Density effects and self-thinning in even-aged pure stands ofEucalyptus camaldulensis Dehn

The competition density effect and changes of mean total tree weight (w) and stand density (ρ) during course of self-thinning were examined in even-aged pure stands ofEucalyptus camaldulensis Dehn. which were planted in the tropical monsoon region. The level of competition was controlled by changing the initial stand density from 625 trees ha⁻¹ to 40,000 trees ha⁻¹. Hozumi's model was used to describe thew-ρ trajectory with aging of each stand and thew-ρ relation between stands of different densities at each time. The higher density produced trees of smaller mean tree sizes. The higher the density, the sooner self-thinning began. The growth curve ofE. camaldulensis followed the logistic growth curve where both maximum size and intrinsic growth rate change with time. Mean intrinsic growth rate was maximized at initiation of growth after lag time and then gradually decreased as time progressed. Hozumi's model was considered to be the best model with wide applicability for describing and comparing the growth characteristics during the course of self-thinning among different species, especially in tropical forest plantations, in which many diverse species were used for reforestation.     

Density effect, self-thinning and size distribution in Pinus densiflora Sieb. et Zucc. stands

The competition-density (C-D) effect for given times and self-thinning over time in even-aged, natural, pure stands of Pinus densiflora Sieb. et Zucc. were analyzed with the reciprocal equation of the C-D effect in self-thinning stands, and the equation describing the time-trajectory of mean stem volume and stand density. The C-D effect and self-thinning were consistently well explained by the two equations. Differences in mean stem volume and in stand density among the stands tended to merge with increasing stand age. The self-thinning line with a slope of approximately –3/2 was reached by the higher density stand prior to the medium and lower density stands. The skewness of tree height distribution showed positive values, which means that the distribution is more or less L-shaped, and in addition the skewness decreased with increasing mean tree height, which indicates that smaller trees died as the stands grew. This trend is consistent with the asymmetric (one-sided) competition hypothesis that self-thinning is driven by competition for light. The tree height distribution was analyzed using the Weibull distribution. The location parameter h _min of the Weibull distribution increased with increasing stand age, and the scale parameter a tended to increase slightly with increasing stand age. The range of the shape parameter b of the Weibull distribution corresponded to that of the skewness.     

Growth analysis of the self-thinning stands of Pinus densiflora Sieb. et Zucc

The competition-density (C-D) effect for self-thinning Pinus densiflora Sieb. et Zucc. stands was analyzed. The relationship between biological time and physical time t followed a hyperbolic curve. The coefficients A_t and B included in the reciprocal equation of the C-D effect in self-thinning stands (i.e. 1/w=A_t+B), where w and , respectively, represent the mean stem volume and the realized stand density, were calculated at each time. With increasing , the coefficient A_t increased abruptly up to a maximum value, and then decreased gradually to a constant level, whereas the coefficient B decreased exponentially. The relationship between the realized stand density and the initial stand density _i was confirmed to follow the equation: 1/=1/_i+, where 1/ represents the asymptotic stand density at a given time. The - relationship was represented by the equation: =p(e–1), where p and are constants. The density in the self-thinning stands tended to converge to the same density level after a sufficient lapse of time, irrespective of the difference in initial stand density. The time-trajectory of the mean stem volume and asymptotic stand density on logarithmic coordinates moved gradually toward the self-thinning line with a slope of approximately –3/2, whereas the time-trajectory of the mean stem volume and full stand density moved initially along the self-thinning line with a slope of approximately –3/2, and then changed to move along the maximum yield line with a slope of –1.0.     

Self-thinning lines of organs and aboveground parts based on allometric relationships in overcrowded Pinus densiflora stands

