Stem Diameter Increment Research Articles

The dependency of the size-growth relationship of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in forest stands on long-term site conditions, drought events, and ozone stress

Against a backdrop of increasing climate change, the effects of site conditions, drought events and ozone stress on the size-growth relationship in Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) stands are analyzed. The size-growth relationship is represented by a straight line defined by intercept and slope of a simple linear equation with stem diameter at height 1.30 m as independent variable and annual stem diameter increment at height 1.30 as dependent variable. On the basis of 64 long-term experimental plots dating back to 1871 and representing an ecological gradient from fertile to poor sites, it is shown that poorer sites exhibit shallower slopes of the linear size-growth relationships than fertile sites. Annual measurements of the size-growth relationship, including the extremely dry years of 1976 and 2003, also showed that lower stand growth rates result in shallower size-growth relationship slopes. By comparing stands with and without experimental twice-ambient ozone exposure between 2000 and 2007, it was found that ozone stress can significantly reduce the slope of the size-growth relationship. This indicates that limiting site condition, whether acute or chronic in nature, distinctly reduces the superiority of tall trees, and that a lower degree of resource limitation increases the steepness of the size-growth relationship. The causes for this behavior and the consequences for stand dynamics, silvicultural treatment and prognostication by models are discussed.

Radial stem variations of Tabebuia chrysantha (Bignoniaceae) in different tropical forest ecosystems of southern Ecuador

Stem diameter increments of the broadleaved deciduous tree species Tabebuia chrysantha were measured with high-resolution dendrometers in a tropical lower montane forest and in a dry forest in southern Ecuador, the latter showing a distinct dry season. Those analyses were complemented by wood anatomical studies on regularly collected microcores to determine the season of active cambial growth and the time of formation of annual growth boundaries. The length of the cambial active period varied between 3 and 7 months at the tropical lower montane forest and 2 and 4 months in the dry forest, respectively. During dry days, amplitudes of daily stem diameter variations correlated with vapour pressure deficit. During October and November, inter-annual climate variations may lead to dry and sunny conditions in the tropical lower montane forest, causing water deficit and stem diameter shrinkage in T. chrysantha. The results of the climate–growth analysis show a positive relationship between tree growth and rainfall as well as vapour pressure deficit in certain periods of the year, indicating that rainfall plays a major role for tree growth.

GROWTH AND BIOMASS OF TWO-YEAR-OLD SEEDLINGS OF EUROPEAN CHESTNUT DERIVED FROM THE HALF-SIB FAMILIES OF DIFFERENT ORIGIN

In the spring of 2005, seeds collected in twelve different half-sib families being at the age of 40 years and originated from mother trees grown on four different localities of Slovakia were used to established an experimental plot in the forest nursery Hladomer, Slovakia. At the age of 2 years, in each of 12 sets of seedlings 15 seedlings differing in growth performance were selected (5 from each replication) and subjected to morphometric analysis. In each seedling 5 biometric characteristics (stem height, stem diameter, root length, root diameter, diameter of the root collar), 3 single biomass characteristics (biomass of the stem and branches, root biomass, leaf biomass), 2 combined biomass characteristics (aboveground biomass and total seedling biomass) and three derived parameters (index of annual stem height increment, index of annual stem diameter increment and foliage ratio -proportion of leaf dry matter and total dry aboveground matter of the seedling) were evaluated. All characteristics under study except indices and foliage ratio exhibited significantly highest mean values in the seedlings derived from three half-sib families of Horne Lefantovce origin, particularly from the HL A family. The seedlings derived from this family showed significantly highest values of aboveground and underground biomass but the second lowest foliage ratio. This suggests the high effective use of leaves for biomass production in these seedlings. Foliage ratio was in medium strong negative correlation with most of the growth and biomass characteristics.

Growth of Newly Established Tilia platyphyllos ‘Rubra’ Roadside Trees in Response to Weed Control and Pruning

