North America, extending from the Arctic to the tropics, encompasses a vast range of distinct ecological communities. This continental scale results in a massive gradient of life, from sparsely populated tundra to dense, complex forests. Determining which of these large regions holds the greatest variety of life requires examining species richness across different latitudes and climates. The objective is to identify the single terrestrial biome on the continent with the highest concentration of distinct plant and animal species.
The Apex of North American Biodiversity
The biome recognized for the highest species richness in North America is the Tropical Wet Forest, often referred to as the tropical rainforest. This hyper-diverse environment is concentrated in Southern Mexico and throughout Central America, extending toward the equator. These forests feature a complex, multi-layered structure characterized by dense, broad-leaved evergreen trees and a towering canopy. This structure creates a consistently shaded, humid environment below, supporting a vast array of life forms. A single hectare of this forest type can contain hundreds of tree species, exceeding the total tree species count for all of temperate North America combined.
Ecological Drivers of Species Density
The exceptional species density of the Tropical Wet Forest results from its unique and stable climatic conditions. These equatorial regions receive the highest, most stable energy input from the sun, enabling continuous photosynthesis and maximum net primary production, which forms the energetic base for complex food webs. The climate is defined by high and consistent precipitation, often exceeding 2,000 millimeters annually, and uniformly warm temperatures (typically 20°C to 27°C). This lack of a cold or dry season provides stable conditions, reducing environmental stress and allowing species to specialize over evolutionary time.
The physical structure of the forest itself contributes significantly to niche creation and species separation. The vertical stratification, consisting of the forest floor, understory, canopy, and emergent layers, provides numerous distinct microhabitats. Different species of plants and animals specialize in each layer, such as epiphytes that grow high in the canopy to access sunlight. While the soil is often nutrient-poor, the complexity of the environment drives speciation and coexistence.
Notable Secondary Biomes
While the Tropical Wet Forest holds the overall continental record, other biomes are recognized as regional hotspots of diversity.
Temperate Deciduous Forest
The Temperate Deciduous Forest, found primarily in Eastern North America, supports a moderate level of species richness, with flora adapting to four distinct seasons. The necessity for trees to shed their leaves in winter limits year-round productivity and overall species count compared to the tropics. Temperate forest plots typically contain fewer than 50 tree species, contrasting sharply with the hundreds found in tropical areas, as seasonal shifts prevent hyper-specialization.
Mediterranean Biome
Another globally recognized area is the Mediterranean Biome, exemplified by the California Floristic Province. This region is distinguished by a unique climate of hot, dry summers and cool, wet winters. Its biodiversity is characterized not by sheer species count alone, but by an exceptionally high degree of endemism, meaning species found nowhere else on Earth. Over 60% of the approximately 3,000 vascular plant species in this area are endemic, having evolved in isolation due to geological and climatic factors.
Pressures on High-Biodiversity Regions
High-biodiversity regions face significant human pressures. The Tropical Wet Forest is vulnerable to habitat fragmentation, driven primarily by agricultural expansion and infrastructure development. Conversion of forest for cattle ranching and cash crops reduces the contiguous habitat necessary for wide-ranging species like the jaguar. This fragmentation isolates populations, making them susceptible to local extinction and reducing genetic diversity.
Climate change introduces further complexity, as rising temperatures and altered rainfall patterns push these ecosystems out of equilibrium. Species in tropical forests, having evolved in stable conditions, are less capable of rapid adaptation to new environmental stresses. Projected decreases in rainfall and temperature increases risk pushing tree communities beyond their ability to adapt, threatening the long-term resilience of this diverse terrestrial biome.