TERRESTRIAL HABITATS.

DENSE or MIXED TUSSAC GRASS (Parodiochloa flabellata) typically grows to a height of around 2 metres (although it can reach 3 or 4 metres), and features a tussock-like growth form around a fibrous pedestal. The pedestals accumulate slowly within a skirt of dead leaves, and many of the larger specimens may be 200 or more years of age. The pedestals provide nesting habitat for birds such as magellanic penguins, thin-billed prions, sooty shearwaters and small petrels, which burrow into or beneath it. The leaves, which can grow up to 2 metres in length, bush out from the living crown, and provide valuable nesting cover for passerines (eg. wrens, thrushes, siskins), birds of prey (eg. striated caracara, turkey vulture, short-eared owl), and coastal birds (eg. kelp geese, flightless steamer duck).

Tolerance or requirements for moist, salt-laden air allows tussac grass to become dominant around coastal regions, but more than about 300 metres from the coast, either lack of essential requirements, or competitive exclusion, prevents tussac growth. Therefore, with the exception of small islands of less than about 600 metres diameter, tussac tends to form a strip behind the coastal zone. This natural pattern has been disrupted over the last couple of hundred years by the introduction of livestock, and the sensitivity of tussac grass to over-grazing.

Tussac grass can be split into two categories, Dense Tussac where tussac is the dominant vegetation cover, and Mixed Tussac where tussac is present in another plant community, usually Oceanic Heath Formation (Grass or Dwarf Shrub).

Dense tussac grass modifies its own environment in a number of ways. The leaf litter from tussac grass is slow to decay, and forms a tussac peat, which can be deep, and high in nitrogen and phosphorus. The association of tussac grass with nesting seabirds and hauling-out sea mammals, helps to fertilise the ground with droppings produced from food taken at sea, and provides a valuable nutrient input to the tussac ecosystem. The dense leaf canopy which can form an almost impenetrable growth, and the retention of dead leaves around the pedestal, helps to insulate the tussac grass community against extremes of temperature, and allows water retention. This generates a sheltered micro-climate not only for nesting birds, but also for invertebrates, which in turn provide food for birds, along with the tussac seed. The closed canopy provides a hostile environment for most higher plant species, leaving almost a monoculture of tussac with just a few lower plant species and lichens capable of growing in the poor light available. Amongst the higher plant species which do seem adapted to surviving in tussac grass, are sword grass (Carex trifida), wild celery (Apium graveolens) and chickweed (Stellaria media).

GRASS HEATH is dominated by rough grasses, usually whitegrass (Cortaderia pilosa), and covers the largest areas of the Falklands mainland. The name whitegrass reflects the fact that the growing point of the leaf is generally beneath a longer dead leaf mass, giving the landscape a light buff appearance. On fairly well drained sites it can adopt a tussock growth form, and is often associated with pigvine (Gunnera magellanica), lawn lobelia (Pratia repens) and chickweeds (Cerastium sp.). On poorly drained plains, such as much of Lafonia, it takes on a more lax, less tufted form, and tends to be associated with rushes, sedges, astelia (Astelia pumila) and oreob (Oreobolus obtusangulus). Grass heath supports many flowering plants, invertebrates and a few birds.

DWARF SHRUB HEATH is dominated by low growing shrubs, particularly diddle-dee (Empetrum rubrum), and tends to form on dry, well-drained areas, such as hard peat overlying rocky ridges. It tends to be associated with tall fern (Blechnum magellanicum), small fern (Blechnum penna-marina), mountain berry (Pernettya pumila), teaberry (Myrteola nummularia) and christmas bush (Baccharis magellanica). Dwarf shrub heath also provides shelter for invertebrates, some smaller birds, and flowering plants such as pale maiden (Sisyrinchium jubatum), scurvy grass (Oxalis enneaphylla), vanilla daisy (Leuceria suaveolens), almond flower (Luzuriaga marginata), violet (Viola maculata) and dog orchid (Codonorchis lessonii).

FELDMARK FORMATION is dominated by cushion plants, such as balsam bog (Bolax gummifera) and cushion plant (Azorella sp.), often in association with tall fern (Blechnum magellanicum), small fern (B. penna-marina), dwarf shrubs and coarse grasses. It tends to be found on higher hills and exposed ridges, where the combination of thin shaley soils and exposure to wind exclude faster growing species which lack adaptations to cope with desiccation and nutrient deficiency. Although feldmark does provide habitat for certain invertebrates and birds, the harsh conditions and more open nature of this habitat means it generally lacks the diversity of species found in other habitats such as tussac grass or oceanic heath.

