Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1��

VEGETATIVE CHARACTERISTICS AnD GRASSLAnD PASSERInE USE OF COnSERVATIOn

PLAnTInGS In EASTERn SOUTH DAKOTA

Matt A. Bahm1,4*, Thomas G. Barnes2,Kent C. Jensen1, and Andy E. Gabbert3

1Department of Wildlife and Fisheries SciencesSouth Dakota State UniversityBrookings, SD, USA 57007

2Department of ForestryUniversity of Kentucky

Lexington, KY, USA 405463South Dakota Game, Fish and Parks Department

Sioux Falls, SD 57106 4Current address: Sequoia and Kings Canyon National Parks

Three Rivers, CA, USA 93271*Corresponding author email: bahm.matt@gmail.com

ABSTRACT

Vegetative characteristics and grassland passerine use of conservation plantings were studied in eastern South Dakota Game Production Areas, June 2007-2008. Fourteen fields, from 1 to 8 years old at the onset of the study, were surveyed in each year to describe vegetative characteristics and to correlate grassland pas-serine use. Sites had been planted to a mixture of 5 native warm-season grasses, 3 cool-season grasses, and alfalfa. Grassland passerines were sampled along fixed width transects during June 2007-2008. Vegetation was sampled at 7 points along each of 3 parallel transects within the bird sampling transects. Younger plantings had lower height and percent canopy cover of dead vegetation, greater litter depth, higher coverage of alfalfa and unplanted forbs, and more bare ground than older plantings. Nonmetric multi-dimensional scaling based upon vegetative characteristics showed that sites tended to become more similar with age. A total of fifteen bird species were identified along transects in each year. Six species showed a relationship between abundance and the measured vegeta-tion structure and composition variables. Although research showed that grass-land passerines use these plantings, more research is needed to determine nest success of passerines to determine the true conservation value of these plantings and associated management practices.

KEY WORDS

Conservation planting, grassland passerines, vegetation structure, restoration, South Dakota

1�8 Proceedings of the South Dakota Academy of Science, Vol. 90 (2011)

INTRODUCTION

The primary threat to the viability of wildlife populations worldwide is the loss and fragmentation of natural habitats (Sala et al. 2000, Brooks et al. 2002). That losses of grassland habitat and changes in agricultural land use have had a nega-tive impact on many species of grassland birds has been well documented (Basore et al. 1986; Herkert 1994; Warner 1994; Vickery and Herkert 2001). The Con-servation Reserve Program (CRP) has created large amounts of grassland habitat and has had beneficial impacts on both game (Berthelsen et al. 1989; Kantrud 1993; Riley 1995) and nongame (Johnson and Schwartz 1993; McCoy et al. 2001a) bird species, but conversion of native grassland habitats to other uses is still occurring (Stubbs 2007; Stephens et al. 2008).

To provide habitat for game bird species, many state game and fish agencies have long been restoring cover with perennial grasses. Many of these areas are planted to low diversity plant communities that may not provide adequate veg-etative structural diversity necessary for diverse avian communities (MacArthur and MacArthur 1961; Cody 1968). South Dakota Game, Fish and Parks De-partment (SDGFP) has, in recent years, planted more diverse mixtures of native warm-season grasses (NWSG), native cool-season grasses (NCSG), and alfalfa (Medicago sativa). This mixture is believed to provide seasonal growth and struc-tural diversity more similar to a native prairie than less diverse plantings (Andy Gabbert, SDGFP pers. comm.). Although these plantings are targeted toward improving habitat for game species, they may also provide adequate habitat for nongame species. The objectives of the study were to describe the changes in vegetative structural characteristics with age of planting, and document grassland passerine occurrence in conservation plantings on eastern South Dakota Game Production Areas (GPA).

METHODS

Study Area—Eastern South Dakota lies mostly within the Northern Glaciated Plains ecoregion, with a smaller area in the Western Corn Belt plains ecoregion (Bryce et al. 1998). This region is characterized by heavy agricultural use with corn, soybeans, and winter wheat as the primary crops. Various types of mollisol soils are representative of the region. Topography ranges from level to rolling terrain with wetlands prominent in the Prairie Coteau and James River Low-lands. The average annual precipitation ranges from 457 - 559 mm (Bryce et al. 1998).

