Pacific Southwest: Getting to Know the NEON Domains
This blog series explores each of the 20 NEON ecoclimatic Domains and the field sites within them.
The Sierra Nevada Mountains span 640 km (400 miles) of eastern California, rising from near sea level to more than 4400 m (14,500 ft.). The rugged mountain range is home to 20 wilderness areas; two national monuments; and Yosemite, Sequoia, and Kings Canyon National Parks. They also host all five of the NEON field sites in D17, the Pacific Southwest. The sites are located across the largest elevation gradient in the Observatory, providing a unique opportunity to collect data from the foothills to the higher elevations. They also represent very different land-use models, from cattle grazing to timber production to wilderness recreation.
Defining the Pacific Southwest Domain
The Pacific Southwest is entirely contained within California, encompassing 213,800 km2 (82,540 square miles). It is bounded by the Pacific Ocean on the west and the Great Basin to the east. The Central Valley stretches through the center of the state, in between the Sierra Nevada and the Coast Range.
The two mountain ranges, along with the Central Valley in between, are the defining features for this Domain. Climate and ecosystem characteristics are heavily influenced by the mountains and the proximity of the Pacific Ocean. In the Central Valley and western Sierra Nevada Mountains, the climate is largely Mediterranean with hot, dry summers and cool, wet winters. At higher elevations the climate shifts to alpine, with snow accumulating throughout the winter months. Most of the Central Valley is dependent on this snowpack for water.
The Central Valley is one of the most heavily human-impacted areas in the U.S. The central part of the state was once a diverse mosaic of grasslands, prairie, oak savanna, and riparian wetlands, but has been greatly altered by agriculture and the introduction of non-native herbaceous vegetation, predominately non-native annual grasses. More than 230 different crops are grown in the Central Valley, including tomatoes, almonds, grapes, cotton, and asparagu
A top-down view from Teakettle tower.
In the Sierra Nevada range, where the NEON field sites are located, climate and ecosystems change along the elevation gradient. On the western slope, oak savannas in the lower foothills give way to montane evergreen forests at higher elevations. Lower montane forests, from 760 – 2100 m (2500 – 7000 ft.), feature predominantly Ponderosa pine and Jeffrey pine along with scattered groves of the iconic giant sequoia. In the upper montane forests, 2100 – 2700 m (7000 – 9000 ft.), lodgepole pines, and red firs dominate the canopy. On higher slopes, vegetation consists of subalpine chaparral dominated by low-growing manzanita or ceanothus, while the alpine ecosystems above timberline are characterized by scant populations of herbaceous vegetation with little to no overstory that eventually give way to barren peaks. The eastern side of the range is warmer and drier due to the "rain shadow" effect, which squeezes moisture out of the air as it rises over the peaks.
A diverse range of animal species make their homes in the foothills and mountains of the Sierra Nevada range. Mule deer, black bear, coyotes, and smaller mammals such as rabbits, skunks, grey squirrels, chipmunks, and marmots are just a few of the mammal species found here. There are also dozens of species of endemic and migratory birds found across the domain, including northern goshawk, bald eagle, great grey owl, California spotted owl, pine grosbeak, mountain chickadee, and mountain quail. The southern Sierra Nevada range is home to the California golden trout, the state fish.
Deer in Teakettle Experimental Forest.
The NEON field sites build on a rich history of research in the Sierra Nevada Mountains by the Critical Zone Observatory (CZO) and other organizations and principal investigators. While not all the colocated CZO sites are still active at the NEON field site locations, researchers are able to tap into these historical data and compare them with data collected by NEON over the next three decades. The combined data provide a robust view of how these ecosystems have changed and are continuing to change over time.
Domain 17 has five field sites: three terrestrial and two aquatic.
San Joaquin Experimental Range
Soaproot Saddle and Upper Big Creek
Soaproot Saddle and Upper Big Creek, about 56 km (35 mi.) northeast of Fresno, represent the middle elevation for the Sierra Nevada sites and are situated along the rain-snow transitional area of the gradient. Both sites sit within the Kings River watershed. This area was famous for its Ponderosa pine forests, with vast stands interspersed with incense cedar, canyon live oak and California black oak, and an understory of dense manzanita. However, pine bark beetles, drought, and recent wildfires have heavily impacted the forest ecosystem.
Lower Teakettle Forest and Teakettle Creek
Monitoring Tree Mortality, Drought, and Fire in the Pacific Southwest
Climate change and human activity have combined to put significant stress on Southern Pacific ecosystems. The most visible sign of change in California is vast swaths of dead and dying trees. The U.S. Forest Service estimates that more than 129 million trees have died in California's national forests since 2010.
A meadow in Teakettle Forest in late summer.
For the conifer forests of the Sierra Nevada Mountains, prolonged drought conditions and a population explosion of damaging bark beetles have combined to decimate millions of acres of pine and fir forest. Bark beetles are native to California, but warmer winters have allowed populations to flourish. At the same time, the Pacific Southwest has seen intensifying drought conditions over the last two decades. The region experienced the longest period of sustained drought in recorded history from 2011 – 2017 and entered another period of intensive drought in 2020-21. Trees stressed by drought conditions are weakened and less able to survive a bark beetle infestation, leading to higher levels of tree mortality.
California trees are also threatened by Sudden Oak Death , a disease caused by a fungal pathogen. Sudden Oak Death threatens several oak species and relatives, primarily along the coastline of central and northern California and southern Oregon.
Big Creek in early winter.
Tree mortality is dramatically changing ecosystems in the Sierra Nevada Mountains. The loss of canopy trees such as Ponderosa, lodgepole, and Jeffrey pine create an opening for other types of vegetation cover to take over, including shrubs (such as manzanita) and grasses. It is unclear how these landscapes will evolve over time.
Stands of dead trees and new biomass from fast-growing woody shrubs and grasses create the perfect conditions for the large wildfires that have plagued the region in recent years. While fire has always been part of the native ecosystem, these conditions allow fires to spread further and become hotter, higher, and more intense, threatening even fire-resistant species such as the giant sequoia.
An area within the burn scar of the Creek Fire (2020) which directly impacted Domain 17 field sites.
Drought and a warming climate also impact the amount of snowpack that accumulates in the mountain peaks. The snow-rain transition zone is slowly moving up the mountainsides, and a smaller snowpack is accumulating on the peaks during the winter months. This has critical implications for the entire watershed of the western Sierra Nevada range and the Central Valley, which relies on snowmelt for much of its water supply through the spring and summer months. Water availability is expected to be a growing issue for the region in the coming years and could have profound impacts on agricultural productivity. The NEON field sites are well positioned to collect data along the elevation gradient for the Sierra Nevada watershed.
