DOI: 10.5061/dryad.zkh189361
title: A preliminary field trial to compare control techniques for invasive Berberis aquifolium in Belgian coastal dunes

description: Non-native Berberis aquifolium is notoriously invasive in Belgian coastal
 dunes. With its strong clonal growth through suckers, this evergreen shrub
 outcompetes native species and affects dune succession. To prevent further
 secondary spread and mitigate its impact, there was an urgent need for
 knowledge on the effectiveness of control measures, both at the plant and
 habitat level. Here, we report on a first control experiment. Individual
 B. aquifolium clones were subjected to one of four treatments (manual
 uprooting, foliar herbicide application, stem cutting followed by
 herbicide or salt application), with regrowth being measured up to one
 year after treatment. Plants proved most susceptible to foliar herbicide
 application (5% glyphosate solution), resulting in 77% of the clones
 apparently killed. We discuss the limitations of our experiment and the
 potential for actual field application of the different treatments. We
 present some guidelines for future control that may become further refined
 as experience builds up.
description: Experimental treatment of a selection of individuals with limited
 clonal extension was set up in four heavily infested dune sites
 (fieldcode <strong><em>region</em></strong>).
 Individual <em>B. aquifolium</em> plants
 (fieldcode <strong><em>plant_id</em></strong>)
 selected for treatment were
 located (fieldcode <strong><em>x_proj,
 y_proj</em></strong>) on a certain day (fieldcode
 <strong><em>date</em></strong>) with a hand-held
 Garmin Foretrex 401 GPS, photographed and marked with a flag so as to
 easily relocate them in the field after treatment. Height (cm)
 (fieldcode <strong><em>height</em></strong>) and
 diameter (cm)
 (fieldcode <strong><em>diameter</em></strong>)
 were measured and the number of stems
 (fieldcode <strong><em>n_stems</em></strong>) was
 counted to get an idea of the dimension of each individual or clone.
 Within the selected plants, clone diameter was 85 cm on average (minimum
 10 cm, maximum 6 meter). In April/May 2013, plants were subjected to one
 of the following management treatments (fieldcode
 <strong><em>treatment</em></strong>): (1) manual
 uprooting by digging with shovels (DIG), (2) leaf treatment using a spray
 bottle with a 5% Roundup Max (450g/l glyphosate) solution (LEAF), (3) stem
 treatment (cut and paint) with the same glyphosate solution (STUB) or
 (4) stem treatment with a saturated salt (NaCl) solution (SALT). Each
 ramet of a clone was treated similarly. We alternated treatments in
 sequence to different plants. When one plant received a given treatment,
 we moved to the next plant and applied the following different treatment,
 making sure plants were sufficiently far apart (minimally 10 meters) so as
 not to treat the same plant clone and making sure the most closely located
 plants got different treatments. The 5% glyphosate solution corresponds
 with the recommended concentration for cut stump treatment of <em>P.
 serotina</em> which is higher than the recommended concentration
 (1.5–2%) for leaf treatment (Agentschap voor Natuur en Bos 2013). The salt
 treatment is regarded as an environmentally friendly alternative because
 the used quantities of salt, considered on a m² basis, result in soil salt
 concentrations far below the natural values (Rozema et al. 1983). The
 direct effect of treatments was compared in terms of categories of stem
 regrowth (dead, limited regrowth, vigorous regrowth) (fieldcode
 <strong><em>regrowth</em></strong>), after six
 months following treatment (November 2013) and after one year (May 2014)
 (fieldcode
 <strong><em>date_regrowth</em></strong>). In
 total, 127 clones were treated. Unfortunately, nine could not be
 retrieved, probably because flags were removed by site visitors.
 Nonetheless, the resulting 118 clones measured were more or less equally
 distributed over sites and treatments.