During June 2007-2008, we evaluated vegetative characteristics and grassland passerine use of grassland conservation plantings on 14 South Dakota Game, Fish and Parks (SDGFP) GPAs. The same fields were studied each year. All plantings were located within the James River Lowlands (Johnson et al. 1995) and ranged in size from 5.7-26.4 hectares (Figure 1). Fields were 8 (1 & 2), 7 (3-6), 6 (7), 4 (8-10), 3 (11-12), 2 (13), and 1 (14) years old at the onset of the study. Sites were planted in spring with a seed mix containing big bluestem (andropogon gerardii), switchgrass (Panicum virgatum), indiangrass (sorghastrum

Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1�9

nutans), little bluestem (schizachyrium scoparium), sideoats grama (Bouteloua curtipendula), Canada wildrye (Elymus canadensis), slender wheatgrass (agropyron trachycaulus), green needlegrass (Nassella viridula) and alfalfa (Medicago sativa).

Vegetation Measurements—Vegetation structure of the conservation plant-ings was measured in late June along three parallel transects spaced 30 m apart. Vegetation was measured at seven equally spaced points along each transect. At each sample point, visual obstruction was measured by reading a Robel pole at a distance of 4 m and height of 1 m (Robel et al. 1970). Height of vegetation limiting visibility of the pole by 100% was recorded in each of the four cardinal directions to the nearest 0.25 dm. Maximum height of live and dead vegeta-tion within a 5-cm radius of the Robel pole was recorded to the nearest 0.25 dm. Percent canopy cover of live vegetation, dead vegetation, bare ground, na-tive warm-season grasses (NWSG), native cool-season grasses (NCSG), alfalfa, non-planted grasses, and non-planted forbs was estimated within a 20 × 50-cm frame, positioned immediately north of the Robel pole. Individual species oc-curring within each sampling frame were recorded. Vegetation canopy cover

Figure 1. Map of eastern South Dakota showing location of 14 sites sampled to assess vegetative characteristics and grassland bird use of conservation plantings.

1�0 Proceedings of the South Dakota Academy of Science, Vol. 90 (2011)Ta

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Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1�1

was estimated on an overlapping basis and could equal more than 100% at each sample point.

Grassland Passerine surveys—We surveyed grassland passerines using fixed-width belt transects from sunrise to 0900 hours twice each June 2007-2008. Surveys were not conducted during periods of adverse weather, such as high winds (> 20 kph) or low visibility (rain or fog). Fixed width transects were 150 m in length and all birds seen or heard within 50 m of either side of the transect were recorded. One transect was surveyed at each GPA along the center transect used for the vegetation measurements. Transects were walked slowly with pauses every 25 m or as necessary to identify species. Birds flying over the transect were not counted, and bird movements were noted to avoid re-counting individuals.

Statistical Analysis—Nonmetric Multidimensional Scaling (NMS) (Kruskal

1964; Mather 1976) was used to illustrate differences in vegetation composition and structure among conservation plantings. NMS is suitable for data that does not meet normality assumptions or is of questionable scale by avoiding the as-sumption that variables have a linear relationship (McCune and Grace 2002). NMS tests were conducted in PC-ORD Version 5 software (McCune and Mef-ford 2006) using the Relative Sorenson distance measure with 50 runs with real data and reached the final solution in 44 iterations. Stability was tested by plotting stress versus iterations, and 100 Monte Carlo permutations with ran-dom starting points were run to ensure ordination axes did not occur by chance. ANOVA was used to determine differences between sites and year of vegetative characters. Fisher’s Protected Least Significant Difference was used for compari-son of treatment means when ANOVA results were significant. Spearman rank correlation was used to determine relationships between vegetation variables and grassland passerine species. JMP statistical software (JMP 2007) was used for ANOVA, multiple comparison, and Spearman rank correlation tests. The level of significance for all statistical procedures was set at P = 0.05.

