R. Neville, J.Y. Fujikawa and M. Halabisky
Neville, R.; J.Y. Fujikawa and M. Halabisky. Eradication programmes complicated by long-lived seed banks: lessons learnt from 15 years of miconia control on O’ahu Island, Hawai’i

Eradication programmes complicated by long-lived seed banks: lessons
learnt from 15 years of miconia control on O'ahu Island, Hawai'i
R. Neville1, J.Y. Fujikawa1 and M. Halabisky2
1

O'ahu Invasive Species Committee, Pacific Cooperative Studies Unit, University of Hawai'i at Mānoa, 743 Ulukahiki
St. Kailua, HI 96734, USA. <oiscmgr@hawaii.edu>. 2University of Washington, Remote Sensing and Geospatial
Analysis Laboratory, School of Forest Resources, Seattle, WA 98195, USA.

Abstract The invasive tree Miconia calvescens (Melastomataceae) is a priority for control on the Hawaiian Island ofOʽahu due to its potential to replace native ʽōhiʽa (Metrosideros polymorpha, Myrtaceae) forests and degrade watershedfunction if allowed to establish. The Oʽahu Invasive Species Committee (OISC) is attempting to eradicate this species
from the island of Oʽahu. OISC uses a buffer strategy based on estimated seed dispersal distance to determine the area
under surveillance. This strategy has worked well enough to suppress the number of trees reaching reproductive age. The
number of mature trees removed annually is now less than the number initially removed when the programme started in
2001. In 2016, just 12 mature trees were removed from 54.71 km2 surveyed compared to 2002, when 40 mature trees were
removed from 8.26 km2 surveyed, a 96% drop in mature trees per square kilometre surveyed. However, miconia has along-lived seed bank and can germinate after 20 years of dormancy in the soil. Funding shortages and gaps in surveys due
to refusal of private property owners to allow access have resulted in some long-range extensions. OISC’s results suggestthat seed bank longevity is an important factor when prioritising invasive species risk and that allocating more resourcesat the beginning of a programme to eradicate a species with long-lived seed banks may be a better strategy than starting
small and expanding.
Keywords: invasive species, invasive plants, watershed, outreach, cloud water interception, Miconia calvescens,
Metrosideros polymorpha

INTRODUCTION
The tree miconia (Miconia calvescens –Melastomataceae) has been recognised as a threat to forests
on Pacific Islands where it has been introduced (Meyer, etal., 2011; Medeiros, et al., 1997). Native to tropical Central
and South America, it is under control programmes in
French Polynesia, New Caledonia and Hawaiʽi (Meyer,
et al., 2011). In areas where miconia has invaded, it hasformed monospecific stands, shading out all plant species
beneath it (Meyer, 1996). A miconia-dominated forest
would likely not perform watershed services as well as
Hawaiʽi’s multi-layered native forests. Runoff and water
would likely increase and replenishment of the islands’
freshwater aquifer through cloud water interception would
likely decrease. (Nanko, et al., 2013; Takahashi, et al.,2011). Because of its potential to outcompete native forest
flora and its potential deleterious effects on watershedfunction, miconia has been prioritised for eradication on
the Hawaiian Island of Oʽahu. Miconia was introduced toOʽahu at the Wahiawā botanical garden in 1961 (Medeiros,
et al., 1997). It was not until the late 1990s that its invasive
potential became known and efforts to control it began(Medeiros, et. al., 1997). Here we describe the resultsof the island-wide eradication programme for miconia
implemented by the Oʽahu Invasive Species Committee(OISC) since 2002.
The Koʽolau Range forms the eastern spine of theisland of Oʽahu and is the location of the island’s primaryaquifers supplying water to the urban centre of Honolulu(Board of Water Supply, 2016). Data from miconia’s
native and invaded ranges shows that this species occurs intropical areas with more than 1,500 mm of rainfall (Libeau,
et al., 2017). Oʽahu rainfall data indicates that most of theKoʽolau Range, including the areas encompassing theisland’s most important aquifers, could support miconia(Giambelluca, et al., 2013).
Miconia’s potential to replace forest ecosystems withmonospecific stands is evident from its invasion history in
French Polynesia (Meyer, et al., 2011). There, dense stands
occur over 80,000 ha from sea level to 1,400 m (Meyer,

