A Life Form is a group of plants having certain morphological features in common (Kuechler and Zonneveld, 1988).
A further distinction is made between Lichens/Mosses and, according to the quality of the main axis or shoots, Woody or Herbaceous. For further subdivision, additional growth form criteria are: the quality of the main axis or shoots, subdividing Woody from Herbaceous; branching symmetry, subdividing Trees from Shrubs; and physiognomy of the herbaceous plants, subdividing Forbs and Graminoids from Lichens/Mosses (Strasburger et al., 1983; Kuechler and Zonneveld, 1988).
The Life Form is the first classifier the user will use and therefore the most critical one. Depending on the main Life Form selected, the classification and its software program will reduce the number of options available for the second and third strata.
In selecting the main Life Form, two main criteria have to be considered:
Life Form of a plant is defined by its physiognomic aspect. This is the case when Woody plants, subdivided into Trees and Shrubs, are distinguished from Herbaceous plants, subdivided into Forbs and Graminoids, and Lichens/Mosses.
A condition of Height is applied to separate Trees from Shrubs: woody plants higher than 5 m are classified as Trees. In contrast, woody plants lower than 5 m are classified as Shrubs. This general rule is subject to the following exception: a woody plant with a clear physiognomic aspect of trees can be classified as Trees even if the Height is lower than 5 m but more than 3 m. In this case, a subcondition of physiognomic aspect is added to the Height condition.
These are the recommended thresholds for Life Form characterization, but exceptions are allowed:
The dominance of the Life Form is based on the "uppermost canopy" level, ranging from Trees to Shrubs to Forbs/Graminoids. This main condition for uppermost canopy has to be considered in conjunction with the sub-condition Cover, ranging from Closed or Open to Sparse. In other words, the uppermost canopy concept is only valid if the dominant Life Form has a cover either Closed or Open. If the Life Form is Sparse then the dominance goes to another Life Form which has a Closed or Open cover.
This can be illustrated by the following example from A12:
What is normally called "Tree Savannah" consists of a closed herbaceous vegetative cover that forms the main layer, with a second layer of sparse trees projecting above. In this case, the use of the uppermost canopy concept would designate the trees as a dominant layer over the herbaceous layer. Because of the sub-condition of cover, sparse trees cannot be the dominant Life Form with the presence of the closed herbaceous layer. This concept must be carefully considered due to the in-built conditions in the classification system. If the user starts with the wrong main Life Form, i.e., sparse trees, the option to select closed herbaceous as second layer will not be available because the system excludes any closed vegetation layer if the main stratum is sparse.
The following table summarizes the above criteria for determining the dominant Life Form:
Layering conditions for the dominant life forms are illustrated graphically below: Trees (Figure A), Shrubs (Figure B) and Herbaceous/Forbs/Graminoids (Figure C).
FIGURE A.
FIGURE B.
FIGURE C.
Woody (A12 and A24)
Defined as perennial plants with stem(s) and branches from which buds and shoots develop (Ford-Robertson, 1971). Semi-woody plants are included here (Eiten, 1968). Depending on the branching symmetry, a distinction is made between Trees and Shrubs (Strasburger et al., 1983). With reference to the International Classification and Mapping of Vegetation (UNESCO, 1973), bamboos and tuft plants (palms, tree ferns, etc.) belong to this category. Depending on their height, they are classified as Trees or Shrubs.
The classifier Woody can be applied in two cases:
The first case is related to a specific structural aspect of vegetation, whereas the second one is related to the detail of information, which the user is able to define.
A tree is defined as a woody perennial plant with a single, well-defined stem carrying a more-or-less-defined crown (Ford-Robertson, 1971) and being at least 3 m tall.
A condition of Height is applied to separate Trees from Shrubs: woody plants higher than 5 m are classified as Trees. In contrast, woody plants lower than 5 m are classified as Shrubs. This general rule is subject to the following exception: a woody plant with a clear physiognomic aspect of trees can be classified as Trees even if the Height is lower than 5 m but more than 3 m. In this case, a subcondition of physiognomic aspect is added to the Height condition.
