Translator Disclaimer
1 May 2009 Regeneration Response of Juniperus procera and Olea europaea subsp cuspidata to Exclosure in a Dry Afromontane Forest in Northern Ethiopia
Ermias Aynekulu, Manfred Denich, Diress Tsegaye
Author Affiliations +

The Afromontane forests of northern Ethiopia have been degraded and fragmented for centuries. Recently, efforts have been made to restore these forests by protecting them from livestock interference. In this study, the natural regeneration of Juniperus procera Hochst. ex Endl. and Olea europaea L. subsp cuspidata (Wall. ex G. Don) Cif. is investigated under protected conditions after 3 years of enclosure and under open management systems in a dry Afromontane forest in northern Ethiopia. Data on the floristic and structural compositions of the vascular plants were collected using 32 randomly selected plots (20 m × 20 m), while nested plots (10 m × 10 m) were used to investigate the seedling bank at the protected and adjacent open sites. The results reveal that there was a significantly higher regeneration of O. europaea on the protected site than on the open site (P  =  0.01). However, there was no significant difference between the 2 sites for J. procera (P  =  0.16). Thus, protecting the degraded forest in northern Ethiopia seems to be an appropriate management option for the regeneration of O. europaea. The regeneration status of J. procera at both sites is poor, which indicates that protecting the forest from livestock and human disturbance is unlikely to lead to regeneration of this species. Further investigation of other factors that hinder the regeneration of J. procera is therefore recommended.


In many tropical forests, excessive deforestation has hampered natural regeneration and seedling establishment and affected the diversity and structure of plant communities (Denslow 1980, 1987; Runkle 1982; Bussmann 2001). Similarly, forests in Ethiopia have been affected by climatic and anthropogenic factors for centuries (Friis 1992; Machado et al 1998; Tekle and Hedlund 2000; Zeleke and Hurni 2001; Dessie and Kleman 2007). Historically, soil erosion as a result of vegetation clearing in the highlands of Tigray, for instance, is recorded in the Middle Holocene (Bard et al 2000; Darbyshire et al 2003). The vascular plants of the Afromontane forests of Ethiopia maintain their population through natural regeneration (Teketay 1997). However, large-scale degradation of natural forest in Ethiopia has created a major challenge with respect to the regeneration of key native tree species (Wassie 2009a) while favoring herb and shrub colonizers. For instance, Dessea Afromontane forest, which was dominated by Juniperus procera and Olea europaea prior to disturbance, has been gradually replaced by encroaching light-demanding shrubs such as Cadia purpurea L. and Tarchonanthus camphoratus L. In response to such disturbances, area exclosures have been introduced in some Afromontane forests in northern Ethiopia in recent years (eg Yayneshet et al 2009).

Natural regeneration is a site-specific ecological process, and it is usually difficult to characterize the factors that control the regeneration processes (Schupp 1988; Khurana and Singh 2001). Protecting areas from livestock intervention—a practice termed exclosure—is an assisted natural regeneration strategy to restore degraded forests in the tropics (Parrotta et al 1997; Shono et al 2007). Many degraded sites have been managed as exclosures in northern Ethiopia, and attempts have been made to document the regeneration and ecology of the plants in these exclosures.

Although it is difficult to generate a specific management plan for exclosures (Mengistu et al 2005a; Muys et al 2006), many studies have indicated that vegetation recovery in the exclosures is quick, particularly in the younger stages (Mengistu et al 2005a; Abebe et al 2006). Assefa et al (2003) and Yayneshet et al (2009) found that exclosures do not significantly contribute to the diversity and biomass of plants after 8 years of exclosure, suggesting the need to introduce additional management measures to restore key native species. Some studies on vegetation restoration in Ethiopia have suggested that the presence of matured trees as useful seed sources (Tekle and Bekele 2000), plantations (Senbeta and Teketay 2001; Yirdaw 2001; Lemenih et al 2004), and minimization of livestock pressure (Aerts at al 2007) create favorable environments for the regeneration of native species.

