**1. Introduction**

Invasive species are either indigenous or exotic which are being taken over a particular habitat [1, 2]. Invasive alien species are species that are introduced intentionally or unintentionally into new areas and cause loss on an environment they invade [2]. In recent decades, biological invasions are increasing [3, 4] and threaten ecosystems, biodiversity, and food security [5]. Invasive alien species are representatives of all taxonomic levels of viruses, bacteria, algae, plants, invertebrates, and large mammals [6].

In the world database, *P. juliflora* is one of the 100 worst invasive alien species [7]. The report by Ethiopian Biodiversity Institute showed 35 invasive alien plant species (IAPS) in the country [8]. Some of these invasive alien plants include *P. juliflora*, *Parthenium hysterophorus*, *Eichhornia crassipes*, *Lantana camara*, *Acacia drepanolobium*, *Orobanche,* and *Cuscuta* species, which are identified as major plant invaders [2]. It was found that there were emerging plant invaders such as *Cryptostegia grandiflora*, *Parkinsonia aculeate*, *Mimosa diplorotricha*, *Mimosa pigra*, and *Argemone Mexicana,* and *Nicotine glauca* [8]. In Ethiopia, plant species including *P. juliflora*, *P. hysterophorus*, *E. crassipes*, *L. camara,* and *A. drepanolobium* are the worst that threatened biodiversity losses [9]. These species were overtaking other land uses such as woodlands, grazing lands, parklands, urban greening, farmlands, which had reduced their ecosystem services of the land uses.

*P. juliflora* is a perennial evergreen multipurpose tree or shrub native to the Caribbean, North and South America transported out of its ranges through human activities [10–12]. It was introduced to African countries, for instance, since 1822 in Senegal, South Africa in 1880, Egypt in 1900, Kenya since 1973, and into Eritrea from Sudan probably during the early 1980s [2]. There is contradicting information regarding the introduction of *P. juliflora* into Ethiopia. For example, it was introduced in the late 1970s from India into Goro nursery-Dire-Dawa. On the other hand, *P. juliflora* was first introduced to the Afar region in the late 1970s. The introduction of *P. juliflora* in the Afar region was through coordinated efforts between government and communities to stop desertification, greening up the region, and mitigate the impacts of drought [12]. *P. juliflora* was then planted over large areas up to 1982, and the sector Food for Work Program in 1986–1988 continued to expand its plantation. This species now exists in most regions of Ethiopia for instance, Afar, Oromia, Amhara, Somali, and Southern Nations and Nationalities Region States. It was reported as one of the invasive and problematic invasive alien species in Afar and Somali Regions and expanded to Great Rift Valley toward South Omo in Southern Nations and Nationalities Regional State of Ethiopia [13] and is the dominant invasive tree species in semiarid and arid ecosystems in the tropical regions of Eastern Africa [14]. During 2019 in Afar Region, Shiferaw et al. [15] reveal that there were 1.2 million ha of *P. juliflora* invaded lands that expanded at the rate of 31,127 ha per annual. It established 12.3% of *P. juliflora* land surface invasions in Afar region. Moreover, other information of Pitroff [16] reported by Farm-Africa that *P. juliflora* invaded over 1.8 million ha in Afar region*.*

Several research works show that *P. juliflora* had environmental effects, which is aggravating and influencing invasions into various ecosystems [10] that significantly had weaken ecosystem services [17, 18]. It reduced palatable grasses of livestock and replaced grass species such as *Chrysopogon plumulosus, Cenchrus ciliaris* and *Setaria verticillata,* and valuable woody species *Acacia tortilis, Acacia Senegal,* and *Acacia nilotica*. *P. juliflora* resulted also in social instability and economic hardship, placing constraints on sustainable development, economic growth, poverty alleviation, and food security in Afar region [19–21]. It caused harm or is likely to cause harm to the environment, people, economy, or human health [22, 23]. *P. juliflora* pods fed by livestock caused tooth decay and death through indigestion in the absence of supplementary feeds in the dry seasons [24, 25]. In arid and semiarid areas, ecosystem services obtained from woodlands, rangelands, livestock production, groundwater, and benefits of conservation areas and tourism were also under threat [26].

