(DRAFT) - Taxonomy
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
TAXONOMY
NAME - 'AKOKO, EWA PLAINS
OTHER COMMON NAMES - 'AKOKO, EWA PLAINS; 'AKOKO and 'EWA PLAINS;'AKOKO; KOKO; KOKOMALEI
ELEMENT CODE -
CATEGORY - Angiosperm
PHYLUM AND SUBPHYLUM - MAGNOLIOPHYTA,
CLASS AND SUBCLASS - MAGNOLIOPSIDA,
ORDER AND SUBORDER - EUPHORBIALES,
FAMILY AND SUBFAMILY - EUPHORBIACEAE,
GENUS AND SUBGENUS - EUPHORBIA,
SPECIES AND SSP - SKOTTSBERGII, VAR.
SCIENTIFIC NAME - EUPHORBIA SKOTTSBERGII VAR.
AUTHORITY -
TAXONOMY REFERENCES -
COMMENTS ON TAXONOMY -
Ewa Plains 'Akoko
Euphorbia skottsbergii var. kalaeloana Sherff
KINGDOM: Plant GROUP: Angiosperm
DIVISION: Magnoliophyta CLASS: Magnoliopsida
ORDER: Euphorbiales FAMILY: Euphorbiaceae
The 'Ewa Plains 'akoko is a shrub 1 to 1.3 m (occasionally 2 m)
tall, with milky sap. The young stems are finely puberulous, and the
older stems are gray and glabrate. The leaves are opposite in
arrangement, with petioles 1 to 2 mm long and puberulous. The leaf
blades are 5 to 20 mm long, 4 to 13 mm wide, elliptic, firm, and gray
green. The inflorescences are axillary, 6 to 10 mm long, bearing a
single head with a stalk 2 to 6 mm long and puberulous. The flower
head is 2 mm tall and puberulous. The flower cup 1 mm, puberulous,
with 4 to 5 glands on the rim. The pod is 2 to 3 mm, globose, 3-lobed
and stalked, with 3 gray seeds per pod (03,20).
The endemic species E. skottsbergii has four varieties, all of
which are endangered and two of which were once considered possibly
extinct (10). The variety skottsbergii occurred on O'ahu, but is
believed to be extinct (03,14). Many botanists feel that the
differences between the two O'ahu varieties were merely the result of
Taxonomy - 1 (DRAFT) - Taxonomy
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
habitat conditions (02). Two varieties occur on Moloka'i.
Euphorbia skottsbergii was first described by E.E. Sherff (21) in
the Botanical Gazette in 1936 from specimens collected on O'ahu's 'Ewa
Plains; the type specimen was collected by C. Skottsberg (no.122) in
1922 from the "Ewa coral plain, Isl. Oahu." The variety kalaeloana
was also described from the same area; J.F. Rock's 1919 collection
(no.17034) from "coral plain under Algaroba, back of Barber's Point,
Isl. Oahu" is the type specimen. Varieties skottsbergii and
kalaeloana were found on O'ahu, and varieties audens and vaccinioides
on Moloka'i. In 1821 S.F. Gray (11) described the genus Chamaesyce,
which became a controversial taxon, often treated as a subgenus of
Euphorbia. Croizat (05) amended Gray's description and published the
new combination C. skottsbergii (Sherff) Croiz. and Deg. Sherff (22)
did not accept Croizat and Degener's genus, publishing Euphorbia
skottsbergii as occurring "near southern coast of Oahu, from Barbers
Point eastward toward Pearl Harbor," and variety "B" kalaeloana as
"known only from type vicinity of Barbers Point (Kalaeloa), southern
coast of Oahu." In 1959, Otto and Isa Degener (06) published the new
combination Chamaesyce skottsbergii var. kalaeloana (Sherff) Deg. and
Deg. In St. John's (19) 1973 checklist of Hawaiian plants, Croizat
and Degener's genus is not recognized. The question of generic rank
continues.
Koutnik's (15) treatment of the native species of Chamaesyce is
included in Wagner, Herbst, and Sohmer's (13) "Manual of the flowering
plants of Hawai'i". The species C. skottsbergii will now have only
two varieties. Variety skottsbergii will also include varieties
kalaeloana and audens, thus increasing the range of C. skottsbergii to
Molokai. Variety vaccinioides on Moloka'i will remain distinct.
There is some feeling among botanists that variety audens should
remain distinct as well (02). This taxonomic revision will not affect
the listed status of this plant, though its range and present
distribution will increase. The change in the generic name is a
result of recognition of Chamaesyce as a full genus rather than as a
subgenus of Euphorbia; the change in variety name is the result of the
determination that three previously described varieties are actually
one variety.
The species E. skottsbergii is named in honor of Dr. Carl
Skottsberg, who was Director of the Arboretum of Gothenburg, Sweden
(21). Variety kalaeloana was named for its location at Kalaeloa, or
Barbers Point, O'ahu, and is commonly known as the 'Ewa Plains 'akoko.
Members of the genus Euphorbia have been known by the Hawaiian names
'akoko, koko, and kokomalei (03,18). No Hawaiian name is known to
have been applied particularly to this variety.
The type specimen of the species, E. skottsbergii is in the
herbarium of the Bernice P. Bishop Museum, Honolulu. The type of
variety kalaeloana is at the Gray Herbarium of Harvard University,
Cambridge; the isotype is at the Bishop Museum (21,22). Other
specimens of the variety are at the herbarium of the Field Museum of
Natural History, Chicago, the Bishop Museum, and the herbarium of the
University of Hawai'i Botany Department, Honolulu (12,21,22).