et al., 2011). To put those numbers in perspective, theforested area of the Koʽolau Mountains is approximately
40,469 ha and its highest peak is 960 m (Koʽolau Mountain
Watershed Partnership, 2017). The rainfall and elevationof the Koʽolau Range are similar to those areas in Tahiti
where miconia has formed monospecific stands and istherefore vulnerable to the transformative effects of amiconia invasion (Fig. 1).
Miconia leaves can reach up to one metre in length(Chimera, et al., 2000) (Fig. 2). These large leaves
reduce light levels so dramatically that understorey andgroundcover vegetation under a miconia canopy areseverely reduced (Meyer 2004; Nanko, et al., 2013).
Rainwater collects on the large leaves and funnels it toFig. 1 Miconia calvescens occurs in areas with more than
1,500 mm rainfall annually. The area shown encompasses
almost all of the Ko’olau mountain range on the easternside of the island. (Rainfall data from Giambelluca, et al.,
2011)

In:
C.R. Veitch, M.N. Clout, A.R. Martin, J.C. Russell and C.J. West (eds.) (2019). Island invasives: scaling430
up to meet the challenge, pp. 430–434. Occasional Paper SSC no. 62. Gland, Switzerland: IUCN.

Neville, et al.: Miconia control on O’ahu Island, Hawai’ithe bare ground with a velocity high enough to accelerate
erosion when hitting bare ground (Nanko, et al., 2013).
Water recharge of the island’s aquifers may also
be at risk. A study on Hawaiʽi Island found that nativedominated ‘ōhi’a forest intercepted 454 mm more cloudwater than strawberry guava (Psidium cattleyanum –Myrtaceae) dominated forests due to the differences in barkstructure and tree shape (Takahashi, et al., 2011). Miconia
has smooth bark similar to strawberry guava and would
likely have similar rates of cloud water interception. Thisis important as cloud water interception may contributeup to 32% of total precipitation in Hawaiʽi’s montane wet
forests (Giambelluca, et al., 2011). Based on these studies,
we surmise that a structurally complex, native forest is
likely better at condensing fog and cloud drip and directing
rain into the islands’ aquifer than a forest dominated bymonospecific stands of miconia.

The frequency interval of every three years is necessary
since miconia can mature in as little as four years (Meyer,1996). Areas within this 800 m ground buffer that are too
steep to survey by ground are surveyed by helicopter every
two years.
Ground crews locate miconia visually during both
ground and air surveys. In addition to their large size,
miconia’s leaves have vibrant purple undersides and thismakes it fairly easy to detect on both types of surveys

CONTROL OF MICONIA ON OʽAHU
Control of miconia in the Hawaiian Islands began in1991 after scientists and conservationists saw the damage
it was causing in Tahiti (Medeiros, et al., 1997). OnOʽahu, miconia was planted at three botanical gardens,
at two private residences and a commercially operated
park (Medeiros, et al., 1997). All voluntarily destroyed
their trees when requested by the state Departments ofAgriculture (HDOA) and Land and Natural Resources(DLNR). Follow-up surveillance and control wereconducted by volunteers and HDOA and DLNR employees
until the Oʽahu Invasive Species Committee was formed asa project of the University of Hawaiʽi in 2001.
The miconia eradication project strategy is based ondelimitation, defined as conducting enough surveillance
to be sure that we know how far the invasion extends;
containment, defined as containing the population byremoving plants before they can mature; and extirpation,
defined as removing immatures until the seed bank is
exhausted (Panetta & Lawes, 2005; Panetta, 2007). In orderto achieve the benchmarks of delimitation, containment
and extirpation, OISC designates areas within a certain
radius around reproductive trees for ground or helicopter
surveys and conducts outreach to property owners andoutdoor enthusiasts. The search area is currently at 91.39
km2 and encompasses 4,000 different private property lots
for which we must acquire permission to access in order tosurvey (Fig. 3).

