Geology topics

Ellis Q. Margolis

Publications and source records attributed to Ellis Q. Margolis.

34 records · Page 2Linked to original sources

USGS2021

Native American fire management at an ancient wildland–urban interface in the Southwest United States

The intersection of expanding human development and wildland landscapes—the “wildland–urban interface” or WUI—is one of the most vexing contexts for fire management because it involves complex interacting systems of people and nature. Here, we document the dynamism and stability of an ancient WUI that was apparently sustainable for more than 500 y. We combine ethnography, archaeology, paleoecology, and ecological modeling to infer intensive wood and fire use by Native American ancestors of Jemez Pueblo and the consequences on fire size, fire–climate relationships, and fire intensity. Initial settlement of northern New Mexico by Jemez farmers increased fire activity within an already dynamic landscape that experienced frequent fires. Wood harvesting for domestic fuel and architectural uses and abundant, small, patchy fires created a landscape that burned often but only rarely burned extensively. Depopulation of the forested landscape due to Spanish colonial impacts resulted in a rebound of fuels accompanied by the return of widely spreading, frequent surface fires. The sequence of more than 500 y of perennial small fires and wood collecting followed by frequent “free-range” wildland surface fires made the landscape resistant to extreme fire behavior, even when climate was conducive and surface fires were large. The ancient Jemez WUI offers an alternative model for fire management in modern WUI in the western United States, and possibly other settings where local management of woody fuels through use (domestic wood collecting) coupled with small prescribed fires may make these communities both self-reliant and more resilient to wildfire hazards.

Arizona, New Mexico↗

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↗

USGS2021

Tamm review: Postfire landscape management in frequent-fire conifer forests of the southwestern United States

The increasing incidence of wildfires across the southwestern United States (US) is altering the contemporary forest management template within historically frequent-fire conifer forests. An increasing fraction of southwestern conifer forests have recently burned, and many of these burned landscapes contain complex mosaics of surviving forest and severely burned patches without surviving conifer trees. These heterogeneous burned landscapes present unique social and ecological challenges. Severely burned patches can present numerous barriers to successful conifer regeneration, and often contain heavy downed fuels which have cascading effects on future fire behavior and conifer regeneration. Conversely, surviving forest patches are increasingly recognized for their value in postfire reforestation but often are overlooked from a management perspective. Here we present a decision-making framework for landscape-scale management of complex postfire landscapes that allows for adaptation to a warming climate and future fire. We focus specifically on historically frequent-fire forests of the southwestern US but make connections to other forest types and other regions. Our framework depends on a spatially-explicit assessment of the mosaic of conifer forest and severely burned patches in the postfire landscape, evaluates likely vegetation trajectories, and identifies critical decision points to direct vegetation change via manipulations of fuels and live vegetation. This framework includes detailed considerations for postfire fuels management (e.g., edge hardening within live forest patches and repeat burning) and for reforestation (e.g., balancing tradeoffs between intensive and extensive planting strategies, establishing patches of seed trees, spatial planning to optimize reforestation success, and improving nursery capacity). In a future of increasing fire activity in forests where repeated low- to moderate-severity fire is essential to ecosystem resilience, the decision-making framework developed here can easily be integrated with existing postfire management strategies to optimize allocation of limited resources and more actively manage burned landscapes.

Arizona, Colorado, New Mexico, Utah↗

USGS2020

Wildfire-driven forest conversion in western North American landscapes

Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest type or nonforest vegetation. Conversion implies major, extensive, and enduring changes in dominant species, life forms, or functions, with impacts on ecosystem services. In the present article, we synthesize a growing body of evidence of fire-driven conversion and our understanding of its causes across western North America. We assess our capacity to predict conversion and highlight important uncertainties. Increasing forest vulnerability to changing fire activity and climate compels shifts in management approaches, and we propose key themes for applied research coproduced by scientists and managers to support decision-making in an era when the prefire forest may not return.

