Geology topics

Margot W. Kaye

Publications and source records attributed to Margot W. Kaye.

5 recordsLinked to original sources

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↗

USGS2017

Variability of dissolved organic carbon in precipitation during storms at the Shale Hills Critical Zone Observatory

Organic compounds are removed from the atmosphere and deposited to the earth's surface via precipitation. In this study, we quantified variations of dissolved organic carbon (DOC) in precipitation during storm events at the Shale Hills Critical Zone Observatory, a forested watershed in central Pennsylvania (USA). Precipitation samples were collected consecutively throughout the storm during 13 events, which spanned a range of seasons and synoptic meteorological conditions, including a hurricane. Further, we explored factors that affect the temporal variability by considering relationships of DOC in precipitation with atmospheric and storm characteristics. Concentrations and chemical composition of DOC changed considerably during storms, with the magnitude of change within individual events being comparable or higher than the range of variation in average event composition among events. While some previous studies observed that concentrations of other elements in precipitation typically decrease over the course of individual storm events, results of this study show that DOC concentrations in precipitation are highly variable. During most storm events concentrations decreased over time, possibly as a result of washing out of the below-cloud atmosphere. However, increasing concentrations that were observed in the later stages of some storm events highlight that DOC removal with precipitation is not merely a dilution response. Increases in DOC during events could result from advection of air masses, local emissions during breaks in precipitation, or chemical transformations in the atmosphere that enhance solubility of organic carbon compounds. This work advances understanding of processes occurring during storms that are relevant to studies of atmospheric chemistry, carbon cycling, and ecosystem responses.

Pennsylvania↗

USGS2016

Expansion of forest stands into tundra in the Noatak National Preserve, northwest Alaska

Temperatures across the northern regions of North America have been increasing for 150 years, and forests have responded to this increase. In the Noatak National Preserve in Alaska, white spruce (Picea glauca [Moench] Voss) forests reach their northern limit, occurring primarily on well-drained sites and as gallery forests along streams. Rolling plateaus of tundra separate the white spruce forests into disjunct stands. We examined patterns of tree age, tree growth, and tree encroachment into tundra ecosystems in six stands along the Agashashok River. Warming over the past 150 years appears to have increased tree growth and resulted in forest expansion into adjacent tundra ecosystems. The forest/tundra ecotone shifted by about 80 to 100 m into the tundra in the past 200 years, as evidenced by declining maximum tree age with distance towards the tundra. The decadal-scale pattern of tree establishment at the farthest extent of trees into the tundra (the tundra-forest ecotone) correlated with the detrended growth index for trees within the forests; climate conditions that led to higher tree growth appeared to foster tree establishment in the tundra. This recent forest expansion has occurred across topographic boundaries, from well-drained soils on slopes onto poorly drained, flatter areas of tundra. Further expansion of the forests may be limited by more severe wind exposure and poor drainage that make the majority of tundra less suitable for trees.

Écoscience↗

USGS2003

Aspen structure and variability in Rocky Mountain National Park, Colorado, USA

Elk, fire and climate have influenced aspen populations in the Rocky Mountains, but mostly subjective studies have characterized these factors. A broad-scale perspective may shed new light on the status of aspen in the region. We collected field measurements of aspen (Populus tremuloides Michx.) patches encountered within 36 randomly located belt transects in 340 km2 of Rocky Mountain National Park, Colorado, to quantify the aspen population. Aspen covered 5.6% of the area in the transects, much more than expected based on previously collected remotely sensed data. The distribution and structure of aspen patches were highly heterogeneous throughout the study area. Of the 123 aspen patches encountered in the 238 ha surveyed, all but one showed signs of elk browsing or had conifer species mixed with the aspen stems. No significant difference occurred in aspen basal area, density, regeneration, browsing of regeneration and patch size, between areas of concentrated elk use (elk winter range) and areas of dispersed elk use (elk summer range). Two-thirds of the aspen patches were mixed with conifer species. We concluded that the population of aspen in our study area is highly variable in structure and that, at a landscape-scale, evidence of elk browsing is widespread but evidence of aspen decline is not.

Landscape Ecology↗

USGS2000

Using new video mapping technology in landscape ecology

Biological and ecological monitoring continues to play an important role in the conservation of species, natural communities, and landscapes ( Spellerberg 1991 ). Although resource-monitoring programs have advanced knowledge about natural ecosystems, weaknesses persist in our ability to rapidly transfer landscape-scale information to the public. Ecologists continue to search for new technologies to address this problem and to communicate natural resource information quickly and effectively. New video mapping technology may provide much-needed help. Ecologists realize that only a small portion of large nature reserves can be monitored because of cost and logistical constraints. However, plant and animal populations are usually patchily distributed in subpopulations scattered throughout heterogeneous landscapes, and they are often associated with rare habitats. These subpopulations and rare habitats may respond differently to climate change, land use, and management practices such as grazing, fire suppression, prescribed burning, or invasion of exotic species ( Stohlgren et al. 1997b ). In many national parks, monuments, and wildlife reserves, a few long-term monitoring plots are used to infer the status and trends of natural resources in much larger areas. To make defensible inferences about populations, habitats, and landscapes, it is necessary to extrapolate from a few monitoring plots (local scale) to the larger, unsampled landscape with known levels of accuracy and precision. Recent technological developments have given population biologists and landscape ecologists a unique tool for bridging the data gap between small, intensively sampled monitoring plots and the greater landscape and for transferring this information quickly to resource managers and the public. In this article, we briefly describe this tool, a hand-held video mapping system linked to a geographic information system (GIS). We provide examples of its use in quantifying patterns of native and exotic plant species and cryptobiotic crusts in the new Grand Staircase–Escalante National Monument, Utah, and in surveying aspen clones and regeneration in Rocky Mountain National Park, Colorado.

BioScience↗