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Conservation Evidence Journal

Publishing evidence to improve practice


The Conservation Evidence Journal shares the global experience of those on the front line of conservation practice about the effectiveness of conservation actions. All papers include monitoring of the effects of the intervention and are written by, or in partnership with, those who did the conservation work. We encourage articles from anywhere around the world on all aspects of species and habitat management such as habitat creation, habitat restoration, translocations, reintroductions, invasive species control, changing attitudes and education. 

The Conservation Evidence Journal publishes peer-reviewed papers throughout the year collected in an annual Volume. We publish Special Issues and collate Collections on specific topics, such as management of particular groups of species or habitats. To search for papers on a specific topic within the journal select Advanced search, enter your keyword(s) and within the Source box type: "conservation evidence". This will take you to a list of actions that contain Conservation Evidence Journal papers. In order to see the list of individual Conservation Evidence Journal papers on the topic, please click on 'You can also search Individual Studies' at the top of this page.

Creative Commons License Copyright is retained by the author(s). All papers published in the Conservation Evidence Journal are open access and licensed under a Creative Commons Attribution 4.0 International License

The Conservation Evidence Journal is a separate publication within the Conservation Evidence project. Conservation Evidence is a free, authoritative information resource designed to support decisions about how to maintain and restore global biodiversity. You can search for summarised evidence from the scientific literature about the effects of actions for species groups and habitats using our online database

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Volume 6

The release and establishment of Mauritius fodies Foudia rubra on Ile aux Aigrettes, Mauritius

Cristinacce A., Handschuh M., Switzer R.A., Cole R.E., Tatayah R.V.V. & Jones C.G. (2009), 6, 1-5


The Mauritius fody Foudia rubra is threatened by habitat loss and nest predation from introduced mammalian predators. The establishment of populations on predator-free smaller islands around 'mainland' Mauritius is one of the main conservation strategies for endangered Mauritian birds. Ninety-three Mauritius fodies were released on Ile aux Aigrettes in three breeding seasons between November 2003 and March 2006. The first fledglings were produced on the island during the 2004-05 breeding season, and by the following season sufficient numbers of juveniles were being produced on the island to render further releases unnecessary. The population has since increased to 47 breeding pairs and 142 individuals as of December 2008.


Provision of brood-rearing cover on agricultural land to increase survival of wild ring-necked pheasant Phasianus colchicus broods at Seefeld Estate, Lower Austria, Austria

Draycott R.A.H., Bliss T.H., Carroll J.P. & Pock K. (2009), 6, 6-10


Wild ringed-necked pheasants Phasianus colchicus have declined throughout their naturalized European range as a result of habitat loss and a reduction in food resources on farmland. To ameliorate the reduction in chick food availability on arable farmland, 'brood-rearing' seed mixtures (to provide insect-rich foraging areas) were sown on rotational set-aside on a large commercial farming estate in Lower Austria during 2001-2003. The use of these areas by wild pheasant broods and their effect on brood survival was determined by radio-telemetry. Areas of planted brood-rearing cover were positively selected by pheasant broods and survival rates were highest amongst broods which incorporated these brood rearing areas into their home ranges.


Linking 'citizen scientists' to professionals in ecological research, examples from Namibia and South Africa

Araya Y.N., Schmiedel U. & von Witt C. (2009), 6, 11-17


The use of trained members of the public ('citizen scientists') to help monitor and collect data in science-driven environmental research projects is not a new concept e.g. the Cornell bird program, USA, has been 'partnering' with the public since the 1960s (University of Cornell 2008). However, this concept has yet to find much following in developing countries where often the greatest need for conservation lies. We examine the effectiveness of citizen scientists ('plant custodians', 'paraecologists' and 'eco-club volunteers') in monitoring (e.g. species rediscovery, red list classification, range extension) and how it integrates with ecological research (e.g. ethnobotany, livestock census), citing examples from three biodiversity hotspots in Southern Africa (Namibia and South Africa). Information collected by custodians has helped to prioritise plant species that are in need of conservation attention. Paraecologists have played a key role in supporting the fieldwork of researchers. Various eco-club activities have been undertaken with schools, and a network of eco-club volunteers has been developed.


