Neelain Journal of Science and Technology.

Volume 1, Issue 1, May 2017, 21–28

Original article

Changes in Plant Species Richness and Density along Altitudinal Gradient in

Rashad and Alabassia Localities, South Kordofan, Sudan

Ismail Mirghani Ismail1* and Alawia Abdalla ELawad2

1 Botany Section-Forestry Research Centre, Agricultural Research Corporation, Khartoum, Sudan

2 Faculty of Science and Technology-Alneelain University, Khartoum, Sudan. Email address: ismail.mirghani@yahoo.com

ARTICLE INFO Abstract

Article history:
Received 2016 October 26th This study was carried out at Rashad and Alabassia localities, South Kordofan, Sudan.
Reviewed 2017 February 3rd The objective of the study is to assess the impact of elevation on species richness and
Accepted 2017 April 8th
density. To understand the dynamic trends of the vegetation across the studied area, the

Keywords: compositional and structural features of three plant layers (mature tree and shrubs,
Margalef index, regeneration and herbaceous) at 14 investigation sites were compared, in terms of
Shannon index,
species richness, species evenness and density. Shannon Biodiversity index (H),
Pielou index,
vegetation assessment, Margalef index (Species richness (D) and Pielou index for species evenness (E) were
calculated. Results of ecological indices show that their values in the mature trees and
shrubs and regeneration layers increase with increment of elevation, while they decrease
with increment of elevation in herbaceous layer, the density of mature trees and shrub
and regeneration layers decreases with increment of elevation and increases with
increment of elevation in herbaceous layer. More research is needed to assess the
altitudinal effect in the natural vegetation in the other Localities of the Nuba Mountains.
*
Corresponding author: ismail.mirghani@yahoo.com
higher latitudes has been documented for woody plants (Currie
Introduction and Paquin, 1987). According to Valdovinos et al. (2003), this
Large-scale vegetation inventory and monitoring programs are trend is not universal but more pronounced in the Northern
rare (Stohlgren, 1994) but valuable for regional and national Hemisphere than the Southern Hemisphere (Platnick, 1991).
condition assessments. Such large-scale assessments provide Species evenness is a measure of how equitably abundances are
broad overviews to help strategic policy development and allow distributed among species (Polley et al., 2003).
land managers to place local assessments into regional or Biodiversity is a short form for biological diversity which is to
national perspectives, which facilitate the prioritization of describe the total number, variety and variability of living
limited resources available to managers (Heinz Center 2006, organisms as well as the diversity of the ecosystems they are
Ingerson and Loya 2008). Plant community structure and living in (Krebs, 1999). The concept of biodiversity is
diversity are influenced by many interacting biotic and abiotic considered to be the integration of biological variability across
factors. At the local scale, ecological variables and disturbance all scales, from genetic level, through species and ecosystems,
are key factors that interact with plant strategies to determine to the landscapes that they form, or are part of, and the
vegetation composition and structure (Ribichich and ecological processes that support them (Purvis and Hector,
Protomastro, 1998). Species richness refers to the number of
2000). Generally, biodiversity measurement typically focuses
species present in a given area or habitat (Polley et al., 2003).
on the species level and species diversity as the most important
Local plant species richness can vary considerably across a
indices used for the evaluation of ecosystems at different scales
landscape, suggesting that local factors are important for these
(Ardakani, 2004). Plant diversity is determined by both species
variations (Huston, 1999). The latitudinal gradient in species
richness and species evenness. Local diversity can be studied
richness remains one of the most ubiquitous patterns in ecology
with various indices, such as number of species per unit area
(Pianka, 1966). The trend for species richness to decline at

