Richard A. Olson

Influence of Topsoil Depth on Plant and Soil Attributes of 24-Year Old Reclaimed Mined Lands

ABSTRACT Topsoil replacement on reclaimed mine lands is vital for improved infiltration, plant rooting media, enhanced nutrient cycling, and as a potential source of plant propagules to increase plant community diversity. Varying topsoil depth may influence reclamation success. This study assessed the long-term (24 years) effects of four topsoil replacement depths (0, 20, 40, and 60 cm) on plant community attributes (species richness, diversity, canopy cover, and production) and soil characteristics [organic carbon (C), total nitrogen (N), available phosphorus (P), pH, soluble cations, electrical conductivity (EC), and cumulative water infiltration]. Species richness and diversity were highest at the 0 cm topsoil depth and lowest at the 60 cm topsoil depth. Percent canopy cover of grasses was highest (25%) at 60 cm and lowest (15%) at 0 cm topsoil depth. Percent forb cover was highest (6%) at the 0 cm depth and lowest (2%) at 60 cm topsoil depth. Seeded species cover was highest (12%) at the 40 cm depth, but was not significantly different from the other depths. Aboveground biomass was similar between the 40 (727 kg ha−1) and 60 cm (787 kg ha−1) topsoil depths and higher than the 0 (512 kg ha−1) and 20 cm (506 kg ha−1) replacement depths. Plant species richness and diversity decreased with increasing topsoil depth, while biomass increased. Organic C mass in the soil profile (75 cm) was greatest in the 60 cm topsoil replacement (18.7 Mg C ha−1) and lowest in the 0 and 20 cm treatments (11.3 and 10.5 Mg C ha−1, respectively). N mass (75 cm profile) exhibited a similar pattern with 60 cm of topsoil having the highest (1.9 Mg N ha−1) and the 0 and 20 cm the lowest (0.8 Mg N ha−1and 0.9 Mg N ha−1, respectively). Cumulative water infiltration was highest (134 mm) for the 40 cm topsoil depth followed by 60 cm (116 mm), and lowest (61 mm) for the 0 cm treatment. Soil N, organic C, and infiltration data indicate topsoil replacement depths of 40 and 60 cm provide the best nutrient status and water storage potential for sustainable reclamation. Placement of shallow topsoil replacement depths should be carefully planned to ensure topsoil thickness is adequate to sustain a vegetative community capable of protecting the soil surface against erosion. Variable topsoil replacement depths can be used in reclamation to manipulate plant community characteristics and create a mosaic of vegetation types. However, the reduced vegetation cover observed at the shallower topsoil depths may not protect against soil erosion; therefore, using variable topsoil depth replacement as a reclamation practice will require careful planning and implementation.

Functional Group and Species Responses to Precipitation in Three Semi-Arid Rangeland Ecosystems

The objective of this study was to compare forage production and foliar and basal cover responses of plant communities, plant functional groups, and individual species between years with below average (2004) and well above-average (2005) spring precipitation in three semi-arid rangeland ecosystems (shortgrass steppe, northern mixed-grass prairie, and sagebrush grassland). Foliar and basal cover at the time of a peak standing crop were visually estimated using modified Daubenmire cover categories, and forage production by species was harvested from areas that had been excluded from large herbivores. Responses of forage production to precipitation, but not foliar and basal cover, were similar for the three semi-arid ecosystems. Total forage production was more responsive (75–159%) than basal (8–35%) or foliar (2–29%) cover to increasing precipitation. Absolute (1016 kg·ha−1) and relative (159%) increases in total forage production from 2004 to 2005 were greatest for the shortgrass steppe. Forage production increases were largely attributable to greater production by C3 perennial graminoids in each ecosystem; increases in basal and foliar cover for this plant functional group were observed in shortgrass steppe and sagebrush grassland, but not in northern mixed-grass prairie. Fine-scale inputs of species and plant functional group responses to precipitation will further the accuracy of forage prediction models in predicting both total biomass production and relative proportions of plant biomass.