Comparing the benefits to wintering birds of oil-seed rape establishment by broadcast and non-inversion tillage at Grange Farm, Cambridgeshire, England

Dillon I.A., Morris A.J. A.J. & Bailey C.M. (2009), 6, 18-25


There is extensive and compelling evidence that suggests changes in farmland bird abundance have been driven by changes in agricultural practice. Among these, the wide-scale change from spring to autumn cropping has consequences for the amount of food available to farmland birds over winter and associated survival rates. Oil-seed rape (OSR) Brassica napus is one crop that is primarily established in the autumn. While the leaves provide a valuable source of food for a few species, e.g. woodpigeon Columba palumbus, and may provide cover and micro-climates for invertebrate food for others, e.g. thrushes, there has been concern that autumn sowing of crops such as OSR removes the need to leave land fallow during the winter months. Fallow land in the form of over-winter crop stubble is a key foraging habitat for many birds, particularly granivorous species. It has been hypothesised that the recent wide-scale adoption of the broadcast method of establishment for OSR crops may have benefits for some species reliant on over-winter stubbles, as the crop is established into existing cereal stubble. However, our study indicates that bird densities are similar on broadcast OSR fields compared to non-inversion tillage OSR, and that densities in the broadcast OSR were lower than in many studies of bird use of over-winter cereal stubbles. This may perhaps be due to the rapid growth of OSR in the autumn, shading out the stubble and thus making it an unsuitable feeding habitat for many birds for much of the winter. As the available evidence suggests that cereal stubbles broadcast with OSR are unlikely to provide the benefits to farmland birds of traditional over-wintered stubbles, the decision on method of establishment for oilseed rape crops should be based on agronomic considerations.


Recolonization of Raoul Island by Kermadec red-crowned parakeets Cyanoramphus novaezelandiae cyanurus after eradication of invasive predators, Kermadec Islands archipelago, New Zealand

Ortiz-Catedral L., Ismar S.M.H. & Baird K. (2009), 6, 26-30


The Kermadec red-crowned parakeet Cyanoramphus novaezelandiae was driven to extinction on Raoul Island over 150 years ago by introduced cats Felis catus and rats (Rattus norvegicus and R.exulans). These predators were eradicated from the island (2,938 ha) between 2002-04 during the world's largest multi-species eradication project. In 2008 we documented a unique recolonisation event when parakeets were observed to have returned to Raoul, presumably from a nearby island group, The Herald Islets (51 ha). We captured and aged 100 parakeets, of which 44% were born in 2008, and breeding was observed on Raoul Island. This represents the first evidence of nesting of this species on Raoul Island since 1836. Our findings highlight the global conservation potential for island avifaunas by prioritising eradication areas through consideration of proximity of remnant populations to target management locations, instead of the classical translocation approach alone. The natural recolonization of parakeets on Raoul Island from a satellite source population is to our knowledge, a first for parrot conservation and the first documented population expansion and island recolonization of a parrot species after removal of invasive predators.


Efficacy of sod removal in regenerating fen vegetation for the conservation of the marsh fritillary butterfly Euphydryas aurinia, Montiaghs Moss Nature Reserve, County Antrim, Northern Ireland

Reid N. & McEvoy P.M. (2009), 6, 31-38


The efficacy of 'sod removal' as a fenland restoration technique was tested using an experimental approach at Montiaghs Moss Nature Reserve, Northern Ireland, from 2006 to 2008. The site suffered from rank growth of purple moor-grass Molinia caerulea which was out-competing herbaceous species. Soil was removed up to a depth of 15 cm completely denuding vegetation in the experimental plot exposing bare peat. By July 2007, 15.2% of sod-removal areas were revegetated; by October 2008 cover had risen to 64.6%. Of this cover, purple moor-grass accounted for only 9-11% compared to 78-79% on control plots. Cover of other rank-forming grass species was also significantly reduced. Sod removal significantly increased the cover of species characteristic of fenlands including sedges Carex spp., rushes Juncus spp., marsh pennywort Hydrocotyle vulgaris and lesser spearwort Ranunculus flammula. It seems likely that sod removal, which lowered the surface of the peat, restored minerotrophic conditions and exposed the historical seed bank stimulating regeneration of some fenland specialists and pioneer species; this resulted in significantly higher species richness on sod removal plots than control plots two years after treatment. There was no demonstrable effect of sod removal on abundance of devil's-bit scabious Succisa pratensis, the larval food plant of the Annex II listed marsh fritillary butterfly Euphydryas aurinia. We recommend that consideration should be given to artificially seeding devil's-bit scabious soon after sod removal treatment to promote early recolonisation and to increase plant abundance on the site.



