Sapwood Area Research Articles

Responses of mature roadside trees to root severance treatments

Conflicts between trees and infrastructure installation or repair occur frequently in the urban environment and may result in damage to or complete removal of tree roots. We monitored the responses of trees to linear root cutting and examined the effects of the presence of a road within tree root zones. Mature Quercus virginiana Mill trees (n = 31) were exposed to three root pruning treatments (plus a control) consisting of a trench on one side of the tree, offset by a distance as a multiple of trunk diameter (3x, 6x and 12x). Roots were severed manually, and their diameters were measured at the cut point to estimate a total cross-sectional area of severed roots. The total severed root cross-sectional area was subsequently expressed as a ratio of whole trunk cross-sectional areas (termed Ar(BH)), as well as trunk conductive sapwood areas (termed As(BH)) at breast height (1.4 m). The shortest horizontal distance between the tree bases and the edge of a nearby road was also recorded and included in statistical analyses as a continuous variable. Linear root cutting reduced shoot extension and leaf area by as much 146.13 mm (p < 0.01) and 2.92 cm2 (p < 0.001) respectively, one growing season after root severance. Trees nearer the road had significantly reduced trunk diameter growth (p < 0.05), independent of root severance effects, i.e. 12x, 6x and 3x treatments. Pre-dawn leaf water potential was negatively affected for all treatments (p < 0.05) and the symptoms of water stress persisted in the 3x treatment for 440 days. Ar(BH) and As(BH) ratios were regressed against physiological (predawn leaf water potential (Ψ), stomatal conductance (gs), leaf temperature (T) and two chlorophyll fluorescence variables (Fv/Fm and Fv/Fo)) and growth (trunk diameter, shoot extension and leaf area) responses. Ar(BH) was a significant predictor of Ψ, Fv/Fm, Fv/Fo, shoot extension and leaf area responses after one growing season, although model strength varied (R2 = 0.75, 0.14, 0.16, 0.18, 0.24 respectively). To avoid sustained water stress symptoms, linear root cutting on Q. virginiana should not be undertaken closer to trees than six times DBH, equating to ≈ 25% root system loss.

Air cooling by tree transpiration: A case study of Olea europaea, Citrus sinensis and Pinus pinea in Mediterranean town

Transpiration and surface temperature of Olea, Citrus and Pinus trees in an urban garden in southern Italy were studied from May until August, the hottest period of the year in the investigated area. Transpiration was measured by sap flow heat dissipation method at 10-min scale, while the surface-air temperature difference was estimated by energy balance approach. The radial trend of sap flow density at tree scale was modelled as a function of the sapwood area, while the upscaling to garden level was performed using the quantile method integrated by trunk diameter classification. The results at hourly and daily time scales showed that Olea had the highest transpiration followed by Citrus and Pinus trees. The cooling effect resulted dependent on the species showing Citrus as the most efficient species among the investigated ones. The study might contribute to a better understanding of cooling effect due to tree transpiration under rainfed conditions.

Spatio-temporal transpiration patterns reflect vegetation structure in complex upland terrain

Topography exerts control on eco-hydrologic processes via alteration of energy inputs due to slope angle and orientation. Further, water availability varies with drainage position in response to topographic water redistribution and the catena effect on soil depth and thus soil water storage capacity. Our understanding of the spatio-temporal dynamics and drivers of transpiration patterns in complex terrain is still limited by lacking knowledge of how systematic interactions of energy and moisture patterns shape ecosystem state and water fluxes and adaptation of the vegetation to these patterns. To untangle the effects of slope orientation and hillslope position on forest structure and transpiration patterns, we measured forest structure, sap flux, soil moisture, throughfall and incoming shortwave radiation along two downslope transects in a forested head water catchment in south-east Australia. Our plot locations controlled for three systematically varying drainage position levels (topographic wetness index: 5.0, 6.5 and 8.0) and two levels of energy input (aridity index: 1.2 and 1.8). Vegetation patterns were generally stronger related to drainage position than slope orientation, whereas sap velocity variations were less pronounced. However, in combination with stand sapwood area, consistent spatio-temporal transpiration patterns emerged in relation to landscape position, where slope orientation was the primary and drainage position the secondary controlling factor. On short temporal scales, radiation and vapor pressure deficit were most important in regulating transpiration rates, whereas soil water limitation only occurred on shallow soils during summer. The importance of stand structural parameters increased on longer time scales, indicating optimization of vegetation in response to the long-term hydro-climatic conditions at a given landscape position. Thus, vegetation patterns can be conceptualized as a ‘time-integrated’ predictor variable that captures large fractions of other factors contributing to transpiration patterns.