Small mammal populations occurring in a diversified winter wheat cropping system

Abstract Some Triticum aestivum (winter wheat) growers in the western region of the Northern Great Plains, USA, use a 3-year rotational, diversified dryland cropping system consisting of alternating strips of T. aestivum , fallow, and an additional spring sown crop such as Avena sativa (oats) or Zea mays (corn). Small mammal population characteristics (species richness, abundance, diversity) of the crops associated with this cropping system are unknown. Small mammal populations and vegetation characteristics (habitat) were evaluated at two sites in June 1998 and 1999 in three crops of the rotation and on undisturbed Conservation Reserve Program (CRP) grasslands. Small mammal abundance and diversity were highest in T. aestivum and grassland at both sites each year. Peromyscus maniculatus (deer mouse) was the most abundant species. Percent vegetation cover was significantly higher in T. aestivum and grassland, respectively, at both sites each year. Regression analyses using pooled data indicated a significant relationship between percent vegetation cover and small mammal species richness, abundance, and diversity. T. aestivum provided valuable habitat for small mammals in winter, spring, and early summer. Alternate grain crops in the diversified cropping system, which is absent in traditional 2-year systems, probably offered additional valuable protective cover for small mammals following T. aestivum harvest.

LONG-TERM PLANT COMMUNITY RESPONSES TO TOPSOIL REPLACEMENT DEPTH ON RECLAIMED MINED LAND 1

The use of topsoil on reclaimed mine lands may enhance plant community development and influence reclamation success. This study assessed the long-term (after 24 years) effects of different topsoil replacement depths (0, 200, 400, and 600 mm) on plant community cover, production, and diversity at a research site established in 1977 in south-central Wyoming. Plant species richness (number of species), canopy cover, aboveground biomass, and diversity were evaluated at the four topsoil depths in 2001. Plants were clipped, by species, to obtain mean biomass and to calculate importance values. Shannon-Weiner diversity indices were calculated for each topsoil depth. Species richness was highest (7.5) at the zero topsoil depth and lowest (5.6) at the 600 mm topsoil depth. Total canopy cover was greatest (average 26.7%) at 400 and 600 mm of topsoil and least (21.5%) at the zero topsoil depth. Seeded species canopy cover and seeded species biomass were also greatest at the 400 mm topsoil depth. Total biomass was similar for the 400 (734 kg/ha) and 600 mm (727 kg/ha) topsoil depths and lower but similar at the 200 mm depth (506 kg/ha) and 0 mm depth (513 kg/ha). Plant species richness and diversity index were highest at 0 mm (7.5 and 2.36, respectively) and lowest at 600 mm (5.6 and 1.87, respectively) of topsoil. Number of species and diversity decreased as topsoil depth increased. Increased plant biomass at the 400 and 600 mm depths and increased diversity at the 0 and 200 mm topsoil depths, indicate that variable replacement depths of topsoil can enhance reclamation success through greater species diversity and by creating a greater mosaic of vegetation. However, the reduced cover observed at these shallower topsoil depths may not be adequate to protect the soil from erosion.

Small mammal and plant community responses to mechanical disturbance and rest in Wyoming big sagebrush grassland.

Our aim in this study was to evaluate short-term (2 years) responses of several attributes of small mammal populations (species richness, abundance, diversity, and similarity) and plant community dynamics (species richness, canopy cover, above-ground biomass production, and diversity) to the mechanical disturbance associated with interseeding. Small mammal live trapping and vegetation sampling were conducted in 2004 and 2005 on replicated 1 ha study plots in a native Wyoming big sagebrush (Artemisia tridentata Nutt ssp. wyomingensis Beetle & Young)-grassland that were: 1) mechanically disturbed in April 2003 and rested from grazing during the study (mechanical); 2) rested from grazing (rested); and 3) moderately grazed by cattle (grazed). Deer mice (Peromyscus maniculatus), northern grasshopper mouse (Onychomys leucogaster), and sagebrush vole (Lemmiscus curtatus) were the primary small mammal species captured during 7776 trap nights in 2004 and 2005. Small mammal diversity was greater for the mechanical (H′ = 1.22) than the rested (H′ = 0.85) treatment with the grazed treatment intermediate. Plant community variables of species richness, diversity, similarity, and above-ground biomass production did not differ among treatments. Canopy cover of the dominant species, Wyoming big sagebrush, was reduced 20–34% by the mechanical disturbance (6.9% ± 1.0) compared to rested (8.6% ± 0.6) and grazed (10.4% ± 1.0) plots. The mechanical disturbance affected approximately 10.5% of the ground surface area but this had little impact on short-term small mammal or plant community dynamics in this rangeland ecosystem.

