Impact of grazing on range plant community components under arid Mediterranean climate in northern Syria

A.A. Niane

Research output: Thesisinternal PhD, WU


Keywords: Rotational grazing, full protection, continuous grazing species richness,

species diversity, soil seed bank, Bayesian methods, Salsola vermiculata, seed

longevity, rangeland management, Syria.


Rangelands represent 70% of the semi-arid and arid Mediterranean land mass. It is a

natural habitat for millions of people whose livelihood depends on animal husbandry.

The revolutionary developments in the animal husbandry and veterinary medicines

resulted in exponential increases in human and livestock population living on and from

dry lands. To respond to population growth, urbanization and transportation means

and expanded road networks, land reform and rural development policies forced

nomads to adopt semi to fully sedentary lifestyles with disintegrated traditional

community structures and organizational frameworks. Under these demographic

changes coupled with national and international border crossing restrictions, there was

an escalation in opportunistic cultivation, and excessive exploitation of the scarce and

slowly renewable vegetation cover resulting in a steep decline in the primary

production components of the rangeland ecosystems. In an attempt to stop and reverse

the degradation process, large-scale re-vegetation programs based on transplanting and

reseeding with perennial shrubs, resting and grazing management systems were

devised and implemented. This study aimed to evaluate the impacts of the

rehabilitation programs on the above-ground vegetation cover and soil seed bank

replenishment in the Syrian rangelands. The underlying assumption of the

rehabilitation program is that with a well-established perennial plant cover and proper

grazing management, top soil is stabilized, soil moisture, nutrients and seed bank are

replenished, organic matter is accumulated and microorganisms’ activity is promoted

resulting in greater abundance, species richness and diversity of annuals. To test the

above hypothesis, field and controlled environment based studies were carried out with

quantitative data collection and processing on plant species abundance, richness and

diversity of above-ground vegetation and soil seed bank for fully protected rotationally

and continuously grazed areas of 10 rangeland sites in northern Syria for three

consecutive seasons.

In addition to the use of frequentist statistical approaches for species diversity

estimation in the studies, the Bayesian method was explored. Moreover, the crucial

issues of seed quality in re-vegetation were tackled through a study on seed viability

and longevity in Salsola vermiculata L., which is a highly palatable, well adapted and

widely used species in the arid Mediterranean rangeland rehabilitation programs.

The major findings are indicated below.

Above ground vegetation cover

The vegetation cover data analysis using ANOVA showed that overall plant density

consistently declined from full protection to rotational and then continuous grazing in

9 out of the 10 sites studied, whereas the trends of change in species richness and

diversity were not consistent.

Pair-wise comparison showed that plant density, species richness and diversity

were lowest for the overall plant population under rotational grazing in which plant

density of perennial grasses was highest. This suggests that rotational grazing has

reshaped the composition of the plant communities under the study areas by promoting

the perennial grasses that are more arid rangeland adapted and ecosystem significant.

Higher plant density under rotational grazing and similarity in species diversity under

the three grazing treatments for perennial grasses imply that a longer period of

rehabilitation and/or probably incorporating inter-seasonal rotational grazing and

variation in herbivore types into the current intra-seasonal rotational grazing system

will be required to cross the line of no return in plant community composition

optimization through the prevalent arid Mediterranean rangelands rehabilitation


Soil seed bank assessment

The soil seed bank data analysis using ANOVA showed no significant differences in

the overall physical and germinable soil seed bank size and diversity along the grazing

gradient. However, there was a significant grazing-by-site interaction for both and a

significant grazing-by-year interaction for germinable seed bank size showing that the

change in seed bank size is moderated by physical and environmental characteristics

and human-induced disturbances. Continuous grazing treatments for some sites were

located near agglomerations of people and animals, main roads and water points.

Under such conditions the more disturbance-adapted ephemerons and non-palatable

plants with limited constraints for seed setting dominated and this resulted in a larger

soil seed bank under continuous compared to rotational and full protection grazing

treatments. For the more human-induced disturbance distanced sites, the soil seed bank

was at larger or similar under full and/or rotational compared to continuous grazing.

Results from pair-wise comparisons showed a simultaneous decline and surge in

physical and germinable soil seed bank size of annuals and those of perennials under

the grazing treatments over sites. This suggests relative differences in root competition

and gap exploitation characteristics among plant functional groups; these differences

could be considered indicative to rangeland status and a guide to vary herbivores in

order to maintain optimum plant species diversity in the target rangelands.