Increased streamflow in catchments affected by a forest disease epidemic.

Natural disturbances help maintain healthy forested and aquatic ecosystems. However, biotic and abiotic disturbance regimes are changing rapidly. For example, the Swiss needle cast (SNC) epidemic in the Coast Range of Oregon in the U.S. Pacific Northwest has increased in area from 53,050 to 238,705ha over the 1996-2015 period. We investigated whether the hydrologic regime (i.e., annual streamflow, runoff ratio, and magnitude and timing of peak flows and low flows) was affected by SNC in 12 catchments in western Oregon. The catchments ranged in size from 183 to 1834km2 and area affected by SNC from 0 to 90.5%. To maximize the number of catchments included in the study, we analyzed 20years of SNC aerial survey data and 15-26years of stream discharge (Q) and PRISM precipitation (P) and air temperature (Tair) data to test for trends in hydrologic variables for each catchment. As expected, we found that runoff ratios (Q/P) increased in five catchments, all with an area impacted by SNC >10%. This was likely due to the effects of SNC on the hydraulic architecture (i.e., needle retention, sapwood area, sapwood permeability) of affected trees, leading to decreased canopy interception and transpiration losses. Interestingly, two catchments with the greatest area affected by SNC showed no changes in hydrologic regime. The lack of hydrologic response could either be due to compensatory transpiration by vegetation unaffected by the disease or sub-canopy abiotic evaporation, which counteracted reductions in transpiration. This study is the first to illustrate that chronic canopy disturbance from a foliage pathogen can influence catchment scale hydrology.

Mechanisms for minimizing height‐related stomatal conductance declines in tall vines

The ability to transport water through tall stems hydraulically limits stomatal conductance (gs ), thereby constraining photosynthesis and growth. However, some plants are able to minimize this height-related decrease in gs , regardless of path length. We hypothesized that kudzu (Pueraria lobata) prevents strong declines in gs with height through appreciable structural and hydraulic compensative alterations. We observed only a 12% decline in maximum gs along 15-m-long stems and were able to model this empirical trend. Increasing resistance with transport distance was not compensated by increasing sapwood-to-leaf-area ratio. Compensating for increasing leaf area by adjusting the driving force would require water potential reaching -1.9MPa, far below the wilting point (-1.2MPa). The negative effect of stem length was compensated for by decreasing petiole hydraulic resistance and by increasing stem sapwood area and water storage, with capacitive discharge representing 8-12% of the water flux. In addition, large lateral (petiole, leaves) relative to axial hydraulic resistance helped improve water flow distribution to top leaves. These results indicate that gs of distal leaves can be similar to that of basal leaves, provided that resistance is highest in petioles, and sufficient amounts of water storage can be used to subsidize the transpiration stream.

Estimation of water use of Pinus tabulaeformis Carr. in Loess Plateau of Northwest China

Abstract Tree transpiration plays a determining role in the water balance of forest stands and in seepage water yields from forested catchments, especially in arid and semiarid regions where climatic conditions are dry with severe water shortage, forestry development is limited by water availability. To clarify the response of water use to climatic conditions, sap flow was monitored by heat pulse velocity method from May to September, 2014, in a 40–year–old Pinus tabulaeformis Carr. plantation forest stands in the semiarid Loess Plateau region of Northwest China. We extrapolated the measurements of water use by individual plants to determine the area–averaged transpiration of the woodlands. The method used for the extrapolation assumes that the transpiration of a tree was proportional to its sapwood area. Stand transpiration was mainly controlled by photosynthetically active radiation and vapor pressure deficit, whereas soil moisture had more influence on monthly change in stand transpiration. The mean sap flow rates for individual P. tabulaeformis trees ranged from 9 to 54 L d−1. During the study period, the mean daily stand transpiration was 1.9 mm day−1 (maximum 2.9 and minimum 0.8 mm day−1) and total stand transpiration from May to September was 294.1 mm, representing 76% of the incoming precipitation over this period. Similar results were found when comparing transpiration estimated with sap flow measurements to the Penman–Monteith method (relative error: 16%), indicating that the scaling procedure can be used to provide reliable estimates of stand transpiration. These results suggested that P. tabulaeformis is highly effective at utilizing scarce water resources in semiarid environments.