Wildlife Impacts to Big Sagebrush on Reclaimed Mined Lands

Wildlife browsing of Artemisia tridentata ssp. wyomingensis (big sagebrush) on reclaimed coal mined land threatens long-term, sustainable reclamation success. A wildlife-proof exclosure was constructed in 2001 on a 10-year old A. tridentata ssp. wyomingensis reestablishment research site at North Antelope Coal mine in northeastern Wyoming to assess wildlife browsing impacts. Artemisia tridentata ssp. wyomingensis survival, growth, and plant community attributes (species richness, canopy cover, and diversity) were evaluated inside and outside the exclosure, across the original grass seeding rate treatments (0, 16, 32 kg PLS ha−1). Long-term A. tridentata ssp. wyomingensis density decreased across all seeding rates from 1994 to 2002. Higher A. tridentata density, leader (shoot) growth, and canopy cover, along with lower mortality, occurred inside the exclosure across all seeding rates. Lower winter use, higher survival, and lower mortality of A. tridentata ssp. wyomingensis in the 32 compared to the 0 and 16 kg PLS ha−1 seeding rates suggest a beneficial relationship between A. tridentata ssp. wyomingensis survival and higher grass seeding rate. Approximately 33% mortality of marked A. tridentata ssp. wyomingensis plants occurred outside the exclosure. Lepus townsendii campanius (white-tailed jackrabbit), L. californicus melanotis (black-tailed jackrabbit), and Sylvilagus audubonii baileyi (cottontail rabbit) were identified as primary browsers of A. tridentata. Plant species richness, cover, and diversity decreased from 2001 to 2002, probably due to below average precipitation during the study. Defoliation of A. tridentata ssp. wyomingensis was severe, indicating the magnitude of impact from browsing wildlife. Post mining wildlife management and habitat manipulation on adjacent rangeland is suggested to ensure successful reclamation of coal mined lands.

LONG-TERM PLANT COMMUNITY DEVELOPMENT IN RESPONSE TO TOPSOIL REPLACEMENT DEPTH ON MINED LAND IN WYOMING 1

Effects of topsoil replacement depth on plant community development of reclaimed mined lands has been discussed for nearly three decades. Numerous research projects assessing topsoil depth effects were initiated during the 1970s. However, data collection for many of these studies was limited to 3-5 years. Plant community establishment, development, and stabilization through successional processes require considerable time. Only aboveground biomass and plant cover were reported in these short-term studies. In 2001, a research project initiated in 1977 was re-evaluated to assess the long-term effects of topsoil replacement depth (0, 20, 40 and 60 cm) on plant community development in south-central Wyoming. Percent grass cover and aboveground biomass were highest on the 40 and 60 cm topsoil depths, while forb cover was highest on the 0 and 20 cm depths. Percent bare ground was lowest on the 60 cm depth (30%) and highest on the 0 cm topsoil depth (62%). Plant species richness and diversity were significantly higher on the 0 cm topsoil depth and lowest on the 60 cm depth. Many native plant species established naturally in the abundant open space of the 0 cm topsoil replacement treatment. Variable topsoil replacement depth is a good management practice to enhance plant community diversity on reclaimed mined lands. However, placement of variable topsoil depths must consider erosion potential during the early years of reclamation. Areas of shallow topsoil should be limited to sites not prone to erosion, limited in size, and intermingled with other areas of greater topsoil replacement to ensure early stabilization and plant diversity of the reclaimed landscape.