Alaska, Alberta, Arizona, British Columbia, Califo↗

USGS2020

Climate relationships with increasing wildfire in the southwestern US from 1984 to 2015

Over the last several decades in forest and woodland ecosystems of the southwestern United States, wildfire size and severity have increased, thereby increasing the vulnerability of these systems to type conversions, invasive species, and other disturbances. A combination of land use history and climate change is widely thought to be contributing to the changing fire regimes. We examined climate-fire relationships in forest and woodland ecosystems from 1984 – 2015 in Arizona and New Mexico using 1) an expanded satellite-derived burn severity dataset that incorporates over one million additional burned hectares when compared to MTBS data, and 2) climate variables including temperature, precipitation, and vapor pressure deficit (VPD). Regional climate-fire relationships were assessed by correlating annual area burned, area burned at high and low severity, and percent high severity with fire season (May-August) and water-year (October-September) climate variables. We also analyzed relationships between climate and high-severity fire at the scale of the individual fires using a hurdle model. We found that increasing temperature and VPD and decreasing precipitation were associated with increasing area burned regionally, and that area burned at high severity had the strongest relationships with climate metrics. The relationship between climate and fire activity in the Southwest appears to be strengthening since 2000. VPD-fire correlations were consistently as strong as, or stronger than, temperature or precipitation variables alone, both regionally and at the scale of the individual fires. Notably, at the scale of the individual fires, temperature and precipitation were not significant predictors of fire activity. Thus, our results support the use of VPD as a more integrative climate metric to forecast fire activity. We suggest that the strong relationship between VPD and fire activity may be useful to assess the likelihood of high-severity fire occurrence through continued development of the high-severity fire threshold model we present. The link between increasing aridity and increasing wildfire activity suggests a future with more fire in Southwest forests and woodlands with projected warming, underscoring the urgency of restoration in dry forests to reduce the likelihood of uncharacteristic, large high-severity fires.

Arizona, New Mexico↗

USGS2020

Dendrochronology of a rare long-lived mediterranean shrub

Ceanothus verrucosus (CEVE) is a globally rare, long-lived, chaparral shrub endemic to coastal southern California (CA) and northern Mexico. There is concern for CEVE persistence because of habitat loss, fire, and climate change, yet little is known about basic features of the plant, including whether it contains annual rings, plant age, and climate–growth response. Growth-ring analysis was challenging because of semi-ring-porous structure, false, and missing rings. We successfully crossdated CEVE annual rings, primarily from Cabrillo National Monument, CA, using a nearby Pinus torreyana chronology. The oldest living individual had 116 rings; the oldest inner-ring date was 1873; and most of the plants established between 1894 and 1905, all older than previous estimates. CEVE mortality occurred during a dry period from the late 1940s through the early 1960s. Correlations between age and stem measurements were weak to moderate (r = 0.10 to 0.56) posing challenges for field-based estimates of plant ages, which are important for population modeling. Variability in CEVE ring width had a strong positive correlation with prior cool-season (October–April) precipitation, yet 2- to 7-day warm-season precipitation events were recorded as rare false rings in multiple years, indicating extreme plasticity in cambial phenology and growth response to moisture.

California↗

USGS2019

Spatio-temporal variability of human-fire interactions on the Navajo Nation

Unraveling the effects of climate and land-use on historical fire regimes provides important insights into broader human-fire-climate dynamics, which are necessary for ecologically-based forest management. We developed a spatial human land-use model for Navajo Nation forests across which we sampled a network of tree-ring fire history sites to reflect contrasting historical land-use intensity: high human use, primarily in the Chuska Mountains, and low human use, primarily on the central Defiance Plateau. We tested for and compared human- and climate-driven changes in the fire regimes by applying change point detection, regression, and superposed epoch analyses. The historical fire regimes and fire-climate relationships reflect those of similar forests regionally, and are similar between the two Navajo landscapes until the early 1800s. We then determined that a previously identified, localized, early (1830s) decline in fire activity was geographically widespread across higher human use sites. In contrast, fires continued to burn uninterrupted through this period at the lower use sites. Though the 1830s included significantly wet and cold periods that could have contributed to fire regime decline, human factors pose a more spatio-temporally consistent explanation. A rise in Navajo pastoralism in the 1820s-1830s was concentrated seasonally in the heavy use sites. By the 1880s, livestock numbers more than doubled, grazing became far more spatially widespread, and frequent fire regimes of Navajo forests collapsed. The last widespread fire recorded on either landscape was in 1886. In the Chuska Mountains, livestock and fire co-existed for over 50 years between the initial 1832 fire decline and the end of frequent fires after 1886, an exceptional pattern in the western US. Though unique in its timing, character, and spatial dynamics, the collapse of historical fire regimes in Navajo forests contributed to now over a century without frequent surface fire, leaving Navajo forests at risk for large, uncharacteristic high-severity fires.