Although some studies exist regarding the regeneration and ecology of J. procera and O. europaea in the northern Ethiopian highlands (Aerts et al 2006b; Wassie et al 2009a) and other parts of Ethiopia (Senbeta and Teketay 2001; Tesfaye et al 2002; Bekele 2005), little is known about regeneration in the degraded Afromontane forest in northern Ethiopia. Thus, the aim of this study is to investigate the ways in which exclosure, protecting forests from livestock and human interference, affects restoration of the degraded forests in this region. Specifically, we studied the seedling abundance of J. procera and O. europaea in a forest that had been protected for the past 3 years in comparison to an open-management system.

Material and methods

Study site

The study was conducted in the Dessea forest, which is one of the Afromontane (White 1983) forest remnants in northern Ethiopia. The site is located at 13°55′3″N, 39°48′46″E at an altitude of 2700 m above sea level (Figure 1). The physiographic units map of the forest vegetation of eastern and northeastern Africa (Friis 1992) illustrates that the study site is located on the Tigrean Plateau, which lies immediately above the escarpment of the Rift Valley in northern Ethiopia. A large part of the site is located on shale, limestone, and sandstone of the Tertiary and Mesozoic era (TFAP 1996). Based on the diverse geological formations, the soils are variable; the dominating soil types in the study region are Leptosols, Cambisols, Vertisols, Regosols, and Arenosols (TFAP 1996).

Figure 1

Location of the study plots used in the protected and open sites at Dessea forest in northern Ethiopia (Map projection: UTM Zone 37N, Datum: Adindan); the topographic map (EMA 1998) is used as background. (Map by authors)


Study species

The forests of eastern and northeastern Africa are categorized into 9 major floristic groups (see Friis 1992). Accordingly, the Dessea forest is categorized as a dry single-dominated Afromontane forest, which is characterized by a dry climate (annual precipitation less than 1000 mm) and Juniperus procera Hochst. ex Endl (Cupressaceae) in the canopy and Olea europaea subsp cuspidata (Oleaceae) in the understorey as dominant species. Juniperus procera is widely grown from Arabia to Zimbabwe (Hall 1981). Due to heavy pressure on this species, the Food and Agriculture Organization (FAO) has listed it as a threatened species that requires in situ conservation priority beginning 1985–1989 (FAO 1975). James Bruce first documented J. procera as a common forest tree species in the highlands of northern Ethiopia during his expedition to trace the origin of the Blue Nile (1768–1773) (Bruce 1790, cited in Friis 1992). Juniperus procera has a slow germination rate (Yirdaw and Leinonen 2002) and low germination capacity, which are mainly attributed to seed dormancy (Tigabu et al 2007).

The genus Olea has 33 species, and Olea europaea subsp cuspidata is one of the subspecies that was previously named Olea africana. The species is commonly called the African olive and is widely distributed from Arabia to southern Africa. Although it is a useful tree species in its natural habitat, it is categorized as an invasive plant in countries like Australia (Cuneo and Leishman 2006) and Hawaii (Santos et al 1992). Olea europaea is a common species in the highlands of Ethiopia. The natural regeneration of the species in Ethiopia has been studied and documented by many authors (eg Bekele 2005; Teketay 2005; Aerts et al 2006a).

Sampling design

A small part of the Dessea forest has been protected from human and livestock interference for the last 3 years in order to restore the degraded forest (hereafter referred to as protected forest). The area is protected by forest guards. We mapped the protected site and the adjacent open forest, which has similar geology, soils, and vegetation to the protected site, using a global positioning system (GPS). Later, the GPS data were transferred to a geographic information system (GIS) environment for further mapping. The protected and open sites have a size of 33 and 43 ha, respectively. Regeneration at the two sites was compared using a total of 32 randomly selected plots, ie 16 from each site. A plot size of 20 m × 20 m was used to collect data on floristic compositions of woody species and structural composition of J. procera and O. europaea, while nested plots (10 m × 10 m) were used to identify and record seedlings. Emphasis was placed on the 2 key native target species (ie Juniperus procera and Olea europaea).

Data analysis

The relative dominance of all woody species was determined using the importance value index (IVI) (Mueller-Dombois and Ellenberg 1974). The IVI of a species was computed by summing up the relative density, relative dominance, and relative frequency of individual species. Dominance is the basal area of each species (sum of the basal area of each plant: g  =  π[Dbh2/4], where Dbh is the diameter at breast height), and frequency is the percentage of plots in which a species is recorded. Species diversity was determined using the Shannon Wiener diversity index and Simpson's Index of Diversity given by Magurran (1988).

