Optimizing the Management of a Butt-rotted Picea abies Stand Infected by Heterobasidion annosum from the Previous Rotation

There are no instructions on the management of stands of Norway spruce [ Picea abies (L.) Karst.] in which butt rot caused by Heterobasidion annosum coll. (Fr.) Bref. was not discovered until the time of first thinning. A stochastic simulation model describing the spread of butt rot in a stand of Norway spruce was used with a new submodel describing the butt rot of young trees. Non-linear stochastic optimization was used to determine the most profitable management schedule of a young Norway spruce stand with butt rot. If the initial level of butt rot was 5% or 10%, or the stand was thinned in summer with stump treatment, one thinning with a rotation of 55 yrs was optimal. Two winter thinnings with a rotation of 61 yrs was optimal in an initially healthy stand. Optimizations indicated that silvicultural measures that decrease the transfer of H. annosum to next generation at clear-cuttings could be economically fulfilled.     

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.     

Snow damage in lodgepole pine stands brought into thinning and fertilization regimes

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.     

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.     

Trade-offs between seedling growth,thinning and stand stability in Sitka spruce stands: a modelling analysis

The forest industry is increasingly adopting alternative silvicultural systems, involving regeneration beneath an existing forest canopy, rather than clear-felling and replanting. To apply these silvicultural systems in windy regions such as Britain and Ireland, it is essential that the interactions between thinning intensity, stand stability and seedling growth are properly understood. Here, we present a modelling analysis of the three key relationships between: (i) stand density and the proportion of incident radiation transmitted through a forest canopy as a stand is thinned; (ii) transmitted radiation and seedling growth, and (iii) stand density and stand stability. These relationships were examined using separate models of radiative transfer (MAESTRO), seedling growth, and stand stability/wind risk (ForestGALES). Output from the three models was synthesised to calculate whether a given stand thinned to a pre-defined stability limit would allow sufficient light to penetrate the canopy for seedling growth. A minimum transmittance of 20% was identified as a requirement for seedling growth, which corresponds to removing 45% of stand basal area. A thinning of this intensity left some stands susceptible to unacceptable wind damage, especially in old or previously thinned stands on soils where rooting is impeded. The results emphasised the fact that rooting conditions, thinning history and age of intervention are major constraints on the silvicultural options. In general, older stands are not suitable for conversion to continuous cover forestry (CCF) systems, and the transformation process should begin at pole stage, when heavy thinning does not leave the stand unstable. The analysis approach used here illustrates the potential for combining models to address complex forest management issues.     

Optimizing the management of a Picea abies stand under risk of butt rot

A simulation model was developed to predict the growth of a Norway spruce stand under risk of butt rot caused by Heterobasidion annosum stump infection and logging injuries. The simulation model was distance‐dependent; tree growth was predicted with a distance‐dependent model, and the spread of butt rot through root contacts depended on tree location. Infection of stumps and injured trees, and the spread of butt rot in the stand were stochastic processes whereas tree growth and mortality were treated as deterministic processes. The simulation model was used with the nonlinear optimization algorithm of ooke and J eeves (J. Assoc. Comput. Mach, 8, 212–229, 1961) to find the most profitable management schedule for an even‐aged, young stand. Optimization used four different stump infection rates and two spreading capacities from infected stumps. The profitability was evaluated by the expected soil expectation value (SEV) at a 3% interest rate. Two thinnings, both in winter‐time, and hence without H. annosum infections, resulted in the highest SEV. If any stump infection by H. annosum occurred, only one thinning and a shortened rotation were suggested. The optimal thinning rate tended to decrease but also large trees were removed with the increasing infection rate. With one thinning during a rotation, stump treatment was profitable above a stump infection rate of 10%     

Natural thinning and structural patterns of intermediate cutting intensity in a Cunninghamia lanceolata stand

