SEARCH · USGS Science

Results for “Complexity”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,711 records · Page 95Linked to original sources

USGS2024

Real-time invasive sea lamprey detection using machine learning classifier models on embedded systems

Invasive sea lamprey ( Petromyzon marinus ) has historically inflicted considerable economic and ecological damage in the Great Lakes and continues to be a major threat. Accurately monitoring sea lampreys are critical to enabling the deployment of more targeted and effective control measures to minimize the impact associated with this species. This paper presents the first stand-alone system for real-time detection of sea lamprey attachment on underwater surfaces through the use of classifier models deployed on a microcontroller system. A range of low-complexity models was explored: single-layer artificial neural networks, logistic regression, Gaussian Naive-Bayes, decision trees, random forest, and Scalable, Efficient, and Fast classifieR (SEFR). Threshold models tuned using a multi-objective optimization formulation were also considered. Classifier models were trained with a dataset generated through live animal testing and presented accuracies between 80 and 86%. The models were deployed on an Arduino microcontroller platform and compared in classification accuracy, detection performance, time complexity, and memory size using real-time detection testing. Classification accuracies between 65 and 75% were observed during validation. Models demonstrated good capture rates for lamprey attachments (63–85%), and average detection delays ranging from 9 to 36 s. A video demonstrating the operation of the system during a real-time validation test is also included in this work. While there is room for improving the accuracy of the system, this research presents the first step toward an electronic sea lamprey monitoring system that can provide a detailed view of sea lamprey activity enhancing control and conservation efforts across its entire range.

Neural Computing and Applications↗

USGS2008

Interactive effects of fire, soil climate, and moss on CO 2 fluxes in black spruce ecosystems of interior Alaska

Fire is an important control on the carbon (C) balance of the boreal forest region. Here, we present findings from two complementary studies that examine how fire modifies soil organic matter properties, and how these modifications influence rates of decomposition and C exchange in black spruce (Picea mariana) ecosystems of interior Alaska. First, we used laboratory incubations to explore soil temperature, moisture, and vegetation effects on CO 2 and DOC production rates in burned and unburned soils from three study regions in interior Alaska. Second, at one of the study regions used in the incubation experiments, we conducted intensive field measurements of net ecosystem exchange (NEE) and ecosystem respiration (ER) across an unreplicated factorial design of burning (2 year post-fire versus unburned sites) and drainage class (upland forest versus peatland sites). Our laboratory study showed that burning reduced the sensitivity of decomposition to increased temperature, most likely by inducing moisture or substrate quality limitations on decomposition rates. Burning also reduced the decomposability of Sphagnum-derived organic matter, increased the hydrophobicity of feather moss-derived organic matter, and increased the ratio of dissolved organic carbon (DOC) to total dissolved nitrogen (TDN) in both the upland and peatland sites. At the ecosystem scale, our field measurements indicate that the surface organic soil was generally wetter in burned than in unburned sites, whereas soil temperature was not different between the burned and unburned sites. Analysis of variance results showed that ER varied with soil drainage class but not by burn status, averaging 0.9 ?? 0.1 and 1.4 ?? 0.1 g C m -2 d -1 in the upland and peatland sites, respectively. However, a more complex general linear model showed that ER was controlled by an interaction between soil temperature, moisture, and burn status, and in general was less variable over time in the burned than in the unburned sites. Together, findings from these studies across different spatial scales suggest that although fire can create some soil climate conditions more conducive to rapid decomposition, rates of C release from soils may be constrained following fire by changes in moisture and/or substrate quality that impede rates of decomposition. ?? 2008 Springer Science+Business Media, LLC.

Ecosystems↗

USGS2003

Three-dimensional geologic modeling and visualization of the Virttaankangas aquifer, southwestern Finland

A need exists for a reliable and long-term water supply for the 285,000 inhabitants of the Turku area in southwestern Finland . In response to this need, there are plans to replace the present water supply from the surface sources with artificially infiltrated groundwater from a Quaternary esker aquifer called the Virttaankangas aquifer . New sedimentological studies of the Virttaankangas area have revealed the complexities of the esker system and its surrounding glacial, glaciofluvial, and glaciolacustrine geology. This led to the characterization of the hydrogeological units of the aquifer , the result of which has been a three - dimensional (3-D) truly integrated solids model that represents the geometry, interrelationships, and hydrostratigraphy of the study area. The 3-D model was made with Earth Vision geologic modeling software. The 3-D geological model of the Virttaankangas aquifer can be used for planning the infiltration of river water into the aquifer and to understand the geologic and geographic boundaries of the hydrogeologic units hosting the groundwater reserve and the geologic relationships between the units. Another major outcome of this study is a powerful visualization tool that will be provided to municipal and government authorities who must understand the geologic complexities involved with water-resource planning prior to their decision making.