The generalized linear model (GLM) with quasi-Poisson distribution (with log link) was used to determine the effect of management on seedling abundance of J. procera and O. europaea using R software version 2.7.0 (R Development Core Team 2008). The family quasi-Poisson distribution was used because there were overdispersions when Poisson distribution was run (Crawley 2007). For a better visualization and consideration of spatial correlations (Webster and Oliver 2001), the spatial distribution of seedling density (number of seedlings per plot) was mapped using the ordinary kriging interpolation method with the Integrated Land and Water Information System (ILWIS 3.3) GIS software (ITC 2001).


Floristic compositions

In total, 17 vascular plant species (with measured Dbh) belonging to 12 families were recorded at the open and protected sites, and J. procera Hochst. ex Endl. was the dominant species with the highest relative importance value (Table 1ATable 1A and 1B). This species, together with Olea europaea L. subsp cuspidata (Wall. ex G. Don) Cif., Solanum schimperianum Hochst. ex A. Rich., and Maytenus senegalensis (Lam.) Exell., was the most common species, found in more than 75% of the plots, while Erica arborea L. was among the rare species, recorded only once in a plot.

Table 1A

List of overstory species recorded in the protected and open sites in Dessea forest, northern Ethiopia. (Table continued on next page.)


Table 1B

List of seedling species recorded in the protected and open sites in Dessea forest, northern Ethiopia.


Species richness and diversity of woody plants were higher at the protected than at the open site (Table 2). The stem density (number of stems per hectare) of J. procera was higher at the open (1272 ± 170, mean ± SE) than at the protected site (947 ± 252). In contrast, the density of O. europaea was higher at the protected (87 ± 19) than at the open (67 ± 22) site. The average density of all woody plants at the open site (1853 ± 75) was higher than at the protected site (1499 ± 264). The mean basal areas of the woody plants at the protected and open sites were 19.4 and 21.1 m2 ha−1, respectively.

Table 2

Summary of vegetation attributes (mean ± SE) of all woody species and densities (number of stems per ha) of J. procera and O. europaea in protected and open sites in Dessea forest, northern Ethiopia.


Structural compositions of J. procera and O. europaea

The diameter distribution of J. procera indicates that the number of individuals in the lower-diameter class, including seedlings, is very low (Figure 2). The highest numbers of J. procera individuals were found in the diameter class of 2–6.9 cm, declining with increasing diameter. Although the number of individuals at the open site was a bit higher than at the protected site, the population structure in both sites followed a similar trend. The seedling population of O. europaea was much higher than the subsequent higher-diameter classes. Although the number of individuals was low, more O. europaea saplings were recorded at the protected than at the open site.

Figure 2

Diameter (Dbh) class distribution of (A) J. procera and (B) O. europaea L. subsp cuspidata in the protected and open sites. Diameter classes (cm): 1  =  < 2; 2  =  2–6.9; 3  =  7–11.9; 4  =  12–16.9; 5  =  17–21.9; 6  =  22–26.9; 7  =  27–31.9; 8  =  32–36.9; 9  =  37–41.9; 10  =  > 42.


Natural regeneration

In total, 10 species of vascular plants were recorded in the seedling bank. As for the overstory plants, O. europaea, J. procera, and M. senegalensis seedlings were the most dominant species and were recorded in more than 65% of the plots (Table 1ATable 1B). The seedling density (number of seedlings per hectare) of O. europaea was significantly higher at the protected site (3113 ± 1852, mean ± SE) than at the open site (1450 ± 929) (F1,30  =  7.29, P  =  0.01). The seedling density of J. procera was slightly higher at the open site (275 ± 156) than at the protected site (156 ± 104), but the difference was not statistically significant (F1,30  =  2.1, P  =  0.16) (Table 3).

Table 3

Seedling density (mean ± SE) of J. procera and O. europaea under open and protected management systems in Dessea forest, northern Ethiopia.


The spatial distribution of J. procera and O. europaea seedling densities at the open and protected sites is depicted in the kriged maps (Figure 3), which indicate that forest protection has a different effect on the species abundance of the 2 species.

