Influences of Thinning and Prescribed Fire on Water Relations of Jeffrey Pine I. Xylem and Soil Water Potentials

Abstract

Forest thinning accomplished with cut-to-length and whole-tree harvesting systems, and prescribed underburning were assessed for their impacts on water relations in eastern Sierra Nevada Jeffrey pine (Pinus Jeffreyi Grev. & Balf.) during a period of extended drought. Predawn and midday measurements of xylem water potential in dominant and codominant crown class trees more than a century old were made on six days spread over three growing seasons, accompanied by measurements of soil water potential completed between the predawn and midday sessions of each day. With the exception of a single predawn session, the only one of a total of 12 in which xylem water potentials did not differ among treatments, the potentials in trees of thinned stand subunits were 0.67 MPa higher on average during predawn sessions and 0.71 MPa higher during midday sessions than those in trees of the unthinned treatment. Differences between the cut-to-length and whole-tree treatments were marginal and uncommon, but when they occurred, potentials were higher in the former. Prescribed fire effects on xylem water potential were also uncommon, but when occurring generally indicated lower stress levels in the burned than in the unburned treatment. Soil water potentials largely coincided with those of xylem water, with higher potentials in either the cut-to-length or whole-tree treatments, and usually both, than in the unthinned treatment on each of the six days of measurement. Underburning influences on soil water were rare, but when evident, potentials were higher in the burned than in the unburned treatment by substantial margins. For a majority of the measurement sessions, xylem water potential was found to be negatively correlated with residual basal area but positively correlated with soil water potential. In turn, coarse fragments and organic matter in the soil profile intermittently influenced soil water potential, with the former a negative factor while the latter was positive. Overall, results of this study suggest that substantial ecophysiological advantages can be derived from density management in older, dry site forests, which at minimum are not compromised by subsequent implementation of controlled underburning.     

Stem dimensional fluctuation in Jeffrey pine from variation in water storage as influenced by thinning and prescribed fire

Forest thinning utilizing cut-to-length and whole-tree harvesting systems with subsequent underburning were assessed for their impacts on water storage in the extensible tissues of dominant and codominant trees in an uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand on the east slope of the Sierra Nevada. Prior to the onset of the third growing season following thinning and the second season after burning, manual band dendrometers were installed at breast height on the selected trees and readings of diurnal fluctuation in stem circumference, an indication of bole water status, were taken monthly for one year. Diameter and relative diameter fluctuation were calculated from the circumference measurements. Overall, thinning had a positive influence on stem water recharge capacity, with the most pronounced effects evident in the latter part of the growing season. During this period, bole contraction in thinned stand portions was 49 to 55% greater than in the unthinned control, suggesting that both a greater volume of stored water was available for transpiration and was transpired in trees of the former treatment. There was no clear evidence that harvesting method affected stem water storage and influences of underburning were also absent entirely. Seasonal effects on diurnal changes in stem diameter were prominent, as the extent to which boles contracted generally increased over the course of the growing season, whereas fluctuations were at a minimum during the colder months. The magnitude of stem dimensional flux was found to be negatively correlated with initial tree DBH in one instance, while negative relationships between the former and live crown length as well as percentage were also revealed, albeit infrequently. Changes in bole size were positively correlated with residual basal area in some cases. These results suggest that improvement in water relations can be realized from density management in a dry site forest type with no apparent compromise of this benefit by broadcast underburning.     

Influences of Mechanized Thinning and Prescribed Fire on Natural Regeneration in an Uneven-Aged Jeffrey Pine Stand

Thinnings using cut-to-length or whole-tree harvesting systems followed by underburning were evaluated for their effects on seedling and sapling demography in a pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand containing a minor component of California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Depression of seedling counts due to forest floor disturbance associated with thinning was followed by a recovery largely confined to Jeffrey pine in the whole-tree treatment where final seedling counts exceeded those found initially. The postburn substrate was more favorable for establishment of Jeffrey pine than white fir seedlings, and the largest increase in seedling counts between the initial and final inventories occurred in the burned portion of the whole-tree treatment. Live sapling losses from thinning were greatest in the cut-to-length treatment, while underburning induced complete sapling mortality. Absent treatment, several stand and site variables influenced seedling and sapling abundance, prominent among them a propensity for mahala mat (Ceanothus prostratus Benth.) to elevate counts of white fir within both size classes. These results provide land managers insight into the impacts of six combinations of thinning and burning treatment on natural regeneration in eastern Sierra Nevada Jeffrey pine and similar dry site forest types.     

