Height increment of Cycas micronesica informs conservation decisions

Area of Science:

• Botany
• Ecology
• Conservation Biology

Background:

• Pachycaulous stem growth in arborescent cycads remains poorly understood, with limited data from wild populations.
• Most existing knowledge on cycad growth dynamics stems from observations of cultivated garden specimens.

Purpose of the Study:

• To investigate the factors influencing stem growth in *Cycas micronesica* across different geographic locations.
• To assess the impact of herbivory by non-native insects on cycad growth and population demography.
• To compare growth rates between wild and managed cycad populations.

Main Methods:

• Studied *Cycas micronesica* in Guam, Tinian, and Yap, measuring height increment (HI) across various plant sizes, sexes, and herbivory levels.
• Quantified the effects of chronic herbivory by non-native insect herbivores on stem growth.
• Compared growth rates of plants in managed gardens versus wild habitats.

Main Results:

• Height increment (HI) showed a declining relative growth rate with increasing plant height.
• Female *Cycas micronesica* exhibited 68% of the HI of male trees; Yap plants had 87% of Guam plants' HI.
• Chronic herbivory led to a mean 44% reduction in HI, with managed plants growing faster than wild ones.

Conclusions:

• Geography, plant size, sex, and herbivory significantly influence *Cycas micronesica* stem growth dynamics.
• Non-native insect herbivory has severely impacted cycad growth, leading to an estimated loss of 70 years of demographic depth in Guam.
• Height increment data can serve as a crucial metric for evaluating the success of future conservation efforts and plant health recovery.