Sapwood Area Research Articles

Aleppo pine forests from across Spain show drought-induced growth decline and partial recovery

Drought-induced growth decline is a phenomenon widely described in forests growing in regions subjected to seasonal water shortage such as the Mediterranean Basin. However, how tree species react to drought by modifying their growth pattern across the species distribution range is a question that remains to be answered.We investigate this question using a network of 27 Aleppo pine forests distributed across the eastern Spain and encompassing diverse site characteristics and climatic conditions. Using dendrochronology we quantify the radial growth responses of this Mediterranean tree species in 1994–1995, when the most severe drought after 1950 affected the study area. We quantify the variation between trees and sites in terms of growth resilience to drought, i.e. the resistance to the drought event and the recovery after it. Then, we quantify the relationship of these responses to tree traits (tree diameter and height, tree age, sapwood area) at the individual tree level, and to site characteristics (climate conditions, stand structure–tree density, basal area and the presence of co-dominant tree species) at the site level.We found that 1994–95 dry spell strongly impacted tree growth since 25 out of 27 sites and about 88% of trees showed a marked growth reduction of around 60% in radial growth. Climatic conditions were by far more important than tree traits on explaining resilience indices. In particular, the resistance to drought decreased with the increase in drought intensity, whereas the post-drought recovery was linked to site precipitation. Trees from dry sites were less resistant but recovered faster than trees from wet sites.We demonstrate that the reaction of different tree populations to drought is structured according to local climate conditions. If droughts become more severe and frequent as predicted in the Mediterranean region where climate warming is forecasted, Aleppo pine stands growing in the driest regions will be increasingly more sensitive to intense dry spells.

Equations for Estimating Biomass, Foliage Area, and Sapwood of Small Trees in the Southern Appalachians

Small trees and shrubs play an important role in forest diversity and regeneration and may contribute substantially to ecosystem fluxes of carbon and water; however, relatively little attention is given to quantifying the contribution of small trees to forest processes. One reason for this may be that the allometric equations developed for large trees tend to systematically underestimate structural variables such as biomass and foliage area when applied to small trees, both on an individual tree level and at the stand level. To test this hypothesis, we developed allometric equations for trees 10 cm dbh (D) for seven dependent variables (woody, foliage, and total biomass; woody, foliage, and whole-plant surface area; and sapwood area) and compared these new equations with the existing equations for large trees. We found significant differences between small tree and large tree equations for most variables and showed that equations for large trees tend to underestimate the structural characteristics of small trees. When we applied new size-specific equations to forest survey data representing a chronosequence of forest development, estimates of small tree biomass increased 30‐73% and estimates of foliage area increased 72‐142% compared with results using only equations for large trees. These results suggest that small trees can contribute substantially to forest structure and associated ecosystem fluxes, especially in stands with a large proportion of small trees. However, size-specific equations for small trees did not substantially change the estimates of forest biomass in these stands, and the need to develop size-specific equations may depend on the variables of interest.

The effect of competition on responses to drought and interannual climate variability of a dominant conifer tree of western North America

SummaryTo accurately predict how ecosystems will respond to climate change – and how management actions can influence such responses – scientists and managers need a better understanding of how and when biotic interactions modify climate–growth relationships. However, current research has largely ignored the role of competition in modulating climate–growth relationships of mature trees. In this study, we assessed the effect of competition on tree responses to drought and interannual climate variability as well as linkages between climate sensitivity and morphological characteristics of the stem wood.We sampled 10 sites in north‐eastern Washington,USA, and used dendroecology to quantify responses of Douglas‐fir (Pseudotsuga menziesii) to drought and climate variability. Tree‐ring series were converted to basal area increment series, and the effects of competition on climate–growth relationships were assessed at the tree and site levels using a combination of correlation analyses and linear mixed‐effects models.Competition did not affect tree responses to extreme drought. When soil moisture was below average, tree growth was tightly coupled to climate variability for all trees, regardless of their competitive status. However, in wet years, competition had a pronounced, positive effect on climate sensitivity of growth.Trees with more competition from neighbours exhibited a significantly higher proportion of sapwood area in latewood (a morphological trait associated with greater drought resistance).Synthesis. Our results suggest that a tree's ability to cope with environmental variability is driven not just by the proximate effects of neighbours on resource availability, but also by phenotypic plasticity and long‐term adaptations to competitive stress (such as changes in carbon allocation). Findings have important implications for individual‐tree and stand‐level growth models and may help managers better understand how their activities will modify tree responses to climate change.

