Journal Article

Species assemblage patterns around a dominant emergent tree are associated with drought resistance

Sarah V. Wyse, Catriona M.O. Macinnis-Ng, Bruce R. Burns, Michael J. Clearwater and Luitgard Schwendenmann

Edited by Guillermo Goldstein

in Tree Physiology

Volume 33, issue 12, pages 1269-1283
Published in print December 2013 | ISSN: 0829-318X
Published online December 2013 | e-ISSN: 1758-4469 | DOI: https://dx.doi.org/10.1093/treephys/tpt095
Species assemblage patterns around a dominant emergent tree are associated with drought resistance

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Water availability has long been recognized as an important driver of species distribution patterns in forests. The conifer Agathis australis (D. Don) Lindl. (kauri; Araucariaceae) grows in the species-rich forests of northern New Zealand. It is accompanied by distinctive species assemblages, and during summer the soil beneath A. australis is often significantly drier than soils beneath surrounding broadleaved angiosperm canopy species. We used a shade house dry-down experiment to determine whether species that grow close to A. australis differed in drought tolerance physiology compared with species that rarely grow close to A. australis. Stomatal conductance (gs) was plotted against leaf water potential (ψ) to identify drought tolerance strategies. Seedlings of species that occur in close spatial association with A. australis (including A. australis seedlings) were most resistant to drought stress, and all displayed a drought avoidance strategy of either declining gs to maintain ψ or simultaneous declines in gs and ψ. The species not commonly occurring beneath A. australis, but abundant in the surrounding forest, were the most drought-sensitive species and succumbed relatively quickly to drought-induced mortality with rapidly declining gs and ψ values. These results were confirmed with diurnal measurements of gs and assimilation rates throughout the day, and leaf wilting analysis. We conclude that the varied abilities of the species to survive periods of drought stress as seedlings shapes the composition of the plant communities beneath A. australis trees. Furthermore, forest diversity may be impacted by climate change as the predicted intensification of droughts in northern New Zealand is likely to select for drought-tolerant species over drought-intolerant species.

Keywords: Agathis australis; drought tolerance; kauri; soil moisture; stomatal conductance

Journal Article.  7748 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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