Vol 31, Part I - forums.sou.edu • Index page - Southern Oregon ...

ABSTRACTS – Symposia
Climate change and land use could trigger extensive and
possibly abrupt shifts in vegetation, wildfire regimes, and
fire-related erosion. Our ability to anticipate such changes
depends on our understanding of these past relationships.
However, detailed records of vegetation, fire and geomorphic
regimes are rarely all available at sensitive sites, for
example along the edges of species distributions. At City
of Rocks National Reserve (CIRO), south-central Idaho,
we used fossil woodrat middens to reconstruct local vegetation
and alluvial charcoal stratigraphy to evaluate fire and
fire-related geomorphic responses at the migrating front of
single-needle pinyon (Pinus monophylla) and Utah juniper
(Juniperus osteosperma), the dominant trees in the Great
Basin. Frequent fires burned in the periods 10,700-9500 cal
yr BP and 7200-6700 cal yr BP. Fire-free conditions characterized
the intervals 9500-7200 and 6700-4700 cal yr BP.
Episodic debris flows were deposited during early and late
Holocene wetter climate, when vegetation was denser. Frequent
sheetfloods were deposited during mid-Holocene drier
climate. Utah juniper colonized CIRO at ~3800 cal yr BP.
Frequent fires were recorded 2400-2000, 850-700 and 550-
400 cal yr BP. Although single-needle pinyon colonized by
2800 cal yr BP, it did not expand broadly across CIRO until
after 700 yr BP. Replication of our methodologies at other
sites in the region may confirm associations and causal relationships
between Holocene changes in vegetation, fire, and
sedimentation.
41 At home on the Range: Loss of Sagebrush May Open
New Habitat for Harvester Ants, and Imperil a Threatened
Mustard Endemic to Southwest Idaho, IAN ROBERTSON
(Department of Biological Sciences, Boise State University,
1910 University Drive, Boise, ID 83725; iroberts@boisestate.edu).
Throughout the Great Basin, disturbance events such as
wildfire are causing sagebrush stands to be replaced by open
grassland. In southwestern Idaho, the shift from sagebrush to
grassland may allow Owyhee harvester ants, Pogonomyrmex
salinus, to colonize areas that historically were unsuitable
for nesting. Because harvester ants are generalist granivores,
large influxes of ants could have a profound effect on plant
communities, with the rarest species being most vulnerable.
We have been studying the dynamics of harvester ant colonization
in areas occupied by slickspot peppergrass, Lepidium
papilliferum, a rare mustard endemic to southwest Idaho.
Several years of monitoring suggest that Owyhee harvester
ant numbers are on the rise. For example, between 2010
and 2011 the number of ant colonies recorded at 15 populations
of L. papilliferum increased by 7.6% (from 841 to
905 colonies over 85.3 ha surveyed). At one location there
has been a 64% increase in harvester ant colonies over the
past three years (from 53 to 87 colonies over a 5.1 ha area).
The abundance of harvester ant colonies is negatively associated
with sagebrush cover and positively associated with
the availability of non-Bromus grasses. Foraging studies
have shown that P. salinus prefer the seeds of Poa secunda
(Sandberg bluegrass) and various mustards over the seeds of
Bromus tectorum (cheatgrass). Slickspot peppergrass seeds
are among those readily consumed by P. salinus. Thus, the
expansion of harvester ant colonies into L. papilliferum habitat
represents a serious threat to the survival and long-term
viability of this threatened mustard.
42 Insect Responses to Intra- and Interannual Variations
in Weather: Implications for Climate Change in Sagebrush
Steppe, ASHLEY ROHDE 1,2 *, DAVID PILLIOD 1 , and
STEPHEN NOVAK 2 ( 1 U.S. Geological Survey, Forest and
Rangeland Ecosystem Science Center, 970 Lusk St. Boise,
ID 83706; 2 Department of Biology, Boise State University,
Boise, ID 83725; arohde@usgs.gov; dpilliod@usgs.gov;
snovak@boisestate.edu).
Climate has shaped the distribution of plants and animals
throughout biological evolution and the recent accelerated
climate change caused by human activities is no exception.
Species distributions are expected to shift as local and
regional climates change, but this process may be inhibited
by modern landscapes that are fragmented by human infrastructure
and land use. Reductions in biodiversity due to
climate change are predicted to be most severe in grassland
ecosystems, such as sagebrush steppe. These systems are
particularly susceptible to climate change because of their
aridity, high level of conversion, and low level of protection
relative to other major habitat types. The goal of this study
is to document the climatic conditions associated with distinct
insect communities and determine how land management
actions may influence these relationships. We identified
>50,000 insects to family using pitfall and flight traps
placed in arrays within the Bureau of Land Management
Jarbidge Field Office in southwestern Idaho. Sampling was
conducted from 2009-11. We examined the relative influence
of weather and habitat conditions to determine the most
important factors influencing insect community composition.
Preliminary results from this study show that intra- and
inter-annual weather patterns, particularly temperature, have
a strong effect on insect community composition.
Computability and Complexity
in Mathematics
Tuesday, 9:00 a.m. in PONDEROSA PINES 1 and 2
43 Elliptic Curves: From Diophantus to Modern Cryptography,
LAWRENCE C WASHINGTON (Department of
Mathematics, University of Maryland, College Park, MD
20742; lcw@umd.edu).
What do the motion of a pendulum, the possible areas
of right triangles with rational sides, and identity based cryptography
have in common They all involve elliptic curves.
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