Figure 3

Kriged maps showing spatial distribution of seedling density of J. procera (A) and O. europaea (B) at the open and protected sites. Numbers in the legend indicate the number of seedlings per plot (10 m × 10 m).



Our results show higher species diversity and seedling abundance at the protected than the open site, suggesting that protection of the forest contributes positively to Dessea forest restoration in northern Ethiopia. Similar findings have been reported for other protected areas located in relatively mesic environments in northern Ethiopia (eg Mengistu et al 2005b; Yayneshet et al 2009). Although J. procera and O. europaea are the dominant species (ie the target species in this study) in Dessea forest, they responded differently in terms of regeneration to the restoration intervention (Figure 3). We found significantly higher seedling abundance of O. europaea at the protected site than at the open one. However, there was no evidence of any direct effects of exclosure on the abundance of J. procera, calling for further investigation on other influencing factors.

The structural composition analysis for J. procera (Figure 2) indicates that this species is less represented in the lower-diameter classes, in which higher regeneration and recruitment are needed for a viable population of the species. Although J. procera is the most dominant species in the overstory and has higher availability of seeds in the study area, seedling abundance in both protected and open sites was very low. This is also in agreement with the findings of Wassie et al (2009a), who found lower regeneration of J. procera in church forests in other parts of northern Ethiopia. Although not statistically significant, we found higher regeneration of J. procera at the open than at the protected site (Table 3). Our results thus reinforce the findings of Mamo et al (2006), who reported that J. procera has poor germination capacity under field conditions, suggesting a need for additional manipulation.

Although some studies have indicated that light may not be a major limiting factor for the germination of J. procera (Sharew et al 1997; Wassie et al 2009a), the dense grass and herb cover at the protected site might prevent optimum radiation of the forest floor (Yirdaw and Leinonen 2002; Teketay 2005) and thus influence germination (Cabin et al 2002). The thick, less decomposable litter of J. procera (Prescott et al 2000) at the protected site also prevents seeds from contacting the soil. This might slow down the breaking of seed dormancy, which would ultimately hamper germination (Rotundo and Aguiar 2005; Cierjacks et al 2008). The thick litter might also have influenced emergence of newly germinated seedlings (Yirdaw and Leinonen 2002; Teketay 2005).

Seed dormancy, which varies depending on the provenance of J. procera in Ethiopia (Tigabu et al 2007), might also influence germination. Sharew et al (1997) found that land preparation by raking and burning increased the germination capacity of this species. Hence, the relatively higher abundance of J. procera seedlings at the open compared to the protected site indicates that other factors such as absence of shade, less litter, low livestock preference, and the breaking of seed dormancy through livestock pressure and erosion processes may determine regeneration. As reported by Cierjacks et al (2008) for Polylepis species in Ecuador, trampling by livestock may have contributed to the better regeneration of J. procera in the open than in the protected site.

We found higher seedling abundance of O. europaea at the protected site than at the open one (Table 3), indicating that this species is negatively influenced by livestock browsing and other microsite characteristics such as shade. Studies have indicated that the establishment and recruitment of O. europaea are better under shaded and protected conditions (Fetene and Feleke 2001; Bekele 2005; Aerts et al 2008). In contrast, Tesfaye et al (2002) found that O. europaea was a light-demanding species in the Harena forest in the southeastern highlands of Ethiopia, which is wetter than our study site. This indicates that O. europaea requires shade in drier environments, which also supports our findings. Holmgren et al (1997) indicated that shade lessens the water deficit by reducing moisture loss during the dry season and improves seedling establishment in dry areas. In line with this, Aerts et al (2006a) also found successful regeneration of O. europaea under Euclea shrubs, which create a better moisture regime through thick humus and organic matter accumulation (Descheemaeker et al 2006) in protected sites in northern Ethiopia. Rey et al (2000) also found that regeneration of O. europaea is influenced more by abiotic than by biotic factors, and that availability of moisture is the limiting factor. Although trees of this species are more resistant to browsing (Tesfaye et al 2002; Aerts et al 2007), seedlings are more sensitive to herbivory (Tesfaye et al 2002). Thus, protection of O. europaea seedlings from herbivory at the protected site contributed to a higher abundance of seedlings than at the open site. Like Aerts et al (2008), we observed a good proportion of coppice shoots of this species in the protected site, which may assist restoration of the degraded dry forest in the study site.

