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R E S E A R CH A R T I C L E
Temporal heterogeneity has no effect on the direction ofsuccession in abandoned croplands in a semiarid area ofnorthwest China
An Hu | Sheng-Hua Chang | Xian-Jiang Chen | Fu-Jiang Hou | Zhi-Biao Nan
State Key Laboratory of Grassland Agro-
Ecosystems, Key Laboratory of Grassland
Livestock Industry Innovation, Ministry of
Agriculture, College of Pastoral Agriculture
Science and Technology, Lanzhou University,
Lanzhou, Gansu, PR China
Correspondence
Fu-Jiang Hou, State Key Laboratory of
Grassland Agro-Ecosystems, Key Laboratory of
Grassland Livestock Industry Innovation,
Ministry of Agriculture, College of Pastoral
Agriculture Science and Technology, Lanzhou
University, Lanzhou, 730000, Gansu, PR
China.
Email: [email protected]
Funding information
Changjiang Scholar Program of Chinese
Ministry of Education, Grant/Award Number:
IRT17R50; Chinese Academy of Sciences,
Grant/Award Number: XDA2010010203; Key
R & D Program of Ningxia Hui Autonomous
Region, Grant/Award Number:
2019BBF02001; National Natural Science
Foundation of China, Grant/Award Number:
31172249
Abstract
Space for time substitution has been widely used in the study of succession in aban-
doned croplands worldwide but it is often accompanied by time heterogeneity. How-
ever, the effect of temporal heterogeneity on succession dynamics over decades is
not well understood. Here, we studied croplands with the same history that were
abandoned in 1998, 1999, and 2000 in northwest China (temporal heterogeneity)
and continuously monitored for vegetation characteristics for 10 years. Aboveground
biomass, taxonomic, and functional diversity were compared in the three cropland
groups over time. Our results showed that the direction of succession in the three
cropland groups was similar, from a community with single dominant species with
higher aboveground biomass to a community with multiple dominant species with
lower aboveground biomass. Taxonomic and functional diversity increased rapidly in
the first 5–6 years, followed by slow increase, decrease, or stabilization. In years 1–5,
aboveground biomass, taxonomic, and functional diversity were affected by rainfall,
time of abandonment, time since abandonment, or their interactions. However, in
years 6–10, biomass was only affected by rainfall, and functional evenness was
affected by rainfall and time since abandonment; there was no time of abandonment
effect. We conclude that temporal heterogeneity can initially affect the succession
process but has no effect on the direction of community succession in the longer
term. Our findings provide evidence for using space for time substitution with tem-
poral heterogeneity to study succession in abandoned croplands in semiarid areas.
K E YWORD S
abandoned cropland, aboveground biomass, functional diversity, taxonomic diversity,
temporal heterogeneity
1 | INTRODUCTION
Heterogeneity is increasingly recognized as a foundational character-
istic of ecological systems (Collins et al., 2018). In this context, hetero-
geneity refers specifically to spatiotemporal variability of an ecological
factor (McIntosh, 1991). The spatiotemporal heterogeneity can influ-
ence plant community structure and soil physicochemical properties
(Limb, Hovick, Norland, & Volk, 2018; Zhang et al., 2017a). The space
for time substitution approach was used in early ecological studies
(Smith, 1940) as well as recent studies in ecology (Mcgranahan
et al., 2012). Recently, the space for time substitution approach has
again become a topic of interest in the context of community succes-
sion, especially in the succession of abandoned croplands (Thomas,
Knops, & Dave, 2018; Zhang et al., 2018a). Studies of natural and arti-
ficial revegetation of abandoned croplands during succession have
focused on changes in vegetation composition (Hodapp et al., 2018),
Received: 18 January 2020 Revised: 24 August 2020 Accepted: 22 September 2020
DOI: 10.1002/ldr.3780
Land Degrad Dev. 2020;1–10. wileyonlinelibrary.com/journal/ldr © 2020 John Wiley & Sons, Ltd. 1
structure (Zhang, Ren, et al., 2018b), coverage, species diversity (Veen,
Van Der Putten, & Bezemer, 2018), functional diversity (Thomas
et al., 2018), soil properties (Deng et al., 2018), and soil microbes (Zhang
et al., 2017b; Zhong, Yan, Wang, Wang, & Shangguan, 2018). However,
space for time substitution in succession studies in abandoned croplands
is also accompanied by time heterogeneity, the result of cropland rep-
resenting different succession years at T0, which means these croplands
will have been abandoned in different years (Figure 1).