Long-Term Growth Responses of a Jeffrey Pine Stand to Mechanized Thinning and Prescribed Fire

Forest thinnings implemented with cut-to-length and whole-tree harvesting systems followed by underburning were evaluated for their effects on individual tree and stand level growth responses in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) accompanied by isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on both dimension and volume measures, trees of the unburned whole-tree treatment combination exhibited the greatest individual growth responses. At the stand level, a diminished volume growth response in the whole-tree treatment was especially pronounced in the burned portion, mostly attributable to exaggerated stocking losses, while a superior response in the unburned cut-to-length combination likely reflected not only the absence of detrimental fire impacts but also benefits of on-site slash retention. For stand level biomass, diminished growth in the whole-tree treatment was again evident, with that in the burned portion again most pronounced, while biomass accrual in the unburned cut-to-length treatment combination was generally comparable to that in the unthinned control. Increasingly utilized in forest restoration efforts in the western USA, the responses presented herein to these thinning and burning practices provide natural resource managers insight into potential compromised outcomes when implemented in Jeffrey pine and similar dry site forest types.     

Evaluation of Mechanized Thinning and Prescribed Fire Effects on Long-Term Fuels Accumulations in Uneven-Aged Jeffrey Pine

Forest thinnings implemented through cut-to-length and whole-tree harvesting followed by underburning were evaluated for their effects on long-term downed and dead fuels accumulations in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) accompanied by isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on an initial inventory consisting of dry weight and fuel bed depth measurements conducted posttreatment, accumulations in the cut-to-length treatment were elevated according to most measures. Burned stand portions exhibited smaller quantities of fuels initially in individual timelag categories and in total as well as reduced fuel bed depths compared to their unburned counterparts except for the 1,000-hr fuels in the whole-tree treatment where postburn mortality of small stems nullified this effect. A linkage between initial mortality resulting from prescribed fire and final 1,000-hr fuels, as measured 8 yr later, was established but was probably attributable to combined thinning and burning effects. Over the course of the study, either greater accruals or diminished reductions in loading were apparent within burned stand portions compared to unburned portions, most notably in the whole-tree treatment. Results presented here provide insight into potentially compromised fuels reduction outcomes when implemented in uneven-aged stands on dry forest sites.     

Thinning and prescribed fire effects on dwarf mistletoe severity in an eastern Cascade Range dry forest,Washington

Forest thinning and prescribed fire practices are widely used, either separately or in combination, to address tree stocking, species composition, and wildland fire concerns in western US mixed conifer forests. We examined the effects of these fuel treatments alone and combined on dwarf mistletoe infection severity immediately after treatment and for the following 100 years. Thinning, burning, thin + burn, and control treatments were applied to 10 ha units; each treatment was replicated three times. Dwarf mistletoe was found in ponderosa pine and/or Douglas-fir in all units prior to treatment. Stand infection severity was low to moderate, and severely infected trees were the largest in the overstory. Thinning produced the greatest reductions in tree stocking and mistletoe severity. Burning reduced stocking somewhat less because spring burns were relatively cool with spotty fuel consumption and mortality. Burning effects on vegetation were enhanced when combined with thinning; thin + burn treatments also reduced mistletoe severity in all size classes. Stand growth simulations using the Forest Vegetation Simulator (FVS) showed a trend of reduced mistletoe spread and intensification over time for all active treatments. When thinned and unthinned treatments were compared, thinning reduced infected basal area and treatment effects were obvious, beginning in the second decade. The same was true with burned and unburned treatments. Treatment effects on infected tree density were similar to infected basal area; however, treatment effects diminished after 20 years, suggesting a re-treatment interval for dwarf mistletoe.     

