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Aliens - Invasive Aliens? Himalayan Balsam (alas, now Indian Balsam) 31Invasive Aliens? Himalayan Balsam (alas, now Indian Balsam)DAVID PEARMAN, Algiers, Feock, Truro, Cornwall, TR3 6RA; Tel: 01872 863388;dpearman4@aol.comMembers might recall my by now probablyboring and predictable views on the fuss createdby the conservation guardians on non-existentthreats, including one recent mailing by a wellknownplant conservation charity with a luridrepresentation of this species and JapaneseKnotweed coming to bite innocent bystanders!I have written before that whilst HimalayanBalsam was often cited as a threat, I had notseen any evidence, other than its visibledominance.Two papers have been published this year, onewhilst saying it might reduce native richness,many of the species affected are widespreadruderals, and if it was removed, its place wasoften filled by other aliens or nitrophiles! Theother effectively said there is no evidence at allto support the thug status.The first is Hulme, E H & Bremner, E T 2006.Assessing the impact of Impatiens glanduliferaon riparian habitats: partitioning diversitycomponents following species removal. Journalof Applied Ecology 43: 43-50.Their summary:1. Attempts to quantify the impact of nonnativeplants on the vegetation of invadedhabitats have often been criticized because ofthe frequent use of observational assessments(invaded/uninvaded comparisons) focused onlocal- rather than community-level effects. Thisstudy highlights how removal experimentscombined with partitioning of diversity componentsacross spatial scales can provide keyinsights into invasive species' impacts.2. Impatiens glandulifera (Balsaminaceae) isa widespread invasive riparian weed, yet fewquantitative assessments of its impact on naturalvegetation exist. Thus replicated experimentswere used to compare the impact of Impatiensremoval on (1, ~, 'Y components of speciesrichness, diversity and evenness in open riparianhabitats in north-east England.3. Plant community response to Impatiensremoval was rapid, with a significant increase inseedling recruitment resulting in an averageincrease of four species m- 2 • The impact ofImpatiens invasion was most marked for lightdemandingspecies. Eight non-native species (inaddition to Impatiens) occurred in the communityand these responded proportionally more toImpatiens removal than native species. As aresult the proportion of non-native species inremoval plots was higher than in invaded plots.4. The increase in (1 richness and diversityfollowing Impatiens removal was matched by asimilar increase in the 'Y components. Thus theeffect of Impatiens was significant at both thelocal plot scale and at the scale of the ripariancommunity, although the former effect wasmore marked. Species accumulation curvessuggested that extensive Impatiens stands mayreduce species richness by as much as 25%.5. Synthesis and applications. Removal experimentsappear particularly well suited to assessthe impacts of herbaceous non-native plants onruderal communities. By partitioning diversitycomponents, impacts were consistently assessedat local and community scales and, whencombined with analysis of species accumulationcurves, provided a comprehensive assessmentof impact on the plant community. Theapproach adopted in this study highlights thatalthough Impatiens reduces native speciesdiversity in open and frequently disturbed riparianvegetation, many of the species negativelyinfluenced by Impatiens are widespread ruderalspecies. Furthermore, management may lead toa compensatory increase in the abundance ofother non-native species and thus fail to achievedesired conservation goals.The second appears in October. HEIDA, M &PYSEK, P. 2006. What is the impact of Impatiensglandulifera on species diversity of invadedriparian vegetation? Biological Conservation132(2): 143-152.Their abstract:The effect of invasion by Impatiens glandulifera(Balsaminaceae) on the community characteristicsand species composition of invadedriparian communities was studied at six rivers inthe Czech Republic. Two approaches wereused: space for time substitution approach, i.e.,comparing invaded and uninvaded sites underthe same habitat conditions, and removal of theinvader from experimental plots. Differences inthe number of species, Shannon diversity indexH' and evennes J were compared betweeninvaded and uninvaded plots. Uninvaded plotsof the comparative study harboured by 0.23more species per 16 m 2 , and had higher value ofH' and J, calculated with species covers asimportance values; however only the difference