Calibration of Granier-Type (TDP) Sap Flow Probes by a High Precision Electronic Potometer.

Thermal dissipation probe (TDP) method (Granier, 1985) is widely used to estimate tree transpiration (i.e., the water evaporated from the leaves) because it is simple to build, easy to install, and relatively inexpensive. However, the universality of the original calibration has been questioned and, in many cases, proved to be inaccurate. Thus, when the TDP is used in a new species, specific tests should be carried out. Our aim was to propose a new method for improving the accuracy of TDP on trees in the field. Small hazelnut trees (diameter at breast height 5 cm) were used for the experiment. The response of TDP sensors was compared with a reference water uptake measured with an electronic potometer system provided with a high precision liquid flow meter. We equipped three stems where we measured the sap flow density, the sapwood area (by using fuchsine), the total tree water uptake (reference), and the main meteorological parameters during summer 2018. Results confirmed that the original Granier’s calibration underestimated the effective tree transpiration (relative error about −60%). We proposed a new equation for improving the measurement accuracy within an error of about 4%. The system proposed appeared an easier solution compared to potted trees and particularly suitable for orchards, thus contributing to improve the irrigation management worldwide.

Rainfall exclusion and thinning can alter the relationships between forest functioning and drought.

Increasing drought caused by the ongoing climate change, and forest management by thinning that aims at mitigating its impact, may modify the current relationships between forest functions and drought intensity and preclude our ability to forecast future ecosystem responses. We used 15yr of data from an experimental rainfall exclusion (-27% of rainfall) combined with thinning (-30% stand basal area) to investigate differences in the drought-function relationships for each component of above-ground net primary productivity (ANPP) and stand transpiration in a Mediterranean Quercus ilex stand. Rainfall exclusion reduced stand ANPP by 10%, mainly because of lowered leaf and acorn production, whereas wood production remained unaffected. These responses were consistent with the temporal sensitivity to drought among tree organs but revealed an increased allocation to wood. Thinning increased wood and acorn production and reduced the sensitivity of standing wood biomass change to drought. Rainfall exclusion and thinning lowered the intercept of the transpiration-drought relationship as a result of the structural constraints exerted by lower leaf and sapwood area. The results suggest that historical drought-function relationships can be used to infer future drought impacts on stand ANPP but not on water fluxes. Thinning can mitigate drought effects and reduce forest sensitivity to drought.

Relationship between stem diameter and transpiration for Japanese cypress trees: Implications for estimating canopy transpiration

AbstractPrevious studies reported relationships between stem diameter at breast height (DBH) and whole‐tree transpiration (Qt) across a variety of species and locations. It might be possible to develop a relationship between DBH and Qt with smaller variations when we focused on a single species. We attempted to develop such a relationship for Japanese cypress (Chamaecyparis obtusa), which is one of the major plantation species in Japan. We collated Qt for 51 Japanese cypress trees from nine different‐sized and different‐aged stands using the sap flux method. We found a strong linear correlation between DBH and the reference value of Qt at a vapour pressure deficit of 1 kPa (R = .883). This was a consequence of a strong correlation between DBH and sapwood area (AS_tree; R = .973) and the absence of a correlation between DBH and sap flux density (R = −.043). We confirmed that using the relationship between DBH and AS_tree, while assuming typical responses of sap flux density to meteorological factors, provides reasonable Qt estimates. This study also demonstrated how the DBH–Qt relationship can be applied to estimate changes in EC with changing forest management.

