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Little is known about how drought-related mortality influences light absorption of surviving trees and consequent changes in tree species interactions. Here, we used the detailed tree-level light model (Maestra) in combination with measurements of tree dimensions, crown architectures, and stand structures to examine experimental mixing effects of Fagus sylvatica , Alnus glutinosa , and Betula pendula on light dynamics following a drought in Bangor, Wales. The experimental stands, planted in 2004, were composed of clusters with one to three species in different combinations. Droughts occurred in 2011 and 2014 during the growing seasons, and trees were measured in 2014 and 2015. Species mixing resulted, on average, in higher tree growth, absorption of photosynthetically active radiation (APAR), and light-use efficiency (LUE) compared with the mean of the monocultures. An exception was the monoculture of B. pendula , which was the most productive species and had higher growth, APAR, or LUE than some mixtures. Drought-related mortality reduced the stand basal area across all plots by an average of 8.3% and tree density by 11%. This moderate change in the structure did not result in significant increases in individual tree APAR, LUE, or growth. From a management perspective, mortality might need to reduce stand density more strongly than it did in this study before light absorption or LUE is altered. [ABSTRACT FROM AUTHOR]

In Europe, mixed mountain forests, primarily comprised of Norway spruce (Picea abies (L.) Karst.), silver fir (Abies alba Mill.), and European beech (Fagus sylvatica L.), cover about 10 x [10.sup.6] ha at elevations between ~600 and 1600 m a.s.l. These forests provide invaluable ecosystem services. However, the growth of these forests and the competition among their main species are expected to be strongly affected by climate warming. In this study, we analyzed the growth development of spruce, fir, and beech in moist mixed mountain forests in Europe over the last 300 years. Based on tree-ring analyses on long-term observational plots, we found for all three species (i) a nondecelerating, linear diameter growth trend spanning more than 300 years; (ii) increased growth levels and trends, the latter being particularly pronounced for fir and beech; and (iii) an elevation-dependent change of fir and beech growth. Whereas in the past, the growth was highest at lower elevations, today's growth is superior at higher elevations. This spatiotemporal pattern indicates significant changes in the growth and interspecific competition at the expense of spruce in mixed mountain forests. We discuss possible causes, consequences, and silvicultural implications of these distinct growth changes in mixed mountain forests. Key words: climate change, competition shift, dominance of beech, growth trends, relative loss of Norway spruce. En Europe, les forets mixtes de montagne, surtout composees d'epicea commun (Picea abies (L.) Karst.), de sapin blanc (Abies alba Mill.) et de hetre commun (Fagus sylvatica L.), couvrent 10 x [10.sup.6] ha a des altitudes de ~600 a 1600 m ASL. Ces forets fournissent de precieux services ecosystemiques. Cependant, on s'attend a ce que la croissance de ces forets et la competition entre leurs principales especes soient fortement perturbees par le rechauffement climatique. Dans cette etude, nous avons analyse l'evolution de la croissance de l'epicea, du sapin et du hetre dans les forets mixtes humides de montagne en Europe au cours des 300 dernieres annees. Sur la base des analyses des cernes annuels des arbres dans des parcelles d'observation a long terme, nous avons note chez les trois especes (i) une croissance lineaire en diametre qui ne ralentit pas s'etendant sur plus de 300 ans; (ii) une croissance plus elevee, particulierement chez le sapin et le hetre et (iii) un changement dans la croissance du sapin et du hetre relie a l'altitude. Alors que dans le passe la croissance etait plus forte a basse altitude, elle est maintenant plus forte a haute altitude. Cette configuration spatio-temporelle temoigne de changements dans la croissance et la competition interspecifique aux depens de l'epicea dans les forets mixtes de montagne. Nous discutons des causes possibles, des consequences et des implications sylvicoles de ces changements marques dans la croissance des forets mixtes de montagne. [Traduit par la Redaction] Mots-cles : changement climatique, changement dans la competition, dominance du hetre, tendances de la croissance, perte relative d'epicea commun., 1. Introduction Intemperate Europe, mixed mountain forests of Norway spruce (Picea abies (L.) Karst.), silver fir (Abies alba Mill.), and European beech (Fagus sylvatica L.) connect the lowland beech forest [...]

A. N. Wilson's review of the new biography of George V by Jane Ridley (October 29) is spoiled only by the anachronistic reference to H. H. Asquith as 'Herbert Asquith'. [...]

