Australian Vegetation Attribute Manual

National Vegetation Information System, Version 6.0
Executive Steering Committee for Australian Vegetation Information (ESCAVI)
Department of the Environment and Heritage, 2003
ISBN 0 642 54953 2

Section Two: The NVIS Framework - Concepts and Standard Procedures (continued)

Structural Information

(Sub-)Strata, Stratum Dominance and Growth Forms

The stratum codes in Table 2 show the relationship between the NVIS (sub-)stratum codes, traditional names (Walker & Hopkins, 1990) and the growth forms within each (sub-)stratum. The definitions for growth forms are in GROWTH_FORM_CODE in the Growth Form table (see Section 3). The maximum number of sub-strata within level VI (Sub-Association) is eight. The stratum code can be selected from the list in Table 2. When describing the stratum at level IV (the Sub-Formation) and level V, the data codes U, M and G are obtained from U1, M1 and G1 respectively.

The dominant (sub-)stratum is estimated by the interpreter across the vegetation type as the (sub-)stratum with the most biomass, relative to other (sub-)strata. This used to provide a summary of the vegetation description at the simpler levels (Levels I to III) in the NVIS Information Hierarchy (Table 1). For data entered at level VI, the sub-stratum that is dominant over all other sub-strata in the vegetation type is indicated with a plus "+" symbol. For data entered at level V, the stratum that is dominant over all other strata in the vegetation type is indicated with a plus "+" symbol. For data entered at level V or VI, the "+" notation is carried through to level IV. The record in the detailed vegetation data corresponding to the dominant (sub-)stratum has the Boolean attribute DOMINANT_STRATUM_FLAG set to "Y" (for Yes) or "T" (for True).

For further details, see the examples in Table 6, the Vegetation Description attributes: L6_SUB-ASSOCIATION, L5_ASSOCIATION and L4_SUB-FORMATION and the Stratum attribute: DOMINANT_STRATUM_FLAG in Section 3.

Table 2. NVIS (sub-)stratum codes and descriptions. Height classes and growth forms in brackets are currently allowed by the rules (see Section 4), but are not recommended.
NVIS Stratum Code NVIS
Sub-stratum
Code
Description Traditional
Stratum
Name
Growth Forms* Height Classes* Not allowed*
U U1 Tallest tree sub-stratum. For forests and woodlands this will generally be the dominant stratum. For a continuum (eg. no distinct or discernible layering in the vegetation) the tallest stratum becomes the defining sub-stratum. Upper, tree Overstorey/Canopy(If only one tree layer occurs it is coded U1) Trees, tree mallees, palms, vines (mallee shrubs)Also: epiphytes, lichens 8,7,6 (5) Grasses & shrubs, low mallee shrubs
U2 Sub-canopy layer, second tree layer
U3 Sub-canopy layer, third tree layer
M M1 Tallest shrub layer. Mid, shrub (if only one mid layer occurs it is coded M1) Shrubs, low trees, mallee shrubs, vines, (low shrubs, tall grasses, tall forbs, tall sedges) grass-trees, tree-ferns, cycads, palms. Also: epiphytes, lichens (6) 5,4,3 Mid and low grasses, sedges, rushes & forbs. Mid & tall trees/ palms.
M2 Next shrub layer.
M3 Third shrub layer
G G1 Tallest ground species Lower, ground (if only one ground layer occurs it is coded G1) Grasses, forbs, sedges, rushes, vines, lichens, epiphytes, low shrubs, ferns, bryophytes, cycads, grass-trees, aquatics, seagrasses. (4,3) 2,1 Trees, tree-mallees, palms.
G2 Ground
* See Table 3 and Section 4 for further details.

Growth Forms and Heights

The NVIS framework compiles a maximum of number of 8 height classes that are linked to growth forms. Growth form codes used in the NVIS are described in the GROWTH_FORM: GROWTH_FORM_CODE attribute. Height classes are used to describe the sub-strata of vegetation found at the vegetation Sub-Association level. The height refers to the 'top height' of the stratum. Height classes used in the NVIS are described in the HEIGHT_CLASS attribute in the Stratum table.

The height classes are assigned to 5 sets of growth forms, as per the columns in Table 3. Woody plants are divided into three classes on the basis of whether they are single-stemmed (trees etc.) or multi-stemmed (shrubs, mallees). The lower-storey growth forms are divided into terrestrial higher plant forms: grasses, grass-like growth forms and forbs and lower-plant and/or aquatic forms. Vines and palms are assigned to particular growth form categories for the assignment of height classes, according to further properties specific to each vegetation description.