Bark Beetle Demography in a Jeffrey Pine Stand as Influenced by Mechanized Thinning and Prescribed Fire

Forest thinnings implemented with cut-to-length and whole-tree harvesting systems followed by underburning were evaluated for their effects on bark beetle prevalence in pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) interspersed with isolated California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Based on pitch tube counts in a stand with a moderate bark beetle population in its pine component, the Jeffrey pine beetle (Dendroctonus jeffreyi Hopkins) generally preferred larger trees before treatment implementation, but after exhibiting mixed pretreatment tendencies concerning stand density demonstrated a posttreatment proclivity toward higher density. Cut-to-length thinning followed by underburning increased the pine beetle population while whole-tree thinning unaccompanied by burning reduced it. Tree mortality was induced by the bark beetle infestation but was not its sole cause. Pitch tube abundance on white fir far exceeded that on Jeffrey pine, and the greatest influence on the fir engraver (Scolytus ventralis LeConte) population was the prevalence of its host tree. The responses presented herein to these thinning and burning practices, which are being increasingly utilized in forest restoration efforts in the western USA, provide natural resource managers insight into potential forest health outcomes when implemented in Jeffrey pine and similar dry site forest types.     

Crown characteristics of juvenile loblolly pine 6 years after application of thinning and fertilization

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.     

Crown radius of pedunculate oak (Quercus robur L.) depending on stem size,stand density and site productivity

Crown size is a good indicator of the growth potential of trees and is often used in forest management for outlining thinning guidelines or constructing forest growth models. The aim of this study was to analyse mean crown radius as a function of stem size, stand density and site productivity in even-aged stands of pedunculate oak (Quercus robur L.). Data included measurements of 620 trees from 53 plots in nine thinning experiments and one operational stand in Sweden, Denmark and Great Britain, representing a wide spectrum of thinning practices ranging from the strictly unthinned control to extremely heavy thinning with essentially solitary trees. Three sets of models were constructed based on different predictor variables, including indicators of individual stem size (diameter at breast height, DBH), stand density/thinning grade (quadratic mean diameter and stand basal area) and site productivity (stand top height). Preliminary results indicated a significant effect of DBH and (nominal) thinning grade on crown radius. The response pattern of the final models indicated an increasing crown radius with increasing DBH, with increasing thinning grade (decreasing stand density) and with decreasing site productivity. The models are valid for predicting the crown radius of pedunculate oak in even-aged forest stands.     

Identifying the biological effects of pre-commercial thinning on diameter growth in young Scots pine stands

Data from seven Scots pine (Pinus sylvestris L.) stands in central Sweden that had undergone pre-commercial thinning (PCT) were used to investigate the biological effect of PCT on the diameter at breast height (DBH) growth of the remaining trees. Two treatments were considered: a PCT treatment and a control (C) with no PCT. The DBH of the trees in each stand was measured on up to four occasions over 15 years. We examined mean DBH and DBH growth of the largest 300, 600, 900 and 1200 trees ha^?1. Two methods of selecting the trees used to calculate the mean DBH values for each measurement occasion were considered: the actual mean DBH (Dma), which is based on the DBH distribution of the trees on the measurement occasion in question, and the genuine mean DBH (Dmg), which is based on the DBH distribution of the trees on the final measurement occasion of the study and therefore focuses on the same set of trees for all measurement occasions. There was no clear difference between the Dma- and Dmg-based DBH increments, but the Dmg values tended to be somewhat larger both for the C and PCT treatments. Over a 15-year period, the relative mean yearly increments (Dma/Dmg) for different tree size classes ranged from 0.91 to 0.98, with lower values for the C treatment and larger DBH size classes. We found that PCT promotes DBH growth: over a 15-year period, the increased growth amounted to about 2.0 mm year^?1 compared to the trees in unthinned plots.     

Effects of selective thinning on growth and development of beech (Fagus sylvatica L.) forest stands in south-eastern Slovenia

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.     

