 |
This
summer golden paintbrush were thriving at a reintroduction site at William L.
Finley National Wildlife Refuge (photo by Caitlin Lawrence). |
Golden Paintbrush, Castilleja
levisecta, is an endangered herb which is endemic to the Pacific Northwest.
While it was once abundant in British Columbia, Washington, and Oregon, there are
only eleven known natural populations remaining. Golden paintbrush has been
lost in many areas due to habitat conversion, and no natural populations remain
in Oregon. Efforts to create new populations of golden paintbrush are ongoing
throughout its natural range, and many of these reintroductions have shown
great success.
 |
Haustorial
connections between a golden paintbrush
and host plant can be seen on the roots
of these
plants (photo by Katie Jones).
|
In one
experiment currently in progress, we are testing the effect of altering plant
community diversity and soil nutrient availability on the success of golden
paintbrush. One interesting characteristic of golden paintbrush is that it is a
hemiparasitic plant. What this means is that while it does not require a host
plant to survive, it can benefit from neighboring plants by attaching
belowground to other species roots and extracting water, nutrients and
secondary compounds via direct root-to-root haustorial connections. One way we
can help recover this species is to provide it with host plants that it can
parasitize. For this experiment, the first treatment was to seed some plots
with multiple host species to see if increasing the diversity of the community will
increase golden paintbrush reintroduction success. We combined this with a
second treatment of altering the soil nutrient levels, both increasing and
decreasing them relative to unmanipulated controls. Varying the levels of
nutrients provides a test of how golden paintbrush will perform under different
levels of available nutrients. This is interesting not only as a restoration
technique but also could aid in the selection of future sites for
reintroduction, and provide insight into how the success of golden paintbrush
could be impacted by nutrient enrichment which could occur though nitrogen
deposition from nearby urban areas, fertilizer runoff, or from other sources.
Additionally, experimental plots without golden paintbrush were included in
this experiment. Comparing these to the ones with golden paintbrush will allow
us to test the effect that the reintroduction of paintbrush has on the
community, since golden paintbrush has been absent from these communities for
some time.
 |
Caitlin
Lawrence using the point-intercept
method to estimate percent cover
of
vegetation in her plots (Photo by Tom Kaye). |
The first data were collected on this project in the spring and summer of
2013. What we’ve seen so far is that in plots where the level of nutrients in
the soil was lowered through the addition of carbon, less golden paintbrush
seedlings established than in the control or fertilized plots. The number of
seedlings was the same in control plots and fertilized plots, but the plants
were larger where we added fertilizer. We also saw differences in the plant communities
caused by nutrient availability. Reducing
nutrients in the soil reduced plant productivity by 20% to 31%, depending on
the site. Adding nutrients caused
productivity to increase by 44% to 59%.
Nutrient availability also changed the relative abundance of invasive
plants. Weed abundance dropped by 20%
to 31% when nutrients were reduced, and increased 0% to 12% when fertilizer was
applied. In 2013 we didn’t see
differences between plots seeded with the additional host species and those
that weren’t seeded, but since the hosts were still very small this year, we
expect to see a greater influence when we collect data again in 2014.
 |
Comparison
between carbon addition (left), control (middle) and fertilized (right) plots
shows the increase in plant biomass in a plot with increasing levels of soil
nutrients (Photos by Caitlin Lawrence). |
What do
these results mean for prairie restoration? With just one year of nutrient
enrichment in the soils we saw increased abundance of invasive plants compared
with native species. This could have implications for the future: if nitrogen deposition
from air pollution increases, we can expect invasive plants to become more
numerous and competitive. Reducing the nutrients in the soil may be a way to
give native plants an advantage over weeds.
With respect
to golden paintbrush specifically, high nutrient conditions can increase the
number of seedlings that emerge, at least in the short term. In 2014 we’ll be
watching for the effect of soil nutrient levels on paintbrush growth and flowering.
And as the seedlings of the host plants grow larger, we will be able to see
whether the growth of paintbrush is affected by increased plant diversity. Golden paintbrush restoration has made some great
progress so far and we hope to continue to learn about and conserve this
species for many years to come.
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