Some have proposed that fire return intervals lengthen with elevation in montane tropical coniferous forests, such as those found in central Mexico. This would generate patterns of synchronous tree establishment in higher elevation forests dominated by Abies sp. Mill., and patterns of continuous tree establishment in lower elevation forests dominated by Pinus sp. L. However, it is common to find codominant stands of both genera at intermediate elevations. The Monarch Butterfly Biosphere Reserve (MBBR) is located in this region, and is covered by Abies religiosa (Kunth) Schltdl. & Cham-dominant forest, A. religiosa–Pinus pseudostrobus Lindley-codominant forest, and P. pseudostrobus-dominant forest. Despite the ecological importance of the MBBR’s coniferous forests, little is known about their fire return intervals, including their relationship with climate, and their effects on tree establishment patterns according to the elevational range proposed above. In this study, using dendrochronological techniques, we reconstructed the historical fire return intervals for each forest type, evaluated their relationship with droughts and with the El Niño Southern Oscillation (ENSO), and assessed the effect of fire return intervals on tree establishment patterns. A total of 110 cross-sections were obtained, from 23 sites across the MBBR. The fire chronology covered the period between 1925 and 2015. Fire return intervals averaged two years in stands dominated by A. religiosa, by P. pseudostrobus, and codominated by both species, regardless of elevation. No fire-free periods were detected, even after the establishment of the reserve in 2000. Fire frequency was not associated with periods of drought and ENSO. There was no relationship between fire return intervals and patterns of tree establishment, which was continuous in all three forest types. Our results suggest that coniferous forests of the MBBR have historically experienced frequent fires that are unrelated to climate and tree establishment. This may be evidence that natural fire regimes in these coniferous forests have been drastically altered by human activities. Although these frequent low-severity fires could adversely affect tree regeneration, and eventually decrease the integrity of the overwintering habitat of the Monarch Butterfly, the continuous tree regeneration observed suggests that these effects have not yet taken place.

中文翻译：

---

墨西哥君主蝴蝶生物圈保护区针叶林火灾历史的树状年代重建

一些人提出，在诸如墨西哥中部的山地热带针叶林中，回火间隔会随着海拔的升高而延长。这将在由Abies sp。主导的较高海拔森林中生成同步树建立的模式。密苏里州占主导地位的低海拔森林中的树木和连续树的建立模式。L.但是，通常在中间海拔找到两个属的显性林分。帝王蝶生物圈保护区（MBBR）位于该区域，并且被Abies religiosa（Kunth）Schltdl覆盖。＆Cham占主导地位的森林，A。religiosa-Pinus假棘为Lindley主导的森林，P。pseudostrobus主导的森林。尽管MBBR的针叶林在生态上很重要，但对其回火间隔的了解却很少，包括它们与气候的关系，以及它们对树木海拔高度的影响。在这项研究中，我们使用树轮年代学技术，重建了每种森林类型的历史回火间隔，评估了它们与干旱以及与厄尔尼诺南方涛动（ENSO）的关系，并评估了回火间隔对树木建立模式的影响。从整个MBBR的23个位置获得了总共110个横截面。火灾发生的时间跨度在1925年至2015年之间。在以菩提树（A. religiosa），假单胞菌（P. pseudostrobus）为主的林分中，两次回火的间隔平均为两年，而不论海拔高低，这两种物种均处于同一水平。即使在2000年建立保护区之后，也没有发现无火时期。火灾频率与干旱和ENSO无关。返火间隔与树木建立模式之间没有关系，这在所有三种森林类型中都是连续的。我们的结果表明，MBBR的针叶林历来经历了频繁的大火，而这种大火与气候和树木的生长无关。这可能证明这些针叶林的自然火灾状况已因人类活动而发生了巨大变化。尽管这些频繁发生的低烈度火灾可能会对树木的再生产生不利影响，并最终降低帝王蝶越冬栖息地的完整性，但观察到的持续树木再生表明这些影响尚未发生。返火间隔与树木建立模式之间没有关系，这在所有三种森林类型中都是连续的。我们的结果表明，MBBR的针叶林历来经历了频繁的大火，而这种大火与气候和树木的生长无关。这可能证明这些针叶林的自然火灾状况已因人类活动而发生了巨大变化。尽管这些频繁发生的低烈度火灾可能会对树木的再生产生不利影响，并最终降低帝王蝶越冬栖息地的完整性，但观察到的持续树木再生表明这些影响尚未发生。返火间隔与树木建立模式之间没有关系，这在所有三种森林类型中都是连续的。我们的结果表明，MBBR的针叶林历来经历了频繁的大火，而这种大火与气候和树木的生长无关。这可能证明这些针叶林的自然火灾状况已因人类活动而发生了巨大变化。尽管这些频繁发生的低烈度火灾可能会对树木的再生产生不利影响，并最终降低帝王蝶越冬栖息地的完整性，但观察到的持续树木再生表明这些影响尚未发生。我们的结果表明，MBBR的针叶林历来经历了频繁的大火，而这种大火与气候和树木的生长无关。这可能证明这些针叶林的自然火灾状况已因人类活动而发生了巨大变化。尽管这些频繁发生的低烈度火灾可能会对树木的再生产生不利影响，并最终降低帝王蝶越冬栖息地的完整性，但观察到的持续树木再生表明这些影响尚未发生。我们的结果表明，MBBR的针叶林历来经历了频繁的大火，而这种大火与气候和树木的生长无关。这可能证明这些针叶林的自然火灾状况已因人类活动而发生了巨大变化。尽管这些频繁发生的低烈度火灾可能会对树木的再生产生不利影响，并最终降低帝王蝶越冬栖息地的完整性，但观察到的持续树木再生表明这些影响尚未发生。