DOT Project Number:  90-00-LRTF-537

Fiscal Year:  1995

Award:  $15,000

Principal Investigator:  Troy Siefert, Iowa State University; Dr. Thomas Rosburg, Department of Biology, Drake University, thomas.rosburg@drake.edu

Summary Report:

MONITORING AND EVALUATION OF NEW IRVM PROGRAM PLANTINGS: INTERSTATE 35 PRAIRIE RECONSTRUCTION

An initial goal of the I-35 research in 1996 was to develop standard methodology that could be used by roadside biologists and other Integrated Roadside Vegetation Management (IRVM) personnel to monitor and compare prairie reconstructions. This requires a method for both measurement of plant abundance in the field and assessment of the quality of the community from data collected. Plant abundance is usually measured with one of three basic techniques. Density is the number of individuals, stems, shoots, or clumps per sample area. While it provides a very good objective and accurate measurement of plant abundance and population size, it is very time-consuming to use and was considered too inefficient for IRVM use.

Cover is the assessment of how much area is occupied by the canopy, foliage, or stems. For herbaceous plants, foliage cover is typically estimated as a percentage of a sample plot (e.g. 30% of a quadrat). Forest ecologists utilize the diameter at breast height of trees to calculate the basal area (or cover) of trunks. Foliage cover provides a good assessment of some of the functional aspects of a community, for example the competitive nature of a species or its amount of resource use. It does not necessarily do a good job representing the population size. Although it can be measured objectively with pins or other time-consuming techniques, it is usually done subjectively by estimation. One problem with aerial cover is that it often varies considerably during the growing season as plants grow.

The third technique is frequency of species in sample plots. A number of quadrats of a standard size are place in the community and the number of quadrats a species is present in is its frequency. This technique does not require tedious stem counting or subjective estimation of area. The measurement is simply made by recording the species that are present in a sample quadrat and therefore is very objective. When many small quadrats are placed within a community, frequency is a good measurement of abundance and population size. Data collection is fairly quick in the field and the data easy to analyze. It does require the same size quadrat be used for all sampling (in order to make fair comparisons), but different numbers of quadrats can be sampled. The more quadrats used, the more resolution available for distinguishing differences in species abundance. A person can balance the logistics of time availability with the desired amount information and accuracy.

Because of the advantages of frequency-based measurements, it was the methodology recommended for species measurement in IRVM plantings and used in the 1996 inventory on I-35. The technique records the frequency of species present in 60 25x25 cm quadrats located in a stratified random manner within a 1x15 m belt transect. The method requires a tape measure to create a 15 m transect, which can be envisioned as a line lying along the center of a 1x15 m belt; the transect effectively bisects 15 contiguous 1x1 m plots. Each of the 1x1 m plots is composed of 4 50x50 cm quadrants (or quarter sections). The quadrants can be roughly formed by placing a meter stick perpendicular to the tape at each 0.5 m mark. One 50x50 cm quadrant is randomly selected from each 1x1 m plot. A cross made from two 25 cm rods welded together perpendicularly is placed within the 50x50 cm quadrant to form four contiguous 25x25 cm quadrats, or total of 60 quadrats along the 15 meter belt transect. Species presence is recorded in each of the 60 25x25 quadrats. Species not observed in the 25x25 cm quadrats, but present within the community sample (i.e, 1x15 m belt transect) are recorded and arbitrarily assigned a frequency of 0.8. The method was designed to be simple, quick, efficient, and quantitative – characteristics deemed necessary for the goals and demands of roadside biologists.

Development of an assessment tool that reflects the progress and success of the prairie reconstructions was also a goal of the initial work done on the I-35 project. Typical assessment of quality begins with a calculation of species richness (i.e., number of species) for both native and exotic species. These may be presented in their raw form, or as a ratio or percentage. As an index of quality, both the proportion of native species and the ratio of native to exotic richness directly reflect quality. While species richness is helpful, it doesn’t directly address an evaluation of the planting. Two criteria were developed to more closely reflect the success of the reconstruction. The relative abundance of seeded species (RASS) and the proportion present of seeded species (PSSP) make assessments that take into account the composition of the seed mix. For the calculation of RASS, the species list for a sample is divided into two groups – those species in the seed mix (desirable) and those resident species not in the seed mix (less desirable). The relative frequency of the seeded species is calculated to derive RASS. For example, if the total frequency of the seeded species is 135 and the total frequency of the resident species is 105, RASS would be 0.56, or 56%. Fundamentally, RASS describes what proportion of the vegetation are desirable prairie plants.