In the intermediate cutting intensity experiment of a Cunninghamia lanceolata plantation for 20 years, the changing pattern of natural thinning in these stands, with different intermediate cutting intensities, was studied. The relationship between the number of trees removed by natural thinning and stand density and site conditions was explained. The mathematical equation M = K ₁·K ₂ of natural thinning lines of C. lanceolata stand density management maps was tested and the relationship of diameter, height and canopy structure of stands with different intermediate cutting intensities are proposed. Our study of natural thinning in these stands indicates that the starting and peak periods of natural thinning in the check and slightly thinned plots were both early. The amount of thinned wood was large and the course of thinning proceeded continuously. The three levels of thinning: the slight thinning period, the intensive thinning period and the continued thinning period could be divided on the basis of the amount of thinned wood. Natural thinning would be a very long process without artificial interference. The starting and peak periods of thinning in the middle and strong intermediate felling are both late and present intermittence. Their thinning stages were not clearly evident. Through our studies, we also discovered that stand density and site conditions had important effects on the number of dead and dying trees, but that density was more important than site conditions. By way of tests, the relative error of the mathematical equation of natural thinning lines of C. lanceolata stand density management maps was 3.91% and the precision was relatively high. The practical test results of the stands, given different intermediate cutting intensities and different site indices, show that the relative error of the check plots was 5.23%, while the relative errors of the other tested items were all < 5%, well within the allowable experimental error. The mathematical equation was comparatively practical. The study demonstrated the distribution laws of diameter and height classes of the stand at different intermediate cutting intensities. From this study we also obtained the growth differences and changing dynamics of the height to the first branch, canopy length and relative canopy height of the stand at different intermediate cutting intensities and various related patterns with an increase of stand age and proposed a mathematical model relating stand age and the single-tree periodic volume increment. __________ Translated from Scientia Silvae Sinicae, 2006, 42(1): 55–62 [[译自: 林业科学]     

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]     

Heterobasidion annosum root rot in Picea abies: Modelling economic outcomes of stump treatment in Scandinavian coniferous forests

Abstract

The economic outcomes of stump treatment against spore infections of the root rot pathogen Heterobasiodion annosum s. l. were analysed based on simulations in four stands typical of Swedish forestry and forest management: (A) Norway spruce [Picea abies (L.) Karst.] stand on former agricultural soil (SI?=?32), (B) Norway spruce stand (SI?=?26) on forest land; (C) Mixed stand of Norway spruce and Scots pine (Pinus sylvestris L.) (SI?=?24) with only H. parviporum present, i.e. no infection of Scots pine and no possibility of interspecies spread of disease between hosts; and (D) same as C, but H. annosum s. str. (Fr.) Bref and H. parviporum Niemelä & Korhonen present, i.e. interspecies spread of disease possible. Models for disease development, growth and yield and cross-cutting were used in the simulations. The simulated decay frequency in Norway spruce trees ranged between 2 and 90%. Stump treatment at the previous final felling and in all thinning operations was profitable at interest rates 1 and 3% in stands A, B and D, but not in stand C. In stand C, no stump treatment at all or treatment in thinnings only gave the highest net future value. Implications for stump treatment in practical forestry are discussed.     

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.     

Incidence of Root and Butt Rot in Consecutive Rotations of Picea abies

The incidence of butt rot in two consecutive rotations of Norway spruce [Picea abies (L.) Karst.] in 28 permanent sample plots at four different sites in Denmark was evaluated. Incidence of butt rot was estimated by visual examination of stumps at final felling of the previous rotation and by examination of bore cores taken at the butt from a random sample of trees before first thinning of the subsequent rotation. There was no correlation between the incidence of butt rot at final felling of the previous rotation of Norway spruce and the incidence of butt rot at first thinning of the subsequent rotation of Norway spruce. The incidence of butt rot at final felling was between 19 and 100%, and at first thinning between 0 and 20%. The S-form of Heterobasidion annosum (Fr.) Bref. was the most commonly found decay-causing organism at all sites. Root systems of 28 trees without decay at stump height in the present rotation were excavated to estimate the incidence of root rot. Heterobasidion annosum was found in only one root. Resinicium bicolor (Alb. & Schw. ex Fr.) Parm. was found in 25% of the excavated root systems. The result of the study shows that the incidence of butt rot at first thinning of Norway spruce is not necessarily higher on sites where the previous rotation was heavily infected than on sites where infection in the previous rotation was low.     

