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Ohia rain forest study: ecological investigations of the ohia dieback problem in Hawaii
Abstract
This final report summarizes the more important results of a two year study of the ohia (Metrosideros collina subsp. polymorpha) rain forest, extending from within Hawaii Volcanoes National Park north across the east flank of Mauna Kea, Island Hawaii. The study focus was on the ohia dieback which occurs in many areas of this terrain. A 1:48,000 vegetation map was produced, which is included in selected copies of this report. In addition, an independent habitat classification was developed from physical soil and moisture regime differences occurring in the area. Over 35 ohia forest stands were sampled in detail for their ohia population structures and 39 releves were analyzed for their floristic content. Five different forms of dieback were recognized. Two of these, called the Dryland and Wetland Diebacks appear to be the more rapid and dramatic forms. Their causes are not from disease or insect attack, but are presumed to be from climatic triggers, acting through the soil. These diebacks are clearly associated with ohia-stand rejuvenation. A third form of dieback, here called Bog-formation Dieback, appears to be a slower form of stand dieback related to permanent site changes. An Ohia-displacement Dieback occurs in the Olaa Tract area, where tree ferns seem to gradually take over the habitats. Here the dieback cause appears to be overmaturity. Individual tree dieback, the fifth form of dieback, is found as an isolated, but common phenomenon in many non-dieback stands examined. All diebacks appear to have natural causes, which are suggested in detail. A new theory is presented, which proposes that there are a number of dynamic phases, including the dieback, which provide for the perpetuation of the shade-intolerant, dominant tree species (ohia) in this rainforest ecosystem. National Park Service Contract No. CX 8000 6 0006
... The primary focus of this research was on the fungal pathogen Phytophtora cinnamomi (Bega, 1974;Kliejunas & Ko, 1973, 1976) that had been implicated in a widespread mortality of Eucalyptus trees in plantations of Western Australia (Newhook & Podger, 1972). Research on the natural succession hypothesis was initiated in 1976 to assess both the extent and ecological characteristics of the M. polymorpha forest impacted by canopy dieback relative to areas that did not exhibit dieback in this same forest zone (Mueller-Dombois, 1980;Mueller-Dombois, Jacobi, Cooray, & Balakrishnan, 1980). This study included (a) identifying spatial patterns and habitat characteristics of areas that were The results of spatial analyses of the 1970s dieback (Akashi & Mueller-Dombois, 1995;Jacobi, 1983;Mueller-Dombois, 1986;Mueller-Dombois et al., 1980) showed that the extent and spread of M. polymorpha dieback in this area, primarily on sites experiencing the wetland dieback type, appeared to be directly related to substrate age and type, and was also correlated with elevation and rainfall. ...
... Research on the natural succession hypothesis was initiated in 1976 to assess both the extent and ecological characteristics of the M. polymorpha forest impacted by canopy dieback relative to areas that did not exhibit dieback in this same forest zone (Mueller-Dombois, 1980;Mueller-Dombois, Jacobi, Cooray, & Balakrishnan, 1980). This study included (a) identifying spatial patterns and habitat characteristics of areas that were The results of spatial analyses of the 1970s dieback (Akashi & Mueller-Dombois, 1995;Jacobi, 1983;Mueller-Dombois, 1986;Mueller-Dombois et al., 1980) showed that the extent and spread of M. polymorpha dieback in this area, primarily on sites experiencing the wetland dieback type, appeared to be directly related to substrate age and type, and was also correlated with elevation and rainfall. The ecology and dynamics of the M. polymorpha dieback forest and potential mechanisms for the 1970s dieback event were summarized by Mueller-Dombois (1985) and Hodges et al. (1986). ...
Questions
(a) Have Metrosideros polymorpha trees become re‐established in Hawaiian forests previously impacted by canopy dieback in the 1970s? (b) Has canopy dieback expanded since the 1970s? (c) Can spatial patterns from this dieback be correlated with habitat factors to model future dieback in this area?
Study Site
An 83,603 ha study area on the eastern slopes of Mauna Loa and Mauna Kea volcanoes on the island of Hawaii, USA .
Methods
We analyzed very‐high‐resolution imagery to assess status of Metrosideros polymorpha forests across the eastern side of the island of Hawaii. We generated 1,170 virtual vegetation plots with a 100‐m radius; 541 plots in areas mapped in 1977 with trees dead or mostly defoliated (dieback), and 629 plots in adjacent wet forest habitat, previously mapped as non‐dieback condition. In each plot we estimated the frequency of M. polymorpha trees that were dead or mostly defoliated, and the frequency of trees with healthy crowns. These results were combined with habitat data to produce a spatial model depicting probability of canopy dieback within the study area.
