Livestock Research for Rural Development 23 (9) 2011 Notes to Authors LRRD Newsletter

Citation of this paper

Changes in plant species composition and diversity along a grazing gradient from livestock watering point in Allaidege rangeland of North-eastern Ethiopia rangelands

Asheber Tegegn, Lisanwork Nigatu and Amaha Kassahun

Ethiopian Institute of Agricultural Research (EIAR), Melkassa Agricultural Research Center,
P.O. Box 436, Nazareth, Ethiopia
ashebertegegn@gmail.com   and   amahakassahun@yahoo.com

Abstract

The Allaidege open wet season grassland was reduced in to all season grazing land due to expansion of large scale irrigated crop agriculture. Development of watering points farther limited free livestock mobility and caused over utilization of the rangeland resources. In this study, four grazing intensities, namely: severely grazed, moderately to severely grazed , moderately grazed and lightly grazed sites, each with 10 sampling units were laid out along a 12.5 km gradient from a livestock watering point. Five 1 m2 quadrants were randomly assigned per sampling unit, and the herbaceous layer was harvested. Accordingly, effects of watering point on plant species composition, spatial distribution and diversity were investigated.

 

Species composition and spatial distribution of the herbaceous layers were highly influenced by levels in grazing intensities. Moreover, reductions in grazing intensity, with increasing distance from watering point, highly favoured Decreasers (highly desirable perennial grass species), whereas, heavy grazing pressures at decreasing distances from watering point favoured Increaser species (less desirable forbs and annual grass). In terms of preference by livestock classes, most perennial grasses species (Decreasers) were highly desirable by grazers (cattle and sheep), while annuals and forbs (Increasers) were highly desired by browsers (goats and camels). Species diversity decreased in areas close to and remote from watering point. This finding suggests that the current grazing management has a negative impact on the rangeland resource and needs improvements.

Key words: Botanical composition, Decreaser, Grazing intensity, Herbaceous layer, Increaser, Livestock preference


Introduction

In arid and semi-arid rangelands, uneven grazing intensity associated with livestock watering points has effects both on vegetation and the physical environments (Todd 2006). This induces over utilization of rangeland resources (Pringle and Landsberge 2004), permanent degradation (Kidane 2005) and losses in vegetation biodiversity (Brooks et al 2006) in rangeland areas around watering points. Effects on physical environments include: depletion of soil nutrients (Brook et al 2003; Kidane 2005), diminish in nutrient recycling (Pringle and Landsberge 2004), increases in soil compaction (Brooks et al 2006) and limitations in infiltration (Trash 1997; Risch et al 2007).

 

High grazing pressure, around watering points, also disturbs floristic composition (Landsberg et al 2003), spatial distribution (Metzger et al 2005) and diversity of herbaceous layers (Brooks et al 2006). The situation further favour annuals (Klintenberg and Verlinden 2008) and unpalatable species (Todd 2006) than perennial grasses (Brook et al 2003 and Kidane 2005), enhance bush encroachments (Ludwig 2004), reduction in vegetation cover (Fahnestock and Detling 1999) and shrinkage of grazing lands (Bastin and James 2002), resulting declines of range forage/fodder production (Fusco et al 1995; Macopiyo 2005). To the contrary, feed mass production increased from grazing areas with increased distances from watering points (Foran 1980; James et al 1999), may be due to under utilization of the forage resources (James et al 1999).

 

Traditionally, the Allaidege open grassland was best used as wet season grazing land, with animals having access to surface water resources under free mobility. However, this trend was interrupted since the 1970th, due to the expansion of irrigated large commercial scale crop agriculture (Kidane 2005). This has, thereof, limited free livestock mobility and the access to surface water resources, posing livestock and human pressures, which farther aggravated over utilization of the range bio-physical resources around watering points (Kidane 2005). On the other hand, there are too little studies under taken to assess the impacts of watering points on biophysical resources of the Ethiopian rangelands in general and the Allaidege open grassland in particular. Moreover, there exists too little information to understand the long term impacts of grazing around livestock watering points. As a result, there exists gap in knowledge to promote sustainable rangeland management strategies.