The complete closing of Dessea forest where the density of trees is low might favor the production of pasture (Richter et al 2001; Cabin et al 2002). Such efforts may cause a gradual shift of forestland to wooded grassland. Hence, it is important to plan other intervention measures alongside protection that regulate the extensive cover of the forest habitat by grass and other herbs (Cabin et al 2002). It is well documented that livestock are important agents of regeneration (eg Cierjacks et al 2008). However, in degraded environments where there is overgrazing, the impact of livestock in enhancing regeneration is limited. Instead, livestock contribute negatively (Wassie et al 2009b) in such environments through intensive browsing. In such degraded environments, species such as O. europaea are frequently browsed and suppressed to the extent of losing their ecological resilience (Gunderson 2000) in the absence of other feed sources, particularly during the long dry season.

Implications for management

Results of many studies have concluded that there is a strong need to give more priority to conservation of the existing natural forest remnants in northern Ethiopia before they lose their ecological resilience (eg Nyssen et al 2004; Aerts et al 2006b). In this regard, our study revealed that protecting the degraded natural forest contributed positively to the natural regeneration of O. europaea in the Dessea forest. The study has, therefore, provided scientific knowledge to support a change from the traditional pattern of exploitation to a targeted management of the species. However, other management options or factors seem to influence the natural regeneration of J. procera other than protecting this species from livestock and related disturbances. It may also be worthwhile to consider other management options such as enrichment planting and reducing litter accumulation and dense grass cover, especially in the protected areas, as suggested by Yirdaw and Leinonen (2002), in order to maintain a viable population of J. procera.

Based on our findings, we conclude that restorion of the degraded dry Afromontane dry forest in northern Ethiopia through exclosures requires a better understanding of the ecological requirements of the different species involved. Since the objective of forest restoration is to improve the status of key native tree species, experience from the exclosures in other areas should be carefully applied when attempting to restore degraded dry forest remnants in the study area. Our study is based on a 3-year protection period, and thus the results should be interpreted cautiously and extrapolated to other forests with care.


The authors acknowledge the financial support of the German Academic Exchange Service (DAAD) and Mekelle University for logistical support during the fieldwork. We thank the forest guards and the local people at Esot village for facilitating our field data collection. We thank the 2 anonymous reviewers for their valuable comments and Margaret Jend for editing the manuscript.



M. H. Abebe, G. Oba, A. Angassa, and R. Weladji . 2006. The role of area enclosures and fallow age in the restoration of plant diversity in northern Ethiopia. African Journal of Ecology 44 (4):507–514. Google Scholar


R. Aerts, W. Maes, E. November, A. Negussie, M. Hermy, and B. Muys . 2006a. Restoring dry Afromontane forest using bird and nurse plant effects: Direct sowing of Olea europaea ssp. cuspidata seeds. Forest Ecology and Management 230 (1):23–31. Google Scholar


R. Aerts, K. Van-Overtveld, M. Haile, M. Hermy, J. Deckers, and B. Muys . 2006b. Species composition and diversity of small Afromontane forest fragments in northern Ethiopia. Plant Ecology 187 (1):127–142. Google Scholar


R. Aerts, A. Negussie, W. Maes, E. November, M. Hermy, and B. Muys . 2007. Restoration of dry Afromontane forest using pioneer shrubs as nurse-plants for Olea europaea ssp. cuspidata. Restoration Ecology 15:129–138. Google Scholar


R. Aerts, E. November, W. Maes, I. Van-der-Borght, A. Negussie, E. Aynekulu, M. Hermy, and B. Muys . 2008. In situ persistence of African wild olive and forest restoration in degraded semiarid savannah. Journal of Arid Environments 72 (6):1131–1136. Google Scholar


D. T. Assefa, G. Oba, R. B. Weladji, and J. E. Colman . 2003. An assessment of restoration of biodiversity in degraded high mountain grazing lands in northern Ethiopia. Land Degradation and Development 14 (1):25–38. Google Scholar


