What Makes a Forest? Forested Field Sites Across the Observatory

oFrom the conifers of the northern boreal forest to the ʻōhiʻa groves of Hawai'i, there are many different types of forests represented among the NEON field sites. Many of our aquatic sites also run through riparian forests. Altogether, these sites showcase the diversity of forests across the North American continent.

Seeing the Forest for the Trees

There are almost as many definitions for the term "forest" as there are types of forests. The Food and Agriculture Organization (FAO) of the United Nations defines a forest as: "Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ." From an ecological perspective, a forest is a biotic community dominated by trees and containing a complex, interconnected web of plant, animal, microbial, and fungal species. Forests play a crucial role in supporting biodiversity, maintaining the global carbon balance, and providing essential resources such as wood, food, and clean water.

Forest composition, structure, and other characteristics vary widely across regions and more locally depending on elevation, topography, soil conditions, land use and management history, and interrelationships among plant and animal species. Some forests have dense understories that are home to an incredibly wide variety of organisms. Others are dominated by a few species and have a more open structure. Old-growth forests (those that have gone a very long time without significant disturbance events like fires) can look dramatically different than younger, second-growth forests.

The NEON field sites include examples of many different types of forests, representing common or iconic forest types for each zone. These are some examples of the forests you will find across the Observatory.

The Boreal Forest (Taiga)

The boreal forest, or Taiga, is one of the largest biomes on Earth, spanning the northern latitudes across Alaska, Canada, Siberia, and Scandinavia. Boreal forests make up about 30% of the total forested areas globally and play an important role in carbon sequestration. These forests are characterized by:

• A forest canopy dominated by evergreen conifers such as spruce, fir, and pine.
• Cold with long, cool winters with temperatures (often far) below freezing and a short growing season.
• Low to moderate precipitation, with much precipitation coming in the form of snow.
• Relatively low biodiversity, with plant and animal species adapted to cold conditions.

The Taiga Domain (D19) for the NEON program is made up primarily of spruce boreal forests interspersed with birch, poplar, aspen, and other deciduous trees and shrubs. All three D19 terrestrial field sites (Delta Junction, Healy, and Caribou Creek) are mostly or partially forested.

The Temperate Rainforest

The Pacific Northwest (D16) is home to several types of forest but is known for its stunning temperate coniferous rainforests. These forests are characterized by high levels of precipitation, a relatively mild climate, and dense vegetation. The coastal areas of Washington and Oregon are home to temperate rainforests dominated by tall coniferous trees such as Douglas fir, western hemlock, Sitka spruce, and western red cedar. The forested NEON field sites at Wind River Experimental Forest and Abby Road are both excellent examples.

Further south, coniferous temperate forests of the Sierra Nevada Range, in the Pacific Southwest (D17), feature species such as lodgepole pine, Jeffry pine, ponderosa pine, cedar, and red and white fir. This region is also home to the stunning giant sequoia forests, found on the western slopes of the Sierra Nevada range in Central California. Coniferous forests in many parts of the Pacific Southwest have been heavily impacted by drought, wildfire, and beetle activity.

Alpine Forests

Alpine forests are found at high elevations, above the montane forests and below the alpine tundra. Similar to the boreal forests of the Taiga and the northern temperate rainforests, alpine forests in the northern Rockies are composed primarily of coniferous species, which can include a mix of spruce, pine, and fir. Species at these high elevations must be able to withstand harsh alpine conditions, which may include extreme cold and heavy snow in the winter months. Our Yellowstone National Park site spans more than 400 meters of elevation, with pine-dominated forest at the upper elevations and sage and grasslands lower down.

Temperate Deciduous and Mixed Forests

Much of the eastern U.S. is characterized by temperate deciduous and mixed forests. These forests can have significant variation by region as well as locally within regions, with specific forest characteristics heavily impacted by local temperatures, topography, and soil type. Most temperate deciduous and mixed forests boast high levels of biodiversity, with some of the most diverse areas in the U.S. found in the forests of the Appalachians, Ozark Plateau, and the coastal plains of the eastern U.S. Many eastern deciduous and mixed forests feature a dense understory of shrubs and herbaceous vegetation.

The hardwood forests of the Northeast Domain (D01) are comprised of sugar maple, American beech, and yellow birch. In contrast, mixed forests may include broadleaf deciduous trees such as oak, hickory, maple, beech, and birch along with coniferous species like pine, hemlock, and spruce. Bartlett Experimental Forest and Harvard Forest both feature eastern deciduous and mixed forest types.

Oak-hickory and oak-pine forests are common in the Mid-Atlantic region (D02), transitioning to bottomland hardwood forests and bald cypress further south. All three D02 field sites (Smithsonian Conservation Biology Institute, Smithsonian Environmental Research Center, and Blandy Experimental Farm) are partially or mostly forested.

The Great Lakes (D05), Appalachian and Cumberland Plateau (D07), and Ozarks Complex (D08) also feature temperate hardwood and mixed forests with a wide variety of species mixtures.

Southeastern Longleaf Pine Forests

The longleaf pine forests are unique ecosystems found in the southeastern United States (D03, Southeast). Historically, these forests covered a vast area stretching from Virginia to eastern Texas and parts of Florida, encompassing approximately 90 million acres. However, due to logging, agriculture, and urbanization, the longleaf pine ecosystem has been reduced to roughly 3% of its original range, making it one of the most endangered ecosystems in North America. The Jones Center at Ichauway and Ordway-Swisher Biological Station both feature longleaf pine ecosystems that provide important habitat for species such as the endangered red cockaded woodpecker.

Subtropical Dry Forest

Guanica Dry Forest, located in Puerto Rico in the Atlantic Neotropical Domain (D04), is a stunning example of a rare forest type; it is the largest remaining dry tropical coastal forest in the world. While rainforests are more common in subtropical and tropical zones, this dry forest is characterized by a warm climate and low rainfall (~840 mm annually). Vegetation is thick and dense, with more than 700 plant species represented. The forest is divided into three main areas: an upland deciduous forest, a semi-evergreen forest, and a scrub forest near the shore.

Tropical Rainforest

On the far side of Observatory, in the middle of the Pacific Ocean, the Pu'u Maka'ala Natural Area Reserve (NAR) is a tropical rainforest ecosystem. Located in the Pacific Tropical Domain (D20), the NAR features wet 'ōhi'a and koa forests with a dense fern understory. It is one of the most ecologically diverse places in the world, home to many endemic species found nowhere else on Earth.

Riparian Forests

Riparian forests are found along the banks of rivers, streams, and other water bodies. These forests are characterized by the presence of water-loving plant species and are shaped by the interactions between the terrestrial and aquatic environments. Riparian forests play crucial roles in maintaining water quality, stabilizing streambanks, providing habitat for diverse plant and animal species, and supporting overall watershed health. Many of the NEON aquatic sites have riparian forests along their sampling reaches.

The wide and varying forests represented in the NEON repertoire are each stunning and essential in their own ways. Many researchers have used NEON's standardized data to inform their studies and publish papers that could help land managers better understand the importance of these ecosystems and how they may be changing.