In different parts of Ethiopia, so as to minimize and control the invasion of *P. juliflora*, different strategies were applied such as eradication through mechanical *Effects of the Invasive Alien* Prosopis juliflora *(Sw.) DC and Its Management Options… DOI: http://dx.doi.org/10.5772/intechopen.108947*

methods and burning and cutting of the juvenile plant at 10 cm and adult plant at 40 cm down to the ground were tried by the Ethiopian Institute of Agricultural Research [27]. These methods were costly to manage the species. In addition, controlling *P. juliflora* invasion through utilization such as charcoal production and animal feeds were also tried [28, 29]. However, most of these efforts failed to control the species. Current management practices are also not satisfactory to sustain the rangelands and woodlands. *P. juliflora* management options counter to environmental effects are not sufficient to control its invasion progress toward rangelands and expand into other land use systems in the invaded regions of the country. Unless improved management interventions are adopted, the sustainability of ecosystem services will be at stake in near future. This paper aims to review the effects of *P. juliflora* on environmental constituents in Ethiopia, review the management options and take up lessons learned elsewhere or in Ethiopia, and review about the utilization and management of *P. juliflora*. Thus, this paper addresses relevant scientific information based on the evaluation of information collected from different journals, books, manuals, and various reports.

#### **2. Review method**

In this paper, relevant pieces of literatures were selected using the systematic review. Based on the specific objectives of the topic, journals, books, manuals, various reports, and related synthesized ideas were screened. Hence, 81 journals, 9 books, 5 proceedings, and 17 various reports were selected. In addition, except for the concept of some terminologies used, update sources were used for the review.

### **3. Environmental effects of** *Prosopis juliflora*

Dense impenetrable thickets of *P. juliflora* compete with native plant species and harms environment thus disrupt ecosystem functions and services. The species affected soil properties, hydrology, land use and land cover changes, rangelands, quality and availability of animal feeds, threat to fertile agricultural lands and loss of their productivity, reduce biodiversity, invaded wildlife reserves and national parks, affect human and livestock health, the economy of the country and the overall livelihoods of pastoralists, social conflicts and cerate political instability, reduce bird diversity, blocks roads of both animal and inhabitants, reduce urban amenity, but induce carbon sequestration in the invaded areas (see **Table 1**).

#### **3.1 Effects of** *Prosopis juliflora* **on soil environment**

#### *3.1.1 Soil physicochemical properties*

Windbreaks, cover crops, and cultivation practices can control loss of soil [64]. Likewise, a shelter belt of *P. juliflora* is planted around fields in many semiarid regions to reduce wind speed and reduce wind induced soil erosion, decrease desiccation by reducing transpiration, and thereby increase plant and animal production [65]. These types of plantation using *P. juliflora* were also practiced in the invaded regions of Ethiopia. The capacity to block the flow of wind depends upon the height, density, and thickness of the stands of plantations. Apart from preventing the loss of fertile


#### **Table 1.**

*Effects of* Prosopis juliflora *on environmental properties and its environmental services.*

soil, *P. juliflora* reduced wind damage from crops, reduced loss of soil moisture, and improved microclimate. A report by Patnaik et al. [43] in Sudan shows that wind speed inside 5-year-old *P. juliflora* plantation reduced an average 14%, while potential evaporation reduced by 22% in the same site. *P. juliflora* was growing quickly, and it was a wind-resistant plant, which could be planted successfully to control soil erosion and could serve as shade and shelter that affected water balance by increasing relative humidity but reducing temperature and evapotranspiration [10]. On the other hand, in low land areas of Central Sudan, a study by Al-Amin et al. [66] shows that *Leptadenia pyrotechnica*l provided relatively good protection windward against consequences from erosion than cover of *P. juliflora*. This study shows protection of *P. juliflora* against soil erosion lower than the later species. Another study in Central Sudan by Al-Amin [67] reveals that the growth of *P. juliflora* in clusters could be more effective against wind protection than individual stems. *P. juliflora* had planted where soil fixing or improvement is an important consideration [68], 1). The authors also proved that *P. juliflora* was particularly suitable for stabilizing dunes and easily erodible soils. This is because of its ability to survive and grow on poor sites in which a few other species could tolerate, and its extensive lateral root system could bind soil particles particularly in the upper 60 cm soil depth.