Scaling-up from tree to stand transpiration for a warm-temperate multi-specific broadleaved forest with a wide variation in stem diameter

Previous studies have demonstrated a clear relationship between diameter at breast height (DBH) and tree transpiration (QT) in multi-specific broadleaved forests. However, these studies were conducted with a limited range of tree sizes and species, and thus many multi-specific broadleaved forests fall outside these conditions. Therefore, this study examined the relationship between DBH and QT in a warm-temperate multi-specific broadleaved forest (n = 12 species) with a wide range of tree sizes (5.0–70.0 cm DBH) using the Granier-type heat dissipation method. The results showed that, although sap flow density varied between individual trees and species, there was a significant relationship between log QT and log DBH (r2 = 0.66, P < 0.001) because of the strong dependence of sapwood area on DBH. This study confirmed the applicability of the relationship for the stand transpiration (EC) estimates even in a multi-specific broadleaved forest with a wide variation in DBH. Our results also revealed that selecting the sample trees in descending order of DBH effectively reduced potential errors in EC estimates for a specific sample size, as larger trees contribute more to EC. This information should be useful for future studies investigating the transpiration of multi-specific broadleaved forests, reducing errors during the scaling-up procedure.

Dominant controls of transpiration along a hillslope transect inferred from ecohydrological measurements and thermodynamic limits

Abstract. We combine ecohydrological observations of sap flow and soil moisture with thermodynamically constrained estimates of atmospheric evaporative demand to infer the dominant controls of forest transpiration in complex terrain. We hypothesize that daily variations in transpiration are dominated by variations in atmospheric demand, while site-specific controls, including limiting soil moisture, act on longer timescales. We test these hypotheses with data of a measurement setup consisting of five sites along a valley cross section in Luxembourg. Both hillslopes are covered by forest dominated by European beech (Fagus sylvatica L.). Two independent measurements are used to estimate stand transpiration: (i) sap flow and (ii) diurnal variations in soil moisture, which were used to estimate the daily root water uptake. Atmospheric evaporative demand is estimated through thermodynamically constrained evaporation, which only requires absorbed solar radiation and temperature as input data without any empirical parameters. Both transpiration estimates are strongly correlated to atmospheric demand at the daily timescale. We find that neither vapor pressure deficit nor wind speed add to the explained variance, supporting the idea that they are dependent variables on land–atmosphere exchange and the surface energy budget. Estimated stand transpiration was in a similar range at the north-facing and the south-facing hillslopes despite the different aspect and the largely different stand composition. We identified an inverse relationship between sap flux density and the site-average sapwood area per tree as estimated by the site forest inventories. This suggests that tree hydraulic adaptation can compensate for heterogeneous conditions. However, during dry summer periods differences in topographic factors and stand structure can cause spatially variable transpiration rates. We conclude that absorption of solar radiation at the surface forms a dominant control for turbulent heat and mass exchange and that vegetation across the hillslope adjusts to this constraint at the tree and stand level. These findings should help to improve the description of land-surface–atmosphere exchange at regional scales.

Trait Acclimation Mitigates Mortality Risks of Tropical Canopy Trees under Global Warming.

There is a heated debate about the effect of global change on tropical forests. Many scientists predict large-scale tree mortality while others point to mitigating roles of CO2 fertilization and – the notoriously unknown – physiological trait acclimation of trees. In this opinion article we provided a first quantification of the potential of trait acclimation to mitigate the negative effects of warming on tropical canopy tree growth and survival. We applied a physiological tree growth model that incorporates trait acclimation through an optimization approach. Our model estimated the maximum effect of acclimation when trees optimize traits that are strongly plastic on a week to annual time scale (leaf photosynthetic capacity, total leaf area, stem sapwood area) to maximize carbon gain. We simulated tree carbon gain for temperatures (25–35°C) and ambient CO2 concentrations (390–800 ppm) predicted for the 21st century. Full trait acclimation increased simulated carbon gain by up to 10–20% and the maximum tolerated temperature by up to 2°C, thus reducing risks of tree death under predicted warming. Functional trait acclimation may thus increase the resilience of tropical trees to warming, but cannot prevent tree death during extremely hot and dry years at current CO2 levels. We call for incorporating trait acclimation in field and experimental studies of plant functional traits, and in models that predict responses of tropical forests to climate change.

