Alexandra Orrego

Years participated in RESESS: 2017, 2016

An Overview

Major: Geoscience

Academic Affiliation: Georgia State University


Growing up in the forested areas of North Georgia, Alexandra always maintained an appreciation for the Earth and its environment. During her first year as an undergraduate she realized that her love for the environment could become a career. Since solidifying her studies in Geoscience she is interested in technologies such as GIS, and applying these technologies to investigate changes in the environment that may have hazardous consequences to the Earth, ecology, and humans. She hopes to pursue a graduate degree in environmental engineering. This summer Alexandra analyzed spatial and temporal patterns of accelerating tree mortality rates in subalpine forests located in the Rocky Mountain eco region. Because observed trends of accelerating tree mortality have been identified all around the world, her results will help in forecasting the future of forest ecosystems globally.


2016- Broad Scale Patterns in Subalpine Fir Mortality Across the U.S. Rocky Mountains

Rising concerns about warming climate and trends in increased rates of tree mortality detected in forest ecosystems globally have sparked studies in determining specific causes for tree mortality. This study analyzes spatial and temporal patterns of tree killing agents in the subalpine forests of the Rocky Mountain eco region in order to determine what drivers are causing such accelerated tree mortality events in Subalpine fir trees (ABLA). Although significant research in subalpine forests has been done to addresses pine tree mortality induced by Mountain Pine Beetle outbreaks and spruce tree mortality induced by spruce beetle outbreaks, the third dominant species of subalpine forests, the subalpine fir tree, has received less attention, while its mortality rates have also increased. Thus a spatially expansive study of relationships between pine, spruce, and subalpine fir mortality is necessary to understand overall accelerating tree decline. With the use of United States Forest Service (USFS) aerial detection surveys (ADS) from 1994-2015, we are able to extrapolate presence/absence distribution analyses using Geographic information Systems (GIS) of the forested study area in which we determine likelihood of co-occurrence of subalpine fir mortality (SFM) versus abiotic/biotic factors. A progression from inclusive, exclusive, to focal scale testing allowed us to detect the appropriate spatial scale/extent to produce meaningful ecological correlations of tree mortality drivers in subalpine forests. Counter-intuitively to climate warming effects, areas of significant SFM are occurring in historically cool and wet environments as opposed to forest sites directly exposed to high amounts of heat. With the results of this study we are able to determine interrelated patterns of drivers that may be indirectly/directly inducing tree mortality in subalpine forest, which will help forecast what is imminent in these forest ecosystems.

2017- Are Hotspots of Biotic Disturbances Increasing in Western U.S. Forests (1997-2016)?

In recent decades, unprecedented outbreaks of biotic disturbances such as insects and pathogens across Western U.S. forests have raised concerns on how a warming climate may continue to affect and alter forest ecosystems. While much research has focused on the dynamics of single biotic disturbances, less is known about the spatial patterns and temporal trends of interacting biotic disturbances in these forests. It is important to understand spatiotemporal trends of co-occurring biotic disturbances, as it may be an indication of a lowered ability for ecological compensation, which may hinder affected forests ability to survive biotic disturbances in the future. More specifically, this study analyzes spatial and temporal patterns of biotic disturbances in western U.S forests and the occurrence of “hotspots” – two or more spatially and temporally intersecting biotic disturbances. Using geographic information systems (GIS) and the United States Forest Service (USFS) Aerial Detection survey (ADS) data from 1997-2016 we ask if hotspots of biotic disturbances are increasing over time, and we assess the spatial distribution of hotspots across western U.S. forests. We found that hotspots of intersecting biotic disturbances in the same year have been increasing exponentially over the past 2 decades. Overall, 30% of affected forested area in the western U.S. is experiencing hotspots. Spatially, hotspots tend to be along mountainous areas of middle to high elevations along The Cascade, The Rocky Mountain, and Sierra Nevada ranges whereas, cold spots occur generally along the Pacific coast and in arid, inland regions. Identifying hotspots is important in order to aid in further investigation of the mechanisms that drive interacting biotic disturbances in an increasingly warming and drying climate.


Broad Scale Patterns in Subalpine Fir Mortality Across the U.S. Rocky Mountains

Are Hotspots of Biotic Disturbances Increasing in Western U.S. Forests (1997-2016)?