[Descriptions of the variety can be found in Sherff (21,22), and St.
John (20). A description of the variety will also be in Koutnik (15)
as part of variety skottsbergii.] Line drawings are included in the
Taxonomy - 2 (DRAFT) - Taxonomy
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
'Ewa Plains Botanical Survey (03) and are reprinted in the Endangered
Species Technical Bulletin (17). Photographs are in the survey
report, "Hawaii's vanishing flora" (14), and "Rare endemic plants of
the Hawaiian Islands" (20). Distribution maps are in the 'Ewa Plains
Botanical Survey and in the ecological and horticultural studies of
the species (01).
Taxonomy - 3 (DRAFT) - Status
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
STATUS
Coded Status
E: Federal Endangered
COMMENTS ON STATUS -
U.S. STATUSES AND LAWS:
The 'Ewa Plains 'akoko (Euphorbia skottsbergii var. kalaeloana)
has been designated an Endangered species pursuant to the Endangered
Species Act of 1973 (50 CFR 17.12; P.L. 93-205, 87 Stat. 884; 16
U.S.C. 1531-1540), as amended. The species has this status wherever
found including the State of Hawaii.
Removal and reduction to possession of any Federally listed plant
from an area under Federal jurisdiction is unlawful (50 CFR 17.61 and
17.71).
RESPONSIBLE FEDERAL AGENCIES:
USFWS -Responsible for the management/recovery, listing, and
law enforcement/protection of this species.
DOD -Responsible for the law enforcement/protection of this
species with applicable State and Federal laws on
public land under their control. Also responsible for
management/recovery on Department of Defense lands.
The U.S. Department of Agriculture, APHIS, is responsible for
enforcing regulations against importing or exporting endangered
species for commercial purposes. No commercial activities are
expected for this plant.
All Federal agencies have responsibility to ensure that any
action authorized, funded, or carried out by that agency is not likely
to jeopardize the continued existence of the species or result in the
destruction or adverse modification of Critical Habitat (50 CFR 402),
and to utilize their authorities to carry out programs for the
conservation of the species.
STATE STATUSES AND LAWS:
STATE: Hawai'i
DESIGNATED STATUS: Endangered
ADMINISTRATIVE AGENCY: State Department of Land and Natural
Resources, Division of Forestry and
Wildlife.
STATE STATUTE: Hawaii Endangered Species Law, Hawai'i Revised
Statutes, Chapter 195D.
INTERNATIONAL STATUSES, TREATIES, AND AGREEMENTS:
None.
Status - 1 (DRAFT) - Status
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
ECONOMIC STATUSES:
None known.
75/07/01:40 FR 27823/27924 - Notice of review
76/06/16:41 FR 25423/25472 - Proposed rule
78/04/26:43 FR 17909/17916 - Summary of comments on proposed rule
79/12/10:44 FR 70796/70797 - Withdrawal of proposed rule
80/09/02:45 FR 58166/58168 - Reproposal as Endangered
82/08/24:47 FR 36846/36849 - Final rule, listed as Endangered
87/07/07:52 FR 25523/25528 - Notice of review
Status - 2 HABITAT ASSOCIATIONS
HABITAT - TERRESTRIAL
TERRESTRIAL
COASTAL
LAND USE -
Commercial and Services
Industrial
Transportation, communications, and Util
Industrial and Commercial Complexes
Evergreen Forest Land
Shrub and Brush Rangeland
Bare Exposed Rock
Strip Mines, Quarries, and Gravel Pits
Transitional Areas
COMMENTS ON HABITAT ASSOCIATIONS -
The 'Ewa Plain is an arid coastal lowland that extends from sea
level to an elevation of about 30 m, seven to eight kilometers inland.
The plain is underlain by a broad elevated coral reef partly covered
by alluvium carried out from the mountains. Over time the calcareous
materials of the exposed reef have been modified, consolidated, and
cemented to form a hard but very permeable surface (16).
The plain has been affected by human activities to such an extent
that virtually no areas of intact native vegetation still occur.
Extensive urban development has significantly altered the pattern of
land use. Of the plain's total area (approximately 10,240 hectares),
12% (1,229 hectares) were not under cultivation or urbanized in 1979.
The remaining 88% (about 9,000 hectares) were in: sugar cultivation
(36%), Barbers Point Naval Air Station (NAS) and other military bases
(32%), Campbell Industrial Park, including the small boat harbor
(13%), with the remainder (7%) in quarries, residential complexes,
recreational areas, and other uses. These figures have changed
slightly with development of the deep draft harbor at the site of the
small boat harbor and adjacent extensive coral quarry (03). Plants
also occur adjacent to roads on Barber's Point NAS and Hanua Street.
The approximately twenty percent (20%) of the plain that is not
developed is covered by "natural vegetation". The vegetation is
secondary in origin and is composed largely of introduced species,
such as Prosopis pallida, Leucaena leucocephala, and Chloris inflata.
Though exotic in composition, it is a natural community. The
vegetation has been severely fragmented by man-made environmental
changes with the result that there is no continuous patch of
vegetation, but rather it occurs as a mosaic. Several rare plants
restricted to the 'Ewa Plains area survive as relict populations
within these undeveloped areas (03).
Vegetation types:
The original habitat of Euphorbia was probably a fairly open
savannah with scattered trees (such as Erythrina sandwicensis) and
shrubs. The 'akoko now occurs in association with three exotic
vegetation types which represent a successional gradient from ruderal
(weed) community, through a scrub-dominated understory with scattered
trees, to closed forest. Understory character changes markedly as the
amount of shade increases (01,02,03).