Comparing the transpirational and shading effects of two contrasting urban tree species

Urban trees are getting increasing attention as a tool to mitigate urban heat island effects. A more functional and quantitative view of transpirational and shading effect, particularly the magnitude of both surface and air cooling potential can further strengthen motivations for urban tree planting. We investigated the transpirational and the surface cooling potential of two contrasting tree species in Munich, Germany: ring porous Robinia pseudoacacia L. and diffuse porous Tilia cordata Mill. Throughout the summer 2016 we monitored meteorological and edaphic variables and tree sap-flow along with the air temperature within and outside tree shade at different heights. With 30% higher leaf area index (LAI), double sap-flux density and sapwood area, T. cordata trees showed three times higher transpiration compared to the R. pseudoacacia. Consequently, T. cordata trees showed higher within canopy air cooling effect. Surface cooling (∆Tshade) were higher under the denser canopies of T. cordata compared to R. pseudoacacia for asphalt surfaces but ∆Tshade for grass surfaces were not significantly different under the canopies of two species. Linear regression indicated a decrease in grass surface temperature of 3 °C with every unit of LAI but for asphalt, the reduction in surface temperature was about 6 °C. Additionally, higher water using efficiencies of R. pseudoacacia coupled with higher soil moisture and radiation probably increased the grass evapotranspiration and subsequently showed positive relationship with the near ground air cooling. Therefore, species with higher canopy density might be preferred over asphalt surfaces but low water using species with lower canopy density could be chosen over grass surfaces.

Hydraulic Traits Emerge as Relevant Determinants of Growth Patterns in Wild Olive Genotypes Under Water Stress.

The hydraulic traits of plants, or the efficiency of water transport throughout the plant hydraulic system, could help to anticipate the impact of climate change and improve crop productivity. However, the mechanisms explaining the role of hydraulic traits on plant photosynthesis and thus, plant growth and yield, are just beginning to emerge. We conducted an experiment to identify differences in growth patterns at leaf, root and whole plant level among four wild olive genotypes and to determine whether hydraulic traits may help to explain such differences through their effect on photosynthesis. We estimated the relative growth rate (RGR), and its components, leaf gas exchange and hydraulic traits both at the leaf and whole-plant level in the olive genotypes over a full year. Photosynthetic capacity parameters were also measured. We observed different responses to water stress in the RGRs of the genotypes studied being best explained by changes in the net CO2 assimilation rate (NAR). Further, net photosynthesis, closely related to NAR, was mainly determined by hydraulic traits, both at leaf and whole-plant levels. This was mediated through the effects of hydraulic traits on stomatal conductance. We observed a decrease in leaf area: sapwood area and leaf area: root area ratios in water-stressed plants, which was more evident in the olive genotype Olea europaea subsp. guanchica (GUA8), whose RGR was less affected by water deficit than the other olive genotypes. In addition, at the leaf level, GUA8 water-stressed plants presented a better photosynthetic capacity due to a higher mesophyll conductance to CO2 and a higher foliar N. We conclude that hydraulic allometry adjustments of whole plant and leaf physiological response were well coordinated, buffering the water stress experienced by GUA8 plants. In turn, this explained their higher relative growth rates compared to the rest of the genotypes under water-stress conditions.

Relevance of wood anatomy and size of Amazonian trees in the determination and allometry of sapwood area

ABSTRACT Hydrological processes in forest stands are mainly influenced by tree species composition and morpho-physiological characteristics. Few studies on anatomical patterns that govern plant hydraulics were conducted in tropical forest ecosystems. Thus, we used dye immersion to analyze sapwood area patterns of 34 trees belonging to 26 species from a terra firme forest in the central Brazilian Amazon. The sapwood area was related with wood anatomy and tree size parameters (diameter-at-breast-height - DBH, total height and estimated whole-tree volume). Exponential allometric equations were used to model sapwood area using the biometrical variables measured. Sapwood area traits (cross-section non-uniformity and heartwood visibility) varied significantly among and within species even though all were classified as diffuse porous. DBH was strongly and non-linearly correlated with sapwood area (R 2 = 0.46, P &lt; 0.001), while no correlation was observed with vessel-lumen diameter (P = 0.94) and frequency (P = 0.58). Sapwood area and shape were also affected by the occurrence of vessel obstruction (i.e., tyloses), hollow stems and diseases. Our results suggest that sapwood area patterns and correlated variables are driven by intrinsic species characteristics, microclimate and ecological succession within the stand. We believe that individual tree sapwood characteristics have strong implications over water use, hydrological stand upsaling and biomass quantification. These characteristics should be taken into account (e.g., through a multi-point sampling approach) when estimating forest stand transpiration in a highly biodiverse ecosystem.

