The Green Status assesses species against 3 essential facets of recovery (Akçakaya et al. 2018):
- A species is fully recovered if it is present in all parts of its range, even those that are no longer occupied but were occupied prior to major human impacts/disruption; AND
- It is viable (i.e., not threatened with extinction) in all parts of the range; AND
- It is performing its ecological functions in all parts of the range.
These factors contribute towards a “Green Score” ranging from 0%-100% which shows how far a species is from its "fully recovered" state.
This definition of recovery is ambitious by design. It is not expected, nor is it a goal that all species will eventually fulfil this definition of full recovery; for many species, large areas of range have been irreversibly converted for human uses. Instead, this definition serves as a way to standardize the assessment approach between species, and to identify areas of opportunity in the context of what has been lost.
It is important to note that any species can be assessed using the Green Status method, including species which have been very negatively impacted by humans and species which are not considered to have been impacted much at all.
Range
If the aim of recovery is to restore species to areas and ecosystems from which they have been extirpated, then the concept of range is central. For the purposes of the Green Status of Species, indigenous range is considered to be
Photo: Indigenous and current range of the Pink Pigeon (Nesoenas mayeri), endemic to Mauritius. By Durrell Wildlife Conservation
the distribution of a species prior to major human disturbance (plus any additional wild populations that have established since then). The date at which indigenous range is inferred can therefore vary from species to species; however, useful anchoring dates include 1500 (pre-European expansion) and 1750 (pre-industrialization). For some species, like island endemics, historical range is easy to delineate. For wider-ranging species, defining historical range may be more challenging.
The definition of recovery under the Green Status also includes “expected additional range.” This takes into account areas that are likely to become occupied by species within 100 years either from range shifts due to climate change or from conservation translocations.
Parts of the Range: Spatial Units
Once relevant range has been defined, a Green Status assessment subdivides the indigenous and expected additional range into spatial units. These spatial units help account for variation in species status across the range, and can be based on species’ biology (e.g. subspecies or subpopulations), ecology (e.g. habitat type, watersheds, dispersal barriers), or even anthropogenic boundaries (e.g. countries).
Species Status: Viability
A species is considered viable in a spatial unit if application of the Regional Red List Guidelines to the population in the spatial unit would result in a categorization of ‘Least Concern’ OR ‘Near Threatened and Not Declining’.
Species Status: Functionality
The ultimate goal of species recovery is to maintain or restore functional populations. The functions that different species perform in the ecosystem are many and varied, so the function of each species must be assessed on a case-by-case basis. See Akçakaya et al. (2019) for proposed methods to assess species functionality.
One fairly straightforward example is the function of wiregrass (Aristida stricta) in acting as tinder and allowing naturally-occurring and ecologically necessary savanna fires to spread. For a wiregrass population to be functional, it would have to be present at a high enough density to allow fire to spread from plant to plant.
Photo: Daniel Goodding
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Photo: Daniel Goodding
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Pine savanna in the southern United States where the open understory is maintained by frequent fire, which wiregrass (the tan-coloured grass) plays a key role in spreading. The photo on the right shows the wiregrass regenerating with char marks evident on the pines (Photo credits: Daniel Goodding) |
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