Arizona, New Mexico↗

USGS2019

Surface fire to Crown Fire: Fire history in the Taos Valley watersheds, New Mexico, USA

Tree-ring fire scars, tree ages, historical photographs, and historical surveys indicate that, for centuries, fire played different ecological roles across gradients of elevation, forest, and fire regimes in the Taos Valley Watersheds. Historical fire regimes collapsed across the three watersheds by 1899, leaving all sites without fire for at least 119 years. Historical photographs and quaking aspen (Populus tremuloides Michx.) ages indicate that a high-severity fire historically burned at multiple high-elevation subalpine plots in today’s Village of Taos Ski Valley, with large high-severity patches (>640 ha). Low-severity, frequent (9–29-year median interval) surface fires burned on the south aspects in nearby lower elevation dry conifer forests in all watersheds. Fires were associated with drought during the fire year. Widespread fires commonly burned synchronously in multiple watersheds during more severe drought years, preceded by wet years, including fire in all three watersheds in 1664, 1715, and 1842. In contrast, recent local “large” wildfires have only burned within single watersheds and may not be considered large in a historical context. Management to promote repeated low-severity fires and the associated open stand structures is within the historical range of variability in the dry conifer forests of these watersheds. In the high-elevation, subalpine forests, different management approaches are needed, which balance ecological and socioeconomic values while providing public safety.

New Mexico↗

USGS2018

Advancing dendrochronological studies of fire in the United States

Dendroecology is the science that dates tree rings to their exact calendar year of formation to study processes that influence forest ecology (e.g., Speer 2010 , Amoroso et al., 2017 ). Reconstruction of past fire regimes is a core application of dendroecology, linking fire history to population dynamics and climate effects on tree growth and survivorship. Since the early 20th century when dendrochronologists recognized that tree rings retained fire scars (e.g., Figure 1) , and hence a record of past fires, they have conducted studies worldwide to reconstruct the historical range and variability of fire regimes (e.g., frequency, severity, seasonality, spatial extent), the influence of fire regimes on forest structure and ecosystem dynamics, and the top-down (e.g., climate) and bottom-up (e.g., fuels, topography) drivers of fire that operate at a range of temporal and spatial scales. As in other scientific fields, continued application of dendrochronological techniques to study fires has shaped new trajectories for the science. Here we highlight some important current directions in the United States (US) and call on our international colleagues to continue the conversation with perspectives from other countries.

Fire↗

USGS2018

Limits to ponderosa pine regeneration following large high-severity forest fires in the United States Southwest

High-severity fires in dry conifer forests of the United States Southwest have created large (>1000 ha) treeless areas that are unprecedented in the regional historical record. These fires have reset extensive portions of Southwestern ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. scopulorum Engelm.) forest landscapes. At least two recovery options following high-severity fire are emerging. One option is for post-fire successional pathways to move toward a return to the pre-fire forest type. Alternatively, an area may transition to persistent non-forested ecosystems. We studied regeneration patterns of ponderosa pine following eight fires in Arizona and New Mexico, USA, that burned in dry conifer forests dominated by ponderosa pine during a recent 18-year regional drought period, 1996 to 2013. Our a priori hypotheses were: 1) the most xeric areas within these severely burned dry conifer forests are least likely to regenerate to the pre-fire forest type due to persistent post-fire moisture stress; and 2) areas farther away from conifer seed sources have a lower likelihood of regeneration, even if these areas are climatically favorable for post-fire ponderosa pine establishment. We evaluated our hypotheses using empirical data and generalized linear mixed-effects models. We found that low-elevation, xeric sites are more limiting to conifer regeneration than higher-elevation mesic sites. Areas >150 m from a seed source are much less likely to have ponderosa pine regeneration. Spatial interpolations of modeled post-fire regeneration of ponderosa pine across the study landscapes indicate expansive areas with low likelihood of pine regeneration following high-severity fire. We discuss multiple post-fire successional pathways following high-severity fire, including potentially stable transitions to non-forest vegetation types that may represent long-term type conversions. These findings regarding landscape changes in Southwest forests in response to fires and post-fire regeneration patterns during early-stage climate warming contribute to the development of better-informed ecosystem management strategies for forest adaptation or mitigation under projected hotter droughts in this region.

Arizona, New Mexico↗

USGS2018

burnr: Fire history analysis and graphics in R

We developed a new software package, burnr , for fire history analysis and plotting in the R statistical programming environment. It was developed for tree-ring fire-scar analysis, but is broadly applicable to other event analyses (e.g., avalanches, frost rings, or culturally modified trees). Our new package can read, write, and manipulate standard tree-ring fire history FHX files, produce fire—demography charts, calculate fire frequency and seasonality statistics, and run superposed epoch analysis (SEA). A key benefit of burnr is that it enables automation of analyses and plotting, especially for large data sets. The package also facilitates creative plotting, mapping, and analyses when combined with the thousands of packages available in R . In this paper, we describe the basic functionality of burnr and introduce users to fire history analyses in R .

