5. Discussion
In this study, we constructed a directed and weighted complex network,
naming the oasis transition network, which was used to express the
transition patterns between different oasis types, identify the key land
type and quantify the oasis structural stability. Compared with
traditional transition analysis, the complex network described the
dynamic process and the influences of different oasis types in the oasis
system. Between centrality was used to identify the key land type, which
was explained the possibility the land type being the transitional type.
The findings of the oasis transition network indicated that the oasis
transitions were increasingly complicated from 1990 to 2020. Grassland
was the key oasis type in the oasis transition process, and the
importance decreased during 1990 and 2020. Bare land had the highest
betweenness centrality in 2015-2020 and cropland ranked third among all
the land types, indicating the important roles and the changes of key
land type in the transition network. According to the relevant report
and statistic year book published by the beau of statistic in Turpan and
Hami region, through the thirteenth ‘five-year’ plan, greening
construction projects like returning farmland to grassland,
afforestation, combating and controlling desertification and three north
protective forests have gained significant effectiveness (Lyu et
al. , 2020). During that period, grassland was not the most important
transitional land type due to the efforts of planting and reclamation of
the bare land.
Notably, in the oasis transition network, the land types with low
proportion of coverage also contacted with other land types frequently.
For example, shrubland expressed high degree values and was one of the
principal components in the oasis transition network and the
interactions with bare land dominated during the sub-periods of
1995-2000, 2000-2005, 2005-2010, 2010-2015 and 2015-2020. According to
the local statistic yearbook, a large proportion of shrubland were
planted artificially to combat wind and sand at the edge of the oasis
and against land degradation in the inner oasis, like shuttle and camel
thorn; the area of shrubland showed a distinct increasing trend in
2015-2020. We were inspired those human forces dominated in the oasis
transition process for most sub-periods.
Oasis structural stability was quantified using average path length in
the oasis transition network, which was a crucial index to express the
oasis sustainability in dryland. So far, few studies had investigated
the structural stability of the entire oasis system in dryland. In this
study, we applied the average path length to reveal the difficulty of
the interactions among the oasis types. With the results of more
unstable oasis structural stability, we concluded that there were easier
transitions among different land types recent years than before.
Therefore, we suggest that more attentions on key land types (e.g.
grassland) should be paid for the dryland sustainable development.
Even though the correlations between oasis and precipitation were
insignificant, water resource was one of the most important restraint
factors in dryland development (Yang et al. , 2021). The surface
water in Tuha Basin is obviously shrinking recent years partly because
of the increasing temperature and intense evaporation (Rodell et
al. , 2018; Wang et al. , 2023) in Tuha Basin. Additionally, water
resources were over-exploited and underground water level had
continuously dropped for agricultural irrigation and mining (Hu et
al. , 2019; Wang et al. , 2022; Cheng et al. , 2023). A more
adaptive strategy for regulating cropland areas and water resource
allocation is needed. From the driving factors analysis, population
played a key role in oasis expansion, for example, to meet the
requirements of the fast-growing population, the urbanization including
artificial reclamation and construction speeded up, making built-up a
most transfer-in type in the oasis transition network. Human factors
including policy factors, economic factor and cultural factors were all
important in the maintaining of the entire oasis system and land
optimization in drylands. Therefore, further survey and analysis for the
oasis driving should be deep considered.