This tree establishment study investigates the effect of weed control and pruning treatments on stem and branch diameter increment of newly planted broad-leaved lime (Tilia platyphyllos ‘Rubra’) roadside trees. Weed control significantly increased stem circumference four years after establishment by 3.6 cm (1.4 in) from 24.5 cm (9.7 in, untreated control) to 28.1 cm (11.1 in). In terms of Danish nursery sales prices, this corresponds to an increase of tree cash value of 1201 DKK (160.90 €, 235.40 US$) per tree. Calculating with 400 DKK (53.60 €, 78.40 US$) as cost for contract weeding per hour, this corresponds to 0.75 hours per tree per year for a period of four years. In addition to weed control treatments, trees were pruned at establishment, two years after establishment, or at both times. None of the pruning treatments affected stem diameter growth, but branch diameter and branch:stem diameter ratio were significantly reduced by all pruning treatments. Branch diameter ranged from 40.1 mm (1.6 in) on unpruned trees to 34.6 mm (1.4 in on trees pruned both times. Branch:stem diameter ratio ranged from 0.54 on unpruned trees to 0.49 on trees pruned both times. In consequence, weed control is recommended as a strong management practice. Mild pruning is also considered advisable, if structural crown problems can be avoided at an early stage, and if the tree has to be prepared for later pruning operations.

Opinion paper: Effects of simulated soil temperature on stem diameter increment of Pinus cembra at the alpine timberline: a new approach based on root zone roofing

For assessing the impact of soil temperature on tree growth in remote areas such as the alpine timberline we introduce a new method for soil temperature manipulations. This new approach is based on roofing of the rooting zone and allows either soil cooling or soil warming without significantly influencing soil water availability and the above ground microclimate.

Effects of climate variables on intra-annual stem radial increment in Pinus cembra (L.) along the alpine treeline ecotone

Within the alpine treeline ecotone tree growth is increasingly restricted by extreme climate conditions. Although intra-annual stem growth recorded by dendrometers can be linked to climate, stem diameter increments in slow-growing subalpine trees are masked by changes in tree water status.We tested the hypothesis that intra-annual radial stem growth in Pinus cembra is influenced by different climate variables along the treeline ecotone in the Austrian Alps. Dendrometer traces were compared with dynamics of xylem cell development to date onset of cambial activity and radial stem growth in spring.Daily fluctuations in stem radius reflected changes in tree water status throughout the treeline ecotone. Extracted daily radial increments were significantly correlated with air temperature at the timberline and treeline only, where budburst, cambial activity and enlargement of first tracheids also occurred quite similarly. A close relationship was detected between radial increment and number of enlarging tracheids throughout the treeline ecotone.We conclude that (i) the relationship between climate and radial stem growth within the treeline ecotone is dependent on a close coupling to atmospheric climate conditions and (ii) initiation of cambial activity and radial growth in spring can be distinguished from stem re-hydration by histological analysis.

Sheep grazing in young oak Quercus spp. and ash Fraxinus excelsior plantations: vegetation control, seasonality and tree damage

An experiment was carried out where sheep were grazed in temporary fenced paddocks at a stocking rate of 178 LSU ha−1 in a 5-year old broadleaf plantation of oak (Quercus spp.) and ash (Fraxinus excelsior) (1.5 m spacing) on fertile, former lowland pasture in Northern Ireland. The grazing regime was rotational and intensive, with two grazing periods of 5 days in February and October 2001. Results showed that a significant proportion of the rank herbage height was removed within the first 24 h of livestock introduction. Herbage biomass was reduced by approximately half after 5 days. Sward height in grazed plots remained significantly lower than control plots for over 6 months after cessation of grazing, whilst biomass remained significantly lower for over 4 months after cessation of grazing. No significant tree damage to either oak or ash was measured during the February grazing trial, however significant damage to the lateral branches of both oak and ash was observed in the October grazing trial. Leader damage did not occur on trees greater than 152 cm. Ash was more commonly browsed than oak. Annual height increment of both tree species was unaffected by grazing, but annual stem diameter increment was significantly reduced in both oak and ash in February grazed plots. Oak trees in both February and October grazed plots were found to have a significantly smaller annual increase in canopy diameter than those in control plots. Results are discussed with regard to practical implementation of controlled grazing in young broadleaf forestry plantations on fertile, lowland soils.

Elevational change in woody tissue CO2 efflux in a tropical mountain rain forest in southern Ecuador

