Browsing by Author "Robertson AW"
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- ItemEffects of vegetative ground cover on seedling establishment of the invasive liana old man's beard (Clematis vitalba)(Cambridge University Press, 2024-11-18) Jarvis-Lowry B; Harrington KC; Ghanizadeh H; Robertson AW; Sarangi DOpportunistic use of limited resources is often attributed to invasive species, and as a mature vine, old man’s beard (Clematis vitalba L.) is known to have devastating negative impacts on the trees it colonizes. No previous experimental studies have been published on how easily C. vitalba seedlings can colonize ground covered by other established vegetation. This species has had an increasing presence in forestry blocks and riparian zones in New Zealand, both of which usually maintain some grass cover. To determine the importance of vegetative ground cover for preventing ingress of new C. vitalba plants, this study looked at seedling emergence through the soil and establishment of C. vitalba within four different levels of grassy cover at three sites: (1) ground kept bare after vegetation removal; (2) ground bare at C. vitalba seed sowing, but thereafter allowed to recover; (3) vegetative cover trimmed to 4 cm high at C. vitalba sowing, and then allowed to recover; and (4) unmanaged vegetation. At the highest level of vegetation density (unmanaged vegetation), no C. vitalba seedlings were ever detected throughout a 1-yr monitoring period. At lower ground cover densities, poor seedling emergence was observed, with a maximum of 36% of seeds sown in bare plots producing a seedling. Also, seedlings did not survive past 1 yr, except in bare plots or in plots where vegetation grew sparsely. However, seedlings that did survive began producing multiple stems within 6 mo of emergence. These results indicate that obstacles to seedling emergence and poor development at the young seedling stage when vegetative cover is dense severely limit C. vitalba’s chances to invade new sites via seed. Yet some successful seedling recruitment does occur due to the magnitude of the propagule pressure on the landscape and the difficulty of maintaining high-density ground cover across large areas throughout the year.
- ItemEfficacy 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 AWOld 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.
- ItemMicro Gondwana: soil and litter mesofauna in the subalpine and alpine of North-West Nelson, southern New Zealand(Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2025-05-21) Minor MA; Robertson AW; Ashwood FAlpine ecosystems are vulnerable to the warming climate, yet alpine soil mesofauna remains the less studied part of NZ biodiversity. Here we present a survey of soil mesofauna communities of three mountain peaks in the Nelson-Tasman and Marlborough regions of the South Island of New Zealand. We assessed changes in abundance, diversity and trophic composition along the elevational gradient from subalpine forests to alpine herb fields (800–1600 m a.s.l.) and analysed the influence of selected environmental factors on mesofauna. Taxon richness was expected to decrease and the proportion of predators to increase in alpine habitats, as has been observed elsewhere. Sub-alpine beech forests harboured a high diversity of soil mesofauna, many of which are Gondwanan relics. There was a decline in abundance and taxonomic richness of mesofauna with increasing elevation. However, no proportional increase in predators with increasing elevation was seen–alpine mesofauna assemblages had lower predator-to-herbivore ratios than upland forests. Several interesting taxa–harpacticoid copepods, moss bugs (Hemiptera: Peloridiidae), unique-headed bugs (Hemiptera: Enicocephalomorpha), micro-spiders, mite harvestmen, Neelidae springtails and acarifauna are discussed in more detail. Baseline data such as these advance the knowledge of native fauna and provide a baseline for ecological monitoring in the alpine zone.
- ItemPlant 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 ALThe 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.
- ItemPotential 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 SIdentifying 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.
- ItemViability 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 LOld 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.
