Impact of disturbance on species diversity and composition of Cyperus conglomeratus plant community in southern Jeddah, Saudi Arabia

1 Introduction

Diversity of plant communities has never been more highly valued than it is now, as they become increasingly threatened by environmental disturbances. In fact, diversity lies at the root of some of the most fundamental and exiting questions in theoretical and applied ecology (Magurran, 1988). Saudi Arabia is an arid desert covers the majority of the Arabian Peninsula. The flora of Saudi Arabia is one of the richest bio diversities in the Arabian Peninsula and comprises very important genetic resources of crops and medicinal plants (Atiqur Rahman et al., 2004). The distribution of life form is closely related to topography and landform (Zohary, 1973, Fakhireh et al., 2012). Establishment, growth, regeneration and distribution of plant communities in deserts of Saudi Arabia are controlled by many factors such as geographical position, physiographic features, and human impact (Alatar et al., 2012, Korkmaz and Ozcelik, 2013). Human activities in the desert landscape have been increased recently, due to rapid development in the study area. Jeddah 2nd Industrial City seen since its inception in 2009, developed rapidly in order to keep pace with the steady increase in demand for industrial land in the region. It occupies an area of about 8 million m². The Industrial City includes 236 factories including productive, existing, under construction and under formation factories in various industrial fields.​ In fact, the Industrial City of Jeddah has been a serious problem and has adversely affected the vegetation in the study area. Local inhabitants of the study area belt livestock rearing, which has always been a problem adversely affected the desert vegetation.

The vegetation in the study area located close to the Industrial City was dominated by the perennial herb C. conglomeratus. It is an Erect, tufted, rhizomatous perennial, 60–70 cm tall, belonging to family Cyperaceae. Much of its economic importance is due to its medicinal properties. The plant is used in traditional medicine as antimicrobial, emollient, diuretic, stimulant, anthelmintic and analgesic treatment (Feizbakhsh and Naeemy, 2011). Al-Hazmi et al. (2018) proved the anti candidal activity of C. conglomeratus and isolate the bioactive compounds from it. Hisham et al. (2012) also showed the antibacterial activities of the essential oil compositions of the rhizomes of C. conglomeratus collected from Oman.

The objective of the present study is to provide an overview of species diversity of C. conglomeratus plant community and to evaluate the impacts of land use and human manipulations on its composition and species diversity.

2 Materials and methods

3 Results

3.2

3.2 Species diversity

Variations in the results of species diversity (Table 2) indicates that species diversity shows a considerable increase in both moderately disturbed and protected sites (H′ = 1.792 and 1.423 respectively), compared to the slightly disturbed site where H′ = 0.929. While a considerable decrease in diversity of species abundance is noticed in the highly disturbed site (H′ = 0.664), accompanied by a considerable increase in dominance as confirmed by Simpson's index (D = 0.656). The number of most frequent species (N2) and the number of equally common species (N1) were estimated to be equal about two and three species respectively in the slightly disturbed site that increased to a maximum of about four and six species respectively under moderate disturbance. While under protection both N2 and N1 equal about four species. This clarifies the increase in evenness of species relative abundance in both the moderately disturbed and protected sites (E1 = 0.646 and 0.731 respectively).

Table 2 Species diversity of Cyperus conglomeratus community in the selected sites southern Jeddah in Saudi Arabia.

Diversity index	Site
	1 HD	2 MD	3 SD	4 PA
Richness (S)	4	16	7	7
Simpson (D)	0.656	0.253	0.462	0.278
Shannon (H')	0.664	1.792	0.929	1.423
Hill no. 1 (N1)	1.943	5.999	2.533	4.151
Hill no. 2 (N2)	1.525	3.957	2.166	3.591
Shannon-evenness (E1)	0.479	0.646	0.478	0.731
Modified Hill's ratio (E5)	0.557	0.591	0.760	0.822

HD: high disturbance, MD: moderate disturbance, SD: slight disturbance, PA: protected area.

Species abundance distribution models are the method of presenting species abundance data. Species abundance was plotted on a logarithmic scale against the species rank in the sequence of species from most to least dominant (Fig. 1). It is notable that the resulting species abundance model representing the highly disturbed site tend toward geometric pattern of species abundances, where species richness is low and only one species (C. conglomeratus) is dominant with the remainder fairly uncommon. The geometric pattern of species distribution appears as a straight line when plotted on a log abundance/species rank graph. The curves representing other sites in the present study are less steep as more species are added, and the species abundance pattern grades into those of the log series distribution, with the increase in species with intermediate abundance. This is more obvious in the moderately disturbed site in the present study.

