62 NPP value indicated as low or sparsely vegetation cover and high NPP value
indicated as dense vegetation cover. Figure 4.14 shows, Aceh province mostly dominated with high NPP value.
Based to estimation result, the province indicated has remained areas which covered by densely vegetation. Result estimation NPP show of low NPP value is
below 15 and it has dominated by NPP value with group 1 to 5. Meanwhile the high NPP value has percentage about 85.
However, yearly of total of NPP in average show the fluctuation results. In year 2001 to 2002 there is an increased of NPP value about 4.4. Different
condition occurred in 2002 to 2003; NPP value decreased about 5.8. Decreased of NPP over the province has followed in year 2003 to 2006 with decreased each
year around 5.2, 4.25 and 14.4. However, NPP has increased during 2006 to 2007 and 2008 to 2009 with increased percentage around 18.4 and 8.9.
Meanwhile during 2007 to 2008, NPP has decreased about 8.9.
4.4.3.2. South Sumatra Province
Within the country, South Sumatra is a province of Indonesia. It is on the island of Sumatra and borders the provinces of Lampung to the south, Bengkulu
to the west and Jambi to the north. Off of the coast are the islands of Bangka and Belitung, which are split from South Sumatra province to form the province of
Bangka Belitung in 2000. The capital of South Sumatra province is Palembang. Administratively, the province is subdivided into 10 regencies and 4 cities and has
an area about 8791496 ha. Estimation of NPP values compare to the area in percentage of South
Sumatra province during years 2001 up to 2009 as shown in Figure 4.16. Based to estimation result of NPP value in South Sumatra province, it has shown that NPP
in percentage are well distributed. Result estimation of NPP distribution in South Sumatra province has shown that lowest NPP value has annual average
changes about 1.4 compare to Aceh annual average of lowest of NPP is 1.3. High NPP value in South Sumatra province are dominated with the third group
range of NPP value 50 – 75 g C m
-2
yr
-1
with annual average NPP is 30.7.
63 Meanwhile another group range of NPP value in Sumatra has annual average NPP
of percentage range 1 - 17.
Figure 4.16 Estimation of NPP compare to the area in South Sumatra Province
4.4.3.3. Compare Result of Ground Truth in Provinces
As stated in previous chapter about estimation result of NPP distribution in Aceh and South Sumatra province. Figure 4.17 shows the estimation result of
NPP distribution in both provinces to make easier in comparing the condition in selected provinces. Information derived from NPP estimation result has validated
using ground truth activity data. Ground truth is usually done on site, performing surface observations and
measurements of various properties of the features of the ground resolution cells that are being studied on the remotely sensed digital image. This set of ground-
truth activity is used for use in an image to validate the estimation of NPP value on the field. The user in the field identifies a homogenous area of identifiable on
the ground and records its location using the GPS receiver. These locations can then be plotted over an image.
In this study, we used result of NPP estimation in year 2009 to validate with ground-truth data. The data for Aceh and South Sumatra province were
obtained from field survey carried out by Zoological Society of London ZSL on July 2009 and June 2010. Various data were obtained from ground-truth such
25 50
75 100
2001 2002
2003 2004
2005 2006
2007 2008
2009
Pe rc
en ta
ge A
re a
Year Period
Annual NPP Estimation of South Sumatra Province percentage areas
0-50 50 - 75
75 - 100 100 - 125
125 - 150 150
64 as open area mix with shrubs area, rubber estate and palm oil estate area also
forest area. There is a limitation in comparing ground-truth data with the NPP
estimation. The satellite images used to NPP estimation were obtained over a year ago. Because of the times difference, perhaps some earth object already changed
their appearance and this may cause an inaccuracy.
Figure 4.17 Estimation of NPP distribution in Aceh left and South Sumatra Province right
Figure 4.17 show estimation of NPP distribution in Aceh and South Sumatra province. There are differences between estimation NPP results in the
provinces. In Aceh province, there are gaps between groups of NPP value. High NPP value six group has reached percentage value more than 80 and low or
medium NPP value are dominated with group 1 to group 5 has reached percentage below 20. However, in South Sumatra province, the NPP value has distributed
in group 1 to 6 with reached percentage around 30. The information derived from ground truth data could explain of kind information behind the NPP
estimation in Aceh and South Sumatra province. Figure 4.18 show areas of ground-truth location in Aceh and South
Sumatra province show in white dot color. Coordinates location of ground data are collected using GPS Garmin 76 which has resolution around 15 meters.
