Influence of Shelterwood Density on Survival and Height Increment of Picea abies Advance Growth

Abstract

The increases in the arithmetic mean diameter at breast height (dbh) of the 100, 200, 300 and 400 largest stems ha^?1 by dbh associated with six different thinning regimens for periods up to 35 years were compared, by analyses of variance, to the corresponding stem fractions in unthinned stands using permanent sample plot data. In addition, the expected mean dbh of these stand fractions at future points in time was modelled, based on site and stand data obtained at the time of the first thinning. Thirty-five years after the first thinning, the thinning from below regimens resulted in actual increases (a measure affected by both the thinning intensity and the thinning method), compared with the unthinned stands, in the mean dbh for the 100, 200, 300 and 400 largest stems ha^?1 of 2.6–9.0 cm. The corresponding genuine increases (a measure principally affected solely by the thinning intensity) were 4–11 cm. The functions predicting the future dbh of these stand fractions yielded good fits.     

辽东栎伐桩萌苗的发育规律

通过对黄土高原黄龙山林区辽东栎林固定样地连续6年的调查,研究间伐强度分别为13.4％(弱度间伐)和30.0％(强度间伐)的辽东栎伐桩萌苗的存活与生长规律.结果表明:1)间伐第1年,辽东栎伐桩均有萌生枝发生,每桩萌生枝数量和萌生枝高度在不同强度间无显著差异;2)萌生枝数量受伐桩高度和直径的影响,当伐桩高度较低时,萌生枝数量随伐桩高度的增加而增加,超过20cm后随之减少,呈三次抛物线关系;伐桩萌生枝数量随着伐桩直径增加呈现先增加后减少的趋势,直径30～50cm的伐桩萌生枝数量最多;3)伐桩萌生枝数量与最长萌生枝高度呈显著线性负相关,存在“萌生枝数量——高度权衡”现象;4)间伐第6年,伐桩的存活率为97.01％,强度间伐区萌生枝高度显著高于弱度间伐区;5)调查期间,辽东栎伐桩萌生枝数量逐年下降,伐桩产生的萌生枝数量越多,后期萌生枝死亡的数量也越多,表明伐桩能够自我稀疏,存在“萌代主”现象.在黄土高原地区,辽东栎伐桩萌芽潜力很大,应合理利用;间伐时伐桩高度应尽量低于20cm;伐桩直径在30～50cm更有利于其无性更新;间伐后伐桩应及时除蘖定株,促进萌生枝生长;间伐强度30.0％(强度间伐)更有利于辽东栎伐桩萌生枝的生长.     

Development of water oak stump sprouts under a partial overstory

A 28-year-old water oak (Quercus nigra L.) plantation was thinned from below to either 254 or 462 stems per hectare to determine the influence of a partial canopy on oak stump sprout development. Sprout clump survival, number of living sprouts in a clump, and height and DBH of the dominant sprout in a clump were measured in years 1–5 and 7 after harvest. By year 7, sprout clump survival under the heavily thinned canopy was 23% higher than under the lightly thinned canopy. Within-clump sprout mortality was not influenced by overstory thinning level, but by year 2 height and diameter increment were 15% and 22% greater, respectively, under the heavy overstory removal. Positive height and diameter growth of dominant sprouts continued under both canopy conditions through year 7, but early benefits of the heavy overstory removal on sprout growth diminished. Additional overstory removal or sprout clump thinning would be necessary to sustain sprout clump survival and sprout growth over extended periods.     

杉木林分密度效应研究

该项试验共分2个部分.(1)造林密度试验,小区面积为600 m2,5个处理,即1 667株.hm-2(A)、3 333株.hm-2(B)、4～983株.hm-2(C)、6 633株.hm-2(D)、9967株.hm-2(E);(2)造林密度调控试验,造林设计方法与造林密度试验相同,但在林分生长过程中,按密度管理图的密管线0.5为标准进行间伐,间伐后保留密度要与临近的下一个初植密度较稀植的林分密度基本相同,两者进行比较.试验结果(1)造林密度试验,优势高、平均高、平均胸径均随年龄的增加而递增,随密度的增加而递减,优势高9a、平均高6 a、平均胸径5 a,密度间差异已达显著性水平;林分蓄积量则随年龄增加而递增,5～7 a,密度间差异显著,8～18a,只有A密度与E、D密度差异显著;枝下高随密度、年龄的增加而递增,12～a后,C、D、E密度间的差异很小;冠幅随密度的增加而递减,随年龄的增加而递增,9～10a后,各密度则随年龄增加而缓慢递减.(2)造林密度调控试验,同一指数级,间伐后的林分与其密度基本相同未间伐的林分比较,其优势高、平均高差异不明显;立木蓄积前者小于后者;总蓄积(立木蓄积+间伐蓄积)前者大于后者;同一指数级,初植密度不同的林分,间伐后与密度基本相同未间伐林分的蓄积百分比,初植密度大的大于初植密度小的;指数级不同,而初植密度相同的林分,间伐后与密度基本相同未间伐的林分总蓄积百分比,高指数级的比值大于低指数级的比值.     

