Results
Our surveys resulted in the identification of 52 and 57 species in 2019 and 2020, respectively. Seven grass species and five forb species present in the seed mix were found in both 2019 and 2020. Both ripping, seeding mixture, and a ripping/seeding interaction showed a significant effect on species richness in 2019 (p< 0.10) (Figure 1). Species richness ranged between an average of 18 and 9 species in 2019, and 16 and 9 species in 2020. However, only seeding mixture influenced species richness in 2020 (p< 0.10) (Figure 2). Treatments planted to G/F had significantly more species in both years, while treatments reclaimed with TSR had significantly more species only in 2019. Simpson diversity showed a wider range of values between treatments in 2019 compared to 2020 with values ranging from 0.75-0.47 and 0.84-0.75, respectively (Figure 3 and 4). Trends show that treatments reclaimed with TSR and treatments planted with G/F have the largest average diversity values in 2019 and 2020, respectively. Mulch did not have any significant impact on either species richness or diversity.
Year (p=0.001) (Figure 5) and two of the main effects, seeding (p=0.002) and ripping (p=0.006), impacted plant community composition, when both years were assessed collectively. Additionally, year and seeding (p= 0.037) and ripping and seeding (p=0.022) interactions influenced species composition and abundance. Consequently, subsequent analyses were separated by year to evaluate how the main effects impacted the plant community. We used functional groups to explain primary drivers of plant composition.
Both seeding and ripping, and a seeding/ripping (p=0.056) interaction had a significant effect on the plant community composition in 2019 (p< 0.10) (Figure 6). The primary functional groups driving the 2019 plant community composition were native, perennial, C3 grasses on NMDS axis 1, short-lived perennials on NMDS axis 2, and annual/biennials and C3 forbs on NMDS axis 3 (p< 0.10) (Table 2). Additionally, percent volumetric soil moisture at 30 and 40 cm depth ranges, around the topsoil/subsoil interface were primary drivers of plant composition on the NMDS 2 and NMDS 1, respectively (Table 2).
Seeding and ripping were significant main effects in 2020 (p< 0.10), and additional analysis revealed a significant seeding/ripping interaction (p=0.016) (Figure 7). Species composition in 2020 was primarily driven by C4 species, and annuals on NMDS axis 1, long and short-lived perennials and native species on NMDS axis 2, and all C3 species on NMDS axis 3 (p< 0.10) (Table 2). Both 30 and 40 cm depth ranges for percent volumetric soil moisture were also a primary drivers of species composition on NMDS axis 2 (Table 2).
Year influenced Kentucky bluegrass abundance (p=0.029) with percent cover increasing by 76% between 2019 and 2020 (Figure 8). Seeding mixture (p=0.017) and ripping (p=0.004) influenced the abundance of KBG when both years were assessed collectively (Figure 7). Treatments planted with G and reclaimed with SSR (plus mulch) had significantly less KBG compared to the site planted to G/F and reclaimed with TSR (Figure 8).
Early trends indicate that treatments reclaimed with SSR and planted with G (plus mulch) have the highest PR values with means of 35.9 (37.1), 44.9 (50.2), and 45.7 (48.7) J/m; respective, to treatment(s) and depths. Furthermore, those treatments planted with G/F and reclaimed with TSR consistently have the lowest PR values with means of 25.6, 28.1, and 33.2 J/m; respective by depth. The treatments with the highest mean PR readings are significantly different than treatments with lowest mean PR readings, at all three depths (p< 0.10) (Figure 9). G, SSR, plus mulch treatments at the 15-30 cm depth bin were statistically different from all other treatments other than the G and SSR treatment. Additional differences between treatments exist at depths of 15-30 and 30-100, but differences in means appear to be between those with the same seeding mixture or the same ripping technique. There was no indication that standard reclamation procedures (i.e., the control) resulted in significantly different penetration resistance readings at any depth, at this time (Figure 9).
Treatments planted with G, SSR, plus mulch were significantly different to treatments planted with G, TSR, plus mulch and treatments planted with G/F and TSR (p< 0.10), at the 20, 30, and 40 depth intervals. Additionally, trends reveal there are significant differences between treatments with the same seed mixtures and/or ripping techniques at both 30 and 40 cm depth intervals. Treatments planted with G/F and reclaimed with TSR (plus mulch) were most frequently different to those treatments across both seeding mixtures and ripping techniques (Figure 9).
Standard reclamation procedures (i.e., reference site) had significantly greater (p< 0.10) volumetric soil moisture at the 40 cm depth than those treatments planted with G/F and reclaimed with TSR. Volumetric soil moisture readings at the 10 and 60 cm depths showed no differences between treatments (p>0.10) (Figure 10). We did not assess the 100 cm depth interval because it likely has no influence over plant community dynamics this early in the reclamation phase. At the 20, 30, and 40 depth intervals mean percent values of those treatments planted with G, SSR, plus mulch (22.3, 23.7, 26.0, respective of depth) had significantly greater volumetric soil moisture compared to treatments planted with G, TSR, plus mulch (16.7, 18.8, 19.4, respective of depth) and treatments planted with G/F and TSR (17.2, 17.9, 15.7, respective of depth). The number of treatments showing significant differences increased with depth with the greatest variability being observed at both the 30 and 40 cm depth intervals. Significant differences between combinations exist between treatments with the same ripping techniques and same seeding mixture (p< 0.10) (Figure 10). Treatments planted with G/F and reclaimed with TSR (plus mulch) were most frequently different to those treatments across both seeding mixtures and ripping techniques (Figure 10). Standard reclamation procedures (i.e., the reference site) had significantly greater volumetric soil moisture at the 40 cm depth than those treatments planted with G/F and reclaimed with TSR (p< 0.10). Volumetric soil moisture readings at the 10 and 60 cm depths showed no differences between treatments (p>0.10) (Figure 10).