Table 3: Height classes defined for the NVIS. The word in the body of the table is used to "qualify" the structural formation.
Height
Growth Form
Height Class Height Range (m) tree, vine (M & U), palm (single-stemmed) shrub, heath shrub, chenopod shrub, ferns,samphire shrub, cycad, tree-fern,grass-tree, palm (multi-stemmed) tree mallee, mallee shrub tussock grass, hummock grass, other grass, sedge, rush, forbs, vine (G) bryophyte, lichen, seagrass, aquatic
8 >30 tall NA NA NA NA
7 10-30 mid NA tall NA NA
6 low NA mid NA NA
5 NA NA low NA NA
4 >2 NA tall NA tall NA
3 1-2 NA mid NA tall NA
2 0.5-1 NA low NA mid tall
1 NA low NA low low
Source: (Based on Walker & Hopkins 1990).

Where vegetation forms structurally complex vertical layers up to 8 classes can be used (see Table 2) e.g. vegetation in a riparian zone may comprise several upper tree layers, several mid layers of trees and shrubs and a number of ground layers. Where the vegetation is relatively simple e.g. savannah grassland, there are often only two strata comprising trees (e.g. height class 7) and grasses (e.g. height class 4).

Stratum Cover and Dominance

The remaining structural attributes needed to describe vegetation structure are cover and an indication of (sub-)stratum dominance. Cover is estimated for each (sub-)stratum and recorded in the Stratum Table. Further details of the cover of each growth form and species can be recorded in separate tables - see later sections.

Cover is an essential attribute (Table 7) in the description of a vegetation type. Cover can be assigned to the stratum (e.g. Fig. 3) and/or sub-stratum as part of the vegetation structure at a summary level in the Stratum table.

A multitude of methods have been used for describing vegetation cover. When providing detailed cover measures in the Stratum table, it is important to fill in the COVER_TYPE attribute in that table. The minimum requirement is for an interpretation of COVER CODE attribute for each (sub-) stratum in the Stratum table. This enables comparison between vegetation descriptions originating from different methods.

Dominance of the (sub-)stratum provides a useful summary of the vegetation description at the simpler levels (Levels I to III) in the NVIS Information Hierarchy (Table 1). The dominance of a (sub-)stratum is indicated by its relative biomass across a vegetation type. The data provider usually estimates the biomass of each (sub-)stratum as a multiple of the cover, height and area covered by the (sub-)stratum within the full extent of the vegetation type.

For data entered at level VI, the sub-stratum that is dominant over all other sub-strata in the vegetation type is indicated with a plus "+" symbol. For data entered at level V, the stratum that is dominant over all other strata in the vegetation type is indicated with a plus "+" symbol. For data entered at level V or VI, the "+" notation is carried through to level IV. For further details, see the attributes L6_SUB_ASSOCIATION, L5_ASSOCIATION and L4_SUB_FORMATION in Section 3.

Component Data for Growth Forms

Detailed source component data about an unlimited number of growth forms can be entered into the Growth_Form table. However, the NVIS Information Hierarchy uses only the top 3 growth forms per stratum at Level V and the top 5 growth forms per sub-stratum at Level VI (See the subsection on the NVIS Information Hierarchy, Table 2 and attribute descriptions in the Veg_Description table in Section 3).

The dominance of a growth form is indicated by its relative biomass in each (sub-)stratum of a vegetation type. The data provider usually estimates the growth form's biomass as a multiple of cover, height and area covered by the growth form within the full extent of the vegetation type. Growth forms must be listed in order of decreasing dominance, using the attribute GROWTH_FORM_RANK in the Growth Form table. Where available, additional data on the type of dominance (or whether it is an "indicator") of the growth form in a (sub-)stratum can be recorded in the GR_FORM_DOMINANCE_QUALIFIER attribute.

Detailed cover values can be provided for each growth form for each (sub-) stratum in the Growth_Form table. It is important to fill in the COVER_TYPE attribute in the same table.

In some cases, where cover and/or height of a growth form has not been recorded in the field survey, frequency is sometimes used to estimate dominance. This is useful attribute in its own right (GROWTH_FORM_FREQUENCY), but its use in isolation to estimate dominance is not recommended.

Where data providers to NVIS want to record the growth form as sometimes present in the vegetation description, the attribute GROWTH_FORM_ALWAYS_THERE in the Growth Form table can be set to "N". This facility and data would provide the raw data for an automated program to generate a "+/-" symbol in front of the growth form in a vegetation description, if this is required in the future.

Putting the Structural Formation Together

The vegetation structural formations are a standardised terminology used to integrate growth form, height and cover within each stratum. The NVIS structural terminology was adapted from Specht (1970), Specht et al (1974), and Walker and Hopkins (1990).

The allocation of a height class to a growth form in a sub-stratum by the data custodian gives rise to a particular height qualifier, from the body of Table 3. The height qualifier and growth form are then added to cover information to define the structural formation (Table 4). The structural formation is used in generating levels I to IV of the NVIS Information Hierarchy and is thus a relatively user-friendly summary of the dominant growth form, cover and height of a vegetation description.