Cherrybark oak stump sprout survival and development five years following plantation thinning in the lower Mississippi alluvial valley,USA

Cherrybark oak (Quercus pagoda Raf.) stump sprouts were studied for 5 years in a 30-year-old plantation thinned to 70–75% stocking (light thinning) and 45–50% stocking (heavy thinning). Sprouting success, survival, number of sprouts per stump, and sprout height differed little between thinning treatments throughout the 5-year study period. Pre-harvest tree d.b.h. also had no influence on sprout survival and development. A 2-year drought reduced survival and may have influenced sprout development. Sprout clump survival dropped from 90% 1 year following thinning to 46% 3 years after thinning. Although sprout height averaged 337 cm 5 years after thinning, annual sprout growth decreased from 166 cm the first year after thinning to 33 cm in each of the last 2 growing seasons. Results indicated that bottomland hardwood regeneration evaluation models may underestimate the potential of oak stump sprouts to contribute to pre-harvest regeneration assessments. Further study in the role of stump sprouts to regenerate bottomland oak species is needed. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged     

长白落叶松人工林间伐林分的生长模拟

利用黑龙江省孟家岗林场长白落叶松人工林间伐标准地定位观测数据,其于间伐林分断面积与相同年龄、相同立地、相同保留木株数的未间伐林分面积,随时间趋于一致的假设,根据未间伐人工林林分断面积生长的一般预测模型导出了间伐林分的断面积生长预测模型,同时,结合抚育间伐技术批示的确定,进行和林分的动态模拟。     

Early regeneration of Fraxinus rhynchophylla in the understorey of Larix kaempferi stands in response to thinning

The effects of thinning were investigated on naturally regeneratedFraxinus rhynchophylla Hance (Korean ash) grown in the understoreyof a Larix kaempferi (Lamb.) Carr. plantation, established ona site that previously supported old growth hardwood forests.The regeneration characteristics were evaluated after thinningof the plantation (about 60 per cent of relative density wasremoved). In the naturally regenerated and mixed stands, Quercusmongolica Fisch. was the most abundant tree species in the overstorey,but the understorey of the thinned plantations was dominatedby F. rhynchophylla with six other minor tree species. Fraxinusrhynchophylla was regenerated by four propagation types includingnatural seedling, stump sprout, root sprout and layering. Beforethinning, the difference of average height growth for each regenerationtype was insignificant. One year after thinning, the stump sproutsshowed the fastest growth among the regeneration types. Heightgrowth of advance regeneration was slow in the year followingthinning but then increased rapidly surpassing the other regenerationtypes 5 years after thinning. Thinning had an effect on thecomposition of regenerated trees also by seedling, stump sprout,root sprout and layering in the understorey. Advance regenerationsoccupied the upper understorey at 5 years after thinning. Alarge number of stump sprouts emerged in the plots 1 year afterthinning, while at 5 years after thinning the occupation ofstump sprouts decreased. Root sprouts and layers faded away.Considering the early growth and the composition of understoreyF. rhynchophylla, its advance regeneration has a high potentialto develop into overstorey trees at this site.     