Scrub clearance and soil disturbance increases bee orchid Ophrys apifera frequency in calcareous grassland at Norton Heath roadside verge, Essex, England

Gardiner T. & Vaughan A. (2009), 6, 39-41


Scrub clearance was undertaken on calcareous grassland along a roadside verge at Norton Heath in Essex. The site was fenced to prevent grazing by rabbits Oryctolagus cuniculus. After scrub clearance, the number of bee orchid Ophrys apifera basal leaf rosettes was counted in a 3 x 3 m area where the soil was disturbed by turning over manually with a fork, and in an adjacent control which had no soil disturbance.  A total of 29 basal rosettes of O.apifera were noted in the disturbed area in the first spring after clearance, contrasting with only seven rosettes in the undisturbed control plot.  These results suggest that it may therefore be beneficial to create scrapes to encourage the establishment of O.apifera and also a range of other calcareous grassland plants.



Establishing a new population of Scalesia affinis, a threatened endemic shrub, on Santa Cruz Island, Galapagos, Ecuador

Atkinson R., Jaramillo P. & Tapia W. (2009), 6, 42-47


Scalesia affinis is a threatened shrub endemic to the Galapagos archipelago. Its population on the island of Santa Cruz is critically endangered, with only 71 adult plants known. The future of these individuals is unclear due to imminent development of land surrounding the largest population. This paper reports on a project to establish a new population of S.affinis on Santa Cruz within its historical native range from plants grown ex situ. As the plant is known to be self-incompatible, cross pollination was carried out in the wild to try and augment viable seed production. Average seed viability from 22 artificial crosses was 0.58 (SE ± 0.043), a level similar to naturally produced seeds. Survivorship from germination was low, with only 17% of plants surviving to three months post germination. Survival following transplanting out in the wild was also low, with just 19% of plants (11 out of 57) alive after one year. The relative roles of genetic and environmental factors are discussed in relation to these results.


Prescribed burning and the role of seed banks in post-fire succession of northern heathlands, Lygra and Lurekalven islands, Hordaland, Norway

Måren I.E. & Vandvik V. (2009), 6, 48-56


Variation in plant species composition, abundance of seeds in the soil seed bank and standing vegetation, over the course of a post-fire succession was investigated in coastal Calluna-heathlands in Western Norway. Vegetation and seed banks were analysed over a 24-year post-fire period. The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa respectively (39 shared species), resulting in 68% similarity. Over the 24 years the heathland community progressed from open newly-burnt ground via species rich graminoid- and herb-dominated vegetation to mature heather Calluna vulgaris-dominated heath. This post-fire succession was not reflected in the seed bank; the 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna (49%; 12,018 seeds/m2) and cross-leaved heath Erica tetralix (34%; 8,414 seeds/m2). Calluna showed significantly higher germination in the two first years following burning. Vegetation species richness (ranging 23 to 46 species/yr) was highest in the middle years of the post-fire succession period. In contrast, the seed bank species richness (21 to 31 species/yr) showed no trend. This suggests that the seed bank act as a refuge, providing a source of recruits for many species that colonize newly-burnt areas. The traditional management regime has not depleted or destroyed the seed banks, and continuing management is necessary to ensure perpetuation of the heathlands.


The effectiveness of a sickle-leaved hare's-ear Bupleurum falcatum subsp. falcatum propagation and introduction programme at Norton Heath roadside verge, Essex, England

Roscoe A., Gardiner T. & Ringwood Z. (2009), 6, 57-61


Sickle-leaved hare's-ear Bupleurum falcatum subsp. falcatum is an umbellifer that has a very limited distribution (currently one native locality) in the UK. Seeds (1,200) were collected from the single wild population in Essex (southeast England) and propagated using conventional techniques over the winter of 2007/08. A high proportion germinated (859; 71%) but 93% of the seedlings subsequently died in the spring and summer of 2008. The 57 young plants that survived were planted out at the donor site in January 2009, established well (all but one alive in July 2009) and competed strongly with other species already present. All grew well, all flowered and some produced seed. Growth was similar to that of plants in the nearby established colony.