 

Therefore, generation of scientific information still remains to be critical in order to design and promote appropriate development interventions and management systems. Therefore, the purpose of this study was to generate information on: i) floristic composition, ii) spatial distribution, iii) desirability by livestock species vi) species richness and diversity of the herbaceous layers along the grazing gradient from a watering point, and to come up with appropriate recommendations.


Materials and Methods

Description of the study Area

 

The study was conducted in the semi-arid Alaidege open grassland, located at 935'17.170''N and 4011'4.161''E, representing a total of 200 000 hectare, with an altitude of 820 to 840 m.a.s.l.. Mean annual minimum to maximum temperature and rainfall range between 25C and 40C and 300 and 560 mm, respectively. Rainfall is bimodal with main rains in July to August and short rains in March and April (WARC 2008). The vegetation types are dominated by herbaceous layers mainly Chrysopogon plumulosus, Panicum maximum as well as scattered woody plants such as Acacia nubica and Prosopis juliflora (Kidane 2005).

 

Site selection

 

A reconnaissance survey was conducted to assess, identify and select an appropriate experimental site using subjective (Van Zyl 1986) and objective (Hardy et al 1999) methods with participation of local elders and range managers. Selection criterion included: availability of watering point, grassland representation, presence of a grazing gradient, similarity in slope and soil types and pastoral livestock production systems as described by Manneteje and Jones (2000) and Reed and Dougill (2002).

 

Field layout and sampling techniques

 

The experimental site was laid out into four plots (treatments) along a 12.5 km grazing gradient from a livestock watering point. These included: i) severely grazed (SG), ii) moderately to severely grazed (MSG), iii) moderately grazed (MG) and vi) lightly grazed (LG) sites as described by Kidane (2005) and Amaha (2008). Farther, each plot was divided into ten sampling units (replicates) of 50 X 50m (0.0025km2) belt transect each. Accordingly, 5 quadrants of 1m2 were randomly thrown per sampling unit.

 

Data Collection

 

The herbaceous layer in a quadrant was harvested, segregated in to their plant forms and thereafter into different species, fresh weight was taken for each species using sensitive scale and sample of each species was put in paper gabs. Species identification was done in the field by an experienced botanist using CADU (1974) guideline, while vernacular names were determined by local community members. Each species was grouped in to its relevant ecological index (i.e. Increasers, Decreasers and Invaders) as described by Tainton (1982). Desirability of each species by livestock classes was categorized based on indigenous knowledge of local pastoralists. Samples of each species were subjected to an oven at 105C for 24 hours and percent dry matter biomass contribution calculated for each species. Species occurrence was expressed in terms of not present, present, common and dominant using values 0, <5, 5-20 and >20 percent dry matter biomass, respectively (Amsalu and Baars 2002)

 

Data analysis

 

Multivariate of correspondence and cluster analysis were applied to assess the individual and community level species response to a grazing gradient. A combination of ordination and dendogram of clustering were used to classify and group the commonly and dominantly occurred plant species with an increasing, decreasing and no change patterns in abundance at high and low grazing pressure, respectively. Averaged percent dry matter biomass of each species within the group was used to determine the community dominance of each group at each study site.

 

The following three indices were applied to estimate species diversity (Pielou 1969):

 

i) Plant richness represented by the number of species recorded in each quadrant;

 

ii) Shannon diversity index,

 

iii) Evenness index,

 

 

Where: Pi = relative importance of species i, S = plant richness

ANOVA was applied to investigate the relationship between grazing response variables against grazing gradients. SAS (1999) was used as software package


Results and Discussion

Botanical composition and related parameters of the herbaceous layers

 

Botanical composition of the herbaceous layer was consisted of 21 species, which included species of 14 grasses and 7 forbs, contributing 67% and 33% of the total herbaceous vegetation composition, respectively. In terms of the grass life forms, 50% were annuals and 50% perennials. In terms of their ecological index, 5(23.8%), 1(4.76%), 7(33.3%) and 8(38.1%) species were Decreasers, Increaser IIa, Increaser IIb and Increaser IIc, respectively. On the other hand, 6 grass species (28.6%) were highly desirable, 6 grass species (28.6%) were desirable, and 4 species (14.3%) were less desirable and 5species (23.8%) undesirable (Table 1).