Influence of thinning time and density on sprout development, biomass production and energy stocks of sawtooth oak stumps

The high potential values of sawtooth oak (Quercus acutissima) in fuelwood or bioenergy are recognized. Sprouting ability, sprout growth, biomass production and energy stocks in coppiced plantations of sawtooth oak were evaluated at the Hongya Mountain Forest Farm in Anhui Province, China. Experimental treatments applied in a split-plot design included three sprout thinning times and four sprout numbers reserved on each stump (1 sprout, 2 sprouts, 4 sprouts stump⁻¹ and check). Sprout growth and biomass production per stump were significantly affected by the treatments and a significant positive relationship between stump basal diameter and sprout numbers produced was observed. After the third growing season, the highest total sprout biomass per stump was achieved in the treatment with thinning excess sprouts at the end of first growing season (December, 2007) and reserving 4 dominant sprouts per stump (T12S4, reaching 8.67 kg stump⁻¹), while the lowest was found in the treatment with thinning the sprouts in August of the first growing season and reserving 1 dominant sprout per stump (T8S1, only 3.40 kg stump⁻¹). Different treatments also influenced gross calorific values (GCV) of the components sampled from 3-year-old sprouts and the mean GCV of stem wood on an oven-dry weight basis was within the range of 18.45 ± 0.15 and 18.83 ± 0.12 kJ g⁻¹. Similar to the sprout biomass production, the greatest total and stem energy stocks per stump were observed in T12S4 treatment, achieving 161.6 and 110.5 MJ stump⁻¹, respectively. Based on the results from this study, thinning excess sprouts to reserve 4 sprouts per stump as early as age 1 could be proposed for the management of sawtooth oak coppice with cutting cycle of 3-5 years and stand density of 5000-6000 stump ha⁻¹.     

Effects of thinning on plant species diversity and composition of understory herbs in a larch plantation

The effects of thinning on plant species diversity and composition of understory herbs in a larch plantation were investigated. The relationships between plant species diversity and composition of understory herbs and light conditions were established. Twenty-five 1 m × 1 m plots and fifteen 13 m × 1 m transects were set up in unthinned and thinned stands, respectively. All the transects in the thinned stands were set across the thinned rows and unthinned rows, and each of them was divided into nine 1 m × 1 m sub-plots. The herb diversity and light conditions were observed in each plot and sub-plot. The results show that there was a significant difference in herb diversity between the thinned and unthinned stands. All biodiversity indices except for evenness index in the thinned stand were higher than those of the unthinned stand, i.e., the herb diversity increased after thinning. According to the changes in herb densities and whether one species could be found in a stand or not before and after thinning, all herb species were classed into three types: positive, neutral and negative species, which referred to a species newly appeared and having an obviously increased density after thinning, with no obvious changes in its appearance and density after thinning, and disappeared and having an obviously decreased density after thinning, respectively. Many new species were found in the thinned stand like Corydalis pallida, Prenanthes tatarinowii, Vicia unijuga and Sonchus brachyotus etc. However, most species found in both the thinned and unthinned stands were negative species. In all nine subplots, only 11 and 10 species were found in spring and in autumn respectively, accounting for 17.74% and 15.15% of all the species in the thinned stand, respectively. All biodiversity indices were the highest in the center sub-plots and most of them tended to reduce from middle to side sub-plots. There was a close correlation between most of the three types of species and light conditions which was similar to each other in the thinned and unthinned stands. __________ Translated from Chinese Journal of Ecology, 2006, 25(10): 1201–1207 [译自: 生态学杂志]     

Effect of thinning on the development of compression wood in stems of Corsican pine

This study considered the effects of thinning on the development of compression wood in stems of 35-year-old stand of Corsican pine (Pinus nigra L.). Part of the stand had been thinned at 5-yearly intervals and part left unthinned. Twenty trees each from the thinned and unthinned stands were randomly selected and felled. Measurements were made on tree height, stem diameter, stem slenderness and canopy depth. Wood samples were removed from the central part of the main log and cross-sectional measurements made on ring width, basic density and compression wood content. Cross-sectional area of compression wood was found to be three time higher in stems from the unthinned trees in comparison with those from the thinned trees. No significant differences in mean radial ring width or basic density were found between treatments. Correlations indicated that, with increasing in stem diameter, compression wood content increased in the unthinned trees, while a decline in compression was observed in the thinned trees. Tree height was also positively correlated with compression wood content in unthinned trees, while no equivalent relationship was observed in thinned trees. Observations from this study, while not conclusive, suggest that phototropic stimulus may be producing stem inclinations in the unthinned stand as trees compete for space in the canopy, whereas crown competition has been largely eliminated in the thinned stand; and that this is responsible for compression wood levels recorded in this study.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Effects of five tree-selection strategies when thinning spruce (Picea abies) stands: a case study in a field trail in southern Sweden

