Impacts of urban growth on vegetation carbon sequestration - Urban Remote Sensing: Monitoring, Synthesis and Modeling in the Urban Environment - page 269

TABLE 19.4 Conversions between settlement-density categories, their area proportions, and associated changes in GPP between 1990
and 2000.

Changes in GPP (g C m −2 day −1 ) Settlement-density Aggregated types Percentage of the

conversion of conversion total area (%)

Mean Std. Dev.

U → U Persistent Urban 1.71 0.138 0.864

S → U Change to Urban 0.42 0.096 1.085

E → U Change to Urban 0.01 0.040 1.110

subtotal 2.13

S → S Persistent Suburban 14.91 1.125 1.158

E → S Change to Suburban 4.78 1.442 1.088

R → S Change to Suburban 0.03 1.071 1.040

subtotal 19.72

E → E Persistent Exurban 33.36 1.778 0.886

R → E Change to Exurban 8.53 1.813 0.946

subtotal 41.89

R → R Persistent Rural 36.05 1.846 0.949

subtotal 36.05

U → S Other Conversion 0.03 0.994 1.196

U → E Other Conversion 0.00 1.102 0.788

S → E Other Conversion 0.05 1.685 0.977

U → R Other Conversion 0.00 0.633 1.411

S → R Other Conversion 0.01 1.214 1.079

E → R Other Conversion 0.12 2.071 0.900

subtotal 0.21

Positive values of changes in GPP indicate increase in GPP by 2001.

19.5 Discussion

This study found that the South Atlantic division, which
consists of eight states and the District of Columbia in the
eastern United States, experienced a similar settlement-density
transition as patterns identified nationwide. Between 1990 and
2000, high-density urban and suburban development ( ≤ 0 . 69
hectares per housing unit) expanded their area by 20-30%.
Although the exurban expansion bore a slower rate of growth
(9%) during the same time period, the area extent of exurban
densities was the highest among all settlement densities by 2001.
In 2000, exurban densities (settled at 0.69-16.2 hectares per
housing unit) were twice as much in area as suburban densi-
ties (settled at 0.1-0.69 hectares per housing unit) and were
approximately 18 times the area of urban densities (settled at 0.1
hectares per housing unit and less). In terms of settlement densi-
fication between 1990 and 2000, exurbanization (the conversion
from rural to exurban densities) occupied 1.8 times of the area
of suburbanization (the conversion from exurban to suburban
densities) and approximately 20 times of the area of urbanization
(the conversion from suburban to urban densities).

19.5.1 Urban growth in the South
Atlantic division

The US urban development has increased rapidly in the 20th
century and was complicated by the decline of average house-
hold size since 1960. By 2000, the number of persons residing
in Census urban areas reached 7.4 times the count of urban
population in 1900 (US Census Bureau, 1995, 2001a). While
the urban population kept growing from 69.9% to 79.0% of
the total US population between 1960 and 2000, the average
household size (i.e., numbers of people living in a housing unit)
continuously shrank from 3.33 to 2.62 persons per housing unit
during the same time period (US Census Bureau, 1995, 2009).
The escalation of urban population and decline in the average
household size accelerated urban sprawl at various development
densities. In previous research, urban and suburban densities
( 0 . 69 hectares per housing unit) were found to expand by

31.5% in private lands by area across the conterminous United
States between 1980 and 2000 (Theobald, 2005). The area of
low-density development (0.4-16.2 hectares per housing unit)
was found to be approximately 14 times greater than the area of
higher-density settlement in the United States by 2000 (Brown
et al ., 2005).

≤

19.5.2 Impacts of urban growth on
vegetation productivities

Photosynthesis measured by GPP based on the LUE approach
was found on average to be the highest at rural and low-density