Fig. 3 The O'ahu Invasive Species Committee search areafor Miconia calvescens.

Ground surveys are conducted for 800 m around every
mature tree and 500 m around every immature tree every
three years. The 500 m or 800 m radius around trees iscalled the ground buffer. An analysis of OISC’s miconia
field data shows that 99% of immature trees fall within
350 m of a mature tree (Fujkawa, pers. comm. 2017),
confirming that the size of the search area is large enough.

Fig. 2 Typical leaf size for Miconia calvescens.

Fig. 4 A sapling growing out of a patch of Clidemia hirta on
O'ahu. The large leaves and striking purple undersides
make miconia fairly detectable, although in heavy
vegetation, trees can still be missed.
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Island invasives: scaling up to meet the challenge. Ch 2E Other taxa: Plants(Fig. 4). However, on ground surveys trees are sometimes
missed due to dense vegetation that limits visibility. Steepterrain can also make trees difficult to detect as simply
getting up a vertical slope safely may distract the surveyor
from finding trees. Large trees that have already breached
the canopy are also difficult to spot from the ground.
Surveyors can visually find miconia trees from ahelicopter but the helicopter must fly very low and slow
above the canopy. The large leaves are visible from theair and the rotor wash from the helicopter often blows
the leaves around so the purple undersides are visible.
Immature trees as tall as four metres have been spottedon helicopter surveys. One disadvantage of helicopter
surveys is that in areas with a thick canopy, trees growing
beneath may be missed. OISC’s observations are that oncea large tree has broken through the canopy it often matures
very quickly, so areas designated as too steep for groundsurveys within the ground buffer are flown every two years
to compensate for the fact that trees will not be found until
they are older.
Another 800 m from all mature trees is flown byhelicopter to check for outliers. Despite the high cost of
paying for helicopter time, the per-hectare cost is actuallyless than ground surveys because so much area can becovered quickly. Residential areas designated for helicopter
surveys are done by ground or road in order not to disturb
the residents. If a tree is found during an outlier survey,
then an 800 m buffer is drawn around it and it becomes partof the area that is searched by ground.
Outreach to hikers, hunters and other outdoor
recreationalists has been helpful in receiving reports of
miconia. OISC engages organised groups of hikers andhunters through presentations, educational materials andsocial media with the aim of informing people how to
identify and report miconia. We also present to schools
and set up educational booths at community festivals in
the areas where we are surveying. We believe that outreachalso assists in gaining entry to private land. Our observationis that property owners who have heard about the invasive
species problem before we call and ask their permission tosurvey, are more likely to let us on, although we have notspecifically measured this.

from the nearest mature tree. The 6,900 m and 2,400 m
extensions were found while the crew was surveying forother plant species.
DISCUSSION
Having the source trees removed from the botanicalgardens and the few private properties, as well as detectionof mature trees by agencies and volunteers before OISC
was even formed in 2001, was a tremendous help to theeradication project. OISC was able to apply its strategy
around the historical points and get a head start on
delimitation. By 2010, the surveillance and delimitation
phase of the project was complete. OISC did not havethe resources to survey all suitable habitat, however, we
took the steps described below to ensure that all known
populations were mapped. We interviewed fellow natural
resource agencies and hiker groups working in suitable
habitats to ensure there was not a population in areas we
did not have the time to look at. We conducted binocularsurveys outside our survey areas in prime miconia habitat
looking for large patches. We also calculated the distanceof immature trees to the nearest mature tree in 2009. We
found that 99% of trees fell within 400 m of a mature tree
and maximum distance of an immature tree was just shortof 1,600 m (Fujikawa, et al., 2009). This gave us confidence
that by 2010, delimiting was complete.
After 2010, the project moved into the containment
phase, but it has been difficult to achieve containment as
defined by eliminating all mature plants. Although OISC
has been able to achieve a significant decrease in thenumber of mature plants per square kilometre surveyed,
we have not been able to completely suppress maturation.
Trees that are missed during one survey cycle aresometimes missed due to human error—thick vegetationand steep terrain are two factors that may decrease theefficacy of surveillance. Although our success rate withgetting property owners to agree to let field crews survey
their property is 95%, there are some property owners who
have been reluctant to agree to surveys. In one case, it took
Table 1 Number of mature, >2m tall trees and km2
surveyed 2002–2016.

