Crown function and dimensions in boreal conifers

树冠的大小与森林的生产力、用水和健康有关。在这项提案中，我和我的学生将探索控制树冠发育的因素。简单地说，树冠大小是由树枝和枝条的垂直和横向伸展以及树冠底部树枝的自我修剪控制的。在自我修剪方面，我们计划进行研究，以检验这一假设，即不耐荫树种的下部枝条进入弱光区域时，这些枝条形成导水率较低的木质部，因此它们往往限制这些下部枝条叶片的水分供应。耐荫树种的枝条导水率变化较小，因此自我修剪较慢。其次，我认为，不耐荫的树种一旦开始经历遮荫，就会倾向于将它们产生的糖更多地分配到上部树枝上，并倾向于从下部树枝上移走可移动的营养物质，如N。在枝条横向伸展方面，探讨枝条伸长与养分供应和枝条导水率变化之间的联动关系。来自田间施肥试验的树木将被用来检查树冠宽度和树干水力。树冠在风中摇摆时的碰撞摩擦也被认为会导致树枝和花蕾的折断，从而限制树冠的横向扩展。这将通过一项区域研究来探索，该研究将在不同风速的地区对蓄积充足的针叶林的树木的树冠宽度进行研究。我们还将研究风对生长在不同风速区域的树木的树干形状和树冠发育的影响。这项工作将为树冠的发展提供新的见解，并帮助管理者控制管理下的树木生长或气候变化的这一重要特征。

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.