ROCKY OUTCROP The thin soils and underlying geology result in many areas of exposed rock, either as exposed bedrock, or surface stones such as stone runs. Such areas provide nesting sites for certain birds such as ground tyrants, red-backed buzzards, crested caracaras and peregrine falcons, and can be colonised by lichens and specialist plants, such as snakeplant (Nassauvia serpens).

FEN is an area surrounding ponds, lakes or streams which features tall freshwater vegetation such as willow herb (Epilobium ciliatum) and rushes (eg. Scirpus californicus and Eleocharis melanostachys). Associated plants include marigold (Caltha sagittata), water-milfoil (Myriophyllum elatinoides), starwort (Callitriche antarctica) and blinks (Montia fontana). Fen is not particularly abundant in the Falklands, although where it does occur it is important as cover for nesting waterfowl, smaller passerines and invertebrates.

BOG is a variable habitat type, usually comprising wet swampy areas of short rushes or astelia (Astelia pumila), often with low cushions of oreob (Oreobolus obtusangulus) or patches of sphagnum. Associated plants include sundew (Drosera uniflora), lawn lobelia (Pratia repens), lilaeopsis (Lilaeopsis macloviana), blinks (Montia fontana), buttercup (Ranunculus trullifolius) and pimpernel (Anagallis alternifolia).

FACHINE or BOX There are no native trees, and only two native species which grow as bushes: FACHINE (Chiliotrichum diffusum) and BOX (Hebe elliptica). Both species are sensitive to grazing by livestock, and as such have declined significantly since human settlement, now being virtually absent from much of East and West Falkland. As well as supporting a variety of invertebrates, such bush formations provide shelter and nesting habitat for several passerines, such as thrushes and siskins.

SAND DUNES are areas of loose or vegetated sand which form behind the littoral zone, and such habitat is therefore generally restricted to coastal areas. The consolidating vegetation can be sand grass (Ammophila arenaria), an introduced species adapted to stabilising highly mobile sand, or other drought-tolerant species more typical of grass and dwarf shrub heath. Such areas can provide cover for nesting waders and other shorebirds, and may well hold specialist invertebrates, although little work has been conducted to determine this.

ERODED AREAS Such areas feature exposed soil, as opposed to bedrock, and can be caused by overgrazing, burning and physical disturbance. If the underlying soil is peaty, it can be prone to drying out and blowing away, which can lead to a hollow that may later be filled with water to create a temporary pond. Such ponds are often devoid of higher lifeforms. Erosion is an increasing problem, especially on coastal areas, and is usually, although not always, a result of human activities.

SETTLEMENTS often provide niches for various species of plants and animals, some of which are dependent on human habitation (eg. House Sparrow). Other species such as the black-chinned siskin and thrush, make use of habitats provided by settlements in the form of planted shrubs and outbuildings. Rats and mice, although able to survive away from settlements, favour close proximity with man. Settlements also provide habitat for plant species which can grow nowhere else. Trees and introduced shrubs are often planted, along with numerous other garden plants, but settlements can also provide refuge for native species which are intolerant of grazing.

PASTURE is characterised by a short turf of fine grasses, as opposed to the coarse grasses of grass heath. These fine grasses provide a higher nutritional value for grazing, but require a more fertile soil to out-compete the coarse grasses which are adapted to thriving in poor soils. In the case of pasture, these nutrients are provided by the droppings of livestock, which tend to be kept at fairly high densities in such areas. Several plant species with a tolerance of being grazed at ground level, such as the daisy (Bellis perennis) and clovers (Trifolium sp.) are associated with pasture, and the nitrogen fixing properties of the clover will help maintain the nutrifying process. In general pasture is too short to provide shelter or nesting habitat for birds, and seems only to be of any real benefit to upland geese and lagomorphs which graze on the nutritional grass species.

GREENS also consist of a short turf of fine grasses, however the nutrient input does not come from livestock but from a variety of natural processes. Coastal greens are often associated with seabird colonies, where nutrients from food caught at sea are deposited on land as guano, providing a major nutrient input to the ecosystem. Similar associations may also result from the presence of high concentrations of geese or lagomorphs. Alternatively nutrient input may result from a topography which has a surrounding catchment area, or from underlying soil or rock with a high mineral content. Whatever the process involved, such areas tend to attract grazing geese, which help maintain the green and keep it short. The associated flora very much depends on the nature of the green, but will predominantly be plants which are tolerant of being grazed at ground level, such as those found in pasture.

TREES / GORSE There are no trees or gorse native to the Falklands, although European Gorse (and some tree species) have been planted at many settlements over the last century as a living stock-proof fence, and for amenity and windbreaks. Although they are introduced species, they can provide roosting and nesting sites for some native species.