 

Based on percent dry matter biomass of the herbaceous species a variation was observed in terms of occurrence along the grazing gradient. Accordingly, 5 (23.8%) were absent in the severely grazed site, while 3 (14.1%) each in the moderate to severely and moderately grazed sites were recorded as absent, whereas only 4 (19%) species were absent in the lightly grazed site. The number of species recorded as present were 9 (42.8%) in the severely grazed, 11(52.3%) each in the moderate to severely and lightly grazed sites and 12(57.1%) in the moderately grazed site. Further, 28.6% of species were commonly present in each of the severely and moderately to severely grazed sites, while 24% were also commonly present in each of the moderately and lightly grazed sites. Only one species in each of the grazing sites was found to be dominant.

 

According to the findings of this study, botanical composition of the herbaceous plants along the grazing gradient showed significant variations in terms of decreases in perennial species regarded as highly desirable and categorized as Decreasers in those sites close to watering point, may be due to increased pressures from livestock grazing.


Table 1. Botanical composition and related parameters of herbaceous layer in the Alaidege open grassland

Herbaceous species

Vernacular name

Ecological Index

Desira-

bility

Life forms

Species occurrence on grazing gradient types

SG

MSG

MG

LD

Grasses

 

 

 

 

 

 

 

 

Chrysopogon plumulosus

Burfu

Decreaser

HD

Perennial

NP

P

D

D

Panicum coloratum

Denekto

Decreaser

HD

Perennial

NP

C

C

C

Cenchrus ciliaris

Serdoyta

Decreaser

HD

Perennial

NP

NP

P

P

Lintonia nutans

Afara mole

Increaser IIb

I

Perennial

NP

P

NP

P

Cynodon dactylon s

Rareta

Increaser IIa

HD

Perennial

P

NP

P

NP

Tetrapogon tenellus

Aytodyta

Increaser IIc

LD

Perennial

P

P

NP

P

Sporobolus ioclados

Denekto

Increaser IIb

I

Perennial

P

P

C

C

Eriochloa nubica

Asayso

Decreaser

HD

Annual

P

P

C

C

Eriochloa Procera

Asayso

Increaser IIb

I

Annual

P

C

P

P

Setaria verticillata

Delayta

Increaser IIb

I

Annual

D

D

C

P

Sporobolus panicoides

Gewita

Increaser IIc

LD

Annual

P

P

P

P

Setaria pumila

Delayta

Increaser IIb

I

Annual

P

C

P

P

Tragus racemosus

Bekelayso

Increaser IIc

LD

Annual

C

C

P

NP

Dactyloctenium aegyptium

Mussa

Decreaser

HD

Annual

P

C

P

P

Forbs

 

 

 

 

 

 

 

 

Ipomoea spp.

Halal

Increaser IIb

I

Annual

P

P

P

C

Blepharis edulis

Yamarukt

Increaser IIc

LD

Annual

NP

NP

P

P

Leucas martinicensis

Ergufuma

Increaser IIb

UD

Annual

C

p

P

NP

Phyllanthus maderaspa

Akelekelmi

Increaser IIc

UD

Annual

C

C

P

P

Amaranthus dubius

Bunkete

Increaser IIc

UD

Annual

C

P

NP

NP

Indigofora amorphoides

Unknown

Increaser IIc

UD

Annual

P

P

P

P

Tribulus terrestris

Suguma

Increaser IIc

UD

Annual

C

P

P

P

HD=highly desirable; I=desirable; LD=Least desirable; UD=Undesirable; C=Common; D=Dominant; P=Present; NP=Not present.