Water use of a multigenotype poplar short-rotation coppice from tree to stand scale.

Short‐rotation coppice (SRC) has great potential for supplying biomass‐based heat and energy, but little is known about SRC's ecological footprint, particularly its impact on the water cycle. To this end, we quantified the water use of a commercial scale poplar (Populus) SRC plantation in East Flanders (Belgium) at tree and stand level, focusing primarily on the transpiration component. First, we used the AquaCrop model and eddy covariance flux data to analyse the different components of the stand‐level water balance for one entire growing season. Transpiration represented 59% of evapotranspiration (ET) at stand scale over the whole year. Measured ET and modelled ET were lower as compared to the ET of reference grassland, suggesting that the SRC only used a limited amount of water. Secondly, we compared leaf area scaled and sapwood area scaled sap flow (F s) measurements on individual plants vs. stand scale eddy covariance flux data during a 39‐day intensive field campaign in late summer 2011. Daily stem diameter variation (∆D) was monitored simultaneously with F s to understand water use strategies for three poplar genotypes. Canopy transpiration based on sapwood area or leaf area scaling was 43.5 and 50.3 mm, respectively, and accounted for 74%, respectively, 86%, of total ecosystem ET measured during the intensive field campaign. Besides differences in growth, the significant intergenotypic differences in daily ∆D (due to stem shrinkage and swelling) suggested different water use strategies among the three genotypes which were confirmed by the sap flow measurements. Future studies on the prediction of SRC water use, or efforts to enhance the biomass yield of SRC genotypes, should consider intergenotypic differences in transpiration water losses at tree level as well as the SRC water balance at stand level.

Predictive models for radial sap flux variation in coniferous, diffuse-porous and ring-porous temperate trees.

Accurately scaling sap flux observations to tree or stand levels requires accounting for variation in sap flux between wood types and by depth into the tree. However, existing models for radial variation in axial sap flux are rarely used because they are difficult to implement, there is uncertainty about their predictive ability and calibration measurements are often unavailable. Here we compare different models with a diverse sap flux data set to test the hypotheses that radial profiles differ by wood type and tree size. We show that radial variation in sap flux is dependent on wood type but independent of tree size for a range of temperate trees. The best-fitting model predicted out-of-sample sap flux observations and independent estimates of sapwood area with small errors, suggesting robustness in the new settings. We develop a method for predicting whole-tree water use with this model and include computer code for simple implementation in other studies.

Comparison of transpiration between different aged black locust (Robinia pseudoacacia) trees on the semi-arid Loess Plateau, China

Black locust (Robinia pseudoacacia) is widely planted throughout the semi-arid Loess Plateau of China. The spatial distribution of this species at different ages is highly heterogeneous due to restoration and management practices. In this study, we aimed to compare the transpiration levels between different aged black locusts at the tree and stand scales, clarifying the physiological status of this species with different ages. Black locust trees with two representative age classes (12 and 28 years) were selected in the Yangjuangou catchment on the semi-arid Loess Plateau. Sap flux density (F d ) and environmental variables (solar radiation, air temperature, relative humidity and soil water content) were simultaneously monitored throughout the growing season of 2014. Tree transpiration (E t ) was the product of F d and sapwood area (A S ), and stand transpiration (E c ) was calculated basing on the stand sap flux density (J s ) and stand total sapwood area (A ST ). Stomatal conductance (g s ) was measured in a controlled environment and hydraulic conductance was estimated using the relationship between transpiration rate and vapor pressure deficit (VPD). Our results showed that E t and E c were higher in the 28-year-old stand than in the 12-year-old stand. The g s and hydraulic conductance of 28-year-old trees were also higher than those of 12-year-old trees, and the two parameters were thus the causes of variations in transpiration between different age classes. After rainfall, mean F d increased by 9% in 28-year-old trees and by 5% in 12-year-old trees. This study thus suggests that stand age should be considered for estimating transpiration at the catchment and region scales in this area. These results provide ecophysiological evidences that the older black locust trees had more active physiological status than the younger ones in this area. These findings also provide basic information for the management of water resources and forests on the semi-arid Loess Plateau.