For example, under the NVIS Structural Formation Terminology, vegetation that comprises shrubs of less than 2m in height and with a foliage cover 10-30% is classed as 'open shrubland'.

Table 4: NVIS Structural Formation Terminology
 
Cover Characteristics
  Foliage cover * 70-100 30-70 10-30 » 0 0-5 unknown
  Crown cover ** >80 50-80 20-50 0.25-20 0-5 unknown
  % Cover *** >80 50-80 20-50 0.25-20 0-5 unknown
  Cover code d c i r bi bc unknown
                 
Growth Form Height Ranges (m)
Structural Formation Classes
tree, palm 30 closed forest open forest woodland open woodland isolated trees isolated clumps of trees trees
tree mallee closed mallee forest open mallee forest mallee woodland open mallee woodland isolated mallee trees isolated clumps of mallee trees mallee trees
shrub, cycad,grass-tree, tree-fern 2 closed shrubland shrubland open shrubland sparse shrubland isolated shrubs isolated clumps of shrubs shrubs
mallee shrub closed mallee shrubland mallee shrubland open mallee shrubland sparse mallee shrubland isolated mallee shrubs isolated clumps of mallee shrubs mallee shrubs
heath shrub 2 closed heathland heathland open heathland sparse heathland isolated heath shrubs isolated clumps of heath shrubs heath shrubs
chenopod shrub 2 closed chenopod shrubland chenopod shrubland open chenopod shrubland sparse chenopod shrubland isolated chenopod shrubs isolated clumps of chenopod shrubs chenopod shrubs
samphire shrub 0.5 closed samphire shrubland samphire shrubland open samphire shrubland sparse samphire shrubland isolated samphire shrubs isolated clumps of samphire shrubs samphire shrubs
hummock grass 2 closed hummock grassland hummock grassland open hummock grassland sparse hummock grassland isolated hummock grasses isolated clumps of hummock grasses hummock grasses
tussock grass 0.5 closed tussock grassland tussock grassland open tussock grassland sparse tussock grassland isolated tussock grasses isolated clumps of tussock grasses tussock grasses
other grass 0.5 closed grassland grassland open grassland sparse grassland isolated grasses isolated clumps of grasses other grasses
sedge 0.5 closed sedgeland sedgeland open sedgeland sparse sedgeland isolated sedges isolated clumps of sedges sedges
rush 0.5 closed rushland rushland open rushland sparse rushland isolated rushes isolated clumps of rushes rushes
forb 0.5 closed forbland forbland open forbland sparse forbland isolated forbs isolated clumps of forbs forbs
fern 2 closed fernland fernland open fernland sparse fernland isolated ferns isolated clumps of ferns ferns
bryophyte closed bryophyteland bryophyteland open bryophyteland sparse bryophyteland isolated bryophytes isolated clumps of bryophytes bryophytes
lichen closed lichenland lichenland open lichenland sparse lichenland isolated lichens isolated clumps of lichens lichens
vine 30 closed vineland vineland open vineland sparse vineland isolated vines isolated clumps of vines vines
aquatic 0-0.5, closed aquatic bed aquatic bed open aquatic bed sparse aquatics isolated aquatics isolated clumps of aquatics aquatics
seagrass 0-0.5, closed seagrass bed seagrassbed open seagrassbed sparse seagrassbed isolated seagrasses isolated clumps of seagrasses seagrasses

Notes
This table is based on native vegetation, but can be used in a similar fashion for non-native vegetation and for describing revegetation.

* Foliage Cover is defined for each stratum as 'the proportion of the ground, which would be shaded if sunshine came from directly overhead'. It includes branches and leaves and is similar to the Crown type of Walker & Hopkins (1990) but is applied to a stratum or plot rather than an individual crown. It is generally not directly measured in the field for the upper stratum, although it can be measured by various line interception methods for ground layer vegetation. For the attribute COVER CODE in the Stratum table, the ground cover category refers to ground foliage cover not percentage cover.
** Crown Cover (canopy cover) as per Walker & Hopkins (1990). Although relationships between the two are dependent on season, species, species age etc (Walker & Hopkins (1990), the crown cover category classes have been adopted as the defining measure.
*** The percentage cover is defined as the percentage of a strictly defined plot area, covered by vegetation. This can be an estimate and is a less precise measure than using, for example, a point intercept transect methods on ground layer, or overstorey vegetative cover. That is for precisely measured values (e.g. crown densitometer or point intercept transects) the value measured would be 'foliage' cover. Where less precise or qualitative measures are used these will most probably be recorded as 'percentage' cover.

The last column of Table 4 is designed to cater for situations, in existing data, where the cover value for the growth form is unknown.