Experimental control of Spanish Broom invading natural grasslands

Abstract

A group of legumes generically known as brooms are among the most successful shrubs invading grasslands in South America and otherregions. These species share a set of biological features that enhance their invasiveness, such as abundant and long-lasting seed banks,aggressive root systems and rapid growth, combined with their ability for re-sprouting after cutting or burning and for avoiding herbivores.They grow in dense stands that exclude native vegetation and are able to change ecological processes, increasing fire frequency and intensity,and fixing atmospheric nitrogen. The Spanish broom (Spartium junceum) is a shrub native form the Mediterranean that was introduced intothe Argentine Pampas grasslands where it spreads over remnants of pristine ecosystems, threatening their biodiversity. This paper reports theresults obtained after an adaptive management strategy aimed at controlling this species in a nature reserve, and compares the efficiency ofdifferent mechanical and chemical control techniques in terms of the number of plants killed and the effects on surrounding vegetation andon the recruitment of broom seedlings. Control was implemented in two phases, the first included three treatments: i) cut at the base of theplant, ii) cut followed by the immediate application of Togar (Picloram 3% + Triclopyr 6%, at a 5% dilution in diesel oil) on top of the cutstump, and iii) foliar spraying with Togar. The follow-up treatments, implemented one year later, consisted of spraying the re-sprouts withTogar (5% in diesel oil) or Glyphosate 36% (2% in water). The best option in terms of controlling Spanish broom was spraying the resproutswith Togar which gave 100% mortality of the treated plants, compared with values of 40% - 100% re-sprouting for the other optionstested. None of the methods was associated with an increase in seedling recruitment, nor with significant changes in the vegetation in theimmediate vicinity of the controlled brooms.