A. K. Bard, M. Coltorti, C. M. Di Blasi, F. Dramis, and R. Fattovich . 2000. The environmental history of Tigray (northern Ethiopia) in the Middle and Late Holocene: A preliminary outline. African Archaeological Review 17 (2):65–86. Google Scholar


T. Bekele 2005. Recruitment, survival and growth of Olea europaea subsp. cuspidata seedlings and juveniles in dry Afromontane forests of northern Ethiopia. Tropical Ecology 46 (1):113–126. Google Scholar


R. W. Bussmann 2001. Succession and regeneration patterns of East African mountain forests. Systematic and Geography of Plants 71:957–974. Google Scholar


R. J. Cabin, S. G. Weller, D. H. Lorence, S. Cordell, R. Montgomery, D. Goo, and A. Urakami . 2002. Effects of light, alien grass, and native species addition on Hawaiian dry forest restoration. Ecological Applications 12 (6):1595–1610. Google Scholar


A. Cierjacks, N. K. Rühr, K. Wesche, and I. Hensen . 2008. Effects of altitude and livestock on the regeneration of two tree line forming Polylepis species in Ecuador. Plant Ecology 194 (2):207–221. Google Scholar


M. J. Crawley 2007. The R Book. Chichester, United Kingdom John Wiley & Sons Ltd. Google Scholar


P. Cuneo and M. R. Leishman . 2006. African olive (Olea europaea subsp. cuspidata) as an environmental weed in eastern Australia: A review. Cunninghamia 9 (4):545–577. Google Scholar


I. Darbyshire, H. Lamb, and M. Umer . 2003. Forest clearance and regrowth in northern Ethiopia during the last 3000 years. The Holocene 13 (4):537–546. Google Scholar


J. S. Denslow 1980. Patterns of plant species diversity during succession under different disturbance regimes. Oecologia 46:18–21. Google Scholar


J. S. Denslow 1987. Tropical rainforest gaps and tree species diversity. Annual Review of Ecology and Systematics 18:431–451. Google Scholar


K. Descheemaeker, B. Muys, J. Nyssen, J. Poesen, D. Raes, M. Haile, and J. Deckers . 2006. Litter production and organic matter accumulation in exclosures of the Tigray highlands, Ethiopia. Forest Ecology and Management 233 (1):21–35. Google Scholar


G. Dessie and J. Kleman . 2007. Pattern and magnitude of deforestation in the south central Rift Valley region of Ethiopia. Mountain Research and Development 27 (2):162–168. Google Scholar


EMA [Ethiopian Mapping Authority] 1998. Map, series ETH 4, sheet 1339 B2, 1st edition. Addis Ababa, Ethiopia EMA. Google Scholar


FAO [Food and Agriculture Organization] 1975. Forest Genetic Resources Information. Forest Occasional Paper (1975/1) 4. Rome, Italy FAO. Google Scholar


M. Fetene and Y. Feleke . 2001. Growth and photosynthesis of seedlings of four tree species from a dry tropical Afromontane forest. Journal of Tropical Ecology 17 (2):269–283. Google Scholar


I. Friis 1992. Forests and Forest Trees of Northeast Tropical Africa: Their Natural Habitats and Distribution Patterns in Ethiopia, Djibouti and Somalia. London, United Kingdom Her Majesty's Stationery Office. Google Scholar


L. H. Gunderson 2000. Ecological resilience—In theory and application. Annual Review of Ecology and Systematics 31:425–439. Google Scholar


J. B. Hall 1981. Data Sheets on Species Undergoing Genetic Impoverishment Juniperus procera Hochst. ex Endl. Forest Genetic Resources Bulletin 010. Rome, Italy FAO (Food and Agriculture Organization). Google Scholar


M. Holmgren, M. Scheffer, and M. A. Huston . 1997. The interplay of facilitation and competition in plant communities. Ecology 78 (7):1966–1975. Google Scholar


ITC [International Institute for Aerospace Survey and Earth Sciences] 2001. ILWIS 3.0 Academic User's Guide. Enschede, The Netherlands ITC. Google Scholar


E. Khurana and J. S. Singh . 2001. Ecology of seed and seedling growth for conservation and restoration of tropical dry forest: A review. Environmental Conservation 28 (1):39–52. Google Scholar