Secondary succession in abandoned cropland without human
interference is an effective means of restoring degraded ecosystems
under extremely poor environmental conditions (Benjamin, Domon, &
Bouchard, 2005; Wang, Liu, & Xu, 2009). The agriculture-pasture eco-
tone in northern China especially in the Loess Plateau gully region is
an excellent example. Characterized by low yet highly variable annual
rainfall, extensive cultivation has been important for farming produc-
tion. The Loess Plateau is now one of the most vulnerable areas in the
F IGURE 1 A conceptual model for the succession of abandonedcroplands in different years. The x-axis (0, t1, t2, and t3) representstime since abandonment. Space for time substitution generally occursat T0 [Colour figure can be viewed at wileyonlinelibrary.com]
F IGURE 2 Taxonomic diversity (left) and functional diversity (right) over time for each abandoned cropland A1998, A1999, and A2000.(a) Species richness, (b) Shannon–Wiener index, (c) species evenness, (d) modified functional attribute diversity (MFAD), (e) functional divergence,and (f) functional evenness. Values represent the mean ± SE for the three cropland groups (replicate succession plots in each cropland). *p < 0.05,**p < 0.01, and ***p < 0.001 is compared among groups of A1998, A1999, and A2000 [Colour figure can be viewed at wileyonlinelibrary.com]
2 HU ET AL.
world owing to poor ecological conditions and pervasive soil erosion.
Vegetation restoration is an effective way to manage water loss and
soil erosion as well as promote restoration of ecosystem services
(Valkó et al., 2016). To solve the problem of ecological degradation on
the Loess Plateau, the Chinese Government initiated a nationwide
ecological programme called the Grain for Green Program to prevent
further soil erosion and improve the quality of the degraded soil,
focusing on restoring vegetation by converting cropland to forest and
grassland. Begun in 1999, this Programme is a major ecological under-
taking; it includes large financial investment, strong policy, wide
involvement, and high levels of public participation in China (Zhang,
Ren, et al., 2018b). The local grassland species on the Loess Plateau
includes herbaceous plants, of which Artemisia capillaris Thunb., Stipa
bungeana Trin., and Lespedeza davurica (Laxm.) Schindl, are dominant
species, accounting for more than 80% of the total biomass (Hu,
Zhang, Chen, Chang, & Hou, 2019).
Rainfall and time since abandonment are the main factors that
affect recovery in abandoned croplands on the Loess Plateau. Rainfall
can directly affect aboveground and underground biomass, and time
of succession has cumulative effects on species diversity and ecosys-
tem productivity (Xu, Xu, & Huang, 2011). Biodiversity and ecosystem
productivity are important indicators for measuring the degree of deg-
radation and restoration in abandoned croplands, and consequently
play important roles in the process of succession.
For this study, we selected croplands in northwest China that
were abandoned in different years (temporal heterogeneity) and con-
ducted 10 years of fixed-point, continuous observation. We analyzed
the plant community structure and six characteristics of diversity for
different times since abandonment. We hypothesize that temporal
heterogeneity may have a different direction during early cropland
succession, but that ultimately, cropland succession proceeds in same
direction (Figure 1). Our study assessed the temporal heterogeneity
by evaluating (a) taxonomic diversity (species richness, Shannon–
Wiener index, and species evenness), and functional diversity (modi-
fied functional attribute diversity, functional divergence, and func-
tional evenness), (b) aboveground biomass and the stability of
biomass, (c) nonmetric multidimensional scaling (NMDS) for biomass
of each aboveground species. In addition, structural equation model-
ing (SEM) was used to model the direct and indirect effects of rainfall
and time since abandonment on total biomass. This study was
designed to assess whether temporal heterogeneity can be used in
succession studies after land is abandoned.