TEMPORARY or PERMANENT PONDS & STREAMS The nature of ponds and streams varies enormously depending on edaphic factors, topography, geology, surrounding vegetation, weather patterns and farming practices. TEMPORARY ponds are subject to drying out periodically, and can be merely muddy hollows, virtually devoid of major lifeforms. PERMANENT ponds can provide a greater stability for aquatic life, and some can be rich in flora and fauna. Streams, and ponds connected to streams, may contain minnows (Galaxias sp.) and sometimes the much rarer zebra trout (Aplochiton zebra). Vegetation is likely to include water-milfoil (Myriophyllum elatinoides), and around the margins there may be species such as marigold (Caltha sagittata), starwort (Callitriche antarctica), blinks (Montia fontana), spike rush (Eleocharis melanostachys) and native rush (Juncus scheuzerioides). Ducks, geese and grebes are also likely to be found on the more biologically diverse ponds. Invertebrates have not been examined in any detail, but it is likely that certain species will have particular associations with ponds and streams.

LITTORAL HABITAT TYPES

For the purposes of survey work, the littoral habitat types are divided into the following basic categories.

a) Physical features:

Each section of shoreline can be categorised according to the ONE definition which best describes its mean high water mark features.

• BOULDER SHORE consisting of stones with an average diameter of more than 300mm. Boulders provide cover for marine invertebrates avoiding desiccation at low tide, and as such attract feeding birds such as black oystercatchers and black-crowned night herons. Such coastlines are generally subjected to high energy waves, and do not offer safe nesting sites for birds, or suitable habitat for plants, except at the very upper reaches of the shore.
  
  
• STONY SHORE consisting of stones with an average diameter of between 2mm and 300mm. The shifting nature of beach stones provides a poor substrate for plants to gain a foothold, and little cover for fauna. Birds such as pied oystercatchers, gulls and terns may nest on the upper reaches of shingle beaches, but most other species prefer sites which offer more seclusion. Elephant seals tend to choose shingle or sandy beaches for breeding.
  
  
• SANDY SHORE consisting of visible grains with an average diameter of less than 2mm. Sandy shores can provide important feeding and nesting areas for breeding waders such as pied oystercatchers and two-banded plovers, and feeding grounds for visiting white-rumped sandpipers. Sandy shores are also favoured by Gentoo and King penguins coming ashore to breeding colonies further inland, as well as by gulls and terns which may nest above the tide line. Plants such as sea cabbage (Senecio candicans), thrift (Armeria macloviana) and sand grass (Ammophila arenaria) are also often associated with the upper reaches of sandy shores, which are frequently backed by a dune system forming the transition into the terrestrial zone.
  
  
• MUDDY SHORE consisting of soft sediment with grains too small to be visible with the naked eye. Such sediments often provide a rich feeding area for waders such as white-rumped sandpipers, because of the invertebrates living in the mud. Low-energy, estuarine environments are usually covered during spring tides, precluding nesting or the establishment of terrestrial vegetation.
  
  
• ROCKY SHORE of exposed bedrock. The bedrock can provide secure attachment for marine invertebrates such as mussels and limpets, and for marine algaes which in turn support other marine creatures. Rockpools also tend to be numerous at low tide, trapping small fish and marine creatures. This wealth of marine creatures provides rich feeding for birds such as black oystercatchers, black-crowned night herons and gulls. The high energy waves prevent nesting, or the establishment of terrestrial plants, except in the upper reaches where species such as native crassula (Crassula moschata) may be found. Rocky shores are the preferred breeding sites of fur seal and sea lion.
  
  
• CLIFF shoreline with steep slopes that exceed 8m in height. The steep slopes and deeper water generally make cliffs unsuitable for most birds as feeding or breeding areas. Cliffs do however provide suitable nesting sites for rock shags, rockhopper penguins, albatross and peregrine falcons which seek out such sites. Birds such as black oystercatchers, kelp geese and flightless steamer ducks can often be seen feeding along the waters edge below the cliffs.

b) Biological features:

In addition to the physical nature of the shoreline, any number of the following biological features may also be present. Despite the fact that these are all essentially sub-littoral habitats, they are included because of their importance as food resources for shorebirds.

• GREEN ALGAE Shoreline where green algae such as sea lettuce (Ulva sp.) is found. Sea lettuce tends to grow around the mean tide level, but also gets washed further up shore, and provides a valuable food resource for birds such as kelp geese.
  
  
• KELP BEDS Shoreline where kelps, such as giant kelp (Macrocystis pyrifera) and tree kelp (Lessonia sp.) can be seen growing in the waters above the lower shore zone. Such marine habitats are important for many marine lifeforms.
  
  
• MUSSEL BEDS Shoreline where large numbers of mussels are present. Mussels can be an important food resource for oystercatchers and gulls, and in the late larval stage for marine ducks.