1. The closed Prosopis (kiawe) forest is the most extensive
vegetation type in undeveloped areas on the 'Ewa Plain. It is
composed of medium to high stature trees, 5 to 12 m tall, which form
extensive stands with greater than 60% cover. The closed forest lacks
Habitat Associations - 1 a shrub layer, and a few tall plants of Leucaena leucocephala form a
sparse sub-canopy layer. Herbaceous ground cover is also sparse and
consists of shade tolerant species such as Asystasia gangetica,
Mavastrum coromandelianum, Achyranthes aspera, and Plumbago zeylanica.
The 'akoko does not thrive in the Prosopis climax community, where it
tends to be found on the fringe of the heavy shade.
2. Open Prosopis forest has trees 2 to 5 m tall with a conopy
cover of 10 to 60%. Because of less shading, a number of shrub
species, such as Acacia farnesiana, Leucaena, Pluchea symphytifolia,
and P. indica, and an herbaceous ground cover are found in this
vegetation type. Disturbances such as wood cutting have maintained
these forests in an open condition; if left undisturbed, they would
eventually become closed.
3. The open area along the fringe of the former quarry supports
a ruderal (weedy) plant community. The vegetation type is
characteristically found in areas which have been disturbed. After
clearing, annual, weedy species colonize an area and include
Pennisetum setosum, Verbesina encelioides, Atriplex semibaccata,
Chloris inflata, and others. When left undisturbed, woody shrubs
replace some of the herbaceous species.
Euphorbia tends to do relatively well in both open communities.
Environmental Parameters:
The 'Ewa Plain, on the southwest leeward side of O'ahu, is
characterized by an average annual rainfall of 50 cm, mean annual
temperatures in the range of 22.2 to 25.5 degrees C, and a long summer
drought from mid-March through mid-October. Most rain falls during
winter "kona" storms (Dec.-Feb.). Cloud cover is less than on the
windward coast, and levels of solar radiation are high. The plain
receives the greatest incident solar radiation of any location on
O'ahu (01,03).
In its natural habitat, the 'Ewa Plains 'akoko is confined to
areas of bare, coralline soils. Near the coast, where the plant
occurs, soil cover is very thin, averaging 0.6 to 1.3 cm in depth,
with occasional pockets of 5-10 cm. The deepest soil was found in an
area in which clearing of Prosopis with a bulldozer had disturbed the
substratus. In many places the limestone (calcium carbonate) is
exposed. The coralline substratum appears to be solid, but in fact
has many fissures and holes as the result of dissolution of the coral
by rainwater over many thousands of years; this type of topography has
been called "karst formation". During rainy periods the water is
channeled down into the cracks, fissures, and sinkholes. 'Akoko seeds
tend to germinate in cracks, and the plants often appear as if they
are growing in solid rock. The lack of soil cover is advantageous to
the Euphorbia, as the seedlings of faster growing weedy species,
particularly grasses, which would compete for rooting space, water,
and light do not do as well in such situations (01).
Larger plants, such as Prosopis trees and Sida and Acacia shrubs,
and Asystasia, also occur on coralline substrata or in sink holes;
these are plants which are long-lived and develop deep rooting
systems. The annual, herbaceous plants occur in areas with shallow
soil and litter; the shallow soil in these areas is often only a few
centimeters deep and dries out quickly. These shallow areas seem to
provide a more suitable habitat for plants which are able to grow
quickly, flower, and produce a seed crop during the relatively brief
wet season when the soil is damp (01).
Euphorbia occurs on soils of three types: a light colored
calcareous sand (Jaucas sand), a dark brown loam (Ewa silty clay
loam), and a greyish brown clay (Keaau clay). Mamala stony silty clay
loam is a thin layer of red, friable soil found, on the 'Ewa Plain, in
cracks and depressions in the limestone surface. Soil data were
Habitat Associations - 2 obtained during an intensive study of the three habitat types in which
Euphorbia occurs on the 'Ewa Plain (01). The open habitat site, the
most recently disturbed, had only the sandy soil. the open canopy and
the closed canopy sites had a layer of more organic, less calcareous
topsoil covering a second horizon of the sandy soil. The calcareous
soils are higher in pH, lower in moisture content, and lower in
concentrations of available nutrients. During the wet season,
regardless of soil type, pH increases and available nutrient
concentration (available N and P) decreases. Soil in an area where
the shrub Leucaena leucocephala, a legume, is the most abundant
species has a considerably higher dry season concentration of
available nitrogen than soils in other areas. The moisture content of
soil from the closed canopy area has a lower moisture content during
the wet season than during the dry season; other areas show the
expected higher moisture content during the wet season (01,09).
The 'akoko shows strong seasonality in vegetative flushing,
flowering, fruiting, and leaf drop dependent upon time and duration of
heavy rains and total amount of rainfall. Seedling survival depends
primarily on moisture availability and secondarily on site factors.
Low moisture availability is the most frequent cause of seedling
mortality. Soil moisture must be adequate during the critical growth
period (approximately three months) to allow the plant to develop to
the juvenile phase. Seedlings are most likely to survive to the
juvenile stage if they occupy a site which is partially shaded and has
a number of crevices or small openings in which they have taken root
(01).
