Introduction

As part of an effort to map terrestrial ecosystems, the U.S. Geological Survey 

(USGS) has generated isobioclimate classes to be used in creating maps depicting 

standardized, terrestrial ecosystem models for the conterminous United States 

(Sayre and others, 2009), using an ecosystems classification developed by NatureServe (Comer and others, 2003). A biophysical stratification approach, developed 

for South America (Sayre and others, 2008) and now being implemented globally 

(Sayre and others, 2007), was used to model the ecosystem distributions. Bioclimate regimes strongly influence the differentiation and distribution of terrestrial 

ecosystems, and are therefore one of the key input layers in this biophysical 

stratification.

The Rivas-Martínez methodology is based on the concept of establishing a 

quantifiable classification system which would closely relate the distribution of 

vegetation to climatic parameters and indices (Rivas-Martínez and others, 1999). 

This method first establishes bioclimatic indices calculated from various ranges of 

temperature and precipitation data, compares these indices to defined thresholds, 

and finally applies sets of decision rules to identify the climate classes. The climate 

classification is hierarchical with four levels: macrobioclimates, bioclimates, 

thermotypes, and ombrotypes. Thermotypes, which represent thermoclimatic belts, 

are identified using the positive annual temperature (Tp) thresholds or the compensated thermicity index (Itc) thresholds (Rivas-Martínez, 2004; Rivas-Martínez and 

others, 1999, 2004). Ombrotypes, which represent ombroclimatic belts, are based 

on the ombrothermic index (Io) which is calculated as a function of both the total 

positive precipitation and temperature (Rivas-Martínez, 2004; Rivas-Martínez and 

others, 1999, 2004). For this national implementation the source data used for 

establishing the bioclimatic indices was Daymet 

(http://www.daymet.org/dataSelection.jsp). Daymet temperature and precipitation 

data were developed from 18 years (1980–1997) of climatological records and is 

available at a spatial resolution of 1 kilometer (Thornton, 1997). This implementation of the Rivas-Martínez methodology resulted in the generation of four climate 

layers for the conterminous United States: macroclimates, bioclimates, thermotypes, and ombrotypes.

However, the biophysical stratification approach used for the ecosystems 

modeling effort required a single climate layer that accurately reflected regional 

variation in wet/dry gradients and hot/cold gradients, with a manageable number of 

classes. Therefore, the data layers for thermotypes and ombrotypes were 

combined, yielding 127 unique thermotype-ombrotype combinations.The isobioclimates image shows ombrotypic regions (dry/wet gradients) for each thermotypic 

(warm/cold) region. Additional information about this map and any of the data 

developed for the ecosystems modeling of the conterminous United States is 

available online at http://rmgsc.cr.usgs.gov/ecosystems/.

References Cited:

Comer, Patrick, Faber-Langendoen, Don, Evans, Rob, Gawler, Sue, Josse, Carmen, 

Kittel, Gwen, Menard, Shannon, Pyne, Milo, Reid, Marion, Schulz, Keith, 

Snow, Kristin, and Teague, Judy, 2003, Ecological systems of the United 

States—A working classification of U.S. terrestrial systems: NatureServe, 

Arlington, Va. Accessed Oct. 2008 at 

http://www.natureserve.org/library/usEcologicalsystems.pdf.

Daymet, 2006, Daymet—Daily surface weather and climatalogical summaries: 

Missoula, Mont., University of Montana, Numerical Terradynamic Simulation 

Group (NTSG). Accessed Jan. 2006 at 

http://www.daymet.org/dataSelection.jsp.

Rivas-Martínez, Salvador, 2004, Global Bioclimatics (Clasificación bioclimática de 

la Tierra): Version 27–08–04. Phytosociological Research Center: Madrid, 

University Complutense of Madrid. Accessed Oct. 2008 at 

http://www.globalbioclimatics.org/book/bioc/global_bioclimatics_2.htm#2. 

Rivas-Martínez, Salvador, Sánchez-Mata, Daniel, and Costa, Manuel, 1999, North 

American Boreal and Western Temperate Forest Vegetation (Syntaxonomical 

synopsis of the potential natural plant communities of North America, II): 

Itinera Geobotanica 12:5–316, Phytosociological Research Center, 2001: 

Madrid, University Complutense of Madrid. Accessed Oct. 2008 at: 

http://www.globalbioclimatics.org/book/namerica2/namerica.htm. 

