The positions of fern species shared by both surveys
along a soil moisture gradient was strongly correlated
(r 0.91, P 0.001; Fig. 6), indicating that species
optima along the soil moisture gradient were highly
conserved between the two survey scales. A graphical
view of distributions along the moisture gradient indicated
that six of the eight common fern species shared
by both data sets showed consistent environmental optima
(Fig. 7). Segregation along this gradient was apparent
among these species: Cystopteris fragilis,
Dryopteris marginalis, and Adiantum pedatum occupied
sites with lower soil moisture; Polystichum acrostichoides
and Athyrium filix-femina were found
mostly in sites with midranges of soil moisture; and
Onoclea sensibilis was found at the wettest sites. The
two species that did not show consistent soil moisture
tolerances, Deparia acrostichoides and Dryopteris intermedia,
did not respond to variation in soil moisture
in either of the surveys