Hay mowing and scrub clearance enhance floristic species richness on a green lane in Norwood End, Essex, England

Gardiner T. & Vaughan A. (2009), 6, 62-65


An experimental hay mowing and scrub clearance regime was introduced to Perryfield Lane - a 'green lane' site (i.e. a double hedged unsurfaced track) in Norwood End, Essex (England), with the aim of increasing floristic species richness. After two years of management, the floristic species richness doubled on the grassy verges of the lane, a smaller increase in the number of plant species was noted for the central track, which is used by (occasional) motorised vehicles due to the legal status of the lane as a public byway. Plants that benefited from hay mowing and scrub clearance included unimproved grassland indicator species such as black knapweed Centaurea nigra, hairy St. John's-wort Hypericum hirsutum and primrose Primula vulgaris. There were substantial reductions in bramble Rubus fruticosus agg. and blackthorn Prunus spinosa achieved, thereby preventing their encroachment and smothering of the remnant grassland flora.


Establishment of a feeding station near the Laterza LIPU Reserve to provide additional food for three declining necrophagous raptor species in Apulia, Italy

Gustin M., Giacoia V. & Bellini F. (2009), 6, 66-70


From February 2004 to September 2007, a raptor feeding station was operational near the Laterza LIPU Reserve (Taranto Province, southern Italy). The feeding station measured 40 x 40 m and was enclosed by a 1.8 m high wire mesh fence to prevent large mammal access. An average of 50 sheep carcasses were supplied at the feeding station each year. Over 2,200 hours of observation at the feeding station were made, averaging about 550 hours per year. During observation periods, black kite Milvus migrans numbers recorded at the feeding station ranged from a minimum of five (in 2004) to a maximum of 53 (2006) annually; red kite Milvus milvus numbers ranged between one (2004) to 23 (in both 2006 and 2007). Only one Egyptian vulture Neophron percnopterus (in 2007) was observed at the feeding station. Provision of supplemental food at the feeding station may represent one factor explaining the establishment of a few breeding pairs of red kites and black kites, and increasing numbers of raptors recorded in the study area.


Comparison of the lethality of lead and copper bullets in deer control operations to reduce incidental lead poisoning; field trials in England and Scotland

Knott J., Gilbert J., Green R.E. & Hoccom D.G. (2009), 6, 71-78


Legislative controls on the use of lead gunshot over wetland areas have been introduced in many countries, including the UK, in order to reduce lead poisoning in waterfowl following ingestion of spent shot. Effective alternatives to lead shot are widely available. However, there is evidence that the problem also affects wildlife in terrestrial ecosystems and that lead bullets are a source of contamination for scavenging birds and mammals. With this in mind, copper bullets were trialled at three varied UK sites during deer control operations undertaken to achieve nature conservation objectives. Their accuracy and killing power were recorded and compared to that of traditional lead bullets. No significant differences were found in accuracy or killing power. These results, coupled with experience elsewhere, suggest that copper bullets are a viable alternative to lead bullets. If this is confirmed in all situations, we consider further restrictions on the use of lead ammunition, designed to encourage a switch to non-toxic ammunition across terrestrial habitats, to be a proportionate response to the problems associated with lead ingestion.


Scrub clearance enhances floristic species richness on a green lane with restricted motorised vehicular access in Stanford Rivers, Essex, England

Gardiner T. & Vaughan A. A. (2009), 6, 79-82


An experimental early-spring scrub clearance regime was introduced in 2008 to Coleman's Lane, a 'green lane' site (i.e. a double hedged, unsurfaced track) in Essex, southeast England, with the aim of increasing floristic species richness. A year after scrub clearance, floristic species richness was higher on both grassy verges either side (average 5.6 species/quadrat) and central track (4.3 species) of the green lane, compared with that recorded a year prior to clearance (4.2 and 2.8 species respectively). Plant species that especially benefited from scrub clearance included cow parsley Anthriscus sylvestris and red dead nettle Lamium purpureum.  New species recorded in 2009 included bush vetch Vicia sepium, sweet violet Viola odorata and wood anemone Anemone nemorosa. There were substantial reductions in bramble Rubus fruticosus and cleavers Galium aparine achieved. Further clearance is planned for winter 2009-10, and subsequently on a 2-3 year rotation.