These are the recommended thresholds for Life Form characterization, but exceptions are allowed:
These are woody perennial plants with persistent and woody stems and without any defined main stem (Ford-Robertson, 1971), being less than 5 m tall. The growth habit can be erect, spreading or prostrate.
Life Form of a plant is defined by its physiognomic aspect. This is the case when Woody plants, subdivided into Trees and Shrubs, are distinguished from Herbaceous plants, subdivided into Forbs and Graminoids, and Lichens/Mosses.
A condition of Height is applied to separate Trees from Shrubs: woody plants higher than 5 m are classified as Trees. In contrast, woody plants lower than 5 m are classified as Shrubs. This general rule is subject to the following exception: a woody plant with a clear physiognomic aspect of trees can be classified as Trees even if the Height is lower than 5 m but more than 3 m. In this case, a subcondition of physiognomic aspect is added to the Height condition.
These are the recommended thresholds for Life Form characterization, but exceptions are allowed:
This category in A12 includes: other Woody plants which are not `shrublike' (e.g., ground lianas), Welwitschia and plants which are definitely not herbaceous (e.g., Agave and cactoids).
Defined as plants without persistent stem or shoots above ground and lacking definite firm structure (Scoggan, 1978). There are two categories, depending on the physiognomy (Kuechler and Zonneveld, 1988; UNESCO, 1973), namely Graminoids and Forbs.
The classifier Herbaceous can be applied in two cases:
All broad-leaved herbaceous plants in the common sense (e.g., sunflower, clover, etc., in A12) and all non-graminoid herbaceous plants (UNESCO, 1973). Therefore ferns, except tree ferns (Kuechler and Zonneveld, 1988), and very low, non-leafy succulents (Eiten, 1968) are included.
The category applies where Forbs comprise more than 75 percent of the overall herbaceous coverage.
In A24, a further distinction can be made into Rooted and Free-floating Forbs.
These are aquatic plants that are growing on a substrate but structurally supported by water (UNESCO, 1973;Cowardin, 1979).
Defined as a non-anchored plant that floats freely in the water or on the water surface, e.g., formations like common duckweed (Lemna minor) or water hyacinth (Eichhornia crassipes) (UNESCO, 1973; Cowardin, 1979).
All herbaceous grasses and other narrow-leaved grass-like plants that are not grasses according to the taxonomic definition (Kuechler and Zonneveld, 1988). Bamboos are technically grasses but they are Woody in form and therefore classed with Shrubs or Trees.
Graminoid vegetation is defined by the presence of more than 75 percent Graminoids in the herbaceous coverage. There is no upper limit of height: the only condition is the physiognomy of the plant.
Lichens are composite organisms formed from the symbiotic association of fungi and algae. They are found encrusting rocks, tree trunks, etc., and they are often found under extreme environmental conditions (Lawrence, 1989). In tundras of North America and Eurasia, lichens (e.g., Cladonia spp.) may cover large areas (Kuechler and Zonneveld, 1988).
Mosses are a group of photo-autotrophic land plants without true leaves, stems or roots, but with leaf- and stemlike organs, e.g., sphagnum (Gray, 1970). Several plants commonly called "mosses" in fact belong to other groups: reindeer moss is a lichen; Spanish moss is a vascular plant (parasite); and Irish moss is an algae (Lawrence, 1989).
This category is only applied if the other Life Forms are not present and when Lichen/Mosses cover more than 20 percent. Otherwise they do not form a specific class but their presence can be mentioned in the description of another land cover class.
Lichens as specific class is applied when both Lichens and Mosses are present and when Lichens contribute 25 percent or more of the total cover.
Mosses as specific class is applied when both Lichens and Mosses are present and when Mosses contribute 25 percent or more of the total cover.
The cover can be considered as the proportion of a particular area of the ground, substrate or water surface covered by a layer of plants, considered at the greatest horizontal perimeter level of each plant in the layer (according to Eiten, 1968). A distinction is made between closed (more than 60-70 percent), open (70-60 percent to 20-10 percent) and sparse (20-10 percent to 1 percent). The reason of expressing the cover through ranges instead of using absolute values will be explained in the respective Guidelines.
As herbaceous plants are seasonal in character, it has to be noted that the cover of herbaceous vegetation is always considered at the time of its fullest development.
