Elements of an ecosystems map: vegetation
Vegetation is the most voluminous expression of life and it creates its own microclimatic conditions. Maps-based physiognomic-ecological characteristics, thus inform us about the vegetation structure, certain ecological conditions and their distribution. For instance, tree species are usually different from shrub species, trees species in closed forest usually are at least partially different from the species making up a savannah, prairies are dominated by non-woody species, while aquatic vegetations again have very different species that make up the dominating structure. Each vegetation structure in part reflects climatic conditions, albeit, that other ecological conditions may also influence the vegetation structure as we have seen previously. The biounits with the distinguished characteristics accommodate species with survival strategies that can survive under those conditions. Each distinguished biounit thus contains a partially different assemblage or set of species. This is not only true for plant species, but for all species, flora, fauna and fungi alike, as each responds to the characteristic ecological conditions of each location. Mutatis mutandis, vegetation maps are at the same time ecosystem maps, but with some additional zoological information, ecosystem maps can be enhanced for distinguishing important locations for certain animal species. Therefore, we use physiognomic ecological vegetation classification systems as the classification basis for ecosystem mapping.
Specific fauna elements that can be added, are periodic concentrations of animals and coral reef formations that predominantly are composed by fauna elements. Whether or not migration routes should be included would be very much an ad-hoc decision. Probably in the case of aerial or aquatic migration routes, usually not, if the migratory species primarily uses the air/water space without using the resources. In the case of land animals, it may make sense, particularly if there is a specific resource-use interaction and/or terrestrial space occupation issue.
The sizes of ecosystems
There is no limitation in the sizes of ecosystems, as some ecosystems may be as small as an isolated pond in the dessert and others may be defined as hundreds of kilometers of similar grasslands or tropical forest.
Recognition from satellite images
The Map of the Ecosystems of Central America has been drawn from Landsat images, partly from printed copies at scale 1:250,000 and partly from computer monitors. Satellite images cannot distinguish physiognomic structures and they can only distinguish between a limited number of other characteristics that lead to the differentiation between ecosystems. Additional modifiers however can be deducted and in combination, they can considerably increase the differentiation in ecosystems. Duivenvoorden et al. (2001)1 concluded that “the similarities in the vegetation are reflected in the patterns on the satellite image”. However, only few floristic groups may be distinguished on satellite images, such as general broadleaved versus coniferous and mangrove forests, which each reflect slightly distinct colors.
Particularly, lowland tropical rainforest remain problematic. Duivenvoorden et al. (2001) warn that one should be careful when extrapolating inventories to an entire area mapped from a satellite image, as one may suppose that other forest types exist within such area, that have not yet been identified. This uncertainty for lowland tropical rainforests is common to all identification methods, although – if existing, they are likely to be included as subdivisions in the larger ecosystem classes. Moreover, it should be noted that lowland tropical ecosystems have relatively few distinguishing ecological classifiers or modifiers. As a result, there is a tremendous species variety within each ecosystem, but relatively little variety in different ecosystems over very large distances (S. Mori, pers. com.), which makes ecosystem mapping of lowland tropical forests a relatively coarse exercise.
Radar imagery has the advantage that they can be taken at any time of the 24-hour day, independent of daylight or cloud-cover. Classification with radar imagery taken from airplanes is possible, which allows processing for stereoscopic viewing (Sader 2001). Quiñones, (2002) has used radar imagery for monitoring purposes, which is particularly valuable in areas frequent cloud cover. Radar images taken from airplanes, however, is a costly technique, which in developing countries also may often still require enormous logistical preparations. Satellite radar images are still rather coarse and differentiation of the vegetation structure still remains very limited. For a while, in many countries ecosystem mapping will still primarily be dependent on applications from satellite images to which considerable progress is made
Although the developers of the UNESCO classification system suggested a mapping detail of 1:000,000 at the time, they had greater levels of detail in mind, for which they laid the basis with classes that would rarely occur on maps of the suggested scale, such as "flushes", "episodical forb communities", "screes", "Lemna-type free floating communities". In the context of the Map of the Ecosystems of Central America, it has become evident that mapping from satellite images at the detail of scale 1:250,000 is possible, while M. Carignan (pers. com.) suggested that mapping from Landsat imagery is possible at the detail of scale 1:100,000, in which the imagery is the limiting factor, not the classification system. After all, the vegetation structure can be described regardless of scale. Limitations of scale for the application of the UNESCO system and its derivates are subject to the remotely sensed imagery, available funding and contract time, but not to the system itself.
Within the Ecosystems of Central America mapping team, a debate took place on the minimum polygon size. Originally, it was set for 150 ha. But then it was found that for some conditions, the size was too small and for others too large. For instance, it may not make sense mapping all individual fragments of an elsewhere abundant biounit of intact habitat in a largely converted landscape. On the other hand, if those biounits are the last fragments of an almost lost ecosystem, like the Mata Atlántica, one would like to find every remaining patch of it. Also, aforementioned minuscule paramo ecosystem on a mountaintop in El Salvador (Ventura & Villacorta 2000) is extremely important for conservation, as it harbours a unique species assemblage. Another example constitutes small isolated rocks, emerging from the sea. There may be nothing on top, but under the high waterline, they represent some of the richest marine habitats – pelagic on the Pacific coast and Coralline on the Atlantic coast of Central America, while they may also be home to important colonies of oceanic birds or marine mammals. Di Gregorio (2000) suggests the definition and application of variable minimal mappable areas, which would provide a workable solution to deal with the previous issue. The ecosystems and protected areas database manual proposes differentiated minimum sizes for a working scale of 1:100,000 - 1:250,000.
Elements of an ecosystems map: fauna
For ecosystem mapping, preferably specific zoological information should also be mapped where possible, such as the distribution of coral reefs and faunal congregation sites (e.g. breeding, rutting and roosting sites). Such detail on faunistic elements must be superimposed on vegetation and/or substrate modifiers in the same way as floristic elements. However, high concentrations of fauna elements are relatively rare and more difficult to categorize as compared to vegetation structures. So often they may be ad-hoc-defined ecosystems for which a specific class description may be needed.
Mapping without classifying
In a discussion with Roger Sayre of the USGS, we discussed the idea of having ecosystem maps without a classification, but based on overlaying layers by classifier or modifier. Ultimately, that would probably be the most accurate map, and for some purposes, such map would be the way to go. However, for the purpose which I particularly have in mind, protected areas gap analysis, such map could become too detailed to handle and it might produce so many - often very small - areas with just a little bit of differentiation, that striving after including each one of them in a protected areas system, would be impossible, and also unnecessary.
Keywords: ecosystem, mapping
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