Currents OnLine: Q: What is the difference between an ecosystem, biomass, and habitat? A: Ah, thank you for this classic ecology textbook question. Are these words like a good vintage wine, getting better with age? Let us see. For the sake of ease to our readers, I will go from the bottom in terms of size – biomass, then habitat, and finally, ecosystem. Biomass is a measure of how much biological material is in a given area. We can limit it to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in a community, including microorganisms, plants and animals. When we measure carbon, which is important for quantifying the global carbon cycle, the definition is refined to include all organically-bound carbon, whether it is alive or dead. This includes decayed or partially-decayed plant, animal, and microorganism material in the soil, which in the northern latitudes, accounts for a large amount of stored carbon biomass. A habitat describes the natural environment in which an organism lives, or the physical environment that surrounds a species population. For example, the habitat of a purple coneflower is prairie or savannah with lots of sunlight and well-drained soils. Finally, an ecosystem consists of all plants, animals and micro-organisms in a discrete area together with all of the non-living physical factors of the environment, including topography, soil type, and climate. How do these concepts connect together? An ecosystem is, in theory, a completely independent unit from other ecosystems and has interdependent organisms which share the same habitat. The biomass within this ecosystem can be estimated from direct measurements at small, discrete, geographic units which are then scaled up to the entire area of an ecosystem. Clear as mud? I thought so. While the biomass of an organism or a community is somewhat easily measured, the problems with ecosystems are their boundaries. Organisms do not often stay confined within a defined area, and ecosystem boundaries can be blurry when you look closely at them. The best we can do is come to a reasonable estimation from isolating the species, populations, and communities. Let’s bring it closer to home. To measure the biomass of Riverwest, we would start at the Milwaukee River, go west to Holton, north to Capitol and south to North Avenue. We would measure the mass of all the humans, dogs, cats, and other pets, birds and other wildlife, soil biomass, trees, gardens, home material, interior furniture and materials made of wood, bamboo, hemp, or other plant material, including – yes – whatever mold and fungus is growing in your basement. The Riverwest habitat can be described as an urban, wooded parcel adjacent to the Milwaukee River. Riverwest’s ecosystem is part of the Southeastern Wisconsin watershed that runs from Racine north to Sheboygan County and west to the Great Lake Basin divide along the Waukesha County boundary. We could also count ourselves within the entire Great Lakes Basin ecosystem from Minnesota and Canada to parts of Illinois, Indiana, Ohio and New York, or even the Northern Great Plains ecosystem from here to the Dakotas. Send your ecological inquiries to our resident ecologist at .