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Towards a mechanistic understanding of spatial patterns of forest transpiration, and its implications for scaling.

机译：机械理解森林蒸腾作用的空间格局及其对尺度的影响。

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摘要

Estimates of forest stand transpiration are typically achieved by scaling a series of representative point measurements to the stand level. This method fails to account for heterogeneity in transpiration at stand boundaries as a result of gradients in key environmental drivers such as soil moisture. To address this problem I made a series of spatially intensive transpiration estimates using sap flux measurements at two sites in northern Wisconsin. An aspen site captured a transition between an early successional forested upland dominated by quaking aspen (Populus tremuloides Michx), and a forested wetland dominated by alder (Alnus incana (DuRoi) and cedar (Thuja occidentalis L.). A maple site captured a transition between a secondary successional sugar maple (Acer saccharum Marsh.) stand and a red pine plantation (Pinus resinosa Ait.).;At the aspen site sapwood area (AS) was used to scale JS to whole tree transpiration ( EC). Because spatial patterns imply underlying processes, geostatistical analyses were employed to quantify patterns of spatial autocorrelation across the site. A simple Jarvis type model parameterized using a Monte Carlo sampling approach was used to simulate EC ( EC-SIM). EC-SIM was compared with observed EC (EC-OBS) and found to reproduce both the temporal trends and spatial variance of canopy transpiration. EC-SIM was then used to examine spatial autocorrelation as a function of environmental drivers. I found no spatial autocorrelation in JS across the gradient from forested wetland to forested upland. EC was spatially autocorrelated and this was attributed to spatial variation in AS which suggests species spatial patterns are important for understanding spatial estimates of transpiration. However, the range of autocorrelation in EC-SIM decreased linearly with increasing vapor pressure deficit, implying that consideration of spatial variation in the sensitivity of canopy stomatal conductance to D is also key to accurately scaling up transpiration in space.;To understand the decreasing range of spatial autocorrelation in EC-SIM with D I examined differences in stomatal conductance (GS) between individual trees using a transpiration model. Values of reference stomatal conductance (GSref) for individual trees from the aspen and maple site were compared to a series of environmental variables. For both sites no relationship was observed between GSref and variables related to hydraulic regulation of GS including soil moisture, sapwood area (AS), and tree height (HT). There was a non-linear inverse relationship between GSref and a canopy competition index (CI) designed to characterize the competitive light environment of an individual tree. This suggests that G S light limited and that differences in stomatal control of transpiration between plants may be related to photosynthetic capacity.;Sap flux data was used to parameterize a series of transpiration models. Models that account for canopy heterogeneity using a clumping parameter (Omega) and 3-dimensional canopy representation (3-D) were compared