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Floristic Quality Assessment for Plant Communities of
North Dakota, South Dakota (excluding the Black Hills),
and Adjacent Grasslands

Results and Discussion

Of the 1584 taxa we considered in this effort, 275 (18%) were determined to be non-native to our region. We assigned a C value of 10 to 20% of the region's native taxa (Figure 1), indicating that these plants are extremely intolerant of disturbance; consequently, these taxa occur only in the highest quality, remnant natural areas of the Dakotas. We assigned C values of 3 or less to 23% of our native taxa and the entire native flora of the Dakotas had a of 6.1. These results are similar to those found in the Chicago region, Illinois, and Michigan where 11%, 17%, and 15% (respectively) of the native plant species were assigned C values of 3 or less and the native floras had s of 7.3, 6.4, and 6.5 (Swink and Wilhelm 1994, Herman et al. 1996, Taft et al. 1997).

Distribution of plant taxa by coefficient of conservitism
Figure 1.  Distribution of the 1309 native plant taxa occurring in North and South Dakota (excluding the Black Hills) by coefficient of conservatism designation.

Grouping taxa by physiognomic class reveals that most native species in the Dakotas are perennial forbs, followed by annual forbs, perennial sedges, perennial grasses, and shrubs, respectively (Figure 2). Conversely, our region's non-native taxa are dominated by annual forbs. Also, although only 16% of our native grasses are annuals, over half (55%) of the non-native grass taxa are annuals. Of the 129 perennial grasses in our area of consideration, only 18 (14%) are non-native; however, of the 44 annual grasses, half are non-native. Much of our current landscape favors annual plants whereas annual species were less prevalent in our region's pre-settlement plant communities. The shift from habitats favorable to perennials to those providing competitive advantages to annuals is clearly reflected in the physiognomic composition of the non-native plant taxa that have successfully invaded our region.

Native & non-native plant taxa by physiognomic class
Figure 2.  Distribution of native and non-native plant taxa occurring in North and South Dakota (excluding the Black Hills) by physiognomic class.

By applying the coefficients of conservatism supplied here and calculating and FQI, an effective means of evaluating the quality of plant communities in our region is obtained. Changes in quality, either positive or negative, can be identified by repeating surveys and calculations over time. Through the use of floristic quality assessment, a preserve manager reintroducing fire to a landscape in a manner approximating pre-European settlement conditions can determine, through changes in and FQI, if the change in management is allowing conservative plant species to repopulate the area. Similarly, a regulator attempting to estimate the consequences of draining a wetland can obtain a clearer idea of the likelihood of recreating a wetland with a comparable plant community elsewhere, and a real estate specialist will have reliable information for ranking tracts of land when acquisition funds are limited.

Floristic quality assessment may help to better focus our efforts in areas of greatest potential benefit as competition for limited natural and financial resources continues. For example, drainage of a wetland with a long history of cropping in the basin during periods of below average precipitation may be easy to mitigate in terms of the native plant communities it supports. The species inhabiting this wetland will be limited to those that can tolerate the extreme disturbances associated with periodic cropping and will quickly repopulate a created or restored basin with minimal effort. However, a similarly sized wetland with soils that have never been tilled may support a native plant community rich in conservative species and be beyond our current abilities to create or restore; loss of this wetland should be considered an immitigable event. Floristic quality assessment allows us to identify high quality natural areas and to measure the quality of native plant communities we have attempted to restore and/or manage, thus providing an objective assessment of our current restoration and management efforts.

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