Contribution of sapwood traits to uncertainty in conifer sap flow as estimated with the heat-ratio method

Abstract Inferring whole-tree sap flow rates (Q) with thermometric sap flow sensors requires specification of physiological and structural attributes of trees. Using sap temperature measurements to estimate Q with the heat-ratio method (HRM) requires quantification of the water content (mc), basic density (ρb), and depth (Rs) of sapwood. Values of mc and ρb serve to estimate sapwood thermal diffusivity (k), a necessary variable in the calculation of heat-pulse velocity (Vh) that is often set to a nominal value (k_nom); mc and ρb are also used to convert Vh to sap velocity (Vs). The sapwood area across which Vs is integrated is often estimated on the basis of Rs. Because mc and ρb are correlated and influence Q through estimation of k and the conversion of Vh to Vs, we sought to quantify the potential error introduced when Q is calculated with k_nom rather than with k as estimated from measurements of mc and ρb in five coniferous species. We also examined how variation in mc, ρb, and Rs across sampling scales may contribute to uncertainty in estimated Q. Across the observed range of mc and ρb, the two traits contributed to a net decline in the process of estimating Vs from Vh (with k_nom). This suggests that the use of k_nom rather than a calculated k may result in overestimation of Q when mc and ρb co-vary as they did in our study. Variability in mc and ρb across sampling scales could induce errors greater than 10% in Vs (and hence Q), while within- and among-tree variability in Rs could impart even greater errors (up to 130%). We propose that this uncertainty be represented in the expression of error in whole-tree sap flow estimates and in statistical analyses involving those estimates.

Predicting long‐term streamflow variability in moist eucalypt forests using forest growth models and a sapwood area index

AbstractA major challenge in surface hydrology involves predicting streamflow in ungauged catchments with heterogeneous vegetation and spatiotemporally varying evapotranspiration (ET) rates. We present a top‐down approach for quantifying the influence of broad‐scale changes in forest structure on ET and hence streamflow. Across three catchments between 18 and 100 km2 in size and with regenerating Eucalyptus regnans and E. delegatensis forest, we demonstrate how variation in ET can be mapped in space and over time using LiDAR data and commonly available forest inventory data. The model scales plot‐level sapwood area (SA) to the catchment‐level using basal area (BA) and tree stocking density (N) estimates in forest growth models. The SA estimates over a 69 year regeneration period are used in a relationship between SA and vegetation induced streamflow loss (L) to predict annual streamflow (Q) with annual rainfall (P) estimates. Without calibrating P, BA, N, SA, and L to Q data, we predict annual Q with R2 between 0.68 and 0.75 and Nash Sutcliffe efficiency (NSE) between 0.44 and 0.48. To remove bias, the model was extended to allow for runoff carry‐over into the following year as well as minor correction to rainfall bias, which produced R2 values between 0.72 and 0.79, and NSE between 0.70 and 0.79. The model under‐predicts streamflow during drought periods as it lacks representation of ecohydrological processes that reduce L with either reduced growth rates or rainfall interception during drought. Refining the relationship between sapwood thickness and forest inventory variables is likely to further improve results.