Much uncertainty exists about the magnitude of woody tissue respiration and its environmental control in highly diverse tropical moist forests. In a tropical mountain rain forest in southern Ecuador, we measured the apparent diurnal gas exchange of stems and coarse roots (diameter 1-4 cm) of trees from representative families along an elevational transect with plots at 1050, 1890 and 3050 m a.s.l. Mean air temperatures were 20.8, 17.2 and 10.6 degrees C, respectively. Stem and root CO(2) efflux of 13 to 21 trees per stand from dominant families were investigated with an open gas exchange system while stand microclimate was continuously monitored. Substantial variation in respiratory activity among and within species was found at all sites. Mean daily CO(2) release rates from stems declined 6.6-fold from 1.38 micromol m(-2) s(-1) at 1050 m to 0.21 micromol m(-2) s(-1) at 3050 m. Mean daily CO(2) release from coarse roots decreased from 0.35 to 0.20 micromol m(-2) s(-1) with altitude, but the differences were not significant. There was, thus, a remarkable shift from a high ratio of stem to coarse root respiration rates at the lowest elevation to an apparent equivalence of stem and coarse root CO(2) efflux rates at the highest elevation. We conclude that stem respiration, but not root respiration, greatly decreases with elevation in this transect, coinciding with a substantial decrease in relative stem diameter increment and a large increase in fine and coarse root biomass production with elevation.

Structure and productivity along a tree height gradient in a Kandelia obovata mangrove forest in the Manko Wetland, Okinawa Island, Japan

Tree height (H) of Kandelia obovata trees decreased sharply from 5 m at the forest interior behind the terrestrial forest to 1.5 m at the forest edge near the river bank according to an increase in the yearly waterlogged period along a belt transect. The decreasing tree stature was attributed to a decrease in the asymptote of H in the D 0.1 (stem diameter at H/10)-H relationship toward the edge. The K. obovata trees were well classified into interior and edge types using a discriminant function based on the habitat-specific D 0.1–H relationships. Allometric equations, as a function of D 0.1 2 H, differed significantly between the interior and edge types in the estimation of the phytomasses of stems and leaves, and the leaf area per tree. On the other hand, common allometric equations were successfully established in the estimation of respective phytomasses of aboveground parts and branches. Biomass and leaf area index decreased toward the forest edge. The biomass allocation to stems decreased toward the edge, whereas those to branches and leaves increased. A dramatic change in stem diameter increment resulted in differences in the D 0.1–H relationship along the tree height gradient. Relative growth rate of biomass and light-saturated net photosynthesis, which paralleled net assimilation rate from the interior to the edge, showed their maximum peaks in the middle of the belt transect. This indicates that there exists an optimal environmental condition for growth of K. obovata trees. Leaf nitrogen content tended to increase to the edge with increasing waterlogged period.

Phenology and Stem Diameter Increment Seasonality in a Costa Rican Wet Tropical Forest

ABSTRACTThe relationship between phenology and tree stem diameter increment is largely unexplored in tropical species, especially in wet tropical forests. To explore links between these phenomena, we measured stem diameter increment and phenology of ten canopy tree species from a range of functional types in the Atlantic lowlands of Costa Rica to test for seasonal and interannual patterns. We measured stem diameter increment using band dendrometers and visually assessed leaf and reproductive phenology monthly from 1997 to 2000. We categorized the species into groups based on patterns of leaf exchange and reproduction. Species were either deciduous with synchronous or asynchronous leaf drop, or evergreen with continuous or seasonal leaf flushing. Flowering occurred supra‐annually, annually, or continuously. Of the ten species studied, four species,Cecropia insignis, Dipteryx panamensis, Lecythis ampla,andSimarouba amara, had consistent seasonal stem diameter increment patterns in both years.Dipteryx panamensisandL. amplawere deciduous with synchronized leaf drop. Cecropia insigniswas evergreen and produced new leaves continuously.Simarouba amara, also evergreen, exchanged leaves over a brief period once a year. We tested whether stem diameter increment was correlated to phenology using logistic regression. Leaflessness significantly explained patterns in stem diameter increment but reproductive phenology did not. Deciduous trees were 2.6–9.3 times more likely to grow less than average the month following leaffall than in months when trees had full crowns.

Six-year time course of light-use efficiency, carbon gain and growth of beech saplings (Fagus sylvatica) planted under a Scots pine (Pinus sylvestris) shelterwood

Two-year-old Fagus sylvatica L. saplings were planted under the cover of a Pinus sylvestris L. stand in the French Massif Central. The stand was differentially thinned to obtain a gradient of transmitted photosynthetically active radiation (PAR(t); 0-0.35). Eighteen Fagus saplings were sampled in this gradient, and their growth (basal stem diameter increment) was recorded over six years. Over the same period, morphological parameters (leaf area, number and arrangement in space) were monitored by 3D-digitization. Photosynthetic parameters were estimated with a portable gas-exchange analyzer. Photosynthesis was mainly related to light availability, whereas sapling morphology was mainly driven by sapling size. Annual stem diameter increment was related to the amount of light-intercepting foliage (silhouette to total leaf area ratio (STAR) x total sapling leaf area (LA)) and light availability above the saplings (PAR(t)). However, light-use efficiency, i.e., the slope of the relationship between STAR x LA x PAR(t) and stem diameter increment, decreased over time as a result of a relative decrease in the proportion of photosynthetic tissues to total sapling biomass.