2 | MATERIALS AND METHODS
2.1 | Study site
The study site is in Huanxian County, eastern Gansu Province, north-
west China (37.14�N, 106.84�E) in the Loess Plateau Ravine at an ele-
vation of �1700 m. The region has a mean daily air temperature of
7.1�C. Average annual precipitation for 1998–2010 was 274 mm but
is highly variable (range 149–433 mm; coefficient of variation = 28%;
Figure S1). More than 70% of the total rainfall occurs from July to
September, and the mean annual potential evaporation is 1,993 mm
(Chen, Hou, Matthew, & He, 2017). Spring and autumn are typically
short, summer is hot and humid, and winter is long and cold. The soil
is classified as sandy, free-draining loess and the rangeland is a typical
temperate steppe (Ren et al., 2008).
The main crops grown in the study area prior to abandonment
were potato (Solanum tuberosum L.), maiz (Zea mays L.), foxtail millet
(Setaria italica [L.] P. Beauv.), and buckwheat (Fagopyrum esculentum
Moench) (Xu, 2015). Farmyard manure was applied to crops before
planting but stopped after abandonment. The area has been part of
the Grain for Green Program since 1999, and this has sought to pre-
vent soil erosion and improve the quality of the degraded soil by
focusing on vegetation restoration through conversion of cropland to
forests and grassland. In this study, we selected croplands abandoned
in the years 1998, 1999, and 2000 (hereafter named A1998, A1999,
and A2000, respectively) and monitored aboveground vegetation
characteristics for 10 years. Four abandoned croplands (area from
5,000 to 6,000 m2) were selected each year to provide replication.
The three different years of abandoned croplands created a temporal
heterogeneity. Considering the strong influence of tillage history on
succession (Benjamin et al., 2005), we selected only croplands that
had same farming history, planted with foxtail millet for at least
F IGURE 3 (a) Aboveground biomass (g m−2) in three croplandgroups A1998, A1999, and A2000 over 10 years. Values representthe mean ± SE for the three treatments; *p < 0.05 is compared amonggroups of A1998, A1999, and A2000. (b) Stability of biomassproduction (mean/SD) of the three cropland groups in three timeperiods of 10 years. Error bars represent ±SE [Colour figure can beviewed at wileyonlinelibrary.com]
HU ET AL. 3
5 years before abandonment. The croplands had been cultivated using
a hoe and plough for more than 20 years. After abandonment, there
were no artificial disturbances (grazing, mowing, or fertilization) were
imposed allowing natural succession to commence. At the peak of the
growing season in August of each year, we randomly selected four
1 m2 quadrats within each abandoned cropland. This provided
16 quadrat measurements in each commencement year annually,
480 over the 10-year study period.
2.2 | Aboveground characterization
In each quadrat, plant density, tiller, and branch numbers for graminoid
and non graminoid species, respectively, was measured. Five plants were
randomly selected for each species per quadrat to measure plant height
(absolute plant height), crown breadth (maximum distance from the top
of the branches or tillers), and branches or tillers numbers. In addition, the
entire aboveground biomass from each quadrat was clipped and sorted
into dead and live fractions, and then dried and weighed. The total above-
ground biomass only included the live fractions.
2.3 | Data analysis
Taxonomic and functional diversity were calculated per abandoned
cropland using the average aboveground biomass for each species
and the 10 traits (Table S1).
Community diversity was estimated by measuring plant species
richness (number of plant species), Shannon's diversity index (H),
H= −XS
ipiln pið Þ,
F IGURE 4 A structural equation modeling describing the effects of rainfall and time since abandonment on total biomass (a), andstandardized total effects (STE, the sum of direct and indirect effects from each variable) from the SEM on total biomass (b). Numbers labeling thearrows are the standardized path coefficients, indicating the strength of the relationships. The grey dotted line indicates no significant correlation,the black line indicates a significant positive correlation, and the red line indicates a significant negative correlation. Significance levels of eachpredictor are *p < 0.05, **p < 0.01, and ***p < 0.001 [Colour figure can be viewed at wileyonlinelibrary.com]
4 HU ET AL.
Where: pi is the biomass of i species and accounts for total species
biomass.
