WILDFLOWER MEADOW RESTORATION ON SURFACE MINES

open_access
Open Access
Author:
Rothman, Sarah
Graduate Program:
Ecology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 03, 2019
Committee Members:
Charles Andrew Cole, Thesis Advisor/Co-Advisor
Maryann Victoria Bruns, Committee Member
Marvin H Hall, Committee Member
Keywords:
restoration
surface mines
soil amendment
wildflowers
Abstract:
Surface mining is a destructive process in which belowground mineral deposits are acquired without tunneling underground. In some instances, known as highwall mining, a coal seam is exposed in an outcrop, allowing miners to access the seam by drilling laterally and leaving surrounding rock layers relatively intact. More frequently in Pennsylvania, excavators expose the coal seam from above by removing topsoil and blasting away the overburden, a process known as strip mining. The overburden is stored for years at a time before being returned to original contour and being revegetated according to the Surface Mining Control and Reclamation Act of 1977. The resulting substrate on a reclaimed surface mine has little organic matter, few nutrients, and scarce microbial communities; additionally, the area often has extreme pH levels, usually representing acidic conditions, and intense compaction due to heavy machinery. Grass seed is widely used as herbaceous cover in revegetation because it is inexpensive and grows quickly, reducing clean-up from runoff as well as time investment to establishment. However, non-native grass species typical in revegetation create intense competition for tree saplings planted afterward and distance the abiotic environment sufficiently from natural conditions that natural succession cannot occur. The resulting ecosystem after typical reclamation is dominated by a couple species of aggressive grass, inviting species invasion, lowering biodiversity, and preventing natural succession. With a multitude of physical, biological, and chemical soil characteristics disrupted or degraded, it is challenging to achieve proper reclamation, much less restoration. While reclamation aims to stabilize terrain, ensure public safety, enhance the site’s aesthetic, and return the land to a useful purpose as defined within a regional context, restoration focuses on helping an ecosystem recover to its historic state. Full restoration requires both structural and functional rehabilitation so that an ecosystem regains, or is on a trajectory to reach, a self-sustaining, resilient state with appropriate community structure comprising an assemblage of native species. A native wildflower seed mix (NWSM) may be able to improve plant-pollinator networks, increase biodiversity, and potentially pave the way for hardwood succession. Previous research has verified that wildflowers can grow in degraded soils, like those found in urban areas and along roadsides; in such situations, adding compost increased the quality and quantity of wildflower growth while inorganic fertilizer made no significant difference. However, the destroyed abiotic environment of surface mines presents a greater challenge to establishing adequate coverage, and thus different types or amounts of soil amendment may be needed. Prior research on a reclaimed surface mine in Virginia found that a combined native wildflower and grass seed mix sown in unamended soil was not on track to meet SMCRA coverage standards by the fifth season. In my thesis, I sought to assess whether a NWSM could meet SMCRA requirements of percent coverage if soil amendments are used; I also evaluated the influence of soil amendments on community composition and soil quality, both of which are important drivers of natural succession. Broadly, my objective was to form a restoration recommendation for mining companies and natural resource managers that will hopefully bolster pollinator networks, increase biodiversity, and improve soil conditions for eventual hardwood succession. I tested a NWSM in plots treated with inorganic fertilizer or one of two levels of spent mushroom compost to compare against unamended control plots. From June through November, I assessed species richness, proportion of species present that came from the NWSM, proportion of seedlings present that came from the NWSM, and vegetative coverage. I also collected soil samples at the beginning and end of the season to analyze texture, organic matter content, labile carbon content, nitrate availability, bulk density, percent stone by volume, and pH. My results counter previous research by demonstrating that plots seeded with a NWSM can successfully meet SMCRA requirements for percent coverage in unamended mine soil. Additionally, with little exception, unamended control plots fared as well or better than amended plots with regard to species richness and proportion of species and seedlings from the mix. Vegetative metrics therefore indicated that soil amendments may not be ecologically necessary or economically sensible in short-term surface mine reclamation using a NWSM as a revegetation method. Though results from soil analyses were insufficient to explain current vegetation patterns, they did suggest that compost may be beneficial to long-term surface mine restoration by improving important soil characteristics that could aid ecosystem recovery, such as percent organic matter, labile carbon, and nitrate content. I recommend that land managers either forgo amendment or apply a low level of compost, depending on whether they prioritize short-term reclamation or long-term restoration goals. The caveat to these results is the heterogeneity that exists between, and even within, surface mines. Overall, the soil on our surface mine was more suitable at the outset for revegetation than many other surface mines, especially in terms of organic matter, rockiness, bulk density, and pH. Research conducted in other degraded and damaged landscapes support the conclusion that initial soil characteristics inherited from the parent material have a substantial influence on the resulting ecosystem and are often a far greater determinant of restoration success than any management action taken. Given the high degree of heterogeneity both within and between surface mines, future work should focus on identifying initial soil characteristics that could enable land managers to meet both reclamation and restoration goals.