Landscape-Scale Ecological Benefits of Properly Managed Free-Roaming Wild Horses in Appropriate Wilderness Ecosystems An Empirical and Scientific Synthesis Mini-Dissertation
Drawing on more than a decade of field observation and supporting scientific literature, this paper examines how properly managed free-roaming wild horses may reduce wildfire fuels, disperse seeds, preserve genetic diversity, and contribute to landscape-scale ecological function.
This paper examines the ecological role free-roaming wild horses can play when they remain in intact family bands, experience natural selection, and occupy suitable landscapes with limited competition from commercial livestock. Drawing primarily on William E. Simpson II and Michelle Gough’s long-term observations at Wild Horse Ranch on the California–Oregon border, and placing those observations alongside peer-reviewed research, it explores four potential benefits: reducing fine wildfire fuels, dispersing viable seeds through dung, maintaining genetic diversity, and providing continuous ecological services at relatively low public cost.
The paper also considers the limits of the evidence. Its primary observational record comes from a single long-term study site, while some supporting research comes from other ecological systems. It argues not that wild horses benefit every landscape or that populations should grow without constraint, but that appropriately sited and naturally managed horses deserve consideration as functional participants in wildfire mitigation and ecosystem stewardship.
This paper was sent by email by Captain William E Simpson, founder of Wild Horse Fire Brigade. It is published with permission.
Primary empirical foundation: Continuous observational research of William E. Simpson II and Michelle Gough (Wild Horse Ranch, California–Oregon border, 2014–present) - Supporting scientific literature on large-herbivore effects on fire regimes, equid foraging and seed dispersal, and equine genetic conservation
Abstract
This dissertation presents a detailed synthesis of the landscape-scale ecological functions of free-roaming wild horses when managed according to principles that preserve naturally-living intact family bands, natural selective pressures, and placement in appropriate remote wilderness or forested landscapes free from intensive commercial livestock competition and chemical fertility control. The core empirical foundation is William E. Simpson II’s continuous, close-range observational research (exceeding 25,000 hours over twelve-plus years) at Wild Horse Ranch, documented in the 2019 Impact of Wild Horses on Wilderness Landscape and Wildfire – Preliminary Findings Report, the Natural Wildfire Abatement and Forest Protection Plan (Wild Horse Fire Brigade), and subsequent writings on genetics, reseeding, and fire behavior. These observations are contextualized and strengthened by peer-reviewed literature, including Ripple et al. (2015) on the collapse of large herbivores and resulting changes in fire regimes; recent studies of equid grazing in Mediterranean and Iberian landscapes demonstrating fuel reduction; research on endozoochorous seed dispersal by equids; and genetic studies of the TBX3 locus and Dun alleles documenting retention of ancestral camouflage traits. The analysis concludes that properly sited free-roaming horses can reduce fine-fuel continuity, facilitate native plant reseeding, maintain genetic diversity under natural selection, and provide these services at low public cost relative to mechanical treatment or long-term holding. Current federal practices of repeated removal and chemical contraception risk forgoing these functions and reducing gene flow.
Chapter 1: Introduction and Research Context
1.1 The Management Problem and Research Opportunity
Under the Wild Free-Roaming Horses and Burros Act of 1971, federal management of free-roaming horses has emphasized removal to appropriate management levels, long-term holding, and, increasingly, chemical fertility control. These approaches address perceived overpopulation on public rangelands but have limited examination of the ecological roles horses may play when located in landscapes where commercial livestock use is minimal or absent and family bands of wild horses remain intact. Simpson’s research, initiated in July 2014, was designed to evaluate impacts of a local free-roaming herd on a wilderness landscape that is largely free of commercial livestock and subject to ongoing natural selection processes including environmental pressures and predation.
The study site at Wild Horse Ranch, contiguous with the Soda Mountain Wilderness, supports a cultural-heritage herd later formally recognized by Siskiyou County as privately owned by Simpson, Gough and the nonprofit Wild Horse Fire Brigade, an IRS accredited 501-c-3 all volunteer public benefit nonprofit corporation. Continuous residence allowed observation across all seasons and times of day, accumulating more than 25,000 hours of direct observation supported by extensive photographic and video documentation. This embedded approach, which Simpson terms the “Goodall Method,” differs from aerial surveys or two-week transects and short-duration agency field visits.
