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

Abstract

Seedfall in a mixed native angiospermgymnosperm forest, Port Hills, Canterbury, was investigated for the period early January 1985-December 1986, using seed traps with a mouth area of 0.1 m 2, 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 (~ 1115 + 768 per trap, range 239-2848). In 1986, corresponding numbers were 28 326 full seeds (~ 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 B93040 Received 12 May 1993; accepted 13 October 1993Schefflera 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 ...

Fruit types and seed dispersal modes of woody plants in Ahuriri Summit Bush, Port Hills, western Banks Peninsula, Canterbury, New Zealand

“…This probably leads to inefficient seed dispersal, since relatively few seeds are likely to be ingested. It may account for groups 40 of crushed Leycesteria and Pseudowintera seeds occasionally found in seed traps (Burrows 1994). For 16 small-fruited species, however, silvereyes are probably reasonably effective seed dispersers.…”

“…Seeds of 33 (80%) of the fleshy fruited woody species (plus Pittosporum spp.) have been caught in seed traps sited in the reserve (Burrows 1994). As the fleshy parts have been stripped off, it is assumed that these clean seeds have passed through birds.…”

“…These birds also visit Pittosporum eugenioides capsules and were seen to swallow seeds. They and bellbirds were seen delving into Burrows 1994) show that seeds are transported over distances of at least a few tens of metres within the reserve and over distances of up to several kilometres to the reserve from localities distant from it: Ripogonum scandens seedlings occur distant from the single plant in the reserve; Prumnopitys taxifolia and Podocarpus hallii seedlings also occur distant from their parent plants; in the reserve are one sapling of each of two species, not otherwise present as adults (Prunus cerasifera and Hedycarya arborea); seeds of several species not present in the reserve are sometimes caught in the seed traps (Solanum nigrum, Coriaria arborea) or found on the ground (Alectryon excelsus). Dispersal distances are considered more fully in Burrows (1994).…”

“…Included, also, are the results of some observations on the occurrence and feeding habits of the extant birds and speculation about the evolution of fruit properties in relation to the extinction (local or total) of many other bird species. Seed trapping in the forest 1985-86 is described in Burrows (1994).…”

“…These planted species are not considered further. The vegetation and environmental conditions of the reserve are described more fully in Burrows (1994).…”