tnc logo
Hawaiian High Islands Ecoregion
This page last revised 31 August  2008 -- S.M.Gon III  
Home
Introduction
Ecoregion
Conservation Targets
Viability
Goals
Portfolio
TNC Action Sites
Threats
Strategies
Acknowledgements
▫
Tables
Maps & Figures
CPT Database
Appendices
Glossary
 Sources
.
Forest bird
Viability of forest bird concentrations were derived from recent assessments by the USGS/BRD.

Rare natural community
Rare plant concentration viability was assessed only for occurrences not nested in ecological systems

Functional landscapes
Ecological systems in the Hawaiian High Islands Ecoregion tend to be of small size.

Lama lowland dry forest invaded by alien grass
Lowland dry forest, such as this stand at Pu'u Wa'awa'a, Hawai'i Island, is often invaded by fire adapted alien grasses that create and maintain destructive fire regimes.

Viability

One school of thought in conservation is that efforts should be devoted to viable ecological systems, communities, and species. Efforts to conserve inviable conservation targets are typically expensive and prone to failure, and are best saved for explicit restoration projects. It is good practice to devote finite conservation capacity to secure the most viable conservation targets. The Conservancy's policy is to maintain viable targets, recognizing that lower viability ecological systems, communities and species require important restoration work led by our partners with mandates and expertise in that realm of conservation, such as the U.S. Fish and Wildlife Service, the U.S. Forest Service, and the National Tropical Botanical Gardens.


Assessing Viability

Viability is difficult to assess, because there are many factors that might affect the fate of species, natural communities, and ecological systems. However, there are some key attributes that contribute to viability, and these have been explored in detail by the Conservancy and its partners (e.g., see current TNC standards). The three standard viability categories are size, condition, and landscape context, discussed briefly below:

SIZE
The size of a population or the areal extent of a natural community or ecological system can affect its viability. Size is a measure of area or abundance of a conservation target occurrence. Size of a species occurrence may include area of occupation or population counts, while size of a natural community or ecological system is typically its areal extent). In general, larger size is related to ability to persist under chronic stress.

CONDITION
Condition is an integrated measure of biotic and abiotic factors, structures, and processes related to the "health" of a conservation target. For a species, this may include reproduction, levels of competition/predation/disease, and population structure. For natural communities and ecological systems, condition relates to overall structure and biotic composition, and presence of typical supportive ecological processes. Good condition is generally related to ability to recover from natural or anthropogenic disturbance.

LANDSCAPE CONTEXT
Landscape context is a description of the spatial aspects of connectivity or access to other populations, species, and ecological processes in the surrounding habitat or landscape. Landscape context rank decreases when surrounding areas are disturbed, fragmented, or lacking supportive processes.

A viability assessment was not developed in the 1998 Hawaiian High Islands Ecoregion Plan, and constitutes a major new component of the current assessment. Applying the above criteria to Hawaiian ecological systems, natural communities, and special features required characterization of the specific biological requirements and supportive ecological process for each. These key ecological factors were then ranked into Very Good, Good, Fair, and Poor categories. A fuller discussion of the size, condition, and landscape context for all conservation targets is provided in the Appendices.

Summary discussions and ranking criteria are provided below.

Criteria for viability ranks

ECOLOGICAL SYSTEMS
Viability of ecological systems is also referred to as ecosystem integrity. Applying the criteria discussed above to Hawaiian ecological systems incorporated sizes appropriate for our islands, condition factors relevant to the structure and composition of our terrestrial (largely vegetated) systems, and landscape context factors considering the major ecological processes and patterns of threats. 

Size - Hawaiian ecological systems are small, even at their full original prehistoric extent, making them particularly vulnerable to disturbance and loss. For example, a loss of 25,000 acres on a smaller island such as Lāna‘i could completely destroy repre­sent­ation of the Lowland Mesic System. Indeed, aside from remnant stands of diverse mesic forest, this has occurred. Relationships between habitat area and species richness in Hawai‘i argues for the need for the largest possible protected areas to prevent species loss. The largest ecological systems in the Hawaiian Ecoregion occur on the Island of Hawai‘i, so an average prehuman ecological system size for that island (ca 75,000 acres) was selected as a reference standard for a rank of "Very Good," with smaller percentage increments of this standard established for lower ranks. Sizes were derived from Hawai‘i GAP landcover, using GIS analyses.