Generally, there was a decline in Decreasers and an increase in Increasers along the gradient from lightly to severely grazed sites. This was in agreement to reports on the Borana rangelands (Gemedo et al 2006; Solomon et al 2006), the Central Rift Valley rangelands (Abule et al 2005), the Allaidegei rangelands (Kidane 2005) and Shinille grasslands of the Somali region of Ethiopia (Amaha 2008).

 

On the other hand, the proportion of highly desirable species decreased with high grazing pressure, while the abundance of herbaceous species with lower forage values tended to increase, which was in agreement to reports by Vallentine (1990) and Ameha (2008). It is therefore, likely that the abundance of species with low forage values increased as a result of livestock grazing at the expense of palatable and less grazing tolerant species (Todd 2006).

 

Furthermore, the results showed the abundance of forbs and annual grass species increased along the gradient from lightly to severely grazed sites, which supports the report by Fusco et al (1995); brooks et al (2006) and Todd (2006). In relation to this also, it was reported that the negative impacts of grazing on perennial grass species were greater in areas close to watering points because of livestock concentrations and trampling (Brooks et al 2006; Fongorana 2006 and Lishan 2007).

 

Species preference by classes of livestock

 

According to indigenous knowledge of pastoralists, the primary desirability by cattle and sheep was skewed towards perennials followed by annual grass species, while the forbs were highly desirable and desirable by camels and goats, respectively. For example, two perennials and four annuals, two annuals, one perennial and two forbs and three forbs were highly desirable, desirable, less desirable and undesirable by cattle, respectively. In view of sheep preference, four perennials and one annual grasses were highly desirable, three perennials and two annuals desirable, one annual and two forbs less desirable and one annual and three forbs undesirable. In relation to goats, two annuals and five forbs were desirable, two perennials and two annuals were less desirable, while two perennials and one annual were undesirable. For the camels, five forbs were highly desirable, two annuals and one forb desirable, three perennials and two annuals less desirable and only one annual undesirable (Table 2).

 

In terms of the interactive preference among the four livestock classes, only two annuals were highly desirable, other two annuals were desirable and one perennial was less desirable by cattle and sheep. But only one annual was desirable by cattle and goats, whereas one perennial was highly desirable and another perennial desirable by cattle and camels, respectively. In terms of the common preferences by goats and camels, one perennial, one perennial and two annuals were described as only desirable and desirable, respectively.


Table 2: Herbaceous species ranked in terms of livestock species preferences as perceived by pastoralists in the Afar region of northeast Ethiopia

Herbaceous species

Preference by different livestock species

Highly desirable

Desirable

Least desirable

Undesirable

Chrysopogon plumulosus

Sheep

Cattle, Camels

Goats

None

Panicum coloratum

Cattle

Sheep

Goats, Camels

None

Cenchrus ciliaris

Cattle

Sheep

Camels

Goats

Lintonia nutans

Sheep

Goats, Camels

Cattle

No

Cynodon dactylons

Cattle, Camels

Sheep

Goats

None

Tetrapogon tenellus

Sheep

Cattle

Camels

Goats

Sporobolus ioclados

Sheep

Cattle, Goats

Camels

None

Eriochloa nubica

Cattle

Sheep

Goats

Camels

Eriochloa procera

Cattle, Sheep

Goats

Camels

None

Setaria verticillata

Cattle

Sheep

Goats, Camels

None

Sporobolus panicoides

Sheep

Cattle

Goats, Camels

None

Setaria pumila

Cattle, Sheep

Camels

Goats

None

Tragus racemosus

Cattle

Goats

Camels

Sheep

Dactyloctenium aegyptium

Cattle

Camels

Sheep

Goats

Ipomoea spp.

