ABSTRACT Growth dynamics of pachycaulous stems of arborescent cycad plants are not well understood, and most observations have been made in cultivated garden plants. We studied Cycas micronesica plants in Guam, Tinian, and Yap to understand the influences of geography, plant size, sex, and herbivory on stem growth. We also determined the changes in demography of Guam’s population after 15 years of damage by non-native insect herbivores. The height increment (HI) was similar for plants within the height range from 100 cm to more than 600 cm, so the relative growth rate declined with height. Female tree HI was 68% of male tree HI, and Yap tree HI was 87% of Guam tree HI. Chronic herbivory by non-native insect herbivores caused a mean 44% decline in HI. Plants in managed gardens grew more rapidly than plants in a wild habitat. The HI was used to estimate that Guam has experienced a complete loss of ≈70 y of demographic depth resulting from the selective mortality of small plants since 2005. When future conservation interventions successfully mitigate the ubiquitous biological threats, our HI may be useful for empirically quantifying recovery of plant health.

中文翻译：

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Cycas micronesica 的高度增量为保护决策提供信息

摘要 乔木苏铁植物粗茎的生长动态尚不清楚，大多数观察都是在栽培园林植物中进行的。我们研究了关岛、天宁岛和雅浦的苏铁植物，以了解地理、植物大小、性别和食草性对茎生长的影响。我们还确定了非本地昆虫食草动物破坏 15 年后关岛人口的人口结构变化。100cm～600cm以上高度范围内植物的高度增量（HI）相似，因此相对生长率随高度下降。雌树 HI 为雄树 HI 的 68%，雅柏树 HI 为关岛树 HI 的 87%。非本地昆虫食草动物的慢性食草动物导致 HI 平均下降 44%。管理花园中的植物比野生栖息地中的植物生长得更快。