FOTG Section II. Natural Resources Information F. Ecological Site Descriptions

F161BY502HI Kona Weather Pattern Wet Forest

Ecological Site Description

Ecological Site Characteristics

Site Identification

Site Type: Forestland / Site ID:F161BY502HI / MLRA: 161B
Colloquial Site Name: Kona Weather Pattern Wet Forest
Official Site Name: Kona Wet Forest; Metrosideros polymorpha-Acacia koa/Cibotium glaucum-Cibotium menziesii/Freycinetia arborea

Physiographic Features

This ecological site occurs on lava flows on sloping mountainsides of shield volcanoes. Lava flows are `a`a (loose, cobbly) or pahoehoe (smooth, relatively unbroken). Volcanic ash flows range from very shallow to deep on the underlying lava.

Landform: (1) `a`a lava flow
Landform: (2) pahoehoe lava flow
Landform: (3) volcanic ash flow / Minimum / Maximum
Elevation (feet): / 1500 / 4500
Slope (percent): / 2 / 40
Water Table Depth (inches): / 3 / --
Flooding:
Frequency:
Duration: / very rare
extremely brief / occasional
extremely brief
Ponding:
Depth (inches):
Frequency:
Duration: /
--
none
--nonevery briefbrieflongvery long
/
2
occasional
very brief
Runoff Class: / negligible / very high
Aspect: (1) W
Aspect: (2) SE

Climatic Features

Average annual precipitation ranges from 45 to 80 inches. Most of the precipitation falls from May through September, with May and June being the wettest months. Average annual temperature ranges from 60 to 67 degrees F. The climate generally can be classified as udic and tropical in nature.

Climate chart

Minimum / Maximum
Frost Free Period (days): / 365 / 365
Freeze Free Period (days): / 365 / 365
Mean Annual Precipitation (inches): / 45 / 80
Monthly Precipitation (inches) and Temperature (0F)
Month / Jan / Feb / Mar / Apr / May / Jun / Jul / Aug / Sep / Oct / Nov / Dec
Precip. Min. / 0.0 / 0.0 / 0.1 / 0.1 / 0.1 / 3.0 / 0.6 / 1.0 / 2.0 / 1.0 / 0.3 / 0.2
Precip Max. / 24.0 / 18.0 / 18.0 / 19.0 / 22.0 / 34.0 / 17.0 / 15.0 / 21.0 / 19.0 / 13.0 / 12.0
Temp. Min / 58 / 58 / 58 / 59 / 61 / 61 / 62 / 63 / 62 / 62 / 60 / 59
Temp. Max / 76 / 75 / 75 / 75 / 76 / 76 / 78 / 79 / 78 / 79 / 79 / 77
Climate Station: (1)
Climate Station: (2) / 70.0 Holualoa 1929-1966
68.5 Holualoa 1905-1928

Influencing Water Features

There are no water features influencing this site.

Representative Soil Features

Typical soils are of three types: highly decomposed plant materials in `a`a or over pahoehoe; shallow to deep, rapidly weathered volcanic ash deposited on `a`a or pahoehoe; and very shallow, rapidly weathered volcanic ash deposited over pahoehoe. Most landscape surfaces in this ecological site are young (generally 750 to 5,000 years old). The youngest surfaces (lava flows from 750-3,000 years old) are covered with soils that are derived primarily from highly decomposed plant materials. Older surfaces (lava flows >3,000 years old) are usually covered with soils with much higher ash content than younger soils. These differences in age and/or ash content can affect the nature of the plant community as well as the trafficability by humans and livestock (and therefore disturbance history) of a given site.

Soils in the Manaha`a and Hokukano series (soil map units 390, 394, 397, and possibly 395) have high water retention properties and are often in kipukas that receive runoff from surrounding, slightly higher lava flows. Some of these kipukas have been used for water catchment areas by ranches. Many of these kipukas are at higher elevations than the main part of this ecological site and receive lower precipitation than is typical for the ecological site. They may represent sites that formerly were high elevation outliers of this wet forest.

Soils of this ecological site are somewhat poorly to well drained. Available water capacity in most soils ranges from one to four inches. Available water capacity refers to the volume of water available to plants in the upper 40 inches of soil, including rocks, at field capacity. Permeability is moderately rapid in soils but can be very slow in underlying pahoehoe. Runoff potential ranges from negligible in `a`a to very high over pahoehoe. Moist colors range from dark reddish brown to black. Soil reactions (pH in CaCl2) range from very strongly acid to strongly acid in surface horizons and very strongly acid to neutral in subsurface horizons. In surface horizons of some soils a pH (in CaCl2) as low as 4.1 may be encountered. Soil temperature regimes are isothermic. Soil moisture regimes are udic (in most years, not dry for as long as 90 cumulative days).

