1 A 2-year field study examined the demographic consequences of association
with shrubs in an herbaceous perennial, Cryptanthaflava. Physiological dat
a were collected to evaluate whether shrub effects were mediated primarily
through water, nutrient or light availability.
2 Microclimatic conditions under the north side of shrubs differed from ope
n microhabitats, primarily in light availability. Due to little photosynthe
tic acclimation to light, daily photosynthesis for plants under shrubs was
reduced proportionally to the light regime.
3 Shading did not reduce stomatal conductance proportionally to photosynthe
sis, which led to decreased water use efficiency for plants under shrubs. F
ew differences were found in leaf water potential between microhabitats, in
dicating that little competition for water was occurring.
4 There was little evidence for shrub-induced nutrient island effects. Soil
nitrogen, phosphorus and organic content did not differ between open and s
hrub microhabitats. Leaf nitrogen content also differed little between plan
ts in the two microhabitats.
5 Growth and flowering responses of individuals under shrubs were reduced r
elative to those in the open, even for plants located on the south side of
6 Over this 2-year period of average to above-average rainfall, association
of C. flava with shrubs was dominated by competition for light, rather tha
n for water or nutrients. Future investigations will address whether this a
symmetric competitive interaction changes during years with below-average r
ainfall to a facilitative interaction, or one of increased competition for