Background

1. Assessing Exotic Plant Naturalizations Caused by Botanical Garden Introductions in Hawai‘iRebecca GilbertHokule‘a Program, Washington University in St. Louis Background The negative environmental and economic effects of invasive plant species are now widely appreciated. However, just 100 years ago, exotic plant introductions were widely celebrated and were part of the mission of botanical gardens around the world. As a result, an important area of research in conservation biology is to evaluate the invasive potential of plants that occur in botanical gardens. Like most botanical gardens, The Honolulu Botanical Gardens (HBG) historically had unregulated plant introductions. The main goals of my research were to examine the flora of the HBG and to ask: What proportion of botanical garden plant introductions have been naturalized in Hawai‘i?   2) What best management practices and policies can we institute to control existing naturalized species and reduce future introduction of new invasive species? Glossary Native (Indigenous/endemic): A species that arrived in Hawai‘i without human introduction, both intentional and unintentional. The species was introduced by natural methods, such as dispersal by wind, water or birds, and adapted to grow naturally in Hawai‘i without human intervention. Non-Native (Exotic, alien, introduced): A species that was introduced to Hawai‘i by humans, whether intentionally or unintentionally. Invasive: A species that poses a threat to the integrity of a plant community. This includes non-native species that adversely affect its introduced area, as well as indigenous species that begin to dominate their communities due to loss of natural controls. Naturalized: A non-native species that established itself in Hawai‘i, being able to sustain itself without cultivation. • Results • Question 1 • Question 2 • Methodology to assess the best management plan for each of the identified naturalized species in the gardens: • Completed site visits to determine the current state of each naturalized species. • Checked each species’ Hawai‘i Pacific Weed Risk Assessment (HPWRA), which gauged plant species’ risk of becoming invasive. • Considered potential removal obstacles such as species’ large seed banks, herbicide resistance, and inaccessible locations. • Determined whether each species should be removed through tree contract, killed with herbicide, or monitored in order to achieve the greatest impact within the constraints of the gardens’ limited budget. • Discussion • Question 1 • Naturalized species are a concern because they run the risk of becoming invasive. Invasive species pose a threat to the integrity of a plant community, which can result in both ecological and economic consequences. Considering the large number of species that had been introduced by HBG as well as the long timespan over which the introductions took place, the number of species that became naturalized could have been greater than what actually occurred. • Question 2 • I worked with the head horticulturist and the director of the gardens to write an invasive species policy for the gardens which outlined: • Guides to the development of the collection • Plant acquisition, distribution • Monitoring • Methods of control for invasive species • Guidelines for the importation and exportation • Role in education • This policy in tandem with National and State invasive policies could help keep the invasive issue under control. • 32 out of 719 species inventoried had become naturalized • 4.45% • 65 out of 1299 species inventoried had become naturalized • 5.00% Further Research I now am looking at the naturalized species to determine if there are patterns of seed dispersal methods. I will compare the dispersal methods of the naturalized species with the dispersal methods found for species from the same families that did not become naturalized. Most studies of this type would have looked at trends in dispersal methods for species that naturalized without intentional human introduction. These findings would be unique because all of the species were intentionally introduced to the gardens. This information would be relevant to botanical gardens or any other organization doing significant plant importation and exportation and could affect their policies regarding those introduction practices. • Methods • For question 1, I examined reports from the Oahu Early Detection Program (OED) which outlined the newly naturalized plant species in the gardens as well as island-wide. • I found additional naturalized taxa from other surveys and references published. • I cross-referenced these naturalized species with the inventories of two sites at HBG. • For question 2, I worked with the head horticulturist at HBG to determine the method to best assess the management plan for each of the identified naturalized species. • Acknowledgements • Honolulu Botanical Gardens • Joshlyn Sand (Horticulturist) • Winnie Singeo (HBG Director) Study Sites An Example of an Invasive Species • Washington University in St. Louis • Environmental Studies Program • Office of Undergraduate Research • Career Center Left: Koko Crater (hot, dry climate) Right: Wahiawa (tropical rainforest) Cissus quadrangularis in Koko Crater