A layer of a certain Life Form covers more than (70-60) percent of a defined area. A closed cover composed of Trees or Shrubs has crowns interlocking, touching, or very slightly separated. In the last named case, the distance between two perimeters is no more than 1/6 of the crown average diameter (Eiten, 1968). The crowns can form an even or uneven closed canopy layer.
If plants are growing in a defined area with the crowns touching each other, presuming that the crowns of a Woody Life Form are round, the cover of the canopy will be approximately 78 percent. However, crowns are in reality often interlocking and small open spaces in the canopy are frequent. Therefore, in a closed canopy layer, the lower limit of closed vegetation is set at 60 percent. Because of the great variability of the horizontal character of closed vegetation, in particular the different crown shapes of the plant species, the range of values can vary from 60 to 70 percent.
Between (70-60) and (20-10) percent of a defined area is covered by a certain Life Form. In the case of Trees and Shrubs, the crowns are usually not interlocking. The distance between the perimeters can range from very small up to twice the average diameter (Eiten, 1968).
This category is further subdivided into Open ((70-60) to 40 percent) and Very Open (40 to (20-10) percent).
In the case of woody vegetation with a cover of between (70-60) and 40 percent, the plants are standing rather close together and, from a distance, they may appear to grow continuously (Kuechler and Zonneveld, 1988). To separate the two subclasses, the limit is set at 40 percent. The practical reason behind this is that at 40 percent coverage with Trees the distance between two perimeters equals the mean radius of a tree crown (UNESCO, 1973).
Between (20-10) and 1 percent of a defined area is covered by a certain layer of plants. The distance between two perimeters of a Life Form is more than twice the average perimeter diameter (Eiten, 1968). In many cases, a sparse Life Form might be associated with another Life Form of greater cover continuity, e.g., savannahs are characterized by sparse trees standing out from a herbaceous closed or open layer. Subdivision is made into Sparse ((20-10) to 4 percent) and Scattered (4 to 1 percent).
There are two reasons for the application of the range of 20 to 10 percent:
The classifier Scattered is only applicable if the total cover of all vegetation (that is all Life Forms) in the area equals or exceeds 4 percent.
The height of a certain layer is measured from the ground to the average top of the Life Form being assessed (Kuechler and Zonneveld, 1988). The fact that single plants of one synusia differ from the average height can be ignored, apart from the fact that they can form their own layer (e.g., the emergents of a rainforest that tower above the rest).
Height subdivisions are: more than 30 m down to 3 m for Trees; 5 m to 0.3 m for Shrubs; and 3 m to 0.03 m for Herbaceous. Each class is further subdivided.
There is an overlap between the lower height limit for trees and the upper limit for shrubs, and also between the minimum height for shrubs and the maximum height for herbaceous.
Height classes are directly related to Life Forms as height plays a complementary role in the definition of the structural classes. When a specific Height class is chosen, the user deliberately decides to give more emphasis to Height in the classification.
Spatial distribution, or Macropattern, is concerned with the horizontal distribution of the vegetation (Feoli et al., 1991).
Macropattern is further subdivided into: Continuous, Fragmented and Parklike Patches.
The Macropattern shows an ecological or a degradation aspect of vegetation (e.g., scattered vegetation in arid areas, agricultural encroachment inside forest areas, degradation due to overgrazing, etc.). In many classifications, one finds terms that are extremely subjective, like "Degraded Forests" or similar. The classification presented here is neutral in land cover description, without including ambivalent terminology. Therefore Macropattern is selected as a neutral classifier to describe the vegetation status:
Macropattern should thus be used to give supplementary ecological information (or to show a human-induced evolution aspect of natural vegetation). The user has the option to skip this classifier if it is felt to be irrelevant information.
Macropattern is defined as the horizontal spatial distribution of vegetation in a certain area. It should not be confused with Cover, which defines the spatial arrangement of Life Forms (e.g., trees, shrubs, etc.). Macropattern describes the spatial arrangement of specific structural vegetation types (e.g., Closed Forest, Closed Shrubs).