PSSP is calculated in a similar way. The species list for a community sample is inspected and the number of seeded species present determined. This number is expressed as a proportion of the number of species planted in the seed mix. PSSP directly evaluates the success in converting seeds planted into established plants. Obviously higher values for RASS and PSSP reflect higher quality, but they are not necessarily correlated. For example, a reconstruction could have a high RASS but low PSSP (e.g., a site planted with 50 species of which only 3 are established, but those three dominate the vegetation).

The effect of seedbed preparation on seedling density was also investigated and presented in this first report. In general, seedbed preparation consisted of first mowing the project area with a rotary mower to mulch existing litter and encourage early growth of resident vegetation. When growth was underway, a glyphosate application was made to the project area to eliminate the cool-season grasses. Within this plan, three seedbed preparation methods were evaluated which resulted in a range of the residual litter on the soil surface at seeding time. The south two-thirds of the project area was mowed and the litter left, resulting in the greatest amount of litter. The north third of the project area was baled after mowing and before herbicide application and produced an intermediate amount of litter. Fire was employed in a couple of small areas in the south after mowing and before herbicide application to create the lowest amount of litter. There were 6 study sites for the mow and mow/bale treatments and 3 study sites for the burn treatment. All seedbed preparation was completed by 7 May 1996, and planting took place between 20 May and 7 June 1996. Although there were about 40 seed mixes utilized for the project area, only two were seeded on the study sites. Nine study sites were planted with a mesic seed mix containing 63 species, and six study sites were planted with a dry-mesic mix containing 62 species.

Litter measurements were made on the study sites prior to planting. Four 50x50 cm quadrats were sampled by clipping all biomass, dead or alive, at the ground surface. Fresh biomass samples were weighed, then dried for 3 days at 60˚C and reweighed. The dry biomass weight and percent moisture (gravimetric) were calculated. Germination surveys were conducted in June and July 4 to 6 weeks after planting using the IRVM sampling method. However, rather than frequency, the number of grass and forb seedlings (density) were counted in the quadrats.

The mean biomass for mow sites (171.8 gm/m2) was not significantly different for mow/bale sites (115.5 gm/m2), but both were significantly greater than the biomass on burn sites (24.6 gm/m2) (one way ANOVA and Bonferroni multiple comparison, p<0.05). Typical above ground annual net primary productivity for tallgrass prairie is in the range of 600 to 1000 g/m2, so these litter amounts are fairly low. There was a large range in percentage moisture of litter biomass among sites, from 125% to 8%. Most sites were within the range of 25 to 65%.

Two way ANOVA using treatments and seed mix as factors showed no significant effects of either factor. Seedling densities of forbs and graminoids were statistically equivalent among all treatments. It appears that the litter amounts on the mow and mow/bale sites, although higher than in burn sites, were not high enough to be a detriment to seedling germination. However, one problem encountered in the study was extremely high variation in seedling densities on the three fire sites, ranging from 41 to 211 seedlings/m2. It appears that the low observation was due to one site being located on very sandy soil, unlike the other two sites, and planted with a mesic mix that was not the best choice for the site. Perhaps if this non-representative site was dropped, the resulting reduction in variation and increase in the mean seedling density would support a significant higher mean on the fire sites. The total seedling densities observed in the first growing season easily exceed the guidelines established by the National Resource Conservation Service for adequate erosion control (43 seedlings/m2) and Ducks Unlimited for a successful planting (43-54 seedlings/m2).

The effect of seedbed on quality of the reconstruction at the end of the first growing season was investigated. The observations of RASS (Relative Abundance of Seeded Species) were statistically equivalent for all three seedbed treatments – mow (38.0%), mow/bale (41.7%) and fire (44.3%). Therefore no evidence was found that any of these seedbed preparation methods provided better success in establishing seeded species. There was a marginally significant difference in the mean RASS and mean RARS (Relative Abundance of Resident Species) for all sites. RARS (59.2%) was marginally greater than RASS (40.8%) (paired t-test, p=0.073). Thus, despite the glyphosate application, resident species maintained a significant dominance over seeded species during the first growing season.

Overall, RASS varied considerably due to specific site conditions, from 13.6% at a dry mesic site to 72.2% at a dry mesic site. Mean RASS for mesic sites (43.2%) was not significantly different from mean RASS for dry mesic sites (37.1%) (two sample t-test, p=0.55). Site values for PSSP ranged from 11.3% to 31.0% for the mesic mix (site mean 21.8%, cumulative PSSP for all mesic sites 45%). For the dry mesic mix, site PSSP ranged from 12.3% to 26.0% (site mean 16.0%, cumulative PSSP for all dry mesic sites 36%). Mesic site PSSP was marginally greater than dry mesic site PSSP (two sample t-test, p=0.10). After the first growing season, efficiency of prairie establishment was marginally better at the mesic sites, perhaps because the more favorable moisture conditions were beneficial in seedling germination and growth.