Defoliation and nitrogen effects on photosynthesis and growth of Eucalyptus globulus

Plant responses to defoliation are complex. We established a field experiment in a nine-month-old Eucalyptus globulus Labill. plantation to examine the effects of pattern (upper crown versus lower crown removal), frequency (single, double or triple defoliation within a 12-month period) and severity (25 versus 38% of leaf area removed) of defoliation and the effect of soil nitrogen (N) on photosynthetic processes and stem growth. The photosynthetic responses observed following defoliation could be attributed to changes in source:sink ratios. Light-saturated CO(2) uptake (A(max)) increased with increasing severity and frequency of defoliation irrespective of defoliation pattern. Seedlings defoliated in autumn did not exhibit increases in A(max) until the following spring, whereas there was no such delay in photosynthetic responses associated with spring defoliation. Application of N before defoliation allowed trees to compensate for the effect of defoliation on stem diameter growth, which could not be explained simply in terms of increases in A(max). The observed increases in stem diameter increment following N fertilization of defoliated trees suggested increases in leaf area development, and there were changes in the leaf area:leaf dry mass ratio that may have increased light absorption by the crown. Nitrogen fertilization also increased partitioning of dry mass to branches at the expense of main stems, suggesting that N supply was important in rebuilding crowns following a defoliation event.

Estimating branch production in trembling aspen, Douglas-fir, jack pine, black spruce, and balsam fir

Measuring net primary productivity of trees requires the measurement of total wood production of branches. Recent work on balsam fir ( Abies balsamea ) has shown that branch-wood production can be estimated as a function of foliage production. We extend the analysis to four other species found in the Canadian forest: black spruce ( Picea mariana ), jack pine ( Pinus banksiana ), Douglas-fir ( Pseudotsuga menziesii ), and trembling aspen ( Populus tremuloides ). Results show that the ratio of annual branch-wood production to annual foliage production is about 1.0 for conifer species (between 0.86 and 1.12) and 0.56 for aspen during a nondrought year. An analysis using field measurements of litterfall and stem-diameter increment from selected forested sites shows that branch-wood production accounts for a smaller proportion of aboveground net primary productivity in trembling aspen (15%–20%) than in conifer species (25%). Also, litterfall capture of small branches (<1 cm diameter) accounts for only 33% of branch detritus production in conifers and 50% in trembling aspen. This study supports the use of an alternative method for estimating branch-wood production that reduces the potential bias in field estimates of net primary productivity.

Modelling net ecosystem carbon and water exchange of a temperate Eucalyptus delegatensis forest using multiple constraints

This study examined the carbon budget of a Eucalyptus delegatensis forest over four years under contrasting weather conditions by using a comprehensive forest-growth model (CenW 3.1). Model parameterisation was constrained through multiple measurements, including daytime eddy flux measurements of CO 2 and water vapour exchange, estimates of above- and below-ground biomass pools, growth rates measured through stem-diameter increments and measurement of specific ecosystem processes, such as litter fall and soil respiration rates. The resultant estimates of net ecosystem exchange ranged from an uptake of 4.0 t C ha −1 year −1 in a year with adequate rainfall to a loss of 0.4 t C ha −1 year −1 in a year affected by drought and insect damage. The simulations indicated that this reduction in carbon gain was primarily due to insect damage rather than a direct consequence of water shortage. Under good growing conditions, carbon gain accumulated equally in stem wood and other biomass pools while soil organic carbon and woody litter were gradually decreasing following harvesting that had occurred 20 years earlier. Under more stressful conditions, net biomass increments decreased, while soil organic carbon and woody litter increased because of greater litter inputs and because drier conditions inhibited decomposition. Modelled estimates of photosynthesis and net ecosystem exchange were similar to estimates from eddy flux observations alone provided that it used a novel routine for deriving night-time carbon fluxes. Estimates of net ecosystem exchange derived in the present work were, however, substantially lower than previous estimates that had been derived using a more traditional analysis of eddy flux data. This study showed that detailed physiological modelling is a valuable technique for combining all available site information as well as further constraints based on broader scientific principles and considerations of the conservation of mass. It can thus provide a powerful constraint on the overall site carbon budget of an ecosystem.