The combinations between Cover and Macropattern are unrestricted (this is nevertheless only valid for Closed Cover and Open Cover, as will be explained later. This means that, for instance, a closed tree formation (Closed Forest) can be either Continuous or Fragmented depending on its spatial distribution in the mapping unit.
Because of this dimensional aspect, Macropattern is linked to the mapping scale. This may seem to contradict the main classification concept explained earlier, which states that the elements of a classification system must be scale-independent. To determine Macropattern, one should refer to the overall appearance of a vegetation formation in a certain area in a homogeneous landscape. However, if one wants to be more precise or objective in the application of this classifier some specific rules are given below to help the user not familiar with this concept, in order to standardize interpretation. Because we are dealing with the practical application of this concept in a cartographic context, the concepts of mixed units and minimum mappable areas will be used.
A certain structural vegetation type has a continuous Macropattern if it covers more than 80 percent of the area inside the minimum mappable area.
A certain structural vegetation type has a fragmented Macropattern if it covers more than 20 percent but less than 80 percent inside the minimum mappable area. This situation is linked with the concept of mixed unit. Three cases are possible:
The Continuous or Fragmented classifiers are linked with Closed Cover or Open Cover (e.g., Closed Continuous Forest, Closed Fragmented Forest, Continuous Woodland or Fragmented Woodland). Fragmentation can be further subdivided into Striped and Cellular (e.g., tiger bush in the Sahel where Closed Shrubs are present in the interdunal areas, which can be represented as Fragmented (Striped) Closed Shrubs).
The Macropattern Parklike Patches is directly linked with the cover Sparse. This is simply redundant information. When the user defines the cover of a certain life form as Sparse, the only Macropattern available for this structural vegetation type is Parklike Patches.
The Macropattern is preferentially used for Woody life forms (Trees, Shrubs). Herbaceous life forms (Graminoids, Forbs) can have a Macropattern, but this is subordinated to the absence of Woody life forms. Thus, when linear patches of dense shrubs (typical of tiger bush) are present together with dense herbaceous vegetation covering the space between the different patches, one can see it in two different ways: either as fragmented shrubs/herbaceous or fragmented herbaceous/shrubs. The abovementioned rule of preferentially favouring Woody life forms obliges the user to always give preference, in the application of the Macropattern, to the Woody component. Macropattern can be applied to Herbaceous life forms only when there is no significant presence of Woody life forms (Trees, Shrubs). For instance, patches of dense Herbaceous vegetation in sandy areas can be called fragmented herbaceous/sand.
A structural vegetation type is fragmented when the sizes of the patches of the vegetation are between 1/15 and 1/2 of the minimum mappable unit. This rule is a very artificial one and does not need to be strictly applied. This rule assists the user by providing some indication of how a fragmented Macropattern should look. If the patches were too small, then at a certain level they could coincide with the life form itself, thus contradicting the basic rule explained above (i.e., Macropattern describes the specific arrangement of structural vegetation types and must not be confused with the cover of the life form).
A given cover can be Open or Closed but to be considered Continuous, the vegetation has to be spread over the area with regularity and without interval or break.
A certain structural vegetation type has a Continuous Macropattern if inside the minimum mappable area it covers more than 80 percent of the area.
A given cover can be Open or Closed but it is interrupted in the sense of Striped or Cellular fragmentation.
A certain structural vegetation type has a fragmented Macropattern if inside the minimum mappable area it covers more than 20 percent but less than 80 percent. This situation is linked with the concept of mixed unit. Three cases are possible:
In the case of woody vegetation, Parklike Patches signifies that trees and shrubs grow singly or in small groups as in parklands and in savannahs. When herbaceous vegetation is present, it signifies disconnected patches (Kuechler and Zonneveld, 1988).
The Macropattern Parklike Patches is directly linked with the cover Sparse. This is simply redundant information. When the user defines the cover of a certain life form to be Sparse, the only Macropattern available for this structural vegetation type is Parklike Patches.
Water Seasonality refers to the type of persistence of the water at or near the surface. A subdivision is made into three classes: (Semi-)Permanent (approximately four months a year, or more than a specific season), Temporary or Seasonal (less than four but more than two months a year, or during a specific season) and Waterlogged.