Predominant Parent Materials:
Kind: highly decomposed plant materials or volcanic ash
Origin: / Surface Texture: (1) --clayclay loamcoarse sandcoarse sandy loamfine sandfine sandy loamloamloamy coarse sandloamy fine sandloamy sandloamy very fine sandsandsandy claysandy clay loamsiltsilty claysilty clay loamsilt loamsandy loamvery fine sandvery fine sandy loam
Surface Texture: (2) --clayclay loamcoarse sandcoarse sandy loamfine sandfine sandy loamloamloamy coarse sandloamy fine sandloamy sandloamy very fine sandsandsandy claysandy clay loamsiltsilty claysilty clay loamsilt loamsandy loamvery fine sandvery fine sandy loam
Subsurface Texture Group: --sandyloamyclayey
Surface Fragments <=3" (%Cover): 0-15
Surface Fragments >3" (%Cover): 0-40 / Rock Fragments <=3" (%Volume): 0-55
Rock Fragments >3" (%Volume): 0-60
Drainage Class: somewhat poorly to well / Permeability Class: very slow to moderately rapid
Minimum / Maximum
Depth (inches): / 2 / >72
Electrical Conductivity (mmhos/cm): / 0 / 2
Sodium Adsorption Ratio: / 0 / 0
Calcium Carbonate Equivalent (percent):
Soil Reaction (1:1 Water): / 4.5 / 7.3
Soil Reaction (.0-1M CaC12): / 4.1 / 7.0
Available Water Capacity (inches): / 1 / 4

Plant Communities

Ecological Dynamics of the Site

This ecological site occurs on a variety of substrates in warm, moist regions of North and South Kona districts of the Island of Hawai`i. Plant communities evolved without the presence of large mammals or the regular occurrence of fires. The original forest plant community is now disturbed and fragmented due to agriculture, urban development, establishment of exotic timber trees, domestic and feral ungulate foraging, and alien species invasion. Foraging by cattle, pigs, and/or goats, or clearing and abandonment accelerate invasion by alien weeds. However, alien weeds appear able to successfully invade native stands regardless of human or ungulate disturbances. Major forest weeds include strawberry guava, christmasberry, African tulip tree, cat’s claw, kahili ginger, desmodium, melastomes, alien ferns, and alien grasses. Kikuyugrass pastures become infested with unpalatable grasses and shrubs under conditions of improper grazing management.

Where the wet forest grades into drier forests at lower elevations the canopy can be dominated by a transitional forest dominated by olopua and papala kepau. Much of this zone was utilized for intensive agriculture by native Hawaiians as part of the Kona Field System. Today, much of this land is utilized for coffee and macadamia orchards and residential development. A table of a composite representation of this plant community is included in this ecological site description. Map units for this transitional forest are correlated to soil map units in the lowest elevations of the Kona Wet Forest ecological site. However, management of this transitional zone is similar to that of the South Kona Dry Forest ecological site; refer to that ecological site description for more details.

State and transition diagram

State 1 – Native Wet Forest

Plant Community 1

This state represents the Historic Climax Plant Community. The general aspect is a forest of tall overstory with an open or closed upper canopy of ohia or koa trees up to 100 feet tall, a secondary canopy of diverse trees species 30 to 60 feet tall, a dense tree fern canopy 10 to 30 feet tall, and a diverse understory of shrubs and ferns. Vines are abundant, particularly `ie`ie, both on the ground and on trees. The mid-canopy is dominated by olapa trees in the southern part of the ecological site; however, olapa is somewhat less abundant in the northern part. These forests have standing live timber of 900 to 8000 cubic feet per acre, with a representative value of about 5500 cubic feet per acre.

Overstory tree canopy cover of ohia and koa can vary from about 10% to 80%. However, understory composition is controlled by the cover of the secondary canopy of medium-stature, secondary canopy tree species and especially by the cover of tree ferns, which is usually in the range of 60% to 90%. Koa and ohia do not reproduce successfully in the typically shady understory of intact Native Wet Forest. Tree ferns, medium-stature trees such as olapa, kopiko, kolea lau nui, kawa`u, and olomea, and shrubs such as kanawao and clermontia reproduce well in the understory. The ground layer of small ferns is typically very dense when ungulates are not present.

