences were found between heavy and moderate thinning stands (750 trees per hectare). At the stand level, the moderately thinned stand had the highest basal area, stock volume and seed cone production per stand. Our results suggest that thinning to 750 trees per hectare will improve timber and cone productivity in 40-year-old P. koraiensis stands.  相似文献   

12.
Crown shyness or canopy disengagement, the phenomenon wherein gaps around trees develop from swaying, whipping and shading, has been identified in the literature since the 1920s. Recent results by researchers at the University of Alberta have clearly described many of the processes involved for lodgepole pine [e.g. Rudnicki, M., Silins, U., Lieffers, V.J., Josi, G., 2001. Measure of simultaneous tree sways and estimation of crown interactions among a group of trees. Trees 15, 83–90; Rudnicki, M., Lieffers, V.J., Silins, U., 2003. Stand structure governs the crown collisions of lodgepole pine, Canadian Journal of Forestry Research 33, 1238–1244; Rudnicki, M., Silins, U., Lieffers, V.J., 2004. Crown cover is correlated with relative density, tree slenderness, and tree height in lodgepole pine. Forest Science 50, 356–363; Fish, H., Lieffers, V.J., Silins, U., Hall, R.J., 2006. Crown shyness in lodgepole pine stands of varying stand height, density, and site index in the upper foothills of Alberta. Canadian Journal of Forestry Research 9, 2104–2111]. However, explicit models of crown shyness are sparse in the literature. This paper describes the development of empirical models of crown shyness in lodgepole pine for British Columbia (BC). We measured crown area and neighbour locations on 60 trees growing in 13 stands in central BC. We estimated potential crown area (AV) using stem maps and Voronoi polygons constrained by estimates of maximum crown width, and then related observed crown area (AC) to AV and additional individual tree variables. One of the nine prediction equations was coded into a spatially explicit tree growth model modified to evaluate the effects of crown shyness at the stand level. Crown shyness models validated well against two independent sources and when linked with a light model tRAYci [Brunner, A., 1998. A light model for spatially explicit forest stand models. Forest Ecology and Management 107, 19–46], increased the below-canopy light by 0.07–0.11.  相似文献   

13.
In this article, we report on the increments in basal area and tree diameter as well as the structural development observed in variously thinned plots that underwent either uneven- or even-sized treatment. The experimental forest was originally an uneven-sized mixed stand dominated by Picea abies. Twenty-eight randomized sample plots underwent each treatment, and the trees were monitored for 15 growing seasons after thinning. The uneven-sized plots retained a reverse J-shaped diameter distribution, but this was changed into a bell shape by low thinning in the even-sized plots. Absolute basal area increment was positively correlated with basal area in the even-sized treatment but not in the uneven-sized treatment. In the latter, all of the plots grew almost equally well, and only the basal area of broadleaves explained slightly positively the increment variation. Relative basal area increment was negatively correlated with basal area in both treatments. Additionally, the basal area of Scots pine was a positive explanatory variable in the relative increment variation in the even-sized treatment. For the dominant Norway spruce trees, diameter increment was negatively correlated with basal area in both treatments and, conversely, heavy removal increased the diameter increment. Relative basal area increment averaged 5% annually in uneven-sized plots representing the “target selection.” This was more than double the increment observed for the even-sized plots that represented the “prevailing practice.” Likewise, the diameter increment of Norway spruce trees was 48% greater in the uneven-sized compared to the even-sized plots.  相似文献   

14.
A 23 factorial experimental testing the effects of urea (N), superphosphate (P) and two thinning types (diagonal-line thinning and thinning from below) on the basal-are increment of 18-year-old Pinus radiata (D. Don) is described. Although the trees had received localized applications of superphosphate shortly after establishment they were considered at the age of 18 years to be phosphate-deficient because concentrations of phosphorus in the foliage were low (0.065% P). Application of superphosphate (200 kg P ha−1) increased concentrations in the foliage (0.132% P) and increased the 7-year basal-area increment by approximately 70%. No growth response was obtained when urea (476 kg N ha−1) was applied alone. When both fertilizers were applied there was a further increase in basal-area increment of 81% on line-thinned plots and 26% on plots which had been thinned from below. This interaction reversed the normal trend in which plots thinned from below, by virtue of their greater initial basal area, produced 11–16% more increment than those which had been line-thinned.

