Alien species rapidly ex­pand­ing – land­mark re­search find­ings

Saturday Star - - METRO -


A THIRD of South Africa’s around 2000 alien species that have be­come in­va­sive are now en­ter­ing a phase of rapid ex­pan­sion.

“So even if no fur­ther alien species are in­tro­duced, the prob­lem will con­tinue to grow due to the species al­ready in the coun­try.”

This is one of the find­ings of a land­mark new re­port, the Na­tional Sta­tus of Bi­o­log­i­cal In­va­sions and their Man­age­ment 2017, com­piled by the SA Na­tional Bio­di­ver­sity In­sti­tute and Cen­tre for In­va­sion Bi­ol­ogy at Stel­len­bosch Univer­sity.

It is the first com­pre­hen­sive na­tional-scale assess­ment of the sta­tus of bi­o­log­i­cal in­va­sions in South Africa, and the first such global coun­try-level assess­ment.

“In­for­ma­tion from the South­ern African Plant In­vaders At­las re­veals all in­va­sive alien plant species not sub­jected to bi­o­log­i­cal con­trol have in­creased their ranges over the past 15 years, some sub­stan­tially.

“Pom­pom weed has in­creased in range by 670% and famine weed, an an­nual in­vader of over­grazed range­lands and sa­van­nahs, by 493%.

“Even long es­tab­lished in­va­sive tree species such as mesquite and river red gum have in­creased in range by 180% and 61% re­spec­tively.” Th­ese species have large im­pacts, which grow as the species spread.

“Thus, even if no fur­ther in­tro­duc­tions of po­ten­tially in­va­sive species takes place, the prob­lems as­so­ci­ated with in­va­sive species will in­crease, a phe­nom­e­non known as ‘in­va­sion debt’.”

Seven new species are in­tro­duced in South Africa an­nu­ally.

“The rate at which species are ar­riv­ing in the coun­try ap­pears to be grad­u­ally in­creas­ing. Once an alien species is in­tro­duced to South Africa… it’s very dif­fi­cult to stop.”

Of the 2034 alien species, 775 are in­va­sive. More than 100 have caused large neg­a­tive im­pacts – th­ese in­clude ter­res­trial or fresh­wa­ter plants, feral pigs, the small-mouth bass and rain­bow trout, the com­mon gar­den snail, the painted lady and the com­mon myna.

In­vad­ing alien plants are the “most di­verse, wide­spread and dam­ag­ing” group of in­vaders in South Africa with the West­ern Cape the most in­vaded province, fol­lowed by Mpumalanga, North­ern Cape and Kwazulu-natal.

In­va­sive trees and shrubs re­duce sur­face water re­sources by be­tween 3% and 5%.

“If no re­me­dial ac­tion is taken, re­duc­tions in water re­sources could rise to be­tween 2600 and 3200 mil­lion m³ per year; and if fully in­vaded, catch­ments in the West­ern and Eastern Cape will de­liver 30% less water to the cities of Cape Town, Mos­sel Bay, Ge­orge, Knysna, Plet­ten­berg Bay and Port Eliz­a­beth se­verely con­strains the prospects for eco­nomic growth.”

De­spite the in­tro­duc­tion of the 2014 Alien and In­va­sive Species Reg­u­la­tions, there are “high lev­els of non-com­pli­ance with some reg­u­la­tions and a short­age of ca­pac­ity within the De­part­ment of En­vi­ron­men­tal Af­fairs, and else­where in gov­ern­ment, to en­sure com­pli­ance”.

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