Age-class distribution and the forest fire cycle

雩风三日

Age-class distribution and the forest fire cycle
林龄-级分布与林火循环

  The main purpose of this paper is to present a theory of the age-class distribution to be expected in a forest dependent on random periodic fire for its maintenance and renewal. A feature of this theory is that the fire history of a forest is reflected in its present age-class distribution. Also presented are examples of how the theory might be applied in analysing the history of actual forests. Finally, there is a discussion of the combined effects of fire and logging on the average age and age-class distribution of managed forests.   It is generally acknowledged that many North American forest types, especially the boreal ones, are mainly dependent in the natural state on periodic fire for their continued existence. Partial evidence of this is the growing literature on forest fire history in which the authors derive an estimate of the average interval between fires in the past. Some items de- scribe the incidence of charcoal in beds of lake sed- invent dating back 1000 years or more (e.g., Swain 1973).Other items deal with more recent fire his- tory, generally based on an examination of fire- scarred trees (e.g., Houston 1973;Arno 1976)，or on the available fire records in recent decades (e.g., Wein and Moore 1977).The most comprehensive fire history study to date is by  Heinselman(1973)， on the Boundary Waters Canoe Area of northern Minnesota, and combines fire-scar data with records of past fires. The only attempt so far to apply math- ematics to the distribution of fire intervals is by Rowe et al.(1975)，using fire-scar data from the Mackenzie River region, and further developed by Johnson and Rowe(1977).(This work is referred to again later.)In contrast, the approach presented in this paper would, for forests normally killed and replaced by fire, enable the fire history to be de- duced from the distribution of present stand ages. For forests normally exposed to periodic sublethal fire, the distribution of intervals between fires at any given point, as determined from fire scars, should follow a similar pattern.
    本文的主要目的是提出一种基于随机周期火灾的森林维持和更新的年龄级分布预期理论。这一理论的一个特点是，森林的火灾历史反映在其目前的年龄级分布中。还举例说明该理论如何应用于分析实际森林的历史。最后，讨论了火灾和伐木对管理森林的平均年龄和龄级分布的综合影响。人们普遍认为，许多北美森林类型，特别是北方森林，在自然状态下主要依靠周期性火灾来继续生存。这方面的部分证据是关于森林火灾历史的日益增长的文献，其中作者推导了过去火灾之间的平均间隔的估计。有些项目描述了sed湖床上的木炭，其发明可以追溯到1000多年前(如Swain 1973年)。其他的条目涉及到最近的火灾，通常是基于对火灾疤痕树的检查(例如，休斯顿1973年;阿诺1976年)，或者是近几十年可用的火灾记录(例如，韦恩和摩尔1977年)。迄今为止最全面的火灾历史研究是由Heinselman(1973)在明尼苏达州北部的边界水域独木舟地区进行的，他将火灾疤痕数据与过去的火灾记录相结合。迄今为止，Rowe等人利用麦肯齐河地区的火痕数据对火灾间隔分布进行了唯一的尝试，并由Johnson和Rowe(1977)进一步发展。(本著作稍后再次提及。)相比之下，本文所提出的方法，对于通常被火烧毁和取代的森林，可以从目前林龄的分布推断火灾历史。对于经常遭受周期性亚致命火灾的森林，根据火灾伤痕确定的任何给定点的火灾间隔分布应遵循类似的模式。