Grassland Alteration
Grasslands are central to the ecology and aesthetic of California. Unfortunately we have very little native grassland remaining anywhere in our state. Waves of invading grasses and other plants from Europe had already made major inroads on Stanford lands before the University was established in 1891. Deliberate introductions of non-native grass for livestock forage, unintended introductions of earthworms, red foxes and other animals, inappropriate grazing practices, and outright habitat destruction have left us with grassland systems barely resembling those of pre-colonization California.
Background
Goal 1: Minimize exotic plant abundance in foothill grasslands.
Several of our experiments seek to minimize the proportion of alien plants colonizing ground denuded by construction activity associated with our flood prevention efforts. In addition to biological efficacy, we are exploring the cost of various restoration/control measures.
Goal 2: Improve the science of restoration by critically evaluating our work.
For a variety of reasons, rigorous restoration monitoring is rarely done. This is unfortunate as we have a poor understanding of what works. Forecasting the likelihood a particular restoration approach will produce a system equivalent to our desired community is, at this point, guess work. Improving restoration success therefore requires detailed information about the performance of past and current restorations. We have been monitoring a variety of grassland functions (seed recruitment, insect productivity, microbial metabolism, etc.) to document the performance of our restored grasslands.
Exp. #1: Which native grass seed mix is optimal?
Our seeding experiment introduced zero, 1 (Nassella pulchra or purple needlegrass), or 8 species (Nassella pulchra plus 7 other species) of perennial native grass by hand to the site. The area was then covered with sterile rice straw to minimize predation and stabilize soils until plants could germinate.
Exp. #2: Which soil preparation method is more effective?
Our soils experiment consisted of four treatments: doing nothing to old and compacted soil, re-introducing topsoil only, re-introducing topsoil and hand seeding in our 8-species grass mix, or re-introducing disced topsoil and hand seeding in our 8-species grass mix zero. Each subsequent treatment increased the restoration cost.
Exp. #3: Can tarping reduce weeds?
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| Pulling up tarp to reveal the weed-free soil underneath. |
Our tarping experiment had two tarping treatments: covered the soil with a plastic tarp for several weeks in early fall or leaving the soil as it was. After tarp removal, we either seeded in our 8-species native grass mix or left the areas bare.
