The effects of fire can be basically divided into three groups: its influence on the physical response of plants; fire's influence on the ecosystem function; and physiological changes in the plants themselves caused by fire. I have tried to organize the Abstract Review topics into these categories.

ABSTRACT REVIEW
PHYSICAL RESPONSES

D.A. Dokken in Proceedings of the Fifth Midwest Prairie Conference reported: on deep soil, stem density of big bluestem was significantly reduced in one year without burning, and for indiangrass and sideoats grama in 3 years. Kentucky bluegrass, in contrast increased in stem density with time after burning. Peterson, looking at the effects of fire, litter, and ash on flowering in big bluestem found that inflorescences per square meter of canopy cover were significantly increased by the presence of fire.
Hulbert reported on the causes of fire effects in tallgrass prairie in Ecology. Warming of the soil in unburned plots resulted in an increase in both total production and flower stalk production of dominant tall grasses, primarily big bluestem and indiangrass, but the increase was small (34% increase in biomass; 78% increase in flower stalks) compared with that in burned plots (151% increase in biomass; 435% increase in flower stalks). Increased surface light intensity also appears to be a factor affecting changes in productivity following burning as suggested by the combined responses of increased productivity with removal of standing dead material, whether by clipping or burning, and decreased productivity with shading. Further, the addition of ammonium nitrate increased yield 41% and flowering 168% for the dominant grasses, suggesting that any factor increasing nitrogen availability would affect vegetative parameters.

A ten year record of aboveground biomass: effects of fire and topographic position, yielded the following, by M.D. Abrams. Lowland sites had significantly greater live biomass than upland sites for both burned and unburned prairie for the 10 year period. Moreover, live biomass was greater on burned than unburned lowland sites, but was not significantly increased by fire on upland sites. Averaged across upland and lowland sites, mid-season live biomass was 422 grams per square meter on annually burned and 364 grams per square meter on unburned sites for the 10 year period.

In Hulberts report on fire effects on tallgrass prairie to the Ninth North American Prairie Conference, production of vegetation on burned areas can be double that on unburned, unmowed, ungrazed areas where the old standing dead vegetation is deep.

Knapp showed that the density and production of flower stalks were usually greater on annually burned sites.

Abrams looked at topographic position and fire's effects on species composition. Abrams found that big bluestem dominance was not significantly affected by topographic position or burn treatment, whereas, little bluestem and indiangrass increased with burning. Switchgrass composition was higher on lowland soils but burning differences were not significant between the two, upland and lowland sites.

Gibson reported that both the percentage of and cover of C4 species (native warm season grasses) and all grasses decrease as the prairie remains unburnt. An interesting study by Gilliam looked at the interception of precipitation by grass canopies. The mean interception for the study period was 38 and 19% for the unburned and burned prairie, respectively, indicating that throughfall volume in burned prairie was approximately 1.3 times that of unburned prairie on a annual basis. Thus, water availability for plant uptake may be initially higher in burned prairie, especially early in the growing season. Briggs in 1992 found that without burning and with adequate moisture levels, the number of trees increased over a five year period by over 60%, while in an area burned annually the number of trees decreased.

ECOSYSTEM FUNCTION

Knapp, now studying the effects of detritus accumulation on productivity, reported a strong negative impact of plant litter production on subsequent ecosystem function. These deleterious effects on plant litter include: a reduction in available light energy to the system; an alteration of the microclimate and physiology of emerging shoots such that carbon dioxide uptake is reduced; a conversion of immediately usable inorganic nitrogen in rainwater to less readily available organic nitrogen in microbial biomass; an inhibition of nitrogen fixation by free living microbes and blue-green algae as a result of phosphorus and/or light limitation; and a reduction in soil temperatures, which diminishes root productivity, invertebrate activities, and probably microbial activities as well. Fire and grazing therefore become necessary, integral ecosystem processes that maintain productivity of tallgrass prairie by the removal of standing and fallen litter.
Seastedt, who was looking at the effects of vegetation, burning and mowing on soil macroarthropods in tallgrass prairie found that annual burning resulted in increased root xylem feeders (cicada nymphs), mowing and raking resulted in increased biomass of root chewing insects (white grubs). Of the arthropods found to be abundant in tallgrass prairie soil, only the white grubs are known to adversely affect plant productivity.

James in 1988 found that the biomass of two native prairie earthworms increased with burning while the biomass of an introduced European species declined. Abrams and Gibson, in a presentation to the Fire and the Environment, International Symposium in 1991, reported the effects of fire exclusion on tallgrass prairie and gallery forest communities in eastern Kansas. Upland and lowland prairie communities burned in spring at intervals from 1 to 11 years were constantly dominated by big bluestem. With increasing intervals between fires other dominant warm season grasses, little bluestem and indiangrass, had decreased cover, whereas forbs and woody species had increased cover. Aboveground biomass was higher on an annual burned versus unburned lowland prairie, due to stimulated grass production. Sites unburned for 10 or more years were converting to woodlands.

