Invasive Alien Plant Species in the Northwestern & Western Provenance of Ethiopia and Linking Its’ Phonological Implication to Management and Control

Biodiversity loss caused by invasive species may soon surpass the damage done by habitat destruction and fragmentation. Biological invasions are an important component of human-caused global environmental change. Invasive alien species are now a major focus of global conservation concern. The decisions need to be made on whether benefits derived from the invasive spread of an alien species outweigh the reduced value of ecosystem services, e.g. the loss of grazing land in areas invaded with Lantana camara and Senna occidentalis . It is necessary to consider actions to deal with the current problems caused by invasive species and to reduce the magnitude of the problem in the future. The present catalogue on invasive alien plant species of the northwestern & Western Ethiopia is therefore timely one. It focuses on some species of invasive alien plants in Ethiopia. These include the most serious invasives, such as Alternanthera philoxeroides, Cassia uniflora, Chromolaena odorata, Eichhornia crassipes, Lantana camara, Parthenium hysterophorus , Senna obtusifolia and others. I am confident that this publication will be immense value to foresters, environmentalists, field researchers and conservation managers to pay attention on the ecological impact of invasive aliens both at the species and at the ecosystem levels. Keywords : Biodiversity, invasive species, conservation, environmental change DOI : 10.7176/ALST/74-04 Publication date :May 31 st 2019


Monitoring:
Monitoring is required in the invasive species management to determine: location/early detection of problematic species, whether a species is likely to become a problem in an area, whether a species is responding to management efforts (if taken?), the impact of alien plant control methods on native species. Monitoring of Invasion can be done through qualitative approach like species inventory (seasonally) and quantitative approach using phytosociological methods and mapping using ground-based methods (via map overlays or GPS), remotely-sensed images (aerial photos, high resolution multispectral digital data).

Control:
Current control methods for invasive aliens are expensive, lengthy, and risky because total eradication is required to prevent reestablishment. Effective site-eradication procedures require multi-year treatments, continued monitoring, and follow-up treatments. All infestations on adjacent lands must be treated to prevent reinvasion. Unfortunately, infestations common along railway tracks, roads, and utility right-of-ways are rarely treated for eradication, fostering widespread immigration to adjacent lands. Common methods for control of invasive weed species are: Mechanical, Chemical and Biological control. Mechanical Control: It is one of the common methods employed for control of invasive species. Mechanical control involves ploughs, scythes, mowers, hoes, cultivators, rotary weeders etc. Using these tools, the weeds are physically lifted from the soil, cut off or buried. But it is laborious and needs lot of man power. Chemical Control: This method has proved costly and partly successful in several cases. Using of chemicals is not desirable due to pollution that they cause. Biological Control: In most cases of alien pest invasions, biological control has proven the most effective and environmentally sound approach to their management. Introducing a natural enemy (e.g. water hyacinth weevil Neochetina spp. for Eicchornia; Lantanophaga pussilidactyla insect for Lantana camara, Zygogramma bicolorata insect and Cassia uniflora plant species for Parthenium hysterophorus) for eradication of invasive species is a current focus of interest for biological conservationists. But biological control may not be evenly effective over all areas infested by the invasive species.
Past research studies for developing eradication methods were often limited in duration (only one or two years) and habitats (one site). Appropriate long-term support and funding has been lacking. Control projects for invasive species, offer a logical, long-term solution but none have been seriously attempted in India. The high investments and longterm research required for control programs have been made only for western rangeland alien plant species, and more recently for tropical aliens in Florida. Crucial aspects of alien plant ecology that influence control strategies are as follows: 1. Invasive aliens continue to spread because natural predators were not imported from the plant's home range and native predators are too weak; 2. After an alien plant is introduced there is a "lag phase" of decades to centuries before an exponential spread phase (Baskin 2002). Thus, some species that currently appear non-invasive may eventually begin to spread rapidly. 3. Invasive alien plants can prevent or retard natural succession and reforestation by forming dense infestations. 4. Invasion by aliens continues to decrease biological diversity and detract from their primary mission; 5. The partial shade tolerance of some alien species (Cassia pumila) allows them to become established under developed forest canopies; 6. Alternanthera philoxeroides, Eicchornia crassipes and Pistia stratiotes are invading riparian/aquatic habitats to the exclusion of native species and regeneration; 7. The initial spread of aliens were observed along highway and utility right-ofways, "disturbed habitats," and riparian systems, greatly facilitates migration into extensive forest areas; and 8. Because many "disturbed habitats" occur in cities, alien plants can present severe problems for urban forestry programs, which is made more difficult by alien species mixtures. 9. Allelopathic effect by species like Prosopis juliflora, Hyptis suaveolens, Lantana camara retard the growth of other species. 10. The invasions potentially lead to an increase in species richness, as invasive species are added to the existing species pool. But also leads to extinction of native species, resulting in decrease of species richness. The negative interactions is primarily the competition with natives for food and sustenance, which may not allow coexistence.