The proportion of individuals in community was estimated by the
Pielou index (E),
E =H=lnS,
Where: S is the total number of species in the community.
The functional diversity was estimated using modified functional
attribute diversity (MFAD), which measures the dispersion of species
in the functional traits space.
MFAD=XNh=1
XNk =1
dhk
!=N;
dhk =Xpi=1
ahiakij j=Xpi=1
max ahi,akif g,
Where: dhk is the dissimilarity between functional units h and k, ahi is
the affinity of functional unit h to trait i and aki is the affinity of func-
tional unit k to trait i, and N is the number of functional units
(Schmera, Er}os, & Podani, 2009).
Functional divergence (Fdiv) is the deviance of species from the
mean distance to the center of the multivariate trait space weighted
by the relative cover of the species. Low functional divergence indi-
cates that abundant species have trait values that are close to the
community-weighted trait average, while high functional divergence
indicates that the most abundant species have more extreme trait
values (Botta-Dukát, 2010).
Fdiv =XNh=1
XNk >1
dhkphpk ,
Functional evenness (Feve) quantifies the distribution of species
traits in the occupied trait space (Villéger, Mason, & Mouillot, 2008).
Feve =XS−1
b=1
min PEWb1=ðS−1Þ½ �−1= S−1ð Þg= 1−1=ðS−1Þ½ �( )
EWb =EWbPS−1
b=1EWb
,
EWb = dhk= ph + pkð Þ:
Before calculating functional diversity, plant traits data were stan-
dardized using a Z-transformation to obtain a mean of zero and a
standard deviation of one, because they were measured in different
units.
Succession stages were to be divided across multiple years or
cohorts of years (Zhong et al. 2018). We thus divided the succession
time into three cohorts, that is, 1–4, 4–7, 7–10 years, as this allowed
us to include the full 10 years of experimental data and examine tem-
poral changes in stability of aboveground biomass (Veen et al., 2018).
We also used NMDS to visualize how the composition of the plant
community changed over time. NMDS was carried out in R version
3.5 (R Development Team, 2013).
One-way ANOVA was used to determine the differences in the
aboveground biomass, stability of biomass, taxonomic diversity (spe-
cies richness, Shannon–Wiener index, species evenness), and func-
tional diversity (MFAD, functional divergence, functional evenness)
among three cropland groups at same time since abandonment in suc-
cessional stages. The statistical significance was considered at
p < 0.05. Mean values (±SE) are presented in Figures 3–5.
As data were not normally distributed (Shapiro–Wilk test), a gen-
eralized linear model (GLIMMIX procedure) was applied to quantify
the effects of rainfall (R, from the previous year's September to cur-
rent August), time since abandonment (Y, one to 10 years), and time
of abandonment (T, the year each of the three cropland groups aban-
doned: A1998, A1999, and A2000) on the aboveground biomass, tax-
onomic diversity (species richness, Shannon–Wiener index, and
species evenness), and functional diversity (MFAD, functional diver-
gence, and functional evenness; Table 1). The model is y = R + Y + T
+ R × Y + R × T + T × Y + R × T × Y+ Γ + ε, where Γ is the random
effect of replicate, and ε is the model error. Based on the observation
of the changes in each indicator, we divided the years into two epi-
sodes, that is, 1–5 and 6–10 years. All data were analyzed using the
SAS software (SAS 9.4, SAS Institute Inc., Cary, NC). Rejection level of
H0 was set at p < 0.05.