The allometric relationships of mean tree height [`(H)]( μ [`(w)]_x^q ) \bar{H}( \propto \bar{w}_{\rm {x}}^{\theta } ) and of organ mass density [`(d)]<sub>x</sub> ( μ [`(w)]_x^d ) \bar{d}_{\rm {x}} ( \propto \bar{w}_{\rm {x}}^{\delta } ) to mean organ mass [`(w)]_x \bar{w}_{\rm {x}} were studied in self-thinning Pinus densiflora Sieb. et Zucc. stands. Tree height increased significantly with increasing mean mass of organs and aboveground parts on log–log coordinates. The value of the allometric constant θ ranged from 0.2878 to 0.3349. On the other hand, the constant value δ was not significantly different from zero, except for leaves. The value of the allometric constant δ ranged from −0.2926 to 0.0120. According to Weller’s allometric model, the slope of the self-thinning line was calculated from the allometric constants θ and δ. The thinning slope was estimated to be −1.51 in stem, −1.39 in branches, −1.00 in leaf and −1.41 in aboveground parts, respectively. Mass density was high in stem, medium in branches and low in leaves. Mean leaf mass density decreased significantly with decreasing stand density on log–log coordinates, which could be interpreted as indicating the importance of the constant final leaf biomass in overcrowded P. densiflora stands. The self-thinning exponents of branch, stem and aboveground parts were not significantly different from 3/2, which indicated that the 3/2 power law of self-thinning holds for stem mass, branch mass and aboveground mass in overcrowded P. densiflora stands.     

Above-ground biomass and structure of pristine Siberian Scots pine forests as controlled by competition and fire

The study presents a data set of above-ground biomass (AGB), structure, spacing and fire regime, for 24 stands of pristine Siberian Scots pine (Pinus sylvestris) forests with lichens (n = 20) or Vaccinium/mosses (n = 4) as ground cover, along four chronosequences. The stands of the “lichen” site type (LT) were stratified into three chronosequences according to stand density and fire history. Allometric equations were established from 90 sample trees for stem, coarse branch, fine branch, twig and needle biomass. The LT stands exhibited a low but sustained biomass accumulation until a stand age of 383 years. AGB reached only 6–10 kg_dw m⁻² after 200 years depending on stand density and fire history compared to 20 kg_dw m⁻² in the “Vaccinium” type (VT) stands. Leaf area index (LAI) in the LT stands remained at 0.5–1.5 and crown cover was 30–60%, whereas LAI reached 2.5 and crown cover was >100% in the VT stands. Although nearest-neighbour analyses suggested the existence of density-dependent mortality, fire impact turned out to have a much stronger effect on density dynamics. Fire scar dating and calculation of mean and initial fire return intervals revealed that within the LT stands differences in structure and biomass were related to the severity of fire regimes, which in turn was related to the degree of landscape fragmentation by wetlands. Self-thinning analysis was used to define the local carrying capacity for biomass. A series of undisturbed LT stands was used to characterise the upper self-thinning boundary. Stands that had experienced a moderate fire regime were positioned well below the self-thinning boundary in a distinct fire-thinning band of reduced major axis regression slope −0.26. We discuss how this downward shift resulted from alternating phases of density reduction by fire and subsequent regrowth. We conclude that biomass in Siberian Scots pine forests is strongly influenced by fire and that climate change will affect ecosystem functions predominantly via changes in fire regimes. Received: 2 July 1998 / Accepted: 10 June 1999     

Linking stand-level self-thinning allometry to the tree-level leaf biomass allometry

Long-term experimental plots of Norway spruce and European beech are investigated for a link between stand-level self-thinning and tree-level leaf biomass allometry. Self-thinning refers to the finding of Reineke (1933), who postulated for unthinned forest stands that with β = −1.605; i.e. an increase of mean (quadratic) diameter d _q by 1% results in a decrease of tree number N by 1.605%. On the individual tree level, leaf biomass (w _L) can be related allometrically to the tree diameter d: w _L = ad ^α. If we assume that (a) the stands have reached the ceiling leaf area, (b) the specific leaf area (leaf area/leaf weight) is constant, and (c) differences resulting from the use of mean quadratic diameter or individual tree diameter are negligible, then the decrease in the stands’ leaf biomass due to the trees lost in self-thinning must be compensated by an equivalent increase in the remaining trees’ leaf biomass. This means, the absolute slope of the individual trees’ leaf biomass allometry α and the self-thinning allometry β would be equal and just have the opposite sign: α = −β. The analysis of the two long-term plots reveals that α is stronger than β, both for spruce (β = −1.744, α = 1.840) and especially for beech (β = −1.791, α = 2.181). The cause is traced back to a changing average specific leaf area during stand development [assumption (b) is wrong]. The results do not only bridge a gap between tree and stand allometry, but also emphasize an important effect for the understanding and modelling of the resource allocations in trees and forests.     

