Download Honolulu Botanical Gardens - Environmental Studies

Background
Results
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.
Question 1
Discussion
Question 1
Koko Crater
Naturalized Species
Introduced Species
The main goals of my research were to examine the flora of the HBG and to ask:
1) What proportion of botanical garden plant introductions have been naturalized in
Hawai‘i?
•
•
32 out of 719 species inventoried had become naturalized
4.45%
Wahiawa
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.
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.
Naturalized Species
Introduced Species
•
•
65 out of 1299 species inventoried had become naturalized
5.00%
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.
 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.
 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.
Study Sites
An Example of an Invasive Species
 I cross-referenced these naturalized species with the inventories of two sites at HBG.
Left:
Koko Crater
(hot, dry climate)
Right:
Wahiawa
(tropical rainforest)
Cissus
quadrangularis
in Koko Crater
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.
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.
Acknowledgements
Washington University in St. Louis
Honolulu Botanical Gardens
• Environmental Studies Program
• Joshlyn Sand (Horticulturist)
• Office of Undergraduate
• Winnie Singeo (HBG Director)
Research
• Career Center