Habitat Associations - 3 (DRAFT) - Food Habits
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
FOOD HABITS
TROPHIC LEVEL -
AUTOTROPH
Food Habits - 1 (DRAFT) - Environment Associations
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Coastal Features: Rocky offshore islands
G Coastal Features: Sandy offshore islands
G Coastal Features: Vegetated offshore islands
G Terrestrial Features: Depressions
G Terrestrial Features: Rock outcrops
G
G
G
G
G
G
Environment Associations - 1 (DRAFT) - Life History
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
LIFE HISTORY
HABIT:
The 'Ewa Plains 'akoko is a shrub (20,21,22).
LIFE CYCLE:
Perennial (20,21,22).
TYPE OF REPRODUCTION:
Euphorbia apparently reproduces only sexually, by seed (01).
However, a search was made to see if runners or evidence of other
modes of vegetative reproduction such as underground stems, rhizomes
and stolons, aerial stems, or root suckers were present. A number of
plants were excavated during the horticultural studies, and a search
was made for signs of vegetative reproduction. A search was also made
throughout the study area for young plants growing from root suckers.
No evidence of any mechanisms of vegetative reproduction was found.
REPRODUCTIVE PHENOLOGY:
The plant exhibits strong seasonality in phenophases - vegetative
flushing, flowering, fruiting, and leaf fall. These phenophases show
single annual peaks, although the exact timing of these peaks may
differ from year to year. Timing of the phases is dependent on the
winter rains, i.e., when heavy rains occur, their duration, and total
rainfall. Onset and cessation of most phenophases is sharply marked
rather than gradual.
Detailed data were obtained during eight months of an
uncharacteristic year (September 1980 to August 1981) in which half of
the total rainfall fell during December, resulting in eleven months of
drought rather than the normal six to seven month drought period.
Germination occurs approximately 2 weeks to 1 month after kona storms
(22 Dec 1980 - 12 Jan 1981). Flushing of leaves and cyanthia began
about two weeks after the first heavy "kona" storm (5 Dec). Leaf, bud
and floral production were very rapid during the next four to five
week period (22 Dec to 26 Jan). Heavy flowering occurred 29 Dec. to 5
Jan. Rainfall during January was below average. Occasional field
observations indicate that the normal flowering period extends over a
period of at least three months. Plants which were transplanted to a
site where they were watered year-round produce fruit all year long.
In general: 1) There is a positive correlation between the
winter rainfall and phenophases. Production of leaves, flowers, and
fruit occurs rapidly after the first heavy winter rains. Peak
activity occurs during the winter months. 2) With decreasing amounts
of rainfall characteristic of the spring and early summer periods,
flowering and fruiting of the plants cease, and leaf fall increases
until all leaves are lost and the plants becove dormant. 3) Although
the majority of the plants follow this sequence of events, not all
individuals within a population exhibit synchrony in phenophases, and
some plants can be found with leaves, flowers, and fruits throughout
the year. 4) Growth (increase in height) appears to be more rapid
during the wet, winter months (Dec - Feb) with lower rates of
increase, or even decreases, in height occurring throughout the rest
of the year (01).
Life History - 1 (DRAFT) - Life History
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
SEX OR SPORE STATUS:
Monecious (01). The genus Euphorbia is characterized by the type
of inflorescence known as a cyathium (pl. cyathia), which is made up
of a cluster of unisexual flowers, several male flowers and one female
flower, that are condensed and congested within a bracteate envelope
from which they emerge at anthesis (flowering) (01).
POLLINATION, SPORE AND SEED DISSEMINATION:
Pollination studies indicated that pollen vectors are required
for successful fertilization. The plant seems to have a large number
of generalist pollinators, non-native insects which are widespread
throughout leeward O'ahu. Sixteen species from twelve families were
collected on one 'akoko and had pollen attached externally. Diptera
(flies) are the chief pollinators; Syrphids (flower flies) are the
most important family with 5 species represented.
The greatest percentage of fruit is set if the "flowers" have
been cross-pollinated. Data are based on only one set of experiments,
which did not include artificial self-pollination or
cross-pollination. Experiments were conducted during the heavy
optimal flowering period. Flowers opening late in the flowering
period usually have a reduced seed set, probably a reflection of
environmental conditions rather than availability of pollinators (01).
Seeds are explosively discharged from the plants (01).
SEED BIOLOGY:
Propagation experiments showed that: 1) propagation by seed is
the easiest method of reproducing the plant; 2) there are no apparent
germination inhibitors present; 3) there is no sensitivity to either
light or dark germination conditions; 4) there is no need for any
special media for germination except that normal good drainage should
be provided; 5) pH is not a factor affecting seeds or seedlings;
6) seed germination is probably quicker at higher temperature (26+
degrees C); temperature is not a factor affecting final germination
percentages: if a seed is viable it will germinate without difficulty
within a wide range of conditions; 7) seeds collected from wild
plants displayed a wide range of viability with most tests yielding
10 to 30% germination.
Data collected in field studies indicate that seedling survival
depends primarily on moisture availability and secondarily on a "safe
site". In general: 1) Low moisture availability is the most frequent
cause of seedling mortality. Mortality is high in years when winter
rainfall is below normal. 2) Germination occurs during the winter
months when the probability of rainfall is highest. 3) The soil
moisture content must be sufficiently high during the critical growth
period, which is approximately three months long. During this period
the plant must go from the seedling stage to the juvenile stage. The
transition is from a newly emerged seedling with a succulent, almost
translucent stem and two cotyledons to a juvenile with a corky stem
(to cut down water loss) and many leaves for photosynthesis. 4)
Seedlings are most likely to survive to the juvenile stage if they
occupy a site which is partially shaded and has a number of crevices
or small openings in which they have taken root. Such sites do not
Life History - 2 (DRAFT) - Life History
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
dry out as quickly as more exposed sites.