PHYSIOLOGICAL

Knapp in 1984 found that standing dead material reduced photosynthetically active radiation incident (amount of sunlight reaching the plants available for photosynthesis) on emerging shoots by 58.8% in unburned vs. burned prairie. Aboveground production in unburned prairie was similarly reduced (55.4%) compared to burned prairie. Leaf temperatures were greater in unburned prairie than in burned prairie and leaf water potential was significantly lower in unburned grass than in burned grasses early in the season but was higher late in the season. Knapp in another study in 1985 found that big bluestem exhibited greater photosynthesis ( CO2 uptake rates) in burned vs. unburned plots. Switchgrass, in the same study, did not show a significant difference between the two treatments.
Seastedt, who was looking at nitrogen and phosphorus dynamics in foliage of annually burned and unburned tallgrass prairie found nearly 3 times the amount of litter was deposited in unburned versus annually burned sites. Editors note: This should be no surprise, however these findings are interesting. Over 3.5 times the amount of nitrogen and 2.7 times the amount of phosphorus occurred in litter of unburned prairie compared to that of burned prairie. Not only was there more litter on unburned prairie but it contained more nutrients per unit of litter, compounding the accumulation. Foliage and stems act as nitrogen and phosphorus sinks during the first 2 years of decomposition.

R.A. Ramundo, the principle researcher in a 1989 study, looked at the effects of manipulation on foliage characteristics of big bluestem. While spring burning usually increased foliage production, burning had no effect on mid-season chlorophyll or nitrogen content. Chlorophyll concentrations were significantly increased by fertilizer and mowing treatments. Nitrogen concentrations were higher on fertilized and mowed plots. These results support other research indicating that nitrogen use efficiency is higher on burned prairie and, removal of foliage by mowing results in more nutrient rich regrowth.

Seastadt and others looked at the relationship between fire frequency and nitrogen (N) limitation to foliage production in tallgrass prairie. Results indicated that fire history affected the magnitude of the vegetation response to fire and N additions. Sites not burned for over 15 years averaged only a 9% increase in foliage biomass in response to N enrichment. In contrast, foliage production increased an average of 68% in response to N additions on annually burned sites, while infrequently burned sites, burned the year of the study, averaged a 45% increase. Interestingly enough, after four years of annual N additions, forb biomass exceeded that of grass biomass on unburned plots, and grasses exhibited a negative response to fertilizer, probably due to competition from the forbs.

SUMMARY

If you are like me, reading research, though I find the topics and results interesting, is rather tedious and boring. The whole process becomes time consuming as well. I will try to bring all of this together in some type of summary that makes sense.
The physical responses of native grasses to fire or lack of fire are well documented and relatively easy to quantify. Fire increases biomass and flowering stems or inflorescences, whereas biomass and inflorescences are reduced without burning. Cool season grasses increase in stem density with time after burning as well. Lowland sites show a much greater response in biomass production than upland sites to annual burning. Switchgrass appears to be less responsive to burning than do big bluestem, little bluestem and indiangrass. Little bluestem and indiangrass increase with burning frequency. The number of trees increase with time since burning, while in annually burned areas the number of trees decrease.

The removal of standing dead material appears to be significant in the response of native grasses. Increased light reaching the leaf surfaces stimulate increased productivity, accomplished by greater photosynthesis. Lower leaf temperatures occur in burned versus unburned grasses which also adds to the efficiency of the plant.

Fire has a physiological affect on native grasses as well. Summarized, burning makes the plants more efficient at what they do. Burned grasses respond to N applications better than do unburned grasses. Converse to that annual N additions to unburned prairies result in an increase of forb biomass over grass biomass.

Finally to answer the question - What effect does not burning have on native grasses? In the absence of any management at all, during the first 3 to 4 years it will provide some good wildlife habitat. From the 4th year on it will be too thick for most wildlife and over time, probably 10 years or less, the native grasses will be overrun with cool season grasses and trees. Grazing and/or haying can negate or delay some of the effects mentioned, but not all. The physiological processes which depend upon burning cannot be replaced by any management means.

If I were planning a planting and knew I would not be able to burn here is what I suggest.

For wildlife: Plant a single species or mixture, including forbs and plan to set up a haying rotation. Use very light seeding rates, 3 to 5 PLS pounds per acre will be plenty. Hay a portion once every 2 to 4 years. It is important that the stand is hayed and not just mowed. In higher rainfall areas of the east, once every two years will probably be necessary to keep out invading trees. If cool season grasses become a problem rely on herbicides. Plateau, a new herbicide should be on the market this spring. Trees and unwanted broadleaves can also be controlled with herbicides. For those of you who caught that earlier about annual N application on unburned grasses increasing the forbs, don't get too excited. The resultant litter accumulation over the period of time necessary to get a response from the forbs will be too thick for most wildlife. In addition, for grazing, the forbs that respond will be poor quality for forage. If you want a lot of forbs, plant them in the beginning.

For forage: Switchgrass production appears to be the least affected by the lack of fire than any of the other native warm season grasses. Don't expect as good as production as stands which are burned and expect less of a response to N addition than with burned stands. However, do plan on N application to enhance production as much as possible. If interested in other native warm season grasses, expect even less of them. Eastern gamagrass could be a possible exception.

If anyone is interested in specific references feel free to write to me for that information. Send a stamped, self addressed envelope or if you prefer send a blank 3.5" floppy disk along with a mailer and appropriate postage. Disks will not be returned without return envelopes and postage.