Unit Of Sapwood Area Research Articles

Summer streamflow deficits from regenerating Douglas‐fir forest in the Pacific Northwest, USA

AbstractDespite controversy about effects of plantation forestry on streamflow, streamflow response to forest plantations over multiple decades is not well understood. Analysis of 60‐year records of daily streamflow from eight paired‐basin experiments in the Pacific Northwest of the United States (Oregon) revealed that the conversion of old‐growth forest to Douglas‐fir plantations had a major effect on summer streamflow. Average daily streamflow in summer (July through September) in basins with 34‐ to 43‐year‐old plantations of Douglas‐fir was 50% lower than streamflow from reference basins with 150‐ to 500‐year‐old forests dominated by Douglas‐fir, western hemlock, and other conifers. Study plantations are comparable in terms of age class, treatments, and growth rates to managed forests in the region. Young Douglas‐fir trees, which have higher sapwood area, higher sapflow per unit of sapwood area, higher concentration of leaf area in the upper canopy, and less ability to limit transpiration, appear to have higher rates of evapotranspiration than old trees of conifer species, especially during dry summers. Reduced summer streamflow in headwater basins with forest plantations may limit aquatic habitat and exacerbate stream warming, and it may also alter water yield and timing in much larger basins. Legacies of past forest management or extensive natural disturbances may be confounded with effects of climate change on streamflow in large river basins. Continued research is needed using long‐term paired‐basin studies and process studies to determine the effects of forest management on streamflow deficits in a variety of forest types and forest management systems.

Sap flux–upscaled canopy transpiration, stomatal conductance, and water use efficiency in an old growth forest in the Great Lakes region of the United States

Combining sap flux and eddy covariance measurements provides a means to study plant stomatal conductance and the relationship between transpiration and photosynthesis. We measured sap flux using Granier‐type sensors in a northern hardwood‐dominated old growth forest in Michigan, upscaled to canopy transpiration, and calculated canopy conductance. We also measured carbon and water fluxes with the eddy covariance method and derived daytime gross primary production (GPP). The diurnal patterns of sap flux and canopy transpiration were mainly controlled by vapor pressure deficit (D) and photosynthetically active radiation (PAR). Daily sums of sap flux and canopy transpiration had exponential relationships to D that saturated at higher D and had linear relationships to PAR. Sugar maple (Acer saccharum) and yellow birch (Betula alleghaniesis) had higher sap flux per unit of sapwood area than eastern hemlock (Tsuga canadensis), while sugar maple and hemlock had higher canopy transpiration per unit of leaf area than yellow birch. Sugar maple dominated canopy transpiration per ground area. Canopy transpiration averaged 1.57 mm d−1, accounting for 65% of total evapotranspiration in the growing season. Canopy conductance was controlled by both D and PAR, but the day‐to‐day variation in canopy conductance mainly followed a negatively logarithmic relationship with D. By removing the influences of PAR, half‐hourly canopy conductance was also negatively logarithmically correlated with D. Water use efficiency (WUE) had a strong exponential relationship with D on a daily basis and approached a minimum of 4.4 mg g−1. WUE provides an alternative to estimate GPP from measurements of sap flux.

Mechanisms contributing to seasonal homeostasis of minimum leaf water potential and predawn disequilibrium between soil and plant water potential in Neotropical savanna trees

Seasonal regulation of leaf water potential (ΨL) was studied in eight dominant woody savanna species growing in Brazilian savanna (Cerrado) sites that experience a 5-month dry season. Despite marked seasonal variation in precipitation and air saturation deficit (D), seasonal differences in midday minimum ΨL were small in all of the study species. Water use and water status were regulated by a combination of plant physiological and architectural traits. Despite a nearly 3-fold increase in mean D between the wet and dry season, a sharp decline in stomatal conductance with increasing D constrained seasonal variation in minimum ΨL by limiting transpiration per unit leaf area (E). The leaf surface area per unit of sapwood area (LA/SA), a plant architectural index of potential constraints on water supply in relation to transpirational demand, was about 1.5–8 times greater in the wet season compared to the dry season for most of the species. The changes in LA/SA from the wet to the dry season resulted from a reduction in total leaf surface area per plant, which maintained or increased total leaf-specific hydraulic conductance (Gt) during the dry season. The isohydric behavior of Cerrado tree species with respect to minimum ΨL throughout the year thus was the result of strong stomatal control of evaporative losses, a decrease in total leaf surface area per tree during the dry season, an increase in total leaf-specific hydraulic conductance, and a tight coordination between gas and liquid phase conductance. In contrast with the seasonal isohydric behavior of minimum ΨL, predawn ΨL in all species was substantially lower during the dry season compared to the wet season. During the dry season, predawn ΨL was more negative than bulk soil Ψ estimated by extrapolating plots of E versus ΨL to E=0. Predawn disequilibrium between plant and soil Ψ was attributable largely to nocturnal transpiration, which ranged from 15 to 22% of the daily total. High nocturnal water loss may also have prevented internal water storage compartments from being completely refilled at night before the onset of transpiration early in the day.

