A fast and reliable method for the delineation of tree crown outlines for the computation of crown openness values and other crown parameters

Numerous crown parameters (e.g., leaf area index, diameter, height, volume) can be obtained via the analysis of tree crown photographs. In all cases, parameter values are functions of the position of the crown outline. However, no standardized method to delineate crowns exists. To explore the effect of different outlines on tree crown descriptors, in this case crown openness (CO), and facilitate the adoption of a standard method free of user bias, we developed the program Crown Delineator that automatically delineates any outline around tree crowns following predetermined sensibility settings. We used different outlines to analyze tree CO in contrasting settings: using saplings from four species in young boreal mixedwood forests and medium-sized hybrid poplar trees from a low-density plantation. In both cases, the estimated CO increases when calculated from a looser outline, which had a strong influence on understory available light simulations using a forest simulator. These results demonstrate that the method used to trace crown outlines is an important step in the determination of CO values. We provide a much-needed computer-assisted solution to help standardize this procedure, which can also be used in many other situations in which the delineation of tree crowns is needed (e.g., competition and crown shyness)

The effect of biodiversity on tree productivity: from temperate to boreal forests

Aim: An important issue regarding biodiversity concerns its influence on ecosystemfunctioning. Experimental work has led to the proposal of mechanisms such as niche complementarity.However, few attempts have been made to confirm these in natural systems, especially in forests. Furthermore, one of the most interesting unresolved questions is whether the effects of complementarity on ecosystem functioning (EF) decrease in favour of competitive exclusions over an increasing productivity gradient. Using records from permanent forest plots, we asked the following questions. (1) Is tree productivity positively related to diversity? (2) Does the effect of diversity increase in less productive forests? (3) What metric of diversity (e.g. functional or phylogenetic diversity) better relates to tree productivity?\ud Location: Temperate, mixed and boreal forests of eastern Canada.\ud Methods: Over 12,000 permanent forest plots, from temperate to boreal forests, were used to test our hypotheses in two steps. (1) Stepwise regressions were used to identify the best explanatory variables for tree productivity. (2) The selected climatic and environmental variables, as well as density and biodiversity indices, were included in a structural equation model where links (paths) between covarying variables are made explicit, making structural equation modelling the best tool to explore such complicated causal networks.\ud Results: This is the first large-scale demonstration of a strong, positive and significant effect of biodiversity on tree productivity with control for climatic and environmental conditions. Important differences were noted between the two forest biomes investigated.\ud Main conclusions: We show for the first time that complementarity may be less important in temperate forests growing in a more stable and productive environment where competitive exclusion is the most probable outcome of species interactions, whereas in the more stressful environment of boreal forests, beneficial interactions between species may be more important. The present work is also a framework for the analysis of large datasets in biodiversity–ecosystem functioning (B-EF) research

Simulating light availability under different hybrid poplar clones in a mixed intensive plantation system

Fast-growing hybrid poplars have been proposed as a means of achieving restoration objectives on former agricultural land by providing shelter for slower-growing species. Intensive two-stage scenarios of mixed plantations are also possible using valuable hardwoods interplanted among hybrid poplars. The latter would be harvested at maturity (approximately 20 years) once their protective role has been accomplished, leaving more space for the full development of the second cohort. We implemented simulations of hybrid poplar growth in the SORTIE-ND model and used it to test scenarios with clones varying in growth and crown allometry, different hardwood species, and spatial arrangements, to maximize production of both groups. Important differences in growth and allometry were manifested among clones over time, which translated into important differences in available light between rows. Sustained growth for most hardwoods appeared optimal using wider spacings of 16 m, compared with 12 m, between poplar rows. To our knowledge, this is the first attempt to integrate fast-growing hybrids and intensive silviculture scenarios into spatially explicit models. These models are necessary support tools for the efforts now being invested in intensive silviculture in the face of diminishing forest resources, increasing wood and fiber demands, and climate change

Fine roots distribution, light conditions and yield in a tree-based intercrop system

Paper presented at the 13th North American Agroforesty Conference, which was held June 19-21, 2013 in Charlottetown, Prince Edward Island, Canada.In Poppy, L., Kort, J., Schroeder, B., Pollock, T., and Soolanayakanahally, R., eds. Agroforestry: Innovations in Agriculture. Proceedings, 13th North American Agroforestry Conference, Charlottetown, Prince Edward Island, Canada, June 19-21, 2013."In tree-based intercrop systems (TBI), trees are planted in widely spaced rows to allow agricultural activities to continue. These agroforestry systems are new in Qu_bec but well known in Europe, USA and China (Baldy et al., 1993; Rivest and Olivier, 2007). The integration of trees into an agroforestry system has the potential to enhance soil fertility, reduce erosion, improve water quality, increase biodiversity and aesthetics, and sequester carbon (Jose, 2009; Montagnini and Nair, 2004). However, the presence of trees also results in aboveground and belowground interspecific interactions with crop, which can include competition, facilitation or complementarity (Jose et al., 2004; Rivest and Olivier, 2007; Van Noordwijk et al., 1996). In theory, TBI systems can be more productive than the respective monocultures if trees have the capacity to take resources like water and nutrients in deeper soil layers than those used by crops (Cannell et al., 1996)."--Introduction.L�a Bouttier (1), Alain Paquette (2), Christian Messier (2) and Alain Cogliastro (1) ; 1. Institut de Recherche en Biologie V�g�tale, 4101 Sherbrooke Est, Montr�al, QC H1X 2B2, Canada. 2. Universit� du Qu�bec a Montr�al, 270 Rue Saint Antoine Ouest, Montreal, QC H2Y 0A3, Canada.Includes bibliographical references

