Clematis vitalbain a New Zealand native forest remnant: does seed germination explain distribution?

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Abstract
The pattern of distribution of the invasive vine Clematis vitalba in a typical New Zealand native forest remnant and the influence of chilling duration (chilling), nitrate (NO3 -), and light on germination of C. vitalba were investigated. In the forest remnant, C. vitalba was not established in undisturbed forest where light levels were ≤3% fall sunlight and rarely established where light levels were ≤5%. Clematis vitalba was, however, established in forest gaps and margins where light levels exceeded 5%, particularly when these areas were associated with recent soil disturbance. Under controlled environment conditions, germination in the absence of chilling, NO3 -, or light was low (3%). When applied alone, chilling and NO3 - increased germination. Light, however, only increased germination when applied with one or both other factors. In the presence of light, germination increased up to c. 80% with increased chilling (0–12 weeks), and increased up to c. 50% with increased applied NO3 - in the range 0.1–2.5 mol/m3 but then changed little with additional NO3 - up to 50.0 mol/m3. In general, germination in the presence of two or three factors was greater than when either factor was applied alone. In the field, seeds remaining on vines over winter retained a high degree of dormancy and viability. We suggest that sporadic release of this seed effectively produces a seed bank. By comparing the levels of chilling, NO3 -, and light that can be expected in the field with the levels that influence germination under controlled environment conditions, and considering a seed bank, we argue that C. vitalba is likely to rapidly establish following soil disturbance. We suggest that rapid establishment may account for the distribution of C. vitalba in recently disturbed, high light sites and, to some extent, the success of C. vitalba in New Zealand native forest remnants.