Refers to the type of environment in which an organism or species occurs, as defined by its physical properties (e.g., rainfall, temperature, topographic position, soil texture, soil moisture) and its chemical properties (e.g., soil acidity, concentrations of nutrients and toxins, oxidation reduction status). Some authors include broad biological characteristics in their definitions, for instance forest versus prairie habitats, referring to the different types of environments occupied by trees and grasses. Within a given habitat there may be different micro-habitats, for example the hummocks and hollows on bogs or the different soil horizons in forests.