The overall research focus of the CSUSM Terrestrial Ecosystem Research Lab (TERL) is to evaluate how human activities affect the structure and function of terrestrial ecosystems. Humans are rapidly and profoundly altering the earth’s atmosphere, climate, and land surface, and these changes have the capacity to affect the carbon (C) and nutrient cycling and storage, plant species composition and diversity, and energy balance of terrestrial ecosystems. To understand how these human activities have altered terrestrial ecosystems, research at the TERL has focused on two main topics:
The central goal of this project is to determine if chronic exposure to experimental nitrogen (N) deposition leads to irreversible changes in the structure and function of semiarid shrublands. Atmospheric N deposition from human activities has significantly increased since the beginning of the industrial revolution. In southern California, nitrogen oxides (NOx) released from automobile exhaust make up the largest contribution to N deposition. Because of air flow patterns and high population density, Mediterranean-type shrublands (chaparral and coastal sage scrub) in urban areas of the Southern California have been exposed to 25-50 kgN ha-1 y-1 for decades. Most of these NOx (ca. 85-90%) fall as dry deposition during the summer when atmospheric inversion conditions trap pollutants near the land surface. This deposited N accumulates on plant and soil surfaces until the first rainfall event, which occurs in the fall or early-winter, causing a large and transient pulse of N to urban shrublands. Because chaparral shrubs are thought to be N limited, these large N inputs have the potential to alter the structure and function of these semi-arid shrublands.
Field manipulative experiments were initiated in September 2002 at two chaparral sites in southern California. Santa Margarita Ecological Reserve (SMER) and the Sky Oaks Field Station (SOFS). SMER is a coastal sage scrub (CSS) stand located in SW Riverside County, California, USA at an elevation of 338 m on a 9-11o S-SW facing slope that is dominated by the semi-deciduous shrubs Artemisia californica Less. (California Sage) and Salvia mellifera Greene (Black Sage). SOFS is a chaparral stand located in NE San Diego County, California, USA at an elevation of 1418 m on a 4-10o SE-SW facing slope that is dominated by the evergreen shrub Adenostoma fasciculatum H. & A. (Chamise). The effects of dry-season N input at both sites is evaluated by a manipulative experiment where four-10 x 10 m plots receive 50 kgN/ha (added N) and an additional four-10 x 10 m plots serve as un-manipulated controls. Nitrogen has been added annually during the dry season because the majority of N deposition (85-90%) in southern California falls as dry deposition during the summer.
Chronic N inputs have altered every aspect of the terrestrial ecosystem, including soil chemistry (pH and nutrient availability), aboveground plant growth, plant species diversity, and rates of N loss from leaching and gaseous emission; however, the effects of N enrichment vary over time. While this research is ongoing, the long-term focus of this research has shed light on how ecosystem responses to chronic perturbations may be short-lived or even lagged over time.
These experiments have been supported by the US National Science Foundation (NSF), National Institutes of Health (NIH), and the United States Department of Agriculture (USDA-NIFA). Results have been published in a variety of scientific journals. These papers are available in the publications page of the TERL website.
Brazilian savanna (locally known as Cerrado, which is the Portuguese word for “dense,” “thick,” or “closed), covers approximately 1.5-2 million km2, or 20-25% of the total land cover of Brazil, and is the second largest vegetation type following Amazonian forest. Over the last several decades, Cerrado has faced multiple human threats to ecosystems structure and function from agricultural expansion and fragmentation, disturbance (primarily fire), climate and land-cover change, and atmospheric deposition. Estimates of cerrado clearing by 1990 ranged from 40-80%, predominantly in response to governmental programs aimed at developing managed pasture and crop agriculture. This is especially true in the state of Mato Grosso, where much of the land-cover change is fueled by logging (both legal and illegal), pasture development, and soybean, corn, and rice production. These practices, while increasing short-term economic gain and material goods, may undermine ecological services over local, regional, and global scales in the long-term. Thus, research on tropical ecosystem ecology, such as processes that affect C, water, and nutrient storage and cycling, is essential for assessing how land-cover change and land-use affect soil, air, and water resources and the potential for ecosystem degradation.
Since 1999, research at TERL, together with faculty and students of the Post-Graduate
Program in Environmental Physics of the Universidade Federal de Mato Grosso (UFMT-PGFA)
has been assessing the impacts of climate variation and land use on the C, water,
and nutrient cycling of Amazonian forests, upland Cerrado, and seasonally flooded
Cerrado of Mato Grosso. Current research is conducted in the Cuiaba Basin and the
Pantanal of southern Mato Grosso, Brazil. Ecosystem C and nutrient storage and cycling
is assessed in forest and woodland fragments with intensive ground-based field research
activities, while whole-ecosystem C and water vapor exchange is measured using a micrometeorological
approached known as “eddy covariance.” Spatial patterns of ecosystem structure and
function are linked to spectral data measured from satellites (LandSat and MODIS)
while temporal variations are linked to climate and hydrological data measured on
Cerrado structure (tree density and species composition) and function (tree growth, C storage) are closely related to soil fertility. In addition, these ecosystems are very sensitive to drought stress that occurs seasonally and over annual time scales such as during El Niño. Thus, warming and drying in response to climate change will likely increase tree mortality and reduce the productivity of Cerrado.
This research has been supported by the US National Science Foundation (NSF), the National Geographic Society, and several Brazilian Federal and State research foundations. Results have been published in a variety of scientific journals. These papers are available in the publications page of the TERL website.