Environmental Engineering Reference
In-Depth Information
the spatial variation was even greater at smaller scales, ranging from zero to more
than 30,000% in major urban centers.
Haberl published his detailed account of the HANPP for Austria, i rst in German
and then in English (Haberl 1997), and the method he chose for that assessment
was eventually used by a group he led to prepare yet another global estimate of
human claims on the biosphere (Haberl et al. 2007). That study followed Wright's
(1990) suggestion and dei ned the HANPP as the difference between the net pro-
ductivity of an ecosystem that would be in place in the absence of humans (potential
NPP, labeled NPP
0
) and the net productivity that actually remains in an existing
ecosystem (labeled NPP
t
). NPP
t
is thus the difference between the NPP of the actual
vegetation (NPP
act
) and the NPP harvested by humans (NPP
h
): NPP
t
= NPP
act
- NPP
h
,
and HANPP = NPP
0
- NPP
t
.
NPP
0
was calculated using the Lund-Potsdam-Jena model of global vegetation
(PIK 2012), and the FAO's country-level data were used to derive crop and forest
harvests. Aggregate global HANPP added up to 15.6 Gt C, or nearly 24% of poten-
tial NPP, with 53% of the total attributable to phytomass harvests, 40% to land-
use-induced changes in primary productivity, and 7% to anthropogenic i res.
A regional breakdown showed HANPP values ranging from 11% for Australia
and Oceania to 63% for South Asia, with Western Europe averaging 40% and North
America 22%. Haberl et al. (2007) also recalculated the global HANPP according
to the method used by Vitousek et al. (1986) and, despite the substantial difference
in dei nitions and accounting procedures, wound up with a virtually identical value
of 37%. Table 11.1 summarizes the mean HANPP values of these i ve assessments
and also lists their ranges: the mean of means is just over 25%, the extreme low
values are just 3%-10%, and the maxima range from 26% to 55%. Except for
Wright (1990), these rates were calculated using standard estimates of global NPP
values close to 60 Gt C, but if Welp et al. (2011) are correct, those values may be
as high as 75-88 Gt C. In that case, all the values presented in table 11.1 would
have to be reduced by at least 20% and perhaps by as much as 32%, and the mean
rate of the i ve HANPP studies would thus fall to between 17 and 20%.
National assessments of HANPP have been done for only a few countries, but
in some of these cases the analysis has been extended into the past and has uncov-
ered some clear historical trends. The longest span has been covered by the HANPP
study of the UK between 1800 and 2000, performed in Austria (Musel 2009).
During those two centuries—when the country's population nearly quadrupled,
cropland i rst expanded and then declined, the forested area nearly doubled, and
urban land increased by an order of magnitude—the HANPP showed i rst a steady