短周期尾巨桉能源林生物量与能量特征研究

为开发和利用尾巨桉能源林,通过测量1~4年生植株的叶片、树枝、树根、树干和树皮的热值和生物量,对短周期尾巨桉能源林的生物量和能量特征进行了研究。结果表明,尾巨桉叶片、树枝、树干、树根、树皮和林分生物量均随林龄增加而增加,叶片、树枝、树皮生物量占单株总生物量的比例逐年减小,而树干则呈逐年升高趋势。1~4年生尾巨桉单株和林分的生物量分别为4.32~66.29 kg和10.68~153.33 t hm-2。生物量的结构特征表明,尾巨桉林分在第4年开始郁闭,生长以增加树干的生物量为主。尾巨桉各组分的平均干质量热值为17.23~20.56 kJ g-1,且差异极显著(P<0.01),以叶片的值最高、树皮的最低;同一组分不同林龄的热值差异不显著(P>0.05)。1~4年生尾巨桉的单株和林分能量现存量为81.61~1255.22 MJ和201.83~2903.32 GJ hm-2,其变化趋势及大小排列顺序与生物量相同。因此,对尾巨桉能源林可以4年短周期进行经营。     

Density effects on organs in self-thinning <Emphasis Type="Italic">Pinus densiflora</Emphasis> Sieb. et Zucc. stands

Although much research on the density effect in nonself-thinning populations has been conducted, there has been very little research on density effects in self-thinning populations. Furthermore, the density effect of plant organs in self-thinning populations is little reported. The present study analyzed the yield–density (Y–D) effects on organs, such as stem, branch and leaf, together with that on stands of self-thinning Pinus densiflora Sieb. et Zucc.. The stand yield- and organ Y–D effects were well described by reciprocal and parabolic equations, respectively, throughout the experiment. The value of coefficient B in the reciprocal equation decreased monotonically with increasing stand age and became significantly closer to zero at the end of experiment (33-year-old stand), indicating that the constant final stand yield was established regardless of the density realized. The value of the relative growth coefficient h in the allometric equation between mean organ weight and mean aboveground weight was significantly smaller than 1.0 for stem, indicating that stem yield increases monotonically with increasing realized density. The h-value was significantly larger than 1.0 for branch throughout the experiment, and for leaf except at 33 years old, indicating that optimum densities exist. The h-value for leaf was not significantly different from 1.0 at 33 years old, indicating that the leaf yield reached a constant level regardless of realized density. The constant final leaf yield was established at almost the same growth stage as the establishment of constant final stand yield.     

Structure, above-ground biomass and dynamics of mangrove ecosystems: new data from French Guiana

The article presents new results on the structure and the above-ground biomass of the various population types of mangroves in French Guiana. Nine mangrove stands were studied, each composed of three to ten adjoining plots with areas that varied depending on the density of the populations. Structural parameters and indices were calculated. Individuals representative of the three groups of taxa present were felled:Avicennia germinans (L) Stearn, Rhizophora spp., and Laguncularia racemosa (L) Gaertn. The trunks, branches and leaves were sorted and weighed separately. The biomass was obtained by determining the allometric relationships, the general equation selected being of the type y = a _o x ^a1, where the diameter (x) is the predictive variable. The total above-ground biomass varied from 31 t ha⁻¹ for the pioneer stages to 315 t ha⁻¹ for mature coastal mangroves, but with large variations depending on the structural characteristics at each site. The results place the Guianese mangroves among those with high biomass, although lower than those reported for Asia. Based on the relationships between structural parameters and standing biomass, in particular with the use of the “self-thinning rule”, population dynamics models are proposed. Received: 16 August 1996 / Accepted 17 January 1998     

Competition between two annual herbs,Atriplex gmelini C.A. Mey and Chenopodium album L., in mixed cultures irrigated with seawater of various concentrations

Summary Atriplex gmelini and Chenopodium album were grown in mixed stands with various combinations of plant density and mixing ratio, and irrigated with seawater of different concentrations (f) to formulate the effect of changing concentration on the competitive relationship between the species.In single-species stands, the mean plant weight (w)plant density () relation for each level of seawater concentration could well be described by Shinozaki-Kira's reciprocal equation of crowding effect. On the other hand, the response of w to f followed Hozumi-Shinozaki's formulation for an optimum growth factor at respective levels of .By introducing the density conversion factor (q) that enabled the conversion of the density of one species to that of the other species on the basis of their effects on growth of respective species, the results of mixed culture experiments could be successfully formulated by similar reciprocal equations. The dependence of q and coefficient values of the equations on seawater concentration was also formulated in a way similar to the case of pure stands.Based on all these quantitative relations, a comprehensive formulation was developed to describe the effects of plant density and seawater concentration on the growth of two species in mixed stands. The behavior of species biomass in mixed stands was then examined by means of the formulation.It was thereby demonstrated that the relative dominance of two species in a mixed stand was strongly affected not only by total plant density and density ratio between the two species but also by concentration of irrigated seawater. Even the optimum seawater concentration that resulted in the maximum species biomass differed between pure and mixed cultures.     