Effects of pruning on radial growth and biomass increment of trees growing in homegardens of Kerala, India

To evaluate the effects of pruning on stem radial growth increment and leaf and twig biomass production, an experiment with four pruning intensities (0, 50, 75 and 90%) on ten locally important tree species (Ailanthus triphysa, Albizia odoratissima, Artocarpus hirsutus, Bombax malabarica, Bridelia crenulata, Erythrina indica, Grewia tiliifolia, Macaranga peltata, Terminalia paniculata and Xylia xylocarpa ), was carried out. The results did not support the contention that a certain level of pruning promotes stem growth in trees. Instead, all species have a level of pruning that reduces annual increment in stem diameter. In Ailanthus triphysa and Artocarpus hirsutus trees subjected to different pruning intensities showed a decline in the annual increment in stem diameter while in other species diameter increment reduced when the pruning intensity was 75% and 90%. Response to pruning in terms of biomass production also varied from species to species. In Erythrina indica, Macaranga peltata and Terminalia paniculata annual foliage and branch production in pruned trees was significantly more than that of the un-pruned trees. However, in Ailanthus triphysa, Albizia odoratissima, Artocarpus hirsutus, Bridelia crenulata, Grewia tiliifolia and Xylia xylocarpa pruned trees produced comparatively more amount of foliage and branches produced annually than that by the un-pruned trees when the pruning was carried out once in 2 years. Based on these observations it is recommended that trees of Erythrina indica, Macaranga peltata and Terminalia paniculata may be pruned at 50% level annually while the trees of Ailanthus triphysa, Albizia odoratissima, Artocarpus hirsutus, Bridelia crenulata, Grewia tiliifolia and Xylia xylocarpa may be pruned at the same pruning intensity once in 2 years.

Growth response of Acacia koa trees to thinning, grass control, and phosphorus fertilization in a secondary forest in Hawai‘i

Koa ( Acacia koa A. Gray) is an endemic Hawaiian hardwood tree of high ecological, cultural and economic value. Despite its multiple values, research on the silviculture of koa has been minimal until recently because the preferred land-use was pasture for livestock, and logging was done mainly to facilitate and reduce the costs of conversion. This study examined growth response of selected potential crop trees to three treatments: (1) thinning of surrounding non-crop koa trees; (2) herbicide control of exotic grasses; and (3) herbicide grass control plus phosphorus (P) fertilization. These treatments were applied in a split-plot design to a 24-year-old stand of koa located at 1700-m elevation on the island of Hawai‘i. Treatments had variable effects on stem diameter increment of crop trees, measured at breast height during the second and third years after treatments were imposed. Neither thinning alone nor grass control alone significantly increased stem diameter increment or leaf nutrient concentrations of crop trees, or soil nitrogen (N) or P availability. Grass control in combination with P fertilization in the unthinned plots increased stem increment by 50% compared with unthinned control subplots, but again not significantly so. In these unthinned plots, grass control plus P fertilization greatly increased soil P availability and foliar P, but not those of other nutrients. Thinning in combination with grass control and P fertilization significantly increased annual diameter increment at breast height by 118%. Crown vigor and live crown to total tree height ratio were correlated with crop tree growth rate, which emphasizes the need to select crop trees that have healthy, full crowns and maintain a high live crown ratio, in addition to straight, defect-free stems. Overall, our results suggest that the benefits of release thinning of intermediate age koa crop trees on similar sites can be enhanced when combined with weed control and fertilization. Although even greater benefits might be realized if treatments are imposed before crown vigor and live crown ratio decline, the timing will need to be balanced against higher cost of thinning denser stands and the ability of managers to identify potential crop trees.

Fontes e doses de boro em porta-enxertos de seringueira

Este trabalho teve por objetivo avaliar o efeito da aplicação de boro sobre o incremento do diâmetro do caule no ponto de enxertia, 5 cm acima do coleto, número e diâmetro de raízes laterais e estado nutricional de porta-enxertos para produção de toco enxertado de raiz nua. O delineamento experimental foi o de blocos ao acaso, em esquema fatorial 2x5: duas fontes (ulexita, 10% de B e ácido bórico, 17% de B) e cinco doses de B (0, 2, 4, 8 e 16 kg ha-1) com quatro repetições. Em condições edafoclimáticas locais, curvas de resposta indicam aumentos significativos, no incremento do diâmetro do caule, no ponto de enxertia, nas doses 6,5 e 16 kg ha-1 de B, e no número de raízes laterais, nas doses 13,9 e 16 kg ha-1 de B, com aplicação de ácido bórico e de ulexita, respectivamente. As doses de B não afetaram o número de raízes. O nível crítico de B na folha de mudas de seringueira, alcançado com aplicação de ácido bórico, é de 31,8 mg kg-1. As doses de B apresentam interações significativas com os teores foliares de B, Mn e Zn, enquanto os teores foliares de N, P, K, Ca, Mg, S, Na, Cu e Fe não variaram significativamente em razão das doses de B.