1.2 Thesis
Free-roaming wild horses, when managed so as to preserve intact family bands and natural selection and when placed in appropriate remote landscapes, deliver measurable landscape-scale benefits. These include reduction of fine wildfire fuels, reseeding of native vegetation via seed passage in dung, maintenance of genetic diversity (including ancestral alleles), and support for ecosystem processes at low public cost. These outcomes are most evident where commercial livestock competition is limited and chemical interventions that disrupt social structure and gene flow are avoided.
Chapter 2: Wildfire Fuel Reduction and Fire Behavior
2.1 Theoretical and Empirical Foundations from Large-Herbivore Ecology
Large herbivores influence fire regimes by consuming fine fuels and altering fuel continuity and structure. Ripple et al. (2015) documented that the global decline of large herbivores (body mass ≥100 kg) can increase the quantity and continuity of fine fuels, thereby elevating fire frequency, intensity, and spatial extent. The authors explicitly noted that large herbivores shape fire regimes “by altering the quantity and distribution of fuel supplies.” Subsequent reviews, including the Nature-based Solutions Initiative synthesis (2021), confirm that herbivores reduce fuel loads most effectively when grazing preferences match available vegetation and when densities and distribution allow continuous offtake without localized overuse.
Recent European studies provide direct evidence for equids. A three-year study in Portugal’s Greater Côa Valley (Frontiers in Ecology and Evolution, 2025) found that semi-wild horse grazing reduced grass height and biomass, thereby lowering wildfire risk, while promoting forb representation. Dietary studies of Przewalski’s horses, Pottoka, and crossbred horses in Mediterranean forests (Agroforestry Systems, 2025; Universitat Autònoma de Barcelona and University of Lleida) demonstrate that horses preferentially consume highly flammable fine grasses and can shift to woody species as grasses deplete, effectively managing both fine and coarser fuels. Remote-sensing work on Galician feral horses showed measurable reductions in surface rate of spread in grazed versus ungrazed gorse-dominated plots.
2.2 Simpson’s Empirical Observations
Simpson’s 2019 Preliminary Findings Report and contemporaneous documentation record continuous year-round grazing by the local herd. Each horse consumes approximately 30 pounds of grass and brush daily. Over multi-year observation, this activity created and maintained extensive zones of reduced fine fuels. During the 2018 Klamathon Fire (~38,000 acres), Simpson served nine days as a volunteer technical advisor to CAL FIRE. Horses remained calm and continued grazing rather than panicking. Previously grazed areas—estimated at roughly 5,000 acres of moderated fuels—limited fire spread and provided safer staging zones for firefighters. The fire did not successfully advance through the primary grazed zones in the manner observed in adjacent ungrazed landscapes.
2.3 Landscape-Scale Implications
When free-roaming herds occupy suitable remote wilderness or forested landscapes year-round, continuous offtake reduces the probability that ignitions will transition into high-intensity, fine-fuel-driven fires. Placement away from commercial livestock avoids economic conflict while delivering continuous, low-cost fuel abatement. Simpson’s comparative analyses indicate that the combination of long-term holding of removed horses plus mechanical or chemical fuel treatment is substantially more expensive than strategic rewilding into appropriate landscapes.
Chapter 3: Reseeding, Soil Function, and Vegetation Dynamics
3.1 Endozoochorous Seed Dispersal by Equids
Horses, as non-ruminant hindgut fermenters, pass a substantial fraction of ingested seeds intact in dung. Multiple studies document endozoochory by large herbivores, including equids. Greenhouse and field work show that horse dung can support germination of grasses and forbs and can contribute to soil seed banks. While outcomes vary by plant species and dung microenvironment, the mechanism of seed transport and deposition is well established. Dung also adds organic matter and can create favorable microsites for seedling establishment. In contrast, ruminant grazers remasticate the cud, producing extensive mechanical damage to seeds and thereby reducing reseeding effectiveness. This reseeding process is also beneficial in post wildfire landscape to reestablish soil stability and help reduce post-wildfire erosion, which can adversely impact downslope salmon and trout streams via silting-in of spawning gravels.
3.2 Field Observations at the Study Site
Simpson’s multi-year observations document that horses rotate across the landscape, self-regulating use of forage and water. The Preliminary Findings Report records no significant degradation of springs or riparian areas attributable to the horses over five years of intensive observation in a livestock-free setting. Photographic evidence supports the conclusion that localized overuse is avoided when family bands remain intact and natural predation is present. On fire-scarred ground, dung containing viable seeds from adjacent unburned areas accelerates recolonization by native plants—a function of particular relevance where other seed-dispersal agents have declined.