Drought Differentially Affects Growth, Transpiration, and Water Use Efficiency of Mixed and Monospecific Planted Forests

Drought conditions may have differential impacts on growth, transpiration, and water use efficiency (WUE) in mixed species and monospecific planted forests. Understanding the resistance (i.e., the capacity to maintain processes unchanged) of different tree species to drought, and how resistance is affected by complementary interactions within species mixtures, is particularly important in the seasonally dry tropics where projected increases in the frequency and severity of drought threaten tree planting efforts and water resources. Complementary interactions between species may lead to more resistant stands if complementarity leads to greater buffering capacity during drought. We examined growth, transpiration, and WUE of mixtures and monocultures of Terminalia amazonia (J.F. Gmel.) Exell and Dalbergia retusa Hemsl. before and during a prolonged drought using intensive measurements of tree sap flow and growth. Tree sapwood area growth was highest for T. amazonia in mixtures during normal (6.78 ± 4.08 mm2 yr−1) and drought (7.12 ± 4.85 mm2 yr−1) conditions compared to the other treatments. However, stand sapwood area growth was greatest for T. amazonia monocultures, followed by mixtures, and finally, D. retusa monocultures. There was a significant decrease in stand transpiration during drought for both mixtures and T. amazonia monocultures, while Dalbergia retusa monocultures were most water use efficient at both the tree and stand level. Treatments showed different levels of resistance to drought, with D. retusa monocultures being the most resistant, with non-significant changes of growth and transpiration before and during drought. Combining species with complementary traits and avoiding combinations where one species dominates the other, may maximize complementary interactions and reduce competitive interactions, leading to greater resistance to drought conditions.

Adjustments and coordination of hydraulic, leaf and stem traits along a water availability gradient.

Trait variability in space and time allows plants to adjust to changing environmental conditions. However, we know little about how this variability is distributed and coordinated at different organizational levels. For six dominant tree species in northeastern Spain (three Fagaceae and three Pinaceae) we quantified the inter- and intraspecific variability of a set of traits along a water availability gradient. We measured leaf mass per area (LMA), leaf nitrogen (N) concentration, carbon isotope composition in leaves (δ13 C), stem wood density, the Huber value (Hv, the ratio of cross-sectional sapwood area to leaf area), sapwood-specific and leaf-specific stem hydraulic conductivity, vulnerability to xylem embolism (P50 ) and the turgor loss point (Ptlp ). Differences between families explained the largest amount of variability for most traits, although intraspecific variability was also relevant. Species occupying wetter sites showed higher N, P50 and Ptlp , and lower LMA, δ13 C and Hv. However, when trait relationships with water availability were assessed within species they held only for Hv and Ptlp . Overall, our results indicate that intraspecific adjustments along the water availability gradient relied primarily on changes in resource allocation between sapwood and leaf area and in leaf water relations.

Specific responses of sap flux and leaf functional traits to simulated canopy and understory nitrogen additions in a deciduous broadleaf forest.

To investigate the effects of atmospheric nitrogen (N) deposition on water use characteristics and leaf traits of trees, we performed canopy (C50) and understory (U50) N additions as NH4NO3 of 50 kg N ha-1 year-1 in a deciduous broadleaf forest of central China. We measured xylem sap flux, crown area:sapwood area ratio (Ca:As), specific leaf area (SLA), mass-based leaf nitrogen content (Nmass) and leaf carbon isotope ratio (δ13C) of Liquidambar formosana Hance, Quercus acutissima Carruth. and Quercus variabilis Blume. Functional traits under different N addition treatments and their responses among tree species were compared and the relationship between xylem sap flux and leaf functional traits under N additions were explored. Results showed that under U50 sap-flux density of xylem significantly decreased for three tree species. But the effect of C50 on sap flux was species-specific. The decrease of sap-flux density with N additions might be caused by the increased Ca/As. δ13C remained constant among different N addition treatments. The responses of SLA and Nmass to N additions were species- and N addition approaches-specific. The correlation of xylem sap flux with leaf traits was not found. Our findings indicate that the effects of canopy N addition on xylem sap flux and leaf functional traits were species-specific and it is necessary to employ canopy N addition for exploring the real responses of forest ecosystems to climate changes in the future researches.

