Arthur Groot

Microclimate of Clear-Cut, Forest Interior, and Small Openings in Trembling Aspen Forest

Abstract Solar radiation and air temperature near the soil surface and soil temperatures were measured from 15 June to 6 September 1993 in a 100m × 150m clear-cut, an 18m × 150m east-west strip, a 9m × 150m east-west strip, a circle of 18m diameter, a circle of 9m diameter, and a closed canopy trembling aspen forest near Chapleau, Ontario. Seasonal solar radiation totals were highest in the clear-cut and decreased by 32% in the 18m strip, 43% in the 9m strip, 45% in the 18m circle, 74% in the 9m circle, and 82% in the forest. The seasonal decline of daily radiation totals was greatest in the 18m strip, 9m strip and 18m circle as the radiation regime shifted from one dominated by direct radiation at midsummer to one dominated by diffuse radiation in late summer. The seasonal average air temperature at seedling height varied by only 0.7°C among treatments, but greater temperature extremes occurred in larger canopy openings. Average maximum-minimum temperature differences were 17.1°C in the clear-cut, but these decreased to 10.1°C in the forest. Average daytime-night-time seedling height air temperature differences were twice as large in the clear-cut as they were in the forest. Differences in daytime air temperature among openings were related to differences in shortwave irradiance. Both seasonal average soil temperatures and soil temperature extremes became higher as canopy opening size increased. Differences in soil temperatures among openings were greatest early in the season, and diminished as regeneration of shrubs, herbs, and grasses developed. Consideration of the autecology of white spruce and trembling aspen suggests that the circle of 18m diameter and strip of 9m width are best suited for white spruce establishment.

Measurement of sap flow by the heat balance method: numerical analysis and application to coniferous seedlings

Abstract The heat balance method has been used successfully to measure sap flow in a number of plant species. This study was conducted to determine whether the method was applicable to coniferous seedlings, which have comparatively low rates of sap flow, and to investigate aspects of the method thought to be important at low flow rates. Flow gauges were constructed and used to measure sap flow rates in coniferous seedlings. A three-dimensional, transient, numerical model was developed to examine the effects of shortwave radiation, heat conduction along sensor leads, and transient characteristics on gauge accuracy. The model performed well and indicated that, for flow rates typical of conifers, shortwave radiation does not cause a significant error in measurement of the across-heater temperature difference ( ΔT ). When no reflective covering was used, shortwave radiation produced orientation-dependent deviation in modeled radial temperature gradients of up to 50% of the mean value. Heat conduction along thermocouple wires produced a measurement error of up to 15%, which can be minimized by using small-diameter wire. Gauge accuracy is poor at low flow rates because the convective heat flux and ΔT are small, and because the transient response of the gauge is slow. For coniferous seedlings, the method fails at low flow rates and measurements should be rejected when the convective heat flux is less than 5% of the heater power or when ΔT is small (less than 2.5°C in this study). At low flow rates, the heat storage term should be included in the heat balance.

Modeling the physical environment of tree seedlings on forest clearcuts

Abstract A soil and atmospheric boundary layer model has been developed to predict soil temperature, soil moisture, air temperature and humidity on forest clearcuts. The model comprises a numerical solution to the one-dimensional transfer equations for energy and water in the air and soil near a surface. Heat and water transport in the soil are coupled using a linked source-term approach. Model predictions were compared with field observations from three forest clearcuts in northern Ontario. Soil temperatures on all sites were predicted with less than 1°C bias. It was necessary to increase the value for soil hydraulic conductivity in the model to obtain good agreement between predicted and observed soil water contents. During lapse conditions on two sand flat sites, air temperature at 20 cm was predicted with less than 0.1°C bias and water vapor pressure at 20 cm with less than 10 Pa bias. As a consequence, the 20-cm saturation deficit was predicted with less than 10 Pa bias. On a swamp site, however, bias in predicted air temperature was much larger, possibly because of heterogeneity of the surface. In most instances, uncertainty in observed or predicted values was of similar magnitude to the differences between predicted and observed values. The model is suitable for examining the effects of soil and surface properties and of boundary conditions on the physical environment of flat, homogeneous, unvegetated forest clearcuts.

Models of the longitudinal distribution of ring area as a function of tree and stand attributes for four major Canadian conifers

ContextIt is widely accepted that ring area increment generally increases from the tree apex to the crown base and is more-or-less constant below the crown base (Pressler’s law), but few quantitative models of this distribution have been developed.AimsThe aim of this study was to develop a model of ring area increment using easily obtained crown features and other tree or stand characteristics in order to further the understanding and prediction of tree growth, form, and wood quality.MethodsThe models were fit to stem analysis observations from white spruce, black spruce, balsam fir, and lodgepole pine.ResultsIn the final model, which includes tree crown and stand variables, ring area increment within the crown region was slightly curvilinear, the slope of ring area increment below the crown was non-zero, and the effect of butt swell was appreciable up-to a relative height of 0.10.ConclusionsThe high accuracy of the mixed effects model suggests that the three-component model form is appropriate for describing ring area profiles, whereas some tree-to-tree variation remains unexplained. The tree and stand variables used in these models can be easily measured in the field or obtained from remote sensing techniques.

The effect of the interaction of tree slenderness and relative height with ring width on wood density in Abies balsamea and Picea glauca

Wood density affects the strength of lumber and paper products. Despite considerable research, however, the key factors influencing wood density are still not fully understood. The aim of this study was to analyze the effects of variables within and among trees on the density of current wood growth along the stem in order to further understanding and prediction of wood quality. Correlation analyses together with linear mixed effects and randomForest modelling were carried out using stem analysis and tree-level data from long-term balsam fir and white spruce stand density experiments in Eastern Canada. Wood density showed highly structured patterns of variation among trees. Mixed effects and randomForest models, which incorporated tree-level effects accounted for much of the wood density variation. The three most influential variables identified by randomForest analysis for both species were tree slenderness, relative height and ring width. Wood density increased with slenderness and relative height, and these variables affected relationships of wood density to ring width. Wood density is associated with interacting variables within and among trees including tree slenderness and relative height. Wood density is related to ring width, but this relationship is modulated by tree-level influences which likely reflect mechanical stability requirements.