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.     

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.     

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.     

Natural mortality in thinning and fertilisation experiments with pine and spruce in Sweden

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.     

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。     

Stamm- und Wurzelfäulen in Douglasien,Pseudotsuga menziesii (Mirb.) Franco1

Stem and root rot of Douglas fir, Pseudotsuga menziesii (Mirb.) Franco. In 20 year old Douglas fir most of the butt rot was caused by Fomes annosus. Stem decay was central as well as eccentric reaching the sap wood in either case. The side roots of 20 year old Douglas fir were compared with those of a 40 year old stand with butt rot. In individual trees with decay there were less roots with Fomes annosus decay in the younger stand. Calocera viscosa was more abundant in the older stand. Soil conditions which might have favoured root rot in the young stand are discussed.     

Leaf photosynthetic responses and related nitrogen changes associated with crown reclosure after thinning in a young Chamaecyparis obtusa stand

In order to quantify the effects of thinning on biochemical photosynthesis parameters and changes in leaf nitrogen contents associated with the process of crown reclosure, the maximum rate of carboxylation (V _cmax), the leaf nitrogen concentration per unit area (N _a), and the photosynthetic photon flux density (PPFD) were measured at four crown heights in both thinned (1500 trees ha⁻¹) and unthinned control (3000 trees ha⁻¹) stands of ten-year-old Chamaecyparis obtusa (36°3′N, 140°7′E) trees during four consecutive growing seasons after thinning. Thinning increased V _cmax in the lower and middle crowns in the first year after thinning, and leaves in the lower crown of the thinned stand maintained high V _cmax for four years, whereas they abscised in the second year in the control stand. Significant increases in V _cmax were detected even in the upper crowns of trees in the thinned stand in the second year. Thinning did not affect N _a at any of the crown positions in the first year, but significantly increased N _a in the middle crowns from the second year after thinning. Thus, the redistribution of nitrogen between leaves, driven by increases in light and nutrient availability due to the 50% thinning, appears to have enhanced photosynthetic rates in the thinned stand. Thinning also significantly affected the slope of the linear relationship between N _a and V _cmax initially after thinning, but its effect on this relationship was negligible after the second year. These quantitative results may be used to simplify the estimation of the likely effects of management practices on carbon fixation in forest canopies.     

Tree vigour and the susceptibility of Douglas fir to Armillaria root disease

In this study the effects of thinning, fertilization and pruning on the vigour of Douglas fir (Pseudotsuga menziesii) and its susceptibility to Armillaria root disease were explored. Tree vigour was defined as the relative capacity for tree growth, expressed as the above-ground biomass increment per unit of photosynthetic tissue, or growth efficiency (GE). It has been hypothesized that trees with higher GE can better resist pathogen attack, and that GE can be used as a predictor of tree susceptibility to disease. In a previous study, four Douglas fir plantations were thinned, fertilized and pruned in all combinations, and the effects of these treatments on tree vigour were measured after 10 years. Root disease was not a factor in the initial study design, and mortality was ignored until 8 years after the treatments were applied. The results of an earlier study were utilized and the correlation between Armillaria root disease incidence and the effects of earlier stand treatments on tree growth was tested. Armillaria ostoyae was the primary mortality agent in the study area. Disease incidence on infested subplots ranged from 2 to 20%. Armillaria ostoyae incidence was the highest at medium tree density (6.1%), slightly lower on the low density (5.6%), and lowest on the unthinned plots (3.8%). There were no significant correlations between disease incidence and previous tree growth. The vigour of trees that became symptomatic or died by 1993 was not significantly different in 1983–85 from the vigour of trees that remained asymptomatic. On these sites, in areas of infestation, A. ostoyae is killing the largest, fastest growing trees, as well as less vigorous trees. Armillaria continues to cause mortality, regardless of the growth efficiency or growth rate of the host.     

Thinning effects on pine-spruce forest transpiration in central Sweden

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.