ECOLOGICAL SYSTEM
SIZE VIABILITY RANKS
VERY GOOD

37,500 - >75,000 acres
(50 – 100% of reference occurrences)
GOOD

18,750 – 37,500 acres
(25 - 50% of reference occurrence)
FAIR

3,750 – 18,750 acres
(5 – 25% of reference occurrence)
POOR

<3,750 acres
(<5% of reference occurrence)
 
Condition - Condition of terrestrial vegetated ecological systems was assessed via the prevalence of native plant composition and structure in canopy and understory of vegetation across a given occurrence of an ecological system, compared to reference conditions of exemplary stands of natural communities described for the system. Expert opinion assessing native cover in canopy and understory, and comparisons of vegetation structure and composition to exemplary stands were combined.  We acknowledge that this is a surrogate for the full complement of associated vertebrate and invertebrate fauna accompanying vegetation, and that the faunal elements play an important role in condition: providing ecological functions such as pollination, propagule dispersal, selective herbivory, trophic guilds, etc. A fuller discussion of the condition aspects of viability is provided in the Appendices . The criteria for the condition ranks are summarized in the table below.

ECOLOGICAL SYSTEM
CONDITION VIABILITY RANKS
VERY GOOD >90% of vegetation in ecological system with major elements of native composition and structure in canopy and understory.
GOOD
 75 – 90% of prevailing vegetation with native composition and structure.
FAIR 50 – 75% of prevailing vegetation with native composition and structure.
POOR <50% of prevailing vegetation with native composition and structure.

Landscape Context - The landscape context of Hawaiian ecological systems recognizes that the status of lands surrounding a particular system occurrence plays a role in its viability. The optimum condition is to have an ecological system entirely surrounded by native-dominated adjacent systems that buffer the focal system from stresses, and contribute to its ecological processes. The worst situation is a system surrounded by degraded lands (and their anthropogenic stresses), or alien-dominated vegetation bearing potential invasive species, or lands that otherwise interfere with normal ecological processes.

(continued next column)

(continued from previous column)

Landscape context percentages were derived from Hawai‘i GAP landcover, using GIS boundary analyses. The assessment criteria are summarized in the table below:

ECOLOGICAL SYSTEM (ES)
LANDSCAPE CONTEXT VIABILITY RANKS
VERY GOOD   >90% of ES boundary with native- dominated surrounding lands.
GOOD   75 – 90% of ES boundary with native- dominated surrounding lands.
FAIR   50 – 75% of ES boundary with native-dominated surrounding lands.
POOR   <50% of ES boundary with native-dominated surrounding lands.

After size, condition, and landscape context ranks were assessed and assigned to every ecological system occurrence in the ecoregion, overall ranks were assigned for each system according to standard TNC algorithms used in Conservation Area Planning (CAP).

STREAM COMMUNITIES
Recent assessments of Hawaiian continuous perennial streams (e.g., Hawai‘i Stream Assessment, 1992), provided an outstanding set of criteria for assessing size, condition, and landscape context. The factors that were considered included stream flow, water quality, channel disturbance (e.g., channelization), channel heterogeneity, and adjacent vegetation. The "outstanding" streams in Hawai‘i (per Kido et al 1999) shared the following characteristics: 
 
  1. watersheds with native, or at least forested vegetation cover,
  2. large watersheds or otherwise higher overall stream flow conditions,
  3. no channel modifications (e.g., no artificial channelization),
  4. deep channels with frequent pool/riffle alternation
  5. high interstitial water flow, high flow rate heterogeneity, low erosion/sedimentation,
  6. high water quality and oligotrophic conditions.


Reference streams of highest quality were found on Kaua‘i, Maui, Moloka‘i, and Hawai‘i islands, and their biotic composition is highly consistent. Where the above conditions are met, a complement of native stream macrobiota are present, and the stream community is ranked "very good" or "unimpaired" and capable of supporting aquatic species that are most sensitive to habitat conditions. At the opposite end are streams that are considered "poor," "impaired," and "non-supporting" of the native biota that comprise the Hawaiian continuous perennial stream community. Thus, we adopted the ranking criteria of the Hawai‘i Stream Assessment (HSA) and the Kido et al 1999 bioassessment:
STREAM COMMUNITY
SIZE VIABILITY RANKS
VERY GOOD Primary stream length >3 miles and/or stream flows in range of highest quality reference streams (>50 cfs median flow) or average flows >80 cfs.
GOOD Stream length [1.5 – 3] miles and/or
10-50 cfs median or average 20-80 cfs.
FAIR Stream length [0.25 – 1.5] miles and/or <10 cfs median or average <20 cfs.
POOR not considered in HSA

STREAM COMMUNITY
CONDITION VIABILITY RANKS
VERY GOOD "Unimpaired" and "supporting" streams in Kido et al 1999.
"Outstanding" streams in HSA.
GOOD "Mildly impaired" and "partially supporting" streams in Kido et al 1999. "Substantial" streams in HSA.
FAIR "Moderately impaired" and "partially supporting" streams in Kido et al 1999. "Moderate" streams in HSA.
POOR "Impaired" and "non-supporting" streams in Kido et al 1999.
"Limited/Without" in HSA.

