The Tree That Outstayed Its Welcome

New herbicide treatment might control pervasive spread of the blue acacia.

The green cloaking the Jerusalem hills and southern coastal plain recalls a typical Middle Eastern landscape. However, a closer look reveals that these trees are not local breeds, but rather dense groves of blue acacia, a tree imported from southwestern Australia and the most invasive species on Israeli soil.

The Israel Nature and National Parks Protection Authority recently conducted trials on the use of a herbicide that could halt the spread of some of the tree populations.

Dr. Jean-Marc Dufour-Dror, a specialist in pervasive plant species, was invited by the science division at INNPPA to research the effectiveness of a glyphosate-based herbicide on controlling the blue acacia. Dufour-Dror examined 98 mature acacias and 98 younger samples that were injected with the herbicide, which stunts the trees? growth.

The trees were given regular injections for two years, and 90 percent of them did not produce seeds. The herbicide treatments significantly reduced the trees? ability to proliferate.

The blue acacia was first brought to Israel in 1920 to help dry up swamps, create forests and stabilize sand dunes. At that time its pervasive nature was unknown, and by the time it was discovered, it was already too late.

Official bodies such as INNPPA found themselves helpless against the spread of the acacia, which produced large quantities of seeds and could flourish under almost all Israeli soil and climate conditions.The areas that have been damaged the most are the coastal beaches, which were covered by a thick growth of acacia trees at the expense of local species of plants, and the animals native to open sand dunes.In recent years the acacia has also spread in the Jerusalem hills, mainly in the Nahal Sorek and Sha?ar Hagai regions, which were badly damaged by forest fires in the mid-1990s.

?This invader could be destroyed, but that would cause tremendous environmental pollution,? explains Hanoch Tzoref, of the Jewish National Fund. ?In order to destroy one dunam ?(1/4 acre?), we would have to spread several liters of highly toxic herbicide.?

Dufour-Dror?s report, however, on the glyphosate-injection method, notes that no damage is caused to the surrounding ecosystem, thanks to the localized use of the herbicide and the tiny quantities used.

?Following this study, we can declare that the chemical treatment provides an initial solution to the spread of the blue acacia and other invasive species as well,? wrote Dufour-Dror?s in the report submitted to INNPPA.

?The implementation of this method can also eradicate small- and medium-sized existing [acacia] populations and halt the spread of the large populations.?

Even so, Dufour-Dror notes that work should continue on the development of other, more effective methods for dealing with the acacia. Researchers from Ben-Gurion University of the Negev have already conducted trials using controlled burns to destroy the millions of seeds on the ground.

Dufour-Dror recommends the immediate implementation of the chemical injection treatment in the nature reserves, as well as in areas with small concentrations of blue acacia, as it will be possible to clear them within a relatively short space of time.