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(species richness) or the Shannon index. These are used as

indicators of the degree of complexity of the under study Data analysis
communities and to provide information on the homeostatic Shannon Biodiversity index (H) was calculated as given by
capacity of the system to unforeseen environmental changes Shannon & Weaver (1963). Species richness is a biologically
(Magurran, 1988). appropriate measure of alpha (α) diversity and is usually
The savanna areas are considered as important productive parts expressed as number of species per sample unit (Whittaker
in Sudan, they are mainly classified as savanna woodlands, tree 1972). Margalef index (Species richness (D)): was calculated
and shrub savannas, grasslands or steppes (Menaut, 1983). as given by Margalef, (1958). Pielou index for species
evenness (E): was calculated as given by Pielou (1966).
Nuba Mountains belongs to the low rainfall woodland savanna
(Harrison and Jackson, 1958). In this work the community
Results and Discussion
structure and composition of selected 14 sites in Rashad and
The results of the different studied ecological parameters are
Alabassia Localities, South Kordofan, Sudan were analyzed.
presented in table (2):
The aim of this study was to assess the species richness,
For mature trees and shrubs layer both site 6 (Elawai north
taxonomic composition and stand structure in the studied sites
Rashad) and site 8 (Rashad Dam), had the highest species
and to estimate the effect of elevation on the studied parameters. richness (21 species), while site 1 (Um-Fakareen) and site 13
This study is expected to provide a botanical reference for (Tandek) are species poor sites (6 species) (table 2).
future ecological research and conservation efforts of one of the
productive areas in the Sudan, which is now facing political The rest of the areas had comparable species richness values.
crisis. Although site 1 and site 13 had evident variation in their
elevation, they are similar in soil type as cracking clay. The
Materials and Methods results of this study have proved that species richness is
Description of the study area positively linearly correlated with elevation (r = 0.675, P =
The study area is located in the northern part of eastern Nuba 0.008). The Regeneration layer showed that Site 9 (Jebel
Mountains of South Kordofan State and including two Rashad) has the highest species richness (19 species), while
localities (Rashad and Alabassia), extending from latitude the lowest value (6 species) was recorded by site 1 (Um-
11º 33` to 12º 33` N and from longitude 31º 08` to 31º 18` Fakareen) and site 2 (Jebel Damra).
E. Most of the area under study is covered by scattered
isolated hills and is dissected by many seasonal watercourses Table (1): Characteristic feature of selected sites
(KHORS). Rashad and Alabassia localities occupy a total
area of 7872 km2 (UNDP, 2003). Annual average
Site Location Latitude Longitude Elevation Type of
temperature and precipitation is are 29.9ºC and 542 mm,
(N) (E) (M) soil
respectively (Sudanese Metrological Authority, 2004). The
precipitation is seasonally distributed, with a distinct wet 1 Um Fakareen 12 o 33` N 31o 18` E 500 m Cracking
clay
season from May to October and a dry season from
November to April. 2 Jebel Damra 12o 10` N 31o 15` E 739 m Rocky soil
3 Elmigreh 12o 02` N 31o 14` E 826 m Rocky soil

Data collection 4 Um Zamboor 12o 00` N 31o 13` E 885 m Rocky soil

The study was conducted during the years 2010-2011. After 5 Sug-Eljabal 11o 57` N 31o 12` E 914 m Rocky soil

the reconnaissance survey, 14 sites were selected, based on 6 Elawai North 11o 52` N 31o 08` E 849 m Rocky soil
Rashad
observed variations in vegetation types, topographical
features and soil types to represent most of the study area 7 Tabaldia 11o 50` N 31o 09` E 860 m Rocky soil

(Table, 1):. For vegetation assessment within the natural 8 Rashad Dam 11o 52` N 31o 02` E 894 m Rocky soil

stands 70 circular 0.1 ha (17.84 m in radius) sample plots 9 Jebel Rashad 11o 49` N 31o 03` E 852 m Rocky soil

modified from Adam and Eltayeb (2008). 14 transects were 10 South Rashad 11o 45` N 31o 02` E 781 m Rocky soil

made to cover the whole study area. Along each transect 5 11 Um Abdalla 11o 45` N 30o 52` E 664 m Gardud soil

circular 0.1 ha plots were conducted for studying trees and

12 Awai South 11o 43` N 31o 03` E 723 m Rocky soil
shrubs and natural regeneration. The first plot was
Rashad
established randomly, the number of trees and shrubs species
13 Tandek 11o 42` N 31o 02` E 695 m Cracking
and the number of individual of each species per/plot were
clay
counted. For assessing herbaceous plants four 50X50 cm
14 Dibekkir 11o 33` N 31o 08` E 618 m Cracking
quadrate were randomly established in each 0.1ha. main plot.
clay