Relationships between tree size and water use indicate how soil water is partitioned between differently sized individuals, and hence competition for water. These relationships are rarely examined, let alone whether there is consistency in shape across populations. Competition for water among plants is often assumed to be size-symmetric, i.e. exponents (b1) of power functions (water use ∝ biomassb1) equal to 1, with all sizes using the same amount of water proportionally to their size. We tested the hypothesis that b1 actually varies greatly, and based on allometric theory, that b1 is only centered around 1 when size is quantified as basal area or sapwood area (not diameter). We also examined whether b1 varies spatially and temporally in relation to stand structure (height and density) and climate. Tree water use ∝ sizeb1 power functions were fitted for 80 species and 103 sites using the global SAPFLUXNET database. The b1 were centered around 1 when tree size was given as basal area or sapwood area, but not as diameter. The 95% confidence intervals of b1 included the theoretical predictions for the scaling of plant vascular networks. b1 changed through time within a given stand for the species with the longest time series, such that larger trees gained an advantage during warmer and wetter conditions. Spatial comparisons across the entire dataset showed that b1 correlated only weakly (R 2 < 12%) with stand structure or climate, suggesting that inter-specific variability in b1 and hence the symmetry of competition for water may be largely related to inter-specific differences in tree architecture or physiology rather than to climate or stand structure. In conclusion, size-symmetric competition for water (b1 ≈ 1) may only be assumed when size is quantified as basal area or sapwood area, and when describing a general pattern across forest types and species. There is substantial deviation in b1 between individual stands and species. [ABSTRACT FROM AUTHOR]

The choice of planting density is a primary silvicultural decision in plantation management which considers the trade-off between individual tree size and total stand production, affecting the type, quantity and quality of products throughout the rotation. Trends in size and production with planting density are generally well known, however, less so is the interacting effect of site quality. Consequently, a case study in which basal area and basal area growth of Eucalyptus globulus Labill. plantations on five site qualities (122-435 [m.sup.3]*[ha.sup.-1]) planted at six densities (625 trees*[ha.sup.-1], 4 m x 4 m; 833 trees*[ha.sup.-1], 3 m x 4 m; 1000 trees*[ha.sup.-1], 4 m x 2.5 m; 1250 trees*[ha.sup.-1], 4 m x 2 m; 1667 trees*[ha.sup.-1], 3 m x 2 m; and 2000 trees*[ha.sup.-1], 3 m x 1.75 m) were used to investigate this interaction. As expected, both mean tree diameter of the whole stand and the basal area of the largest diameter 200 [treesxha.sup.-1] ([D.sub.200] trees) were higher at lower planting densities, whereas whole stand basal area was greater at higher planting densities. However, there were no significant (P > 0.32) interactions between planting density and site quality for [D.sub.200] or stand basal area, which contrasts with thinning responses in similar stands. This simplifies management considerations and suggests that trials at a given site quality may provide useful information about responses to planting density at other site qualities for the studied species. Resume: Le choix de la densite de plantation est une decision sylvicole importante lors de l'amenagement d'une plantation qui implique un compromis entre la taille des arbres et la production totale du peuplement, ce qui influence le type, la quantite et la qualite des produits tout au long de la rotation. En general, on connait assez bien l'effet de la densite de plantation sur la taille des arbres et la production du peuplement, mais ce n'est pas le cas de la qualite de la station qui pourrait interagir avec la densite de plantation. Par consequent, cette interaction a ete etudiee en analysant la surface terriere et la croissance en surface terriere de plantations d'Eucalyptus globulus Labill. etablies selon un dispositif comprenant cinq qualites de station (de 122 a 435 [m.sup.3]*[ha.sup.-1]) et six densites de plantation (625 arbres*[ha.sup.-1], espacement de 4 m x 4 m; 833 arbres*[ha.sup.-1], 3 m x 4 m; 1000 arbres*[ha.sup.-1], 4 m x 2,5 m; 1250 arbres*[ha.sup.-1], 4 m x 2 m; 1667 arbres*[ha.sup.-1], 3 m x 2 m; et 2000 arbres*[ha.sup.-1], 3 m x 1,75 m). Comme prevu, les plus faibles densites de plantation etaient associees a de plus fortes valeurs de diametre moyen de l'ensemble des arbres du peuplement et de surface terriere des 200 plus gros arbres a l'hectare ([D.sub.200]), alors que les plus fortes densites de plantation etaient associees a des surfaces terrieres du peuplement plus elevees. Toutefois, il n'y avait pas d'interaction significative (P > 0,32) entre la densite de plantation et la qualite de station pour la surface terriere [D.sub.200] et celle du peuplement, ce qui contraste avec les resultats obtenus a la suite d'une eclaircie dans des peuplements semblables. Ces resultats simplifient les facteurs dont l'amenagement doit tenir compte et indiquent que des essais realises sur une station d'une qualite donnee peuvent fournir de l'information utile sur la reaction d'une plantation de la meme espece en fonction de la densite, mais etablie sur des stations de qualite differente. [Traduit par la Redaction], Introduction Planting density can strongly affect tree- and stand-level growth dynamics. At higher densities, stand leaf area and biomass develop more rapidly and the site is 'fully occupied' sooner. Peak [...]

