Aspects of the biology and control of old man's beard (Clematis vitalba) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand

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Massey University
Corrected thesis was uploaded in Dec 2023.
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Old man’s beard (Clematis vitalba) is an increasingly problematic liana in New Zealand, but the factors that contribute to its invasiveness are not fully understood. The work in this thesis investigated elements of old man’s beard seed biology and ecology, seedling establishment, and vegetative reproduction that were unclear or unknown. The findings point to a reproductive diversification strategy that contributes to old man’s beard’s success as an invasive plant, due in part to dual dispersal mechanisms (by wind and water), dual seed banks (aerial and soil), dual seed dormancies (physiological and morphological), and dual reproductive modes (seeds and vegetative spread). Summary of findings regarding the biology • The aerial seed bank is transient: half of all achenes tagged and monitored were dispersed via anemochory during complete dormancy in autumn, and all but 5% of the remainder were gone by early spring. • The likelihood of secondary water dispersal is high, as seeds tolerated up to 6 weeks of immersion, germinated readily in water, and produced seedlings that remained robust, if removed from water within the 6-week period. • Pre-chilling was found to be unnecessary for germination, even for seeds that had not undergone a full winter of after-ripening: although it increased the speed at which seeds incubated at constant temperatures germinated, it did not promote total germination as successfully as a fluctuating temperature regime without pre-chilling. • Seeds collected off the vine and tested for germination over a 2-year period were fully physiologically dormant until completely senesced. Thereafter, dormancy declined during winter, and seeds were largely non-dormant by early spring. However, morphological dormancy did not change until seeds were exposed for several days to suitable germination conditions. Fewer than 72% of seeds were ultimately viable. • The soil seed bank was confirmed to be relatively small but persists at least for two years. Seeds in the soil experience the same cyclic physiological dormancy changes as those in the aerial seed bank, though can also enter a secondary dormancy when appropriate germination conditions are not met. • Seedlings were not able to survive competition exerted by established perennial grass cover unless the cover was very sparse. However, seedlings that survived began producing multiple, elongating stems within six months of emergence. • Vegetative growth produces an extensive network of creeping stems on the ground. Also, two-node woody stem fragments from both creeping and climbing stems are capable of rooting and growing vigorously as individual, clonal plants. Current management of old man’s beard infestations necessarily involves chemical control. The efficacy of two types of herbicide control was also assessed. As a precision technique for climbing vines that avoids non-target damage, the basal bark method with triclopyr in oil provides highly effective chemical control of individual stems, with >95% mortality. The cut stem method, using a 45% glyphosate gel formulation was less effective (55% mortality). For creeping stems, triclopyr alone and a triclopyr/picloram/aminopyralid mixture were effective herbicide sprays that preserved grass cover. Favouring a dense grass cover can help suppress subsequent establishment of old man’s beard by seed. Management should also consider that waterways are potential conduits of propagule spread, and that mechanical fragmentation of stems serves to produce more individuals, due to regeneration.
Clematis vitalba, Reproduction, Control, old man's beard, liana, woody invasive, riparian, seed bank, seed dispersal, germination, dormancy, seedling competition, vegetative growth, basal bark method, cut stem method, foliar herbicide, weed control