Impacts of urban growth on vegetation carbon sequestration - Urban Remote Sensing: Monitoring, Synthesis and Modeling in the Urban Environment - page 268

Persistent Urban

Change to Urban
Persistent Suburban
Change to Suburban
Persistent Exurban

Value
High : 8.0

Change to Exurban

Low : -8.0
Removed CS

Persistent Rural
Other conversion
Removed CS

N

0 100 200 km

(a) (b)

FIGURE 19.4 Changes in settlement-density categories (a) and in GPP (g C m −2 day −1 ; b) between 1990 and 2000. The
pixel-wise changes in GPP range between - 5.31 and 7.94 g C m −2 day −1 . CS stands for county subdivision.

At the pixel level, the average value of changes in GPP varied
between − 5.31 and 7.94 g Cm − 2 day − 1 , with the mountain areas
to the north and plain areas around Florida Panhandle appearing
to be related to the enhanced photosynthesis (i.e., positive values;
Fig. 19.4b). Changes inGPPwere found to be positive, on average,
for all individual settlement-density transitions; however, the
amount of change varied by transitional types (Table 19.4). The
persistent Rural densities (R → R; 1.846 g C m − 2 day − 1 ), Rural
densities converted to Exurban (R → E; 1.813 g C m − 2 day − 1 ),
and persistent Exurban densities (E

categorical changes. The persistent types referred to areas iden-
tified as the same settlement-density category in both Census
years; for example, Persistent Rural represented areas identified
as Rural densities in 1990 and remaining Rural densities in 2000.
The actual categorical changes were divided into four groups:
(1) Change to Urban represented conversions from any of the
three lower-density categories to Urban densities; (2) Change to
Suburban included conversions from Exurban or Rural densities
to Suburban densities; (3) Change to Exurban was equivalent to
the conversion from Rural to Exurban densities; and 4) Other
Conversion referred to any conversion from higher to lower
densities. From the perspective of photosynthesis, Change to
Urban resulted in the lowest value of GPP increment (0.068 g
Cm − 2 day − 1 ), followed by Persistent Urban (0.138 g C m − 2
day − 1 ), Persistent Suburban (1.125 g C m − 2 day − 1 ), and Change
to Suburban (1.257 g C m − 2 day − 1 ). All four types associated
with persistent Urban/Suburban densities or being densified into
Urban/Suburban densities yielded a smaller amount of GPP
increment than the regional average, whereas the persistent
Exurban densities (1.778 g C m − 2 day − 1 ) and Rural densified
into Exurban densities (1.813 g C m − 2 day − 1 )resultedinan
enhanced amount of GPP increment than the regional average
(Table 19.4).

E; 1.778 g C m − 2 day − 1 )
were associated with the highest amount of increase in GPP,
higher than the regional average difference (1.7 g C m − 2 day − 1 ).
They were followed by Exurban densities converted to Suburban
(E

→

S; 1.442 g C m − 2 day − 1 ), persistent Suburban densities
(S → S; 1.125 g C m − 2 day − 1 ), and Rural densities converted
to Suburban (R → S; 1.071 g g C m − 2 day − 1 ). Persistent Urban
densities (U

→

U; 0.138 g C m − 2 day − 1 ), Suburban densities
converted to Urban (S

→

U; 0.096 g Cm − 2 day − 1 ), and Exurban
densities converted to Urban (E → U; 0.04 g C m − 2 day − 1 )held
thelowestvaluesofincreaseinGPP.
Eight groups of settlement conversion were generated to
characterize transitions among different settlement-density cat-
egories between 1990 and 2000 (Table 19.4). This grouping
system separated the persistent types from those experiencing

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