Crown function and dimensions in boreal conifers

树冠的大小与森林的生产力、用水量和健康状况有关。 在这个计划中，我和我的学生将探索控制树冠生长的因素。 简单地说，树冠的大小是由枝条和枝条的垂直和横向延伸以及树冠底部枝条的自我修剪控制的。 在自我修剪方面，我们计划的研究，将测试的假设，作为较低的分支的阴影不耐受的物种进入低光区，这些分支发展木质部具有较低的水力传导性，因此，他们往往会限制供水这些较低的分支的叶子。 耐荫树种的枝条导水率变化较小，因此自修剪较慢。 其次，我建议，不耐荫的物种将倾向于分配更多的糖，他们生产的上部分支，并倾向于删除移动的营养物质，如N从下部分支，一旦他们开始经历阴影。 在枝的横向延伸方面，我想探讨分支延伸与养分供应和分支导水率变化的联系。 从田间施肥试验的树木将被用来检查冠宽和茎水力学。 树木在风中摇摆时碰撞产生的树冠摩擦力也被认为会导致树枝和芽的断裂，从而限制树冠的横向扩张。 这将探索的树冠宽度的区域研究，从充分放养的针叶林在不同的风速区。 我们亦会研究在不同风速的地区，风对树木的树干形状和树冠生长的影响。这项工作将为树冠的生长方式提供新的见解，并帮助管理人员在管理或气候变化下控制树木生长的这一重要特征。

The size of tree crowns is linked to the productivity, water use and health of forests. In this proposal my students and I will explore the factors that control the development of crowns in trees. Put simply, crown size is controlled by the vertical and lateral extension of shoot and branches and the self-pruning of branches at the bottom of the crown. In terms of self-pruning, we plan studies that will test the hypothesis that as the lower branches of shade intolerant species enter zones of low light, these branches develop xylem with lower hydraulic conductivity and therefore they tend to restrict the water supply to the leaves of these lower branches. Shade tolerant species are proposed to have less change in hydraulic conductivity in branches and therefore slower self-pruning. Secondly, I propose that shade intolerant species will tend to allocate more of the sugars that they produce to upper branches and tend to remove mobile nutrients such as N from lower branches once they begin to experience shading. In terms of lateral extension of branches, I want to explore the linkage of branch extension with nutrient supply and changes in hydraulic conductivity of branches. Trees from field fertilization trials will be used to examine crown width and stem hydraulics. Crown friction from the collision of trees during their sway in wind is also thought to cause breakage of twigs and buds, thereby limiting lateral expansion of crowns. This will be explored by a regional study of crown width of trees from fully-stocked conifer forests in zones of different wind speeds. We will also study the effects of wind on stem shape and crown development in trees growing in zones of different wind speed. This work will provide new insights into the way that crowns develop and help managers control this important feature of tree growth under management or climate change.