Seed trapping in Ahuriri Summit Bush Scenic Reserve, Port Hills, western Banks Peninsula, 1985–1986

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Abstract
Seedfall in a mixed native angiosperm-gymnosperm forest, Port Hills, Canterbury, was investigated for the period early January 1985–December 1986, using seed traps with a mouth area of 0.1 m2, sited in a restricted random fashion within a 25 × 25 m marked quadrat (16 traps in 1985, 20 in 1986). All plants 1 m tall or more in the quadrat were mapped, with dimensions recorded. From the total of 56 wild woody plant species in the forest (22 tree species, 20 shrubs, 14 vines) in 1985, 19 were represented in the total seed catch of all traps by 50 or more seeds and a further 12 by 10 or more seeds. Corresponding numbers in 1986 (adjusted in proportion to the increased number of traps) were 18 species represented by 62 or more seeds and a further five by 12 or more seeds. For many of the species there were notable differences in total numbers of seeds caught in the 2 years, and the temporal distribution and length of seedfall (and fruiting peaks) also differed. In 1985, a total of 17 847 full (i.e., potentially germinable) seeds was caught ( x 1115 ± 768 per trap, range 239–2848). In 1986, corresponding numbers were 28 326 full seeds ( x 1416 ± 1639 per trap, range 468–7861). The catch per trap for particular seed species was highly variable, and it is proposed that this is a reality of nature arising from non-random influences on the deposition of individual seeds. Most seeds were probably derived from nearby plants, especially those fruiting individuals which overhang the traps. This was most notable for species which fruited very abundantly (Pseudopanax crassifolius in 1985, Fuchsia excorticata and Schefflera digitata in 1986). Nevertheless, seeds of some species were caught in small to moderate numbers although they were not represented at the immediate trap site by fruiting parent plants. The most even distribution of seeds in traps was for species with relatively low seedfall numbers; most are absent from the immediate trap site. Seeds of a few species absent in Ahuriri Summit Bush were also trapped. Minimum distances from fruiting plants to traps for the species not at the trap site range from a few tens of metres to at least 1.5 km for two. These data show that it is virtually impossible to know the exact provenance of any seeds reaching the traps. The important seed-dispersing birds in the forest are bellbirds (Anthornis melanura), silvereyes (Zosterops lateralis), kereru (Hemiphaga novaeseelandiae), and blackbirds (Turdus merula). Evidence is adduced to show that these birds actually eat fruit and disperse seeds, and it is assumed that this can occur for 75% of the woody plant species in the forest. The frugivorous birds appear to be generalists, feeding on many fruit species. The variety of fleshy fruit, available over the long period from mid December to August, attracts birds. Other attractions are flowers and invertebrates, as some of the frugivores are also nectarivores and “insectivores”. Pre-dispersal seed predation by birds was negligible. Moth larvae were the main seed predators. Only five species appear to have many seeds eaten and only three of these suffered heavy predation; each also produced abundant unharmed seeds. Few of the woody species have wind-dispersed seeds; their dispersal distances are relatively short. Some wind-dispersed seeds from adjacent herbaceous communities have probably travelled for hundreds of metres. Very few seeds of forest species were caught by four traps set up in an open enclave in the forest. Overall, seed dispersal in the forest is not very efficient (in the sense of escape of most seeds from proximity to parents), but it is apparently adequate for regeneration of most of the woody plants present there.