Field observations indicate that seedlings which germinate in
cracks and crevices in the coralline substratum are more likely to
survive through the dry summer months than those which germinate in
the shallow soil areas. It is suggested that the number of suitable
habitat sites can be increased by bulldozing parts of proposed
transplant areas. Such disturbance would provide more cracks,
crevices, and rubble for the plants, while at the same time
eliminating some weedy plant species (01).
POPULATION BIOLOGY:
Euphorbia skottsbergii var. kalaeloana is described as "locally
common" in its restricted habitat on the 'Ewa Plain (03). A total of
six colonies, ranging in size from a single individual to a few
thousand plants, are currently known. Other colonies on the plain
have been destroyed by various development activities, and one of the
largest known colonies is threatened by plans for harbor support
facilities (01,02,03,04,07,08).
Population sizes in the specific colonies vary from year to year
depending on environmental conditions. Seed germination occurs during
winter months when the probability of rainfall is highest. Seedling
survival depends first on availability of sufficient moisture to reach
the juvenile stage of development. Low moisture availability is the
most frequent cause of seedling germination period did not survive.
Survival is most likely if seedlings occupy partially shaded sites
with cracks or small openings in which they have taken root.
Seedlings are particularly susceptible to destruction by trampling.
Timing and duration of phenological phases differ from year to year
depending on the onset, duration, and amount of heavy winter rains
(01).
ECOLOGICAL/EDAPHIC FACTORS:
The 'Ewa Plain is an arid coastal lowland that extends from sea
level to an elevation of about 30 m, seven to eight km inland. The
plain is underlain by a broad elevated coral reef partly covered by
alluvium carried out from the mountains. Over time the calcareous
materials have been modified, consolidated, and cemented to form a
hard but extremely permeable surface. Most of the storm runoff from
the mountains and elsewhere permeate rapidly through the porous coral
substrate.
The 'Ewa Plains 'akoko occurs on substrate classified by the U.S.
Soil Conservation Service (09) as "coral outcrop" (code CR). Coral
outcrop consists of coral or cemented calcareous sand on the island of
O'ahu. The coral reefs formed in shallow ocean water during the time
the ocean stand was at a higher level. Small areas of coral outcrop
are exposed on the ocean shore, on the coastal plains, and at the foot
of the uplands, where rainfall is 45 - 100 cm. Coral outcrop is
geographically associated with Jaucas, Keaau, and Mokuleia soils. The
land type is used for military installations, quarries, and urban
development. Vegetation is sparse, consisting of Prosopis, Leucaena,
and Chloris. Deposition of the erosion products of the Wai'anae
Mountains on the raised coral bedrock forms the alluvium found on the
landward side of the area.
Life History - 3 (DRAFT) - Life History
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
Pockets of soil found on the plain are broadly classified as
"Lualualei-Fill Land-Ewa association", which consists of well-drained,
fine-textured to moderately fine-textured soils on the coastal plains
and alluvial fans. Lualualei soils (approx. 20%), fill land (approx.
20%), 'Ewa soils (approx. 15%), Jaucas, Kawaihapai, Keaau, and Mamala
soils make up this association.
Euphorbia occurs on soils of three types: a light colored
calcareous sand (Jancas sand), a dark brown loam (Ewa silty clay
loam), and a greyish brown clay (Keaau clay). Mamala stony silty clay
loam is a thin layer of red, friable soil found, on the 'Ewa plain, in
cracks and depressions in the limestone surface. Data on soil
characteristics were obtained during an intensive study of the three
habitat types in which Euphorbia occurs on the 'Ewa Plain (01). The
open habitat site, the most recently disturbed, had only the sandy
soil. The open canopy and the closed canopy sites had a layer of more
organic, less calcareous topsoil covering a second horizon of the
sandy soil. The calcareous soils are higher in pH, lower in moisture
content, and lower in concentrations of available nutrients. During
the wet season, regardless of soil type, pH increases and available
nutrient concentration (available N and P) decreases. Soil in an area
where the shrub Leucaena leucocephala, a legume, is the most abundant
species had a considerably higher dry season concentration of
available nitrogen than soils in other areas. The moisture content of
soil from the closed canopy area was lower during the wet season than
during the dry season; other areas showed the expected higher moisture
content during the wet season. Data from all habitats were grouped by
soil type for characterization by pH, moisture, CaCl, total exchange
bases, cation exchange capacity, nutrient content, and particle size,
are summarized in "Ecological and horticultural studies of Euphorbia
skottsbergii at Barbers Point, O'ahu, Hawai'i, Volume 1" (01).
In its natural habitat, the 'Ewa Plains 'akoko is confined to
areas of bare, coralline substrate with very thin soil cover,
averaging 0.6 to 1.3 cm in depth with occasional pockets of 5 - 10 cm.
The deepest soil was found in an area in which clearing of Prosopis
with a bulldozer had distrubed the substratum. In many places the
limestone (calcium carbonate) is exposed. The coralline substratum
appears to be solid, but in fact has many fissures and holes as the
result of dissolution of the coral by rainwater over many thousands of
years; this type of topography has been called "karst formation".
During rainy periods the water is channeled down into the cracks,
fissures, and sinkholes. 'Akoko seeds tend to germinate in cracks,
and the plants often appear as if they are growing in solid rock. The
lack of soil cover is advantageous to the Euphorbia, as the seedlings
of faster growing weedy species, particularly grasses, which would
compete for rooting space, water, and light do not do as well in such
situations.
