An ecosystem is characterized by its collection of species, the physical environment in which these species live, and the sum total of their interactions, with each other and with their shared environment.
Tropical rainforests, coral reefs, and freshwater marshes are examples of ecosystems. The Earth’s ecosystems provide goods and services that sustain all life on this planet, including human life. Tragically humanity often takes these services, delivered free of charge, for granted.
Ecosystem services are commonly divided into four categories:
1. provisioning services like supplying food, fuel, and medicines;
2. regulating services like purifying air and water, mitigating floods, and detoxifying soils;
3. cultural services that meet our aesthetic, spiritual, and intellectual needs;
4. and supporting services, which make possible all other ecosystem services, and include: pollination, nutrient cycling, and the photosynthetic capture of the sun’s energy and production of biomass by plants (called “primary production”).
While we know a great deal about how many ecosystems function, they often involve such complexity and are on a scale so vast that humanity would find it impossible to substitute for them, no matter how much money was spent in the process. Examples are: the breakdown and decomposition of dead organisms and wastes; the recycling of nutrients for new life on land, in rivers, lakes, and streams, and in the oceans; and the regulation of climate.
A temperate forest well illustrates the abundance and complexity of the services ecosystems may provide. Temperate forests: serve as sinks for CO2 by storing carbon in trees and soils, thereby helping to mitigate human-caused climate change; maintain the water cycle and precipitation levels, thereby stabilizing local climates, through the uptake of water by tree roots, transport through the trees, and evaporation from the leaves back to the atmosphere; reduce soil erosion by dampening the power of rain, and by tree roots binding soils; purify air by filtering particulates and providing chemical reaction sites on leaf surfaces where pollutants can be converted into harmless compounds; purify water by soils acting as massive filters that bind toxic substances; provide goods such as timber, medicines, and food; and reduce the risk of some human infectious diseases, such as Lyme disease, when they provide adequate habitats to maintain vertebrate diversity.