Environmental Problems, Their Causes, and Sustainability 1

transmissible disease A disease that iscaused by living organisms (such as bacteria,viruses, and parasitic worms) and canspread from one person to another by air,water, food, or body fluids (or in some casesby insects or other organisms). Comparenontransmissible disease.transpiration Process in which water isabsorbed by the root systems of plants,moves up through the plants, passesthrough pores (stomata) in their leaves orother parts, and evaporates into the atmosphereas water vapor.tree farm See tree plantation.tree plantation Site planted with oneor only a few tree species in an evenagedstand. When the stand matures it isusually harvested by clear-cutting andthen replanted. These farms normally areused to grow rapidly growing tree speciesfor fuelwood, timber, or pulpwood. Seeeven-aged management. Compare old-growthforest, second-growth forest, uneven-agedmanagement.trophic level All organisms that are thesame number of energy transfers away fromthe original source of energy (for example,sunlight) that enters an ecosystem. Forexample, all producers belong to the firsttrophic level, and all herbivores belong tothe second trophic level in a food chain or afood web.troposphere Innermost layer of the atmosphere.It contains about 75% of the massof earth’s air and extends about 17 kilometers(11 miles) above sea level. Comparestratosphere.true cost See full cost.ultraplankton Photosynthetic bacteria nomore than 2 micrometers wide.undergrazing Reduction of the net primaryproductivity of grassland vegetationand grass cover from absence of grazing forlong periods (at least 5 years). Compareovergrazing.undernutrition Consuming insufficientfood to meet one’s minimum daily energyneeds for a long enough time to causeharmful effects. Compare malnutrition,overnutrition.undiscovered resources Potential suppliesof a particular mineral resource,believed to exist because of geologic knowledgeand theory, although specific locations,quality, and amounts are unknown.Compare identified resources, reserves.uneven-aged management Method of forestmanagement in which trees of differentspecies in a given stand are maintained atmany ages and sizes to permit continuousnatural regeneration. Compare even-agedmanagement.upwelling Movement of nutrient-rich bottomwater to the ocean’s surface. This canoccur far from shore but usually occursalong certain steep coastal areas where thesurface layer of ocean water is pushed awayfrom shore and replaced by cold, nutrientrichbottom water.urban area Geographic area with a populationof 2,500 or more. The number of peopleused in this definition may vary, withsome countries setting the minimum numberof people at 10,000–50,000.urban growth Rate of growth of an urbanpopulation. Compare degree of urbanization.urbanization See degree of urbanization.urban sprawl Growth of low-densitydevelopment on the edges of cities andtowns. See smart growth.utilitarian value See instrumental value.vertebrates Animals that have backbones.Compare invertebrates.volcano Vent or fissure in the earth’s surfacethrough which magma, liquid lava, andgases are released into the environment.warm front The boundary between anadvancing warm air mass and the coolerone it is replacing. Because warm air is lessdense than cool air, an advancing warmfront rises over a mass of cool air. Comparecold front.water cycle See hydrologic cycle.waterlogging Saturation of soil with irrigationwater or excessive precipitation sothat the water table rises close to the surface.water pollution Any physical or chemicalchange in surface water or groundwaterthat can harm living organisms or makewater unfit for certain uses.watershed Land area that delivers water,sediment, and dissolved substances viasmall streams to a major stream (river).water table Upper surface of the zone ofsaturation, in which all available pores inthe soil and rock in the earth’s crust arefilled with water.watt Unit of power, or rate at which electricalwork is done. See kilowatt.weather Short-term changes in the temperature,barometric pressure, humidity,precipitation, sunshine, cloud cover, winddirection and speed, and other conditions inthe troposphere at a given place and time.Compare climate.weathering Physical and chemicalprocesses in which solid rock exposed atearth’s surface is changed to separate solidparticles and dissolved material, which canthen be moved to another place as sediment.See erosion.wetland Land that is covered all orpart of the time with salt water or freshwater,excluding streams, lakes, and theopen ocean. See coastal wetland, inlandwetland.wilderness Area where the earth and itscommunity of life have not been seriouslydisturbed by humans and where humansare only temporary visitors.wildlife management Manipulation ofpopulations of wild species (especiallygame species) and their habitats for humanbenefit, the welfare of other species, and thepreservation of threatened and endangeredwildlife species.wildlife resources Wildlife species thathave actual or potential economic value topeople.wild species Species found in the naturalenvironment. Compare domesticatedspecies.windbreak Row of trees or hedgesplanted to partially block wind flow andreduce soil erosion on cultivated land.wind farm Cluster of small to mediumsizedwind turbines in a windy area to capturewind energy and convert it into electricalenergy.worldview How people think the worldworks and what they think their rolein the world should be. See environmentalwisdom worldview, planetary managementworldview, spaceship-earth worldview, stewardshipworldview.zero population growth (ZPG) State inwhich the birth rate (plus immigration)equals the death rate (plus emigration) sothat the population of a geographic area isno longer increasing.zone of aeration Zone in soil that is notsaturated with water and that lies above thewater table. See water table, zone of saturation.zone of saturation Area where all availablepores in soil and rock in the earth’scrust are filled by water. See water table, zoneof aeration.zoning Regulating how various parcels ofland can be used.zooplankton Animal plankton. Smallfloating herbivores that feed on plantplankton (phytoplankton). Comparephytoplankton.GLOSSARYG19