RESULTSOISC hired its first staff in November of 2001 andsurveys started in 2002. The number of square kilometressurveyed per year has grown as more funding became
available. Since 2002, OISC has been able to achieve a
96% reduction in mature plants from 4.8 mature trees per
km2 surveyed to 0.2 mature trees per km2 surveyed (Table1). There were 40 mature trees found and removed over
8.26 km2 in 2002 and just 12 found and removed over
54.71 km2 in 2016.
OISC also counts and takes GPS points for trees thatare immature but over two metres tall. Trees over two
metres that are missed will likely be mature the next time
the field crew surveys. Therefore, the number of trees overtwo metres should also be at zero in order to achieve andensure containment. OISC has achieved an 81% decreasein trees over two metres from 6.8 to 1.3 trees per km2.
Three significant range extensions have recently
occurred. As stated above, OISC’s data shows that 99%
of immature plants fall within 350 m of a mature plant.
However, in 2015, one immature tree was found 6,900 m
from the nearest mature tree. In 2016, another was found
1,600 m from the nearest mature tree. In 2017, a small
patch of mature and immature plants was found 2,400 m

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Year
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016

No. mature
trees
40
4
7
9
6
6
0
4
1
3
5
2
5
12
12

No. trees >2m
94
21
14
54
27
25
37
89
48
27
83
94
97
123
94

Km2
surveyed
8.26
9.37
9.00
21.00
25.16
29.37
20.53
14.07
23.25
27.00
14.87
22.20
21.59
39.44
54.71