Findings by Giessen et al. [69] show that *P. juliflora* enriched SOC, total P, total N, and available P under its canopies of topsoil in semiarid of Northeast Brazil. In Kenya, results by Mwangi and Swallow [24] reveal that biomass of understory plant species was five times lower under the canopy of *P. juliflora* than open grasslands. SOC and

#### *Effects of the Invasive Alien* Prosopis juliflora *(Sw.) DC and Its Management Options… DOI: http://dx.doi.org/10.5772/intechopen.108947*

total N concentrations in soils under *P. juliflora* were higher than those under open grassland areas. In Afar region of Ethiopia, a study by Shiferaw et al. [14] shows that invasion of *P. juliflora* changed the physicochemical properties in Teru and Yalow Woredas. Several findings show that positive effects of *P. juliflora* on soil properties overweight the negative ones. For instance, *P. juliflora* significantly affected soil pH, exchangeable Na+ , water-soluble Ca2+ + Mg2+, water-soluble Na+ , and exchangeable Na percentages. The invasion of *P. juliflora* significantly increased soil pH but decreased exchangeable Na<sup>+</sup> , exchangeable Na percentage, and water-soluble Ca2+ + Mg2+ than non-invaded open grazing lands. The clay content of *P. juliflora* invaded lands was higher than non-invaded open grazing lands. However, the sand content of the soil was higher under non-invaded grazing lands than *P. juliflora* invaded lands. In this study, though in most of the findings, the invasion of *P. juliflora* had positive effects on physicochemical properties, Shiferaw et al. [2] show negative effects on plant diversity, human and livestock health, economic losses, and it means that negative effects are outweighing its positive effects.

According to Sadeq et al. [35], SOC, total N, available P, total S, and total soluble salts were higher under canopy of *P. juliflora* than outside in soil depth of 0–45 cm, but total Na increased within this soil depth. In Kenya, Muturi *et al*. [70] show that soil characteristics such as %sand, %clay, N, P, K, Mg, Mn, Fe, and Cu under *P. juliflora* species and mixed species of *Acacia* and *P. juliflora* canopies were similar except that pH and calcium were higher under the *P. juliflora* species and mixed species of *Acacia* than under canopy of *P. juliflora*. But, in Turkwel riverine forest, silt and carbon were lower under *Acacia* canopy than under *P. juliflora*. In terms of soil salinity, neutralizing alkaline, sodicity, and soil nutritional status, physical properties such as soil moisture, bulk density, and soil texture, *P. juliflora* have ameliorating effects. These are primarily due to complex interactions between the effects of nitrogen fixation, incorporation of leaf litter, changes in microclimate, and changes in the floral soil fauna and soil microbial populations [10]. In Kenya, research by Kahi et al. [71] reveals that organic matter and total N were higher under *P. juliflora* canopy than under open areas. However, available P, soil pH, soil bulk density were lower under *P. juliflora* canopy than under open areas. Thus, growth of *P. juliflora* implications for creation of suitable soil microclimate probably due to litter turnover and its facilitation of infiltration and draw water from ground to surface soil.

#### *3.1.2 Soil biological properties*

Mehadi et al. [72] indicate that invasion of *P. juliflora* increased total mycorrhizal colonization of roots and reduced heavy metals such as Cadmium (Cd) levels in plants. In addition, the intensity of mycorrhization under canopy of *P. juliflora* was significantly higher than under species of native *Acacia*. Results in Saudi Arabia revealed that Cmic under *P. juliflora* was greater in rhizosphere for *P. juliflora* than in rhizosphere of *Acacia ehrenbergiana* and *A. tortilis*. As a result, extracts from parts of *P. juliflora* were used in disinfecting and bio-functions against different bacterial pathogens. But, litter fall of *P. juliflora* inhibited plant growth and their Arbuscular Mycorrhizal Fungi colonization of roots [34]. For instance, the litter and leaf extracts of *P. juliflora* significantly inhibited the germination of *Sorghum bicolor*. On the other hand, *P. juliflora* stimulated soil microbial biomass of carbon, soil metabolic quotient, and activities of soil enzymes.

#### *3.1.3 Hydrology*

Moisture and nutrients that were taken from deep soils under *P. juliflora* were beneficial to the herbaceous plants. The removal of trees from the savannah ecosystems during wet and dry seasons supported large numbers of grazers that facilitates the growth of herbaceous plants. But, during the dry periods, the survival of the shallow-rooted herbaceous plants could be endangered by removal of trees [71]. During this season, transportation of moisture from deep soil by trees was encountered in semiarid and arid regions. Extensive lateral root systems of *P. juliflora* capture surface water after rain, but its deep tap roots allowed them to survive prolonged drought through accessing the water table [10]. However, in dry areas, evapotranspiration of plants was escalated than their transpiration. For example, Shiferaw et al. [40] indicate the daily average transpiration of *P. juliflora* lower than the daily average evapotranspiration of a dense *P. juliflora*.