3.3 Controlled Seed-Passage Trial with California State University Students
As part of ongoing fieldwork at Wild Horse Ranch, Simpson and Gough oversaw a controlled germination trial conducted with California State University, Sacramento students participating in the Fellowship of the Wild Horses program. Selected free-roaming horses were offered measured quantities of three grass species commonly used in regional reseeding and forage contexts: winter rye (Secale cereale), fescue (Festuca spp.), and oat (Avena sativa). Dung was subsequently collected from multiple individual horses to account for digestive variation among animals.
Each dung sample was separated and placed in a sterile soil in labeled germination trays (identified by source horse) and maintained in an enclosed hot-house environment that excluded external seed contamination. The trial replicated prior findings in the literature that a substantial fraction of ingested grass seeds survive passage through the equine digestive tract and remain viable. Germination was observed for seeds of all three species. An additional observation, not anticipated in the initial protocol, was the rapid emergence of fungal fruiting bodies identified as Pilobolus crystallinus (the “dung cannon” fungus) beginning on day three. Pilobolus is a zygomycete whose mycelium colonizes herbivore dung; the visible sporangiophores develop from that mycelium and forcibly eject sporangia for dispersal. The survival of both viable seeds and mycelium through the equine digestive tract further distinguishes horses from ruminants, in which remastication damages seeds and limits comparable fungal and seed passage.
These results provide direct, site-specific confirmation of endozoochorous seed and mycelial passage under the conditions of the study herd. They align with broader peer-reviewed work on germinable seed content in equid dung while adding an empirical data point from the continuous observational setting at Wild Horse Ranch. The multi-horse design reduced individual digestive variance, and the sterile hot-house protocol minimized contamination risk, strengthening attribution of observed germination and fungal growth to material that had passed through the horses.
Photographic sequence from the trial (all images by William E. Simpson II © 2025):
Horse dung samples at the start of the sterile germination trial, with intact seeds still visible after digestive passage via wild horse.
First appearance of Pilobolus crystallinus fruiting bodies on the dung samples. (image below)
Close-up of Pilobolus crystallinus sporangiophores and sporangia on horse dung.
Initial grass germination emerging from the wild horse dung samples in the sterile trays.
Three grass species (winter rye, fescue, and oat) germinating vigorously from the horse dung.
3.4 Implications for Post-Disturbance Recovery
The combination of fuel reduction and seed dispersal creates a dual service: lowered probability of high-intensity fire and enhanced capacity for native vegetation recovery after disturbance. These processes operate continuously under free-roaming conditions and do not require annual mechanical intervention. The student trial supplies controlled confirmation that both seeds and fungal mycelium can survive equine digestion, supporting the field observation that horses function as effective reseeding agents relative to ruminant grazers.
Chapter 4: Genetic Integrity Under Natural Selection
4.1 Ancestral Alleles and the Dun Factor
Genetic studies of the TBX3 locus demonstrate that the Dun allele (producing asymmetric pigment deposition and primitive markings such as dorsal stripe, leg bars, and body barring) is ancestral. The non-dun1 allele predates domestication and is present in ancient horse DNA (~42,700 years old); the non-dun2 allele is more recent and associated with domestication-era selection for solid colors (Imsland et al., Nature Genetics, 2016; subsequent studies on Polish Konik, Mongolian, and other primitive horses). Retention of Dun-factor phenotypes therefore indicates preservation of pre-domestication genetic variation.
4.2 Effects of Current Federal Practices
Simpson’s 2026 analysis of fifty-five years of federal management argues that repeated removals, gelding of breeding stallions, and chemical fertility control (PZP and GonaCon) reduce gene flow and can produce bottlenecks. These interventions disrupt the natural social and demographic processes that maintain diversity. In contrast, a herd maintained under natural selection with intact family bands and predator-mediated regulation preserves the full range of alleles present in the population.
4.3 Population Thresholds
Long-term genetic vigor requires effective breeding populations of sufficient size. Conservation literature commonly references thresholds in the range of 150–200 animals (and higher figures in some frameworks) as minima when natural selection operates. Proper management prioritizes these conditions and avoids artificial barriers to gene flow.
Chapter 5: Principles of Proper Management and Appropriate Landscapes
5.1 Defining Proper Management
Simpson’s framework emphasizes:
- Retention of intact family bands under natural selection (predation, climate, forage availability).
- Avoidance of chemical sterilization and large-scale removals that fragment social structure and reduce gene flow.
- Continuous observational monitoring.
- Location in remote wilderness, designated wildlands, or private forest lands unsuited to commercial livestock because of terrain, predators, or logistics.