Stand and self-thinning dynamics in natural <Emphasis Type="Italic">Abies</Emphasis> stands in northern Hokkaido,Japan

Stand dynamics and self-thinning were analyzed in relation to the dynamics of above-ground biomass in natural Abies sachalinensis stands growing on sand dunes in northern Hokkaido, Japan. This was done in order to examine wave-type regeneration in the stands. Fifty-two plots were established in almost pure Abies stands that ranged from saplings to the mature and collapsing growth stages. Above-ground biomass and tree height reached asymptotic levels prior to the collapsing phase, unlike wave-regeneration Abies stands in central Japan and North America. Stand density was high in the young growth stages, but the self-thinning rate, that is, the density decrease per biomass growth in the study stands was greater than in wave-regeneration stands in central Japan, as indicated by a large self-thinning exponent (–1.26 by reduced major axis regression). The range of tree height distribution was very narrow, and the stands vertical structure was typically single-layered. The slenderness ratio of trees was large, except in young stands. In mature and collapsing stands, advanced seedling density increased markedly. These stand and tree characteristics were considered to be correlated with the wave-type regeneration in the study stands, and it is assumed that prevailing winds affect tree mortality.     

The difference between above- and below-ground self-thinning lines in forest communities

Quantifying the self-thinning process in various plant communities has been a long-standing issue in both theoretical and empirical studies. Most studies on plant self-thinning have centered only on aboveground parts, and rarely on belowground parts. There is still a general lack of comparison between above- and belowground self-thinning processes, especially for forest communities. The fundamental mechanistic difference and the functional association between above- and belowground competition indicate that the self-thinning process of belowground parts may be different from that of aboveground parts. We investigated the self-thinning lines for above-ground (M _A), below-ground (M _B), and total biomass (M _T), respectively, across forest communities in China. The results showed that neither the classical self-thinning rule (−3/2 exponent) nor the universal scaling rule (−4/3 exponent) can apply to all the self-thinning relationships across these forest communities and that the self-thinning lines for belowground biomass were flatter and lower than those for aboveground biomass across most of these forest communities.     

Alpha and beta subunits of F1-ATPase are required for survival of petite mutants in Saccharomyces cerevisiae

Although Saccharomyces cerevisiae can form petite mutants with deletions in mitochondrial DNA (mtDNA) (ρ⁻) and can survive complete loss of the organellar genome (ρ^o), the genetic factor(s) that permit(s) survival of ρ⁻ and ρ^o mutants remain(s) unknown. In this report we show that a function associated with the F₁-ATPase, which is distinct from its role in energy transduction, is required for the petite-positive phenotype of S. cerevisiae. Inactivation of either the α or β subunit, but not the γ, δ, or ɛ subunit of F₁, renders cells petite-negative. The F₁ complex, or a subcomplex composed of the α and β subunits only, is essential for survival of ρ^o cells and those impaired in electron transport. The activity of F₁ that suppresses ρ^o lethality is independent of the membrane F_o complex, but is associated with an intrinsic ATPase activity. A further demonstration of the ability of F₁ subunits to suppress ρ^o lethality has been achieved by simultaneous expression of S. cerevisiae F₁α and γ subunit genes in Kluyveromyces lactis– which allows this petite-negative yeast to survive the loss of its mtDNA. Consequently, ATP1 and ATP2, in addition to the previously identified AAC2, YME1 and PEL1/PGS1 genes, are required for establishment of ρ⁻ or ρ^o mutations in S. cerevisiae. Received: 20 March 1999 / Accepted: 18 July 1999     