Dendrochronologia↗

USGS2017

Long-term persistence and fire resilience of oak shrubfields in dry conifer forests of northern New Mexico

Extensive high-severity fires are creating large shrubfields in many dry conifer forests of the interior western USA, raising concerns about forest-to-shrub conversion. This study evaluates the role of disturbance in shrubfield formation, maintenance and succession in the Jemez Mountains, New Mexico. We compared the environmental conditions of extant Gambel oak ( Quercus gambelii ) shrubfields with adjoining dry conifer forests and used dendroecological methods to determine the multi-century fire history and successional dynamics of five of the largest shrubfields (76–340 ha). Across the study area, 349 shrubfields (5–368 ha) occur in similar topographic and climate settings as dry conifer forests. This suggests disturbance, rather than other biophysical factors, may explain their origins and persistence. Gambel oak ages and tree-ring fire scars in our sampled shrubfields indicate they historically (1664–1899) burned concurrently with adjoining conifer forests and have persisted for over 115 years in the absence of fire. Aerial imagery from 1935 confirmed almost no change in sampled shrubfield patch sizes or boundaries over the twentieth century. The largest shrubfield we identified is less than 4% the size of the largest conifer-depleted and substantially shrub-dominated area recently formed in the Jemez following extensive high-severity wildfires, indicating considerable departure from historical patterns and processes. Projected hotter droughts and increasingly large high-severity fires could trigger more forest-to-shrub transitions and maintain existing shrubfields, inhibiting conifer forest recovery. Restoration of surface fire regimes and associated historical forest structures likely could reduce the rate and patch size of dry conifer forests being converted to shrubfields.

New Mexico↗

USGS2017

Drought, multi-seasonal climate, and wildfire in northern New Mexico

Wildfire is increasingly a concern in the USA, where 10 million acres burned in 2015. Climate is a primary driver of wildfire, and understanding fire-climate relationships is crucial for informing fire management and modeling the effects of climate change on fire. In the southwestern USA, fire-climate relationships have been informed by tree-ring data that extend centuries prior to the onset of fire exclusion in the late 1800s. Variability in cool-season precipitation has been linked to fire occurrence, but the effects of the summer North American monsoon on fire are less understood, as are the effects of climate on fire seasonality. We use a new set of reconstructions for cool-season (October–April) and monsoon-season (July–August) moisture conditions along with a large new fire scar dataset to examine relationships between multi-seasonal climate variability, fire extent, and fire seasonality in the Jemez Mountains, New Mexico (1599–1899 CE). Results suggest that large fires burning in all seasons are strongly influenced by the current year cool-season moisture, but fires burning mid-summer to fall are also influenced by monsoon moisture. Wet conditions several years prior to the fire year during the cool season, and to a lesser extent during the monsoon season, are also important for spring through late-summer fires. Persistent cool-season drought longer than 3 years may inhibit fires due to the lack of moisture to replenish surface fuels. This suggests that fuels may become increasingly limiting for fire occurrence in semi-arid regions that are projected to become drier with climate change.

New Mexico↗

USGS2016

Historical dominance of low-severity fire in dry and wet mixed-conifer forest habitats of the endangered terrestrial Jemez Mountains salamander ( Plethodon neomexicanus )

Anthropogenic alteration of ecosystem processes confounds forest management and conservation of rare, declining species. Restoration of forest structure and fire hazard reduction are central goals of forest management policy in the western United States, but restoration priorities and treatments have become increasingly contentious. Numerous studies have documented changes in fire regimes, forest stand structure and species composition following a century of fire exclusion in dry, frequent-fire forests of the western U.S. (e.g., ponderosa pine and dry mixed-conifer). In contrast, wet mixed-conifer forests are thought to have historically burned infrequently with mixed- or high-severity fire—resulting in reduced impacts from fire exclusion and low restoration need—but data are limited. In this study we quantified the current forest habitat of the federally endangered, terrestrial Jemez Mountains salamander (Plethodon neomexicanus) and compared it to dendroecological reconstructions of historical habitat (e.g., stand structure and composition), and fire regime parameters along a gradient from upper ponderosa pine to wet mixed-conifer forests. We found that current fire-free intervals in Jemez Mountains salamander habitat (116–165 years) are significantly longer than historical intervals, even in wet mixed-conifer forests. Historical mean fire intervals ranged from 10 to 42 years along the forest gradient. Low-severity fires were historically dominant across all forest types (92 of 102 fires). Although some mixed- or highseverity fire historically occurred at 67% of the plots over the last four centuries, complete mortality within 1.0 ha plots was rare, and asynchronous within and among sites. Climate was an important driver of temporal variability in fire severity, such that mixed- and high-severity fires were associated with more extreme drought than low-severity fires. Tree density in dry conifer forests historically ranged from open (90 trees/ha) to moderately dense (400 trees/ha), but has doubled on average since fire exclusion. Infill of fire-sensitive tree species has contributed to the conversion of historically dry mixedconifer to wet mixed-conifer forest. We conclude that low-severity fire, which has been absent for over a century, was a critical ecosystem process across the forest gradient in Jemez Mountains salamander habitat, and thus is an important element of ecosystem restoration, resilience, and rare species recovery.