Tree growth, mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought

A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning (carbon uptake and biomass accumulation) of these Mediterranean forests.

Short-term effects of wood ash on the soil and the lignin concentration and growth of Pinus sylvestris L.

Short-term effects of different doses of wood-ash application (0.25 kg m −2; 0.5 kg m −2; control without treatment) on soil chemical properties, tree growth and lignin concentration was investigated in a young Scots pine ( Pinus sylvestris) forest stand in northern Estonia from 2000 until 2003. Changes in the soil upper horizon (30 cm) showed an increase of pH and concentration of available K, Ca and P and a decrease of N after treatment. Later, from the second year after treatment, a decrease of P was found if compared to the control. The changes in the Mg concentration were very small at the beginning of the experiments, but an increase in the Mg concentration in soil was established a year after the treatment. Statistically significant stimulation of lignification in shoots was found after wood-ash treatment, but the pattern of seasonal changes in the rate of lignin concentration in needles and shoots was similar to control. It was found that the increase of Klason lignin as a result of wood-ash application correlated negatively with N and positively with K, Mg and Ca in soil. The diameter increment of pines had a negative correlation with lignin concentrations in shoots and needles. The increment of stem biomass, diameter and height was stimulated, but not significantly, by the wood-ash dose of 0.25 kg m −2.

Forest structure and carbon dynamics in Amazonian tropical rain forests.

Living trees constitute one of the major stocks of carbon in tropical forests. A better understanding of variations in the dynamics and structure of tropical forests is necessary for predicting the potential for these ecosystems to lose or store carbon, and for understanding how they recover from disturbance. Amazonian tropical forests occur over a vast area that encompasses differences in topography, climate, and geologic substrate. We observed large differences in forest structure, biomass, and tree growth rates in permanent plots situated in the eastern (near Santarém, Pará), central (near Manaus, Amazonas) and southwestern (near Rio Branco, Acre) Amazon, which differed in dry season length, as well as other factors. Forests at the two sites experiencing longer dry seasons, near Rio Branco and Santarém, had lower stem frequencies (460 and 466 ha(-1) respectively), less biodiversity (Shannon-Wiener diversity index), and smaller aboveground C stocks (140.6 and 122.1 Mg C ha(-1)) than the Manaus site (626 trees ha(-1), 180.1 Mg C ha(-1)), which had less seasonal variation in rainfall. The forests experiencing longer dry seasons also stored a greater proportion of the total biomass in trees with >50 cm diameter (41-45 vs 30% in Manaus). Rates of annual addition of C to living trees calculated from monthly dendrometer band measurements were 1.9 (Manaus), 2.8 (Santarém), and 2.6 (Rio Branco) Mg C ha(-1) year(-1). At all sites, trees in the 10-30 cm diameter class accounted for the highest proportion of annual growth (38, 55 and 56% in Manaus, Rio Branco and Santarém, respectively). Growth showed marked seasonality, with largest stem diameter increment in the wet season and smallest in the dry season, though this may be confounded by seasonal variation in wood water content. Year-to-year variations in C allocated to stem growth ranged from nearly zero in Rio Branco, to 0.8 Mg C ha(-1) year(-1) in Manaus (40% of annual mean) and 0.9 Mg C ha(-1) year(-1) (33% of annual mean) in Santarém, though this variability showed no significant relation with precipitation among years. Initial estimates of the C balance of live wood including recruitment and mortality as well as growth suggests that live wood biomass is at near steady-state in Manaus, but accumulating at about 1.5 Mg C ha(-1) at the other two sites. The causes of C imbalance in living wood pools in Santarém and Rio Branco sites are unknown, but may be related to previous disturbance at these sites. Based on size distribution and growth rate differences in the three sites, we predict that trees in the Manaus forest have greater mean age (approximately 240 years) than those of the other two forests (approximately 140 years).