Alien Plant Species


Recent articles in the "Island" (e. g.  Dr Lalith Gunasekera on "Yoda Nidikumba" on 28 September, 2011) have drawn attention to the problems that alien species could generate. Sri Lanka has had several earlier examples like Gorse (Ulex sp.) in the Up-country, Lantana, Wal Suriyakantha (Tithonia diversifolia), Salvinia, Japan jabara (Eichhornia crassipes), Alligator Weed (Alternanthera sp.), Katu Andara (Prosopis Juliflora) and lately Yoda Nidikumba (Mimosa pigra)

It is understandable, and even somewhat fashionable to regard them with some horror! An alien is something foreign, from outside. Few would consider Col. Olcott, Madame Blavatsky, Rev A.G.Frazer and Sir Ivor

Jennings, - all "aliens", in a negative light.

Alien plants, if brought in deliberately are introductions, if unwittingly, they are invasives. It must be remembered that almost all of our "useful" plants are introduced aliens -  rice, tea, rubber, jak, breadfruit, manioc, pineapple, papaw, mango (except Wal Amba), teak, mahogany and many, many more. A rare exception is coconut which possibly drifted in on ocean waves naturally! Most invasive aliens are feared as potential weeds. Interestingly, weeds may be described as "extremely successful plants which we have not yet learnt to use!" They are successful because they are extremely resilient, grow without care, often in climates very hostile to cultivated plants, compete successfully and propagate and spread readily. Most would be familiar with the "foxtail grass" which has invaded vast extents of the Mid-country. It is a close relation of millet. My Chairman at CRI, Dr Leslie Pieris a pioneer rice breeder would remark that if only we could genetically manipulate this nuisance to produce larger, edible grain, we would be well on our way to cereal self-sufficiency! We also know that our paddy farmers use Wild Sunflower as an excellent green manure, weed though it is!

The Water Hyacinth,( Eichhornia crassipes) is reported to be grown in "holding ponds" for radioactive waste water, for its propensity to absorb heavy metals, including radio-isotopes. I am particularly concerned about the apparent "war" declared against the "Katu-andara" that covers large extents of the sand dune areas around Hambantota/Ambalantota. A few decades ago, these areas (including the sand dunes) were dry, desolate and forbidding. In a relatively short time, the area metamorphosed into one which almost looked like an orderly plantation of this lusciously growing shrub Prosopis juliflora. The tale behind this is fascinating. Apparently, many years ago, the Forest Department saw a need to provide a protective cover for the windswept sand dune areas. Prosopis which is a success in the arid zones of Tropical America was considered a promising candidate. The preferred species was probably P. dulcis whose pods are eaten and relished by the natives. Apparently, an "administrative lapse" got the species mixed up and the less satisfactory Prosopis juliflora arrived and was planted. When the mistake was discovered, it seemed wise to sweep it under the carpet - or more correctly the sand! The secret held for a long while. Then a few stragglers pushed their way through the sand. All went well until the grazing buffaloes realized the "yumminess" of the pods!. The seeds need a passage through the cattle gut to germinate well. So wherever a "cowpat" fell, there grew a Prosopis! This would explain the sudden appearance and the semblance of orderly spacing. Unable to vouch for the veracity of this forestry blunder, I would thank any senior hand to shed light. In any event, it is too good a yarn not to share!

The village of Palugama near Welimada was aptly named for its character 50 years or so ago. The Forest Department planted an avenue of Gums (Eucalyptus sp), an alien species. The transformation was dramatic. Today’s Keppetipola is a very far cry from its ancestral Palugama.

Likewise, Prosopis juliflora may well prove to be a fine "pioneer" species which could allow a successor like Cashew or other fruits (under irrigation). If this is done with selective avenue thinning of the Andara, it may even fulfil a great function as a "nurse" crop for the introduction. Villagers consider it a fine fuel wood. The late Dr Ray Wijewardene did a test, using chain and tractor to harvest the thorny scrub. He found the wood to burn fiercely and to be of high calorific value (personal communication).

It is well to remember that almost every important crop plant in the World has virtually girdled half the globe from its place of origin to find its most comfortable and permanent home.

Therefore, while not denying the need for careful surveillance of newcomer species, let us not be fanatical or hasty in blind condemnation and possibly even eradication.

Dr.  U.Pethiyagoda

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