Published On:Tuesday, December 6, 2011
Posted by Sri Lanka Guardian
l by Dr. Lalith Gunasekera
(December 06, Melbourne, Sri Lanka Guardian) During the past decade, there has been increasing attention on invasive plants spreading in Sri Lanka. Of the many exotic invasive plants, katu andara has been considered as a major invasive plant along with salvinia, giant mimosa, waterhyacinth, lantana.
Mesquite ((Prosopis juliflora) is English name for katu- andara originally from Central and South America. Europeans introduced this plant around the world during the past 200 years, as they were seen to be very useful and drought resistant species. It was introduced to Sri Lanka in 1880 by the British. It was introduced to its present highly populated location of Hambantota lagoon in 1950-1955 as a shade and erosion control tree. Coessentially this plant is invading very important ecosystems in Bundala National Park which is one of the important wetland under the RAMSAR convention. Katu-andara is confined to Hambantota district in the southern province and Puttlum district in north central province. In the southern region it has spread towards the sea and in Bundala National Park where the brackish water lagoons are found. In Puttlum district it has colonized a different habitat, about 20 km inland from sea. A few individual plants have been observed in the northern peninsula and on Nagadeepa island.
Katu-Andara flowers and leaves
This plant genus has been planted in different parts of the globe. Currently Australia has over 800000 hectares of infestation and considered as a Weeds of National Significance.
Kalapu andara is a thorny shrub or small tree that usually grows up to 3 metres but can reach to 15 metres. The plant look rather untidy, with zigzag shaped branches. Leaves are fernlike and racy in shape depending on the species. Foliage is usually dark green but can be blue-green. Small greenish, cream lamb’s tails flowers grow near ends of branches in whale like spikes. Seed pods are 10-20 cm long with slight constructions between the seeds. Each pod contains 5-20 hard seeds. Spines range in size from 4-75 mm long and contributed to form impenetrable barriers.
Katu-andara possesses characteristics that make it very competitive including rapid germination of seedlings under a wide range of conditions, rapid vertical penetration of taproots and long shallow lateral roots, an ability to respond from dormant stem buds following injury, drought, resistance, spines, rapidly dispersed hard coated seed, long seed dormancy and high fecundity.
The writer is inspecting Katu-Andara invasion at Bundala area
The plant generally produces a single crop of seeds per season. Numbers recorded overseas include 63,000 – 98,000 seeds/tree/year but these numbers have not been recorded in Sri Lanka. In the field it is thought that most seeds may not survive longer than 2-3 years due to fungal attack or predation but no accurate studies have been carried out. Seedling recruitment depends on standing densities of reproductive trees. Despite the level of recruitment, seedling mortality was also high, resulting in an average of 836 seedlings per hectare after a year.
Katu-andara pods are high in sugar (16%) and protein (12%) and therefore are sought by herbivorous animals. Of these cattle and monkey’s are the most effective dispersal agents due to their high populations in infested areas, movement and high seed germination after passing through the gut. The trial conducted by the scientists from University of Colombo reported that the highest seed germination of katu- andara was observed in seeds present in cow dung (86.7%) than elephants (65%) and gray monkeys (29.3%) dung. Seed pods can also be spread by seawater. Perhaps the most effective dispersal vectors of katu andara are humans, since they have transported the plant across the landscape and across the world for use as an ornamental, shade and fodder tree. Based an experience in the United States, favourable climatic conditions foe katu-andara germination occurs sporadically, possibly once every 20-50 years. In general soil moisture appears to determine its distribution rather than soil type since the plant tends to establish most successful on clay and alluvial soils that have good moisture retention.
Some impacts of katu-andara
• Formation of thickets that out compete ground vegetation through competition for light, water and nutrients and impact of fauna.
• Potentially all river systems and tidal estuaries in the southern and coastal areas of Puttalam are vulnerable to further distribution of infestations.
• Open grasslands and native thorn less woody shrub lands are vulnerable to being changed to thorny shrub lands with potentially large effects on native flora and fauna.
• Increased difficulty and expense of mustering animals.
• Impeded movement and access to water.
• Thorns damage to vehicle tyres, animals and humans.
• Increased water loss form and maintenance cost of watering points.
• Exacerbates and accelerates soil erosion.