M. Lemenih, T. Gideyelew, and D. Teketay . 2004. Effects of canopy cover and understory environment of tree plantations on richness, density and size of colonizing woody species in southern Ethiopia. Forest Ecology and Management 194 (3):1–10. Google Scholar


J. M. Machado, A. Pérez-González, and G. Benito . 1998. Paleoenvironmental changes during the last 4000 yr in the Tigray, northern Ethiopia. Quaternary Research 49 (3):312–321. Google Scholar


A. E. Magurran 1988. Ecological Diversity and its Measurement. Princeton, NJ Princeton University Press. Google Scholar


N. Mamo, M. Mihretu, F. Miftah, M. Tigabu, and D. Teketay . 2006. Variation in seed and germination characteristics among Juniperus procera populations in Ethiopia. Forest Ecology and Management 225 (1–3):320–327. Google Scholar


T. Mengistu, D. Teketay, H. Hulten, and Y. Yemshaw . 2005a. The role of communities in closed area management in Ethiopia. Mountain Research and Development 25 (1):44–55. Google Scholar


T. Mengistu, D. Teketay, H. Hulten, and Y. Yemshaw . 2005b. The role of enclosures in the recovery of woody vegetation in degraded dryland hillsides of central and northern Ethiopia. Journal of Arid Environments 60 (2):259–281. Google Scholar


D. Mueller-Dombois and H. Ellenberg . 1974. Aims and Methods of Vegetation Ecology. New York, NY John Wiley & Sons, Ltd. Google Scholar


B. Muys, K. Gebrehiwet, and S. Bruneel . 2006. The ecology and silviculture of dryland forest rehabilitation in Ethiopia. Journal of the Drylands 1 (1):1–2. Google Scholar


J. Nyssen, M. Haile, J. Moeyersons, and J. Poesen . 2004. Environmental policy in Ethiopia: A rejoinder to Keeley and Scoones. Journal of Modern African Studies 42:137–147. Google Scholar


J. A. Parrotta, J. W. Turnbull, and N. Jones . 1997. Catalyzing native forest regeneration on degraded tropical lands. Forest Ecology and Management 99 (1–2):1–7. Google Scholar


C. E. Prescott, L. K. Zabek, C. L. Staley, and R. Kabzems . 2000. Decomposition of broadleaf and needle litter in forests of British Columbia: Influences of litter type, forest type, and litter mixtures. Canadian Journal of Forest Research 30:1742–1750. Google Scholar


R Development Core Team 2008. R: A Language and Environment for Statistical Computing. Vienna, Austria R Foundation for Statistical Computing. Google Scholar


P. J. Rey, M. Julio, and M. Alcantara . 2000. Recruitment dynamics of a fleshy-fruited plant (Olea europaea): Connecting patterns of seed dispersal to seedling establishment. Journal of Ecology 88 (4):622–633. Google Scholar


C. G. F. Richter, H. A. Snyman, and G. N. Smit . 2001. The influence of tree density on the grass layer of three semi-arid savanna types of southern Africa. African Journal of Range and Forage Science 18 (2–3):103–109. Google Scholar


J. L. Rotundo and M. R. Aguiar . 2005. Litter effects on plant regeneration in arid lands: A complex balance between seed retention, seed longevity and soil–seed contact. Journal of Ecology 93 (4):829–838. Google Scholar


J. R. Runkle 1982. Patterns of disturbance in some old-growth mesic forests of eastern North America. Ecology 63 (5):1533–1546. Google Scholar


G. L. Santos, D. Kageler, D. E. Gardner, L. W. Cuddihy, and C. P. Stone . 1992. Herbicidal control of selected alien plant species in Hawaii volcanoes national park. In: C. P. Stone, C. W. Smith, and J. T. Tunison . Alien Plant Invasions in Native Ecosystems of Hawaii: Management and Research. Honolulu, HI University of Hawaii Press. 341–342. Google Scholar


E. W. Schupp 1988. Factors affecting post-dispersal seed survival in a tropical forest. Oecologia 76 (4):525–530. Google Scholar


F. Senbeta and D. Teketay . 2001. Regeneration of indigenous woody species under the canopies of tree plantations in central Ethiopia. Tropical Ecology 42 (2):175–185. Google Scholar