southwest Finland↗

USGS2018

Groundwater salinity mapping using geophysical log analysis within the Fruitvale and Rosedale Ranch oil fields, Kern County, California, USA

A method is presented for deriving a volume model of groundwater total dissolved solids (TDS) from borehole geophysical and aqueous geochemical measurements. While previous TDS mapping techniques have proved useful in the hydrogeologic setting in which they were developed, they may yield poor results in settings with lithological heterogeneity, complex water chemistry, or limited data. Problems arise because of assumed values for empirical constants in Archie’s Equation, unrealistic porosity and temperature gradients, or bicarbonate-rich groundwater. These issues become critical in complex geologic settings such as the San Joaquin Valley of California, USA. To address this, a method to map TDS in three dimensions is applied to the Fruitvale and Rosedale Ranch oil fields near Bakersfield, California. Borehole resistivity, porosity, and temperature data are used to derive TDS using Archie’s Equation, and are then kriged to interpolate TDS. Archie’s a and m (tortuosity factor and cementation exponent, respectively) are found by comparing model predictions, after kriging, to TDS measurements, and minimizing the differences via mathematical optimization. Contributions of abundant bicarbonate ions to TDS were corrected using an empirical model. This work was motivated by federal and state law requirements to monitor and protect underground sources of drinking water. Modeling shows the legally significant boundary of 10,000 ppm TDS is at ~1,067 m below sea level in Rosedale Ranch, and deepens into Fruitvale to ~1,341 m. Mapping groundwater TDS at this resolution reveals that TDS is primarily controlled by depth, recharge, stratigraphy, and in some places, by faulting and facies changes.

California↗

USGS1999

Relation of streams, lakes, and wetlands to groundwater flow systems

Surface-water bodies are integral parts of groundwater flow systems. Groundwater interacts with surface water in nearly all landscapes, ranging from small streams, lakes, and wetlands in headwater areas to major river valleys and seacoasts. Although it generally is assumed that topographically high areas are groundwater recharge areas and topographically low areas are groundwater discharge areas, this is true primarily for regional flow systems. The superposition of local flow systems associated with surface-water bodies on this regional framework results in complex interactions between groundwater and surface water in all landscapes, regardless of regional topographic position. Hydrologic processes associated with the surface-water bodies themselves, such as seasonally high surface-water levels and evaporation and transpiration of groundwater from around the perimeter of surface-water bodies, are a major cause of the complex and seasonally dynamic groundwater flow fields associated with surface water. These processes have been documented at research sites in glacial, dune, coastal, mantled karst, and riverine terrains.

Hydrogeology Journal↗

USGS2015

Habitat selection and movements of Piping Plover broods suggest a tradeoff between breeding stages

In precocial birds, adults select breeding areas using cues associated with habitat characteristics that are favorable for nesting success and chick survival, but there may be tradeoffs in habitat selection between these breeding stages. Here we describe habitat selection and intra-territory movements of 53 Piping Plover ( Charadrius melodus ) broods (320 observations) during the 2007–2008 breeding seasons on mainland- and island-shoreline habitats at Lake Sakakawea, North Dakota, USA. We used remotely sensed habitat characteristics to separately examine habitat selection and movements at two spatiotemporal scales to account for potential confounding effects of nest-site selection on brood-rearing habitat used. The scales used were (1) the entire brood-rearing period within available brood-rearing areas and (2) 2-day observation intervals within age-specific discrete habitat selection choice sets. Analyses at both scales indicated that broods selected areas which were non-vegetated, moderately level, and nearer to the shoreline. Rate of brood movement increased with age up to 5 days, then stabilized; broods that hatched >50 m away from the shoreline moved toward the shoreline. Brood movements were greater when they were in vegetated areas, when the brood-rearing area was of greater topographic complexity, and when broods aged 6–25 days were further away from the shoreline. Using inferences from our results and those of previously published work, we postulate how a potential tradeoff in habitat selection between nesting and brood-rearing can contribute to an ecological trap in a novel habitat. This work, in the context of published works, suggests that plover breeding habitat is a complex of both nesting and brood-rearing habitats and provides a basis for making remotely sensed abundance estimates of suitable breeding habitat for Piping Plovers.

