Shona L. Lamoureaux

The potential global distribution of the invasive weed Nassella neesiana under current and future climates

Nassella neesiana (Trin. and Rupr.) (Chilean needle grass), native to South America, has naturalised sporadically in the UK, France, Italy and Spain, and more widely in Australia and New Zealand, where it has become a serious grassland weed. As a first step towards a global risk analysis we project a CLIMEX model of N. neesiana distribution globally under current climate and six future climate scenarios. Under current climate, areas not yet invaded, but climatically suitable, are eastern and south-western Africa, the north-west coast and south-eastern USA in North America, high-elevation areas in Central America, south-eastern China, northern Africa along the Mediterranean Sea, parts of Nepal, India and Pakistan, and Europe. Under the future climate scenarios, a mean global reduction of 32% in the area of suitable climate is projected, with marked reductions in the native range (34%) and also in Africa (67%), Asia (30%), North America (36%), and Australia (42%). These range contractions are primarily attributable to projected increases in temperatures leading to lethal heat stress excluding the plant from areas currently designated as sub-tropical and tropical humid. By contrast, projected expansions eastward in Europe and westward in New Zealand, result in increases in suitable area of 70 and 60%, respectively. Based on these results, which were consistent across the climate-change scenarios, the countries most at risk from N. neesiana are located in western and eastern Europe. A prudent biosecurity strategy would be to prevent the species spreading from the nascent foci already established there. Such a containment strategy would require controls to limit human-assisted dispersal of the species’ fruit and to ban the species from propagation and distribution throughout Europe.

Population dynamics in mature stands of Hieracium pilosella in New Zealand

The dynamics of a mature population of Hieracium pilosella under four different treatments (± irrigation, ± fertiliser, ± defoliation, and ± fungicide & insecticide, in a full factorial design) were compared in the Mackenzie Basin, New Zealand. H. pilosella had been growing at the site for at least 30 years. Recorded variables included rosette density, inflorescence and stolon production, recruitment and mortality, and plant cover. The population appears to be regulated through density-dependent mortality interacting with density-independent reproduction. In the treated plots, irrigation and fertiliser had the greatest effects, increasing both the proportion of established rosettes producing stolons and stolon length. Irrigation also increased the likelihood of a daughter rosette becoming reproductive and decreased inflorescence abortion. Fertiliser increased the probability of an established rosette reproducing and the number of daughter rosettes produced. In unmanipulated plots H. pilosella appeared to be at or near an equilibrium density of ca. 3200 rosettes m−2, but over longer time scales the low reproductive rates shown in this study may presage slow population decline due to plant-induced environmental degradation.

The Potential Global Distribution of Tall Buttercup (Ranunculus acris ssp. acris): Opposing Effects of Irrigation and Climate Change

Abstract Tall buttercup, a native of central and northern Europe, has become naturalized in the United States and Canada, and in South Africa, Tasmania and New Zealand. In Canada and New Zealand it has become an economically significant weed in cattle-grazed pastures. In this study we develop a CLIMEX model for tall buttercup and use it to project the weeds potential distribution under current and future climates and in the presence and absence of irrigation. There was close concordance between the models projection of suitable climate and recorded observations of the species. The projection was highly sensitive to irrigation; the area of potentially suitable land globally increasing by 30% (from 34 to 45 million km2) under current climate when a “top-up” irrigation regime (rainfall topped up 4 mm d−1 on irrigable land), was included in the model. Most of the area that becomes suitable under irrigation is located in central Asia and central North America. By contrast, climate change is projected to have the opposite effect; the potential global distribution diminishing by 18% (from 34 to 28 million km2). This range contraction was the net result of a northward expansion in the northern limit for the species in Canada and the Russian Federation, and a relatively larger increase in the land area becoming unsuitable mainly in central Asia and south eastern United States. Nomenclature: Tall buttercup, Ranunculus acris L. ssp. acris.

Modelling Tradescantia fluminensis to assess long term survival

We present a simple Poisson process model for the growth of Tradescantia fluminensis, an invasive plant species that inhibits the regeneration of native forest remnants in New Zealand. The model was parameterised with data derived from field experiments in New Zealand and then verified with independent data. The model gave good predictions which showed that its underlying assumptions are sound. However, this simple model had less predictive power for outputs based on variance suggesting that some assumptions were lacking. Therefore, we extended the model to include higher variability between plants thereby improving its predictions. This high variance model suggests that control measures that promote node death at the base of the plant or restrict the main stem growth rate will be more effective than those that reduce the number of branching events. The extended model forms a good basis for assessing the efficacy of various forms of control of this weed, including the recently-released leaf-feeding tradescantia leaf beetle (Neolema ogloblini).

Ranunculus acris control in dairy pasture – a comparison of herbicides, plant growth promoters, a bioherbicide and pregraze mowing

ABSTRACT The efficacy of control tactics for Ranunculus acris was quantified on poorly- and well-drained soils in a factorial experiment conducted over three years in 18 dairy pastures. Soil drainage, gibberellic acid and nitrogenous fertiliser (growth promoters), and a bioherbicide utilising Sclerotinia sclerotiorum had no effect on the cover of R. acris. The herbicides aminopyralid and aminopyralid+triclopyr, by contrast, gave long-lasting reductions in the cover of the weed and substantial temporary reductions in the clovers. Flumetsulam, thifensulfuron methyl, MCPA, MCPB and MCPB+bentazone were less effective overall. Pregraze mowing reduced R. acris as the frequency of mowing increased. For all herbicides, there was a 1:1 replacement of R. acris by grasses and clovers. The efficacy of the treatments varied greatly between pastures, possibly due to genetic differences between the R. acris populations and their historical exposure to the herbicides.

Molecular markers for Nassella trichotoma (Poaceae) to study genetic variation in New Zealand

Premise of The Study Simple sequence repeat (SSR) markers were developed for the study of genetic diversity of New Zealand Nassella trichotoma (Poaceae) and to support future studies in its native range. Methods and Results Genomic DNA was extracted from N. trichotoma leaf material and subjected to Roche 454 sequencing. From a total of 745 putative SSRs, 48 with di‐ to pentanucleotide repeats were screened, 32 primer pairs were designed, and 15 polymorphic markers were optimized for multiplex PCR on 105 N. trichotoma samples from four New Zealand regions. Each locus resulted in two to six alleles per locus, and four of the loci cross‐amplified in N. tenuissima. The mean observed and expected heterozygosity ranged from 0.00 to 0.90 and 0.00 to 0.50 per locus, respectively. Conclusions The novel SSR markers are valuable for the study of genetic diversity of N. trichotoma and might also be useful for closely related species.