However, NPP estimation are derived from MODIS data which has gridded type for each cell 1 km x 1 km. There are the differences of resolution between NPP
estimation from MODIS and ground truth data and in these cases the ground-truth
25 50
75 100
2001 2002
2003 2004
2005 2006
2007 2008
2009 P
e r
c e
n tage
A r
e a
Year Period
Annual NPP Estimation of Aceh Province percentage areas
0-50 50 - 75
75 - 100 100 - 125
125 - 150 150
25 50
75 100
2001 2002
2003 2004
2005 2006
2007 2008
2009 P
e rc
e n
ta g
e A
re a
Year Period
Annual NPP Estimation of South Sumatra Province percentage areas
0-50 50 - 75
75 - 100 100 - 125
125 - 150 150
65 activity in this study only to performing of object or surface information on the
ground compare with the NPP estimation.
Figure 4.18 Land-cover information derived from Ground-truth in Aceh above and South Sumatra province below
66 Compared result between ground-truth location data and NPP estimation
in Aceh province has shown that high NPP value 150 g C m
-2
month
-1
mostly located in forest area which dominated with dense vegetation. An example of
types of land cover derived from ground-truth information as show in Figure 4.17 left side.
However, compared result between ground-truth location data and NPP estimation in South Sumatra province has shown that NPP distribution value
ranges between 100 to 125 g C m
-2
month
-1
and mostly dominated by oil-palm estate and rubber estate. NPP values between 50 -75 mostly dominated by
sparsely small tress mix with shrubs.
4.5 Validation and Assessments
4.5.1. Net Ecosystem Production NEP
It is widely known that tower flux measurements of NEP can be used for model validation at the small site scale. Nevertheless, we have not included
comparisons of tower-based NEP to NASA-CASA modeled NEP in this island study, because tower eddy flux estimates are not designed to represent large-scale
e.g., 8 km NEP fluxes that we model with NASA-CASA. NEP is named ecosystem carbon sink positive value or carbon source
negative value. It is a key characteristic to measure ecosystem carbon uptake or release. Theoretically, when an ecosystem matures, e.g. climax, it is in
equilibrium with the climate and soil environment, so the carbon uptake and release are balanced, and NEP approximates to zero. But if the environmental
conditions, such as climate, changed, the ecosystem carbon budgets will not be balanced.
In any year over the past nine years, net ecosystem production can be very large in one location but very small or negative in another location because of the
spatial heterogeneity of vegetation, soils and climate. Locations with large positive annual NEP are often those that receive a high amount of precipitation. In
contrast, locations with negative NEP are often those that receive little
67 precipitation. Year-to-year changes in spatial pattern of NEP were most probably
caused by changes in the spatial pattern of precipitation, which can be changed dramatically by the El Nino events Vorosmarty et al., 1996.
Ecosystem maintenance involves two tasks: 1 keeping the system‟s carbon and nutrient stocks organized; and 2 minimizing net losses of carbon and
nutrients from the system. Both tasks require energy investments in the system. A useful relative index of the magnitude of this investment in maintenance appears
to be net ecosystem production NEP. Net ecosystem production refers to the net change in organic matter stocks
in the system for some defined period of time. For agricultural systems NEP is the sum of NPP and organic matter inputs associated with maturing minus the sum
of heterotrophic respiration plus organic matter outputs associated with harvest and erosion. If NEP is negative, then the system is probably losing nutrients. The
optimum rate of NPP in agricultural systems is that where a sufficient fraction of the NPP is invested to maintain NEP equal tu or greater than zero. Agriculturalists
should be “caretakers” or “builders” and not “miners”.
Refer to the previous research in various areas of tropical forests Potter et al., 2003 showed that the average Rh total respiration of vegetation about
850 g C m
-2
yr
-1
. Results of this measurement, also have done by Chamber et al., 2004 which measures the risk of canopy cover, tree trunks and forest soil
surface, with estimation result about 900 g C m
-2
yr
-1
, with an annual average of Rh g C 850 m
-2
yr
-1
, with a range between 846 to 857 g C m
-2
yr
-1
. Based on results of from previous research, the assumption of estimated annual average of
Rh total respiration on island of Sumatra is 850 g C m
-2
yr
-1
. Estimation of annual Net Ecosystem Productivity NEP obtained from the
calculation of total annual NPP subtracted with total respiration. Furthermore, result of estimation average annual carbon fluxes Net Ecosystem Productivity,
NEP of Sumatra terrestrial as show in Figure 4.19.