The aim of this study was to show the effects of five tree-selection strategies when thinning on quality and growth properties of Norway spruce stands, and their potential for improving quality in the stands. The five strategies were thinning to retain high-quality (HQ) and low-quality (LQ) trees, thinning from above (A) and below (B) and thinning to obtain an even distribution of residual trees (S). The study was conducted in two planted stands close to rotation age, located in southern Sweden, which had been thinned twice since the establishment of the thinning experiment. In the two quality-based treatments trees were selected for harvest on the basis of the following growth and quality traits: tree class, vitality, dbh, height, straightness, branch diameter and quality defects. The quality traits were found to be largely independent of tree size, thus the selection strategies based solely on dbh (A and B) did not improve quality within the stands. Thinning targeting HQ traits promoted the retention and growth of HQ trees, and improved overall quality of the stands compared to the other treatments. HQ thinning increased the share of straight trees by 15%, on average. Significant proportions of stem crooks and quality defects detected before the first thinning were invisible 21 years after it. All thinned stands had higher proportions of naturally pruned trees than unthinned stands. The selection method had no influence on periodic annual increment after thinning.     

Oak/Douglas-fir/sheep: A three-crop silvopastoral system

A small scale agroforestry study which was begun in 1952 was revisited in 1985 to evaluate the long-term influence of site preparation and grazing on tree growth and survival in a Douglas-fir (Pseudotsuga menziesii)-white oak (Quercus garryana)-sheep silvopastoral system. In 1952–1953, two-year-old Douglas-fir seedlings were planted at the rate of 2500 trees/ha under three levels of site preparation: (1) no treatment, (2) oak thinned by 50%, and (3) oak clearcut. From 1954 to 1960, yearling ewes grazed one-half of each of the three thinning treatments for 3–4 weeks each spring. The conifers have been undisturbed since grazing was discontinued in 1960. Survival of planted conifers averaged 64% in 1985 and did not vary among either site preparation or grazing treatments. From 1964 to 1985, trees on the thinned and clearcut plantations grew an average of 1060 and 990 cm in height, respectively, compared to 900 cm on the unthinned plantation. Diameter at breast height (dbh) averaged 3.8 and 5.6 cm greater on thinned or clearcut plantations, respectively, than on the unthinned control by 1985 (p < 0.05). Conifers on grazed plantations had increased height and dbh growth during the first 12 years of plantation life, averaging 63 cm taller (p < 0.10) and 0.7 cm greater in dbh (p < 0.05) than the ungrazed plots by 1964. By 1985 the difference in height (122 cm) and dbh (1.0 cm) between grazed and ungrazed plantations was not statistically significant. These data suggest that although site preparation can positively influence conifer growth, total clearfelling is no better than thinning oaks. Furthermore, proper grazing can increase height and dbh growth of the conifers during and immediately after the grazing years.     

Canopy density in stands of Picea abies and Pinus sylvestris after different thinning methods

Altogether 82 plots (261 estimations) of Picea abies (L.) Karst, and 193 plots (360 estimations) of Pinus sylvestris (L.) stands were estimated by a vertical tube. The “crown free projection”, CFP, of stands thinned in three methods with different thinning grades was measured: unthinned, heavily and very heavily thinned, heavily thinned delayed first thinning, extra heavily thinned and thinned from the top. Basal area (m²ha^?1) density (stems ha^?1) and diameter sum (m ha^?1) were plotted against CFP. Basal area was the best practical measure of stand in this study. Generally Scots pine stands have higher CFP and the curves are steeper than in Norway spruce stands. Depending on the grade of thinning, heavily and very heavily thinned spruce stands, delayed first thinning included, have CFP values of 10–15% and stands thinned from the top, 20–40%, compared with 30–80% and 30–60% respectively in pine stands. Extra heavily thinned stands have the highest CFP, 20–80% in spruce and 50–90% in pine stands. The CFP levels after thinning are too high in pine stands for avoidance of sucker and sprout production of aspen and birch. In dense Norway spruce stands thinned from the top or heavily and very heavily thinned, the CFP values are low enough (≤30%) to diminish the production of suckers.     