STREAM COMMUNITY
LANDSCAPE CONTEXT VIABILITY RANKS
VERY GOOD >95% of stream surroundings in natural setting from source to mouth w/intact riparian vegetation and <5% in disturbed, erosion-prone, urban, or intensive agricultural landscape, lacking intact riparian corridor.
GOOD 85 – 95% of stream runs through natural setting. 5 - 15% lacking intact corridor.
FAIR 75 – 85% of stream runs through natural setting. 15 - 25% lacking intact corridor.
POOR <75% of stream runs through natural setting. >25% lacking intact corridor.

SPECIES CONCENTRATIONS
The three species concentration targets selected (rare plants, native forest birds, and endangered waterbirds) have been the focus of a variety of conservation agencies. We used information from experts, existing assessments, and field surveys, as well as recent statewide assessments of these targets by the US Fish and Wildlife Service, the US Geological Service, Biological Resources Discipline, and the State of Hawai‘i Department of Land and Natural Resources, Division of Forestry and Wildlife, that identified trends in size, condition and landscape context leading to the criteria provided in the appendices.

Summarizing the viability ranks assigned to all selected conservation targets across the ecoregion yielded the summary table (see below), documenting a pattern of highest viability for remote, high-elevation ecological systems, as well as good viability for all species concentration targets except rare plant concentrations.

The next step in the assessment process is establishment of conservation goals via selection of viable conservation targets to add to a portfolio of  sites.

lehua

Continue to Conservation Goals
 


In the summary viability assessment table (right) colored cells indicate presence of all conservation targets among the four stratification units, eight islands, and 15  conservation areas. Colors indicate summary viability ranks:

VERY GOOD = dark green
GOOD = light green
FAIR = yellow
POOR = red
VIABILITY RANKS OF CONSERVATION TARGETS OF THE HAWAIIAN HIGH ISLANDS ECOREGION
viability table
Abbreviations: SU = Stratification Unit; ES = Ecological System target; ALP = Alpine System; SUB = Subalpine System; MD = Montane Dry System; MM = Montane Mesic System; MW = Montane Wet System; WC = Wet Cliff System; LW = Lowland Wet System; LM = Lowland Mesic System; LD = Lowland Dry System; DC = Dry Cliff System. Other Conservation Targets: CPS = Continuous Perennial Stream; FBC = Forest Bird Concentration; RPC = Rare Plant Concentration; WBC = Waterbird Concentration. Islands: NII = Ni'ihau; KAU = Kaua'i; OAH = O'ahu; MOL = Moloka'i; LAN = Lāna'i; KAH = Kaho'olawe; MAU = Maui; HAW = Hawai'i. Conservation Areas: NII = Ni'ihau; KAU = Kaua'i; OAH = O'ahu; EMO = East Moloka'i; LAN = Lāna'i; KH = Kaho'olawe; EMA = East Maui; WMA = West Maui; KOH = Kohala; MK = Mauna Kea; WML = Windward Mauna Loa; K-K = Ka'ū-Kapāpala; KON = Kona; P-P = Pōhakuloa-Pu'u Wa'awa'a.
[under construction]

[coastal images]		 [under construction]
2008 Coastal Target Viability Assessment

When applying viability ranking to coastal conservation targets, a number of differences with terrestrial targets emerge, because of different natural disturbance regimes, as well as biogeographical attributes such as dispersability, connectivity, and endemism. Therefore, a different set of viability criteria were established for coastal targets, and these are discussed by target type below.

COASTAL VEGETATION

Coastal vegetation tends to occupy a narrow zone along the coastline, undergoes more frequent natural disturbance, bears generally lower levels of endemicity, and is more dynamic in both structure and composition, than terrestrial vegetated ecological systems. That is, adaptation to natural disturbance regimes results in a coastal system that is more variable in space and time. The influence of the ocean is strongest along the interface between sea and land, a linear boundary feature. In this regard coastal and riparian vegetation both tend to be more linear, and it is difficult to apply areal size criteria in the same manner as for terrestrial ecological systems. 

Size -

COASTAL VEGETATION
SIZE VIABILITY RANKS
VERY GOOD
GOOD
FAIR
POOR

Condition -

COASTAL VEGETATION
CONDITION VIABILITY RANKS
VERY GOOD
GOOD
FAIR
POOR

Landscape context -

COASTAL VEGETATION
LANDSCAPE CONTEXT VIABILITY RANKS
VERY GOOD
GOOD
FAIR
POOR


ANCHIALINE POOLS

Viability of anchialine pools was assessed by using the number of pools in a single geographically isolated pool complex as a surrogae for size, presence of native anchialine pool species (and absence of alien species) as an indicator of condition, and nature of land use and vegetation surrounding the anchialine pools as a measure of landscape context.


SEABIRD NESTING CONCENTRATIONS

Size of seabird nesting concentrations can be assessed by the number of species breeding, and the sheer numbers of individual birds typically present at an occurrence. Condition is likewise correlated with the numbers of birds that can be consistently supported at an occurrence, and landscape context was assessed by the vegetation and land use patterns adjacent to the occurrences.

[under construction]
place holder for coastal target viability summary table