Most riparian forest
restoration projects have focused on restoring overstory
species, and few studies have experimentally assessed factors limiting
recruitment at multiple spatial scales.
The goal of this research is determine which factors most strongly
affect seedling recruitment of native understory
plants along the Sacramento River in order to
inform restoration efforts. In fall 2005,
we established experimental plots at six restoration sites of different ages to
test the effects of grass competition, overstory
cover, and distance to the forest edge on native understory
establishment. We broadcast seeded and
planted seven species (Aristolochia californica,
Artemisia douglasiana, Carex
barbarae, Clematis ligusticifolia,
Euthamia occidentalis, Rubus ursinus, and Vitis californica). During winter-spring 2006 most plots flooded
three times. By September 2006,
seedlings showed relatively high overall survival given that they were not
irrigated (range: Carex - 68% to Euthamia - 23%). Survival of most species
was higher in older restoration sites and in plots with overstory
cover. Treatments to reduce grass
competition had minimal effect on survival and growth, which is likely due to
extensive growth of broadleaved weeds in herbicided
plots. Establishment from seeds was low
(<5 seedlings/m2) for all species. We are also monitoring natural
recruitment of native understory species in all treatments
at two distances from remnant forest edge.
To date, too few plants have recruited to draw conclusions about spatial
effects. We replanted some species and
reseeded all species in December 2006 and will continue monitoring natural
recruitment, seed germination, and seedling growth and survival through fall 2008.