Browsing by Author "Robertson AW"

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    Efficacy of herbicides for selective control of an invasive liana, old man's beard (Clematis vitalba)
    (Published by Cambridge University Press on behalf of the Weed Science Society of America, 2023-06-02) Jarvis-Lowry B; Harrington KC; Ghanizadeh H; Robertson AW
    Old man's beard is a woody liana that has become an invasive weed in many areas of its introduction, through its vigorous spread and negative impacts on the tree hosts it climbs. Control techniques that improve precision and reduce non-target damage are increasingly preferred for weed control yet have not been compared in published research for use against old man's beard. Field experiments in New Zealand were conducted to: (i) assess targeted herbicide techniques for control of this weed's climbing stems when growing among trees and (ii) assess foliar herbicides for control of creeping stems in ruderal sites. For climbing stems, triclopyr in oil was applied around the circumference of woody stems near their base, which was compared with cutting the stems and applying concentrated glyphosate gel (45% ai) to each cut end. Herbicides were applied in autumn directly to individual stem bases of the weed, thereby protecting tree hosts and other non-target vegetation. The basal application of triclopyr to intact stems was highly effective (>95% mortality) with no damage to nearby trees noted. The glyphosate gel applications to cut stems were less effective (56% mortality by 2 yr after treatment). For creeping stems in grass-dominated ruderal sites, selective foliar herbicide sprays had not been previously juxtaposed to compare control of old man's beard. Three selective sprays that do not damage existing grass cover were applied in autumn at their recommended rates: (i) metsulfuron; (ii) triclopyr; and (iii) a mixture of triclopyr, picloram, and aminopyralid. All herbicide treatments provided effective control, although metsulfuron had a negative effect on grass vigor, which might allow new establishment of old man's beard seedlings by competitive release. These results provide effective options that reduce non-target damage for control of both climbing and creeping old man's beard stems.
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    Plant invasion down under: exploring the below-ground impact of invasive plant species on soil properties and invertebrate communities in the Central Plateau of New Zealand
    (Springer Nature Switzerland AG, 2024-09-15) Pearson BM; Minor MA; Robertson AW; Clavijo McCormick AL
    The impacts of invasive plants on arthropod communities are often reported to be negative and have predominantly been explored aboveground, but there is a paucity of information regarding what happens belowground. To address this gap, we compared soil properties and soil fauna communities associated with two native plant species (Leptospermum scoparium—mānuka and Chionochloa rubra—red tussock) and two invasive species (non-N-fixing Calluna vulgaris—European heather and N-fixing Cytisus scoparius—Scotch broom) in the Central Plateau of New Zealand. We expected that (1) at individual plant level soil properties would be different under invasive and native plant species, with higher soil nutrient concentrations under invasive species, especially N-fixing broom; (2) total abundance of soil fauna would be higher under invasive plant species, as generally positive impact of invasive plants on soil invertebrates is indicated in the literature; (3) invasive plants, and especially N-fixing broom, will be associated with greater abundances of soil decomposer groups. We found that soil properties and soil fauna assemblages did not cluster by plant invasive status as initially predicted. At individual plant level, there was similarity in soil conditions between mānuka and broom, and between red tussock and heather. The invasive N-fixer (broom) had positive effects on soil N availability, with higher N pool and lower C/N ratio in soil under this species. There were no consistent differences in total soil fauna abundance between invasive and native plants. Broom and mānuka were associated with higher abundances of Collembola, Oligochaeta and Diplopoda; heather and red tussock had higher abundances of Hymenoptera and Hemiptera. Significantly more Oligochaeta and Collembola under broom matched the prediction of invasive plants (and especially N-fixing invasives) being associated with greater abundances of decomposers. However, another important decomposer group—oribatid mites—did not show the same tendency. These results evidence that simplified generalizations regarding the impacts of invasive plants are unlikely to be justified, since the ecological effects of plant invasions are complex and do not always follow the same pattern. Therefore, we need to take into consideration the ecological context and the traits of individual plant species and target organisms in an unbiased manner to fully understand the impacts of plant invasions.
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    Potential importance of vegetative spread and fragment regeneration for invasiveness of Clematis vitalba
    (John Wiley and Sons Ltd on behalf of European Weed Research Society, 2024-05-12) Jarvis-Lowry B; Harrington KC; Ghanizadeh H; Robertson AW; Novak S
    Identifying characteristics of invasive species or growth forms that facilitate their range expansion is critical for management. Clematis vitalba L. (old man's beard) is an invasive temperate liana in many areas of its introduction, yet its seedlings do not thrive in circumstances where resources are limited. Although some lianas in both tropical and temperate climates have been shown to spread by clonal stems along the ground, the bulk of previous research on C. vitalba reproduction has focused largely on aspects of seed ecology. The vegetative growth of the species is poorly understood. The first objective of our study was to evaluate the use of vegetative spread by C. vitalba as a means of local dispersal and population growth. We excavated ten 1-m2 plots in infested riparian zones and found an extensive, branching network of creeping stems, both above and below ground. Our second objective was to test the ability of C. vitalba stem fragments to act as vegetative propagules. After 4 months, ~50% of two-node fragments had regenerated, from both creeping and climbing stems. These studies help explain how a temperate liana forms populations and dominate ecological communities. The findings provide good evidence that C. vitalba may rely quite heavily on asexual reproduction. In addition, the results document liana stem phenotypic plasticity; fragmented climbing stems are just as likely as fragmented creeping stems to reprogram shoot tissue systems, generate roots and regrow as independent plants.
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    Viability and dormancy of the Clematis vitalba aerial seed bank.
    (John Wiley & Sons, Inc on behalf of German Society for Plant Sciences, Royal Botanical Society of the Netherlands., 2024-04-01) Jarvis-Lowry B; Harrington KC; Ghanizadeh H; Robertson AW; Bentsink L
    Old man's beard (Clematis vitalba L.) is a liana species that has become invasive in many areas of its introduced range. Seeds are produced in abundance and are both physiologically and morphologically dormant upon maturity. To understand the importance of seeds to its invasiveness, changes in viability and dormancy of the aerial seed bank were tracked throughout the after-ripening period and during storage. Seeds collected every second month for 2 years were subjected to germination tests. Other seeds stored in outdoor ambient conditions or in a dry, chilled state were dissected before, during, and after imbibition, as well as during incubation, to measure embryo size. Less than 72% of seeds on the mother plant were viable. Viable seeds remained completely morpho-physiologically dormant throughout autumn, even when treated with nitrate. Physiological dormancy declined in response to seasonal changes, yet morphological dormancy did not change until seeds had been exposed to appropriate germination conditions for several days. Fully dormant autumn seeds decayed at higher rates during incubation than partially or fully after-ripened seeds, which were also more germinable and less dormant. Furthermore, seeds incubated in complete darkness were more likely to decay or remain dormant than those exposed to light. This study demonstrates that fewer than three-quarters of seeds produced are viable and further decay occurs after dispersal, yet total fertility is still very high, with enormous propagule pressure from seeds alone. Viable seeds are protected with two forms of dormancy; morphological dormancy requires additional germination cues in order to break after seasonal changes break physiological dormancy.