<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="1156" name="terrestrial ecosystems" parent="319" scope="Communities of living organisms in a specific geographical location which exist primarily on land and not in water."/><uf><usefor name="rangeland ecosystems"/></uf><bt><term thcode="2" code="319" name="ecosystems" parent="921" scope="The interacting populations of plants, animals, and  microorganisms occupying a certain area, and their relationship to the environment."/><term thcode="2" code="921" name="population and community ecology" parent="1174" scope="Interactions of a single species (population) or an association of different species (community) occupying a particular region, including their biotic and abiotic environments."/><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="174" name="coastal ecosystems" parent="1156" scope="Biological communities and habitats within the narrow zones of land between the margin of oceans or seas and large landmasses."/><term thcode="2" code="245" name="desert ecosystems" parent="1156" scope="Biological communities and habitats in arid areas with little precipitation, sparse, highly adapted vegetation, and extreme temperatures."/><term thcode="2" code="410" name="forest ecosystems" parent="1156" scope="Biological communities and habitats in geographic areas with dense growths of trees and associated vegetation."/><term thcode="2" code="499" name="grassland ecosystems" parent="1156" scope="Biological communities and habitats with ground cover of grasses and other herbaceous plants, but few trees.  Examples include prairies, meadows, and savannas."/><term thcode="2" code="1706" name="island ecosystems" parent="1156" scope="Communities of living organisms on islands."/><term thcode="2" code="1059" name="shrubland ecosystems" parent="1156" scope="Biological land communities and habitats with sparse, low-growing vegetation."/><term thcode="2" code="1196" name="tundra ecosystems" parent="1156" scope="Biological communities and habitats located in the treeless plains of Arctic regions where the subsoil is permanently frozen."/></nt><rt><term thcode="2" code="311" name="ecology" parent="650" scope="Study of the relations between living plants and animals and their environment."/><term thcode="2" code="2289" name="state and transition modeling" parent="2286" scope="Modeling of systems such as ecosystems to predict the consequences of natural events and management actions by describing how specified events and actions may change the components and relationships in the system."/><term thcode="2" code="1326" name="wetland ecosystems" parent="319" scope="Ecosystems whose soil is saturated for long periods seasonally or continuously, including marshes, swamps, and ephemeral ponds.  More detailed terms for wetlands can be selected from the FGDC Wetland Classification &lt;http://fgdc.gov/standards/status/sub3_4.html&gt;."/></rt></descriptor>