Evaluation of fine root length and diameter measurements obtained using RHIZO image analysis

Image analysis systems facilitate rapid measurement of root length and diameter, but their accuracy is not easily determined. The objective of this study was to develop a set of simple experiments for evaluating the accuracy of fine root measurements obtained using image analysis. Using the system RHIZO (trademark of Regent Instruments, Quebec), we tested the accuracy of (i) length measurements made over a range of root lengths per unit area, (ii) average diameter measurements and length per diameter distributions in string, wire, and fine root samples of varying diameter, and (iii) diameter measurements on short segments of diagonally oriented objects. Our results suggest that preliminary testing of image analysis systems is absolutely necessary for producing reliable root measurements. Total length was accurately determined for typically encountered length per unit areas of <1.5cm cm-2. For samples with higher values, however, the method underestimated total length by >5%. It is therefore recommended that users of image analysis systems determine this maximum length per unit area for accurate determinations of total root length. In samples that contained different string diameters, the total sample length and average string diameter could accurately be measured. However, the length per diameter class was underestimated by >20% when the string diameter was less than one pixel smaller than the upper limit of the diameter class. Adjustment of diameter intervals and increasing the scanner resolution are required to reduce this underestimation. Both the length and the angle of the short segments analyzed were found to influence diameter measurements. Similar sets of experiments are proposed for a rigorous evaluation of the performance of other image analysis systems on root measurements

Effects of presenting forest simulation results on the forest values and attitudes of forestry professionals and other forest users in Central Labrador

This research tested whether demonstration of the long term effect of different forest management scenarios in a large forested area changes people's forest values and attitudes. Forestry professionals and other forest users in Central Labrador were shown simulation results of three alternative forest management scenarios illustrating possible long term effects on various indicators. Forest values and attitudes towards forestry were measured before and after the presentation. Our conception of values and attitudes is based on the cognitive hierarchy model of human behaviour which states that values are more enduring and more difficult to change than attitudes. It was thus hypothesized that attitudes would change but not values and that change in forestry professionals would be less than in other forest users since foresters are trained to think about long-term effects and large-scale processes of forest management scenarios. We also hypothesized that a greater number of people would have an opinion on forest management after the presentation. All three hypotheses were partially supported by the results. The results indicated that some attitude change occurred, but that values also changed somewhat. Most of the significant changes occurred when persons with no clear opinion on several forest-related questions formed an opinion. Long-term, landscape simulation results provide valuable information and enhance understanding of both forestry professionals and other forest users. However, being provided the same information, the two groups learned different things. While forest users gained more confidence in the current forest management plan and were motivated to further participate, professionals learned more specific things. This reflects differences between technical and local knowledge

Effect of branch position and light availability on shoot growth of understory sugar maple and yellow birch saplings

Phenotypic plasticity enables tree saplings to change their morphology according to their environment to grow toward a better light micro-habitat. Therefore, processes of crown development could be expected to vary as a function of light. The objectives of this study were to (i) evaluate the effects of position and light availability on shoot growth within the crowns of understory saplings of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton.); (ii) develop a new vigour index for shoots; and (iii) evaluate the possible factors relating to branch mortality in the crown of sugar maple saplings. The results revealed that there is a clear branch position effect on shoot growth in the crown for yellow birch saplings and that it is partly related to the presence of two types of shoots. Dead branches were located at the bottom of the crown of sugar maple saplings; they were smaller in size, had wider angles and had lower indexes of vigour than live branches found nearby. Preliminary results obtained on the vigour index indicate that it is a potentially useful tool for predicting the growth and vigour status of a branch

Fine-root dynamics in mixed boreal conifer-broad-leafed forest stands at different successional stages after fire

Fine-root (diameter ≤ 10 mm) standing biomass, length, distribution, production, and decomposition were studied in mixed conifer broad-leafed forest stands 48, 122, and 232 years after fire on clay soils in the southern boreal forest of Quebec. A combination of ingrowth bags, soil cores, and root litter bags was used. Forest composition changed from trembling aspen- (Populus tremuloides Michx.) dominated stands in the youngest stage to balsam fir (Abies balsamea (L.) Mill.), and then to eastern white-cedar (Thuja occidentalis L.) stands in the oldest stage. The fine- and small-root standing biomass did not differ significantly between the forest successional stages. However, the total root length was significantly more developed in the 48-year-old successional stand than in the 232-year-old stand. Within the investigated soil profile (depth = 30 cm) most roots (>80%) were found in the 5 to 8 cm thick organic layer and the top 10 cm of the mineral soil. Root biomass in the organic layer increased significantly after fire, and a simultaneous increase in thickness of the organic layer was observed. The ingrowth of roots into ingrowth bags during one and two growing seasons was more than twice as high m the youngest stand as in the oldest one. However, the differences were not statistically significant because of high variation. Fine roots of aspen decomposed significantly faster than those of balsam fir and cedar in all forest stands. The results suggest that root production, the rate of decomposition, and presumably the rate of turnover are higher in forest stands dominated by early successional broad-leafed species such as aspen than in stands composed of late successional coniferous species such as fir, spruce, and cedar. Differences in root dynamics may contribute significantly to the change in the carbon and nutrient cycling often reported with succession in the boreal forest