Structural equation modeling was utilized to estimate above-
ground biomass response to rainfall and time since abandonment
based on the hypothesis that rainfall and time since abandonment had
F IGURE 5 Ordination diagram for three cropland groups (A1998,A1999, and A2000) for the aboveground biomass in 10 yearssuccession using NMDS [Colour figure can be viewed atwileyonlinelibrary.com]
HU ET AL. 5
the potential to directly alter aboveground biomass, taxonomic, and
functional diversity, as well as indirectly through changing the taxo-
nomic and functional diversity of aboveground biomass (Ali
et al., 2019). We used the Chi-square (χ2) test to judge the fit of the
model which has a good fit when 0 ≤ χ2/df ≤ 2 and .05 < p ≤ 1
(Grace, 2006). The SEM's were calculated using AMOS
21 (Arbuckle, 2010).
3 | RESULTS
3.1 | Taxonomic diversity
There were significant differences in taxonomic diversity in the first
year after abandonment (Figure 2a–c). Taxonomic diversity of the
three cropland groups increased during the first 5–6 years, with signif-
icant differences in some years. Species richness (Figure 2a) differed
significantly in the first, sixth, and seventh year. The Shannon–Wiener
index differed significantly in the first, fifth, sixth, and eighth year.
Species evenness differed significantly in the first, third, sixth, and
eighth year. There were no differences in other years. During years
1–5, species richness was only regulated by time since abandonment
(p < 0.05); Shannon–Wiener index was only affected by time of aban-
donment; and species evenness was not affected by any factors
(Figure 2a–c). Rainfall, time since abandonment, time of abandonment,
and their interactions had no effect on species richness and Shannon–
Wiener index at 6–10 years. Species evenness was affected by the
interaction of time since abandonment and time of abandonment
(p < 0.05; Table 1).
3.2 | Functional diversity
Our findings for functional diversity are summarized on the right side
of Figure 3. The MFAD (Figure 2d) of the three cropland groups had
no difference at first 4 years (p > 0.05), but differed significantly in
the fifth, sixth, and eighth years. The MFAD was significantly regu-
lated by time of abandonment (p < 0.01) in the first 5 years but was
not affected by any factors at 6–10 years (Table 1). The functional
divergence (Figure 2e) of all the three cropland groups differed signifi-
cantly in the second, third, and eighth year. It was affected by rainfall
(p < 0.05) and time since abandonment (p < 0.01) in first 5 years, but
it was not affected by any factors in years 6–10 (Table 1). There was a
significant difference in functional evenness (Figure 2f) for the three
cropland groups in the first and fifth year. It was affected by rainfall in
all years of the observation period (10 years), but it was also affected
by time since abandonment from the sixth year (Table 1).
3.3 | Aboveground biomass and stability of thethree cropland groups
The three cropland groups showed a similar trend in aboveground bio-
mass over the study period (Figure 3a). Biomass was greatest at the
beginning of succession and decreased over the next 5–6 years,
exhibiting increased variation with ongoing succession (Figure 3a).
The highest aboveground biomass was reached in the second year for
A1998 and A2000 (297.5 ± 45.0 and 652.8 ± 92.3 g m−2, respec-
tively) and in the first year for A1999 (265.7 ± 12.0 g m−2). Above-
ground biomass varied significantly with rainfall, time of
TABLE 1 The effect of rainfall (R), time since abandonment (Y), time of abandonment (T, A1998, A1999, A2000) and their interactions onaboveground biomass, taxonomic and functional diversity (F and P; *p < 0.05, **p < 0.01, and ***p < 0.001)
Stage VariablesAbovegroundbiomass
Taxonomic diversity Functional diversity
Speciesrichness
Shannon-Wienerindex
Speciesevenness MFAD
Functionaldivergence
Functionalevenness
1–5 years R 9.1** 2.07 0.07 0.01 0.02 2.89* 9.35**
Y 1.38 4.67* 1.24 0.46 0.52 8.11** 0.04
Tr 3.42* 0.16 2.52* 1.79 6.86** 0.95 1.55
R * Y 11.66** 1.44 2.06 0.36 0.98 1.84 0.46
R * T 4.66* 0.14 2.41 1.55 7.83** 1.57 2.71*
Y * T 4.52* 0.15 2.91* 2.12 9.17*** 1.54 4.42*
R * Y * T 6.09** 0.22 2.52* 1.46 9.37*** 2.05 0.46
6–10 years R 5.02* 0.96 0.18 0.25 0.63 0.17 3.20*
Y 3.03 0.93 0.53 1.19 1.26 0.16 4.31*
T 1.12 0.45 1.41 2.61 1.09 1.88 2.32
R * Y 2.80 0.69 0.39 0.83 1.29 0.04 3.70*
R * T 1.24 0.05 0.51 1.38 0.64 1.30 1.32
Y * T 0.82 0.73 2.07 3.55* 1.10 2.05 2.83*
R * Y * T 0.84 0.26 1.17 2.29 0.79 1.53 1.93
aNote: The bold values in the table indicates that the variable has a significant effect at the 0.05, 0.01, or 0.001 level.