Does the removal of avian brood parasite eggs increase host productivity? A case study with brown-headed cowbirds Molothrus ater and song sparrows Melospiza melodia near Ithaca, New York, USA

Hauber M.E. (2009), 6, 83-88


Avian brood parasitism lowers host fitness through several mechanisms, including the reduction of productivity of parasitized breeding attempts. Even when both host and parasite are native species, anthropogenic factors (e.g. habitat alteration) may increase local parasitism burden on rare hosts so as to require conservation action. To reduce brood parasitism rates by brown-headed cowbirds Molothrus ater (an increasingly abundant species within its North American range), most conservation action currently involves the removal of adult cowbirds in the hosts' breeding habitat. An alternative, but more labour intensive, management action is to remove cowbird eggs from host nests, but the benefits of such egg removal may be outweighed by the predatory behavior of cowbird females on host eggs if nests lack cowbird eggs. In this present study, parasitism of song sparrows Melospiza melodia near Ithaca, New York (USA) was used as a case study to evaluate the effect of removing cowbird eggs on productivity (i.e. young fledged per nest) of the host species. Although parasitized nests had naturally fewer host eggs than non-parasitized nests, there were no consistent differences in the numbers of host nestlings produced in non-parasitized, non-removal parasitized, and parasite-egg removal broods. Counter to the goal of removing parasite eggs, the proportion of host eggs producing nestlings was lower in egg-removal nests than in non-removal parasitized nests. It is therefore concluded that at this locality, conservation management to remove the eggs of brood parasitic brown-headed cowbirds is unlikely to increase song sparrow productivity.


Assessing the vegetation response to differing establishment methods of skylark plots in winter wheat at Grange Farm, Cambridgeshire, England

Dillon I.A., Morris A.J., Bailey C.M. & Uney G. (2009), 6, 89-97


Skylarks Alauda arvensis have declined by 53% across Britain since 1970, primarily in regions dominated by lowland farmland. To improve breeding opportunities in arable farmland, 'Skylark Plots' i.e. small (16-24 m2) unsown areas within winter cereal crops, were developed by the RSPB and tested in the Sustainable Arable Farming For an Improved Environment (SAFFIE) project. These plots increased the number of late summer breeding attempts and the number of chicks fledged per nest, compared to conventional crops. Skylark Plots are now included as a prescription in the Entry Level Stewardship (ELS) agri-environment scheme in England. The plots are usually created by turning off the seed drill during sowing. However, take up of this prescription has been very low; pernicious weed control and technical difficulties with sowing machinery have been cited as reasons for this. To broaden the appeal to farmers, the option to create the plots through herbicide spraying to remove the germinating crop, was introduced in 2008. Data on the optimum period for spraying and differences in vegetation architecture between undrilled and sprayed skylark plots was lacking however. As evidence from the SAFFIE project showed that plots with greater vegetation cover had higher invertebrate abundance and that skylarks use plots primarily when foraging for invertebrate chick food, the present study was conducted to compare the vegetation cover in undrilled plots with plots sprayed either in December, January or February (during crop germination).

The study showed that undrilled plots consistently had greater vegetation cover than sprayed plots, with the cover increasing in all plots from May to July (whilst remaining suitable for skylark use), the peak period of the skylark breeding season. Vegetation cover within sprayed plots was generally very low, particularly in February-sprayed plots. These differences in vegetation cover are likely to subsequently impact the abundance and accessibility of invertebrate prey available to skylarks during the breeding season with February-sprayed plots in particular being unsuitable for skylark foraging even in July. Our recommendation is that where possible, plots should be created at the time of sowing (turning off the seed drill) in autumn; if spraying is the favoured method of creation then this should take place no later than the end of December.


