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__TREE_RECORD Definitions:

validated
	 a boolean variable where true = tree record has been certified for use
     by the growth model and false = not certified

tree              
     tree identifier.  No meaning to the growth model other than a guarantee of
     uniqueness

point_id
     id number of the point or plot on which the tree was observed. Some models
     treat the tree list as a compiled list -- after sample expansion (e.g.,
     ORGANON), others require plot specific information (e.g., FVS).  It is up
     to the model to deal with this information.  The specification does not
     require it generically.

sp_code
     numeric species code uniquely identifying a tree species, conforming to the
     xxxxxxxx standard species code list

total_age
     years from germination

bh_age
     breast height age -- years from point at which tree met or exceeded 4.5
     feet above ground level

x_pos
     x position of a location coordinate.  Coordinate system is model/user
     defined.
y_pos
     y position of a location coordinate.  Coordinate system is model/user
     defined.

dbh
     diameter at breast height (4.5 feet above ground level)

basal_diameter
     diameter at root collar

total_height
     distance from ground level to tip of tree or top of bend for trees with a
     drooping leader

crown_ratio
     percentage of total height occupied by live crown as defined by the xxxxx
     method

crown_width
     diameter of the live crown

expf
     expansion factor -- number of trees per unit area represented by this tree
     record

damage_code
	a model-defined damage code (could be a bit mask)

damage_severity
	the severity of the damage indicated by damage_code (severity levels need
	to be defined.

dbh_change
     change in dbh over one projection cycle

basal_diameter_change    
     change in basal_diameter over one projection cycle

ht_change
     change in total_height over one projection cycle

cr_change  
     change in crown_ratio over one projection cycle

cw_change 
     change in crown_width over one projection cycle

expf_change    
     change in expf (mortality and/or thinning) over one projection cycle

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