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             FSH 2090.11 - ECOLOGICAL CLASSIFICATION
                     AND INVENTORY HANDBOOK
                    WO AMENDMENT 2090.11-91-1
                        EFFECTIVE 4/26/91

   CHAPTER 2 - CLASSIFICATION OF POTENTIAL NATURAL COMMUNITIES


                            Contents

2.1      POTENTIAL NATURAL COMMUNITY 
2.11     Sampling
2.12     Classification
2.13     Successional Relationships
2.14     Naming Potential Natural Communities
2.15     Potential Natural Community Descriptions


2.1 - POTENTIAL NATURAL COMMUNITY.  Identify and describe 
potential natural communities as defined in FSM 2060.5.  A 
potential natural community is not a precise assembly of species 
with identical proportions of a species from place to place or 
even in the same place from year to year.  Variability appears in 
productivity and occurrence of individual species.  Determine the 
limits of variability to distinguish them through use of the 
classification.  If variability is too great for acceptable 
management application, use further classification subdivisions.

2.11 - Sampling.  Sample sites that have vegetation expression 
presumed to be representative of potential natural community.

2.12 - Classification.  Develop the classification of the 
potential natural community by grouping sites with similar 
floristics and composition.

The description of the potential natural community shall include 
information on species composition and a measure of species 
dominance such as cover, weight, and basal area.  Regions are 
responsible for correlating potential natural community 
classifications between forests and regions.  The examination of 
vegetation for potential natural community classification should 
integrate soils and physical characteristics.

2.13 - Successional Relationships.  Base the potential natural 
community on the best available representation of the community 
type.   Many influences modify or even temporarily destroy 
vegetation on a site, but may not preclude recovery or 
reestablishment of a potential natural plant community.  If the 
disturbance factor ceases to be an effective influence, the 
potential natural community of the site will eventually be 
restored.  The potential natural community, identified within the 
framework of its environment as a part of an ecological type, 
represents a relatively stable environment even if the vegetation 
is modified or temporarily changed.

Deterioration of the plant community is sometimes followed by 
site deterioration.  The cumulative effect of such detrimental 
influences reduces the opportunity for reestablishing the 
potential natural community and the productive capacity of the 
site.  Severe site deterioration may permanently alter the 
potential of the site.  In such instances, recognize a different 
potential natural community and describe it on the basis of the 
altered potential.

2.14 - Naming Potential Natural Communities.  Use two or more 
common names of characteristic, diagnostic, or prominent species 
to name potential natural communities.  Where one layer exists, 
choose two names; for example, Western Wheatgrass - Green 
Needlegrass.  Where more than one vegetation layer exists, names 
should come from each layer beginning with the tallest layer; for 
example, Mountain Big sagebrush/Idaho Fescue.  Exceptions are 
possible; for example, where the shrubs are shorter than the herb 
layer, the herb species will precede the shrub species.  For 
convenience, additional names may be used to denote phases of a 
potential natural community or other local variations.  According 
to local convention, scientific names may be substituted for common 
names or used in combination with them.

2.15 - Potential Natural Community Descriptions.  A minimum set 
of description core data includes:

    1.  A species list.

    2.  Some measure of composition or dominance. 

    3.  Production parameters such as weight, cover, basal area, 
incremental growth and site index.

    4.  A measure of constancy, by species.

    5.  Some general environmental data.

Ideally, a well described potential natural community will show 
all communities within the sere to be expected following 
different kinds of disturbance.