RESULTS

Vegetation—Strong site by year interactions (P < 0.0001) were present for all vegetative variables, except litter depth, native warm-season grasses (NWSG), and alfalfa, so each year’s data were analyzed separately. Height of live vegetation showed much overlap between sites in 2007, but was lower in younger plantings in 2008 (Table 1). Height of dead vegetation was lower in younger plantings in both years (Table 1). Litter depth was lower in younger planting in each year and showed much overlap in sites after three growing seasons (Table 1). Visual obstruction measurements showed much overlap between sites in each year and did not show distinct differences by field age (Table 1). Percent canopy cover of live vegetation showed little variation by field age, but did show site variation in each year (Tables 2 and 3). Percent canopy cover of dead vegetation was greater in older plantings in each year (Tables 2 and 3). Older sites tended to have higher percent canopy cover of NWSG, but several older sites had cover similar

1�2 Proceedings of the South Dakota Academy of Science, Vol. 90 (2011)Ta

ble

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n (S

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Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1��

to the young plantings in each year (Tables 2 and 3), and NCSG canopy cover varied by site rather than field age in each year (Tables 2 and 3). New plantings showed an increase in NCSG from 2007 to 2008 (Tables 2 and 3). Percent canopy cover of non-planted grasses tended to be greater in older plantings in each year (Tables 2 and 3). New plantings tended to have higher amounts of alfalfa, other forb and bare ground cover compared to older plantings (Tables 2 and 3). Site 14 was an exception for alfalfa and non-planted grass, and tended to have cover similar to older plantings (Tables 2 and 3).

The NMS ordination revealed a similar trend among older plots in the study (Figure 2). The grouping of plots shows similarity based upon the averages of the measured variables for each site. The youngest plots were outliers to the main group in 2007 (Figure 2). The successional vector overlay shows a trend toward the main group for all sites except 12, 13 and 14 (Figure 2). The amount of bare ground (BG) and alfalfa cover were variables that separated younger from

Figure 2. Nonmetric multidimensional scaling, with successional vectors, of vegetative character-istics of grassland conservation plantings in eastern South Dakota, June 2007-2008.

1�� Proceedings of the South Dakota Academy of Science, Vol. 90 (2011)Ta

ble

3.

Mea

n (S

E) p

erce

nt c

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of

live

and

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Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1��

older plots (Figure 2). The final NMS ordination had the best fit as a two-di-mensional solution as determined by a Monte Carlo randomized test (P = 0.02). The two axes accounted for 96.2% of the data variability (axis 1 = 62.6%, axis 2 = 33.6%), with a final stress of 7.1 and final instability of 0.09.

Grassland Passerines—Total species documented per transect ranged from 3-10 in 2007 and 2-7 in 2008, and totaled 15 for each year (Table 4). Sedge wrens (Cistothorus platensis) and common yellowthroats (Geothlypis trichas) were the most commonly encountered species in 2007, occurring in 9 of 14 (64%) transects. Common yellowthroats were the most common species in 2008, occurring in 12 of 14 (86%) transects. American goldfinch (Carduelis tristis), mourning dove (Zenaida macroura), and vesper sparrow (Pooecetes gramineus) were counted in only 1 transect in 2007 and 2008. Grasshopper sparrow (am-modramus savannarum) and yellow-headed blackbird (Xanthocephalus xantho-cephalus) were documented in only one transect in 2007 and 2008, respectively.

Six species showed a relationship between abundance and the measured veg-etation structure and composition variables. American goldfinch abundance was positively correlated with alfalfa and non-planted forb cover and negatively correlated with litter depth (Table 5). Common yellowthroat abundance was positively associated with height of live and dead vegetation (Table 5). Dickcis-sel (spiza americana) abundance was negatively correlated with height of dead vegetation, litter depth, percent cover of dead vegetation, and cover of NWSG, and positively correlated with percent cover of live vegetation, alfalfa, non-planted forbs, and bare ground (Table 5). Sedge wren abundance was positively correlated with height of dead vegetation, litter depth, and percent cover of dead vegetation and negatively correlated with percent cover of live vegetation, alfalfa, and bare ground (Table 5). Savannah sparrow abundance was negatively corre-lated with height of live vegetation and visual obstruction (Table 5). Red-winged blackbird (agelaius phoeniceus) abundance was negatively correlated with height of dead vegetation, litter depth, percent canopy cover of dead vegetation and of NWSG and positively correlated with visual obstruction, percent canopy cover of live and dead vegetation, alfalfa, and bare ground (Table 5). No correlations were found between NCSG or non-planted grass percent canopy cover and any of the passerine species.

