Geography – Vegetation and soils in arid environments | e-Consult

Limited nutrient cycling in nutrient-poor environments is a fundamental driver of low biodiversity. In such environments, essential nutrients are locked up in biomass and unavailable for uptake by producers. This creates a strong selective pressure, favouring organisms that are highly efficient at nutrient acquisition and retention. The lack of readily available nutrients restricts the biomass production of plants, which forms the base of the food chain. This, in turn, limits the number of herbivores that can be supported, and consequently, the diversity of carnivores.

Example 1: Boreal Forests (Taiga)

Boreal forests are characterized by cold temperatures, a short growing season, and acidic soils with slow decomposition rates. The slow decomposition means nutrients are held up in the litter layer, making them unavailable to plants. This limits plant growth to slow-growing, often coniferous species like pines and spruces, which are adapted to conserve nutrients. The limited plant diversity restricts the range of herbivores (e.g., caribou, moose) that can thrive. Consequently, the predator diversity is also low. The slow nutrient cycling also impacts soil microbial communities, further limiting nutrient availability.

Example 2: Tropical Podsol Soils

Tropical Podsol soils are highly weathered and acidic, resulting in low nutrient availability, particularly phosphorus and magnesium. This limits plant growth and leads to a relatively simple vegetation structure, often dominated by grasses and shrubs. The low plant diversity restricts the diversity of herbivores and the predators that depend on them. The nutrient-poor soils also affect the decomposition rates of organic matter, further hindering nutrient cycling. The lack of nutrient availability also limits the diversity of soil organisms.

In both examples, the limited nutrient cycling creates a negative feedback loop: low nutrient availability leads to low biomass production, which in turn limits the diversity of organisms that can survive. While other factors like climate and competition also play a role, the constraints imposed by nutrient availability are often the primary determinants of low biodiversity in these environments. The degree to which nutrient cycling is limited varies, but the fundamental principle remains the same.