Neville, et al.: Miconia control on O’ahu Island, Hawai’i

several years to acquire access from a property owner who
owned an entire valley. By the time the crew was able tosurvey, trees had matured. Sometimes the 5% that say noor take a long time to say yes can be critical. In some years
decreases in funding meant we did not have the resources tosurvey the area required by our strategy. The combinationof funding fluctuations and time spent negotiating property
access allowed some trees to mature. The presence of
mature trees may have resulted in range extensions into
new watersheds from long-distance dispersal events.
A review of the distances between immature and mature
trees conducted in 2017 resulted in 99% of immaturemiconia falling within 350 m of a mature tree (Fujikawa
pers. comm. 2017), which was similar to our 2009 results.
However, the furthest immature miconia was now 6,900 m
away from the nearest mature tree.
Miconia’s long-lived seed bank is a complicating factor
in achieving containment. Research by Meyer (2010) has
estimated the seed bank at 16 years in French Polynesia,
but observations on Oʽahu suggest it may be as long as 20
years. The Wahiawā botanical garden where miconia wasoriginally introduced has found seedlings and reported themto OISC as late as 2016. They removed their mature tree in1996 (Medeiros, et. al., 1997) and OISC has surveyed theentire area at least three times without finding any miconia
whatsoever, so the likelihood that the seedlings are fromthe 1996 mature tree is very high.
Lessons learnt
The long-term work done on miconia in French
Polynesia is key to OISC’s success in preventing a fullscale miconia invasion on Oʽahu. The research was criticalto raising the alarm about the species and mobilising
control efforts early. Miconia is one of the few species that
OISC has taken on where the seed-bank longevity is known
thanks to the long-term studies done by Jean-Yves Meyer(Meyer, et al., 2011). Research from Tahiti also formed thebasis of the outreach narrative. For example, one of the key
talking points for outreach was the enormous area of forestthat had been turned into monotypic stands of miconia anda photograph of a landslide in Tahiti was a mainstay ofstate-wide outreach to explain the potential erosion effects.
Both Tahiti and Oʽahu offer lessons to islands where
miconia might be dispersed in the future.
If possible, having adequate funds at the beginningof an eradication project to complete delimiting as soon
as possible may shorten the containment phase. It took
OISC eight years to be sure where the miconia populationwas. Private property was a complicating factor. A small
percentage of larger landowners would not let the fieldcrew survey in a timely manner and trees were allowed
to mature while we negotiated access. Delimiting andcontaining a species before it spreads to additional private
property owners will be immensely helpful in achieving
eradication as quickly as possible. Taking on additional
species can also be helpful in detecting long-distancedispersal events. OISC volunteered to do aerial surveys for
a forest pathogen because it would require us to fly over
all habitat suitable for miconia. The small patch of matureand immature trees 2,600 m away from the nearest known
mature tree was discovered during this survey.
Outreach has also been helpful for the survey effort
and programme managers should consider dedicating
funds and employees for outreach from the beginning of
the programme. OISC did not have a full-time outreachspecialist until four years after the programme started.
OISC has had trees reported to us but more importantly,

we believe outreach has helped OISC get access to survey
on private land. People seem more willing to grant accessif they have heard of the invasive species problem andmiconia before they receive the call asking for permission
to survey.
OISC’s outreach is a combination of talking directly tocommunity groups, hiking and hunting groups and schools
through presentations, participating at events and social
media. We have not had the ability to scientifically test
the outreach and see which methods or messages work
best. Anecdotally, we believe that explaining the larger
ecosystem effects and the possible effects on the island’swater supply will persuade a wider group of people thanthose who might be motivated by preserving the nativeflora of Hawaiʽi. Research about which messages would
be received best would be welcomed.
Although completely suppressing maturation of miconia
has proved difficult due to the long-lived seed bank, OISC
has been able to achieve a 96% reduction in mature trees
per square kilometre since the programme began in 2002.
In 2016, only 12 mature trees were found across 54.71 km2.
OISC has been able to keep the density of mature trees
very low, but the long-lived seed bank means that a missed
tree due to human error, an area that the field crew cannot
survey due to lack of funding or the inability to get accessto private property will likely result in a mature tree oncethe crew has access to the area. Containment for species
with long-lived seed banks will be long-term projects.
For this reason, when evaluating feasibility, prioritising
species for control and planning eradications, seed banklongevity should always be taken into account (Panetta
and Timmins 2004). Policymakers deciding which species
should be restricted for import should also consider seedbank longevity as a critical factor. While a long-lived seedbank is certainly not the only factor that makes a species
invasive, if a species with a long-lived seedbank starts tobecome a problem, eradication will be a long-term andexpensive project. Seed-bank longevity is not known formany species, and conducting longevity studies to answer
that question for species under management would be very
helpful to plan eradication efforts.
ACKNOWLEDGEMENTS
The authors would like to thank the Department ofLand and Natural Resources/Division of Forestry andWildlife, Hawaiʽi Invasive Species Council, Honolulu
Board of Water Supply, US Forest Service and the Hawaiʽi
Tourism Authority for funding this project; the members of
OISC’s steering committee for guidance and moral support
over the years; OISC’s Principal Investigator Dr. David
Duffy and the staff of the Pacific Cooperative Studies Unit
and OISC volunteers, field crew and staff past and present.
The Oʽahu Invasive Species Committee is a project of
the Pacific Cooperative Studies Unit at the University of
Hawaiʽi at Mānoa.
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