The area, on the southwest leeward side of O'ahu, is
characterized by an average annual rainfall of 50 cm, mean annual
temperatures in the range of 22.2 to 25.5 degrees C and a long summer
drought. Most rain falls during winter "kona" storms. Cloud cover is
less than on the windward coast, and levels of solar radiation are
high (03).
The 'Ewa Plains 'akoko occurs in both closed and open Prosopis
Life History - 4 (DRAFT) - Life History
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
forest and in the open area fringing a quarry. The three habitats
represent a successional gradient from a ruderal community, through a
scrub-dominated understory with scattered trees, to closed forest.
Understory character changes markedly as the amount of shade
increases. The 'akoko does not thrive in the closed canopy forest
where shade is too great.
TROPHIC STATUS:
Phototrophic (01).
CHARACTERISTIC DOMINANCE:
Euphorbia is a component of its vegetative community; typically
constituting less than 5% of the total ground cover (01,02,03).
COMMUNITY ECOLOGY:
The 'akoko now occurs in association with three non-native
vegetation types which represent a successional gradient from a
ruderal community, through a scrub-dominated understory with scattered
trees, to closed forest. Understory character changes markedly as the
amount of shade increases.
1. The closed Prosopis (kiawe) forest is the most extensive
vegetation type in undeveloped areas on the 'Ewa Plain. It is
composed of medium to high stature trees, 5 to 12 m tall, which form
extensive stands with greater than 60% cover. The closed forest lacks
a shrub layer, and a few tall plants of Leucaena leucocephala form a
sparse sub-canopy layer. Herbaceous ground cover is also sparse and
consists of shade tolerant species such as Asystasia gangetica,
Mavastrum coromandelianum, Achyranthes aspera, and Plumbago zeylanica.
The 'akoko does not thrive in the Prosopis climax community, where it
tends to be found on the fringe of the heavy shade.
2. Open Prosopis forest has trees 2 to 5 m tall with a conopy
cover of 10 to 60%. Because of less shading, a number of shrub
species, such as Acacia farnesiana, Leucaena, Pluchea symphytifolia,
and P. indica, and an herbaceous ground cover are found in this
vegetation type. Disturbances such as wood cutting have maintained
these forests in an open condition; if left undisturbed, they would
eventually become closed.
3. The open area along the fringe of the former quarry supports
a ruderal (weedy) plant community. The vegetation type is
characteristically found in areas which have been disturbed. After
clearing, annual, weedy species colonize an area and include
Pennisetum setosum, Verbesina encelioides, Atriplex semibaccata,
Chloris inflata, and others. When left undisturbed, woody shrubs
replace some of the herbaceous species.
Euphorbia tends to do relatively well in both open communities.
SPECIES INTERRELATIONSHIPS:
A number of insect pests have been observed on Euphorbia, and
monitoring for harmful infestations is recommended. Small bore-holes
containing beetle larvae have been observed on Euphorbia branches; the
insects were found only in branches which were already dead. During
January 1981, infestations of the croton moth caterpillar (Achaea
janata) were very heavy on many Euphorbia plants, and in some cases
Life History - 5 (DRAFT) - Life History
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
the caterpillars totally denuded the plants of leaves, flowers, and
fruit within a few days. However, the plants grew new foliage after
the larvae population declined. Spiraling whitefly (Aleurodicus
dispersus) occasionally have been found on plants in the area.
Infestation was heavy at one transplant site, probably because, during
the drier months, other plant species dried up and died back while the
Euphorbia plants were watered regularly throughout the year and did
not go dormant and lose their leaves.
The parasitic vine Cassytha filiformis (family Lauraceae) has
been observed on some plants. Host plants usually succumb to heavy
infestation due to a weakened condition that reduces resistance to
other disease-causing organisms (01). Hand removal of the parasitic
plants has been recommended.
OTHER LIFE HISTORY DESCRIPTORS:
None.
Life History - 6 (DRAFT) - Management Practices
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Beneficial Suppressing wildfire
Beneficial Maintaining undisturbed/undeveloped areas
Beneficial Controlling/Removing Nonnative Vegetation
Beneficial Maintaining Sperm/Seed Banks
Adverse Parasites
Existing Parasites
Adverse Predation
Existing Predation
Adverse Surface Mines
Existing Surface Mines
Adverse Soil compaction by heavy equipment in mine areas
Existing Soil compaction by heavy equipment in mine areas
Adverse Shoreline modification/development
Existing Shoreline modification/development
Adverse Competition
Existing Competition
Adverse
Existing
Adverse Vegetation Composition Changes
Existing Vegetation Composition Changes
COMMENTS ON MANAGEMENT PRACTICES -
The main factors which have contributed to the current status of
the 'Ewa Plains 'akoko are destruction and modification of habitat and
lack of legal protection.
The precise natural range of the taxon is unknown, but probably
did not extend beyond the coralline plains of the 'Ewa area. The
loss of native habitat within this area began with Polynesian
settlement of the islands and has continued to the present. Habitat
alteration has been so thorough that no completely native habitat is
present any longer. Documented loss of the predominantly non-native
vegetation in which the taxon now occurs, with concomitant loss of a
significant number of Euphorbia plants, has continued to the present
time (07,08).
An extensive coral quarry was operated in what was probably the
center of the largest concentration of Euphorbia plants at the time;
this is evidwent by the previous location of large colonies around
three sides of the quarry. During development of a deep draft harbor,
the old quarry and some adjacent land was dredged. Plants occurring
on the mauka (landward) and north sides of the quarry were lost when
the areas were cleared of vegetation prior to dredging; plants which
could be removed from the ground were saved by transplantation.