Coppice growth on cut stumps in thinned Eucalyptus plantations has the potential to compete with and reduce the growth of retained sawlog crop trees (SCTs). This study examined to what extent SCT growth was reduced by coppice in two stands in southeastern Australia: (i) a Eucalyptus globulus Labill. plantation thinned at age 10 years and (ii) a slower growing Eucalyptus tricarpa L.A.S. Johnson & K. Hill (syn. Eucalyptus sideroxylon subsp. tricarpa L.A.S. Johnson) plantation thinned at age 62 years. After 5 years, thinning E. globulus from 850 to 400 trees * [ha.sup.-1] increased the basal area of the largest diameter 200 SCTs * [ha.sup.-1] ([SCT.sub.200]) by 11% when coppice was removed. There was no significant thinning response by [SCT.sub.200] when coppice was retained. After 10 years, thinning E. tricarpa from about 600 to 100 trees * [ha.sup.-1] increased the basal area of the largest diameter 100 SCTs trees * [ha.sup.-1] ([SCT.sub.100]) by about 10% whether coppice was removed or not. At the time of measurement, coppice contributed 17% and 36% of stand sapwood area in thinned E. globulus and E. tricarpa treatments, respectively, and possibly competed with SCTs for water. This study shows the significant competitive effect that coppice can have in thinned eucalypt plantations and the importance of coppice management to the growth of retained trees. Resume: Les rejets de souche qui apparaissent a la suite d'une eclaircie dans les plantations d'Eucalyptus peuvent concurrencer les arbres d'avenir destines au sciage (AAS) et reduire leur croissance. Cette etude vise a determiner l'ampleur de la reduction de croissance des AAS causee par les rejets de souche dans deux peuplements du sudest de l'Australie: (i) une plantation d'Eucalyptus globulus Labill. eclaircie a l'age de 10 ans et (ii) une plantation a croissance plus lente d'Eucalyptus tricarpa L.A.S. Johnson & K. Hill (syn. Eucalyptus sideroxylon subsp. tricarpa L.A.S. Johnson) eclaircie a l'age de 62 ans. Apres 5 ans, l'eclaircie dans la plantation d'E. globulus, qui a reduit le nombre de tiges a l'hectare de 850 a 400, a fait augmenter de 11 % la surface terriere des 200 plus gros AAS a l'hectare ([AAS.sub.200]) lorsque les rejets de souche etaient enleves. Les [AAS.sub.200] n'ont pas eu de reaction significative a l'eclaircie lorsque les rejets de souche etaient conserves. Apres 10 ans, l'eclaircie dans la plantation d'E. tricarpa, qui a reduit le nombre de tiges a l'hectare de 600 a 100, a fait augmenter d'environ 10 % la surface terriere des 100 plus gros AAS a l'hectare ([AAS.sub.100]), que les rejets de souche soient enleves ou non. Au moment de la prise de mesures, les rejets de souche representaient respectivement 17 % et 36 % de la surface d'aubier des peuplements eclaircis d'E. globulus et d'E. tricarpa et concurrencaient possiblement les AAS pour l'eau. Cette etude met en evidence l'effet concurrentiel significatif que les rejets de souche peuvent avoir dans les plantations eclaircies d'eucalyptus et l'importance de l'amenagement des rejets de souche pour la croissance des arbres residuels. [Traduit par la Redaction], Introduction Thinning increases the availability of light, water, and nutrients for retained trees and can increase growth rates of sawlog crop trees (SCTs) in Eucalyptus plantations by as much as [...]