The present findings revealed that species richness is also

positively linearly correlated with elevation in this layer (r=

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0.561, P= 0.0369). dispersion behavior of tree species (Eilu and Obua, 2005).
The highest richness value in the herbaceous layer (19 species) Elevation gradients create varied climates, along with resultant soil
was recorded in site 2 (Jebel Damra) while the lowest value (8 differentiation; promote the diversification of plant species (Brown,
species) was recorded in site 9 (Jebel Rashad). This result showed 2001). It has been reported that woody species richness showed a
that species richness is negatively linearly correlated with elevation linear decrease in relation to elevation (Chiarucci and Bonini, 2005).
in the herbaceous layer (r= -0.274, P =0.343). Decrease of species richness of the woody plants at low elevations
The highest plant species richness of mature trees and shrubs may be due to th e fact that low elevation sites are relatively
layer in this study is less than the 32 species of Ismail & Mahmoud densely populated and human interference in these sites facilitates
(2010) from Jebel El Dair. Also it was observed that the highest negative impact on the species composition by selective felling of
values of richness of mature tree and shrubs and regeneration layers economically valuable species and overgrazing.
occurred in mountainous sites and increases with the elevation Margalef index (Species richness (D)) and its relation to
increment, while the lowest values occurred in clay plains sites and elevation
decreases with elevation increment. This partly agreed with the fact Margalef index results (Figure 2) and (table 2) show that the highest
stated by Meihe and Meighe (1994) that the proportion of endemic value in mature trees and shrubs layer (D = 11.17), has been
plants strongly increases with altitude. It has been suggested that recorded in site 8 (Rashad Dam), while the lowest value (D = 2.84),
different altitudes and slopes influence species richness and has been recorded by site 1 (Um-Fakareen).

Table (2): Ecological indices and density of different vegetation layers along different elevations.

Trees and shrubs layer Regeneration layer Herbaceous layer

Altitude Shannon Pielou Margalef No. of Density Shannon Pielou index Margalef No. of Density Shann Pielou Margalef No. of Density
(m) index (H) index index (D) Species (stem/ha) index (H) (E) index (D) Specie (Stem/ha) on index index Species (plant
(E) s Index (E) (D) /m2)
(H)
500 1.18 1.51 2.84 6 114 1.6 2.05 2.28 6 306 1.96 1.56 7.66 18 52
712 2.13 1.64 8.92 20 268 1.48 2.12 2.58 6 174 2.2 1.72 7.47 19 51.64
826 2.33 2.16 6.88 12 72 1.84 1.7 5.91 11 144 1.88 1.11 4.63 13 77.4
885 2.18 2.02 7.24 12 66 1.16 1.12 4.39 11 384 2.16 1.71 6.54 18 80.4
914 2.2 1.75 10.37 18 88 2.32 1.97 6.7 15 244 1.47 1.41 3.65 11 110
849 2.63 1.99 9.71 21 228 2.35 1.87 8.13 18 244 1.21 1.09 4.65 13 76
860 2.17 1.81 8.38 16 574 1.9 1.71 5.91 13 216 1.65 1.53 4.76 12 41.2
894 2.68 2.03 11.17 21 122 2.18 1.89 6.84 14 160 2.19 1.83 5.79 16 78.1
852 1.86 1.45 7.32 19 124 2.31 1.01 8.45 19 294 1.98 1.77 3.11 9 73.6
781 2.43 1.9 9.63 19 148 2.33 2.1 7.84 13 68 1.82 1.69 4.65 12 57.2
664 1.63 1.51 6.4 12 106 1.82 1.54 6.39 15 310 1.65 1.49 4.47 13 76.2
723 1.76 1.59 6.67 13 126 1.595 1.3 7.27 17 316 2.45 1.94 7.08 18 48.4
695 1.25 1.6 3.62 6 48 0.88 0.93 3.2 9 628 1.46 1.4 4.43 11 36
618 0.695 0.7 3.49 10 766 0.59 0.6 3.06 10 1738 1.8 1.67 4.64 12 46.8