6 HU ET AL.
abandonment, and the interactions of three factors in the first 5 years,
but only with rainfall in years 6–10 (Table 1).
The SEM explained 44 and 42% of the variation in aboveground
biomass in years 1–5 and 6–10, respectively (Figure 4). Rainfall con-
tributed a little to aboveground biomass in years 1–5 (Figure 4-a3).
Time since abandonment had a strong direct effect on the above-
ground biomass with standardized path coefficients (spc) of −0.59
(p < 0.01) in years 1–5. Only functional divergence had a strong direct
effect on the aboveground biomass (spc = 0.46, p < 0.05) in 1–5 years
(Figure 4-a1). However, in years 6–10, rainfall had a direct effect on
the aboveground biomass (spc = 0.23, p < 0.05). Time since abandon-
ment had a standardized total effect on aboveground biomass of 0.35,
including direct and indirect effects though functional evenness
(Figure 4-b3).
Stability of aboveground biomass was initially highest in A1998,
but declined during the second period, and then increased in the third
period. Stability of A1999 and A2000 vegetation increased during
over time. There were no differences among the three cropland
groups for the last two periods (Figure 3b).
3.4 | NMDS ordination of the cropland groups
The vegetation composition of three cropland groups was clustered in
the first year following abandonment, but diverged from the second
to fourth year, and subsequently, clustered again (Figure 5). The
annual Salsola collina Pall, a pioneer species, colonized the abandoned
cropland in the first year since abandonment; it accounts for more
than 95% of total biomass in all the three cropland groups (Figure S2
and Table S1).
4 | DISCUSSION
4.1 | Taxonomic and functional diversity
Taxonomic and functional diversity increased rapidly in the first
5 years; subsequently both aspects of diversity stabilized, and these
results are consistent with previous studies (Kou et al., 2015; Liu, Wu,
Ding, Tian, & Shi, 2017). Species richness of the three cropland groups
initially displayed a rapid increase followed but leveled off succession
progressed. This is consistent with other studies, in which the species
richness first increased and then reached a steady state in the vegeta-
tion succession (Bonet & Pausas, 2004; Wang et al., 2009). Prior
observations might explain these dynamic trends. During the early
stages of succession, abandoned croplands have been found to be ini-
tially colonized by fast-growing annual species (Rees, Condit, Crawley,
Pacala, & Tilman, 2001), and Salsola collina Pall is the fast-growing
annual species in this study (Figure S2). Thus, the rate of species gains
or colonization generally overcomes early successional changes
(Anderson, 2007) and may cause a rapid increase in species richness
(Huston, 1997). Subsequently, richness plateaus when the species
gain and loss rates equalize and the communities approach an
equilibrium state (Cardinale et al., 2007; Marquard et al., 2009). In the
later stages of succession, the annual species S. collina failed to com-
pete against long-lived and highly resilient perennial late-successional
dominants and was ultimately replaced by these late species (-
Figure S2), it was consistent with the studies of Pickett (1982) and Liu
et al. (2017).