Forest Ecology and Management↗

USGS2016

Pruning high-value Douglas-fir can reduce dwarf mistletoe severity and increase longevity in central Oregon

Mid- to very large-sized Douglas-fir (Pseudotsuga menzieseii var. menziesii) that were lightly- to moderately-infected by dwarf mistletoe (Arceuthobium douglasii) were analyzed over a 14-year period to evaluate whether mechanical pruning could eradicate mistletoe (or at least delay the onset of severe infection) without significantly affecting tree vitality and by inference, longevity. Immediate and longterm pruning effects on mistletoe infection severity were assessed by comparing pruned trees (n = 173) to unpruned trees (n = 55) with respect to: (1) percentage of trees with no visible infections 14 years post-pruning, (2) Broom Volume Rating (BVR), and (3) rate of BVR increase 14 years postpruning. Vitality/longevity (compared with unpruned trees) was assessed using six indicators: (1) tree survival, (2) the development of severe infections, (3) the development of dead tops, (4) tree-ring width indices, (5) Normalized Difference Vegetation Index (NDVI) from high-resolution multi-spectral imagery, and (6) live-crown ratio (LCR) and increment. Twenty-four percent of the pruned trees remained free of mistletoe 14 years post-pruning. Pruning is most likely to successfully eradicate mistletoe in lightly infected trees (BVR 1 or 2) without infected neighbors. Pruning significantly decreased mean BVR in the pruned versus the unpruned trees. However, the subsequent average rate of intensification (1.3–1.5 BVR per decade) was not affected, implying that a single pruning provides ~14 years respite in the progression of infection levels. Post-pruning infection intensification was slower on dominant and co-dominants than on intermediate or suppressed trees. The success of mistletoe eradication via pruning and need for follow-up pruning should be evaluated no sooner than 14 years after pruning to allow for the development of detectable brooms. Based on six indicators, foliage from witches brooms contribute little to long-term tree vitality since removal appears to have little effect on resources available for tree growth and maintenance. In the severely pruned trees, tree-ring width was reduced for several years post-pruning, but then compensated with larger ring width in later years. Both NDVI and LCR increment were significantly higher for the pruned trees than the control trees, while the development of severe infections and/or dead tops was significantly (5X and 3X) higher for the controls. If possible, multiple indicators of tree vitality should be evaluated. Pruning can be worthwhile even if all the mistletoe is not removed, because mistletoe intensification is delayed. The impact of removing the brooms seems to be minimal, and post-pruning crowns had greater NDVI values.

Oregon↗

USGS2013

Unsupported inferences of high-severity fire in historical dry forests of the western United States: Response to Williams and Baker

Reconstructions of dry western US forests in the late 19th century in Arizona, Colorado and Oregon based on General Land Office records were used by Williams & Baker (2012; Global Ecology and Biogeography, 21, 1042–1052; hereafter W&B) to infer past fire regimes with substantial moderate and high-severity burning. The authors concluded that present-day large, high-severity fires are not distinguishable from historical patterns. We present evidence of important errors in their study. First, the use of tree size distributions to reconstruct past fire severity and extent is not supported by empirical age–size relationships nor by studies that directly quantified disturbance history in these forests. Second, the fire severity classification of W&B is qualitatively different from most modern classification schemes, and is based on different types of data, leading to an inappropriate comparison. Third, we note that while W&B asserted ‘surprising’ heterogeneity in their reconstructions of stand density and species composition, their data are not substantially different from many previous studies which reached very different conclusions about subsequent forest and fire behaviour changes. Contrary to the conclusions of W&B, the preponderance of scientific evidence indicates that conservation of dry forest ecosystems in the western United States and their ecological, social and economic value is not consistent with a present-day disturbance regime of large, high-severity fires, especially under changing climate

Arizona, Colorado, Oregon↗