Camels

Goats

Cattle, Sheep

None

Blepharis edulis

Camels

Goats

Cattle

Sheep

Leucas martinicensis

Camels

Goats

Cattle

Sheep

Phyllanthus maderaspa

None

Camels

Goats

Sheep

Amaranthus dubius

None

None

Goats, Camels

Cattle

Indigofora amorphoides

Camels

Goats

Sheep

Cattle

Tribulus terrestris

Camels

Goats

Sheep

Cattle


According to the analysis, however, neither the ruminants (cattle and sheep) nor the browsers (camels and goats) showed an equal preference for all perennial and annual grasses. In relation to this, sheep and cattle showed higher desirability for perennial grasses, except that sheep showed more preference for forbs than cattle. With regard to camels and goats, the goats showed similar preference in terms of the annuals, perennials and forbs, while camels were inclined to perennial and annual grasses than forbs. In general, most perennial and partly annual grasses were within highly desirable and desirable preference indices for cattle and sheep, while less desirable for camels and goats, but observed to be less desirable by camels and goats. On the other hand, most of forb species were within the category of highly desirable to desirable for camels and goats, and less desirable for cattle and sheep. From this context and given the higher cattle and sheep population in the area, therefore, the results indicate that, the perennial grass species are subjected to heavy grazing with subsequent opportunities to be replaced by Increaser plant species of low palatability and feeding values, which demand for well designed and systematic grazing management around watering points.

 

Patterns in composition of individual and community level of the herbaceous species

 

Two dimensions (Dimension 1 and 2) of correspondence analysis, yielded an eigen value of 180.1, which in aggregate explained about 99% of total variation (Figure 1), explaining a high association between the grazing intensities and the type of herbaceous species. In terms of individual species responses to the grazing intensities along the gazing gradient, most of the annual grasses and forbs on the left of the ordination belonged to severely grazed site. Where as most of the highly desirable and perennial grasses on the right side of the ordination belonged to the moderately and lightly grazed sites. Besides, the species at the mid of the positive side of ordination, mainly: Ericholea nubica, Ipomoea and Sporobolus ioclados were found adjacent to areas where livestock grazing pressure was moderate (Figure 1).


Figure 1: Ordination of common (% DM biomass >5% and < 15%) and dominant (% DM biomass >15%) species along the degradation gradient in the study area.

(Where: Chr-plumulosus= Chrysopogon plumulosus ; P-coloratum =Panicum coloratum; Te-tenellus =Tetrapogon tenellus; Sp-ioclados =Sporobolus ioclados; Er-nubica =Eriochloa nubica; Er-procera =Eriochloa procera; Se-verticillata =Setaria verticillata; S-pumila =Setaria pumila; Tr-racemosus =Tragus racemosus ; D-aegyptium =Dactyloctenium aegyptium ; Ipomoea =Ipomoea spp.; Le-martinicensis =Leucas martinicensis; Phy-maderaspa =Phyllanthus maderaspa; Ama-dubius =Amaranthus dubius and Tri-terrestris =Tribulus terrestris)


In terms of community level responses of the plant species, combination of the ordination and cluster analysis, the herbaceous species were aggregated in to four community groups, each having similar ecological niches, that is, soil nutrient and moisture requirements (Fig. 1 and 2). The community Group 2 consisted of annual grasses and forbs, found closer to the watering point, showed a higher response to heavy grazing pressure and trampling. As opposed to Group 2, the annual grass species namely Setaria verticillata behaved differently due to it’s abundance between the severe to moderate and severely grazed sites (Group 4).On the other hand, Group 1, mainly perennial grasses, showed a higher abundance in those grazing sites remote from the watering point. Similarly, Plant community Group 3, specifically dominated by Ericholea nubica, Ipomoea and Sporobolus ioclados showed increasing patterns in abundance at moderate grazing intensity (Figure 2).



Figure 2: Cluster analysis of average linkage method and average distance between clusters

On the other hand, the average percent DM biomass contribution of the herbaceous species within the community or cluster groups in the four grazing gradients was affected by the different levels of grazing intensities. Accordingly, cluster group 1and 3 showed a remarkable increase as the level of grazing pressure decreased. In contrast, cluster group 2 showed a declining contribution as grazing pressure increased. Whereas group 4, behaved differently by contributing the highest percent DM biomass under moderate to severe grazing pressure with decreasing patterns towards the severely and lightly grazed sites (Table 3).

