Re-envisioning the structure of last glacial vegetation in New Zealand using beetle fossils

Abstract

A series of 18 fossil beetle assemblages are used to reconstruct the paleoenvironment of the northwest West Coast, New Zealand, over the period of the last interstadial–stadial transition (ca. 37,000–21,300 cal yr BP). The samples were recovered from an in-filled hollow within a dune field ca. 9 km south west of Westport (41°47′S, 171°30′E). This fossil beetle reconstruction is compared to an existing palynological reconstruction from the same site. The beetle assemblages indicate an environment of marshy shrubland interspersed with closed canopy coastal vegetation prior to glacial onset, and a mosaic of closed canopy patches and open tussock grassland during full glacial conditions. These interpretations, contrast with the palynologically based interpretation which indicates subalpine shrubland prior to glacial onset and widespread grassland with little woody vegetation during the period of maximum glacial cooling. This study is consistent with other non-pollen studies in New Zealand and indicates that the palynological interpretation of the paleoenvironment of the Westport region downplays the importance of closed canopy vegetation in the area during the transition from interstadial to full glacial (stadial) conditions. It challenges the interpretation of open vegetation at low elevations during glacial periods from pollen studies.

The vegetation cover of New Zealand during the Last Glacial Maximum: Do pollen records under-represent woody vegetation?

“…We note that in the beetle faunas from this site classic wet-forest saproxylic taxa like Pycnomerus and other zopherids, for example, are completely absent from this sequence, terra australis 32 Burge and Shulmeister (2007) propose 'The contrast between the pollen and beetle reconstructions may thus simply represent a combination of an enlarged pollen-collection area and low pollen-producing taxa (including arboreal taxa) being overshadowed by abundant input from increased areas of grassland and local wetland taxa such as Myriophyllum and Cyperaceae' (p 129). At this particular site, Myriophyllum and Cyperaceae did not affect the pollen sum in this way.…”

“…Burge and Shulmeister (2007) claim that beetle fossils indicate much more closed woody vegetation than pollen evidence would suggest. This claim relies primarily on their beetle fossil sites in the Westport area (coastal northwestern South Island), which they say demonstrate the close-by presence of closed canopy woodland, while the pollen interpretation (Moar and Suggate 1979) is of an open grassland with a woody element.…”

“…As pollen evidence clearly points to the presence of forest, albeit in limited amounts, throughout non-glaciated regions, and recent beetle evidence (Marra and Leschen 2004;Burge and Shulmeister 2007) shows that trees were growing in inland eastern South Island locations, the near absence of woody plant macrofossils is significant. Absence of tree wood or other macrofossils can probably be explained by two factors.…”

“…Although the attribution of beetle fossils to closed woody vegetation or litter under closed woody vegetation (Marra and Leschen 2004;Burge and Shulmeister 2007) seems well founded, there is little specificity in the attributions and no basis for conclusions about plant abundance. According to the brief descriptions given, most of the beetles could persist under any sort of woody vegetation.…”

Phylogeography of six codistributed New Zealand cicadas and their relationship to multiple biogeographical boundaries suggest a re‐evaluation of the Taupo Line

“…The late Pleistocene was characterized by extreme cycles of warm and cold periods, occurring about every 100,000 years (Carter & Gammon, 2004). Accompanying low temperatures, increased aridity and dramatic vegetational shifts resulted in uninhabitable areas of the North Island for many lineages during each glacial advance (Burge & Shulmeister, 2007;McGlone et al, 2010). In addition, the central North Island (centred on the Taupo Volcanic Zone, TVZ) was affected by major volcanic eruptions in the late Pleistocene (Bunce et al, 2009) that caused habitat destruction and isolated disjunct populations (McDowall, 1996).…”