Research Issues, Legal and Institutional Needs:
There is no question that understanding and dealing with the invasive problem is an enormous challenge. To meet this need SCOPE (Scientific Committee on Problems of Environment) is calling for a focused, coordinated, and broadly based approach to the invasive species problem that would engage the large, and global concerned with these issues. It is recognized that research initiatives in India are now needed to improve the understanding of the ecology of the invasive process, the knowledge on predictive powers on which species are likely to become invasive and under what conditions, characteristics of invasive species, impacts of global climate change on invasive species.
It is realized that a legal and institutional approach to the country's biosecurity threat is a prerequisite to long-term success against introduction of invasive species. The government should strengthen its quarantine authority through new legislations which prohibits the introduction of alien species without an approved consent or permit. Also unauthorized introduction of wild and domesticated animals and plants into new areas, between states and within the country should be reviewed and monitored by several government departments, viz. Forest, Agriculture, Environment, Veterinary and Public Health.
We need to develop techniques to make rapid assessment of the status and movement of invaders and of their potential ecosystem impacts. At present our knowledge about the status of invaders is generally of two states only -it is present (which is derived from flora lists) or it is firmly established and doing devastating damage (often learned from the popular newspapers). Information is needed between these two extremes. In order to acquire this information a rapid sapling approach is needed that would produce a quantitative assessment of the status of invading species, that could be repeated at intervals, to provide a clear focus on emerging problems, helping to alleviate the crisis management approach to invaders. Efforts are needed to utilize developing technologies for tracking invasives including remote sensing and GIS. Further, we need to develop global maps of the distributions of the most abundant and most devastating invasive species, as well as the most sensitive ecosystem types (Mooney, 1999).

Ethiopia (study area)
Ethiopia is located in the horn of Africa between 3º and 18º North latitude, 33º and 48º east longitude, and lies within the tropics. It has diverse Physiogeographic features with high and rugged mountains, flat topped plateau, deep gorges, incised river valleys and rolling plains. The altitudinal variation ranges from 110m below sea level in same areas of Kobar Sink, to 4,620 meters above sea level (masl) at Ras Dashen. The Great Rift Valley runs from northeast to southwest of the country and separates the western and southeastern highlands. The high lands on each side of the rift valley give way to extensive semi-arid lowlands to the east, south and west of the country.

Figure 1: Map of Ethiopia (the Northwestern provenance)
Ethiopia is a tropical country with varied macro and micro-climatic conditions that have contributed to the formation of diverse ecosystems inhabited with a great diversity of life forms of both animals and plants. The rain fall distribution is seasonal and is mainly governed by the inter annual oscillation of the surface position of the Inter-Tropical Convergence Zone (ITCZ), that passes over Ethiopia twice a year. This causes variations in the wind flow patterns and the onset and withdrawal of winds from north and south. The mean annual rainfall patterns range from 500 mm to 2,800 mm. The South western region receives the heaviest annual rainfall which goes up to 2,800 mm in some areas. The central and northern central regions receive moderate rainfall that declines towards northeast and eastern Ethiopia, and the southeastern and northern regions receive an annual rainfall of about 700 mm and 500 mm. respectively. The relative humidity regimes that closely follow the rainfall pattern, the rainfall pattern itself and the high variation in temperature (> 300 C and < 100 C) influence types and diversity of the vegetation and their distribution over the country (Leipzig,1996). Flora: According to World Conservation Monitoring Centre (WCMC), 1,604,000 species have been described at the global level. Thus Ethiopia accounts for 4.4 % of the global biodiversity existing in only 2.4% land area of the world. According to Tesfaye Awas (2007) the number of flowering plant species endemic to the present political boundaries of this country is 840 out of a total of 7000, i.e. 12 %. (Tesfaye Awas 2007). Ethiopia is an important center of agri-biodiversity having contributed 167 species to the world agriculture and homeland for 320 species of wild relatives of crops. Ethiopia's rich vegetation wealth and diversity is undoubtedly due to the immense variety of the climatic and altitudinal variations coupled with varied ecological habitats.