North Dakota↗

USGS2011

Natural and human dimensions of a quasi-wild species: The case of kudzu

The human dimensions of biotic invasion are generally poorly understood, even among the most familiar invasive species. Kudzu ( Pueraria montana (Lour.) Merr.) is a prominent invasive plant and an example of quasi-wild species, which has experienced repeated introduction, cultivation, and escape back to the wild. Here, we review a large body of primary scientific and historic records spanning thousands of years to characterize the complex relationships among kudzu, its natural enemies, and humans, and provide a synthesis and conceptual model relevant to the ecology and management of quasi-wild invasive species. We documented over 350, mostly insect, natural enemy species and their impacts on kudzu in its native East Asian range. These natural enemies play a minor role in limiting kudzu in its native range, rarely generating severe impacts on populations of wild kudzu. We identified a number of significant influences of humans including dispersal, diverse cultural selection, and facilitation through disturbances, which catalyzed the expansion and exuberance of kudzu. On the other hand, harvest by humans appears to be the major control mechanism in its native areas. Humans thus have a complex relationship with kudzu. They have acted as both friend and foe, affecting the distribution and abundance of kudzu in ways that vary across its range and over time. Our conceptual model of kudzu emphasizes the importance of multiple human dimensions in shaping the biogeography of a species and illustrates how kudzu and other quasi-wild species are more likely to be successful invaders.

Biological Invasions↗

USGS2016

Cryptic invasion of Northern Leopard Frogs ( Rana pipiens ) across phylogeographic boundaries and a dilemma for conservation of a declining amphibian

Anthropogenic introduction of species is a major contributor to loss of biodiversity. Translocations within the range of a species are less frequently recognized, but have the potential for negative effects as well. Genetic mixing may lead to loss of local adaptations or further decline through outbreeding depression. These cryptic invasions may be quite difficult to recognize, but genetic tools can be used to recognize and monitor such intraspecific introductions. Conversely, translocations within species can be an important conservation tool to reduce inbreeding depression and replace lost genetic diversity. Thus, cryptic invasions can be either an aid or a hindrance to conservation efforts. We tested for the presence of non-native genotypes and assessed the extent and nature of introgression in populations of Northern Leopard Frog ( Rana pipiens ) in the southwestern US, where populations have declined to a few remnant populations. The most abundant and diverse complex of populations in the region contained a mitochondrial haplotype that was not native to the western US, probably resulting from the introduction of released pets, laboratory animals, or release during fish stocking. These non-native haplotypes were well integrated into a large complex of ponds and lakes, contributing to high genetic diversity in this area. Logistically, the geographic extent of non-native genetic influence within this population precludes eliminating or controlling the non-native component of this population. We recommend assessing the progress and fate of the introgression over time—along with population fitness parameters—to determine whether this introduction is beneficial or detrimental to population persistence. Meanwhile, translocations from nearby locations with similar environmental conditions have the best prospects for avoiding problems with outbreeding depression in other declining populations and will also most effectively preserve regional genetic diversity.

Biological Invasions↗

USGS2010

Atmospheric stability effects on wind fields and scalar mixing within and just above a subalpine forest in sloping terrain

Air temperature T a , specific humidity q , CO 2 mole fraction χ c , and three-dimensional winds were measured in mountainous terrain from five tall towers within a 1 km region encompassing a wide range of canopy densities. The measurements were sorted by a bulk Richardson number Ri b . For stable conditions, we found vertical scalar differences developed over a “transition” region between 0.05 < Ri b < 0.5. For strongly stable conditions ( Ri b > 1), the vertical scalar differences reached a maximum and remained fairly constant with increasing stability. The relationships q and χ c have with Ri b are explained by considering their sources and sinks. For winds, the strong momentum absorption in the upper canopy allows the canopy sublayer to be influenced by pressure gradient forces and terrain effects that lead to complex subcanopy flow patterns. At the dense-canopy sites, soil respiration coupled with wind-sheltering resulted in CO 2 near the ground being 5–7 μmol mol −1 larger than aloft, even with strong above-canopy winds (near-neutral conditions). We found Ri b -binning to be a useful tool for evaluating vertical scalar mixing; however, additional information (e.g., pressure gradients, detailed vegetation/topography, etc.) is needed to fully explain the subcanopy wind patterns. Implications of our results for CO 2 advection over heterogenous, complex terrain are discussed.

