Well Drained Udic and Perudic Forest
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Transition T1B More details
- Transition T1C More details
- Restoration pathway R2A More details
- Transition T2A More details
- Transition T2B More details
- Restoration pathway R4A More details
- Transition T4A More details
- Transition T4B More details
- Restoration pathway R5A More details
- Restoration pathway R6A More details
- Transition T6A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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State 1
Reference State
Description
The Reference State consists of one plant community. Under a regime of natural disturbances, this community has probably been stable through post-glacial time frames and from a broad-scale spatial perspective. A matrix of variations in canopy cover and species composition in all canopy levels is observable. This matrix variability does not appear to be connected to soils, climate, or landscape features, but rather is probably due to wind throw, deaths of large trees, and other chance occurrences.
State 1 will transition into State 2, Grassland State, by either active clearing by humans or by heavy foraging over time by feral ungulates. It can transition into State 4, Invaded Understory State, by gradual weed invasion, which is exacerbated by feral ungulates.
Submodel
State 2
Naturalized Grassland State
Description
The elevation range of the forest found in the Reference State does not coincide perfectly with the elevation range of the dominant grass species within the Grassland State. In some areas at the higher elevation range of this ecological site, kikuyugrass (Pennisetum clandestinum) replaces guineagrass as the dominant species. More detailed information, including forage production estimates, about these kikuyugrass grasslands can be found in Ecological Site Description F160XY502 Isomesic-Cool Isothermic Forest.
This state consists of three grassland community phases. These phases are maintained by grazing, which keeps preferred species from becoming too tall, and adequate recovery periods, which ensure vigor and cover of preferred species. High production of preferred grass species and extensive cover allow for increased soil moisture retention, vegetative production, and overall soil quality. These factors are degraded by grazing practices that result in loss of preferred grass species leading to increase in less desirable grasses, weed invasion, and an increase in the extent of bare soil.
Prescribed burning generally is not allowed due to high risks to structures, fences, and native forest stands. Wildfires caused by lightning or arson sometimes occur. They are very intense and difficult to contain, because guineagrass produces huge amounts of fuel and grows to a height of almost 10 feet (3 meters), while kikuyugrass produces large amounts of fuel and has rhizomes that can smolder underground for days, sometimes reigniting a surface fire.
Most of the grasslands in this ecological site are on former sugar plantations where guineagrass (Urochloa maxima) was a species of roadsides and waste areas (Earl Spence, rancher and manager, personal communication). Guinea grass now has taken over these lands as the dominant forage grass. All grass, sedge, forb, vine, shrub, and tree species found in this state have been introduced to Hawaii by humans within the past two centuries, either inadvertently or intentionally. Scattered, remnant native trees, either koa or ohia lehua, sometimes occur in these naturalized grasslands, but they are unable to reproduce without protection from ungulates and control of grasses and weeds. Occasionally, western brackenfern (Pteridium aquilinum) and uluhe or Old World forkedfern (Dicranopteris linearis) occur; both of these fern species are native to Hawaii.
Community Phase 2.1 mostly consists of guineagrass, sometimes with an admixture of glycine or perennial soybean (Neonotonia wightii). Continuous grazing that does not allow the preferred forage species to recover from defoliation results in Community Phase 2.2, which is dominated by lower value grass species but contains enough remnant guineagrass to allow for a shift back to Plant Community 1 with prescribed grazing. Longer-term continuous grazing leads to Community Phase 2.3, which consists of low value grass species and increasing cover of alien shrubs and tree saplings. Improvement of this Plant Community requires weed control followed by prescribed grazing.
Submodel
State 3
Planted Timber State
Description
This state consists of one community phase, which is a plantation of introduced timber tree species that have been established on former sugarcane or grazing lands. With typical management, it is not susceptible to unplanned transitions or restorations to other states. However, if native koa are planted and managed properly, future restoration in the direction of the Reference State would be facilitated. There also is the possibility that some introduced timber species may provide a favorable environment for eventual restoration of native species.
Submodel
Description
This state consists of one community phase. It arises by invasion by introduced species of intact native forest (the Reference State) or, in some cases, of native overstory stands from which the original understory has been cleared. Native species are unable to regenerate in the highly competitive understory of introduced plants and eventually die out. With time, large introduced tree species will emerge to replace the native overstory trees and form a new overstory. When this last step has occurred, the site will have transitioned to State 5, Invaded Overstory and Understory State.
Disturbance of the soil and direct damage to native understory plants by introduced ungulates, particularly pigs and cattle, will speed the transition to this state by killing native plants and by creating better germination sites for introduced species.
Restoration to the Reference State or a facsimile of it is possible by fencing the site, removing all ungulates, applying herbicides, and replanting native species when needed. Restoration efforts will be affected depending on the degree of invasion by introduced species and by the species that have invaded the site. Long term weed management and fence maintenance will be necessary.
Submodel
State 5
Invaded Overstory and Understory State
Description
This state is comprised of one plant community dominated by introduced species in both the overstory and understory. Understory vegetation usually is very sparse to nonexistent. Remnant individuals of a few native species may persist. This state might be considered a dead end as far as further succession or transition to another state. Restoration to a facsimile of the Reference State could probably be done with expensive and intensive practices followed by long-term weed management. Clearing of the site followed by establishment of an overstory of noninvasive, introduced timber trees with a native understory as an intermediate step to native forest restoration may also be done.
