Phytosociology Equations

Total basal area (ba)
ba for species x in m2/ha:

for 1991:
bax=(for all dbh for spp. x, S (p ½dbh) 2)* (1m2/100cm2)* (1/2900m2)* (10,000m2/1ha)

for 1999:
bax= (for all dbh for spp. x, S (p ½dbh) 2)* (1m2/100cm2)* (1/3000m2)* (10,000m2/1ha)

also, S all ba for the total woody stem basal area of all species per hectare.

Relative basal area
species x % basal area of total:

rel.ba=(bax/S all ba)* 100

Total density (dens)
number of stems of species x per hectare (#/ha):

for 1991:
#/ha=S #stemsx in study site* 3.45

for 1999:
#/ha=S #stemsx in study site* 3.33

also, S densities of all species for the total woody stem density per hectare.

Relative density
species x % density of total:

rel.dens.=(densx/S all dens)* 100

Frequency
% of plots on which species x occurs:

for 1991:
# stemsx/116

for 1999:
# stemsx/120

Relative Frequency
% of total frequency:

rel.freq=(freq. speciesx/S freq. for all species)* 100

Importance Value
An index of the "importance" or how much space each species occupies at the site:

imp.val=(rel.ba+rel.dens+rel.freq)/3

Diversity Indices

Two indices calculated to compare woody species diversity on the site between years and between different portions of the Ridge. (equations source: Smith, Robert Leo. Student Resource Manual to accompany Ecology and Field Biology, 4th ed. Harper and Row, NY. 1990.)

Shannon Diversity Index:
H=-S(ni/N)log(ni/N)
where ni is the number of individuals of species i and N is the total number of individuals of all species.

Simpson's Diversity Index:
D=[N(N-1)]/[Sni(ni-1)]
where ni is the number of individuals of species i and N is the total number of individuals of all species.