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

在上个世纪，由于人类活动，大气CO2浓度和氮（N）沉积速率大幅增加，并且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，主要是因为越来越需要立即获得投资回报。因此，在了解和预测树木生长、碳储存和木材质量将如何受到未来环境条件和管理做法变化的影响方面存在着相当大的压力。鉴于木材是来自采伐森林的主要商品，木材形成可以说是与森林树木常年生长有关的最重要的经济过程。该研究计划致力于开发模型，可以帮助预测和了解木材特性的茎内分布，并可以与树木生长模拟器相关联，以预测造林实践对木材产品流和价值的影响。在接下来的五年里，我们的模型的发展将集中在获得更好的基本理解环境因素对木材物理力学性能的影响。这将通过追求三个具体目标来实现：1）调查气候的影响和与CO2浓度升高对木材性能的潜在相互作用; 2）了解在主要干扰（如火灾或皆伐）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能树间变化的影响。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。将研究的关键物种是来自生长受温度限制的魁北克北方森林的黑云杉（Picea mariana）和2）来自北卡罗来纳州杜克大学FACE实验的火炬松（Pinus taeda）树木，这些树木暴露于富集的CO2水平（+200 PPM）15年和氮肥5年。不同木材特性的径向变化模式，如密度，机械刚度和强度，化学成分和细胞尺寸，将在4000多个木材圆盘上测量。开发的模型不仅将为我们关于不断变化的环境条件对木材结构的长期影响的最新知识的整合提供一个共同的平台，它们还将有助于在森林价值链的早期为决策提供信息，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.