Boundary-Layer Meteorology↗

USGS2011

Potential increase in floods in California's Sierra Nevada under future climate projections

California’s mountainous topography, exposure to occasional heavily moisture-laden storm systems, and varied communities and infrastructures in low lying areas make it highly vulnerable to floods. An important question facing the state—in terms of protecting the public and formulating water management responses to climate change—is “how might future climate changes affect flood characteristics in California?” To help address this, we simulate floods on the western slopes of the Sierra Nevada Mountains, the state’s primary catchment, based on downscaled daily precipitation and temperature projections from three General Circulation Models (GCMs). These climate projections are fed into the Variable Infiltration Capacity (VIC) hydrologic model, and the VIC-simulated streamflows and hydrologic conditions, from historical and from projected climate change runs, allow us to evaluate possible changes in annual maximum 3-day flood magnitudes and frequencies of floods. By the end of the 21st Century, all projections yield larger-than-historical floods, for both the Northern Sierra Nevada (NSN) and for the Southern Sierra Nevada (SSN). The increases in flood magnitude are statistically significant (at p <= 0.01) for all the three GCMs in the period 2051–2099. The frequency of flood events above selected historical thresholds also increases under projections from CNRM CM3 and NCAR PCM1 climate models, while under the third scenario, GFDL CM2.1, frequencies remain constant or decline slightly, owing to an overall drying trend. These increases appear to derive jointly from increases in heavy precipitation amount, storm frequencies, and days with more precipitation falling as rain and less as snow. Increases in antecedent winter soil moisture also play a role in some areas. Thus, a complex, as-yet unpredictable interplay of several different climatic influences threatens to cause increased flood hazards in California’s complex western Sierra landscapes.

California↗

USGS2012

Identification of metapopulation dynamics among Northern Goshawks of the Alexander Archipelago, Alaska, and Coastal British Columbia

Northern Goshawks occupying the Alexander Archipelago, Alaska, and coastal British Columbia nest primarily in old-growth and mature forest, which results in spatial heterogeneity in the distribution of individuals across the landscape. We used microsatellite and mitochondrial data to infer genetic structure, gene flow, and fluctuations in population demography through evolutionary time. Patterns in the genetic signatures were used to assess predictions associated with the three population models: panmixia, metapopulation, and isolated populations. Population genetic structure was observed along with asymmetry in gene flow estimates that changed directionality at different temporal scales, consistent with metapopulation model predictions. Therefore, Northern Goshawk assemblages located in the Alexander Archipelago and coastal British Columbia interact through a metapopulation framework, though they may not fit the classic model of a metapopulation. Long-term population sources (coastal mainland British Columbia) and sinks (Revillagigedo and Vancouver islands) were identified. However, there was no trend through evolutionary time in the directionality of dispersal among the remaining assemblages, suggestive of a rescue-effect dynamic. Admiralty, Douglas, and Chichagof island complex appears to be an evolutionarily recent source population in the Alexander Archipelago. In addition, Kupreanof island complex and Kispiox Forest District populations have high dispersal rates to populations in close geographic proximity and potentially serve as local source populations. Metapopulation dynamics occurring in the Alexander Archipelago and coastal British Columbia by Northern Goshawks highlight the importance of both occupied and unoccupied habitats to long-term population persistence of goshawks in this region.

Alaska, British Columbia↗

USGS2021

Landscape and stocking effects on population genetics of Tennessee Brook Trout

Throughout their range, Brook Trout ( Salvelinus fontinalis ) occupy thousands of disjunct drainages with varying levels of disturbance, which presents substantial challenges for conservation. Within the southern Appalachian Mountains, fragmentation and genetic drift have been identified as key threats to the genetic diversity of the Brook Trout populations. In addition, extensive historic stocking of domestic lineages of Brook Trout to augment fisheries may have eroded endemic diversity and impacted locally adapted populations. We used 12 microsatellite loci to describe patterns of genetic diversity within 108 populations of wild Brook Trout from Tennessee and used linear models to explore the impacts of land use, drainage area, and hatchery stockings on metrics of genetic diversity, effective population size, and hatchery introgression. We found levels of within-population diversity varied widely, although many populations showed very limited diversity. The extent of hatchery introgression also varied across the landscape, with some populations showing high affinity to hatchery lineages and others appearing to retain their endemic character. However, we found relatively weak relationships between genetic metrics and landscape characteristics, suggesting that contemporary landscape variables are not strongly related to observed patterns of genetic diversity. We consider this result to reflect both the complex history of these populations and the challenges associated with accurately defining drainages for each population. Our study highlights the importance of genetic data to guide management decisions, as complex processes interact to shape the genetic structure of populations and make it difficult to infer the status of unsampled populations.