DISCUSSION

Grassland bird abundance is believed to be affected by vegetation structural characteristics such as vertical cover, canopy cover of grasses and forbs, and verti-cal and horizontal heterogeneity (Weins 1974). Grassland restoration plantings attempt to provide a diversity of these characteristics by planting a diverse seed mixture. Although many of these plantings are intended to provide habitat for game species, nongame species may benefit as well.

Percent canopy cover of non-planted grasses tended to increase with field age. These grasses were typically introduced species, including quackgrass (Elymus repens), Kentucky bluegrass (Poa pratensis), smooth brome (Bromus inermis), and cheatgrass (Bromus tectorum). The cover of non-planted grass in site 14 oc-

1�� Proceedings of the South Dakota Academy of Science, Vol. 90 (2011)Ta

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Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1��

curred due to the presence of foxtail barley (Hordeum jubatum), a native species common throughout the state. Alfalfa and other forb canopy cover tended to decrease with age of the field. Commonly occurring non-planted forbs included thistles (Carduus spp. and Cirsium spp.), sowthistles (sonchus spp.), blue lettuce (Lactuca tartarica), prickly lettuce (Lactuca serriola), bindweed (Convolvulus ar-vensis), sweetclover (Meliotus spp.), and milkweed (ascelpias spp.). The decrease in forb cover within older fields is similar to McCoy et al. (2001a, 2001b), who reported CRP fields to be characterized by annual weed communities with abun-dant bare ground and little litter during the first two years following establish-ment and within three to four years fields became dominated by perennial grasses with little bare ground and substantial litter accumulation in northern Missouri. Higgins and Barker (1982) found that seeded grasslands declined in vegetation structure with age. Both researchers suggested that vegetation conditions might limit the value of fields for wildlife and suggested incorporating disturbance, such as prescribed fire or disking, to maintain the wildlife habitat value. The loss of forb cover can also be attributed to land-management practices. Many of the species present are agricultural weeds and often require treatment with mowing and herbicides to comply with local and regional weed laws. These practices can lead to a loss of forb cover over time (Fuhlendorf et al. 2002; Tunnell et al. 2006), which causes a concomitant loss of structural diversity and potential food resources (Fuhlendorf et al. 2002). The lack of alfalfa in Site 14 can be attributed to spraying of herbicide(s). The field was sprayed for thistles prior to initiation of the study and injury to plants was visually evident. This can also potentially account for low cover of NCSG in some plots as well. Although regional habitat managers typically use broadleaf specific herbicides to treat noxious weeds, injury to NCSG was noted on multiple occasions after fields were sprayed.

American goldfinch is considered a generalist (McGraw and Middleton 2009) and was negatively correlated with litter depth and positively correlated with

Table 5. Spearman rank correlation coefficient (ρ) values for significant (P < 0.05) relationships between bird density (birds/100 ha) and vegetation characteristics in eastern South Dakota grassland restoration plantings, 2007-2008. Only species with ≥ 5 observations were included in analysis.

Species

Height Percent Canopy Cover

Live DeadLitter Depth Robel Live Dead nWSG Alfalfa

Other Forb

Bare Ground

Americangoldfinch -0.38 0.39 0.41

Commonyellowthroat 0.43 0.51*

Dickcissel -0.63* -0.72* 0.63* -0.68* -0.37 0.43 0.49* 0.71*

Sedge wren 0.59* 0.67* -0.64* 0.70* -0.47* -0.44

Savannahsparrow -0.46 -0.53*

Red-wingedblackbird -0.50* -0.39 0.39 0.50* -0.56* -0.65 0.54* 0.42*

*P < 0.01

1�8 Proceedings of the South Dakota Academy of Science, Vol. 90 (2011)

alfalfa and other forb cover during our study. These correlations are likely due to the presence of thistles, an important food source, in fields with the corre-lated characteristics. Common yellowthroats are considered habitat generalists, but use grasslands for foraging and nesting (Guzy and Ritchison 1999; Bakker 2000). During our study common yellowthroats were positively correlated with height of live and dead vegetation. Common yellowthroats are often correlated with thick tangled vegetation (Guzy and Ritchison 1999) and high vegetation volume (Delisle and Savidge 1997), and observations tended to be in fields with dense grass or forb growth.

Dickcissels were associated with many vegetative characteristics during our study. Positive correlations to percent cover of live vegetation, alfalfa, other forbs and bare ground, and negative correlations to height of dead vegetation, litter depth and percent cover of NWSG were recorded during our study. Our results confirm the findings of previous researchers that found a high proportion of forb cover provided song perches, nesting cover, nest support, and increased abundance of invertebrate prey for dickcissels (Zimmerman 1971; Frawley and Best 1991; Patterson and Best 1996). Negative correlations were likely due to the lack of these features in younger fields where dickcissels were recorded dur-ing our study.

Savannah sparrow abundance was negatively correlated with height of live veg-etation and amount of visual obstruction during our study. Savannah sparrows are associated with dense ground vegetation, especially grasses, in undisturbed grasslands (Weins 1969; Johnson and Schwartz 1993). In our study, fields with dense grass cover tended to have lower stature live vegetation and high litter depths, explaining the negative correlations observed.

Sedge wren abundance was positively correlated with height of dead vegetation and litter depth and negatively correlated with greater percent cover of live veg-etation, alfalfa, and bare ground. Delisle and Savidge (1997) found sedge wrens to be positively correlated with greater vertical density and litter depth, similar to our results. Sample (1989) found sedge wrens to be positively correlated with maximum vegetation height, vegetation height-density, cover of herbaceous veg-etation, and cover of standing residual vegetation. The negative correlation with greater percent cover of live vegetation, alfalfa, and bare ground is due to the lack of these characteristics in older plantings where sedge wrens were recorded during our study.

Red-winged blackbirds are usually negatively associated with grass cover and bare ground (Johnson and Schwatrz 1993). The negative correlation with greater NWSG canopy cover and litter depth and positive correlation with bare ground appear to agree and disagree with these findings. Eggebo (2001) found a positive correlation between red-winged blackbirds and Robel readings, and the same correlation was observed during our study. Red-winged blackbirds were observed most frequently in young fields that tended to be dominated by forb cover, live vegetation, and little litter accumulation. High cover of alfalfa tended to coincide with higher cover values of “other forbs”, which red-winged blackbirds favor for perching and nesting (Johnson and Schwartz 1993).

Although our research showed that grassland passerines use these plantings, more research is needed to determine nest success of passerines to determine

Proceedings of the South Dakota Academy of Science, Vol. 90 (2011) 1�9

the true conservation value of these plantings and associated management prac-tices. Recent nesting studies of similar plantings in eastern South Dakota found extensive use of plantings by ring-necked pheasant (Phasianus colchicus) and waterfowl, but found few passerine species nests (Rohlfing 2004; Rock 2006; Hankins 2007). Future research is needed to determine if the low nesting use of these plantings is accurate, or if the lack of passerine nests is an artifact of the sampling methodology used during the studies.

ACKNOWLEDGMENTS

We wish to thank the South Dakota Game, Fish and Parks Department for allowing us access to the sites. Funding was provided by Federal Aid in Wild-life Restoration administered by South Dakota Department of Game, Fish and Parks, Study No. W-75-R-75108. T. Runia and L. Erickson provided field as-sistance. The manuscript has been assigned number 10-09-033 by the office of the Associate Dean for Research, UK College of Agriculture.

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