by Svetlana Savin | 30 January 2019
Published in Computers and Electronics in Agriculture 97: 15-20. http://dx.doi.org/10.1016/j.compag.2013.06.004
This paper describes SOLARCALC 7.0, a new implementation of a computer program designed for the analysis of hemispherical photographs. Our aim was to recode, optimize, enhance and recompile the previous version of SOLARCALC program using REALBASIC, a modern, cross-platform BASIC language programming environment. The main improvements of the new version are described as follows: Programming and layout – a revision and enhancement of the original source code in a new, redesigned and user-friendly interface; Calculations – the possibility of allowing calculations for a growing season length, the possibility of defining the number of zenith and azimuth angles used for the calculations, the calculations of direct, indirect and total site factors, the inclusion of two versions of the Standard Overcast (SOC) sky weighting formula, the ability to compute leaf area index using two different methods and to compute the sky view factor, the ability to compute the total daily extraterrestrial radiation, the capacity of handling grayscale and color images and to manually or automatically threshold the images. The performance of the new version of SOLARCALC was assessed using a series of hemispherical images taken along a light gradient. Comparisons of calculated canopy light and structural indices between the new version of the program and GLA (Gap Light Analyser) show highly significant positive correlations (R2 = 1.00), indicating that SOLARCALC performs similarly to GLA across a variety of forest canopy openings. The incorporated modifications in the new version of the program allows for more detailed and more versatile analyses of hemispherical photographs and as such, represent a significant improvement in comparison with the previous version of the program. Finally, one of the most salient feature of SOLARCALC compared to other similar software is the possibility of using compiled versions of the program compatible with Macintosh, Windows and Linux/Unix operating systems, localised in English, French and Spanish languages.
by Marie-Claude Boileau | 30 January 2019
Published in Canadian Journal of Forest Research 43: 224-233
Estimating residual tree survival and growth is crucial for evaluating the overall merit of partial harvesting. In this case study, we present the effects of different cutting intensities (0%, 40%, 50%, and 60% of merchantable (diameter at breast height ≥ 9.1 cm) basal area (BA)) on the response of residual trees in two mixed yellow birch (Betula alleghaniensis Britt.) – conifer stands in eastern Quebec, Canada. Primarily aimed at promoting regeneration establishment, the experiment was conducted in two sites 90 km apart (Armagh and Duchesnay), each one containing four replicates of treatments in a randomized block design. Mortality after cutting decreased with increasing BA removal, but losses were two to three times higher at Armagh (62–138 stems/ha) than at Duchesnay (22–88 stems/ha). Loss of conifer stems involved primarily balsam fir (Abies balsamea (L.) Mill.) under natural conditions (control), whereas fir and red spruce (Picea rubens Sarg.) were equally affected in partial cuts. Red maple (Acer rubrum L.) and paper birch (Betula papyrifera Marsh.) were lost regardless of treatment. As a whole, growth in merchantable BA increased with cutting intensity. Uniform partial cuts produced good BA growth response from conifers at Armagh (0.27–0.28 m2·ha−1·year−1) and from hardwoods at Duchesnay (0.16–0.25 m2·ha−1·year−1), whereas BA growth was negligible for both species groups in the control. We examine the role of species composition and stand structure before cutting in the response of residual trees.
by Marie-Claude Boileau | 30 January 2019
Published in Journal of Forest Research 18: 168-178
Composition, structure, and species-specific patterns of recruitment and growth were characterized in two yellow birch (Betula alleghaniensis Britt.)–conifer stands in Quebec, Canada, to improve our understanding of the dynamics of these complex ecosystems. The mixture of mid- and shade-tolerant species in the canopy, the inverse J-shape stem diameter distribution, and the age distribution were indicative that the two stands were in a late-successional stage. Recruitment of mid-tolerant species above 1.3 m in height appeared to be periodic and synchronized with historical spruce budworm (Choristoneura fumiferana Clem.) outbreaks, while the coniferous component of these mixedwood stands recruited continuously. Results suggest that recruitment of yellow birch and red maple (Acer rubrum L.) requires disturbances of a certain intensity that affect at least 25 % of the forest cover. In contrast, balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) can recruit under the canopy without relying on moderate or large canopy disturbances. Results suggest that the historical disturbance regime, and differences in shade tolerance between species, largely govern the contemporary composition of these stands. This study improves the comprehension of mechanisms that regulate the dynamics of yellow birch-conifer stands and will be useful for the subsequent elaboration of forest management strategies.
by Claire Morin | 30 January 2019
Published in Forest Ecology and Management 310: 10-18 http://dx.doi.org/10.1016/j.foreco.2013.08.011
Clear-cutting and fire are the two main disturbances affecting the boreal forest of eastern Canada. These two disturbance types exert different effects on forest dynamics, which can have major implications in terms of economic and ecological sustainability. This study compared the long-term effects of these two disturbance types on stand composition, stand density, and merchantable volume on eastern Canadian mesic boreal forests dominated by black spruce and balsam fir. We used 157 permanent sample plots (PSP), 41 of which originated from fire and 116 were from clear-cuts. Model selection with finite-sample corrected Akaike Information Criterion (AICc) was used to understand which factors had the greatest influence on relative stand density and merchantable volume. Our results indicate that merchantable volume was positively influenced by stand density, which in turn was primarily influenced by disturbance origin, with post-cutting stands being denser than post-fire stands. These results indicated that an increase in stand density is an important mechanism through which disturbance acts upon merchantable volume. We also found differences in forest composition between stand-origin categories, with balsam fir being more abundant post-clearcutting; this was likely because advance regeneration was mainly composed of balsam fir, whereas post-fire stands are dominated by black spruce. Differences in merchantable volume between post-fire and post-clearcut stands become non-significant with time, likely because of higher tree growth and lower mortality in the dominant canopy of clearcut-origin stands. Overall, the results indicate that stand origin is an important determinant of stand composition and stand yield, but that the latter effect tends to disappear after a few decades. The higher balsam fir content generally observed in naturally regenerated, clear-cut origin stands could have potentially negative economic and ecological impacts at the landscape scale, which may call for mitigation strategies.
by Audrey Verreault | 30 January 2019
Published in PeerJ https://doi.org/10.7717/peerj.428
Sugar maple syrup production is an important economic activity for eastern Canada and the northeastern United States. Since annual variations in syrup yield have been related to climate, there are concerns about the impacts of climatic change on the industry in the upcoming decades. Although the temporal variability of syrup yield has been studied for specific sites on different time scales or for large regions, a model capable of accounting for both temporal and regional differences in yield is still lacking. In the present study, we studied the factors responsible for interregional and interannual variability in maple syrup yield over the 2001–2012 period, by combining the data from8 Quebec regions (Canada) and 10 U.S. states. The resulting model explained 44.5% of the variability in yield. It includes the effect of climatic conditions that precede the sapflow season (variables from the previous growing season and winter), the effect of climatic conditions during the current sapflow season, and terms accounting for intercountry and temporal variability. Optimal conditions for maple syrup production appear to be spatially restricted by less favourable climate conditions occurring during the growing season in the north, and in the south, by the warmer winter and earlier spring conditions. This suggests that climate change may favor maple syrup production northwards, while southern regions are more likely to be negatively affected by adverse spring conditions.