The dominant tree canopy can be ohia trees or a combination of ohia and koa trees. Ohia dominates the forest canopy on younger lava flows, which also tend to be organic (highly decomposed plant material) soils rather than mineral (ash) soils. Older lava flows with ash-derived soils may have a greater likelihood of koa occurrence. Koa is able to grow on both organic and mineral soils. It may be that landscape surface age, and hence stage of succession, is more important to koa occurrence than is soil type. Koa is an opportunistic species that is often seen along roadsides or near old sawmills in areas where it does not occur in the forest proper. Ash soils historically have been more desirable for ranching operations than organic soils on `a`a lava. Remnant koa trees are often seen in or around ash soil pastures, and it is difficult to determine whether these sites were originally in koa-dominated forest or were invaded by koa due to increased light availability. In general, koa is more abundant at higher elevations (above 2800 feet) of the Kona Wet Forest ecological site. The lowest natural koa occurrences in this ecological site are at about 2000 feet elevation. It is possible that populations of koa were more widespread at lower elevations of Kona in the past (personal communication, Rick Warshauer, 2006).

Some of the youngest lava flows, especially on Mawae soil series, can have large ohia trees but an understory with much less tree fern cover, more abundant `ama`u (Sadleria) fern cover, and more abundant kolea lau li`i (Myrsine sandwicensis) than is typical for this ecological site.

Hua soil series is very shallow and poorly drained and becomes anaerobic when wet. Runoff is high or very high, particularly on steep slopes. Sites with this soil may support typical wet forest, but often have sparser trees and tree ferns and abundant uluhe fern.

Pathways from this state/plant community

To State 2, Pastures, via “B&(E or G)”:

B = pasture establishment; G = native forest clearing.

Native Forest can be converted to Pasture by clearing the forest with heavy machinery and planting desirable pasture species, usually kikuyugrass, pangolagrass, and desmodium. Native forest may be cleared gradually by allowing cattle access to the forest. Cattle eventually eat or destroy understory ferns, forbs, shrubs, and saplings, opening up the forest so that pasture grasses will thrive. On lava substrates, underlying lava rock often is ripped and crushed by heavy machinery to produce Udarents (sandy, organic) soils. Ripping and crushing produces some fine mineral particles and small, abundant gaps between the rock fragments. However, about 50% of the soil organic matter may be lost in the process due to exposure to air and higher temperatures.

To State 3, Tree Plantation with Alien Understory, via “G&H&J”:

G = native forest clearing; H = exotic timber or koa planting; J = gradual weed invasion.

Native Forest is converted to Tree Plantation with Alien Understory by mechanical removal of the original forest over story and understory followed by planting of exotic timber species or koa. This practice was common in Kona in the mid-20th century. When the surrounding area is infested with alien weeds such as Koster’s curse, strawberry guava, or kahili ginger, those species will invade and take over the tree plantation understory unless controlled by herbicides. Restoration of native forest would be extremely difficult, but may be possible in koa plantations.

To State 4, Native Wet Forest with Alien Understory, via “J&K&L”:

J = gradual weed invasion; K = disturbance by ungulates; L = lack of native plant regeneration.

Native Forest can convert to Native Forest with Alien Understory by gradual replacement of the understory by alien shrubs, vines, and small trees that outcompete the native understory species. This process is accelerated by ungulate foraging that disturbs the soil surface and directly destroys native plants and prevents their regeneration.

To State 6, Tree Plantation with Native Understory, via “G&H&I”:

G = native forest clearing; H = exotic timber or koa planting; I = surrounding native seed source.

Native Forest is converted to Tree Plantation with Native Understory by mechanical removal of the original forest overstory and understory followed by planting of exotic timber species or koa. This practice was common in Kona in the mid-20th century. When the surrounding area contains native understory species and is fairly weed-free, native plants such as tree ferns, `ie`ie vines, and small native trees reestablish themselves beneath the canopies of many exotic timber species. An exception is redwood plantations, which appear to exclude establishment of most native plants. The ultimate plant community that will develop from Tree Plantations with Native Understory is unknown.

Plant species listed in the following tables have been observed in the course of field work or are derived from reliable records.

Abbreviations:

Origin: n = native (endemic or indigenous); a = alien (introduced by humans).

Type: t = tree; tf = tree fern; s = shrub; h = herb (forb); v = vine; f = fern; g = grasslike (grasses, sedges, rushes).

Composite representation of State 1, Plant Community 1, Native Wet Forest.

Scientific name / %Canopy cover by height class (ft) / Total Cover / Local
common name / NRCS
common name / Origin / Type / NRCS
Code
0.1 -
2 / 2.1 -
4.5 / 4.6 -