However, adult plants are so firmly rooted in the substrate that
transplantation is not possible; smaller plants can be moved with some
success. An area adjacent to the south side of the old quarry has
been designated for dockside facilities; in 1983, 200 to 500 Euphorbia
occurred in the area.
A colony of 100 plants at another site was reduced to a single
Management Practices - 1 (DRAFT) - Management Practices
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
plant when the area was bulldozed and cleared of vegetation; the
plant survived because it was protected by the base of a fence (01,02,
04).
Although the principal factor endangering this species is past
and potential loss of habitat, competition from aggressive weedy plant
species that now dominate vegetation in the area has also undoubtedly
been a factor in its decline (07,08). The parasitic vine Cassytha
filiformis (family Lauraceae) has been observed on some plants. Host
plants usually succumb to heavy infestation due to a weakened
condition that reduces resistance to other disease-causing organisms.
It is also possible that Euphorbia's reproductive success has
been affected by decline of native pollinating insects (07,08). The
plant is now pollinated by a large number of generalist pollinators,
exotic insects which are widespread throughout leeward O'ahu (01).
Insect infestations have been noted on Euphorbia and may be an
important threat in the future. During January, infestations of the
croton moth caterpillar were very heavy on many Euphorbia plants, and
in some cases the caterpillars totally denuded the plants of leaves,
flowers, and fruit within a few days. However, plants grew new
foliage as the larvae quickly declined in abundance. Spiraling
whitefly occasionally have been found on plants in the area.
Infestation was heavy at one transplant site, probably because, during
the drier months, other plant species dried up and died back while the
Euphorbia plants were watered regularly throughout the year and did
not become dormant and lose their leaves. Branches with small
bore-holes containing beetle larvae have been observed on Euphorbia;
the insects were found only in branches which were already dead (01).
Plants are vulnerable to trampling, especially during the drier
months, when stems of older, dormant plants are dry and brittle, and
during the wet season, when newly emerged seedlings are especially
vulnerable (01).
Fire caused by human activities is a continual threat to the
plant throughout its range. One population is located adjacent to a
business in which considerable welding takes place (02). Especially
during the drier months, an accidental fire could destroy the habitat
in which the plant occurs at that site.
The makai (seaward) portion of the 'Ewa Plains is within the zone
designated as tsunami inundation area. Tsunamis are not common, but
could destroy habitat and possibly Euphorbia plants. Most of the
plants are near this designated area (01,02,03,04,07,08,14,20).
UNAPPROVED PLAN:
A recovery plan for this species has not yet been initiated.
About 98% of the 'Ewa Plains 'akoko population grows on the
Barbers Point Naval Air Station. This population is robust and
appears to be maintaining itself. Probably the best management
activities would be to prevent further modification or degradation
of its habitat (e.g., from development), control and remove exotic
plant species, and develop a fire prevention plan, at least for the
dry season. The population should be monitored annually, and as a
safeguard, seeds should be collected and stored.
Management Practices - 2 (DRAFT) - Management Practices
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
The historic range of this plant is presently being developed as
an urban/industrial area. It is planned as the second center of
urbanization for the island of O'ahu. Therefore it probably will not
be possible to reintroduce the plant into other parts of its historic
range. Management activities should concentrate on maintaining the
existing Naval Air Station population.
Management Practices - 3 (DRAFT) - References
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
References
***** REFERENCES FOR ALL NARRATIVES EXCEPT N-OCCURRENCE *****
01 AECOS. 1981. Ecological and horticultural studies of Euphorbia
skottsbergii at Barbers Point, O'ahu, Hawai'i. Final report: vol.1
(text), vol.2 (appendices). AECOS No. 264. Prep. under contract
DAWC84-80-C-0017. Unpublished report available from: U.S. Army
COE, Pacific Ocean Division, Honolulu. 168 pp.
02 Char, W.P. August 1985. Personal communication. Biologist,
Natural Area Reserves System, Hawaii Dept. of Land and Natural
Resources, 1151 Punchbowl St., Honolulu, HI 96813.
03 Char, W.P. and N. Balakrishnan. 1979. 'Ewa Plains botanical
survey. University of Hawaii Botany Dept. Unpublished report
available from: U.S. Fish and Wildlife Serv., Honolulu.
119 pp + App. + maps.
04 Corn, C. August 1985. Personal communication. Chairman, Native
Plant Committee, Hawaiian Botanical Society, c/o University of
Hawaii Botany Dept., 3190 Maile Way, Honolulu, HI 96822.
05 Degener, O. and L Croizat. 1936. Flora Hawaiiensis, fam. 190.
Chamaesyce, Part 4. Publ. Priv., 2 pp. [Reprinted, 1946.]
06 Degener, O. and I. Degener. 1959. Flora Hawaiiensis, fam. 190.
Chamaesyce, Part 5. Publ. Priv., 2 pp.
07 U.S. Government. 1980. Endangered and Threatened wildlife and
plants; proposed Endangered status for the 'Ewa Plains 'akoko
(Euphorbia skottsbergii var. kalaeloana). Federal Register
45(171):58166/58168.
08 U.S. Government. 1982. Endangered and Threatened wildlife and
plants; determination that Euphorbia skottsbergii var kalaeloana
('Ewa Plains 'akoko) is an Endangered species. Federal Register
47(164):36846/36849.