to a simple Big-Leaf model (big-leaf) that does not account for heterogeneity among individuals. Values of GSref for individual trees remained consistent between models for aspen and maple. For aspen values of transpiration per unit ground area (ECG) simulated using the Omega and 3-D models showed better agreement with observations that those simulated with the big-leaf model. At the maple site differences in model agreement were less pronounced, the Omega model slightly improved agreement, while the 3-D model resulted in a slight decrease in agreement between simulated and observed ECG. Clumping parameters for the Omega model did not exhibit a relationship with any physically meaningful variables and so do not appear to be useful for purposes of characterizing heterogeneity between individuals. In shade intolerant aspen trees with more neighboring competitors experienced a greater increase in model agreement as a result of accounting for canopy heterogeneity. For shade tolerant maple the 3-D model likely over compensated for competitive shading. The results suggest that substantial variability in stand transpiration exists. However it is explained largely in part by tree size, and so current point-to-area scaling methods will work as long as sample plots are appropriately selected. Additionally the results offer evidence of a link between plant hydraulics and photosynthesis, and a tie between ecosystem function and structure that could allow remote sensing to be used to characterize ecosystem processes.
机译：通常通过将一系列代表性点的测量结果缩放到林分水平来估算林分蒸腾量。由于主要环境驱动因素（例如土壤水分）中的梯度，该方法无法解决林分边界蒸腾作用的异质性。为了解决这个问题，我在威斯康星州北部的两个地点使用树液通量测量进行了一系列空间密集的蒸腾估算。白杨站点捕获了由地震白杨（Populus tremuloides Michx）为主的早期演替森林高地与and木（Alnus incana（DuRoi）和雪松（Thuja occidentalis L.）为主的森林湿地之间的过渡。在次生的连续枫糖枫（Acer saccharum Marsh。）林分和赤松人工林（Pinus resinosa Ait。）之间；在白杨站点，边材区（AS）用来将JS缩放到整棵树的蒸腾（EC）。模式暗示潜在的过程，地统计学分析用于量化整个站点的空间自相关模式；使用蒙特卡罗采样方法参数化的简单Jarvis类型模型用于模拟EC（EC-SIM）；将EC-SIM与观察到的EC进行比较（EC-OBS）并重现了冠层蒸腾的时间趋势和空间方差，然后使用EC-SIM检验了空间自相关与环境驱动力的关系。而且在从森林湿地到森林高地的整个梯度范围内，JS中都没有空间自相关。 EC在空间上是自相关的，这归因于AS的空间变化，这表明物种的空间格局对于理解蒸腾作用的空间估计很重要。然而，EC-SIM中的自相关范围随蒸气压亏缺的增加而线性减小，这表明考虑冠层气孔导度对D的敏感性的空间变化也是准确扩大空间蒸腾量的关键。 EC-SIM中具有DI的空间自相关分析，利用蒸腾模型检验了单棵树之间气孔导度（GS）的差异。将来自白杨和枫树站点的单个树木的参考气孔导度（GSref）值与一系列环境变量进行了比较。对于两个站点，在GSref和与GS的水力调节相关的变量（包括土壤湿度，边材面积（AS）和树高（HT））之间均未发现任何关系。 GSref与树冠竞争指数（CI）之间存在非线性反比关系，该指数旨在表征单个树木的竞争光照环境。这表明G S光有限，并且植物之间的蒸腾气孔控制差异可能与光合作用能力有关。汁液通量数据用于参数化一系列蒸腾模型。将使用集总参数（Omega）和3维冠层表示（3-D）解释冠层异质性的模型与不考虑个体异质性的简单大叶模型（big-leaf）进行比较。在白杨和枫树模型之间，单个树木的GSref值保持一致。对于使用Omega和3-D模型模拟的单位地面蒸腾量（ECG）的白杨值，与使用大叶模型模拟的观测值显示出更好的一致性。在枫树位置，模型一致性的差异不太明显，Omega模型的一致性稍有改善，而3-D模型导致模拟和观察到的ECG之间的一致性略有下降。 Omega模型的聚集参数与任何物理上有意义的变量都没有关系，因此对于表征个体之间的异质性似乎没有用。在考虑到树冠异质性的结果下，在耐荫性差的白杨树中，与更多相邻竞争者的模型协议经历了更大的增长。对于耐荫的枫木，3-D模型可能会过度补偿竞争性的阴影。结果表明，林分蒸腾存在很大的变异性。但是，这在很大程度上是通过树的大小来解释的，因此，只要适当选择样本图，当前的点到区域缩放方法就可以使用。此外，结果提供了植物水力学与光合作用之间联系的证据，以及生态系统功能与结构之间的联系，可以使遥感用于表征生态系统过程。

著录项

  • 作者

    Loranty, Michael M.;

  • 作者单位

    State University of New York at Buffalo.;

  • 授予单位 State University of New York at Buffalo.;
  • 学科 Biology Ecology.;Physical Geography.;Biology Plant Physiology.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 155 p.
  • 总页数 155
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 生态学（生物生态学）;植物学;自然地理学;
  • 关键词

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