Ecosystem warming increases sap flow rates of northern red oak trees

AbstractOver the next century, air temperature increases up to 5°C are projected for the northeastern United States. As evapotranspiration strongly influences water loss from terrestrial ecosystems, the ecophysiological response of trees to warming will have important consequences for forest water budgets. We measured growing season sap flow rates in mature northern red oak (Quercus rubra L.) trees in a combined air (up to 5.5°C above ambient) and soil (up to 1.85°C above ambient at 6‐cm depth) warming experiment at Harvard Forest, Massachusetts, United States. Through principal components analysis, we found air and soil temperatures explained the largest amount of variance in environmental variables associated with rates of sap flow, with relative humidity, photosynthetically active radiation and vapor pressure deficit having significant, but smaller, effects. On average, each 1°C increase in temperature increased sap flow rates by approximately 1100 kg H2O m−2 sapwood area day−1 throughout the growing season and by 1200 kg H2O m−2 sapwood area day−1 during the early growing season. Reductions in the number of cold winter days correlated positively with increased sap flow during the early growing season (a decrease in 100 heating‐degree days was associated with a sapflow increase in approximately 5 kg H2O m−2 sapwood area day−1). Soil moisture declined with increased treatment temperatures, and each soil moisture percentage decrease resulted in a decrease in sap flow of approximately 360 kg H2O m−2 sapwood area day−1. At night, soil moisture correlated positively with sap flow. These results demonstrate that warmer air and soil temperatures in winter and throughout the growing season lead to increased sap flow rates, which could affect forest water budgets throughout the year.

Crown allometry and application of the pipe model theory to white spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx.) in the western boreal forest of Canada

White spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx.) from unmanaged stands in the boreal forest of Alberta, Canada, were examined for two of the main structural assumptions in the process-based model CROBAS: (i) a constant allometric relationship between foliage mass and crown length and (ii) a constant relationship between foliage mass and sapwood area. We evaluated these relationships at both at the whole-crown and within-crown levels. Results indicated that for both species, a constant allometric relationship between foliage mass and crown length was maintained at the whole-crown level over a period exceeding the peak mean annual increment of each species. Within the crowns of spruce, foliage mass accumulated faster near the tree apex as total crown length increased. For aspen, the increase in foliage mass per unit crown length for any section within the crown showed greater similarity to the relationship observed at the whole-crown level. The assumption of a constant relationship between foliage mass and sapwood area at the crown base generally held for spruce but showed considerable variation for any given diameter class. For aspen, this assumption did not appear to be appropriate. For both species, there was more foliage mass per unit sapwood area with increasing height from the ground for nearly all tree size classes. This latter finding was in conflict with the pipe model theory but could not be explained by the hydraulic theory of crown architecture, which predicts a decrease in the ratio of foliage mass to sapwood area with increasing path length.

Differences in sap flux‐based stand transpiration between upper and lower slope positions in a Japanese cypress plantation watershed

AbstractThis study investigated the difference in stand transpiration (E) between upper (UP) and lower (LP) slope plots of a Japanese cypress (Chamaecyparis obtusa) watershed to obtain catchment‐scale E estimates. Sap flux‐based stand‐scale E estimates were conducted on the UP and LP, which had contrasting stand structures (diameter at breast height and tree height) despite being the same age. The plant area index was similar in the UP and LP, while the total sapwood area (AS_stand) and the mean sap flux density (JS) in the UP were 23% and ~30% lower, respectively, than those of the LP. Stand‐scale E is the product of the AS_stand and JS in a stand. As a result, E in the UP was ~50% lower than that in the LP. This ratio was relatively constant throughout the year, which was supported by a similar decline in E, which resulted from soil water decline in the UP and LP. Canopy conductance (GC) in the UP was ~50% smaller than that of the LP. In contrast to previous studies that showed a consistent JS along a slope, the differences in E between the UP and LP were caused by differences in AS_stand and JS, probably because the UP exhibited a lower GC per unit leaf area than the LP. Additionally, evapotranspiration (ET), the sum of sap flux‐scaled E plus rainfall interception, was 8–14% lower than the catchment water balance ET (precipitation minus runoff), which suggests the feasibility of calculating sap flux‐scaled E for the two slope positions. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Biophysical controls on canopy transpiration in a black locust (Robinia pseudoacacia) plantation on the semi‐arid Loess Plateau, China