Réhabilitation de fôrets par la plantation sous couvert : écologie des arbres plantés dans le sud-ouest du Québec

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal

Homogeneous light in shade-house experiment overestimates carbon gains in Norway maple seedlings

We set up a shade-house experiment with Norway maple growing at two light intensities typical of a disturbed and undisturbed forest canopy from either a homogeneous or a dynamic regime that mimics sunflecks. We show that although horticultural-grade shade-cloths can be finely tuned to provide daily averages of any light intensity, they do not appropriately mimic natural forest understories which are characterized by dynamic light environments composed of intense but short direct light events interspaced with prolonged period of low diffuse light. The results suggest that replicating the dynamic light environment of forests could be very important in experiments aimed at identifying the traits responsible for invasiveness in exotic species in forest understories, such as Norway maple in North America

The economics of ecosystem services of tree-based intercropping systems

Paper presented at the 13th North American Agroforesty Conference, which was held June 19-21, 2013 in Charlottetown, Prince Edward Island, Canada.In Poppy, L., Kort, J., Schroeder, B., Pollock, T., and Soolanayakanahally, R., eds. Agroforestry: Innovations in Agriculture. Proceedings, 13th North American Agroforestry Conference, Charlottetown, Prince Edward Island, Canada, June 19-21, 2013.The paper aims to determine the potential environmental benefits of multifunctional tree-based intercropping (TBI) systems. Here we evaluate ten ecosystem services using a mix of mathematical models for quantification and economic valuation. The results reveal a total annual margin of 2 558 CAN$ha-1y-1. The economic value of combined non-market services is 1 634 CAN$ ha-1y-1, which is higher than the value of marketable products (i.e. timber and agricultural products). The present value of the services for a rotation of 40 years is 54 782 CAN$ ha-1, about a third of which is contributed by agricultural products. Water quality regulation ranked highest among the non-market benefits followed by air quality maintenance, soil quality regulation, biological control, and pollination.Mahbubul Alam (1), Alain Olivier (1), Alain Paquette (2), J�rôme Dupras (3), Jean-Pierre Rev�ret (4) and Christian Messier (5) ; 1. D�partement de phytologie, Facult� des sciences de l'agriculture et de l'alimentation, Universit� Laval, Qu�bec City, G1V 0A6, Canada. 2. D�partement des sciences biologiques, Universit� du Qu�bec � Montr�al, Case postale 8888, Succursale Centre-ville, Montr�al, H3C 3P8, Canada. 3. D�partement de g�ographie, Universit� de Montr�al, Montr�al, Canada. 4. D�partement strat�gie, responsabilit� sociale et environnementale, Universit� du Qu�bec � Montr�al, Montr�al, Canada. 5. Institut des Sciences de la For�t temp�r�e (ISFORT), Universit� du Qu�bec en Outaouais, Ripon, JOV 1V0, QC, Canada.Includes bibliographical references

Intercropping trees' effect on soil oribatid diversity in agro-ecosystems

The benefits of tree-based intercropping (TBI) compared to conventional agro-ecosystems in North America could include climate change mitigation and adaptation, although enhancing resilience to climate change through increasing soil diversity remains poorly explored. Diversity of soil microarthropods supports a series of ecological services that may be altered by soil desiccation due to climate change. Here we study the effect of red oak and hybrid poplar TBI on soil oribatid mite species assemblages associated to forage crops (mix of Timothy-grass and red clover). Abundance and species density of oribatids were affected by treatment, depth and the interaction of both variables. Abundance of oribatid mites was significantly lower in the oak TBI, showing a homogeneous vertical distribution in opposition to a decreasing with depth distribution under poplar TBI and conventional crops. Species density was significantly higher in the conventional crop, showing again significant differences in depth that were not present in both TBI treatments. Distance to tree did not affect mite abundance nor species density. TBI increased oribatid richness (obtained by sample-based rarefaction and extrapolation) only in the presence of oaks. The distribution of oribatids was strongly associated to tree fine root biomass and stress the importance of underground organic resources for the oribatid fauna and their ecological functions. If increasing drought associated with climate change desiccates superficial levels of agro-ecosystem soils, deeper sources of organic resources, such as tree roots, should become crucial in the maintenance of diverse microarthropod communities