Stand density and fertilization effects on aboveground allocation patterns and stem form of Pinus sylvestris in young stands

The increasing demand for forest biomass for energy generation could be partially met by growing denser stands and use of fertilizer. Before this is done at large scale, more knowledge of the effects of stand density and fertilization on aboveground allocation patterns and stem form is needed. Therefore, effects of pre-commercial thinning (PCT) to 3000 stems ha^?1, an unthinned dense control (C), and PCT combined with two levels of fertilization (100 kg ha^?1 of nitrogen applied either during the establishment of the field experiment (F1) or annually (F2)) were examined in 23- to 26-year-old Scots pine (Pinus sylvestris L.) stands six years after the establishment of the field experiment. In total, 114 sample trees were harvested using destructive biomass sampling. The growth allocation and stem form of trees with diameter at breast height (DBH; 1.3 m height) >5.0 cm were not affected by either the PCT or fertilization. Small trees (DBH < 5 cm) in denser, unthinned control plots had more slender stems (lower DBH/height ratios) and allocated less growth to branches and foliage than trees in PCT plots. Fertilization had little effect on the stem form and growth allocation of the smallest trees. Therefore, effects of stem density and fertilization on stem form and growth allocation to foliage were only found for small suppressed trees, and the treatments had very little influence on dominant and codominant trees.     

Line thinning promotes stand growth and understory diversity in Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantations

We studied the effects of line thinning on stand structure, microclimate and understory species diversity of two Cryptomeria japonica D. Don plantations in south-central Japan. In each of two study sites we compared stand structure between the thinned stand and an adjacent unthinned stand and found that line thinning increased the growth rate of residual trees such that stand basal area may recover within 10 years after thinning. In the thinned stand, more open canopy conditions resulted in higher maximum temperatures on the forest floor during the early growing season than in the unthinned stand. The thinned stand had greater understory plant species richness and biomass than the unthinned stand. This study suggested that line thinning could potentially enhance biodiversity while simultaneously increasing tree-growth rates in overstocked Cryptomeria japonica plantations.     

Effects of thinning level and site productivity on age-related changes in stand volume growth can be explained by a single rescaled growth curve

In this study, I developed a nonlinear mixed-effects model based on the Richards curve that describes the effects of thinning and site productivity on stand volume growth. I fitted the model to data from 29 long-term experimental monitoring plots in Japanese cedar (Cryptomeria japonica D. Don) plantations in northeastern Japan. Simulations using the model on high-productivity sites and at moderate thinning intensities indicated that net yields after ca. 80 years were lower in unthinned stands than in thinned stands; in other cases, such as at younger ages and at sites with low and average productivities, net yields were similar for each thinning intensity (including no thinning). These results could be attributed to the fact that the net current annual increment in stand volume (CAI_net) in the thinned stands exceeded that of the unthinned stands after a certain age (the “inversion” age) and to the negative correlation between site productivity and the inversion age. In addition, I found that a single rescaled growth curve was capable of describing the growth in stand volume at sites with different thinning histories and site productivities. This rescaled curve simply and clearly explained the effects of thinning and site productivity on stand volume growth. The existence of a single curve suggests that the positive effect of thinning on stand volume growth does not depend on site productivity, but it will require patient measurements over longer periods to reveal a positive effect at sites with low productivity.     

白桦伐根萌芽幼、中龄林生长规律的初步研究

对内蒙古乌兰察布市卓资县上高台林场的白桦伐根萌芽幼、中龄林实施长期封禁,通过固定标准地对白桦萌芽林多项生长因子进行定期调查测定,开展白桦萌芽林不同龄级年均生长量和根系生长发育、林木分化和自然稀疏强度以及立地条件变化对生长的影响等的分析研究,结果表明：全封育的白桦萌芽林树高年均生长量最大期在6～15年之间;胸径年均生长量...     

林分断面积生长模型研究评述

林分断面积生长模型是林分生长和收获预估模型的体系的主要组成部分。在对常用的新面积生长模型Ｒｉｃｈａｒｄｓ型和Ｓｃｈｕｍａｃｈｅｒ型分析的基础上，总结出断面积生长模型研究中应注意的４个问题；（１）选择的自变量应为３个，即立地质量指标、年龄和林分密度指标；（２）间伐林分模型应与未间伐林分模型同时考虑，进而详细介绍了用于间伐林分断面积预估的被压指数法；（３）间伐指标的构造需要伐前和后伐后的林分因子；（４     

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.