Tennessee↗

USGS2011

Pre-spawning migration of adult Pacific lamprey, Entosphenus tridentatus , in the Willamette River, Oregon, U.S.A.

We describe the migration distances and timing of the adult Pacific lamprey, Entosphenus tridentatus , in the Willamette River Basin (Oregon, U.S.A.). We conducted aerial surveys to track radio-tagged fish upstream of a major waterfall and hydropower complex en route to spawning areas. We detected 24 out of the 43 fish that passed the waterfall-hydropower complex. Of the detected fish, 17 were detected multiple times. Their maximum migration distance upstream in the mainstem Willamette approximated a normal distribution. The maximum distance migrated upstream did not significantly correlate with total body length ( r  = −0.186, P  = 0.385) or date that the fish passed Willamette Falls ( r  = −0.118, P  = 0.582). Fish migrated primarily during the spring to early summer period before stopping during the summer, when peak river temperatures (≥20°C). However, at least three fish continued to migrate upstream after September. Behavior ranged from relatively slow migration, followed by holding; to rapid migration, followed by slow migration further up in the basin. This study provides a basis for informing more detailed research on Pacific lamprey in the future.

Oregon↗

USGS2019

Spatial variation in aquatic invertebrate and riparian songbird mercury exposure across a river-reservoir system with a legacy of mercury contamination

Mercury (Hg) loading and methylation in aquatic systems causes a variety of deleterious effects for fish and wildlife populations. Relatively little research has focused on Hg movement into riparian food webs and how this is modulated by habitat characteristics. This study characterized differences in Hg exposure in aquatic invertebrates and riparian songbirds across a large portion of the Willamette River system in western Oregon, starting at a Hg-contaminated Superfund site in the headwaters (Black Butte Hg Mine) and including a reservoir known to methylate Hg (Cottage Grove Reservoir), all downstream reaches (Coast Fork and Willamette River) and off-channel wetland complexes (Willamette Valley National Wildlife Refuge Complex). After accounting for year, date, and site differences in a mixed effects model, MeHg concentrations in aquatic invertebrates varied spatially among habitat categories and invertebrate orders. Similarly, THg in songbird blood varied by among habitat categories and bird species. The highest Hg concentrations occurred near the Hg mine, but Hg did not decline linearly with distance from the source of contamination. Birds were consistently elevated in Hg in habitats commonly associated with enhanced MeHg production, such as backwater or wetlands. We found a positive but weak correlation between aquatic invertebrate MeHg concentrations and songbird THg concentrations on a site-specific basis. Our findings suggest that Hg risk to riparian songbirds can extend beyond point-source contaminated areas, highlighting the importance of assessing exposure in surrounding habitats where methylmercury production may be elevated, such as reservoirs and wetlands.

Oregon↗

USGS2019

Distribution of contaminants in the environment and wildlife habitat use: A case study with lead and waterfowl on the Upper Texas Coast

The magnitude and distribution of lead contamination remain unknown in wetland systems. Anthropogenic deposition of lead may be contributing to negative population-level effects in waterfowl and other organisms that depend on dynamic wetland habitats, particularly if they are unable to detect and differentiate levels of environmental contamination by lead. Detection of lead and behavioral response to elevated lead levels by waterfowl is poorly understood, but necessary to characterize the risk of lead-contaminated habitats. We measured the relationship between lead contamination of wetland soils and habitat use by mottled ducks ( Anas fulvigula ) on the Upper Texas Coast, USA. Mottled ducks have historically experienced disproportionate negative effects from lead exposure, and exhibit a unique nonmigratory life history that increases risk of exposure when inhabiting contaminated areas. We used spatial interpolation to estimate lead in wetland soils of the Texas Chenier Plain National Wildlife Refuge Complex. Soil lead levels varied across the refuge complex (0.01–1085.51 ppm), but greater lead concentrations frequently corresponded to areas with high densities of transmittered mottled ducks. We used soil lead concentration data and MaxENT species distribution models to quantify relationships among various habitat factors and locations of mottled ducks. Use of habitats with greater lead concentration increased during years of a major disturbance. Because mottled ducks use habitats with high concentrations of lead during periods of stress, have greater risk of exposure following major disturbance to the coastal marsh system, and no innate mechanism for avoiding the threat of lead exposure, we suggest the potential presence of an ecological trap of quality habitat that warrants further quantification at a population scale for mottled ducks.

