Development and Calibration of a New Method of Reconstructing Fire History in Low-Severity Fire Regimes

这项研究项目将解决生物地理学中的一个基本假设，即像黄皮松这样的干燥松林的结构以低密度的大树为主，并由频繁的低强度火灾维持，这限制了树木的再生。这一假设在一定程度上是基于低严重性火灾在历史上频繁发生的假设，这一假设在很大程度上依赖于使用复合火灾间隔的火灾历史方法。分析、模拟和初步的现代校准已经提供了一些证据，表明使用复合射击间隔是有偏见的和不准确的。为了克服复合射击间隔法的局限性，研究人员提出了一种新的方法--全树射击间隔法(ATFI)，并通过模拟表明，该方法的使用是公正和准确的。该项目将完成基于现场的现代校准，并将ATFI方法应用于历史火灾历史重建，使ATFI方法便于使用该方法来帮助检验基本假设。调查人员将首先收集和分析伤疤比例的现场数据，这是使用ATFI方法所需的一个核心参数，方法是对亚利桑那州北部黄松林燃烧的22场火灾的约48个地块进行采样。亚利桑那州北部是目前了解低强度火灾的关键地区。这种疤痕比例分析将有助于开发空间模型，以根据环境设置、树木特征(如密度和直径)以及燃料来预测疤痕比例。然后，伤疤分数模型将用于完成ATFI方法的现代校准，并在大峡谷国家公园和堡谷实验森林的1000公顷区域内使用ATFI方法重建历史火灾历史。调查人员将提取并交叉测定大约640个增量岩芯的年代，以及大约105个火疤，以计算ATFI校准和重建所需的火灾数量。最后，他们将完成对这两个地区现存的前欧洲美洲火疤证据的空间分析，以提高对火疤证据如何在整个景观中发生的基本理解。在完成这三部分研究的过程中，研究人员将检验关于疤痕形成比例的七个具体假设，三个关于火灾历史的假设，以及三个关于现有火灾疤痕证据的假设。他们希望能够极大地提高对火灾是如何留下火疤证据的理解，以及如何利用这些证据准确地重建整个景观的低严重性火灾的历史。该项目将测试和验证一种准确重建森林火灾历史的新方法。火灾历史提供了管理国家公园、国家森林和其他公共土地上的森林所需的基本信息。更具体地说，该项目将进一步开发一种新的火灾历史方法，并有助于解决有关黄松林历史火灾烧毁速度的不确定性。火太多或太少都会对老树、林下植物和野生动物产生不利影响，因此解决这种不确定性很重要。该项目的研究将为一名研究生和几名本科生提供实地和实验室教育机会。

This research project will address a basic hypothesis in biogeography -- that the structure of dry pine forests like ponderosa pine is dominated by a low density of large trees and is maintained by frequent low-severity fires that limited tree regeneration. This hypothesis rests in part on the assumption that low-severity fires were historically frequent, an assumption largely dependent on a fire-history method that uses composite fire intervals. Some evidence has been presented from analysis, simulation, and an initial modern calibration that the use of composite fire intervals is biased and inaccurate. To overcome limitations of the composite-fire-interval method, the investigators have developed a new approach, the all-tree-fire-interval (ATFI) method, and showed by simulation that the use of is new method is unbiased and accurate. This project will complete a field-based modern calibration and apply the ATFI method in a historical fire-history reconstruction to bring the ATFI method to facilitate use of this method to help test the basic hypothesis. The investigators will first gather and analyze field data on scarring fraction, a central parameter needed for using the ATFI method, by sampling about 48 plots in 22 fires that burned in ponderosa pine forests in northern Arizona, a key area for current understanding of low-severity fire. This scarring-fraction analysis will facilitate development of a spatial model to predict scarring fraction from environmental setting, tree characteristics like density and diameter, and fuels. The scarring-fraction model then will be used to complete a modern calibration of the ATFI method and historical fire-history reconstructions using the ATFI method in 1000-ha areas in Grand Canyon National Park and Fort Valley Experimental Forest. The investigators will extract and cross-date about 640 increment cores to date trees and about 105 fire scars to count fires for the ATFI calibration and reconstruction. Finally, they will complete a spatial analysis of extant pre-EuroAmerican fire-scar evidence in these two areas to improve basic understanding of how fire-scar evidence occurs across landscapes. In the process of completing these three parts of the research, the investigators will test seven specific hypotheses about scarring fraction, three about fire history, and three about extant fire-scar evidence. They expect to be able to greatly improve understanding of how fire-scar evidence is left by fires and how to use this evidence to accurately reconstruct the history of low-severity fire across landscapes. This project will test and validate a new method for accurately reconstructing fire history in forests. Fire histories provide fundamental information needed in managing forests in national parks, national forests, and on other public lands. More specifically, this project will further develop a new fire-history method and help to resolve uncertainties about the rate that historical fires burned in ponderosa pine forests. Too much fire or too little fire can have adverse effects on old-growth trees, understory plants, and wildlife, so it is important to resolve this uncertainty. The research undertaken in this project will provide both field and laboratory educational opportunities for a graduate student and several undergraduate students.