In this class, areas are considered which are covered by water for a substantial period, but which is not directly linked to a specific season. The class can be further subdivided into two subclasses: one where water is persistent the whole day (no tidal influences), and one where there is a tidal influence.
This class covers areas that are regularly flooded, but where the water cover does not remain for a substantial period of time or other than for a particular season.
The water table is very high and at or near the surface. These areas could be occasionally flooded, but the main characteristic is the high level of the water table (e.g., bogs).D. LEAF TYPE (A12 and A24)
Leaf type is applied only when characterizing Trees and Shrubs. A distinction is made between Broadleaved, Needleleaved and Aphyllous.
This refers to trees and shrubs of the botanical group Angiospermae, with Gingko (Gingko biloba) as an exception, as it taxonomically belongs to the Gymnospermae. Both Evergreen and Deciduous species belong to this category.
This refers to trees and shrubs of the botanical group Gymnospermae (Ford-Robertson, 1971), carrying typical needle-shaped leaves.
Both evergreen conifers like pines (Pinus spp.), hemlock (Tsuga spp.), and firs (Abies spp.), etc., as well as deciduous conifers like the larch (Larix spp.), are included in A12. It is also applied to scale-like leaves, especially leaves of arbor vitae (Thuja occidentalis). Contrary to usual definitions, this category includes all plants with needle-like leaves, even though they are not conifers, such as some Australian acacias (e.g., Acacia asparagoides).
This category includes plants without any leaves and plants that apparently do not have leaves in the common sense. In the first case, photosynthesis takes place through other organs, like stems, branches and twigs; in the latter case, the leaves are very short-lived or extremely reduced to scales and thorns.
Characteristic genera in A12 are: Casuarina, Euphorbia, Tamarix and many others mostly found in arid and semi-arid regions (Kuechler and Zonneveld, 1988).
The leaf phenology is for the general behaviour of woody plants throughout the year. Two types have to be distinguished: Evergreen and Deciduous. A further distinction is made between Mixed and Semi-Deciduous or Semi-Evergreen. The leaf phenology of herbaceous plants is classified through the mixed category. A separation can be made between Perennial and Annual vegetation.
This term as such describes the phenology of perennial plants that are never entirely without green foliage (Ford-Robertson, 1971).
For this class to be applicable, there must be a whole layer that is more than 75 percent evergreen vegetation.
This applies to the phenology of perennial plants which are leafless for a certain period during the year (Ford-Robertson, 1971). The leaf shedding usually takes place simultaneously in connection with the unfavourable season (UNESCO, 1973).
For this class to be applicable, there must be a whole layer that is more than 75 percent deciduous vegetation.
This category is limited exclusively to a layer with a mixture of broadleaved deciduous and needleleaved evergreen vegetation (Kuechler and Zonneveld, 1988).
Within this combination, it is necessary that each of the two components occupy at least 25 percent of the area.
This applies to the broadleaved category, as under tropical conditions deciduousness is difficult to define, especially as seasonal variation influences the time of leaf-shedding; plants are deciduous in certain areas, evergreen in others.
This term applies to a combination of broadleaved deciduous that is dominant and broadleaved evergreen being more than 25 percent.
This term applies to a combination of dominant broadleaved evergreen and with broadleaved deciduous being more than 25 percent.
This category is limited to a layer with a mixture of perennial or annual herbaceous plants.
Perennial: plants living more than one year
Annual: plants living one year.
With both perennial and annual plants being present, each type must cover at least 25 percent of the area.
Stratification, or layering, is defined as the vertical layering of vegetation. It should not be confused with Macropattern, which describes the horizontal distribution of Life Forms, nor with Cover, which describes the presence of one single Life Form.
The user can describe up to three layers for (Semi-)Natural Terrestrial Vegetation (A12) and two layers (including the main layer) for Aquatic or Regularly Flooded Vegetated Areas (A24). The limited number of layers at their disposal may disappoint users, but the classifier Stratification should contribute to the structural definition of a vegetation class. This means that this classifier must consider all the possible combinations with the main Life Form selected and its Cover (e.g., if we can have layering for Closed Trees, the same must be valid for Closed or Open Shrubs or Closed Graminoids, etc.). The layering is an active component of the class set-up; it is not a mere descriptive (optional and unsystematic) item of the class. The proposed classification allows the user to first build up a land cover class with the use of the classifier Stratification and, if more details are wanted, add a user's description to the standard one, which can contain information on any additional layers/strata.
