TY - JOUR

T1 - Climate-Induced Forest Mortality in the Tropical Pacific Islands: What Do We Really Know?

AU - Boehmer, Hans Juergen

AU - Galvin, Stephen

N1 - Funding Information: We would like to thank Bruce Burns and two unknown reviewers for helpful comments on an earlier version of the manuscript. We gratefully acknowledge the German Volkswagen Foundation for funding the workshop 'Crossing scales and disciplines to identify global trends of tree mortality as indicators of forest health' (Herrenhausen Castle, Hanover, Germany, June 2017; co-Pi HJB) which inspired the authors to write this paper. Dieter Mueller-Dombois was a guest of honor at this symposium with 70+ participants from six continents-tree physiologists, forest ecologists, forest inventory experts, remote-sensing scientists, and vegetation modelers-where he provided guidance for a new generation of tree mortality and forest decline researchers. Dieter's foresight for global developments and relationships in vegetation dynamics across all scales made him the pioneer of global forest mortality research. His fundamental contribution to the development of modern forest decline and tree mortality research and his efforts to synthesize related studies at the global level through extensive interdisciplinary research into the causes of large-scale forest dieback can be considered exemplary for modernmulti-causal researchonforestdecline. Dieter's legacy will live on through the countless students he taught and mentored, and the many people he inspired by his knowledge and dedication for forest ecology and conservation.

PY - 2024/2/1

Y1 - 2024/2/1

N2 - Between 1954 and the mid-1980s, about 50,000 ha of native montane rainforest on the island of Hawai'i experienced a decline in canopy trees ("'ohi'a dieback"), leading to great concern about the future of Hawai'i's rainforests. Dieback symptoms particularly affected the dominant tree species, the endemic Metrosideros polymorpha. Early hypotheses postulated that the forest decline was caused by a virulent pathogen or a combination of biotic disease and pest agents. This was ruled out after a decade of intensive disease research in the 1970s. Instead, it turned out that dieback patterns were significantly related to the physical environment, particularly the slope, topography, relative position on the hill slope, annual rainfall, and the type of substrate. Thus, an alternative hypothesis proposed that dieback is initiated by climate anomalies that manifest through soil moisture regimes under certain conditions of forest stand demography. Ironically, scientific perception of this interdisciplinary groundbreaking research that stimulated a global perspective on forest decline vanished while the awareness of climate change and its potential impact on the world's forests started to grow, rapidly becoming a major focus of research in recent years. In this paper, we reinforce memory of the world's first complex discussion on the natural causes of forest dieback as a showcase for the complexity of modern forest mortality research. This case demonstrates the need to rigorously identify, quantify, and fully understand all drivers of tree mortality to realistically project future climate-driven and other risks to forest ecosystem functions and services. Moreover, we summarize recent findings on forest mortality and climate change in the Pacific islands and beyond.

AB - Between 1954 and the mid-1980s, about 50,000 ha of native montane rainforest on the island of Hawai'i experienced a decline in canopy trees ("'ohi'a dieback"), leading to great concern about the future of Hawai'i's rainforests. Dieback symptoms particularly affected the dominant tree species, the endemic Metrosideros polymorpha. Early hypotheses postulated that the forest decline was caused by a virulent pathogen or a combination of biotic disease and pest agents. This was ruled out after a decade of intensive disease research in the 1970s. Instead, it turned out that dieback patterns were significantly related to the physical environment, particularly the slope, topography, relative position on the hill slope, annual rainfall, and the type of substrate. Thus, an alternative hypothesis proposed that dieback is initiated by climate anomalies that manifest through soil moisture regimes under certain conditions of forest stand demography. Ironically, scientific perception of this interdisciplinary groundbreaking research that stimulated a global perspective on forest decline vanished while the awareness of climate change and its potential impact on the world's forests started to grow, rapidly becoming a major focus of research in recent years. In this paper, we reinforce memory of the world's first complex discussion on the natural causes of forest dieback as a showcase for the complexity of modern forest mortality research. This case demonstrates the need to rigorously identify, quantify, and fully understand all drivers of tree mortality to realistically project future climate-driven and other risks to forest ecosystem functions and services. Moreover, we summarize recent findings on forest mortality and climate change in the Pacific islands and beyond.

KW - cavitation

KW - climate change

KW - dieback

KW - Metrosideros polymorpha

KW - montane rainforest

KW - novel ecosystem

KW - tree mortality

KW - vulnerability

UR - http://www.scopus.com/inward/record.url?scp=85184066337&partnerID=8YFLogxK

U2 - 10.2984/77.2.2

DO - 10.2984/77.2.2

M3 - Article

AN - SCOPUS:85184066337

VL - 77

SP - 139

EP - 161

JO - Pacific science

JF - Pacific science

SN - 0030-8870

IS - 2-3

ER -