Influence of crown class and shade tolerance on individual tree development during deciduous forest succession in Connecticut, USA

Sixty years of individual tree crown class records were used to elucidate the influence of crown class (dominant, codominant, intermediate, or suppressed), shade tolerance (intolerant, midtolerant, or tolerant), and their interactions on the probability of individual tree movement among crown classes. Trees were measured at 10 year intervals between 1927 and 1987, excluding 1947, on 364 nominal 0.01 ha plots. A total of 14 154 individual tree records were used in this analysis. The transition rates among crown classes for 30 year intervals (1927–1957 and 1957–1987) were examined for all combinations of antecedent crown classes and tolerance rankings. The distribution of ingrowth among tolerance rankings was also examined.

Mortality rates increased with decreasing crown class for all tolerance rankings, and mortality rates increased with decreasing tolerance. Compared with tolerant trees, midtolerant and intolerant trees had higher rates of ascension into dominant and codominant crown classes and exhibited higher persistence rates in the dominant crown class. These factors suggest that midtolerant and intolerant trees have an advantage over tolerant trees in the higher crown classes, In contrast, tolerant trees had the advantage in suppressed and intermediate crown classes, with lower mortality rates, higher persistence, and higher rates of crown class ascension than for midtolerant or intolerant trees. Crown class stratification was driven by the change in relative advantage of each tolerance ranking among the crown class.

Results of this study suggest that the canopy stratum (upper canopy, lower canopy, or mixed) affected by disturbance is as important as disturbance scale, intensity, and frequency in influencing the composition of the suppressed crown class. Because the suppressed crown class is in a constant state of high flux, with fewer than 30% of the suppressed trees remaining in the suppressed crown class for any 30 year period, a small change in the relative persistence or ascension rates among tolerance rankings, whether by a different disturbance or climate regime, could alter the proportion of tolerance rankings in the suppressed crown class and ultimately result in an alternative succession.     

Restoration thinning and influence of tree size and leaf area to sapwood area ratio on water relations of Pinus ponderosa

Ponderosa pine (Pinus ponderosa Dougl. ex P. Laws) forest stand density has increased significantly over the last century (Covington et al. 1997). To understand the effect of increased intraspecific competition, tree size (height and diameter at breast height (DBH)) and leaf area to sapwood area ratio (A(L):A(S)) on water relations, we compared hydraulic conductance from soil to leaf (kl) and transpiration per unit leaf area (Q(L)) of ponderosa pine trees in an unthinned plot to trees in a thinned plot in the first and second years after thinning in a dense Arizona forest. We calculated kl and Q(L) based on whole- tree sap flux measured with heat dissipation sensors. Thinning increased tree predawn water potential within two weeks of treatment. Effects of thinning on kl and Q(L) depended on DBH, A(L):A(S) and drought severity. During severe drought in the first growing season after thinning, kl and Q(L) of trees with low A(L):A(S) (160-250 mm DBH; 9-11 m height) were lower in the thinned plot than the unthinned plot, suggesting a reduction in stomatal conductance (g(s)) or reduced sapwood specific conductivity (K(S)), or both, in response to thinning. In contrast kl and Q(L) were similar in the thinned plot and unthinned plot for trees with high A(L):A(S) (260-360 mm DBH; 13-16 m height). During non-drought periods, kl and Q(L) were greater in the thinned plot than in the unthinned plot for all but the largest trees. Contrary to previous studies of ponderosa pine, A(L):A(S) was positively correlated with tree height and DBH. Furthermore, kl and Q(L) showed a weak negative correlation with tree height and a strong negative correlation with A(S) and thus A(L):A(S) in both the thinned and unthinned plots, suggesting that trees with high A(L):A(S) had lower g(s). Our results highlight the important influence of stand competitive environment on tree-size-related variation in A(L):A(S) and the roles of A(L):A(S) and drought on whole-tree water relations in response to thinning.     

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.     