Effects of sandplain revegetation on avian abundance and diversity at Skogasandur and Myrdalssandur, South-Iceland

Gunnarsson T.G. & Indridadottir G.H. (2009), 6, 98-104


In a European context, Iceland has some of the highest levels of desertification (due primarily to historic overgazing, frequent volcanic eruptions and subsequent erosion) and also vast naturally occurring barren areas (mainly formed and maintained by  flooding of glacial rivers). Since 1988 efforts have been made, by the Icelandic Soil Conservation Service, to reduce sandstorms by revegetation on some sandplains in the region of South-Iceland. Action includes sowing strips of Nootka lupin Lupinis nootkathensis, and lyme grass Leymus arenarius and other grasses, with repeated fertilization. Very few bird species occur on Icelandic barren sands and if present, occur only at low densities. The effects of revegetation on avian abundance and diversity were evaluated by comparison to adjacent barren areas. Revegetation has a clear and a positive effect on some species which benefit from vegetated land. Meadow pipit Anthus pratensis and common snipe Gallinago gallinago occurred in high densities, particularly in mature strips of lupins, and other species of birds were colonising. These bird species are absent from barren sandplains.


The invertebrate population of a created reedbed after seven years: Lakenheath Fen RSPB reserve, Suffolk, England

Booth V. & Ausden M. (2009), 6, 105-110


Created reedbed at Lakenheath Fen (southeast England) supports an abundant and diverse invertebrate population, including rare Diptera and reedbed specialists, just seven years after it was transformed from agricultural land.


Effectiveness of head-starting to bolster Philippine crocodile Crocodylus mindorensis populations in San Mariano municipality, Luzon, Philippines

van de Ven W.A.C. , Guerrero J.P., Rodriguez D.G., Telan S.P., Balbas M.G., Tarun B.A., van Weerd M., van der Ploeg J., Wijtten Z., Lindeyer F.E. & de Iongh H.H. (2009), 6, 111-116


The freshwater Philippine crocodile Crocodylus mindorensis (endemic to the Philippine archipelago) is the most threatened crocodilian in the world with an estimated wild population of less than 100 mature individuals. Due to low survival of wild hatchlings, a head-starting program was initiated in 2005. Hatchlings are collected from the wild just after hatching and released back into their natural habitat after being raised in captivity for 14-18 months. Several ponds were created to provide suitable release habitat. Between 2005 and 2008, 88 hatchlings were collected. Hatchling survival after one year in captivity was 63 out of 88 (72%), compared to 47% for 36 hatchlings monitored in the wild (as low as 13% in some areas). Thirty two head-started crocodiles were released back into the wild (31 still held in captivity in 2009). Of the 32 released crocodiles, minimum survival after one year in the wild was 50%. Post release observations and recaptures showed that the released juvenile crocodiles adapted well to natural conditions and were increasing in size. The ultimate goal of the program will only be achieved if the head-started crocodiles survive to maturity and reproduce.



Evaluation of a large-scale invasive plant species herbicide control program in the Berkshire Taconic Plateau, Massachusetts, USA

McAlpine L. & Porder S. (2009), 6, 117-123


In the late 1990s, The Nature Conservancy (TNC) documented a rise in five invasive plant species, barberry Berberis thunbergii, bittersweet Celastrus orbiculatus, garlic mustard Alliaria petiolata, buckthorn Frangula alnus, and honeysuckle Lonicera morrowii on the periphery of the relatively intact and uninvaded 14,600 ha Berkshire Taconic Plateau in Massachusetts (USA). The Plateau comprises an ecologically significant block of forest. In response, TNC began a large-scale herbicide-based control program on approximately 3,600 ha of land with the goal of reducing invasive cover to less than 10%. Our objective was to evaluate the efficacy of this effort, but this was hampered by a dearth of untreated control sites and pretreatment data on invasive species cover. Four sites (three treated, one untreated) on the plateau periphery similar in understory vegetation, overstory cover, slope, and proximity to a hiking trail were surveyed and compared. Across each site, native and invasive plant percent cover within 44, 1m² plots was measured, and native and invasive presence absence recorded on an additional 2,000m² area. All five target invasives were present at all four sites 5-years post-treatment. In two of the treated sites, invasive percent cover significantly exceeded the 10% goal, largely due to the abundance of garlic mustard. Without garlic mustard, all the sites (including the untreated one) had < 10% invasive cover. Surprisingly, the high level of invasive cover did not have a significant negative impact on native cover (native species richness was not quantified), although a hypothesized negative relationship was invoked as justification for the herbicide treatment.

Given the difficulty in finding comparable treated and untreated sites after herbicide application, we suggest 1) that quantitative data on invasive abundance be gathered prior to a control program and 2) that treated and untreated plots be allocated to monitor outcomes. Without this, determination of effectiveness is difficult and likely to be inconclusive.


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