Texas↗

USGS2024

The reach-scale biogeomorphic effect of submerged macrophytes on trout habitat suitability

Submerged macrophytes have complex effects on spatiotemporal characteristics of river ecosystems, including trout habitat. We investigated the impact of submerged macrophyte coverage on trout habitat in the Henrys Fork of the Snake River, Idaho, USA. We hypothesized that higher submerged macrophyte coverage would create new habitat types beneficial for trout growth. We assessed river physical and biotic attributes, trout habitat preferences, and estimated trout growth potential with bioenergetics models across a gradient of submerged macrophyte coverage (32–94%). We identified four distinct habitat types within the riverscape shaped by submerged macrophyte coverage. Increased submerged macrophyte coverage increased the frequency of habitat types with higher trout growth potential but reduced the occurrence of preferred habitat types. We observed no relationship between reach-scale trout growth potential and submerged macrophyte coverage. However, an outlier of very high trout growth potential at 94% submerged macrophyte coverage suggests a potential threshold effect. More study is required but our observations suggest macrophyte growth homogenized physical habitat characteristics, reduced flow velocities, and increased invertebrate drift, thereby enhancing trout growth potential. Our findings underscore the complex interplay between submerged macrophytes and trout habitat dynamics across scales, emphasizing the importance of considering both physical and biological effects on trout habitat.

Idaho↗

USGS2009

Addressing foundational elements of regional land-use change forecasting

Regional land-use models must address several foundational elements, including understanding geographic setting, establishing regional land-use histories, modeling process and representing drivers of change, representing local land-use patterns, managing issues of scale and complexity, and development of scenarios. Key difficulties include managing an array of biophysical and socioeconomic processes across multiple spatial and temporal scales, and acquiring and utilizing empirical data to support the analysis of those processes. The Southeastern and Pacific Northwest regions of the United States, two heavily forested regions with significant forest industries, are examined in the context of these foundational elements. Geographic setting fundamentally affects both the primary land cover (forest) in the two regions, and the structure and form of land use (forestry). Land-use histories of the regions can be used to parameterize land-use models, validate model performance, and explore land-use scenarios. Drivers of change in the two regions are many and varied, with issues of scale and complexity posing significant challenges. Careful scenario development can be used to simplify process-based land-use models, and can improve our ability to address specific research questions. The successful modeling of land-use change in these two areas requires integration of both top-down and bottom-up drivers of change, using scenario frameworks to both guide and simplify the modeling process. Modular approaches, with utilization and integration of existing process models, allow regional land-use modelers the opportunity to better represent primary drivers of land-use change. However, availability of data to represent driving forces remains a primary obstacle.

Landscape Ecology↗

USGS2021

Valleys of fire: Historical fire regimes of forest-grassland ecotones across the montane landscape of the Valles Caldera National Preserve, New Mexico, USA

Context Montane grasslands and forest-grassland ecotones are unique and dynamic components of many landscapes, but the processes that regulate their dynamics are difficult to observe over ecologically relevant time spans. Objectives We aimed to demonstrate the efficacy of using grassland-forest ecotone trees to reconstruct spatial and temporal properties of the historical fire regime in a complex landscape of montane forests and adjacent grasslands. Methods We sampled and crossdated fire-scarred trees along ecotones and compared variations in historical fire occurrence within and among nine adjoining valle basins in a 10,158 ha landscape. We analyzed fire year extensiveness, climate regulation, and the occurrence of consecutive fire years. Results The resulting tree-ring record covers 1240–2005 AD, with 296 trees recording 125 replicated fire years during the analysis period 1601–1902 AD . Mean fire intervals for all events recorded on two or more trees ranged from 4.7 to 13.6 years in individual valles , and a mean of 2.4 ± 1.7 (SD) years at the landscape scale. Between 1660 and 1902, extensive fires occurring in six or more valles occurred 15 times, on average at ~ 17-year intervals; 29 moderately widespread fires (3–5 valles ) occurred during this period, at 8.7 year intervals on average. Widespread events occurred in years with a significantly lower Palmer Drought Severity Index (PDSI) preceded by years of significantly positive PDSI, indicating conditions favorable for fine fuel production. Spatial reconstruction of fire extent revealed multiple occurrences of consecutive-year fires burning non-overlapping areas, associated with persistent low PDSI anomalies preceded by positive conditions in antecedent years. Conclusions A landscape spatiotemporal approach to reconstructing fire regimes of montane forest-grassland complexes provides a valuable baseline for guiding prescribed and natural fire management at large spatial scales.

New Mexico↗