09 Foote, D.E., E.L. Hill, S. Nakamura, and F. Stephens. 1972. Soil
Survey of Islands of Kauai, Oahu, Maui, Molokai, and Lanai, State
of Hawaii. U.S. Soil Conservation Service, Washington, D.C.
10 Fosberg, F.R. and D. Herbst. 1975. Rare and endangered species of
Hawaiian vascular plants. Allertonia 1(1):1-72.
11 Gray, S.F. 1821. A natural arrangement of British plants.
Vol.2:260.
12 The Nature Conservancy of Hawai'i. August, 1985. Hawai'i Heritage
Program (Data Base); Element Occurrence Records: Euphorbia
skottsbergii var. kalaeloana (PDEUP0D292). (Review of records and
current maps; updates available upon request).
13 Wagner, W.L., D.R. Herbst, and S.H. Sohmer. [In prep.] Manual of
the flowering plants of Hawai'i.
14 Kimura, B.Y. and K.M. Nagata. 1980. Hawaii's vanishing flora.
The Oriental Publ. Co., Honolulu, HI. 88 pp.
15 Koutnik, D. [In prep.] Chamaesyce. IN: Manual of Flowering
Plants in Hawai'i. Wagner, W.L., D.R. Herbst, and S.H. Sohmer,
eds.
16 Macdonald, G.A., A.T. Abbott, and F.L. Peterson. 1983. Volcanoes
in the sea, 2nd edition. Univ. Hawai'i Press, Honolulu. 517 pp.
17 U.S. Fish and Wildlife Service. 1980. 'Ewa Plains 'akoko proposed
as Endangered. Endangered Sp. Tech. Bull. 5(10):5-6.
References - 1 (DRAFT) - References
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
18 Porter, J.R. 1972. Hawaiian names for vascular plants. Univ.
Hawaii, Hawaii Agric. Exper. Sta., Departmental Paper 1.
[Reprinted 1977.] 63 pp.
19 St. John, H. 1973. List and summary of the flowering plants in
the Hawaiian Islands. Pacific Trop. Bot. Gard. Mem. No.1, Lawai,
HI. 519 pp.
20 St. John, H. (C. Corn, ed.). 1981. Rare endemic plants of the
Hawaiian Islands. State of Hawaii, Dept. of Land and Nat. Res.,
Honolulu, HI. 68 pp.
21 Sherff, E.E. 1936. Additions to the genus Euphorbia L. and to
certain genera of the Compositae. Bot. Gaz. 97:580-609.
22 Sherff, E.E. 1938. Revision of the Hawaiian species of Euphorbia.
Ann. Miss. Bot. Gard. 25(1):54-56.
***** REFERENCES FOR N-OCCURRENCE NARRATIVE ONLY *****
01 AECOS. 1981. Ecological and horticultural studies of Euphorbia
skottsbergii at Barbers Point, O'ahu, Hawai'i. Final report: vol.1
(text), vol.2 (appendices). AECOS No. 264. Prep. under contract
DAWC84-80-C-0017. Unpublished report available from: U.S. Army
COE, Pacific Ocean Division, Honolulu. 168 pp.
02 Char, W.P. August 1985. Personal communication. Biologist,
Natural Area Reserves System, Hawai'i Dept. of Land and Natural
Resources, 1151 Punchbowl St., Honolulu, HI 96813.
03 Char, W.P. and N. Balakrishnan. 1979. 'Ewa Plains botanical
survey. Prep. by the University of Hawai'i Botany Dept. under
contract. Unpublished report available from: U.S. Fish and
Wildlife Serv., Honolulu. 119 pp + App. + maps.
04 Corn, C. August 1985. Personal communication. Chairman, Native
Plant Committee, Hawaiian Botanical Society, c/o University of
Hawai'i Botany Dept., 3190 Maile Way, Honolulu, HI 96822.
05 U.S. Government. 1980. Endangered and Threatened wildlife and
plants; proposed Endangered status for the 'Ewa Plains 'akoko
(Euphorbia skottsbergii var. kalaeloana). Federal Register
45(171):58166/58168.
06 U.S. Government. 1982. Endangered and threatened wildlife and
plants; determination that Euphorbia skottsbergii var kalaeloana
('Ewa Plains 'akoko) is an Endangered species. Federal Register
47(164):36846/36849.
07 The Nature Conservancy of Hawaii. August, 1985. Hawaii Heritage
Program (Data Base); Element Occurrence Records: Euphorbia
skottsbergii var. kalaeloana (PDEUP0D292). (Review of records and
current maps; updates available upon request).
08 Kimura, B.Y. and K.M. Nagata. 1980. Hawaii's vanishing flora.
The Oriental Publ. Co., Honolulu, HI. 88 pp.
09 Koutnik, D. [In prep.] Chamaesyce. IN: Manual of Flowering
Plants in Hawai'i. Wagner, W.L., D.R. Herbst, and S.H. Sohmer,
eds.
10 St. John, H. 1973. List and summary of the flowering plants in
the Hawaiian Islands. Pacific Trop. Bot. Gard. Mem. No.1, Lawai,
HI. 519 pp.
11 St. John, H. (C. Corn, ed.). 1981. Rare endemic plants of the
References - 2 (DRAFT) - References
Species 'AKOKO, EWA PLAINS
Species Id ESIS701002
Date 13 MAR 96
Hawaiian Islands. State of Hawaii, Dept. of Land and Nat. Res.,
Honolulu, HI. 68 pp.
12 Wagner, W.L., D.R. Herbst, and S.H. Sohmer. [In prep.] Manual of
the flowering plants of Hawai'i.
References - 3