Both MFAD and Feve increased soon after abandonment, indicat-
ing that the functional traits space more dispersion and species traits
occupied more space in the first 5 years after croplands were aban-
doned. Functional traits and species traits generally became homoge-
neous as succession proceeded, facilitating a more stable community
(Veen et al., 2018). Veen et al. (2018) found that taxonomic and func-
tional diversity changed over time. We found that time of abandon-
ment had a strong effect on the taxonomic diversity and Feve at first
year since abandonment (Figure 2). This indicates that temporal het-
erogeneity can lead to differences in early succession years, especially
taxonomic diversity and Feve. González-Megías, Gómez, and Sánchez-
Pinero (2007) also found that taxonomic diversity was affected by
temporal heterogeneity and controlled by the sampling scale. From
the sixth to the tenth year, temporal heterogeneity had no effect on
taxonomic and functional diversity (Table 1). Temporal heterogeneity
had minimal effect on both taxonomic and functional diversity after
about 8 years (Figure 2) suggesting that time heterogeneity results in
minimal the differences in taxonomic and functional diversity after
this period of time.
4.2 | Aboveground biomass and stability
In this study, biomass in each cropland group was highest soon after
abandonment and declined over time (Figure 3a). Some previous stud-
ies have not reported this pattern (Asefa, Oba, Weladji, &
Colman, 2003; Bonet & Pausas, 2004) while other studies have found
that aboveground biomass may be highest in the early stages of suc-
cession and that this depends on the plant species first occupying the
niche (Clark, Knops, & Tilman, 2018; Zhang, Liu, Xue, & Wang, 2016).
In this study, the first species S. collina has high single-plant biomass,
and that was the reason for high total biomass in the beginning time
since abandonment (Figure S2). The first species in a niche depends
on soil fertility (organic carbon, total nitrogen, nitrate nitrogen, and
available phosphorus, etc.), which in turn depends on prior farming
practices including the use of farmyard manure (Zhang et al., 2016).
Zhang, Ren, et al. (2018b) found strong reciprocity between vegeta-
tion and soil resources. The croplands used in this study were fertil-
ized with farmyard manure which tends to release nutrients slowly,
influencing succession processes including biomass production. Bio-
mass is higher in the early years following abandonment and then
gradually declines in years 5–6, after that the biomass increased
slowly (Figure 3a). That was because the nutrients accumulate in the
soil in part from the decomposition of litter and from root exudates
(Zhang et al., 2016). Furthermore, Jiao, Wen, An, and Yuan (2013) and
Jucker, Bouriaud, Avacaritei, and Coomes (2014) also concluded that
the establishment of plants improved the soil environmental
HU ET AL. 7
conditions. The biomass is relatively stable in all cropland groups after
the fifth year (Figure 3). We believe that the effect of time of aban-
donment on biomass declines over time.
4.3 | Community succession
The annual pioneer species S. collina colonized abandoned cropland
early and became the dominant species in the first few years after
abandonment (Figure S2). Its greater adaptability to the environment
and competitiveness for resources has been shown to negatively
affect the growth of other species (Zhang et al., 2016), consistent with
the low diversity (taxonomic and functional) that we observed at this
stage of succession (Figure 3). But a 3-years period of community
development is too short to enable S. collina to colonize bare soil.
Later more species established (including A. capillaris, S. bungeana, and
L. davurica; Figure S2), and taxonomic and functional diversity were
correspondingly higher (Figure 2).
The vegetation composition was differed among the three
cropland groups from second to fifth years (Figure 5 and Figure S2).
All three cropland groups started with bare land after abandon-
ment, but these differences may be caused by different rainfall
events at the time of abandonment (Table 1). In years 3–8, all three
cropland groups exhibited a change in community structure, with a
large number of new species (Figure S2), and a change in the com-
position of the community (Figure 5). The main reason for this
change may have been the germination of a large number of seeds
in the soil seed bank (Hu, Chen, Chen, & Hou, 2015). However,
because of continuous elimination due to competition, several well
adapted indigenous species (A. capillaris, S. bungeana, L. davurica,
Heteropappus altaicus (Willd.) Novopokr. and Pennisetum cen-
trasiaticum Tzvel.) survived (Hou, Xiao, & Nan, 2002; Zhang, Ren,
et al., 2018b). This is the reason for the similarity of the composi-
tion of the three cropland groups in the 10th year post abandon-
ment (Figure 5 and Figure S2).