Rivas-Martínez, Salvador, Sánchez-Mata, Daniel, and Costa, Manuel, 2004, 

Synoptical Worldwide Bioclimatic Classification System: Madrid, University 

Complutense of Madrid. Accessed Oct. 2008 at: 

http://www.globalbioclimatics.org/book/bioc/tabla3.htm.

Sayre, Roger, Yanosky, Alberto, and Muchoney, Doug, 2007, Mapping global 

ecosystems—The GEOSS approach: Group on Earth Observations, ed.: 

London, U.K., Tudor Rose.

Sayre, Roger, Bow, J., Josse, C., Sotomayor, L., and Touval, J., 2008, Terrestrial 

ecosystems of South America, Campbell, J.C., Jones, K.B., and Smith, J.H., 

eds., in North America Land Cover Summit—A Special Issue of the Association of American Geographers: Association of American Geographers, p. 

131–152.

Sayre, Roger, Comer, Patrick, Warner, Harumi, and Cress, J.J., 2009, A new map of 

standardized terrestrial ecosystems of the conterminous United States: U.S. 

Geological Survey Professional Paper 1768, 17 p. Accessed July 20, 2009 at 

http://pubs.usgs.gov/pp/1768.

Thornton, P.E., 1997, Daymet—Climatological summaries for the conterminous 

United States, 1980–1997, User’s Guide: Missoula, University of Montana. 

Accessed Oct. 2008 at: http://www.daymet.org/daymetus_userguide.pdf.

Thornton, P.E., Running S.W., and White, M.A., 1997, Generating surfaces of daily 

meteorological variables over large regions of complex terrain: Journal of 

Hydrology, 190, p. 214–251.

Terrestrial Ecosystems—Isobioclimates of the Conterminous United States

By Jill J. Cress, Roger Sayre, Patrick Comer,1 and Harumi Warner2

2009

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3084

Version 1.0

Publishing support provided by: 

Denver Publishing Service Center

Manuscript approved for publication on June 29, 2009.

For more information concerning this publication, contact:

USGS Central Region Geospatial Information Office

Federal Center

Box 25286

Denver, CO 80225

1-888-ASK-USGS or

Jill Cress

Rocky Mountain Geographic Science Center

U.S. Geological Survey

(303) 202-4275

jjcress@usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and 

does not imply endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it 

also contains copyrighted materials as noted in the text. Permission to 

reproduce copyrighted items for other than personal use must be 

secured from the copyright owner. 

For sale by U.S. Geological Survey Information Services

Box 25286, Federal Center, Denver, CO 80225

1-888-ASK-USGS

This and other USGS products are available on the World Wide Web at:

http://store.usgs.gov/

This report is available at:

http://pubs.usgs.gov/sim/3084

1

 Ecology Department, NatureServe, Boulder, Colo.

2

 Parallel Inc., Lakewood, Colo.

Prepared in collaboration with NatureServe

Suggested citation:

Cress, J.J., Sayre, Roger, Comer, Patrick, and Warner, Harumi, 2009, Terrestrial Ecosystems—Isobioclimates 

of the conterminous United States: U.S. Geological Survey Scientific Investigations Map 3084, scale 

1:5,000,000, 1 sheet.

SCALE 1:5 000 000

100

100

100

100

0

0 200

200 300

300 400

400 500 MILES

500 KILOMETERS

Map projection: Albers Equal Area Conic

NAD 83 DATUM

Thermotropical

Hyperarid

Subhumid

Mesotropical

Humid

Arid

Inframediterranean

Hyperarid

Subhumid

Thermomediterranean

Hyperarid

Humid

Mesomediterranean

Arid

Hyperhumid

Supramediterranean

Arid

Hyperhumid

Oromediterranean

Semiarid

Humid

Thermoboreal

Subhumid

Hyperhumid

Mesoboreal

Humid

Hyperhumid

Supraboreal

Hyperhumid

Infratemperate

Semiarid

Humid

Thermotemperate

Semiarid

Ultrahyperhumid

Mesotemperate

Semiarid

Ultrahyperhumid

Supratemperate

Semiarid

Ultrahyperhumid

Cryorotemperate

Ultrahyperhumid

Dry

Orotemperate

Ultrahyperhumid

Dry

Tropical Thermotypes Mediterranean Thermotypes Temperate Thermotypes Boreal Thermotypes

EXPLANATION

125°

50°

120°

120°

115°

115°

110°

105°

100° 95° 90°

85°

80°

75°

70°

70°

50°

45°

25°

75°

35°

80°

85°

100° 95° 90°

105°

110°

30°

30°

35°

40°

45°

25°