Mortality and Self-thinning in Postfire Black Spruce

Using age-structure determinations on both living and dead stemsin censused plots, coupled with stem analysis techniques, anhistorical picture of mortality and above-ground tree stem growthwas recreated for ten stands dominated by black spruce in northeasternOntario, Canada. No evidence of mortality was seen in any plot prior to 30 yearsfollowing postfire initiation. Each of the eight oldest standsshowed a linear decline in numbers for a 20–25 year period.The steepness of the mortality slope was proportional to initiallive stem density within and among plots during this phase.The final 10–20 years was marked by a less steep declinein numbers. The log density vs log mean tree volume curves in the eightoldest stands were doubly asymptotic and were fitted to a logisticcurve very tightly in each case. At the point of inflectionthe curves' slopes ranged from –2.14 to –3.89. However,log density vs log mean stem volume among stands at this pointof inflection had a slope of –0.96. Reasons for the inconsistency between within-stand and among-standself-thinning estimates are considered, as well as the poorfit to the –3/2 rule. Ecosystem processes related to thechange in nutrient relations during stand growth are identifiedas a prime influence on self-thinning behaviour in natural blackspruce stands. Mortality, stem analysis, self-thinning, Picea mariana, black spruce     

Allometric equations and biomass expansion factors of Japanese red pine on the local level

This study was conducted to evaluate site-specific allometric equations and biomass expansion factors (BEF) of Japanese red pine (Pinus densiflora S. et Z.) at five sites in the Hadong, Hamyang, Jinju, Sancheong, and Uiryeong regions, situated in the western part of Gyeongnam province, Korea. Biomass in each tree component, i.e., needle, branch, stem wood, and stem bark, was quantified by destructive tree harvesting. Site-specific as well as generalized allometric equations were developed for each tree component across the entire sites. Both allometric regression equations were significant (P < 0.05), with diameter at breast height (DBH) accounting for 69–99% of the variation (as indicated by coefficients of determination, r ²) in aboveground biomass. The stem densities at different sites were significantly different (P < 0.05) from each other, but no significant difference was observed for stem bark density. The aboveground BEFs also showed a significant variation (P < 0.05) at a landscape scale and ranged from 1.19 to 1.46 among the sites. The results suggest that application of site-specific allometric equations and aboveground BEFs are likely to improve the reliability of biomass estimates on the local level.     

Interrelationships between water and cellular metabolism inArtemia cysts

Cysts of the crustaceanArtemia are a useful model for studies on intracellular water because they are capable of essentially complete and reversible desiccation. We have used a variety of techniques on this system, the present work being an attempt to estimate the density of intracellular water (ρ_w). The density of individual cysts was evaluated from sedimentation velocity. Heptane displacement methods were used to determine the volume of a known mass of cysts, from which the density was calculated. The two methods produce comparable results. It was shown that the densities and water contents of large masses of cysts accurately reflect those of individual cysts. Cyst densities (ρ_c) were determined over the entire range of water content from 0 to 0.63 weight fraction of water (W _f), and temperature dependence was measured for 0.61W _f over 2–41°C. The following refer to 25°C. No marked change was detected in ρ_c until the water content exceeded 0.15W _f, at which ρ_c decreased as a linear function of Wf to maximum water content. However, the cyst does not behave ideally in the sense that the densities of the nonaqueous components and added water are not additive as a function ofW _f. The partial specific volume of water in cysts at maximum hydration was estimated to be 3% larger than that of pure water. These observations are compared with density measurements on other systems, and with previous findings on the physical properties of water in this system.     

Soil water availability and rooting depth as determinants of hydraulic architecture of Patagonian woody species

Adaptations of species to capture limiting resources is central for understanding structure and function of ecosystems. We studied the water economy of nine woody species differing in rooting depth in a Patagonian shrub steppe from southern Argentina to understand how soil water availability and rooting depth determine their hydraulic architecture. Soil water content and potentials, leaf water potentials (Ψ_Leaf), hydraulic conductivity, wood density (ρ_w), rooting depth, and specific leaf area (SLA) were measured during two summers. Water potentials in the upper soil layers during a summer drought ranged from −2.3 to −3.6 MPa, increasing to −0.05 MPa below 150 cm. Predawn Ψ_Leaf was used as a surrogate of weighted mean soil water potential because no statistical differences in Ψ_Leaf were observed between exposed and covered leaves. Species-specific differences in predawn Ψ_Leaf were consistent with rooting depths. Predawn Ψ_Leaf ranged from −4.0 MPa for shallow rooted shrubs to −1.0 MPa for deep-rooted shrubs, suggesting that the roots of the latter have access to abundant moisture, whereas shallow-rooted shrubs are adapted to use water deposited mainly by small rainfall events. Wood density was a good predictor of hydraulic conductivity and SLA. Overall, we found that shallow rooted species had efficient water transport in terms of high specific and leaf specific hydraulic conductivity, low ρ_w, high SLA and a low minimum Ψ_Leaf that exhibited strong seasonal changes, whereas deeply rooted shrubs maintained similar minimum Ψ_Leaf throughout the year, had stems with high ρ_w and low hydraulic conductivity and leaves with low SLA. These two hydraulic syndromes were the extremes of a continuum with several species occupying different portions of a gradient in hydraulic characteristics. It appears that the marginal cost of having an extensive root system (e.g., high ρ_w and root hydraulic resistance) contributes to low growth rates of the deeply rooted species.     