The present finding revealed that Margalef index of mature trees and et al., 2011).
shrubs layer is positively linearly correlated with elevation (r = 0.798, The highest values of Margalef index of trees and shrubs layer
P = 0.0006). and regeneration layer occurred in mountainous sites and
On the other hand site 9 (Jebel Rashad) shows the highest value (D = increases with the elevation increment, while the lowest values
8.45) of regeneration layer, while site 1 (Um-Fakareen) shows the occurred in clay plains sites and decreases with elevation
lowest value (D = 2.28). Also Margalef index of regeneration layer is increment. These results agreed with that of species richness
positively linearly correlated with elevation (r = 0.636, P= 0.0146). (species number).
Margalef richness index in the herbaceous layer showed the highest Shannon Wieners Biodiversity index (H) and its relation to
value (D = 7.66) in site 1 (Um-Fakareen), while site 9 (Jebel Rashad) elevation
recorded the lowest value (D = 3.11). Margalef richness index of Shannon index results (Figure 3) and (table 2) show that the
herbaceous layer is negatively linearly correlated with elevation ((r =- highest diversity value of mature tree and shrubs layer (H =
0.43, p= 0.133). These results suggest that the species richness index 2.68) has been recorded in site 8 (Rashad Dam), while site 14
was found to be fluctuating from stand to stand as well as among (Debekir), shows the lowest value (H=0.695). The results of
mature trees and shrubs, regeneration and herbaceous layers (Bharali this study shows that the Shannon index of mature trees and

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shrubs layer is positively linearly correlated with elevation (r= than other species, perhaps in the long run resulting in the
0.796, P = 0.0007). dominance of grazing resistant species.
Regeneration layer shows that the highest value of the Shannon Pielou index of Species evenness (E) and its relation to
diversity index (H = 2.35) has been recorded in site 6 (Elawai elevation
north Rashad), while the lowest value (H=0.59) was recorded Species evenness measures the equity of species in a given
in site 14 (Debekir). Shannon index of regeneration layer is sample area or it is the opposite of dominance by few species.
positively linearly correlated with elevation r = 0.543, P = Pielou index results (Figure 4) and (table 2) show that the
0.0448). highest value of evenness in mature trees and shrubs layer
The herbaceous layer, site 12 (Elawai North Tandek) has the (E=2.16) has been recorded in site 3 (Elmigreh) and the lowest
highest value of Shannon diversity index (H= 2.45), while the value (E = 0.7) has been recorded in site 14 (Debekir). Pielou
lowest value (H=1.21) has been recorded by site 6 (Elawai index of mature trees and shrubs layer is positively correlated
north Rashad). Shannon index of herbaceous layer is with elevation (r = 0.634, P = 0.0148).
negatively linearly correlated with elevation (r = -0.099, P = Regeneration layer shows the highest value (E = 2.1) in both
0.735). site 2 (Jebel Damra) and site 10 (South Rashad), while the
The highest Shannon diversity index (H) of trees and shrubs lowest value (E = 0.6) has been recorded in site 14 (Debekir).
layer in this study is more than that of Ismail & Mahmoud Pielou index of regeneration layer is positively linearly
(2010) (H=2.39) from Jebel El Dair, which is a conserved area. correlated with elevation (r = 0.127, P = 0.665). Pielou index of
Also it is observed that the highest values of the Shannon the herbaceous layer shows the highest value (E = 1.94) in site
index (H) of trees and shrubs layer and regeneration layer 12 (Elawai North Tandek) and the lowest value (E =1.09) in
occurred in mountainous sites and increases with the elevation site 6 (Elawai north Rashad). Pielou index is negatively
increment, while the lowest values occurred in clay plains sites correlated with elevation (r = -0.105, P = 0.720).
and decreases with elevation increment. The highest Pielou evenness index (E) of mature trees and shrubs
Lower diversity in lower elevation could be attributed to heavy layer in this study is more than that of (Ismail & Mahmoud, 2010)
grazing; in addition to the felling of larger trees for charcoal (E= 0.696) from Jebel El Dair, which is a conserved area.
production and shifting cultivation may reduce species The highest values of evenness (E) of mature trees and shrubs
diversity especially in the plains. This agrees with layer and regeneration layer recorded in mountainous sites
McNaughton, (1985) who stated that uncontrolled grazing has increases with the elevation increment, while the lowest values
its own effect on plant species diversity as some well palatable occurred in clay plains sites and decreases slightly with
species are expected to be more severely affected by cattle elevation increment
.