Growth responses to pruning or thinning are well documented but their interactions are not, even though they are sometimes performed simultaneously. Growth responses to thinning and pruning were examined in nine plantation silvicultural experiments at five sites in southeastern mainland Australia. The species studied were Eucalyptus globulus Labill., Eucalyptus nitens (Deane and Maiden) Maiden, and Eucalyptus grandis Hill ex Maiden. Thinning from about 1100-1300 trees * h [a.sup.-1] to about 300 or 500 trees * h [a.sup.-1] at either age 3-4 years or 7-10 years increased the volume of sawlog crop trees in all species. Multiple lift pruning to 6.5 m height on the sawlog crop trees that retained at least 70% of the live crown length at any lift significantly reduced tree growth at only one of the six site-species combinations where both thinning and pruning were studied. And here, thinning interacted with pruning such that the pruning effects were not significant in unthinned stands because only shaded and inefficient foliage was removed. This study shows that thinning and pruning can interact to influence sawlog crop tree growth and this interaction is influenced by site. Resume: La reaction de croissance des arbres a un elagage ou a une eclaircie est. been documentee, cue qui n'est pas le cas de leur interaction meme si ces traitements sont parfois realises simultanement. La reaction de brisance a l'eclaircie et a l'elagage a ete etudiee dans neuf plantations experimentales etablies dans cinq stations du sud-est de l'Australie. Les especes etudiees etaient Eucalyptus globulus Labill., Eucalyptus nitens (Deane and Maiden) Maiden et Eucalyptus grandis Hill ex Maiden. Une eclaircie faisant passer la densite d'environ 1 100 a 1 300 tiges * h [a.sup.-1] a environ 300 ou 500 tiges * h [a.sup.-1], que ce soit a des ages de 3 a 4 ans ou de 7 a 10 ans, a augmente le volume des arbres d'avenir destines au sciage chez toutes les especes. Des elagages multiples jusqu'a une hauteur de 6, 5 m sur les arbres d'avenir destines au sciage qui ont conserve au moins 70 % de cime vivante a chaque intervention ont significativement diminue la croissance des arbres dans seulement une des six combinaisons station-espece pour lesquelles l'eclaircie et l'elagage ont ete etudies. De plus, l'eclaircie a alors interagi avec l'elagage de sorte que l'elagage n'a pas eu d'effet significatif dans les peuplements non eclaircis parce qu'il n'a enleve que du feuillage ombrage et inefficace. Cette etude montre que l'eclaircie et l'elagage peuvent interagir pour influencer la croissance des arbres d'avenir destines au sciage et que cette interaction est influencee par la station. [Traduit par la Redaction], Introduction There are about 20 Mha of Eucalyptus plantations worldwide (Iglesias and Wilstermann 2008). While a large proportion is primarily used for pulpwood or firewood production (FAO 2005), solid wood [...]

Frank Field's 2021 suggestion of a local parliament for England as a means of unlocking the current constitutional logjam in Scotland (Letters, January 1) has an 1889 answer from Henry [...]

Silvicultural practices greatly improve the economic value of wood products from forests. Stem dimensions, wood density, and stem form are closely linked to end-product performance. This research aimed to examine the effects of stand density and stem height on variables that reflect ring growth and wood properties of Sassafras tzumu stands during the self-thinning phase. Between the ages of 10 and 40 years, the number of stems per hectare has declined from 1,068 to 964 due to density-dependent mortality. As the relative stand density decreased, there were significant reductions in the average tree ring width (5.07–3.51 mm) and increases in latewood proportions (49.88–53.49%) and the density of the annual growth ring (165.60–708.58 kg/m3). Therefore, ring density, earlywood density, and latewood density increased with decreasing relative stand density after self-thinning occurred. Ring width, earlywood width, and latewood width significantly increased from the base to the apex of the stem. Stand density and stem height had additive effects on S. tzumu wood properties during the self-thinning phase. A shift in the growth allocation along the longitudinal stem in response to self-thinning resulted in decreasing radial growth, increasing wood density, and improved stem form. In summary, we found a significant influence of stand density on tree ring growth, wood quality, and stem form of S. tzumu trees during the self-thinning phase. [ABSTRACT FROM AUTHOR]

Gerald Mangan (Letters, June 19) accuses me of making political points in my letter (June 5) commenting on his review of a new edition of Lewis Grassic Gibbon's Sunset Song [...]