Woody debris is a critical component of forest ecosystems, contributing to stand productivity, nutrient cycling, soil development, and habitat complexity (Harmon 2021, Vernon et al. 2025). Coarse Woody Debris (CWD) refers to standing or down dead wood larger than 7.5 cm in diameter (Harmon and Franklin 1989, Yan et al. 2006). As a structural and biogeochemical driver, CWD influences soil hydrology, nutrient cycling, and microsite heterogeneity that support seedling emergence and early vegetation development (Harmon 2021, Benoist et al. 2024, Magee et al. 2024). In semi-arid inter-mountain ecosystems where surface soil horizons have been removed, the ecological role of woody debris remains underexplored. The conversion and repurposing of locally available standing or downed woody debris into modified CWD offers a novel low-impact strategy to address accessibility constraints in mountainous environments for ecological recovery.
Soil bioengineering techniques such as modified brush layering and contour-felled logs have been shown to stabilize erosion-prone ecosystems while enhancing vegetation regeneration through microsite-structured facilitation (Polster 2003, Robichaud et al. 2008). In severely degraded environments, slope stabilization requires structural interventions that simultaneously intercept runoff, capture sediment, create microsites, and deliver long-term nutrient inputs for soil development and ecosystem recovery (Lucas-Borja et al. 2021, Benoist et al. 2024, Magee et al. 2024). Modified Contour Log Structures (MCLS) represent an emerging bioengineering technique that functions as a physical catalyst for reestablishing hydrologic, geomorphic, and biological connectivity across degraded environments (Polster 2003, Wang et al. 2021, Vernon et al. 2025).
In this study, a field-based approach was developed to address accessibility limitations at remote locations and logistical constrains, in which nearby woody materials were harvested, modified, and then used for slope stabilization and vegetation regeneration. We applied MCLS as an upland restoration remedy for impacted steep slopes of southwestern Montana. This note discusses installation methods for MCLS varieties that were applied within the Mount Haggin Wildlife Management Area.
The study was conducted on a southeastern aspect of Sugarloaf Mountain (46°00’ N, 112°57’ W; 2,100 m ASL) within the Mount Haggin Wildlife Management Area in Deer Lodge County near the town of Anaconda, Montana. In 1983, the U.S. Environmental Protection Agency (USEPA) listed the Anaconda Smelter site on the Super-fund program’s National Priorities List. During the operational period of refining copper ore (1884 to 1980), smelter emissions released an estimated 2.7 × 10⁴ to 5.2 × 105 kilograms of arsenic, copper, lead, sulfur, and zinc upon the surrounding landscape and significantly impacted terrestrial and aquatic ecosystems over approximately 777 km2 (USEPA 2016, NRDP 2018). Today, the area surrounding the former smelter site is characterized by “moonscape” slopes with exposed C-horizon soils (weathered rhyolitic parent material) and sparse vegetation resulting from prior smelter emissions, deforestation, and ongoing erosion, compounded by harsh climatic conditions, such as aridity and a short growing season (Ng and Pang 2000, Anderson et al. 2009, Osabutey et al. 2020).
Three primary Modified Contour Log Structure (MCLS) designs. A) Conceptual designs of the Single, Wing, and Smile MCLS varieties. B) Top-down approach applied (MCLS were installed starting at the top of the hill, near the existing tree line, and proceeded downslope (top-down approach). C) Staggered formation (“labyrinth-contour”) application result. D) Field sampling above and below a Single MCLS. Illustration and image credits: A, Elise K. Kzaley; B, Daniel O. Kelly; C, Lou Mason; D, Daniel O. Kelly.
The installation process began with harvesting local CWD from the adjacent Pinus contorta (lodgepole pine) stand to the east using a chainsaw and a hatchet. The primary CWD was sourced from forest fuel loads (dead standing and downed beetle-killed pines), with additional material obtained through selective thinning and harvesting of live lodgepole pine guided by stand-level forest health objectives (Castro et al. 2021, Chagnon et al. 2025). All living and nonliving woody materials were harvested within the same lodgepole pine stand. The harvested CWD was then modified into two CWD categories based on intended purpose.
The first category, termed as the catchment log, averaged 16.5 cm in diameter and was placed to intercept runoff and capture mobile debris carried downslope by runoff. Catchment logs were cut into 1–3 m lengths and were placed horizontally to match slope surface contours. The second category, referred to as the anchoring log, was modified from thinner CWD and measured 7.5–10.5 cm in diameter. Installation of anchoring logs required mechanical assistance to achieve sufficient depth for long-term stability. A cordless battery powered drill (½-inch [1.27-cm] chuck, 1,750 RPM) fitted with a 35.6 cm × 10.2 cm auger bit was used to bore holes into the substrate to depths of 20.3–35.6 cm. The anchoring logs, cut to lengths of 40–50 cm, were driven vertically into the soil and then compacted to secure catchment logs in place to strengthen structural stability and resistance to downslope movement.
Three primary MCLS designs (Figure 1A) were developed to capture runoff, stabilize sediments, reduce channelization, increase surface heterogeneity, and enhance vegetation regeneration. The Single MCLS is composed of one catchment log, placed horizontally onto the surface and is 1–1.5 m in length. The catchment log is secured by two anchoring logs. The Wing MCLS builds on the Single MCLS with an additional catchment log attached at an angle to the left or right portion of the Single MCLS catchment log; this design requires an additional anchoring log. The Wing MCLS application addresses surface inconsistency and mitigates the impact of soil channelization from runoff influence. The Smile MCLS design further expands upon the Single MCLS with two additional catchment logs placed at an angle to the left and right of the Single MCLS catchment log and requires two additional anchoring logs.
