Geology topics

W.H. Romme

Publications and source records attributed to W.H. Romme.

4 recordsLinked to original sources

USGS2011

Twenty Years After the 1988 Yellowstone Fires: Lessons About Disturbance and Ecosystems

The 1988 Yellowstone fires were among the first in what has proven to be an upsurge in large severe fires in the western USA during the past 20 years. At the time of the fires, little was known about the impacts of such a large severe disturbance because scientists had had few previous opportunities to study such an event. Ecologists predicted short- and long-term effects of the 1988 fires on vegetation, biogeochemistry, primary productivity, wildlife, and aquatic ecosystems based on scientific understanding of the time. Twenty-plus years of subsequent study allow these early predictions to be evaluated. Most of the original predictions were at least partially supported, but some predictions were refuted, others nuanced, and a few postfire phenomena were entirely unexpected. Post-1988 Yellowstone studies catalyzed advances in ecology focused on the importance of spatial and temporal heterogeneity, contingent influences, and multiple interacting drivers. Post-1988 research in Yellowstone also has changed public perceptions of fire as an ecological process and attitudes towards fire management. Looking ahead to projected climate change and more frequent large fires, the well-documented ecological responses to the 1988 Yellowstone fires provide a foundation for detecting and evaluating potential changes in fire regimes of temperate mountainous regions. ?? 2011 Springer Science+Business Media, LLC.

Ecosystems↗

USGS2008

Mapping "old" versus "young" piñon-juniper stands with a predictive topo-climatic model in north-central New Mexico, USA

Piñon pine and juniper woodlands in the southwestern United States are often represented as an expanding and even invasive vegetation type, a legacy of historic grazing, and culpable in the degradation of western rangelands. A long-standing emphasis on forage production, in combination with recent hazard fuel concerns, has prompted a new era of woodland management with stated restoration objectives. Yet the extent and dynamics of piñon–juniper communities that predate intensive Euro-American settlement activities are poorly known or understood, while the intrinsic ecological, aesthetic, and economic values of old-growth woodlands are often overlooked. Historical changes in piñon–juniper stands include two related, but poorly differentiated processes: recent tree expansion into grass- or shrub-dominated (i.e., non-woodland) vegetation and thickening or infilling of savanna or mosaic woodlands predating settlement. Our work addresses the expansion pattern, modeling the occurrence of “older” savanna and woodland stands extant prior to 1850 in contrast to “younger” piñon–juniper growth of more recent, postsettlement origin. We present criteria in the form of a diagnostic key for distinguishing “older,” pre-Euro-American settlement piñon–juniper from “younger” (post-1850) stands and report results of predictive modeling and mapping efforts within a north-central New Mexico study area. Selected models suggest a primary role for soil moisture in the current distribution of “old” vs. “young” piñon–juniper stands. Presettlement era woodlands are shown to occupy a discrete ecological space, defined by the interaction of effective (seasonal) moisture with landform setting and fine-scale (soil/water) depositional patterns. “Older” stands are generally found at higher elevations or on skeletal soils in upland settings, while “younger” stands (often dominated by one-seed juniper, Juniperus monosperma ) are most common at lower elevations or in productive, depositional settings. Modeling at broad regional scales can enhance our general understanding of piñon–juniper ecology, while predictive mapping of local areas has potential to provide products useful for land management. Areas of the southwestern United States with strong monsoonal (summer moisture) patterns appear to have been the most susceptible to historical woodland expansion, but even here the great majority of extant piñon–juniper has presettlement origins (although widely thickened and infilled historically), and old-growth structure is not uncommon in appropriate upland settings.

Ecological Applications↗

USGS2003

Historic range of variability in landscape structure in subalpine forests of the Greater Yellowstone Area, USA

A measure of the historic range of variability (HRV) in landscape structure is essential for evaluating current landscape patterns of Rocky Mountain coniferous forests that have been subjected to intensive timber harvest. We used a geographic information system (GIS) and FRAGSTATS to calculate key landscape metrics on two ???130,000-ha landscapes in the Greater Yellowstone Area, USA: one in Yellowstone National Park (YNP), which has been primarily shaped by natural fires, and a second in the adjacent Targhee National Forest (TNF), which has undergone intensive clearcutting for nearly 30 years. Digital maps of the current and historical landscape in YNP were developed from earlier stand age maps developed by Romme and Despain. Maps of the TNF landscape were adapted from United States Forest Service Resource Information System (RIS) data. Key landscape metrics were calculated at 20-yr intervals for YNP for the period from 1705-1995. These metrics were used to first evaluate the relative effects of small vs. large fire events on landscape structure and were then compared to similar metrics calculated for both pre- and post-harvest landscapes of the TNF. Large fires, such as those that burned in 1988, produced a structurally different landscape than did previous, smaller fires (1705-1985). The total number of patches of all types was higher after 1988 (694 vs. 340-404 before 1988), and mean patch size was reduced by almost half (186 ha vs. 319-379 ha). The amount of unburned forest was less following the 1988 fires (63% vs. 72-90% prior to 1988), yet the number of unburned patches increased by nearly an order of magnitude (230 vs. a maximum of 41 prior to 1988). Total core area and mean core area per patch decreased after 1988 relative to smaller fires (???73,700 ha vs. 87,000-110,000 ha, and 320 ha vs. 2,123 ha, respectively). Notably, only edge density was similar (17 m ha-1 after 1988) to earlier landscapes (9.8-14.2 m ha-1). Three decades of timber harvesting dramatically altered landscape structure in the TNF. Total number of patches increased threefold (1,481 after harvest vs. 437 before harvest), and mean patch size decreased by ???70% (91.3 ha vs. 309 ha). None of the post-harvest landscape metrics calculated for the TNF fell within the HRV as defined in YNP, even when the post-1988 landscape was considered. In contrast, pre-harvest TNF landscape metrics were all within, or very nearly within, the HRV for YNP While reference conditions such as those identified by this study are useful for local and regional landscape evaluation and planning, additional research is necessary to understand the consequences of changes in landscape structure for population, community, ecosystem, and landscape function.

Landscape Ecology↗

USGS2003

Using tree recruitment patterns and fire history to guide restoration of an unlogged ponderosa pine/Douglas‐fir landscape in the southern Rocky Mountains after a century of fire suppression

Tree age and fire history were studied in an unlogged ponderosa pine/Douglas‐fir ( Pinus ponderosa/Pseudotsuga menziesii ) landscape in the Colorado Front Range mountains. These data were analysed to understand tree survival during fire and post‐fire recruitment patterns after fire, as a basis for understanding the characteristics of, and restoration needs for, an ecologically sustainable landscape. Comparisons of two independent tree age data sets indicated that sampling what subjectively appear to be the five oldest trees in a forest polygon could identify the oldest tree. Comparisons of the ages of the oldest trees in each data set with maps of fire history suggested that delays in establishment of trees, after stand‐replacing fire, ranged from a few years to more than a century. These data indicate that variable fire severity, including patches of stand replacement, and variable temporal patterns of tree recruitment into openings after fire were major causes of spatial heterogeneity of patch structure in the landscape. These effects suggest that restoring current dense and homogeneous ponderosa pine forests to an ecologically sustainable and dynamic condition should reflect the roles of fires and variable patterns of tree recruitment in regulating landscape structure.

Forestry↗