Modelling the effects of environmental conditions on wood physico-mechanical properties

由于人类活动，大气中的二氧化碳浓度和氮 (N) 沉降率在上个世纪大幅增加，并且预计将继续有增无减。与此同时，森林管理实践也在发生变化，这主要是因为人们越来越需要立即获得投资回报。因此，了解和预测未来环境条件和管理实践的变化将如何影响树木生长、碳储存和木材质量面临着相当大的压力。鉴于木材是来自采伐森林的主要商品产品，木材形成可以说是与林木多年生生长相关的最经济重要的过程。该研究项目致力于开发模型，帮助预测和了解木材特性的茎内分布，并且可以与树木生长模拟器相联系，以预测造林实践对木材产品流和价值的影响。在接下来的五年中，我们模型的开发将侧重于更好地了解环境因素对木材物理机械性能的影响。这将通过追求三个具体目标来实现：1）研究气候的影响以及与二氧化碳升高的潜在相互作用对木材特性的影响；2）了解火灾或砍伐等重大干扰后场地特征和林分动态变化的影响；3）测试生物力学刺激对木材机械特性树间变化的影响。来自对比生长环境的木材样本将用于研究森林干扰、树木生长、木材特性、气候和大气条件之间的相互关系。将研究的关键树种是来自魁北克北方森林的黑云杉 (Picea mariana)，该森林的生长受到温度限制；2) 火炬松 (Pinus taeda) 树来自北卡罗来纳州杜克大学的 FACE 实验，暴露于高浓度二氧化碳水平 (200 PPM) 15 年和氮肥施肥 5 年。不同木材特性（例如密度、机械刚度和强度、化学成分和细胞尺寸）变化的径向模式将在 4000 多个木盘上进行测量。开发的模型不仅将为整合我们关于环境条件变化对木结构的长期影响的最新知识提供一个通用平台，还将有助于为森林价值链的早期决策提供信息，从而提高加拿大经济这一重要部门的未来效率。

Atmospheric CO2 concentrations and nitrogen (N) deposition rates have increased substantially over the last century due to human activities and are expected to continue unabated. At the same time, forest management practices are also changing, mainly because of an increased necessity for immediate returns on investment. There is thus considerable pressure to understand and predict how tree growth, carbon storage and wood quality will be affected by changes environmental conditions and management practices in the future. Given that wood is the principal merchantable product derived from harvested forests, wood formation is arguably the most economically important process associated with perennial growth in forest trees. This research program is dedicated to developing models that can help predict and understand the within-stem distribution of wood properties, and that can be linked to tree growth simulators to predict the impact of silvicultural practices on wood product flows and value. Over the next five years, the development of our models will focus on obtaining an improved fundamental understanding of the effects of environmental factors on wood physico-mechanical properties. This will be achieved by pursuing three specific objectives: 1) to investigate the effects of climate and the potential interaction with elevated CO2 on wood properties 2) to understand the effects of changes in site characteristics and stand dynamics after major disturbances, such as fires or clearcut, and 3) to test the impact of biomechanical stimuli on the between-tree variation in wood mechanical properties. Wood samples from contrasted growing environments will be used to study the inter-relationships between forest disturbance, tree growth, wood properties, climate and atmospheric conditions. The key species that will be studied are black spruce (Picea mariana) from the boreal forest of Quebec where growth is temperature-limited and 2) loblolly pine (Pinus taeda) trees from the FACE experiment at Duke University in North Carolina exposed to enriched CO2 levels (+200 PPM) for 15 years and Nitrogen fertilisation for 5 years. The radial patterns of variation of different wood properties, such as density, mechanical stiffness and strength, chemical composition and cell dimensions, will be measured on more than 4000 wood discs. The developed models will not only provide a common platform for the integration of our most up-to-date knowledge on the long-term effects of changing environmental conditions on wood structure, they will also help inform decision-making earlier in the forest value chain, and thus improve the future efficiency of this important sector for the Canadian economy.