ï~~2007
THE MICHIGAN BOTANIST
67
munity structure due to fire suppression, its restoration can prove to be slow and
uneven (Anderson et al. 2000; Abella et al. 2004).
At Hoosier Prairie, a prescribed burn program was initiated in winter of 1978
that sought to simulate a presettlement fire regime. The adopted regimen recognized that regional Amerindians used frequent dormant season burns to drive
game, improve pasture, and increase yields of food plants (Anderson 1990). At
the same time, it ignored the possible role of less frequent summer fires set by
dry lightning (Howe 1994,1995; Loope and Anderson 1998), in part because
their potential importance was unknown at the time. Over the past 27 years, as
many as 13 burns were administered on some sections of Hoosier Prairie Nature
Preserve. The program included late fall as well as spring burns at intervals that
ranged from seven to 72 months apart. In 1978 and 1979, plots were established
with the intent of following the long term changes at Hoosier Prairie and monitoring the effects of the fire management program. The objective of this paper is
to report the changes observed over the past 27 years in understory vegetation including fluctuations in species composition and floristic quality.
METHODS
Site Description
Hoosier Prairie is a 178 hectare site located on the west side of the town of Griffith in Lake
County, Indiana (Figure 1). The property is bounded on the west by Kennedy Avenue and more or
less bisected by the east-west road, Main Street. The topography has only minor relief of less than 2
m. As a result, small changes in elevation result in rapid transitions from the xeric savanna into wet
prairies and marshes. The soils of xeric areas are porous Brems fine sand, Watseka loamy fine sand,
and Maumee Loamy fine sand (NRCS 2006).
Data Collection and Analysis
In 1978 and 1979, 2 permanent plots were established, one south of Main Street (designated
South Block; N 41.521710 / W 87.453150) and the other to the north of road (North Block; N
41.523610 / W 87.454350), separated by a distance of approximately 225 m. These Blocks were randomly placed within areas deemed as having the highest quality oak savanna condition. Each 10 x
10 m plot consisted of 25 contiguous sample areas of 2 x 2 m. Within each sample area the species
present were recorded from a 0.67 m2 area demarked by the more or less blind toss of a circular
hoop. Nomenclature for species follows Swink and Wilhelm (1994); vouchers for Hoosier Prairie are
available at MOR. In the South Block the first sampling was attempted in September 1978 but the
data set is incomplete. Thus, these data provide some useful qualitative information about the site before fire management but could not be used in quantitative analyses. Full data collection on both
Blocks began in 1979, the year following the first prescribed burns, and was performed annually
from 1979 to 1994 during late July / early August. Two additional samplings were completed in early
August 2004 and 2006. No data are available for the North Block in 1980. In the South Block, prescribed burns were administered during the spring of 1984, 1985, 1987, 1988, 1990, 1992, 1994,
1997, 2000, 2006 and early winter of 1978, 1979, and 1982. The North Block was burned during the
spring of 1978, 1984, 1988, 1990, and 1998 and early winter of 1979, 1981, 1985, 1990, 1993, and
2001.
Changes in community structure were examined by Nonmetric Multidimensional Scaling (NMS)
using PC-ORD5 software (McCune and Mefford 2006). Sorenson (Bray-Curtis) served as the distance measure. A random starting configuration was employed in the first run of 50 real data and 50
randomized data iterations. Scree plots recommended that two dimensions be analyzed in the final
runs. The final runs had 200 iterations and in each case an r2 greater than 0.84. The resulting Kruskal
stress was very low (<1) for the combined Block analysis and low (7.5) to moderate (14.3) for the
South and North Blocks respectively. To further quantify the degree of community change over time