A model of tree growth using initial basal area and a competition index as independent variables was adequate to describe differences in basal-area growth between thinning types except where urea and superphosphate had both been applied. In the case of N + P-treated plots, the reciprocal of the competition index was required as an additional variable. Analysis of the development of the growth responses over time indicated that application of superphosphate had produced sustained improvement in growth rates but that the response to urea occurred only in some growing-seasons. In line-thinned plots the response to urea in addition to phosphate occurred in the 2nd, 3rd and 4th growing-seasons, but the response occurred only in the 2nd and 4th growing-seasons in plots thinned from below. It is argued that this differential response between thinning types can be attributed to differences in stand density and water availability. In order to maximise the growth response to added nitrogen it is important to reduce competition by paying particular attention to both tree spacing and residual basal area.  相似文献   


15.
[目的]研究不同强度采伐下马尾松的生长动态,筛选适宜的采伐强度,为马尾松人工林近自然经营提供技术支撑。[方法]2007年10月在14年生马尾松人工林(保存密度1 100株·hm~(-2))内进行采伐试验,设置4个采伐强度,即保留密度分别为225、300、375、450株·hm~(-2),以不采伐为对照;其后,自2008年开始连续8 a,每2 a测定1次马尾松的胸径、树高、枝下高和冠面积等生长指标,并计算单株材积和林分蓄积量,应用方差分析和Duncan多重比较分析生长指标对不同采伐强度的动态响应。[结果]表明:采伐强度显著影响林分生长,其中,林分平均胸径、单株材积、冠面积的年均增长量随保留密度增大而减小,但均显著高于对照(P0.05)。采伐后第1 3年,马尾松冠面积增长量显著高于采伐后期,胸径则在采伐后第3 5年最高,而不同采伐强度对林分树高生长影响不明显。保留密度显著影响林分枝下高和蓄积量的动态变化,其年均增长量随密度增大而递增。5个处理间林分蓄积年均增长量的差异随林龄的增大而逐渐缩小。[结论]马尾松人工林生长对不同强度采伐的动态响应以树冠最敏感,冠面积首先陡然增大,进而引起胸径的快速生长。树高和枝下高在采伐后年均增量变化相对平稳。4个采伐强度均显著促进单株材积生长,而仅保留密度为225株·hm~(-2)的采伐对林分蓄积增长量影响显著。综合比较林分的单株材积和林分蓄积连年增长量,建议在桂西南15年生马尾松人工林近自然经营中宜选择300株·hm~(-2)的保留密度进行采伐。  相似文献   

16.
This study analyses the effects of thinning on stand transpiration in a typical mixed spruce and pine forest in the southern boreal zone. Studies of transpiration are important for models of water, energy and carbon exchange, and forest management, like thinning, would change those processes. Tree transpiration was measured by the tissue heat-balance sapflow technique, on a reference plot and a thinning plot situated in a 50-year-old stand in central Sweden. Sapflow was measured during one season (1998) on both plots before thinning, to establish reference values. In winter 1998/1999 24% of the basal area was removed from the thinning plot. Thinning was done so as to preserve the initial species composition and the size distribution. The measurements continued after thinning during the growing seasons of 1999 and 2000. The climate showed remarkable differences between the 3 years; 1998 was wet and cool, with frequent rain, and the soil-water content was high throughout the year. In contrast, 1999 was dry and warm, and the soil-water content decreased to very low values, ca. 5–6% by volume. In 2000, the weather was more normal, with variable conditions. Stand transpiration was similar on both plots during the year before thinning; the plot to be thinned transpired 6% more than the reference plot. After thinning, transpiration was initially ca. 40% lower on the thinned plot, but the difference diminished successively. When the following drought was at its worst, the thinned plot transpired up to seven times more than the reference plot. During the second season after thinning, the thinned plot transpired ca. 20% more than the reference plot. The increased transpiration of the thinned plot could not be attributed to environmental variables, but was most probably caused by changes in biological factors, such as a fertilization effect.  相似文献   