Table 3: Mean % DM biomass contribution of four clusters to four grazing gradients

Cluster groups

Levels of grazing intensities

Severe

Moderate to severe

Moderate

Light

1

0.00

4.21

19.8

21.7

2

9.28

7.83

3.79

2.30

3

2.40

4.43

7.48

11.2

4

18.6

23.9

9.91

3.66


Generally, heavy grazing around livestock watering points was observed to encourage the succession of annuals and unpalatable species over palatable perennial species. Likewise, Metzger et al (2005) has also made similar conclusions. The findings further revealed that, the abundance of highly desirable indigenous species in the study area increased under moderately to lightly grazing pressure, where as those annuals and less palatable herbaceous species seem to be favoured by severe grazing pressures. The later also has a direct or indirect impact on the percent DM biomass contribution along the grazing gradient. This supports the findings by Harrison (2000), Del-Val and Crawley (2005) and Klintenberg and Verlinden (2008). In relation also, the pastoral elders reported, that the study area was being dominated by perennial species before some decades, but over taken by annual species over time.

 

This further may suggest that the current grazing management results a negative impact on the rangeland vegetation composition and seems to demand improved grazing systems with well designed distribution of watering points. Thus, range degradation has been taking place because of over grazing, which may have altered the ecosystem in favour of the annuals species and vice versa. From this context, it can be suggested that, the individual species or community groups show a difference in abundance due to their ecological niche that encourage them for certain dominance in competition for soil nutrients and moisture regimes. Therefore, high grazing intensities around watering points not only disturb the physical environment but also alter the botanical composition of the herbaceous layers, either by increasing species tolerant to heavy grazing or by reducing species regarded as highly desirable, in agreement to Harrison (2000), Metzger et al (2005) and Wu et al (2008). As a result, those individual species aggregating around similar habitats or that regrouped them selves into community groups could be explained as plant species that require similar ecological niche in terms of soil type, moisture regime, land escape and level of grazing responses.

 

Species richness and diversity along the grazing gradients

 

Species richness defined in terms of number of plant species per unit area, was influenced by the level of grazing intensity along the grazing gradient. Farther also species evenness and dominance were affected by levels in grazing intensities along the gradient from livestock watering point. Accordingly, species richness was significantly higher in the moderate to severely and moderately grazed sites, while lightly grazed site showed a higher species richness than severely grazed site at p<0.05. However, the higher grazing pressure significantly reduced the species evenness and Shannon's index in the severely grazed site, nevertheless, there was no a significant difference among the other three levels of grazing intensities at P>0.05 (Table 4).


Table 4: Species richness, diversity and evenness (mean standard deviation) of herbaceous in relation to the grazing gradients.

Grazing gradients

Herbaceous species diversity

Shannon's index (H')

Species richness (S)

Evenness (J)

Severely grazed

1.99c0.33

10.1c2.09

0.84b0.10

Moderate to severely grazed

2.32ba0.18

13.4a2.19

0.91a0.07

Moderately grazed

2.51a0.20

12.5a1.41

0.93a0.05

Lightly grazed

2.31ba0.25

11.9b1.64

0.92a0.09

Means within a column with different superscripts are significantly different at p<0.05.


In conclusion, the results imply that heavy and light grazing pressure reduced the species diversity, which was supported by findings of (Willoughby 1995) and (Milgo 2006). Farther, heavy grazing pressures decreased the number of less grazing resistant species and increased those grazing tolerant species, but reduced the diversity. Likewise, low grazing pressures enhanced the dominance of some species by reducing the diversity, as reported by (Willoughby and Alexander 2007). In the moderate grazing pressure, the species diversity was generally maximized, and may be induced due to a favourable macro-habitat for both heavy grazing tolerant and susceptible species to harmoniously survive, perform and reproduce (Grime 1973).


Conclusions


Acknowledgements

The authors acknowledge the funding support of the Institute of Pastoral and Agropastoral Study of Haramaya University. The authors are also grateful the support provided by Ethiopian Institute of Agricultural Research.


