Effects of Fountain Grass and Ungulate Fencing on the Health and Natural Regeneration of Wiliwili Trees

Abstract

Invasive species are a serious issue across the world because of the economic and environmental costs involved in managing them. Weeds pose a serious threat to the health of ecosystems as compounding detrimental factors; adding to the strain caused by invasive animals, habitat loss/alteration, and natural phenomena such as drought and fire. Biological control of insects and habitat protection are often used to address these issues. How can the safe removal of weeds affect the health and natural regeneration rate of plant species in an area already employing biological controls and habitat protection? This work is a case study of the effect that the removal of invasive weed species can have on the health and natural regeneration rate of Wiliwili trees (Erythrina sandwicensis) with a focus on the invasive fountain grass (Pennisetum alopecuroides). The study also tested the difference in growth rate and regeneration between trees protected by fencing and those exposed in the wild. Data were collected from the population at Waikoloa, HI on Hawai‘i Island from June 2013 through March 2014 at 4-5 week intervals. Effects of weed removal and ungulate fencing were determined by measuring the growth rate of branches, flower production, and infestation rates by the invasive Eryrhrina Gall Wasp (Quadrastichus erythrinae). Regeneration rates were estimated by counting seedlings. The combination of weeds and fencing had a significant effect on the health and natural regeneration of wiliwili trees.