AbstractIn the semi‐arid Loess Plateau of China, black locust (Robinia pseudoacacia) was widely planted for soil conservation and afforestation purposes during the past three decades. Investigating biophysical controls on canopy transpiration (Ec) of the plantations is essential to understanding the effects of afforestation on watershed hydrology and regional water resources. In addition to monitoring of micrometeorology and soil water content, sap flux densities (Fd) of six representative trees in a 27‐year stand were continuously measured using thermal dissipation probes during the growing seasons in 2013 and 2014. Ec was derived by multiplying stand total sapwood area (AST) with Fd. The daily mean Ec in the growing season was 0.14 and 0.23 mm day−1 in 2013 and 2014, respectively. The responses of daily Ec to Rs and vapour pressure deficit were explained with an exponential threshold model. The variability of monthly Ec was mainly explained by leaf area index (LAI) (R2 = 0.92). The inter‐annual variability of Ec was influenced by LAI that fluctuated dramatically during 2013 and 2014. We found that the status of soil water content at the beginning of the growing season had large impacts on LAI and Ec during the growing season. Contrary to common beliefs that the plantation uses a large amount of water, we found that the black locust plantation had rather low transpiration rates (5.3% of precipitation and 4.6% of ET0). This study suggests that the black locust plantation has adapted to local soil water condition by reducing transpiration, and the major water loss from the plantation was not transpiration. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Models of the Vertical Distribution of Sapwood Area for Lodgepole Pine and Western Hemlock in Western Canada

Models of the Vertical Distribution of Sapwood Area for Lodgepole Pine and Western Hemlock in Western Canada

Water limitations on forest carbon cycling and conifer traits along a steep climatic gradient in the Cascade Mountains, Oregon

Abstract. Severe droughts occurred in the western United States during recent decades, and continued human greenhouse gas emissions are expected to exacerbate warming and drying in this region. We investigated the role of water availability in shaping forest carbon cycling and morphological traits in the eastern Cascade Mountains, Oregon, focusing on the transition from low-elevation, dry western juniper (Juniperus occidentalis) woodlands to higher-elevation, wetter ponderosa pine (Pinus ponderosa) and grand fir (Abies grandis) forests. We examined 12 sites in mature forests that spanned a 1300 mm yr−1 gradient in mean growing-year climate moisture index (CMIgy ), computed annually (1964 to 2013) as monthly precipitation minus reference evapotranspiration and summed October to September. Maximum leaf area, annual aboveground productivity, and aboveground live tree biomass increased with CMIgy (r2 = 0.67–0.88, P &lt; 0.05), approximately 50-, 30-, and 10-fold along this drier to wetter gradient. Interannual fluctuations in CMI affected the annual radial growth of 91 % of juniper, 51 % of pine, and 12 % of fir individuals from 1964 to 2013. The magnitude of the site-average growth–CMI correlations decreased with increased CMIgy (r2 = 0.53, P &lt; 0.05). All three species, particularly fir, experienced pronounced declines in radial growth from c. 1985 to 1994, coinciding with a period of sustained below-average CMIgy and extensive insect outbreak. Traits of stress-tolerant juniper included short stature, high wood density for cavitation resistance, and high investment in water transport relative to leaf area. Species occupying wetter areas invested more resources in height growth in response to competition for light relative to investment in hydraulic architecture. Consequently, maximum tree height, leaf area : sapwood area ratio, and stem wood density were all correlated with CMIgy . The tight coupling of forest carbon cycling and species traits with water availability suggests that warmer and drier conditions projected for the 21st century could have significant biogeochemical, ecological, and social consequences in the Pacific Northwest.

Changes in canopy transpiration of Japanese cypress and Japanese cedar plantations because of selective thinning

AbstractCanopy transpiration (Estand) is a main component of forest water cycle, and forest management including thinning affects canopy transpiration Estand, yet few studies have examined the changes in Estand. In this study, we investigated the changes in Estand after the thinning of Chamaecyparis obtusa and Cryptomeria japonica stands by 50% of their stems. The Estand was estimated using sap flow measurements by Granier‐type thermal dissipation probes. The mean stand sap flow density (JS) after thinning was as high as that before thinning in both plots. Under the same conditions of microclimate, Estand after thinning decreased by 44.0 and 21.2% for the Ch. obtusa plot and the Cr. japonica plot, respectively. The thinning reduced the sapwood area by 44.5% in the Ch. obtusa plot and 34.2% in the Cr. japonica plot. The decreases in Estand were similar to the decline in sapwood area, which indicates that the primary cause of the changes in Estand was the reduction of sapwood area. The reference canopy conductance (Gcref) after thinning was 52.7% and 75.3% lower for Ch. obtusa and Cr. japonica, respectively, whereas stomatal sensitivity to the vapour pressure deficit was similar in both periods. Thus, the changes in canopy conductance after thinning were associated with changes in Gcref, resulting in a decrease of Estand. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Canopy transpiration in two Japanese cypress forests with contrasting structures

