Introduction
Global energy production and activities preceding production are
expected to expand into new landscapes in response to the increased
demand for energy (McDonald et al. 2009) . Numerous negative
consequences are associated with such activities including fragmentation
(Trainor et al. 2016), habitat loss (Shaffer & Buhl 2016), alterations
to soil structure (Stumpf et al. 2016), and the loss of productive
landscapes (Allred et al. 2015). However, in many cases (i.e., surface
mining) reclamation is required post-extraction to promote a return of
productivity to the landscape (SMCRA 1977). Among the many ecosystems
affected by the development of energy-based infrastructure are the
grasslands of the Northern Great Plains (NGP) (Preston & Kim 2016),
which is where multiple forms of non-renewable resources are being
extracted, including lignite coal. Current traditional best reclamation
practices on lignite coalmines result in reclaimed lands being
successfully released from performance bonds after 10 years. Yet,
ensuring soil structural recovery and sustaining a diverse plant
community on reclaimed grasslands remains a challenge, especially as
time since reclamation progresses (Bohrer et al. 2017a; Bohrer et al.
2017b).
Surface mining activities require large-scale excavation of earthen
materials resulting in the complete deconstruction of ecosystems (Holl
2002; Pauletto et al. 2016). Excavation of all existing vegetation and
deconstruction of soil profiles is among the first stages of surface
mining. Such activities results in extreme alterations to soil
structure, specifically larger soil aggregates ( Stumpf et al. 2016).
Soil aggregates are further degraded by the vibrations during the course
of transportation (McSweeney & Jansen 1984). These cumulative impacts
on soil aggregates become problematic during reclamation as heavy
load-bearing pressures from reclamation equipment (responsible for
stabilizing and grading the newly constructed landscape) compress the
degraded soil aggregates (McSweeney & Jansen 1984; Bohrer et al.
2017b). Compression of these altered aggregates creates compacted soil
conditions, and such conditions have the potential to cause many
obstacles when attempting to establish and sustain a desired plant
community.
Connectivity of macropores within the soil matrix is essential for water
infiltration, promotion nutrient of cycling, and providing plant roots
accessibility to resources like nutrients, water, oxygen, and heat (
Stoessel et al., 2018). Soil compaction increases bulk density and
penetration resistance (PR), reducing the distribution of macropores in
the soil profile (Jabro et al. 2014), affecting growth of plant roots
(Tardieu 1994; Unger & Kaspar 1994), the accessibility of water to
plant roots (Haygarth & Ritz, 2009), and the overall movement of water
(Kulli et al. 2003). Plants must exert more energy to obtain water and
nutrients, and if water cannot be obtained the plants become stressed.
Additionally, limited infiltration and pooling may also occur at either
the surface or subsurface, which impacts the availability of water
and/or oxygen to plant roots (Hamza & Anderson 2004; Stoessel et al.
2018) and increase the likelihood of soil erosion (Stoessel et al.
2018). Decreased macropores can also impede the ability of plant roots
to maneuver within the soil profile and altering the growth patterns
(Hernandez-Ramirez et al. 2014; Beckett et al. 2017). Finding a solution
to improve root growth and water movement becomes vital during the
reclamation process.
Alleviating soil compaction can be accomplished using a variety of
anthropogenic methods, including mechanized disruption of soil or
amending the soil with organic matter (Hamza & Anderson 2004). Tilling
is one of the most common land management practices used to decrease
soil compaction (Schneider et al. 2017). This technique breaks up the
compressed layer of soil and increases the amount and distribution of
macropores (Hangen et al. 2002). Tilling-like practices applied to reach
subsoil depths is often referred to as ripping, or subsoiling (Schneider
et al. 2017). An additional means of decreasing compaction is the
integration of organic matter (OM), e.g. material such as straw, into
the soil (Getahun et al. 2018). This management practice can aid in
alleviating compaction in two ways. The capabilities of OM to absorb
water improves the soil water-holding capacity enhancing the
availability of water to plant roots (Zhao et al. 2014). Also, as
organic materials decompose they aid in soil aggregation by adding
organic carbon (Sheoran 2010). The application of these practices
improves the pore space distribution which in turn promotes water
movement, root exploration, and decreases the bulk density and
penetration resistance. Ultimately, these actions have the potential to
improve growing conditions and the establishment of desirable native
grassland species. However, these conditions may also promote invasive
species like Kentucky bluegrass (Poa pratensis ), a cool season
invasive grass of special concern in the NGP.
Grasslands in the NGP are being disturbed to support energy
production-based infrastructure (Preston & Kim 2016), but mandatory
reclamation for surface-mining operations provides an opportunity for
native grasslands to be replaced by new reconstructed grasslands.
Unfortunately, conditions of older reclaimed grasslands, both above and
belowground, are not presenting ecological qualities representative of
functional grasslands (Bohrer et al. 2017a; Bohrer et al. 2017b),
prompting a need to investigate alternative reclamation practices. The
objective of this study was to compare how different combinations of
alternative reclamation practices can influence community composition,
reduce PR, and improve soil water movement. We expect to observe
quantifiable differences between the different combinations when
assessing the plant community composition, PR, and volumetric soil
moisture.