September 2019 Full - page 694

Results
Updated Distribution of Deciduous Rubber Plantations in 2016
Figure 9 shows the updated map of deciduous rubber plan-
tations in Xishuangbanna in 2016. The deciduous rubber
plantations within Xishuangbanna were characterized by
a concentrated spatial distribution, mainly located in the
southeast part of Jinghong City and southwest part of Mengla
County, which closely border Myanmar and Laos. The area
of deciduous rubber plantations was about 3074 km2 in 2016,
slightly higher than the official value (3042 km2) published in
the Xishuangbanna Statistical Bulletin at the end of 2015. It
should be noted our phenology-based CRNBR algorithm mainly
focused on mature rubber plantations rather than young plan-
tations. One major reason could be that newly established
or young plantations tend to have sparse canopies showing
similar spectral features with other land cover types (e.g., bare
land and fallow soil), which is difficult to detect.
Horizontal Expansion of Deciduous
Rubber Plantations During 1991–2016
Figure 7a–e shows that significant encroachment of deciduous
rubber plantations took place in the five epochs, with increas-
ing area between 1991 and 2015 (Figure 7f). Spatial variations
in deciduous rubber plantations were very obvious; planta-
tions have especially expanded in Xishuangbanna since the
late 2000s. These maps clearly illustrate a 6.6-fold increase of
deciduous rubber plantations within the study area of 2611
km2, corresponding to an annual increase of 104 km2. The
relevant proportion of total land covered by deciduous rubber
plantations increased from 2.5% in the early 1990s to 3.1% in
the late 1990s, and then to 6.8% in the early 2000s, 12.3% in
the late 2000s, and 16.7% in 2016, an annual average expan-
sion rate of approximately 8%.
Deciduous rubber plantations covered merely 463 km2 in
the early 1990s (Figure 7a). This figure then increased slightly
during the late 1990s (Figure 7b), reaching an area of 576 km 2,
a limited incremental trend throughout the 1990s. However,
by the early 2000s the planted area of deciduous rubber plan-
tations had obviously expanded (Figure 7c), from 576 to 1253
km2 (a 217% increase), at an annual increment of 677 km2.
The expansion of deciduous rubber plantations mainly took
place around Jinghong City and in Mengla County over this
period, as shown by the yellow ellipses in Figure 7. The total
area of deciduous rubber plantations within the study area
reached 2256 km2 by the late 2000s, mainly due to expansion
into the northern parts of Mengla County and the south-
central parts of Jinghong City (Figure 7d). These plantations
subsequently continued to expand in an almost uncontrolled
fashion across the whole of Xishuangbanna throughout the
early 2010s (Figure 7e), reaching up to 3074 km2 by 2016
(Figure 9). The Landsat-CRNBR maps generated in this study
for the five periods highlight this continuous expansion in
deciduous rubber plantations. In particular, the incremental
growth trend was aggravated during the 2000s because of
robust demand for natural rubber latex in China as well as
further rises in the international price.
As a whole, this study revealed two obvious spatial expan-
sion patterns in deciduous rubber plantations. The first is a
gradual expansion in regions adjacent to where deciduous
Figure 9. The resultant map of deciduous rubber plantations
derived from the tri-temporal CRNBR algorithm in 2016.
Table 1. Accuracy assessments of maps of deciduous rubber plantation in this study.
Period Class
Ground-truth pixels
Classified
pixels User's accuracy
Deciduous rubber
plantations
Natural evergreen
forests
2016 Deciduous rubber plantations 13,511 207 13,718 98%
Natural evergreen forests 1144 9389 10,533 89%
Ground-truth pixels 14,655 9596 24,251 Overall accuracy = 94%
Producer's accuracy 92% 98% κ = 0.93
2011–2015 Deciduous rubber plantations 7864 8 7872 99%
Natural evergreen forests 1415 5406 6821 80%
Ground-truth pixels 9279 5414 14,693 Overall accuracy = 90%
Producer's accuracy 85% 99% κ = 0.88
2006–2010 Deciduous rubber plantations 8921 17 9875 99%
Natural evergreen forests 937 9053 9990 91%
Ground-truth pixels 9858 9070 19,865 Overall accuracy = 95%
Producer's accuracy 90% 99% κ = 0.93
2001–2005 Deciduous rubber plantations 5202 11 5213 99%
Natural evergreen forests 325 5373 5698 94%
Ground-truth pixels 5527 5384 10,911 Overall accuracy = 97%
Producer's accuracy 94% 99% κ = 0.96
1996–2000 Deciduous rubber planta tions 5913 9 5822 99%
Natural evergreen forests 1049 5549 6698 84%
Ground-truth pixels 6962 5558 12,520 Overall accuracy = 92%
Producer's accuracy 85% 99% κ = 0.89
694 September 2019 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING