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)沉积率在上个世纪大幅增加，预计将继续有增无减。与此同时，森林管理做法也在发生变化，主要是因为越来越有必要立即获得投资回报。因此，了解和预测树木生长、碳贮量和木材质量将如何受到未来环境条件和管理实践变化的影响，这是相当大的压力。鉴于木材是森林收获的主要可销售产品，木材的形成可以说是与林木常年生长有关的最重要的经济过程。这项研究计划致力于开发模型，帮助预测和了解木材特性在树干内的分布，并可与树木生长模拟器相关联，以预测营林实践对木材产品流动和价值的影响。在接下来的五年里，我们的模型的发展将集中在对环境因素对木材物理机械性能的影响的更好的基本理解上。这将通过追求三个具体目标来实现：1)调查气候和与二氧化碳升高的潜在相互作用对木材性质的影响；2)了解主要干扰(如火灾或砍伐)后立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力学性质树间差异的影响。来自不同生长环境的木材样本将用于研究森林干扰、树木生长、木材性质、气候和大气条件之间的相互关系。将被研究的关键树种是来自魁北克北方森林的黑云杉(Picea Mariana)，那里的生长受到温度的限制，以及2)来自北卡罗来纳州杜克大学Face实验的火炬松(Pinus Taeda)树，它们在富二氧化碳水平(200ppm)下暴露了15年，并施了5年的氮肥。将在4000多块木片上测量不同木材性质的径向变化模式，如密度、机械硬度和强度、化学成分和细胞尺寸。开发的模型不仅将提供一个公共平台，用于整合我们关于环境条件变化对木材结构的长期影响的最新知识，还将有助于在森林价值链中更早地为决策提供信息，从而提高这一加拿大经济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.