Soil seed banks with no seeds of perennial grasses generated 208 seedlings m-2 of

germinable soil seed bank under continuous grazing. This is probably due to seed

setting failure resulting from overgrazing compensated by vegetative reproduction.

The widely used phanerophytes in the rangeland rehabilitation program had a physical

soil seed bank of 59.7 to 119 seed m-2 and a zero germinable one. This shows high

complementarity between physical and germinable seed testing methods for rangeland


Similarity indices

High Morisita-Horn and Sørensen similarities were recorded between the quadrat and

point intercept measurements of the above ground vegetation and with each of

physical and germinable soil seed banks. However, the similarity indices of the above

ground vegetation measurements were higher with the germinable soil seed bank than

with the physical soil seed bank. This suggests that the germinable soil seed bank is

more suitable for monitoring arid Mediterranean rangeland than the physical soil seed


Correlation coefficients

Based on the coefficients of determination (CDs), the variation in plant density and

seed bank size accounted for a significant portion of the variations in spcies richness

but not of the diversity indices. However, plant density and species diversity

consistently and significantly declined during the season with the lowest mean annual

precipitation showing the crucial role of precipitation in the dynamics of the yet active

soil seed banks of the study areas. The CDs for the germinable soil seed bank size

tested under optimum soil moisture with species richness were also significant

throughout the grazing treatments reflecting the dependence of seed bank dynamics on

soil moisture.

For the physical soil seed bank (PSSB), CDs of its size with species richness

were only significant under rotational grazing implying positive impacts of grazing

management on soil seed bank replenishment. Morover, the CDs of PSSB richness

with the diversity indices were only significant for Singletons but not for Shannon and

Simpson. This is attributable to the fact that the Singleton index is more sensitive to

rare species than Shannon and Simpson. The non-significant correlations between

plant density and species diversity reflect a need to incorporate inter-seasonal

rotational grazing and herbivore variation to the current intra-seasonal rotational

grazing for greater plant community integrity.

Phytogeographic analysis

Using two above and two underground vegetation data collection methods, a total of

137 species, including 102 annuals and 35 perennials from 36 families of 11

chorotypes, were recorded. The number of species recorded were 56, 66, 68 and 98

from physical seed extraction, point intercept, quadrat and grow out test, respectively.

These results showed the superiority of the growing out test over the three other

methods. With its easiness and relative flexibility of application in terms of time and

space, the grow out test seems to be the best method for arid Mediterranean rangelands

monitoring and assessment of rehabilitation impacts in which the frequency of good

rainy season is one out of four years.


 The rotational grazing component of the rangeland rehabilitation program resulted

in a change in plant community composition shown by an increase in low

proportional abundance perennial grasses with greater arid Mediterranean

rangeland adaptation.

 Continuous grazing reduced plant density but not richness and diversity, indicating

that maximum diversity is not a sign of rangeland health and integrity. This also

suggests that inter-seasonal rotational grazing and herbivore variation could

probably improve the shaping effects of grazing on the arid rangeland

rehabilitation programs.

 Capturing more species and higher similarity indices with the above ground

measurements, the simple and flexible, germinable soil seed bank test seems to be

a good monitoring and evaluation method for arid Mediterranean rangelands.

However, results from the tedious and less accurate physical seed extraction

method could be crucial to capture the species with long seed dormancy.

 Larger Bayesian estimates of diversity, smaller standard errors, lower p-values and

more significance of differences in diversity between grazing treatments compared

to the frequentist approaches were observed, thus indicating clear merits for the

approach in estimating diversity.

 The seed longevity study showed that under relatively higher seed moisture

content, longevity increased suggesting that desiccation susceptibility is probably

the cause of short seed longevity of Salsola vermiculata L. Moreover, drying and

packaging alone increased longevity, thus providing a simple, cost-effective and

environmentally friendly method for rangeland rehabilitation programs.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Struik, Paul, Promotor
  • Bishaw, Z., Co-promotor
Award date3 Dec 2013
Place of PublicationWageningen
Print ISBNs9789461734143
Publication statusPublished - 2013


  • rangelands
  • grazing
  • arid grasslands
  • rotational grazing
  • botanical composition
  • biodiversity assessment
  • seed longevity
  • syria


Dive into the research topics of 'Impact of grazing on range plant community components under arid Mediterranean climate in northern Syria'. Together they form a unique fingerprint.

Cite this