Chloroplast from the past: Beech genealogy guides future conservation

‘Plio-Pleistocene environmental changes shape present-day phylogeography of New Zealand’s southern beeches (Nothofagaceae)’ published in the New Zealand Journal of Botany shows how the current beech tree distribution is a result of past climate changes. Island ecosystems are severely affected by climate change; however studying the population dynamics of an abundant island species can shed light on climate and ecosystem interactions, thereby helping us to understand and prepare for future ecological challenges.

One such abundant species is tawai, or southern beech, a keystone species in Aotearoa that features significantly in our forest cover. This research indicates that the present-day distribution of the southern beech in Aotearoa is mainly due to environmental changes during the Pleistocene time period, 2,580,000 to 11,700 years ago.

As beech trees are a keystone species in Aotearoa, the distribution of the species throughout the Pleistocene provides an idea of the forest cover over different times. This helps us understand the ecological challenges and climates that forest fauna and flora were exposed to during the ice ages. Understanding these processes is important for understanding the origin of Aotearoa forest biodiversity, as well as for conservation.

Studying the diversity of chloroplast in the five species of southern beech shows how different species fared throughout the glacial cycles of the Plio-Pleistocene era. The relatively high chloroplast diversity in silver beech (N. menziesii) in the northern South Island indicates that silver beech populations remained intact in that area throughout the Pleistocene period. In the southern South Island, it appears likely that glacial climates reduced the silver beech population to small and isolated forest remnants, resulting in a comparative lack of chloroplast diversity.

In the North Island a lack of chloroplast diversity was also detected, despite the region having much larger areas of consistent forest cover. In this case, the genetic ‘bottleneck’ was caused by unfavourable climate conditions. These findings conclude the northern South Island to be a key refugal region, or ‘safe space’, for conserving tawai.

The present-day geography of Aotearoa forest ecosystems is a genetic signature of shifts in the global climate over time. The current distribution of southern beech forest has been largely moulded by Pleistocene glacial cycles.

The research article ‘Plio-Pleistocene environmental changes shape present day phylogeography of New Zealand’s southern beeches (Nothofagaceae)’ published in the New Zealand Journal of Botany was authored by Nicolas Rawlence (Otago), Benjamin Potter (UoA), Nic Dussex (NRM), Lachie Scarsbrook (Otago), David Orlovich (Otago), Jonathan Waters (Otago), Matt McGlone (Manaaki Whenua) & Michael Knapp (Otago).

Nicolas J. Rawlence, Benjamin C. M. Potter, Nic Dussex, Lachie Scarsbrook, David A. Orlovich, Jonathan M. Waters, Matt McGlone & Michael Knapp (2020) Plio-Pleistocene environmental changes shape present-day phylogeography of New Zealand’s southern beeches (Nothofagaceae), New Zealand Journal of Botany DOI:10.1080/0028825X.2020.1791915