Experimental control of Spanish broom (Spartium junceum) invading natural grasslands

Cristina Sanhueza,Sergio Zalba

doi:10.3391/mbi.2012.3.2.04

Abstract

A group of legumes generically known as brooms are among the most successful shrubs invading grasslands in South America and other regions. 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 into the Argentine Pampas grasslands where it spreads over remnants of pristine ecosystems, threatening their biodiversity. This paper reports the results obtained after an adaptive management strategy aimed at controlling this species in a nature reserve, and compares the efficiency of different mechanical and chemical control techniques in terms of the number of plants killed and the effects on surrounding vegetation and on the recruitment of broom seedlings. Control was implemented in two phases, the first included three treatments: i) cut at the base of the plant, ii) cut followed by the immediate application of Togar (Picloram 3% + Triclopyr 6%, at a 5% dilution in diesel oil) on top of the cut stump, and iii) foliar spraying with Togar. The follow-up treatments, implemented one year later, consisted of spraying the re-sprouts with Togar (5% in diesel oil) or Glyphosate 36% (2% in water). The best option in terms of controlling Spanish broom was spraying the resprouts with Togar which gave 100% mortality of the treated plants, compared with values of 40% - 100% re-sprouting for the other options tested. None of the methods was associated with an increase in seedling recruitment, nor with significant changes in the vegetation in the immediate vicinity of the controlled brooms.

Highlights

Biological invasions by non-native species are one of the worst ecological components of global environmental change
The lowest value of the range for mean peroxidase concentrations was found for Group T in Pond 7 (6.71 μg/gm FW), for Group A in Pond 2 (6.72 μg/gm F.W.) and for Group B in Pond 3 (1.31 μg/gm F.W.)
This study shows evidence in favour of two specific traits of Alternanthera philoxeroides that are reported to facilitate plant adaptations in different environments, namely, its ability to grow even under high strand density and its ability to withstand a broad range of environmental conditions

Summary

Introduction

Biological invasions by non-native species are one of the worst ecological components of global environmental change. Alternanthera philoxeroides (Martius) Griseb (Amaranthaceae), alligator weed, an invasive perennial wetland herb originating from South America (Maddox 1968), has many attributes of a successful invasive weed such as rapid growth and vegetative propagation (Tao et al 2009; Wang et al 2009) as well as a broad ecological amplitude (Geng et al 2007) This amphibious clonal plant has invaded many ecosystems worldwide (Julien et al 1995), including riparian zones (Pan et al 2006) and agricultural lands (Spencer and Coulson 1976), and is regarded as one of the worst weeds of the world (http://www.waikatoregion.nz). Invasive plants posses certain characteristics which make them more competent to adapt and propagate in newer environments/ habitats and understanding these mechanisms is crucial for managing invasive plant species (Mack et al 2000)

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