- Native prairies of the Willamette Valley are considered among the rarest of Oregon’s ecosystems and are in critical need of conservation. Management strategies for increasing the abundance of native species are urgently needed, particularly those
strategies that promote the regeneration of native species from seed. The focus of this
investigation was to address this need. The general approach was to sow seeds of native
species into experimental field plots, which had been burned once, burned repeatedly,
mowed, or unmanaged at three sites at Baskett Slough National Wildlife Refuge.
Seedling numbers were then counted one growing season after sowing. To investigate
mechanisms for the regeneration responses of species to management treatments, selected
abiotic and biotic factors potentially important for seed regeneration were measured in
the field plots.
Seedling establishment rates in unmanaged plots were relatively small, averaging
9.7% for all three sites. Only one species, Danthonia californica, showed a positive response to the mowing treatment. Of the 13 species sowed in the burn plots, six species
(Bromus carinatus, Elymus glacus, Festuca roemeri/rubra, Clarkia quadrivulera,
Prunella vulgaris, Sidalcea campestris) had significant more seedlings in the burn plots
compared to the unmanaged plots. Seedling establishment of two species, Danthonia
californica and Potentilla gracilis, was significantly lower with burn treatments. The
other five species showed no significant responses to the burn treatments: Carex
tumicola, Calochortus tolmiei, Zygadensus venenosus, Balsamorhiza deltoidea, and
The strongest fire effects were generally in plots that had been burned only once,
rather than plots burned more than once. Abundance of litter and vegetation were the
factors that were most often related, both positively and negatively, with seedling
Based on the results of this investigation, prescribed burning, rather than mowing, is a
more viable management option to promote regeneration of native species from seed in
upland prairies. However, prescribed burning must be used with caution as it can reduce
seedling establishment rates for some species. Sowing seeds in unmanaged sites is an option, but sowing rates need to be high to compensate for the small seedling establishment rates in unmanaged prairies.