References

Abule E, Snyman H A and Smit G N 2005 comparisons od Pastoralists’ perceptions about rangeland resource utilization in the Middle Awash Valley of Ethiopia. Journal of Environmental Management 75:21-35

 

Ameha K, Snyman H A and Smith G N 2008 Soil seed bank evaluation along a degradation gradient in Somali Region, Eastern Ethiopia. Agriculture, Ecosystems and Enviroment 129:428-435

 

Amsalu S and Baars R M T 2002. Grass composition and rangeland condition of the major grazing areas in the mid rift valley, Ethiopia. African Journal of Range and Forage Science 9:161-166.

 

Bastin G N and James C 2002 Assessment of Biodiversity Condition in a Rangelands Environment Using Remote Sensing. Centre for Arid Zone Research.CSIRO. Australia. Conberg. http://www.environment.gov.au/land/publications/pubs/monitor-rangelands.pdf.

 

Brook A L, Tynan R W and Fleming M C 2003 Rangeland monitoring in northern South Australia using a grazing gradient method. 0-7803-7031-1/01, IEEE.

 

Brooks M L, Matchett J R and Berry K H 2006 Effects of livestock watering sites on alien and native plants in the Mojave desert, USA. Journal of Arid Environments 67:125-147.

 

CADU (Chilalo Agricultural Development Unit) 1974 An illustrate guide to the grasses  of Ethiopia. CADU, Assella, Ethiopia. 289p.

 

Del-Val E and Crawley MJ 2005 What limits herb biomass in grasslands: competition or herbivory? Oecologia 142, 202–211.

 

Fahnestock J T and Detling J K 1999 The influence of herbivory on plant cover and species composition in the Pryor Mountain Wild Horse Range, USA. Journal of Plant Ecology 144:145-157.
 

Fongorana S 2006 Responses of biodiversity to radial distances from traditional wells in Haoussa, Mali. MSc thesis, Norwegian University of Life Science, Nowray.

 

Foran B 1980 Change in Range Condition with Distance from Watering Point and its implication for Field Survey. Australian Rangeland Journal 2:59-66.

 

Fusco M, Holechek J, Tembo A, Daniel A and Cardenas M 1995 Grazing influences on watering point vegetation in the Chihuahuan desert. Journal of Rangeland Management 48:32-38.

 

Gemedo D, Maass B L and Isselstein J 2006 Rangeland condition and trends in the semi-arid Borana lowlands, Ethiopia. African Journal of range and forage Science 23:49-58

 

Grime J D 1973 Control of species diversity in herbaceous vegetation. Journal of Environmental Management, 1:151-167.

 

Harrison P S 2000 Grass land resource assessment for pastoral systems, FAO plant production and protection. No.162. FAO, Rome.

 

Hardy M B, Hurt C R and Bosch O J H 1999 Veld condition assessment. In: Tainton NM (Ed.). Veld management in South Africa. University of Natal Press, Pietermaritzburg, 472p.

 

James C, Landsberg J and Morton S 1999 Provision of watering points in the Australian arid zone: a review of effects on biota. Journal of Arid Environments 41:87-121.

 

Kidane G 2005 Rangeland Potential, Quality and Restoration Strategies in North-East Ethiopia: A case study conducted in the Southren Afar Region. Doctoral thesis, University of Stellenbosch, Agronomy Department, South Africa. 243 p.

 

Klintenberg P and Verlinden A 2008 Water Points And Their Influence On Grazing Resources In Central Northern Namibia. Land degradation and development 19: 1–20

 

Landsberg J, James C, Morton S, Muller W J and Stol J 2003 Abundance and composition of plant species along grazing gradients in Australian Rangelands. Journal of Applied Ecology 40:1008-1024.

 

Lishan T 2007 Woody and herbaceous species composition and the condition of the rangelands in Shinile zone of Somali Regional State, Ethiopia. M.Sc. Thesis, School of Graduate Studies. Haramaya University. 171p.