5.2 The Wild Horse Fire Brigade Proposal
The Natural Wildfire Abatement and Forest Protection Plan proposes strategic relocation of wild horses from Bureau of Land Management’s long-term holding into suitable landscapes for fuel reduction and ecological function. Hundreds of millions of acres of public and private forest and wilderness land exist where such placement would not conflict with livestock production. Projected benefits include reduced taxpayer costs for holding and fire suppression, improved watershed condition, and preservation of genetic lineages.
5.3 Ownership Model
In 2022, Siskiyou County formally recognized ownership and management authority over the local cultural-heritage herd of 200 horses by Simpson, Michelle Gough, and Wild Horse Fire Brigade. This private-ownership model provides a working example of free-roaming horses maintained outside the federal gather-and-fertility-control cycle.
Chapter 6: Discussion
6.1 Synthesis of Benefits
The observational record, reinforced by peer-reviewed literature on large-herbivore effects on fire regimes and equid foraging and seed dispersal, supports four primary landscape-scale outcomes under the conditions described: (1) continuous reduction of fine-fuel continuity and loading; (2) reseeding and soil conditioning via endozoochory; (3) retention of genetic diversity, including ancestral alleles, under natural selection; and (4) low-cost provision of these services relative to mechanical treatment or long-term holding. These functions are most evident where family bands remain intact and commercial livestock use is limited.
6.2 Limitations
Primary empirical data derive from a single long-term study site. While the duration and intensity of observation are exceptional, broader inference would benefit from additional, comparable pilot sites and, where feasible, controlled comparisons. Genetic claims rest on phenotypic markers (Dun-factor markings) and historical context rather than genome-wide sequencing of the study herd. Supporting literature on fuel reduction and seed dispersal is drawn primarily from European and other systems; direct quantitative fuel-load measurements specific to the Siskiyou study site would further strengthen causal attribution. Nonetheless, the consistency of behavioral and landscape observations over more than a decade, combined with convergent findings in the peer-reviewed literature, provides a robust foundation.
6.3 Policy Implications
Implementation at scale would require identification of suitable pilot landscapes, baseline genetic documentation prior to any fertility-control interventions, if any, and policy recognition of free-roaming horses as potential contributors to wildfire mitigation and ecosystem function when properly sited. The analysis does not argue for unrestricted population growth in all settings; it argues for management that preserves the ecological and genetic attributes observable under natural conditions.
Chapter 7: Conclusions
Continuous close-range observation of free-roaming horses under natural selection in an appropriate wilderness landscape, reinforced by peer-reviewed literature on large-herbivore effects on fire regimes, equid foraging strategies, endozoochorous seed dispersal, and ancestral equine genetics, demonstrates measurable benefits at the landscape scale. These include reduced fine-fuel continuity and wildfire intensity, effective native-plant reseeding, maintenance of genetic diversity (including retention of ancestral Dun-factor alleles), and overall support for ecosystem processes. When horses are managed so as to preserve intact family bands and are located away from conflicting livestock uses, these benefits can be realized at low public cost. The body of work produced by William E. Simpson II, placed in the context of supporting scientific literature, provides both the empirical foundation and the management framework for considering free-roaming horses as functional components of landscape-scale wildfire mitigation and biodiversity stewardship in the American West.
References
Primary empirical sources
- Simpson, W. E., II. (2019). Impact of Wild Horses on Wilderness Landscape and Wildfire – Preliminary Findings Report.
- Simpson, W. E., II. Natural Wildfire Abatement and Forest Protection Plan (Wild Horse Fire Brigade).
- Simpson, W. E., II. (2026). American Wild Horses: Fifty-Five Years of Removals, Gelding, and Pesticide Contraception Have Cut Genetic Flow in BLM Wild-Horse Herds. Pitchstone Waters.
- Wild Horse Fire Brigade documentation and herd records (wildhorsefirebrigade.org).
Supporting peer-reviewed literature
- Ripple, W. J., et al. (2015). Collapse of the world’s largest herbivores. Science Advances.
- Nature-based Solutions Initiative (2021). Effects of large herbivores on fire regimes and wildfire mitigation.
- Frontiers in Ecology and Evolution (2025). Semi-wild horse grazing as a rewilding strategy in the Côa Valley, Portugal.
- Agroforestry Systems (2025). Dietary strategies of feral and domestic horses under varying grazing pressures (UAB/UdL studies).
- Imsland, F., et al. (2016). Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses. Nature Genetics.
- Additional studies on endozoochory by large herbivores and equid foraging (various, as cited in text).
