Comparison of Soil Organic Carbon Stocks Between Residential Turf Grass & Native Soil Acknowledge Dussita Richard V. Pouyat, Ian D. Yesilonis, and Nancy E. Golubiewski

Residential: 40% of urban areas (Nowak et al. 1996) 40 million acres of lawn in conterminous USA (Milesi et al., 2005) 3 times more than acreage of largest irrigated crop (corn) Lawns make up largest component of most urban landscapes, especially residential areas. Read bullets Many articles / discussions about benefits and potential environmental effects of turf grass. From an ecological perspective, low diversity, require maintenance (i.e., use of fossil fuels and other resources), replace more quality habitats Others see turf grass as a good ground cover that prevents erosion, provides recreational space, and is aesthetically pleasing to look at. And more recently, biological virtues that include potential to sequester C in soil and retain N

LIFE ZONE AREA (x10 AREA (x10 12 12 m m 2 2 ) ) C Density (kg m C Density (kg m 2 2 ) Soil C (x10 ) Soil C (x10 15 15 g) g) Temperate forest Temperate forest - - warm warm 8.6 7.1 7.1 61.1 Temperate forest - - cool 3.4 12.7 43.2 Cool temperate steppe 9.0 13.3 119.7 Temperate thorn steppe 3.9 7.6 29.6 Warm desert 14.0 1.4 19.6 Wetlands 2.8 72.3 202.4 Boreal forest - - wet 6.9 19.3 133.2 Cultivated land 21.2 7.9 167.5 Due to differences in sensitivity between decay rates and NPP, get a wide variation is soil C densities. Prior to widespread human modifications, net increase in soil C is estimated at .01-.02% per yr. (Mostly in peatlands! Otherwise, inputs and outputs of soil C are closely balanced) If we compare turf grass with other ecosystems in their capacity to accumulate C in soil, the data so far suggest lawns have a high capacity to sequester C in soil. Comparable to cool temperate steppe. If consider entire urban landscape, more comparable with temperate thorn steppe. Residential turf grass ? 14.4 ? Urban land 1.3 + 7.7 10.0 TOTAL WORLD 1500(±20%) Adapted from Post et al. (1982) and Schlesinger and Andrews (2000) *Milesi et al. 2005

SIMILARITY? Baltimore Phoenix What I find interesting is that urban landscapes, due to human desires and subsequent efforts, often look more similar in vegetation structure than the systems they replaced. In this case, comparing Baltimore and Phoenix metro regions to the right. Native Phoenix landscape is a warm dessert that is characterized by very low stocks of above and below ground C storage. Add people—get increase in both stocks

URBAN LAND USE CHANGE?: Disturbance (initial, post-develop.)- SOC Introduction of impervious surfaces SOC- low, very slow change Introduction of horticultural management (supplements)- SOC Environmental change (biophysical)- SOC If we consider potential impacts of urban land use change on SOC stocks, find that most changes result in a loss of C; however, with the introduction of management (mostly supplements of water and nutrients) potential to increase productivity and thus organic matter inputs into the soil.

TURFGRASS MAINTENANCE $10.4 billion in USA Range of fertilizer rates: Golf courses, athletic fields—490 kg ha-1 yr-1 Residential lawns—50-145 kg ha-1 yr-1 16 million kg pesticides applied yr-1 (Aspelin, 1997) Irrigation use? And American population is willing and able to spend lots of money to maintain turf grass—in fact, Melesi et al. 2005, calculated that the vast majority of land area in conterminous US requires supplements to maintain grass except in north central and eastern US.

Cd Turf grass? 20 Agricultural Conversion Urban Conversion Boreal Cool Temperate Steppe Cool Tropical Forest Moist Tropical Forest Warm Temperate Forest Warm Desert 20 Agricultural Conversion Urban Conversion Cd Urban Range at Equilibrium Global Range at Equilibrium This desire to maintain turf grass, trees and other horticultural plantings regardless of climate results in what has been called an “ecosystem convergence”. Range in ecosystem attributes gets reduced due to human supplements and other activities. In the case of SOC, turf grass is an important component of a “convergence.” 1.4 Time Edaphic Cultivation Urban Turf grass? Milesi et al., 2005 Pouyat et al. (2001) & Pouyat et al. (2003)

OBJECTIVES: Compare residential turf grass vs. native SOC in Baltimore, MD and Denver, CO areas Climatologically distinct regions Compare residential turf grass vs. native cover types (0.2 and 1 m depth) Field collected data, NRCS Soil database, and data from literature To test this idea, we . . .

Estimate net effect of urban land-use change on SOC densities in both metropolitan areas Calculate SOC densities on area weight basis (including impervious areas) Pre-urban, agriculture, and post-urban landscapes

EXPECTED RESULTS: SOC densities of native soils will differ more than for residential soils 2. Net differences between pre- and post-urban SOC densities will be positive in arid shortgrass steppe (Denver) and negative in mid-Atlantic hardwood deciduous forest (Baltimore)

NRCS Soil Characterization Database 1 m DEPTH SOIL CORES NRCS Soil Characterization Database 605 pedons northeastern and north central USA Data required (bulk density, coarse fragments, C fraction, horizon thickness) 0-20 cm, 0-1 m, proportion of C to 1 m depth occurring in surface 20 cm Extrapolated to 1 m only if reached C horizon

BALTIMORE UFORE PLOTS Birdsey (1992) n=19 n=19 n=5 n=7 NRCS DATA

CUB HILL PLOTS Birdsey (1992) n=7 n=8 n=6

DENVER METROPOLITAN AREA Schimel et al. (1985) NRCS Adapted from Galubiewski (2006)

COMPARISON OF RESIDENTIAL AREAS

COMPARISON OF NATIVE SOILS ? n=7 n=19

NET Change? Denver Baltimore (kg m-2) Pre-agriculture 7.3 11.2 (6.7)   Denver Baltimore (kg m-2) Pre-agriculture 7.3 11.2 (6.7) Agriculture ~2.5 5.4 Urban* 8.5 7.1 +1.17 -4.1 (+2.6) *includes impervious surfaces (3.3 kg m-2)

CONCLUSIONS Residential soils differ less than native soils in SOC densities Residential soils in Denver significantly higher than native short grass (Baltimore less clear) Net change Denver (increase SOC), Baltimore (+ or – change?) Turf grass potential to sequester C in soil (BUT, entire budget required)

(x10 (x10 m2) (kg m (kg m ) ) (x10 (x10 g) g) - - LIFE ZONE LIFE ZONE AREA C Density Soil AREA C Density Soil C C (x10 (x10 10 10 m2) (kg m (kg m - - 2 2 ) ) (x10 (x10 14 14 g) g) Northeast Forest* Northeast Forest* 20.81 16.2 16.2 33.7 Northeast Cropland* Northeast Cropland* - - 6.0 6.0 - - Mid Mid - - Atlantic Forest* Atlantic Forest* 20.29 20.29 11.2 11.2 22.7 Mid Mid - - Atlantic Atlantic Cropland* Cropland* - - 4.2 4.2 - - Southeast Forest* 34.22 7.7 26.3 Southeast Cropland* - 2.6 - Urban (residential) 6.35 6.35 14.4 ( ± ± 1.2) 1.2) 9.84 9.84 USA Urban (total) USA Urban (total) 30.06** 30.06 7.7 (±0.2)*** 23.15 USA (total) USA (total) 915.9 915.9 6.8 (?) 6.8 (?) 619.15 * * Birdsey Birdsey (1992) (1992) ***Pouyat et al. (2006) **Nowak et al. (1996)