Submodel
State 6
Grazed Native Overstory State
Description
This state consists of remnant native tree species forming an overstory with well-managed, relatively weed-free grasses. The overstory may have existed for some time, or may be in the process of forming where residual koa seeds are present in the soil.
Submodel
Mechanism
State 1, Reference State, can be converted to State 2, Naturalized Grassland State, by clearing the forest with heavy machinery. Most grasslands in this ecological site were originally cultivated for sugar cane and later converted to grassland. At the highest, coolest elevations of the ecological site, kikuyugrass and/or pangolagrass have been planted. At lower elevations where grasslands are on old sugarcane plantations, guineagrass (a former weed in the plantations) has volunteered and now dominates.
Some grasslands may originally have been cleared by large numbers of feral and/or domestic livestock consuming the understory, including tree seedlings and saplings. This process would have left numerous large trees standing if not cut for timber. Large wildfires in the early 20th century also cleared some forest remnants.
Mechanism
State 1, Reference State, can be converted to State 4, Invaded Understory State, by gradual replacement of the understory by shrubs, vines, grasses, and trees that outcompete the native understory species and hinder or prevent their reproduction. Some introduced vines can directly kill native plants, including large trees. This process is accelerated by ungulate foraging that helps introduced weed seeds, enhances weed germination by soil disturbance, and directly destroys native plants.
Mechanism
This transition occurs by either clearing of native forest by machinery or gradual removal of native forest understory and elimination of native plant reproduction by long-term ungulate grazing.
Mechanism
It may be possible to restore State 2, Naturalized Grassland State, to a plant community resembling State 1, Reference State, by intensive restoration practices followed by long-term maintenance. Control of grasses and any weeds currently in the grassland by mowing and herbicides must precede establishment of native species. Weed control would be a long-term process to maintain the site after establishment. Many weeds are shade-tolerant and would be able to invade the site even after canopy closure of native plants. Domestic and feral ungulates must be fenced out of the restoration site. However, managed grazing by domestic ungulates outside the fence would be useful to manage weedy vegetation outside the perimeter.
Increasing shade from restored tree species may eventually cause a shift from C4 (warm-season) grass dominance (typically guineagrass or kikuyugrass) to C4 or C3 (cool-season) shade-tolerant grasses (typically meadow ricegrass, hilograss, or carpetgrass). This shade tolerant grass layer can be very dense and detrimental to establishment of native plants. Suppression of these grasses by herbicides and/or mulch (cardboard works well) until native plant litter begins to cover the grass.
Mechanism
State 2, Naturalized Grassland State, may be converted to State 3, Planted Timber State, by controlling grasses and weedy shrubs by herbicides and/or mowing prior to and after planting of timber species (usually eucalyptus species).
Mechanism
State 2, Naturalized Grassland State, may be converted to State 5, Invaded Overstory and Understory State, by abandonment. Common weed tree species are strawberry guava, christmasberry, faya tree, and common guava. Seeds of these species as well as weedy understory species are spread by mammals and birds.
Mechanism
State 5, Invaded Understory State, may be restored to a plant community resembling State 1, Reference State. Before restoration of native understory plants, invasive understory plants must be eliminated by herbicide weed control and brush management practices. Also, feral and domestic ungulates must be excluded from the restoration site by a fence, and any remaining ungulates within the fenced site must be eliminated. If feral pigs are present, an intensive, short-term program must be employed to eliminate their population; otherwise, their rate of increase will outpace control efforts.
Key native plant species that have been eliminated or greatly reduced in numbers generally must be restored by replanting. Long-term maintenance of the site using herbicides, hand-weeding, mulching, and fence repair is required.
Mechanism
State 4, Invaded Understory State, can be converted to State 2, Naturalized Grassland State, Pasture by mechanical clearing of introduced plants and remnant native understory plants. Native overstory trees may be harvested for timber, knocked down and piled, or left to provide shade for livestock. If leaving large native trees for shade, care must be taken to not damage roots within about 20 feet (6 meters) of the trees. Introduced pasture grass species may then be seeded or sprigged into the site. Herbicide applications will be necessary before and during pasture establishment to control reemerging weed species.
Mechanism
State 4, Invaded Understory State, transitions to State 5, Invaded Overstory and Understory State, over time. The native ohia lehua and koa trees that remain in the overstory are unable to successfully regenerate in the shady and highly competitive environment of the weedy understory. Eventually the native overstory trees die and are replaced by introduced tree species.
Restoration pathway R5A
Mechanism
State 5, Invaded Overstory and Understory State, may be restored to State 2, Naturalized Grassland State by mechanical clearing of overstory and understory vegetation, followed by herbicide control of re-emerging invasive species. Introduced grasses may then be seeded or sprigged into the site. Herbicide applications, mowing, and careful grazing practices will be necessary during and after pasture establishment to control reemerging weed species.
Mechanism
This restoration occurs by removal of ungulates from the site, eventual removal of forage grasses by mowing, mulching, and herbicide application, replanting native species, and eventual natural reproduction by native species.
Model keys
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