Jírová, Klaudisová, and Prach (2012) found that abandoned fields
were situated in a more humid region in the Czech Republic, would
develop into shrublands and ultimately to the climax vegetation
including forest if succession continues for the long term, over many
decades. Our study area was in semiarid region, without natural
woody plants present in the local grasslands, limiting the potential for
woody vegetation (Sojneková & Chytry, 2015). Consequently, it is
highly unlikely that long-term succession would lead to the presence
of woody vegetation, either indigenous or exotic on this region.
Sojneková and Chytry (2015) found that species composition of
restored sites became similar to native dry grassland species after
40 years. On the Loess Plateau of China, Liu et al. (2017) predicted
the abandoned cropland will take at least 20 years to recover to a sta-
ble community structure. Hou et al. (2002) predicted it would take
8–9 years to establish stable community structure and 9–11 years for
the dominant population to be stable. In this research, the three crop-
land groups reached a stable dominant population to native grassland
species by 10 years, consistent with the prediction of Hou et al. (2002)
but faster than observed by Liu et al. (2017). The rainfall and local
vegetation types may be the main factors governing the speed of suc-
cession, we found that the biomass and some diversity indexes were
strongly influenced by rainfall in this study (Table 1).
5 | CONCLUSIONS
During the succession of all three cropland groups, the plant commu-
nity transitioned from dominance by therophytes with relatively high
aboveground biomass to dominance by perennial species with lower
aboveground biomass. Time heterogeneity affected aboveground bio-
mass, taxonomic, and functional diversity in the progress of succes-
sion, especially for biomass and taxonomic diversity in the first year,
but had no effect on biomass and diversity of taxonomic and func-
tional after 8 years. Therefore, we suggest that it is feasible to study
the succession of abandoned cropland beyond 8 years using temporal
heterogeneity. However, because time heterogeneity in our study
was based on croplands abandoned in three consecutive years, we
cannot yet make conclusions about differences in succession between
croplands with a longer interval between abandonment. Ongoing
monitoring will be necessary for future studies of succession in aban-
doned croplands.
ACKNOWLEDGMENTS
We specially thank Prof. James Millner and Saman Bowatte for editing
the English and providing helpful and constructive comments for
improving the manuscript. And we also thank Prof. Xiongzhao He for
the help in statistical analysis. This research was supported by the
Strategic Priority Research Program of the Chinese Academy of Sci-
ences (XDA2010010203), the National Natural Science Foundation of
China (31172249), the Program for Changjiang Scholars and Innova-
tive Research Team in University (IRT17R50), Key R & D Program of
Ningxia Hui Autonomous Region (2019BBF02001).
CONFLICT OF INTEREST
The authors declare no conflicts of interest.
AUTHOR CONTRIBUTIONS
Conceptualization and supervision, Fu-Jiang Hou; Design and meth-
odology, Fu-Jiang Hou and Zhi-Biao Nan; field investigation, Fu-Jiang
Hou, An Hu, Sheng-Hua Chang, and Xian-Jiang Chen; data analysis,
Fu-Jiang Hou and An Hu; data curation, Fu-Jiang Hou and An Hu;
writing—original draft preparation, Fu-Jiang Hou and An Hu; writing—
review and editing, Fu-Jiang Hou. All the authors have read and
agreed to the published version of the manuscript.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the
corresponding author upon reasonable request.
ORCID
Fu-Jiang Hou https://orcid.org/0000-0002-5368-7147
8 HU ET AL.
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SUPPORTING INFORMATION
Additional supporting information may be found online in the
Supporting Information section at the end of this article.
How to cite this article: Hu A, Chang S-H, Chen X-J, Hou F-J,
Nan Z-B. Temporal heterogeneity has no effect on the
direction of succession in abandoned croplands in a semiarid
area of northwest China. Land Degrad Dev. 2020;1–10.
https://doi.org/10.1002/ldr.3780
10 HU ET AL.