 

Ludwig J A 2004 Monitoring ecological indicators of rangeland functional integrity and their relation to biodiversity at local to regional scales. Austral Ecology 29:108-200.

 

Manneteje L T and Jones R M 2000 Grassland vegetation and its management. Field and laboratory methods for grassland and animal production research. University of Wageningen, the Netherlands, 403 p.

 

Macopiyo L A 2005 Spatially explicit, individual-based modeling of pastoralists’ mobility in the rangelands of east Africa. M.Sc. Thesis, Office of Graduate Studies of Texas A&M University.

 

Metzger K L , Coughenour M B, Reich R M and Boone R B 2005 Effects of seasonal grazing on plant species diversity and vegetation structure in a semi-arid ecosystem. Journal of Arid Environment, 61:147-160.

 

Milgo C 2006 Effects of grazing pressure on plant species composition and diversity in the semi-arid rangelands of Mubulu District, Tanzania. Agricultural journal 1(4): 277-283.

 

Pielou E C 1969 An Introduction to Mathematical Ecology. Wiley: New York, NY. In Wang C T, Long R J, Wang Q L, Jing Z C and Shi J J 2009 Changes in Plant diversity, biomass and soil C, In Alpine Meadows at different degradation stages in the Headwater Region of three Rivers, China. Land Degradation and Development 20: 187–198

 

Pringle H and Landsberg J 2004 Predicting the distribution of livestock grazing pressure in rangelands. Australia Ecology 29(1):31-39.

 

Reed M S and Dougill A J 2002 Participatory selection process for indicators of rangeland condition in the Kalahari. The Geographical Journal, 168(3): 224-234.

 

Risch A C, Jurgensen M F and Frank D A 2007 Effects of grazing and soil micro-climate on decomposition rates in a spatio-temporally heterogeneous grassland. Plant Soil 298:191-201.

 

SAS (Statistical Analysis System) 1999 Institute of Applied Statistics and SAS Programming Language. Cary, North Carolina.

 

Solomon T B, Snyman H A and Smith G N 2006 soil seed bank characterstics in relation to land use systems and distance from water in semi-arid rangeland of southern Ethiopia. Suoth Africa Journal of Botany 27: 263-271

 

Tainton N M 1982 A ststem for assessing range condition in Suoth Africa. In Joss P J, Lynch P W and Williams O B (Eds). Rangelands: a resource under siege. Proceedings of the 2nd rangeland congress, Australian Acadamy of Sciences, Camberra. Pp.524

 

Todd S W 2006 Gradients in vegetation cover, structure and species richness of Nama-Karoo shrublands in relation to distance from livestock waterin points. Journal of Applied Ecology 43: 293-304.

 

Thrash I 1997 Infiltration rate of soil around drinking troughs in the Kruger National Park, South Africa. Journalof Arid Environments, 35, 617–625.

 

Van Zyl E A 1986 Veldtoestandbepaling (Veld condition assessment). Potchefstroom, Department of Agriculture, South Africa, 7 p.

 

Vallentine J F 1990 Grazing management. Academic press, Inc. SanDiego, California, USA.

 

WARC (Werer Agriciltural Research Center) 2008 Agro-meteorology research division annual research report.

 

Willoughby M G 1995 Species diversity and how it is affected by livestock grazing on Alberta’s Eastern Slopes. Proc. 5th Int’l Rangeland Congress, Salt Lake City. Utah. pp610-611.

 

Willoughby M G and Alexander M J 2007 Rangeland Health for Native and Modified Plant Communities in the Rough fescue Ecological Site of the Montane Subregion. Alberta Sustainable Resource Development. ISBN No. 978-0-7785-6523-9. http://www.gov.ab.ca/srd/land/m_rm_monitoring.html

 

Wu R, Tiessen H and Chin Z 2008 The Impacts of Pasture Degradation on Soil Nutrients and Plant Compositions in Alpine Grassland, China. Journal of food, agriculture and environmental science, ISSN 1934-7235, 2(2): 1-14.



Received 14 February 2011; Accepted 10 August 2011; Published 1 September 2011

Go to top