Axial Water Flux Dynamics in Small Diameter Roots of a Fast Growing Tropical Tree

Field measurements of water flux in small diameter roots are important to the study of whole plant water transport systems. Miniature sap flow gauges were used to capture high resolution water flux patterns in small roots of 2 – 5 mm diameter and simultaneously in the canopy branches of a Eucalyptus saligna tree growing in Hawaii. The axial transport flux rates were then correlated with anatomical measurements to describe the internal hydraulic capacity of the tree. The daily patterns of water flux showed a strong coupling between the canopy and root systems and both systems were tightly synchronized with rapid fluctuations in photosynthetic photon flux density, vapour pressure deficit, and wind speed. When flow rates were normalized by the total vessel lumen area, branches had daily totals equivalent to the surface roots. Daily flows of water through surface roots were consistently 30% greater than through deep roots. Results of an experiment where a portion of the canopy was removed showed the decrease in water flux for all roots was in nearly direct proportion to the decrease in leaf area. The root anatomical measurements suggested a high capacity axial root water transport system with roots containing a smaller number of vessels per unit of sapwood area than branches but with vessel diameters twice that of the branches. However, relative conductivity values of roots and branches were similar and comparable to some of the highest values reported. Overall, the results suggested a highly efficient axial water transport system that would help to maintain a favorable plant water status for maximal stomatal opening.

Effects of Fertilization and Thinning on Heartwood Area, Sapwood Area and Growth in Scots Pine

In a fertilization and thinning experiment on Pinus sylvestris L. situated in northern Sweden, the effects on the amount of heartwood and sapwood were examined 12 yrs after treatment. On stem discs taken from the stump up to 75% of tree height, age, diameter, heartwood diameter and growth rings included in the heartwood were measured. Increases in heartwood area following fertilization and thinning were not statistically significant, whereas sapwood area was significantly increased by both fertilization and thinning. There was a significant positive interaction effect of fertilization and thinning on diameter under bark, sapwood area and relative heartwood area. The number of growth rings included in the heartwood at breast height was not affected by treatments. Thinned trees showed a higher needle biomass per unit of sapwood area at breast height. The results show that the possibility of affecting the amount of heartwood in individual trees by thinning and fertilization is limited. The results are discussed in relation to the pipe - model theory and the regulation of sapwood and heartwood.

Transpiration of natural rain forest and its dependence on climatic factors

Sap flow was measured on several species from the tropical rain forest in French Guiana during two successive years over the dry season. On bright days, sap flow densities (i.e. sap flow per unit of sapwood area) exhibited high variations from one species to another. Higher rates (3 to 4 kg dim −2 h −1) were observed on late stage forest species like Dicorynia guianensis, Eperua falcata or E. grandifolia, and lower rates on Vouacapoua americana and Carapa procera (1.0 to 1.5 kg dm −2 h −1). Calculated stand sap flow ( F) was closely dependant on air vapour pressure deficit and less correlated to global radiation. A simple model of canopy conductance variations and hence of stand transpiration was derived from these measurements. Sap flow was linearly related to Penman Evapotranspiration (PET), the ratio F/PET being close to 0.75 under dry canopy conditions, as previously reported by Shuttleworth et al. (1984) in Central Amazon.

Estimation of foliage area in dense Montana lodgepole pine stands

Six stands of lodgepole pine, Pinuscontorta ssp. latifolia (Engelm.) Critchfield, in Montana were sampled to evaluate sapwood area (at 1.37 m and the crown base), basal area (at 1.37 m), tree height, and crown length as predictors of foliage area. Densities of the six stands ranged from 2900 to 17 800 stems/ha. This density range was picked to determine how stand density affects the ratio of foliage area to basal sapwood area. Regression estimates of foliage area using basal area and sapwood area at 1.37 m and the crown base were equally good. Within the sampled range of stand densities, differences in the foliage area to sapwood area ratio were not significant. The amount of foliage area served per unit of sapwood area (at 1.37 m) averaged 0.25 m2/cm2 for all 54 trees sampled. This value of foliage area per unit of sapwood area in dense stands was smaller than most other published values.

Tree vigor and stand growth of Douglas-fir as influenced by laminated root rot

Total stand sapwood basal area, a measure of competing canopy leaf area, was reduced 30% by laminated root rot induced by Phellinusweirii (Murr.) Gilb. in a heavily infected 40-year-old coastal stand of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) compared with that of a similar uninfected stand. Annual basal area increment per unit of sapwood area, an index of tree vigor, was expected to increase in uninfected trees in the infected stand as surrounding trees died from root rot; vigor of the uninfected trees did increase by an average of 30%, offsetting the reduction in canopy leaf area. This increase, although less than might be expected in an evenly spaced thinned stand, was sufficient to maintain stand basal area growth at levels similar to those of unthinned forests. These findings indicate that increased growth by residual trees must be taken into account when the impact of disease-induced mortality on stand production is assessed.