A greater than 10-fold increase in Canada goose (Branta canadensis)
populations over the past several years has resulted in concerns over grazing
impacts on grass seed production in the mid-Willamette Valley, Oregon. This
study was designed to develop methods to quantify and statistically analyze goose-grazing
impacts on seed yields of tall fescue (Festuca arundinacea Schreb.) and
perennial ryegrass (Lolium perenne L.). Yield-mapping-system equipped
combines, incorporating global positioning system (GPS) technology, were used to
measure and map yields. Image processing of ground-level photography to
estimate crop cover and other relevant observations were spatially located via GPS
to establish spatial-temporal goose grazing patterns. We sampled each field semi-monthly
from mid-winter through spring. Spatially located yield data, soils
information, exclosure locations, and grazing patterns were integrated via
geographical information system (GIS) technology. To avoid concerns about
autocorrelation, a bootstrapping procedure for subsampling spatially contiguous
seed yield data was used to organize the data for appropriate use of analysis of
variance. The procedure was used to evaluate grazing impacts on seed yield for
areas of fields with different soils and with differential timing and intensity of
goose grazing activity. We also used a standard paired-plot procedure, involving
exclosures and associated plots available for grazing. The combination of spatially
explicit photography and yield mapping, integrated with GIS, proved effective in
establishing cause-and-effect relationships between goose grazing and seed yield
differences. Exclosures were essential for providing nongrazed controls. Both
statistical approaches were effective in documenting goose-grazing impacts.
Paired-plots were restricted by small size and few numbers and did not capture
grazing impacts as effectively as comparison of larger areas to exclosures.
Bootstrapping to subsample larger areas of yield for comparison was an effective
method of avoiding autocorrelation of data while better representing impacts within
a field. Occasional yield increases, ranging from 1 to 5 percent, were recorded
following goose grazing. Goose grazing generally resulted in seed yield
reductions, ranging up to 20 percent. Later and more intensive grazing tended to
increase yield reductions. Newly seeded tall fescue tended to be the most sensitive
to grazing. Established perennial ryegrass tended to be more resilient. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30906 |
| Date | 06 August 2002 |
| Creators | Louhaichi, Mounir |
| Contributors | Borman, Michael M. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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