The effects of root pruning on growth and physiology of two Acer species in New Zealand

Trees in the urban environment are affected by anthropogenic activities that have the potential to negatively affect tree function, health, and growth. The provision and maintenance of new underground utilities, footpaths, and street furniture all have the potential to result in conflicts with tree root systems leading to root severance. Traditional investigations into the responses of trees to root severance usually involve severing roots indiscriminately in one or more trenches, although root loss may not be fully quantified for individual trees. In the urban environment, root zone alterations may be localised and involve more discriminate methods, and practitioners must rely on experience and often anecdotal information when making decisions about root pruning. In this study, we investigate the suitability of allometric modelling as a tool to quantify root removal treatments. Two species of Acer were exposed to four different root severance treatments (trenching on one, two, three or four sides plus control). Fragments of the severed roots of all trees were excised and their diameters measured at the point of severance and used to estimate root cross-sectional area. Total root cross-sectional areas for each tree were expressed as a ratio of trunk cross-sectional areas at ground level (Ar(GL)) and at 1.4 m (Ar(BH)) as well as conductive sapwood areas in the trunk at each height (As(GL) and As(BH)). Ar and As ratios were used to explain differences in physiology (stomatal conductance and dark-adapted chlorophyll fluorescence) and growth (trunk diameter, shoot growth and specific leaf area) responses using linear regression models. Increasing root removal intensity (trenching treatments) revealed significant differences between treatment trees and control for stomatal conductance in both species (p ≤ 0.02), as well as growth responses (p <0.05). Ar(BH) was a significant predictor of stomatal conductance (p < 0.05), trunk diameter growth (p < 0.05), specific leaf area (p < 0.001) and shoot growth (p < 0.01); although model strength varied (R2 = 0.56, 0.31, 0.16, and 0.03 respectively). This research takes the first steps towards developing a practical tool for practicing arborists who make day-to-day tree management decisions relating to roots and root care practices.

Top-down seasonal streamflow model with spatiotemporal forest sapwood area

Forest growth dynamics affect streamflow with changes in actual evapotranspiration (AET) during forest regeneration. Using a “top-down” model approach, we present a seasonal forest hydrology model that estimates streamflow in forested catchments containing sparse soil and climate data. Across a 1423 km2 remote study area, a rainfall interpolation procedure using available rainfall data and information on terrain was integrated into a new seasonal streamflow model, called ABCF, which uses catchment sapwood area (SA) as the emergent property that equilibrates with potential evapotranspiration (PET), and a soil storage threshold that reduces AET below PET when soil water is limiting. We produce seasonal estimates of streamflow with Nash Sutcliffe efficiencies of 0.85, 0.87, and 0.91 for three major catchments within the study area. A fundamental feature of the “top-down” model approach is the use of LiDAR data and forest inventory data to model forest structural properties that relate strongly with SA. Building on our previous work with this modelling framework, our representation of eco-hydrological properties of the forest has been refined with a more accurate procedure for estimating stand mean sapwood thickness, and hence SA, and a remotely sensed tree stocking density (N) of old-growth forests to correct the temporal evolution of N as a means to improve SA estimates. Regional consistency of model parameters shows that the “top-down” modelling framework may be used to estimate streamflow in ungauged catchments using a forest growth model. The seasonal model generalised for both water-limited and water-unlimited forest conditions has significant potential for application in water supply planning and drought security.

Transpiration in recovering mixed loblolly pine and oak stands following wildfire in the Lost Pines region of Texas

