reverting”, which means an up value is more likely followed by a down value, and vice versa. The strength of “mean-reverting”
increases as H approaches 0 Qian and Rasheed, 2004. A persistent series is trend reinforcing, which means the direction
up or down compared to the last value of the next value is more likely to be followed by current value. The strength of
trend increases as H approaches 1. In this study, the Hurst exponents of ANDVI and SNDVI were calculated by rescaled
range analysis RS analysis to quantitatively characterize
vegetation dynamics. For a time series,
{ }
t
ζ
，t=1,2,3,…, N; taking a sub series
τ
=1,2,3,…, N, the mean of
τ
is defined as:
∑
=
=
τ τ
ξ τ
ζ
1
1
t
t
3 For the cumulative deviate at time t of
τ
, τ
ζ ξ
τ
τ
≤ ≤
− =
∑
=
t u
t X
t u
1 ,
,
1
4 The range series R is calculated as follows:
, max
, max
1 1
τ τ
τ
τ τ
t X
t X
R
T T
≤ ≤
≤ ≤
− =
5 The standard deviation series S is determined by:
∑
=
− =
τ τ
ξ ξ
τ τ
1 2
1
t
t S
6 Rescaled range series RS is calculated by dividing the
range by the standard deviation. Hurst found that RS scales by power-law as time increases, which indicates
H
c S
R
τ τ
τ
=
7 where c is a constant and H is called the Hurst exponent. The
value of H is obtained using an ordinary least squares regression with log
τ
as the independent variable and logR
τ
S
τ
as the dependant variable. The slope of the regression line approximates the Hurst exponent.
4. RESULTS AND DISCUSSION
4.1 Temporal Change of NDVI
The annual average NDVI slightly increased with an undulating trend in the upper and middle reaches of the NRB Table 1.
Wave crest of the ANDVI occurred in 2010, whereas the lowest trough found in 2004. Increased NDVI mean values from 2000
to 2002, 2004 to 2007 and 2009 to 2010 indicated recovery of vegetation. Yearly NDVI decreased by 1.3 and 6.3
implying degraded vegetation cover during 1999–2001 and 2007–2009.
At the seasonal scale, vegetation was most vigorous in summer with the highest NDVI values ranging from 0.182 to 0.245.
NDVI in autumn came second between 0.111 and 0.146. In summer, regional average NDVI almost kept stable for the
study period. NDVI in autumn increased by 5.93 between 1999 and 2010, whereas the spring NDVI decreased by -6.45.
Year NDVI
ANDVI SNDVI
spring
SNDVI
summer
SNDVI
autumn
1999 0.165
0.062 0.232 0.118 2000
0.162 0.059 0.182 0.122
2001 0.163
0.05 0.212 0.119 2002
0.174 0.057 0.213 0.111
2003 0.16
0.059 0.245 0.134 2004
0.154 0.052 0.217 0.139
2005 0.166
0.056 0.238 0.133 2006
0.169 0.051 0.224 0.134
2007 0.177
0.059 0.202 0.136 2008
0.173 0.060 0.237 0.146
2009 0.166
0.068 0.206 0.112 2010
0.180 0.058 0.232 0.125
Table 1. The annual and seasonal NDVI changes
4.2 Spatial Change of Vegetation Cover
Fig. 1 illustrates the spatial pattern of interannual ANDVI during past twelve years. The NDVI values approximately
increased from south to north, which were consistent with the main types of land cover in the study area.
ANDVI values greater than 0.50 overlapped with the distribution of dense
forest. The values of multi-year average NDVI ranging from 0.38 to 0.50 were concentrated in the north indicating forestland
and high to moderate density grassland. The places with
ANDVI values of 0.26-0.38 were dominated by cropland, some scattered grassland of high density and marshland. The regions
with NDVI of 0.14-0.26 were occupied by water area and grassland of moderate density.
Figure 1. Spatial pattern of multi-year average NDVI 26.02 of the study area showed a significant vegetation
increase, while only 1.32 showed a significant decrease Table 2. 72.66 of the study area in the south and north had
no significant change trend. 10 of the upstream and middle
This contribution has been peer-reviewed. doi:10.5194isprsarchives-XLI-B8-889-2016
891
stream regions, the ANDVI indicated a strong significant increase. The area where ANDVI significantly increased mainly
distributed in Oroqen Autonomous Banner, the southeast Huma County, the north of Nenjiang County and the west of
Zhalantun City Fig. 2a. The significant decrease in vegetation cover was observed in the bording area between Huma County
and Oroqen Autonomous Banner, Morin Dawa Daur Autonomous Banner and Nehe City. These results indicated that
a large portion of the upper and middle reaches of the NRB had experienced a significant vegetation increase, and only a small
part had significantly showed vegetation decrease in the past twelve years.
Vegetation change trend
Area percentage Year Spring
Summer Autumn Strongly
significant increase
10.00 0.05 8.20 6.19
Significant increase
16.02 0.94 26.12 20.01
No significant increase
61.44 47.70 62.92 65.73
No significant decrease
11.22 37.98 2.49 7.56
Significant decrease
0.75 7.50 0.20 0.28
Strongly significant
decrease 0.57 5.83 0.07
0.23 Table 2. The area percentage of vegetation change trends
Figure 2. Spatial change of vegetation a total year b spring c summer d autumn
In spring from 1999 to 2010, about 85.68 of the total area had no significant change trend. 13.33 of the study area showed a
significant decrease, whereas 0.99 showed a significant vegetation increase. Most decreased vegetation cover in spring
was observed in downstream region including Nehe City, Arong Banner, Morin Dawa Daur Autonomous Banner, Keshan
County, Kedong County, Baiquan County, Wudalianchi City, Fuyu County, Gannan County,Yian County and Baiquan
CountyFig. 2b. Some vegetation in the northeast of Oroqen Autonomous Banner and the southeast Huma County had
significantly increase trend. Vegetation cover tended to increase significantly in summer probably owing to increasing
agricultural crop production. The improved area occupied about 34.32 of the study area, mainly distributed in the west of
Huma County, the north of Oroqen Autonomous Banner, the west of Zhalantun City, Keshan County, Fuyu County, Gannan
County, Yian County and Baiquan County Fig. 2c. Approximately 65.41 of the total area had no significant
change trend in summer. The area of significantly decreased in vegetation cover took up 0.27 of the total land. In autumn,
26.2 of the study area showed a significant vegetation increase, and 0.51 decreased dramatically. Increasing
vegetation cover was mostly found in most area of Oroqen Autonomous Banner and Zhalantun City Fig. 2d. Except for
spring, the vegetation activity in summer and autumn tended to improved.
This contribution has been peer-reviewed. doi:10.5194isprsarchives-XLI-B8-889-2016
892
4.3 Vegetation Behaviour Persistence
