1994 Proceedings
North American Conference on Savannas and Barrens

Most of the land owned by forest preserves, state Conservation departments and federal conservation agencies was used for agriculture in the past. Agricultural use resulted in a degradation of the native plant communities which ranged from mild to the complete replacement of the original vegetation with pasture grasses of eurasian origin. Frequently native vegetation which survived agricultural land use continues to degrade after land is "preserved" as various landscaping and recreational "improvements" are undertaken by the owning agency. Areas that were not developed for recreation or education, if they were thought about at all, usually were be presumed to return to their original state because of a belief in succession and adaptation. Unfortunately, the rate of return of native vegetation in these areas has been low. Efforts to accelerate the process are being undertaken. A major part of this effort involves removing seeds from native species (where they are doing well) and dispersing those seeds into depauperate areas. The primary focus of this project was to evaluate the importance of timing, planting techniques & seeding density on the recruitment of grasses.

STUDY AREA AND METHODS

Recruitment from seed of 23 native species was studied in both wooded and open habitats in Cook County Palos Forest Preserves. In each of four areas (LRSH, Paddock, Spears & Sagawau) there were 4 plots, each 8 x 24 m. Twelve plots were wooded and four had no trees. Plots received seeds of between four and seven species judged to be appropriate to the habitat. Eight species were planted only in the open plots, 13 species were planted only in wooded plots and two species were in both. The treatments were: 1) fall versus spring planting, 2) raking versus no raking of scattered seeds and 3) 5 versus 50 seeds/m2. Each plot had 8 subplots [4 x 6 m] representing the factorial combination of the two states of each treatment including density.

The seeds were collected during the 1990 growing season and planted in either the fall of 1990 or the spring of 1991. Each plot received a total of 5,280 seeds of each species.

The number of flowering culms in each subplot in 1992 and 1993 were considered as the measure of success. The total precipitation for April, May and June was 13.14", 10.15", 3.86" & 16.32" in '90, '91, '92 & '93, respectively, while the "average" total is 10.68 inches for these three months of the growing season.

RESULTS

Prairie Species

None of the 8 prairie species seeded, Agropyron trachycaulum [1], Andropogon gerardi [4], A. scoparius [2], Panicum leibergii [1], P. virgatum [1], Sorgastrum nutans [3], Spartina pectinata [1] nor Sporobolus heterolepis [4] successfully recruited from seed in 1992 or 93; the number of plots receiving seed is shown in Table 1. No non-flowering individuals of these species were observed in the four open plots except a few Sorgastrum nutans present in 1991 and therefore believed to have been present prior to planting.

Woodland Grasses

These species went into 12 plots and and almost all species were more successful. Success can be measured using culms per 1000 seeds or per gram of seed. The results are shown in Table 1 with the species ordered by a per seed rate of success. The rank order of success per gram of seed is very similar between 1992 and 1993. There were many more flowering culms in 1993 [7386] than in 1992 [1463]. Because of major differences in the seed size of these species the order of success per gram show quite a few differences from success per seed. All of the woodland species except Glyceria striata and Panicum latifolium produced at least one flowering culm from the planted seeds. Non-flowering individuals of Glyceria striata were present but none of Panicum latifolium were detected.

The species that were most successful, Leersia virginica and Agrostis perennans, are probably the most abundant grasses in Palos. Only Muhlenbergia tenuiflora, Elymus villosus, Bromus latiglumis, Panicum latifolium & Bromus kalmii would be described as "rare" in Palos [of the grasses studied]. Success can also be measured by the frequency of plots receiving seed that produced seed. The number of 6 x 4m subplots planted with seed [receiving 1200 and only 120 seeds per subplot (Agrostis perennans always used 1200)] is shown in column 3 and the number of successful ones is shown in culm 4. Both Bromus purgans and Elymus villosus had high frequencies of success on this basis though the number of culms produced per seed was relatively low.

Differences Among Locations

The number of culms of non planted grasses were 311 & 678 per 196m2 plot at LRSH, 67 & 26 at Paddock, 0 & 0 at Sagawau and 211 & 607 at Spears in 92 & 93, respectively. The recruitment of planted grasses averaged 27.1 & 110.4 culms per species per plot at LRSH, 39.9 & 88.6 at Paddock, 5.5 & 17.3 at Sagawau and 52.2 & 291.1 at Spears in 92 & 93, respectively.

Effects Of Planting Season, Raking and Density

Differences among locations and plots and the large number of subplots with zero values generally resulted in non-significant treatment effects in an ANOVA for each species. Despite the lack of statistical significance, numbers of culms produced by plots planted in the fall uniformly were greater than those planted in the spring. There was no consistency among species in success between the raked plots and the unraked plots. One species Festuca obtusa had a large advantage to raking but it was not statistically significant. There were 9 times as many culms in areas planted with 50 seeds/m2 than from 5 seeds/m2, so recruitment is about proportional to planting density.

DISCUSSION AND CONCLUSIONS

Successional Restoration Assumptions And Problems

The woodland plots averaged 437 culms of per planting resident grasses in 93, but 622 culms per plot arose from the plantings. Thus the assumption that current preserves are both depauperate and that native diversity is dispersion limited is supported. The failure of the prairie grasses to recruit into the open plots suggests that competition from current residents is more important than dispersal when grasses are already abundant.

Differences Between Locations And Plots

There were substantial differences between the four locations and between the four plots within a location. Because the mix of species planted was unique to each plot, one must be cautious with the use of the overall numbers, but the differences are so large that location dominate success rates. All four locations had burns during one or more of the three years. The % cover and basal area differed among the plots as did soils. Plots with less basal area seemed to have more grass success but probably BA did not explain a high proportion of the variation.

Prairie Species Failure

The failure of any prairie species to recruit into any of the open plots is attributed to the fact that these plots were already occupied by grasses. Not only were the residents producing more seed than the amount planted but the thick turf provided little opportunity for seed.

Differences Between Woodland Species

The most successful species on a per seed basis were also the most locally abundant species. Why some species are more successful than others is not clear.

Differences Between Years

Comparisons between 92 and 93 confound age and climatic differences. Among the non-planted grasses the ratio of culms in 93 to 92 was 2.2, while among the seeded species the ratio was 5.0. Thus it is likely that age contributed substantially to the total production in 93.

Differences In Seeding Technique

While fall planting can not be said to be statistically significantly greater than spring planting, for all species except Elymus riparius more flowering culms arose from plots with fall than from spring planting. I believe that getting seed into the ground as soon as possible after collecting should be strongly encouraged. Raked plots produced 11% more culms than unraked plots, but this small effect does not seem to be worth the effort that is involved. Unraked plots had higher numbers in some species. The recruitment into flowering culms was pretty much proportional to seeding density. Thus if one wants to restore as much acreage as possible with a given amount of seed, the seed should be spread as thinly as possible. In favorable sites, a density of 5 seeds per m2/species yields a noticeable population of grasses. Remember, however, that recruitment did not occur in all seeded subplots.

ACKNOWLEDGMENTS

The encouragement of the Cook County Forest Preserve Conservation Department is gratefully appreciated. This work was made possible by the granting of sabbatical leave by the Department of Biological Sciences and the College of Liberal Arts and Sciences of the University of Illinois at Chicago. A large number of people helped me with this project. They have my sincere thanks. I hope to acknowledge them individually in a more detailed contribution.

Table 1. Grass species ordered by success rate.

* A substantial proportion of the culms of these two species are believed to be "background" (i.e., from naturally occurring individuals within plots).