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Fig. 1

Species abundance distribution models of Cyperus conglomeratus community in the selected sites southern Jeddah in Saudi Arabia.

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3.3

3.3 Species behavior

Fig. 2 show the species behavior by using importance factor of both C. conglomeratus and P. turgidum in response to some soil factors in different studied sites. The soil salinity was considerably low ranged from 0.08 to 0.28 mmohs cm⁻¹ while organic matter ranges from 0.48 in the highly disturbed site to 1.83 in the moderately disturbed site. It is notable that the EC values attain its maximum under high disturbance while organic matter percentage decreased to a minimum value in the highly disturbed site (Table 3). The behavior of the two most important species in the study area might be affected in response to the change in EC concentration and organic matter percentage. It is remarkable that P. turgidum is negatively affected by disturbance when compared to C. conglomeratus, which attains its maximum dominance under the highest disturbance in the study area. It is also remarkable that protection had a negative effect on C. conglomeratus reducing its importance value to the minimum in the study area, while P. turgidum become the dominant species in the protected site. Gravel percentage attains a maximum percentage at the moderately disturbed site. The highly disturbed site attained with the lowest sand percentage (87) and the highest silt and clay percentages (7.5 and 5.5). Inspection of the results shows that soil texture may have no effect on the behavior of the two species. On the other hand, soil texture may affect species diversity, which increased under moderate disturbance where gravel reaches maximum percentages.

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Fig. 2

Importance values of Cyperus conglomeratus (C. con) and Panicum turgidum (P. tur) in response to soil factors estimated in the selected sites southern Jeddah in Saudi Arabia (HD: high disturbance, MD: moderate disturbance, SD: slight disturbance, PA: protected area).

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Table 3 Comparison between the four selected sites according to soil factors.

Site	Soil Texture				OM% (n = 10)	EC (mmohs/cm) (n = 10)
	Gravel (n = 10)	Sand (n = 10)	Silt (n = 10)	Clay (n = 10)
1 (HD)	18.41b ± 0.67	87d ± 1.0	7.5a ± 1.0	5.5a ± 0.5	0.48c ± 0.03	0.28a ± 0.05
2 (MD)	30.03a ± 2.15	89c ± 1.0	7.0a ± 0.6	4.0b ± 0.6	1.83a ± 0.07	0.11bc ± 0.02
3 (SD)	15.34c ± 0.51	91b ± 1.0	5.5b ± 0.5	3.5b ± 0.5	1.25b ± 0.01	0.08c ± 0.002
4 (PA)	14.86d ± 0.14	92a ± 1.0	2.5c ± 0.5	5.5a ± 0.5	1.04b ± 0.01	0.12b ± 0.001
F	375.753*	49.167*	108.871*	38.288*	2074.222*	111.417*
P	<0.001*	<0.001*	<0.001*	<0.001*	<0.001*	<0.001*
LSD	1.050	0.908	0.619	0.479	0.041	0.029

F and p values for ANOVA test, significance between groups was done using Post Hoc Test (LSD).

Means with common letters are not significant (Means with different letters are significant).

* Statistically significant at p ≤ 0.05.

4 Discussion

The primary cause of the decay of biodiversity is not direct human exploitation or malevolence, but the habitat destruction that inevitably results from the expansion of human populations and human activities (Wilson, 1988). There is a consensus that land use has a negative effect on plant biodiversity and ecosystem processes, but at the same time, there is empirical evidence that there is a large heterogeneity in the response (Rocabado et al., 2016). The study area has been subjected to ecosystem degradation and species impoverishment due to the ways in which man has used and misused the natural resources of the region. The Industrial City of Jeddah has adversely affected the vegetation in the study area especially by solid wastes that thrown from different factories in the nearby area. The net result has been the reduction of vegetation cover and the impoverishment of flora.

The vegetation in the study area located close to the Industrial City was dominated by the perennial herb C. conglomeratus. It is a geophyte belonging to family Cyperaceae. Much of the economic importance of the plant is due to its medicinal value as it was proved by many studies such as Feizbakhsh and Naeemy (2011), Hisham et al. (2012) and Al-Hazmi et al. (2018).