Canopy transpiration (EC) varies among forest stands with different structures. To evaluate different EC for Japanese cypress we observed EC for 5 months, by use of the sap flow technique, in two adjacent stands of different ages with contrasting structures. Mean diameter at breast height was 13.5 and 44.6 cm and stem density was 2100 and 350 trees ha−1 for the Sakuta and Hiwada plots, respectively. Mean EC measured was 1.3 mm day−1 for the Sakuta plot and 0.7 mm day−1 for the Hiwada plot (or 53 % of that for the Sakuta plot). This difference between EC was caused by differences between both mean stand sap flux density (JS) and stand sapwood area (AS__stand): JS for the Hiwada plot was 69 % of that for the Sakuta plot and AS_stand for the Hiwada plot was 75 % of that for the Sakuta plot. The difference between JS was primarily caused by different reference JS for given meteorological conditions, not by the different response of JS to meteorological conditions. Previous studies of coniferous plantation forests in Japan reported that differences between EC among stands with different structures were mainly caused by different AS_stand. This study revealed this is not always true, and that differences between JS should also be considered when predicting differences between EC among stands with different structures.

MODELOS PREDICTIVOS DE BIOMASA AÉREA DE&lt;i&gt; Eucalyptus grandis&lt;/i&gt; PARA EL NORESTE DE ARGENTINA

http://dx.doi.org/10.5902/1980509819611Diferentes intereses industriales, energéticos y ambientales han motivado el análisis de las distintas posibilidades de aprovechamiento de la biomasa forestal, este tema está adquiriendo un creciente protagonismo, por lo que la cuantificación de la biomasa aérea de estos sistemas forestales constituye un primer paso fundamental e ineludible. El objetivo de este trabajo fue desarrollar modelos que permitan estimar la biomasa de los diferentes compartimentos aéreos de Eucalyptus grandis. Para ello se emplearon datos de 41 árboles provenientes de rodales de diferentes edades, entre 4 y 32 años, ubicados en la región NE de Argentina. Se tomaron 23 individuos ubicados en la Zona Norte y Alta de Misiones (zona 1) y 18 en el Sur de Misiones y NE de Corrientes (zona 2). Se determinó la biomasa de hojas, ramas menores a 5 cm, ramas mayores a 5 cm, total de ramas, fuste y biomasa total del árbol. Para el ajuste de modelos se tomaron diversas variables independientes, el diámetro a la altura de pecho (dap), la altura total del árbol (h), el producto (dap2*h) y la variable “dummy” (zona). Para el caso de la biomasa de ramas y de hojas, debido a que no se lograron resultados satisfactorios con el empleo de estas variables, se examinaron modelos que adicionaban índice de sitio, factor de espaciamiento, diámetro en la base de la copa verde (dbcv), altura hasta la base de la copa verde (hbcv), longitud de copa verde (lcv), el área transversal de albura en la base de copa verde (g Alb bcv) y diferentes combinaciones de estas variables. Los modelos fueron seleccionados en base al coeficiente de determinación y el error cuadrático medio. Para la biomasa de ramas menores a 5 cm, ramas mayores a 5 cm, total de ramas, fuste y total, los mejores modelos fueron los que incorporaron como variables regresoras, el diámetro a la altura de pecho, la altura total del árbol y la variable “dummy” (zona). Para la biomasa de hojas, las variables, edad, área basal y número de árboles por hectárea permitieron mejorar la estimación. Los coeficientes de determinación para los modelos de biomasa total y de fuste fueron de 0,99, para el total de ramas fue de 0,83, para ramas menores a 5 cm 0,69, para ramas mayores de 5 cm 0,53 y 0,65 para hojas. Se recomienda incrementar la base de datos a los efectos de intentar mejorar las predicciones de biomasa de hojas y ramas.