Some limitations in the use of the classifier Stratification have been introduced in order to avoid class combinations that are irrelevant from the structural point of view. These limitations prevent introduction of elements that not crucial for the determination of the structural aspects of a land cover class. These elements can be added in the class description in the Legend (see Legend - Edit). These limitations have the practical purpose of reducing the number of possible combinations of classifiers, which otherwise could lead to creation of an even larger number of classes that would all have the same structural meaning. All limits to the use of Stratification are built into the software program.
From a practical point of view in the use of the Stratification concept, it is important to recognize two types of Stratification:
The second case is quite straightforward and does not present any difficulty in the selection of classifier. The first case needs additional explanation. In the case of a dominant Life Form of Trees with a second stratum of Trees , it is important that these layers are clearly distinguishable one from the other (e.g., second stratum of Trees Emergent over a Closed Tree canopy; these emergents must not be part of the discontinuity of the Closed Tree canopy but a clearly distinct layer). The sub-condition of Height will pre-set the available choices of Height for a second, and (for A12 only) a third, layer (e.g., with a main stratum of Closed Low Trees (3-7 m), the emergents to be defined in the second stratum cannot have the same height (option 3-7 m is therefore not available) because the Sparse Trees of the second layer have to be taller).
The Height condition explained above depends on the detailed option for Height chosen for the main stratum; it is not applied if the general Height class is selected. If the user selects the general Height class for the main stratum then for subsequent strata the general Height classes are the only options available.
The main conditions applied for Stratification/Layering are the following:
a1) Forbs and Graminoids are considered always together as Herbaceous.
a2) For Trees three strata including the main, can be considered in A12 (e.g., a main Closed Tree layer with a second, lower, Closed to Open Tree layer, and a third Sparse Tree layer of emergents would be termed a Multi-Layered Forest With Emergents), and in A24 two strata including the main are allowed.
a3) When the main stratum is Closed Trees or Open Trees and there is a second layer Sparse Trees, then the Height of the second layer must be higher, i.e., emergent; if they are lower, they are not considered as an independent stratum.
a4) For Shrubs, the number of strata with the same Life Form is two, including the main stratum.
a5) For Herbaceous only one stratum is possible.
a6) Lichens/mosses are not described in the layering.
a7) If the main stratum is Trees and the Cover is Open, then it is impossible to have the same Life Form with Cover Open To Closed with a different height as a second stratum (e.g., Open High Trees with Open Low Trees is impossible).
a8) If the main stratum is Shrubs and the Cover is Closed or Open, then it is impossible to have the same Life Form with Cover Open To Closed with a different height as a second stratum (e.g.. Open High Shrubs with Closed To Open Low Shrubs is impossible). The only exception to this rule is when the second stratum consists of Dwarf Shrubs.
and
b1) If the cover of the main stratum is Closed Trees or Closed Shrubs then any Herbaceous layer possibly present is not considered or described (this can be added as a user-defined description).
b2) Sparse Herbaceous is never considered as second layer except when the main layer is Sparse Trees or Sparse Shrubs (but it can be added as a user-defined description).
b3) If the main stratum is Shrubs or Herbaceous, only one layer of trees can be considered; this is linked with the criterion of dominance as described earlier, because the Trees or Shrubs can be only Sparse.
b4) Only two layers other than the main layer are considered for Terrestrial Vegetation (A12) and only one additional strata for Aquatic Vegetation (A24).
This attribute has two major divisions based on whether the name is derived from a single plant species or from a group of plants. In the first case, a further subdivision is possible into Dominant Species (Height, Cover or combination of both) or Most Frequent Species. The second subdivision is subdivided again into Plant Groups (e.g., Braun-Blanquet) and Plant Groups Derived Without Statistical Methods (e.g., same ecological significance, same geographic distribution, same dynamic significance, etc.). The specific name of the Floristic Aspect can be added using the User-defined Attribute option in the Legend Module.