The structure of plant communities in many natural ecosystems is largely influenced by the disturbances, frequently occurring in the system naturally or due anthropogenic activities (Lalfkawma et al., 2009). In many of these systems, disturbances change overall community structure (Shea et al., 2004; Shaforth et al., 2002) which in turn can ultimately affect community and population dynamics. The ecological disturbances in the study area have their major effect on species richness, where about 76% of the perennial species in the study area were disappeared as the result of the human impact on C. conglomeratus community in the most disturbed sites. Interspecific competition results from C. conglomeratus indicated that it is a competitor species led to exclusion of the other species from the highly disturbed sites which affected by the Industrial City in Jeddah. Therefore, the resulting of a remarkable decrease in species diversity was coinciding with maximum dominance of C. conglomeratus. Vegetation analysis revealed that only three species C. conglomeratus, P. turgidum, and I. spinosa, could resist the high disturbance exerted by the Industrial City. While C. hystrix was found to adopt post, disturbance condition as it was recorded only in the disturbed sites. T. aegyptiaca is the only species completely disappeared in the all disturbed and protected sites. It is also remarkable that protection had a negative effect on C. conglomeratus reducing its importance value to the minimum in the study area, while P. turgidum become the dominant species. These functional changes within dominant grasses have been also observed in grasslands of Uruguay (Rodriguez et al., 2003). This may support the view of Altesor et al. (2005) which revealed that there was a shift of dominant species between the grazed and protected treatments. Baker et al. (2015) indicate that species with lower wood density, and therefore presumably higher rates of diameter growth, and those with lighter seeds, and therefore greater dispersal ability, are favored by disturbance.

It is notable that species diversity is considerably reduced because of increasing the level of disturbance exerted by the Industrial City of Jeddah, and consequently high dominance is estimated in the highly disturbed site. It is also notable that species diversity increased in the moderately disturbed site. This coincided with the theoretical analysis that often predicts a peak of species diversity at intermediate disturbance intensity (Huston, 1979; Shekhar and Azim 2010). However, it may be argued that the characteristics of the system and the type of disturbance might be responsible for this trend (Rao et al., 1990). Each diversity index tested in the present study indicates that species diversity showed a considerable increase under moderate disturbance.

Species abundance distribution models are the method of presenting species abundance data (Magurran, 1988). In these graphs, the abundance of each species was plotted on a logarithmic scale against the species rank in the sequence of species from most to least dominant. It is notable that the resulting species abundance models representing the community under high disturbance approaches the geometric pattern of species distribution. This is corroborating the niche preemption hypothesis (Whittaker, 1975). Here one dominant species (C. conglomeratus) occupies a large fraction of the total niche; the second species (P. turgidum) occupies a similar fraction of the niche space, and so on. In other words, the ratio of abundance of species to the abundance of its predecessor is almost constant through the ranked list of species, and that is why the series will appear as a straight line when plotted on log abundance/species rank graph. Whittaker (1972) reveals that field data that have shown the geometric series pattern of species abundance is found primarily in species-poor and often harsh environments or in very early stages of succession. This is also found by Ayyad and Fakhry (1996). As conditions improve, the patterns of species abundance grade into those of the log series. This is obvious in the moderately disturbed, slightly disturbed and protected sites in the present study, where the curves become less steep as more species are added.

Zheng et al. (2017) found that tree species diversity influenced the soil texture to some extent, while Species richness did not have a positive influence on the soil properties. In the present study, it is notable that the highly disturbed site shows the highest soil electric conductivity value and the lowest percentage organic matter coincided with the lowest species diversity and highest dominance as compared with other sites in the present study. While the moderately disturbed site shows the highest percentage of both organic matter and gravel, coincided with the highest species diversity and lowest dominance as compared with other sites in the present study.

In conclusion, the nature of human impact on biodiversity of C. conglomeratus community in the study area may be either sudden or radical, such as the effect of the Industrial City, or it may be gradual and conservative such as the effect of protection. In the first case, loss of species is the ultimate result. The few species which are endowed with the ability to survive such drastic changes of the habitat dominate the C. conglomeratus community to a considerable extent, and species diversity deteriorates. In the second case, the effect of protection on species diversity is considered to be gradual and conservative. It is also notable that species diversity increased under moderate disturbance.