A multi‐scale biogeographical analysis of Bambusa arnhemica, a bamboo from monsoonal northern Australia

Abstract

Aims To identify the edaphic, environmental and historical factors influencing the patchy distribution of the semelparous bamboo Bambusa arnhemica F. Muell. at global, catchment and streambank scales.Location The entire range of B. arnhemica, a highly fire-prone savanna matrix with generally infertile soils in the north-west of the Northern Territory of Australia above the 1200 mm mean annual rainfall isohyet.Methods Distribution surveys were conducted by air, boat and on the ground. Plot data were collected throughout the range of the species.Results Bambusa arnhemica occurred predominantly in gallery forests on floodprone but nevertheless well-drained and deep alluvial soils on sloping stream banks. It ranged widely along lentic watercourses from ephemeral headwater streams to the banks of major rivers and levees on the coastal floodplain. The species did not occur in savannas; savannas adjacent to B. arnhemica gallery forests were also flood-prone and on deep alluvial soils, but were upslope on level ground. Bambusa arnhemica's infrequent non-riparian occurrences were on a wide variety of substrates but generally on soils of moderate fertility and in coastal and/or rocky areas where at least partial topographic protection from fire is likely. Within and between catchments, the distribution of B. arnhemica was idiosyncratic, occurrence being almost always continuous downstream from highly variable 'starting' points to the poorly drained coastal floodplain.Main conclusions At local scales, B. arnhemica appears constrained by poor drainage and high fire-frequencies. Enhanced soil fertility may increase its capacity to cope with fire. At the catchment and global scales, we propose that the distribution of B. arnhemica is the product of infrequent and as yet incomplete dispersal across and away from watercourses by seed that lacks specialized dispersal mechanisms, combined with passive dispersal along streams. From this we infer that B. arnhemica is neither a very recent, nor very ancient colonist from Asia. Bambusa arnhemica's circumscribed global distribution has no parallel amongst co-occurring rain forest plants and may be the product of poor dispersal capacity and a substantial rock and floodplain barrier to the east. Limited dispersal capacity may be inextricably linked to local domination of space and the subsequent creation of regeneration space by parental death.

Bamboo, fire and flood: consequences of disturbance for the vegetative growth of a clumping, clonal plant

“…Bambusa arnhemica occurs in the monsoonal northwest of the Top End of the Northern Territory, Australia, where mean annual rainfall exceeds 1,200 mm but is intensely seasonal (Franklin and Bowman 2004). It forms monodominant stands mostly along floodprone river banks that are relatively sheltered from fire.…”

Taxonomic interpretations of Australian native bamboos (Poaceae: Bambuseae) and their biogeographic implications

“…Furthermore, because trepang is most abundant in clear water, the major trepanging grounds in northern Australia were off rocky rather than mangrove-lined coasts. Thus it was that Macassan camp sites were concentrated from Cobourg Peninsula east to the Gulf of Carpentaria, and along the Kimberley coast in the west (Macknight 1973(Macknight , 1976, a distribution that almost perfectly excises the coast adjacent to which B. arnhemica grows (Franklin & Bowman 2004). A plausible but hypothetical case has been made that Aboriginal people could have reached Australia on bamboo rafts (Flood 1995, Bednarik et al 1999.…”

“…However, several strands of ecological evidence suggest that B. arnhemica has been in Australia for a considerable period of time. The first is its primarily riparian distribution, documented in detail by Franklin and Bowman (2004) and which should be interpreted in the absence of any obvious dispersal mechanism (Franklin 2003a) and a generation time of 40-50 years (Franklin 2004). The species occurs in six major and a number of minor adjacent catchments on the Australian mainland and a restricted series of minor catchments on Melville Island.…”

“…It is consistently absent from streams with shallow, poorly-drained profiles, and from rocky stream banks. Franklin and Bowman (2004) suggested these patterns reflect infrequent dispersal across catchment boundaries to random "starting points", followed by downstream dispersal.…”

“…It grows mainly in riparian forests and occasionally on rocky hillsides and other fire-sheltered non-riparian sites, ranging from Kakadu National Park west and south-west to the Daly River and north to Melville Island, often occurring in monodominant stands (Franklin & Bowman 2004). Neololeba atra is a slender, clumping, large-leaved species found in scattered locations in rainforest and vine-thicket along the Queensland coast from Mackay to the Torres Strait and also in New Guinea, the Moluccas, northern Sulawesi and the Philippines (Widjaja 1997).…”