17.
We examined how tree growth and hydraulic properties of branches and boles are influenced by periodic (about 6 years) and annual fertilization in two juvenile lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) stands in the interior of British Columbia, Canada. Mean basal area (BA), diameter at breast height (DBH) and height increments and percent earlywood and sapwood hydraulic parameters of branches and boles were measured 7 or 8 years after the initial treatments at Sheridan Creek and Kenneth Creek. At Sheridan Creek, fertilization significantly increased BA and DBH increments, but had no effect on height increment. At Kenneth Creek, fertilization increased BA, but fertilized trees had significantly lower height increments than control trees. Sapwood permeability was greater in lower branches of repeatedly fertilized trees than in those of control trees. Sapwood permeabilities of the lower branches of trees in the control, periodic and annual treatments were 0.24 x 10(-12), 0.35 x 10(-12) and 0.45 x 10(-12) m2 at Kenneth Creek; and 0.41 x 10(-12), 0.54 x 10(-12) and 0.65 x 10(-12) m2 at Sheridan Creek, respectively. Annual fertilization tended to increase leaf specific conductivities and Huber values of the lower branches of trees at both study sites. We conclude that, in trees fertilized annually, the higher flow capacity of lower branches may reduce the availability of water to support annual growth of the leader and upper branches.  相似文献   

18.
Natural mortality in a 30-year period was examined in thinning and fertilisation experiments with 48 blocks in Scots pine (Pinus sylvstris L.) and 23 blocks in Norway spruce (Picea abies (L.) Karst.) with up to 12 different treatments. Of about 90,000 living trees at start of the experiments 18.7% were registered as dead by natural mortality in the 30-year observation period. In non-thinned stands about 20% of the volume growth disappeared by natural mortality, in thinned stands about 10%. In normally thinned pine stands (repeated thinning from below with moderate intensity) the annual mortality of the basal area at start of an average 7-year period was 0.34%. In spruce stands, on more fertile sites, the corresponding figure was about 0.6%. In an effort to model the mortality, severe damage not leading to final felling was identified in 1.7% of the observation periods. It was assumed that this part of the mortality, representing 24% of the total volume mortality, could be recovered by active thinning. The probability for severe damage increased sharply with stand top height, as shown in a logistic regression. The more sparse mortality was expressed as a function of site fertility, stand density, disturbance by thinning and form of treatment (thinned from above or below or non-thinned). The naturally dead trees were approximately of mean size in normally thinned stands while the self-thinning in non-thinned stands tended to occur amongst smaller than average trees. Diagrams were presented for basal area development and stem number reduction in the non-thinned stands.  相似文献   

19.
A stand basal area growth system for radiata pine (Pinus radiata D. Don) plantations in Galicia (Northwestern Spain) was developed from data corresponding to 247 plots measured between one and five times. Six dynamic equations were considered for analysis and both numerical and graphical methods were used to compare alternative models. The equation that best described the data was a dynamic equation derived from the Korf growth function by the generalized algebraic difference approach (GADA) and by considering two parameters as site-specific. This equation was fitted in one stage by the base-age-invariant dummy variables method. The system also incorporated an equation for predicting initial stand basal area, expressed as a function of stand age, site index, and the number of trees per hectare. This information can be used to establish the starting point for the projection equation when no inventory data are available. The effect of thinning on stand basal area growth was also analyzed and the results showed that the same projection equation can be used to obtain reliable predictions of unit-area basal area development in thinned and unthinned stands.  相似文献   

20.
We investigated whether root grafts between lodgepole pine (Pinus contorta var. latifolia Dougl. ex. Loud.) trees can transfer sufficient carbohydrate reserves from a source tree to a grafted sink tree to affect the vigor of trees growing in a light-limited environment. Eleven plots were established in early spring and two grafted tree pairs and two independent non-grafted trees were selected at each plot. One tree in a grafted pair and one non-grafted tree were shaded at each plot, whereas the remaining trees were non-shaded during the experimental period. Shaded trees had significantly lower carbohydrate reserves and smaller crowns than non-shaded trees following one growing season. Grafted shaded trees had significantly higher root total nonstructural carbohydrate concentrations than non-grafted shaded trees, indicating that root grafts partially offset the effects of shading. Also, large root grafts transferred proportionately more carbohydrates to the shaded trees than small root grafts. Carbohydrates transferred through root grafts could allow grafted trees to persist under conditions where non-grafted trees would be removed by competition.  相似文献   

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