Effect of thinning on allometry and needle-age distribution of trees in natural Abies stands of northern Japan

We tested the effects of thinning on allometry and needle-age distribution in natural stands of Abies sachalinensis Masters by comparing a thinned stand to an unthinned, control stand. Specifically, we attempted to clarify how allometry was altered after a thinning. We assumed that the needle-age distribution of trees in the thinned stand would show a younger composition than in the control stand, given the effect of improved light conditions on needle dynamics following a thinning. These investigations were conducted in dense Abies stands located in central Hokkaido, northern Japan, 19 years post-thinning. In the thinned stand, the ratio of individual needle mass to stem mass increased significantly, as compared to the control. A difference in the H–DBH relationship between the stands was probably related to this tendency. Mean needle age of trees differed significantly between the two stands, and the thinned stand showed a younger needle age than the control. Within each stand, dominant trees showed older mean needle age than codominant or suppressed trees. These tendencies may have been caused by differential needle dynamics affected by light conditions in the stands, and by different crown positions among the trees within a stand. In summary, trees in the thinned stand showed increased growth rates after thinning, which were caused by increased needle mass, younger composition of needles, and improved light conditions.     

Crown structure and leaf area index development in thinned and unthinned Eucalyptus nitens plantations

The crown structure of Eucalyptus nitens (Deane & Maiden) Maiden 6 years after thinning, and the development of stand leaf area index both immediately and 6 years after thinning, were investigated. Thinning did not alter branch angle, branching density or the relationship between branch size and branch leaf area. However, larger branches were found in the lower crown of thinned trees and the increase in leaf area as a result of thinning occurred on the northern aspect of the crown. The vertical distribution of leaf area in unthinned trees was skewed toward the top of the crown and correlated with live crown ratio. The vertical distribution of leaf area in thinned trees tended to be less skewed and was unrelated to tree size or dominance. Leaf area index, as estimated from light interception measurements, increased at a constant rate soon after thinning regardless of residual stocking. In the longer term, residual stocking had a strong influence on leaf area increase per tree and was correlated with changes in crown length.     

抚育间伐对杉木人工林生长及出材量的影响

间伐对人工林生长及木材质量具有重要影响。在浙江开化开展了间伐强度（强度、中度和对照）和间伐方式（间伐1次,间伐2次）对杉木人工林生长及出材量等的影响研究,第1试验区大径材培育林分在第7年和第14年进行了2次间伐,第2试验区中径材培育林分仅在第12年时进行1次间伐。结果表明：22年生大径材培育林分和19年生中径材培育林分不同间伐处理之间树高、总断面积的差异均不显著。间伐显著增加了林木胸径的生长,大径材培育林分强度和中度间伐处理的平均胸径分别比对照增加13.78%和9.69%,中径材培育林分强度和中度间伐处理的平均胸径分别比对照增加12.28%和7.02%。间伐显著促进了林木单株材积的增加,2组试验林分活立木材积随着间伐强度的增加而降低,第1试验区22年生林分不同间伐强度之间活立木材积的差异不显著（P>0.05）,第2试验区强度间伐活立木材积显著低于对照（P<0.05）,中度间伐林分活立木材积与对照和强度间伐之间的差异不显著（P>0.05）。2组试验林分总蓄积和出材量也随着间伐强度的增加而降低,二者在3种间伐处理之间均没有显著差异（P>0.05）。间伐强度不能有效增加林分活立木材积和林分出材量,间伐次数对林分出材量及出材规格有重要影响。试验区杉木大径材培育以2次间伐,总间伐强度50%左右较为适宜,而中径材培育则以1次中度间伐（约25%）为宜。     

The effect of release cutting on the growth and external quality of the dominant trees in a Pinus sylvestris stand established by spot sowing

The effect of the number of Pinus sylvestris trees in seed spots on the growth and external quality of the dominant trees was studied. The trees were monitored during the period between release cutting and the first commercial thinning. The treatments were one, two and four of the tallest seedlings retained per seed spot, and a control. The mean height of the dominant trees was highest in the one‐tree and two‐tree treatments. Diameter at breast height (DBH) increased with increasing spacing. On average, the stump diameter was 1.5–4.7 cm greater in the one‐tree treatment than in the control. Slenderness (height/DBH) was highest in the control treatments. The average living crown limit of the dominant trees was 4.6 m, and was at its highest in the two‐tree treatment. The results indicate that the competition in seed spots decreases the height growth of the dominant trees.     

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.