BLOWOUTS IN THE NEBRASKA SANDHILLS: THE HABITAT OF

                                         PENSTEMON HAYDENII


                                            James Stubbendieck, Theresa R.
Flessner
                               Department of Agronomy, University of Nebraska,
Lincoln, Nebraska 68583
                                                               and
                                                       Ronald R. Weedon
                                Department of Biology, Chadron State College,
Chadron, Nebraska 69337



Abstract. The Nebraska Sandhills is the largest area of sand dunes in the
Western Hemisphere, occupying over 5 million ha in northcentral Ne-
braska. The rolling to steep dunes range in height from a few meters to
over 60 m. Soils are poorly developed in wind deposited sand. The con-
tinental climate is characterized by 425 to 625 mm of annual precipitation,
an average annual temperature of 10 C, and a frost-free period of 130-155
days. Upland vegetation is primarily tall grasses and midgrasses such as
sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern.], prairie
sandreed [Calamovilfa longifolia (Hook.) Scribn.], little bluestem [Schi-
zachyrium scoparium (Michx.) Nash], and switchgrass (Panicum virgatum
L.). Forbs are common. Wind erosion occurs when the protective cover
of vegetation is destroyed. Blowouts are active sites of erosion. Blowouts
are irregular or conical craters formed when the deep, loose sands are
removed by swirling action of the prevailing northwesterly winds. Blowout
penstemon (Penstemon haydenii S. Wats.) is only found on these sites of
active wind erosion and is an early successional species. Important asso-
ciated species in blowouts include blowoutgrass [Redfieldiaflexuosa (Thurb.)
Vasey] and lemon scurfpea (Psoralea lanceolata Pursh). The number of
blowouts has decreased with the control of fire and improved range man-
agement techniques. Loss of suitable habitat is one of the reasons for the
decline of blowout penstemon. At the same time, there are many blowouts
in the Sandhills that seem to offer suitable habitat where blowout penstemon
is not found.
Key Words. blowout penstemon, Penstemon haydenii, blowouts, erosion,
Sandhills, Nebraska
                      INTRODUCTION
  Blowout penstemon (Penstemon haydenii S. Wats.) was placed
on the Federal Endangered Species List in October, 1987. It is
endemic to the Nebraska Sandhills and is the only plant species
in the state to be classified as endangered. It is the rarest plant
species in the Great Plains.
  The Nebraska Sandhills is an extensive area with unique veg-
etation. Blowouts, the habitat of blowout penstemon, are depres-
sions in the topography caused by wind erosion. Vegetation
associated with blowouts is distinctly different than vegetation
associated with adjacent, noneroding areas. The purpose of this
paper is to describe briefly the climate, soils, erosion processes,
blowouts, and vegetation of the Nebraska Sandhills as an intro-
duction to the Symposium on Blowout Penstemon held at the
Eleventh North American Prairie Conference and to the papers on
blowout penstemon which follow in these proceedings.

               REVIEW OF THE LITERATURE
Soils and Climate
  The Nebraska Sandhills occupies over 5 million hectares of
northcentral Nebraska (Keech and Bentall 1971, Bleed and Flow-
erday 1989). It is the largest sand dune area in the Western Hem-
isphere, with nearly level areas and rolling hills with slopes
exceeding 30% (Keech and Bentall 1971, Bleed and Flowerday
1989). The area is primarily used for cattle grazing on relatively
large ranches (Burzlaff 1962, Gosey 1986, Stubbendieck 1989).
The sandy soils (mixed, mesic Typic Ustipsamment) are charac-
terized by low organic matter, low water-holding capacity, low
natural fertility, and a high risk of wind erosion if the soil is



exposed (Elder 1969, Keech and Bentall 1971). The soil is usually
stabilized by a grass cover. Beneath the soil is a thick sequence
of permeable rocks filled to overflowing with water. This water-
filled rock layer, known as the Ogallala aquifer, feeds the many
existing streams and lakes of the area (Bose 1977, Bleed 1989).
  The climate of the area may be classified as continental, with
70% of the total precipitation (425-625 mm) falling during the
growing season (Burzlaff 1962, U.S. Department of Commerce
1973, Wilhite and Hubbard 1989). The frost-free period is 130-
155 days (Neild 1977). Cold winters and warm summers are char-
acteristic. Average maximum and minimum temperatures for Jan-
uary are about I C and -12 C (Neild et al. 1967). Extreme lows
of less than -40 C have been recorded. July is the hottest month
with maximum and minimum temperatures of about 32 C and 15
C (Neild et al. 1967). Extreme highs of more than 45 C have been
recorded.
  Wind is an ever-present part of the climate of the Nebraska
Sandhills. The state has little surface relief, and with the lack of
surface roughness winds can attain high velocities. Winds are
generally strongest in winter and early spring and blow from a
northwesterly direction (Dewey 1977, Wilhite and Hubbard 1989).
During these periods, sustained winds of about 50 m/sec with gusts
to nearly double that velocity are not uncommon.
Wind Erosion
  Wind erosion and blowout formation do not occur as long as
vegetative cover is not disturbed. Once wind erosion starts, it is
difficult to stop. Causes of wind erosion in the Sandhills are best
explained by the physics of wind action on the soil particles. The
mechanism of wind erosion involves three factors: 1) wind veloc-
ity, 2) nature of the surface, and 3) soil (Baver et al. 1972).
Bagnold (1941) reported that almost 75% of the soil particles were
transported from the soil surface by saltation. Several factors are
involved in saltation. Wind may roll sand grains along the surface
until they hit objects such as other sand grains, and then they
bounce back into the air or knock the obstructing sand grains into
the air. These grains fall back to the surface at a rather flat angle
varying from 10 to 16 degrees, depending on the size of grain,
height of rise, wind velocity, and other factors (Ordway 1972).
These falling grains put themselves or other grains in motion by
their impact.
Blowouts
  Blowouts are one of the most striking features of the Sandhills.
These blowouts are different in form and ecological relationships
from those in historical reports from other parts of the world
(Cowles 1899, Gleason 1910, Cockayne 1911). Blowouts originate
on the exposed upper slopes when the vegetative cover is disturbed
or removed. Historically, repeated fires and concentrations of graz-
ing animals caused the disturbance (Pool 1914). Over the period
of a few years to a few decades, an embryonic blowout develops
into a full scale, active blowout. Sand is blown from the exposed
windward side of the slope and deposited onto the leeward size.
As the erosion becomes more active and the blowout deepens,
roots of the prairie vegetation are exposed, and soon whole plants



PROCEEDINGS OF THE ELEVENTH NORTH AMERICAN PRAIRIE CONFERENCE 1989 223