MCLS were installed starting at the top of the hill, near the existing tree line, and proceeded downslope (top-down approach) and were placed along slope surface contours extending north to south (Figure 1B). Overland flow on this slope originates from the east-facing pine stand and moves west downhill. The approach was applied to target the source of runoff and channelization to stabilize the upper hillside to facilitate vegetation regeneration. MCLS were spaced 1–1.5 m apart vertically and horizontally on slope gradients ranging from 10°–35° and were placed directly on the surface to allow for natural soil backfilling through successive deposition, forming staggered, discontinuous rows (Figure 1C). While this layout was designed for east-to-west runoff flow, the same top-down, “labyrinth-contour” method can be applied to slopes with alternate flow directions.
A) Field response to MCLS treatment during the end of the growing season in 2024. B) Same location in 2025. Results support that the number of vascular plants and vegetative ground cover doubled in the experimental grid. Image credits: A, Daniel O. Kelly; B, Robert W. Pal.
The study area was divided into a control and experimental grid. The control grid mimicked current environmental conditions and had an approximate area of 750 m2, with a mean slope angle of 20.5° ± 4.5° compared to the experimental grid with an area of 2,500 m2 and a mean slope angle of 21.1° ± 5.4°. To compare treatments, 32 1 m × 1 m monitoring plots were randomly established within the control grid. Additionally, 66 MCLS were randomly selected in the experimental grid and sampled using paired 1 m × 1 m plots, yielding 132 monitoring plots (Figure 1D). Measured variables for both grids included sediment loss and retention, soil volumetric water content (VWC%), vascular plant abundance, and vegetative ground cover (%) over two growing seasons.
A total of 370 MCLS were installed across the study area, each influencing an estimated 2 m² surface area. Structures were placed from the top of the hill to 25 m downslope and resulted in profound improvements in sediment retention, volumetric water content (VWC%), vegetative ground cover, and vascular plant abundance when compared to the controls. Between August 2024 and September 2025, the control grid lost an estimated 40.7 m³ of sediment reflecting continued surface instability, whereas the experimental grid retained 214.5 m³. The differences suggest that MCLS altered hillslope hydrology by dissipating shear stress and created depositional zones upslope of each catchment log (Robichaud et al. 2008, Adams et al. 2023). Although some sediment retention likely reflected installation associated disturbance (soil movement from foot traffic), the magnitude of sediment storage indicates that MCLS effectively intercepted and retained mobilized sediment and formed terraces.
Across all sampling seasons, MCLS plots consistently maintained higher VWC% compared to the controls, with increases of 28.9% in June, 45.1% in July, and 34.6% in August. The VWC% increases are consistent with previous findings that woody debris reduces overland flow, enhances VWC%, and facilitates early seedling establishment through microsite creation (Robichaud et al. 2008, Lucas-Borja et al. 2021, Magee et al. 2024). Moreover, vegetative ground cover in MCLS plots was more than three times (242%) greater and vascular plant abundance increased by 108.6% compared to those in the controls. Field responses support that MCLS generated microsites, reduced erosion, increased VWC%, and modified micro-topography that enhanced early vegetation recovery during the study (Figure 2). Similar effects of CWD have been reported in other disturbed ecosystems (Lucas-Borja et al. 2021, Magee et al. 2024, Vernon et al. 2025).
Like contour-felled log treatments in Mediterranean and semi-arid ecosystems, MCLS functioned to reduce over-land flow and re-establish hydrologic and biogeochemical connectivity across steep slopes that enhanced early plant recruitment (Robichaud et al. 2008, Lucas-Borja et al. 2021, Magee et al. 2024). The use of on-site beetle-killed lodge-pole pine minimized ecosystem disturbance and material transport while enhancing local ecological conditions. Overall, MCLS represent a process-based bioengineering approach that targets physical slope stabilization with early ecological recovery. By increasing surface heterogeneity, reducing erosive energy, and enhancing soil–water–plant interactions, MCLS should facilitate a transition from physically unstable homogenized environments toward biologically regulated ecosystems. Continued monitoring and assessment will be crucial for understanding the short and long-term trajectory of ecological recovery.
Author contributions: DOK, RWP, RV, BL designed the experiments; DOK, RWP performed the experiments; DOK, RWP, AJK analyzed the data and wrote the manuscript; all authors provided editorial review and contribution.
Acknowledgments
This project was sponsored and funded by the Montana Natural Resource Damage Program and conducted under academic support from Montana Technological University. Contracting crews and logistical support were provided by the Big Hole Watershed Committee. Field crews were supplied by the Youth Employment Program (Dillon, Montana), whose contributions were essential to all fieldwork. We thank Montana Fish, Wildlife and Parks for permission to conduct this study within the Mount Haggin Wildlife Management Area.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (https://creativecommons.org/licenses/by-nc-nd/4.0/) permitting copying and distributing the material in any medium or format in unadapted form only, for noncommercial purposes only, provided the original work is properly cited
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