H. Sharew, J. C. Legg, and J. Grace . 1997. Effects of ground preparation and microenvironment on germination and natural regeneration of Juniperus procera and Afrocarpus gracilior in Ethiopia. Forest Ecology and Management 93 (3):215–225. Google Scholar


K. Shono, E. A. Cadawent, and P. B. Durst . 2007. Applications of assisted natural regeneration to restore degraded tropical forestland. Restoration Ecology 15 (4):620–626. Google Scholar


D. Teketay 1997. Seedling populations and regeneration of woods species in dry Afromontane forests of Ethiopia. Forest Ecology and Management 98 (2):149–165. Google Scholar


D. Teketay 2005. Seed and regeneration ecology in dry Afromontane forests of Ethiopia: II. Forest disturbances and succession. Tropical Ecology 46 (1):45–64. Google Scholar


K. Tekle and T. Bekele . 2000. The role of soil seed banks in the rehabilitation of degraded hillslopes in Southern Wello, Ethiopia. Biotropica 32 (1):23–32. Google Scholar


K. Tekle and L. Hedlund . 2000. Land cover changes between 1958 and 1986 in Kalu district, Southern Wello, Ethiopia. Mountain Research and Development 20 (1):42–51. Google Scholar


G. Tesfaye, D. Teketay, and M. Fetene . 2002. Regeneration of fourteen tree species in Harena forest, southeastern Ethiopia. Flora 197 (6):461–474. Google Scholar


TFAP [Tigray Forest Action Program] 1996. Tigray Forest Action Program Main Report. Ethiopia: Mekelle, Ethiopia Tigray BoANR [Bureau of Agriculture and Natural Resources]. Google Scholar


M. Tigabu, J. Fjellstro, P. C. Ode'n, and D. Teketay . 2007. Germination of Juniperus procera seeds in response to stratification and smoke treatments, and detection of insect-damaged seeds with VIS + NIR spectroscopy. New Forests 33 (2):155–169. Google Scholar


A. Wassie, F. J. Sterck, D. Teketay, and F. Bongers . 2009a. Tree regeneration in Church Forest of Ethiopia: Effects of microsites and management. Biotropica 41 (1):110–119. Google Scholar


A. Wassie, F. J. Sterck, D. Teketay, and F. Bongers . 2009b. Effect of livestock exclusion on tree regeneration in church forests of Ethiopia. Forest Ecology and Management 257 (3):765–772. Google Scholar


R. Webster and M. Oliver . 2001. Geostatistics for Environmental Scientists. Chichester, United Kingdom John Wiley & Sons, Ltd. Google Scholar


F. White 1983. The Vegetation of Africa. A Descriptive Memoir to Accompany the UNESCO [United Nations Educational, Scientific and Cultural Organization]–AETFAT [Association for the Taxonomic Study of the Flora of Tropical Africa]–UNSO [United Nations Sudano-Sahelian Office] Vegetation Map of Africa. Paris, France UNESCO. Google Scholar


T. Yayneshet, L. O. Eik, and S. R. Moe . 2009. The effects of exclosures in restoring degraded semi-arid vegetation in communal grazing lands in northern Ethiopia. Journal of Arid Environments 73 (4–5):542–549. Google Scholar


E. Yirdaw 2001. Diversity of naturally-regenerated native woody species in forest plantations in the Ethiopian highlands. New Forests 22 (3):159–177. Google Scholar


E. Yirdaw and K. Leinonen . 2002. Seed germination responses of four Afromontane tree species to red/far-red ratio and temperature. Forest Ecology and Management 168 (1):53–61. Google Scholar


G. Zeleke and H. Hurni . 2001. Implications of land use and land cover dynamics for mountain resource degradation in the northwestern Ethiopian highlands. Mountain Research and Development 21 (2):184–191. Google Scholar
Ermias Aynekulu, Manfred Denich, and Diress Tsegaye "Regeneration Response of Juniperus procera and Olea europaea subsp cuspidata to Exclosure in a Dry Afromontane Forest in Northern Ethiopia," Mountain Research and Development 29(2), 143-152, (1 May 2009).
Received: 1 March 2009; Accepted: 1 April 2009; Published: 1 May 2009

Back to Top