Biomes are not typically classified by temperature alone because temperature is just one of several interacting environmental factors that shape where organisms can live. A robust biome classification considers multiple dimensions of climate and habitat, not just heat or cold. Key factors in biome classification
- Precipitation: Amount, seasonality, and reliability of rainfall strongly influence plant communities, water availability, and fire regimes. For example, deserts and tropical rainforests can share high temperatures but differ markedly in rainfall, leading to very different biomes.
- Temperature patterns: While average temperature matters, the range and seasonality (how much temperatures vary within a year) are also crucial. Some biomes experience relatively stable temperatures year-round, while others have pronounced seasonal shifts that affect vegetation and animal life.
- Vegetation and productivity: The dominant plant form (trees, grasses, shrubs) and the density of vegetation determine habitat structure, microclimates, and food resources, which in turn shape animal communities and ecosystem processes.
- Soil and nutrients: Soil type, depth, fertility, and drainage influence which plant species can establish and persist, thus helping delineate biome boundaries (even when temperatures might be similar).
- Disturbance regimes: Fire, drought, frost, and grazing pressure interact with climate to influence succession and community composition, contributing to biome distinctions beyond temperature alone.
- Geography and altitude: Elevation and latitude modify climate and moisture, creating gradients where temperature alone would be misleading if used to define distinct biomes.
- Energy input and seasonality: The combination of solar energy, precipitation pattern, and their seasonal timing defines productivity and community structure, leading to different biomes even under similar mean temperatures.
Why temperature-only schemes are insufficient
- Convergent climates: Similar mean temperatures can support different biomes if precipitation or soil conditions differ (e.g., hot deserts vs. hot savannas, both warm but with different rainfall and vegetation).
- Divergent climates: Biomes with similar temperatures can be separated by distinct moisture or disturbance histories, yielding different organisms and ecosystems.
- Temporal variability: Diurnal and interannual temperature fluctuations can have significant ecological effects that a single average temperature value cannot capture.
Common approaches to biome classification
- Global climate-vegetation classifications often use combinations of temperature and precipitation, sometimes summarized as climate zones, rainfall regimes, or aridity indices, to group regions into biomes or climate-biome categories.
- Whittaker’s biome classification prominently used average annual precipitation and average annual temperature as primary axes, but it explicitly acknowledged that other factors modulate outcomes and boundaries.
In short, temperature matters, but biome boundaries reflect an integrated signal from moisture, energy, soils, disturbance, and geography. Using multiple factors yields a more accurate and ecologically meaningful taxonomy of biomes.