Results
Seventy‐nine percent of plots mapped in 1977 in dieback condition recovered their canopy and were now considered in non‐dieback condition. Ninety‐one percent of plots in previous non‐dieback areas were found to still have a healthy M. polymorpha canopy in 2015. A spatial model allowed us to identify areas within the study area with high, medium, and low probability of experiencing this same type of canopy dieback in the future.
Conclusions
Most former dieback areas mapped within the study area in 1977 now show recovery of the tree canopy through growth of new cohorts of young M. polymorpha trees. This suggests these forest communities are resilient to this type of canopy loss and tree death so long as other factors do not disrupt the natural regeneration process.
... A total 200 quadrates (50 in each site) of 10x10 m size were laid randomly for the investigation of trees and saplings 5x5 for seedlings. Standard phytosociological methods were followed to obtain quadrat data [17]. The collected field data were analysed for different compositional or phytosociological component [18]. ...
The present communication aims to envisage the physico-chemical properties of soils in relation to the vegetational parameter in the subtropical and temperate forest stands of Western Himalaya. A total of four forest stands were investigated for various vegetational and physico-chemical properties ranging from 300-2250 m m.s.l. The study revealed that the soil moisture, water holding capacity (WHC) and total nitrogen recorded maximum (26.33%, 63.52%, and 0.41% respectively) in the mixed oak forest stands and minimum (19.09%, 46.28%, and 0.14% respectively) in the sal forest stands, however, the soil organic carbon (SOC) was reported maximum (4.25%) in banj-oak forest and minimum (1.23%) in sal forest stands. Temperate oak forests are richer in terms of specie richness, diversity as well as physical and chemical properties of soil as compare to subtropical sal and chir-pine forest stands. This result indicate that the soil nutrient dynamics is positively correlated with species diversity and richness of forest.
... The detailed locations of these plots and the descriptions of the vegetation have been documented elsewhere (Jacobi et al. 1983(Jacobi et al. , 1988Boehmer et al. 2013). These relevé plots were 20 Â 20 m in size and all of the trees >5 m tall were permanently marked, DBH measured, and assessed for their crown foliage vigor using the five tree vigor classes described by Mueller-Dombois et al. (1980). Additionally, data were recorded on the abundance of all woody species <5 m tall in subplots within the relevé, as well as cover for all plant species within the plot in 1 m height classes. ...
’Ohi‘a (Metrosideros polymorpha) is the most abundant tree species in the native wet and mesic forests throughout the main Hawaiian Islands. In the late 1960s and early 1970s large areas on the wet, eastern side of Hawai‘i island appeared to have extensive defoliation and death of the ’ohi‘a trees. The dieback on Hawai‘i island extended to approximately 49,000 ha of which 24,000 ha was considered to be in heavy to severe dieback (>50% of the canopy trees dead or defoliated), and 25,000 ha characterized as having slight to moderate dieback (25–50% of the canopy trees dead or defoliated). Research was initiated in 1976 to assess both extent and ecological characteristics of the forest impacted by canopy dieback relative to areas that did not experience dieback in this same forest zone. To assess the spread or recovery of the ’ohi‘a dieback forest over time, twenty-six permanent plots were established across the study area. The results from the monitoring of the 26 permanent plots indicate that many of the original dieback sites are now showing strong recovery of the ’ohi‘a tree canopy through recruitment of new seedlings that have now grown into saplings and even taller trees (Boehmer et al. 2013). However, it was not clear if these results truly represented the conditions across the entire original dieback area. Therefore, we conducted a much larger survey of response of the ’ohi‘a forest to that dieback event across the entire wet forest region on the eastern side of the island of Hawai‘i. We did this by analyzing very high-resolution aerial imagery (<10 cm pixels) taken by Pictometry International (POL) to assess both canopy and understory change throughout this region. The POL imagery proved to be an effective and efficient tool to use for assessing the status of ’ohi‘a forest across the eastern Hawai‘i Island study area. The results of this large area survey, using the POL imagery, agree closely with the conclusions presented by Boehmer et al. (J Veg Sci 24(4):639–650, 2013), that most of the ’ohi‘a forests on the eastern side of the island of Hawai‘i that were affected by canopy dieback in the1960s and 1970s have started to recover their tree canopy, as a new cohort of young trees are growing back in these sites.