Microemulsion System with Improved Loading of Piroxicam: A Study of Microstructure

Formulation of a new oil-in-water (o/w) microemulsion composed of castor oil/Tween 80/ethanol/phosphate buffer for enhancing the loading capacity of an anti-inflammatory drug piroxicam has been accomplished. The pseudo-ternary phase diagram has been delineated at constant surfactant/cosurfactant ratio (1:2). The internal structure of so created four-component system was elucidated by means of an analysis of isotropic area magnitudes in the phase diagram. Conductivity (σ), kinematic viscosity (k _η ), and surface tension (γ) studies with the variation in Φ _w (weight fraction of aqueous phase) show the occurrence of structural changes from water-in-oil (w/o) microemulsion to oil-in-water (o/w). Along with the solubility and partition studies of piroxicam in microemulsion components, the changes in the microstructure of the microemulsion after incorporation of drug have been evaluated using pH, σ, γ, k _η , and density studies. Piroxicam, a poorly water-soluble drug displayed high solubility (1.0%) in an optimum microemulsion formulation using ethanol (55.0%), Tween 80 (26.5%), castor oil (7.5%), and phosphate buffer (11.0%). The results have shown that the microemulsion remained stable after the incorporation of piroxicam. Fluorescence spectra analysis taking pyrene as fluorescent probe was performed, and the results showed that pyrene was completely solubilized in the oil phases of the bicontinuous microemulsions. The fluorescence spectrum of the model drug piroxicam was used to probe the intramicellar region of nonionic microemulsion. The results showed that the piroxicam was localized in the interfacial film of microemulsion systems more deeply in the palisade layer with ethanol as the cosurfactant.     

Maintenance cost, toppling risk and size of trees in a self-thinning stand

Wind routinely topples trees during storms, and the likelihood that a tree is toppled depends critically on its allometry. Yet none of the existing theories to explain tree allometry consider wind drag on tree canopies. Since leaf area index in crowded, self-thinning stands is independent of stand density, the drag force per unit land can also be assumed to be independent of stand density, with only canopy height influencing the total toppling moment. Tree stem dimensions and the self-thinning biomass can then be computed by further assuming that the risk of toppling over and stem maintenance per unit land area are independent of stand density, and that stem maintenance cost is a linear function of stem surface area and sapwood volume. These assumptions provide a novel way to understand tree allometry and lead to a self-thinning line relating tree biomass and stand density with a power between −3/2 and −2/3 depending on the ratio of maintenance of sapwood and stem surface.     

Self-thinning lines differ with fertility level

The effect of variations in fertility level of the substrate on the self-thinning lines followed by populations of Ocimum basilicum L. was investigated experimentally by establishing populations over a range of densities at two fertility levels. Populations from each fertility level followed different self-thinning lines for shoot biomass. Self-thinning began at a lower biomass in populations grown at the higher fertility level; the subsequent slope of the thinning line was –0.5 for these stands on a log shoot biomass versus log density plot. The slope of the self-thinning line was flatter (–0.29) at the lower fertility level. Fitting the self-thinning line by the Structural Relationship rather than the Major Axis made little difference to line estimates. Biomass packing differed with fertility level, with plants from the higher fertility stands requiring more canopy volume for given shoot biomass than plants from lower fertility levels. Biologically, this would mean shoot competition intensified more rapidly at the higher fertility level as biomass accumulated in stands. The difference in slope between fertility levels was associated with changes above- and belowground. The radial extension of the canopy versus shoot mass relationships of individual plants differed with fertility level. Plants at the lower fertility level allocated more biomass to root growth, and had less leaf area per unit root length. The differences in slope of the self-thinning lines may have been because of differences in the radial extension of the canopy versus shoot mass relationships of individual plants at each fertility level, and/or to an increase in root competition at the lower fertility level.