Figure 1: Correlation between elevation and species richness for mature trees and shrub, regeneration and herbaceous layers.

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Figure 2: correlation between elevation and Margalef index for mature trees and shrub, regeneration and herbaceous layers.

Figure 3: Correlation between elevation and Shannon index for mature trees and shrub, regeneration and herbaceous layers

Figure 4: Correlation between elevation and Pielou index for mature trees and shrub, regeneration and herbaceous layers.

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Figure 5: Correlation between elevation and Density for mature trees and shrub, regeneration and herbaceous layers.

The low value of the evenness index in lower elevation may be Um Abdalla forest reserve and less than that of Bunderson et al.
attributed to the fact that lower elevations or plains are dominated (1984) (1000 trees/ha) in the Nuba Mountains and of Ismail and
by few species as in case of site 14 which is dominated by few Mahmoud, (2010) (6174.5 trees and shrubs/ha.) in Jebel El Dair.
species as in case of site 14 which is dominated by Dichrostachys The highest values of density of trees and shrubs layer and
cinerea only. Species evenness measures the relative or the regeneration layer occurred in clay plain sites and decreases with
proportional abundance of species in the sample area. Hence, the elevation increment, while the lowest values occurred in
low evenness value indicates the dominance of the environment mountainous sites and decreases with elevation increment.
by few species (Van Breugel et al., 2007).
Density of plants and its relation to elevation Conclusions
Results (Figure 5) and (table 2) shows that the highest value of The study revealed the effect of elevation in the richness and
density in mature trees and shrubs layer is (766 stems/ha.) density of the different natural vegetation layers. Ecological
recorded in site 14 (Debekir), while the lowest density (48 indices; Shannon Biodiversity index (H), Margalef index (Species
stem/ha.) is recorded in site 13 (Tandek). The results showed a richness (D)) and Pielou index for species evenness (E) show that
negative relationship between density and elevation with in the 14 studied sites the mature trees and shrub and the
correlation value r = - 0.18467 and Linear tests revealed a non- regeneration layers increase with increment of elevation, while
significant relationship (p= 0.5274). they decrease with increment of elevation in the herbaceous layer.
The highest density in regeneration layer (1738 stem/ha) has also The density of the mature trees and shrub and the regeneration
been recorded in site 14 (Debekir), while the lowest value (68) has layers decrease with increment of elevation and increases with
been recorded in site 11 (Um Abdalla). The results showed a increment of elevation in the herbaceous layer. This indicated that
negative relationship between density and elevation with elevation has different impact on species richness and density of
correlation value r= -0.425 and Linear tests revealed a non- the vegetation layers in the study area. This is the first
significant relationship p= 0.13. Site 4 (Um Zamboor) shows the contribution in the evaluation of elevation effect in natural
highest value of density in the herbaceous layer (110 plants/m), vegetation of the two selected Localities of South Kordofan State.
while site 13 (Tandek) shows the lowest density (36 plants/m).
The results showed a positive linear relationship between density Recommendations
and elevation with correlation value r= 0.586 and Linear tests More research is needed in the ecology of the Nuba Mountains
revealed a significant relationship p= 0.028. as it represents one of important and unique reproductive
The highest density (766 stems/ha) of mature trees and shrubs ecological zones in the Sudan.
layer is more than that of Ibrahim, (2008) (77.38 trees/ha.) from

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Forestry, University of Khartoum.

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