AbstractDepending on severity, wildfire alters stand biomass, tree species distribution, and age, which may modify stand transpiration (Et) and the amount of water available to other parts of the hydrologic cycle. Our objective was to determine how wildfire severity affected Et in mixed pine/oak (Pinus taeda L./Quercus stellata Wangehn., Quercus marilandica Muenchh.) stands in the Lost Pines eco‐region (Bastrop, TX, USA). Transpiration was estimated for mature pines and oaks at unburned and moderately burned sites and oak resprouts and pine saplings at a severely burned plot. On average, mature pines had 36% greater sap flux rates (Js) than mature oaks in the unburned and moderately burned stands. Under low moisture stress, regenerating pines had greater Js than resprouting oaks, but Js quickly decreased as soil moisture declined. By contrast, mature pines were unaffected by dry periods. Pines contributed most to Et at the unburned and moderate stands. Conversely, oak Et dominated the severely burned stand, contributing over 95%. Transpiration was greatest at the moderately burned stand (2.02 mm day−1), followed by the unburned (1.44 mm day−1), and the severely burned stands (0.46 mm day−1). Despite greater Js in resprouts and saplings, reductions in total sapwood area resulted in lower stand‐level daily Et at the severe site. Although severe fire decreased stand transpiration through reductions in vegetation density, individual oak resprouts appear to thrive, undeterred by high vapour pressure deficit. Without pine planting, oaks will likely dominate severely burned stands that could result in shifts to local hydrology and microclimate.

A test of tree protection zones: Responses of Quercus virginiana Mill trees to root severance treatments

A suite of best management practice documents (BMPs) providing procedures to protect trees are available around the world. An underpinning component of these texts is the provision of a tree protection zone (TPZ), the purpose of which is to define an area of ground surrounding the tree to be excluded from development activities. TPZs 12 times the trunk diameter are common in BMPs, however, the principles of the TPZ have not been extensively tested. The objective of this study was to test the suitability of TPZs by monitoring the responses of trees to different root removal treatments. Mature Quercus virginiana Mill trees (n = 18) were exposed to five root pruning treatments consisting of a circular trench around each tree. Trenches were established with radial offsets from the tree base between 3 and 15 times the trunk diameter in increments of three, plus control. Roots were severed manually, and their diameters measured to obtain a total cross-sectional area of severed roots, which were expressed as ratios of whole trunk cross-sectional areas (Ar(1)) as well as conductive sapwood areas (As(1)). Ar and As ratios were regressed against physiological (predawn leaf water potential (Ψ), stomatal conductance (gs) and chlorophyll fluorescence) and growth (trunk diameter, shoot extension and specific leaf area) responses. Ar(1) was a significant predictor of Ψ (p < 0.0001), trunk diameter growth (p ≤ 0.01), specific leaf area (p ≤ 0.001) and shoot extension (p ≤ 0.001), although model strength varied (R2 = 0.75, 0.47, 0.57, 0.58 respectively). Significant (p ≤ 0.05) differences were observed in Ψ between control trees and all treatments except 15 × . Growth responses were affected for one or more treatments between 3x and 9 × . The results reveal that a TPZ defined by 12 times the trunk diameter was insufficient to adequately avoid short-term physiological perturbations in Quercus virginiana.

Estimating conductive sapwood area in diffuse and ring porous trees with electronic resistance tomography

Accurately estimating sapwood area is essential for modelling whole-tree or stand-scale transpiration from point-flow sap-flux observations. In this study, we tested the validity of electrical resistance tomography (ERT) to locate the sapwood-heartwood (SW/HW) interface for two ring porous (Quercus nigra L. and Quercus virginiana Mill.) and one diffuse porous (Acer rubrum L.) species. Estimates derived from the ERT analyses were compared with the SW/HW interface measured following dye perfusion testing. The ERT results revealed spatial variation in electrical resistance, with higher resistivity in the inner part of the cross sections. Regression analyses showed that ERT was able to accurately account for 97% and 80% of the variation in sapwood area (calculated as R2) for Q. virginiana (n = 19) and Q. nigra (n = 7), respectively, and 56% of the variation in the diffuse porous species (n = 8). Root mean square error (RMSE) values for sapwood areas of the ring porous species were 11.12 cm2 (19%) and 25.98 cm2 (33%) for Q. virginiana and Q. nigra, respectively. Sapwood area estimates for diffuse wood carried greater error (RMSE = 33.52 cm2 (131%)). Model bias for all sapwood area estimates was negative, suggesting that ERT had a tendency to overestimate sapwood areas. Electrical resistance tomography proved to be a significant predictor of sapwood area in the three investigated species, although it was more reliable for ring porous wood. In addition to the results, a comprehensive code sequence for use with R statistical software is provided, so that other investigators may follow the same method.