#### *3.1.4 Soil seed banks*

Soil seed bank is ground flora of various vegetation ecosystems. It is important for shaping the composition, diversity, structure, and regeneration of plant communities and consequently restoration of vegetation ecosystems. Soil seed bank depends on the spatial distribution of vertical and horizontal seeds of different species and vegetation communities. The spatial distribution of seeds in the soil is primarily a function of the dispersal process [73]. Dense thicket of *P. juliflora* hindered the dispersal of other seeds of other plant species in the invaded area. The seeds of *P. juliflora* were characterized by a seed coat-imposed dormancy and established a huge persistent seed bank in the soil. This character makes it easy and continues germination of seeds of the species. In addition, livestock and wild animals are attracted by the green foliage to eat ripened pods and disperse the seeds. Dispersal and successful germination of the seeds of *P. juliflora* were thus through endozoochory of animals' seed ingestion. Seeds subsequently dispersed away from the parent plant and the pods are easily transported by runoff [36].

Land use dynamics, struggle over resources, and change of climate are key factors that influenced the probability in the expansions of *P. juliflora* [2]. When an invasive species became irresolutely verified, its control can often be challenged and eradication is habitually not possible. Subsequently, its impacts on biodiversity, ecosystem progressions, and ecosystem services can be serious [36]. In vegetation ecosystems, the seed bank of soil has been considered as a promising and cost-effective method for reestablishing of other native plant species, but its influence factors have not been clearly understood [74]. Possibility of vegetation restoration from soil seed bank is usually dependent on its seed density and species composition [75, 76]. The increases in the invasion of *P. juliflora* in certain ecosystem inhibit free dispersal of seeds in other native plants. Therefore, seed dispersal determines species diversity, composition, and density of plant species. Studies show that both livestock and wildlife species played a critical role in the dispersal of *P. juliflora* that enhanced the arrival of its seeds and progress into other land uses [77]. These in turn affected the fate of seeds of other native plant species.

### **4. Effects on land use and land cover changes**

In the introduced areas, *P. juliflora* invasion and expansion increased both in coverage of area and density of the species. At global level, PENHA [78] reported that land

#### *Effects of the Invasive Alien* Prosopis juliflora *(Sw.) DC and Its Management Options… DOI: http://dx.doi.org/10.5772/intechopen.108947*

covered by *P. juliflora* was 50 million hectares. In Africa alone, for example, the land covered was about 5 million hectares forming dense thickets of *P. juliflora*. In several African countries such as Kenya, Ethiopia, Sudan, Senegal, and South Africa, it had become an invasive species [10, 79]. In the Afar region in Ethiopia, *P. juliflora* is now threatening serious problems on pastoral areas where its invasion existed in four of five zones and 11 of 32 districts of the region. Among the five administrative zones of the Afar region, the Amibara woreda of Zone 3 is thought to be recognized as the starting point for the introduction and spread of *P. juliflora* [55]. This woreda was represented as a degraded semiarid ecosystem in the region [30, 80]. Zone 1 and Zone 3 were the two zones that severely invaded by *P. juliflora*, and it was expanded to the remaining zones [18]. Dubti, Asayita in Zone 1 and Mile, Gewane, Amibara, Gelealu, and Awash Fentale in Zone 3 were the most severely invaded woredas in Afar region. Reports also show that Zone 4 and Zone 5 were partly invaded woredas of Afar region.

EBI [8] reported that *P. juliflora* was threatening vegetation types including *Acacia-Commiphora* woodland, desert, and semi-desert scrublands in Afar Floristic Region. Within these vegetation types, habitats invaded by *P. juliflora* were river banks, irrigated cropland, roadsides, and the settlement areas [2]. *P. juliflora* displaced grazing lands and threatened wildlife conservation areas [47, 50, 81]. According to Helland [42], *P. juliflora* was associated mostly with the loss of pasture and invasion of woodlands. The major factors that aggravated and influenced invasions into various environments are the changes of land use and land cover and climate change [10], and increase in population pressure and overgrazing of pasture lands owing to large herding were also other causes for the increase of invasion of *P. juliflora* in invaded regions of Ethiopia [15].