... World literature on forest pathology contains references to many similar problems usually called diseases of complex or unknown causes but includes few descriptions of symptoms or investigations into site ecology.-Notable exceptions are descriptions of diebacks in Australia (Weste 1981), ohia dieback in Hawaii / (Mueller-Dombois et al. 1981), and oak diebacks in southern Europe (Vajda 1951). These dieback syndromes show many resemblances to the current situation in-the Kaimai Range. ...
Severe forest decline exists in upland areas of the Kaimai Range, North Island, New Zealand. Stand structure of major affected vegetation types is described. As stand dominants are well represented in induced seral vegetation, the overall species composition of the upland forests is not likely to change following decline. Within the decline zone a considerable range of forest damage is found. Characteristic damage types are described including effects on seedling vigour, root system development, and shoot phenology. The decline appears to result from a sequence of natural phenomena. High fog occurrence coincides with the decline zone producing soil waterlogging and generally poor growth conditions. This predisposes the forests to periodic drought damage.
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 ("'ōhi'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.
Metrosideros polymorpha (‘ohi‘a, ‘ohi‘a lehua) is an important foundation species in Hawaiian forest habitats. The genus originated in New Zealand and was dispersed to the Hawaiian archipelago approximately 3.9 million years ago. It evolved into five distinct endemic species and one of these, Metrosideros polymorpha, further differentiated into eight varieties across what are now the main Hawaiian Islands. ‘Ohi‘a is a tree that has great significance in indigenous Hawaiian culture. It is considered a physical manifestation of several principal Hawaiian deities, and serves a broad range of uses in Hawaiian material culture. It occupies a wide diversity of habitats, extending from sea level to over 2,200 m elevation, occupying habitats that range from extremely wet to dry rainfall zones. It is the dominant or co-dominant tree species in wet and mesic forests and is also one of the first woody species to become established on young lava flows. Although ‘ohi‘a is a dominant forest tree it also exhibits many characteristics of a pioneer species.‘Ohi‘a provides the matrix for a wide diversity of endemic plants and animals found in these habitats and functions as the primary vegetation cover on native Hawaiian watersheds, facilitating groundwater recharge and regulating surface runoff. ‘Ohi‘a has shown remarkable resilience by recolonizing forests that were opened up by disturbance, such as the widespread ‘ohi‘a canopy dieback that occurred on East Maui in the 1900s and on the east side of the Island of Hawai‘i in the 1970s. Several human-related conditions threaten the continued stability of Hawaii’s native ecosystems, including invasive plants, plant diseases, introduced animals, and changing climate. The research and conservation legacy of Dr. Dieter Mueller-Dombois helped to expand our knowledge of the ecology and importance of ‘ohi‘a forests, and to increase awareness and appreciation of the remarkable Hawaiian ecosystems that are unique to the world.
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 forest mortality research, and try to summarize what science has added to our knowledge on the links between tree mortality, forest dynamics and climate change in the Pacific islands in the meantime.
This paper is a short version of a recently published book ‘Ōhi’a Lehua Rainforest, which resulted from studies of vegetation at multiple scales in space and time. The objective of this short version is not only to demonstrate some of these changes in scale, but also to show that different perspectives through scale changes were needed for synthesizing the subject matter into a coherent story. In other words, any vegetation study that aims at comprehensive explanations needs to view the subject matter from several different perspectives or scales. The five decade-long research on native Hawaiian rainforest is such a study. Following the introduction, this study is summarized under five subheadings: A rainforest born among volcanoes Turnover by auto-succession From rainforest to bog and stream formation Fragmentation into smaller units as islands age Conclusion: the rainforest on Windward O’ahu
Forest decline or stand-level dieback is a recurring phenomenon in many of the world’s forests. In industrial countries much public concern and research effort are focused on emission-induced forest decline. However, stand-level dieback in forests is not a new phenomenon. For example, Selling’s (1948) bog-pollen cores on Molokai show fluctuations of Metrosideros pollen, reaching back 10000 years, indicating an oscillating presence or vice versa a recurring stand-level dieback.
Large numbers of Metrosideros polymorpha trees have died in the montane rain forest on the Island of Hawai'i, but previous research has failed to identify a principal cause. This paper describes an experiment that tests the hypothesis that nutrient deficiency is the principal cause of tree death and stand-level dieback. Treatments were fertilizing, stand thinning, and a combination of the two. No significant change in the mortality rate was caused by the treatments; however, stem diameter growth of surviving trees was found to be nutrient limited at all sites. We conclude that nutrient deficiency is not the principal cause of most Metrosideros dieback, but it may be a contributing factor.
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