Mount Haleakalā

Mount Haleakalā, Maui County, Hawaii 

        Mount Haleakalā is a shield volcano on the island of Maui, HI (USGS, n.d.). The summit of Mt. Haleakalā reaches 3,055m (10,023ft)(USGS, n.d.) and the mountain's climate ranges from alpine desert to tropical rainforest (NPS, 2015a). Hawaii’s climate is largely controlled by the Tradewinds that run east to west (Gotsch, 2014), making the eastern side of Mt. Haleakalā the windward side. Notably, all soils on the island are andisols (UCDavis, n.d.; USGS, n.d.)—soils formed from volcanic rock and ash (MacDonald, 2003). The first location of interest, a ranger station in Haleakalā National Park, has an elevation of 2,122m (6,962ft)(NOAA, n.d.) and is located north of the summit, falling slightly towards the leeward side of the mountain. The dominant soil type in this area is Kaipoioi loam (UCDavis, n.d.), which has a deep, illuviated B horizon (MacDonald, 2003). Further, the A and B horizons are very darkly colored, possibly indicating that the soil has a high organic matter content (MacDonald, 2003). Average temperatures range from about 10-15°C, and total monthly precipitation ranges from about 35-194mm, tending to have a drier summer season (NOAA, n.d.). The second location is in Makena, a small, coastal town on the leeward side of Mt. Haleakalā. The dominant soil type in this location is Oanapuka stony silt loam (UCDavis, n.d.), characterized by a deep and complex C horizon of slightly weathered parent rock (MacDonald, 2003). Average temperatures range from about 22-26°C, and total monthly precipitation ranges from about 10-75mm, typically having a drier summer. The third location, ‘Ohe‘o Gulch, is another coastal city on the southeastern part of the island. It is on the windward side of Mt. Haleakalā and Hana stony silty clay loams are the dominant soil (UCDavis, n.d.). The soil has shallower A and B horizons, with a white C horizon of unconsolidated parent rock. The average temperatures range from about 22-26°C, and total monthly precipitation ranges from about 130-220mm where the winter months tend to receive slightly more precipitation than the summer months (NOAA, n.d.).

Climographs and Soil Profiles

        

Haleakalā National Park

• North of Mt. Haleakalā's summit
• Dominant Soil: Kaipoioi (Soil profile from UCDavis, n.d.)

        

Makena

• Leeward side of Mt. Haleakalā
• Dominant Soil: Oanpuka (Soil profile from UCDavis, n.d.)

‘Ohe‘o Gulch

• Windward side of Mt. Haleakalā
• Dominant Soil: Hana (Soil profile from UCDavis, n.d.)

Biotic Communities and Disturbance Regimes

Haleakalā National Park Biotic Communities

    

    The area around the Haleakalā National Park NOAA station is predominantly subalpine forest (Cuddihy, 1988), with invasive plant communities consisting of species such as Eucalyptus spp., Ulex europaeus (Gorse), and several species in the class Conifer (Loope et al., 1992). Many of these invasive species spread through Hawaii, but can mainly be found at elevations with a cooler, more temperate climate (Loope et al., 1992). This area, also known as Hosmer Grove, has unique vegetation as several tree stands were planted with experimental non-native species by Ralph Hosmer—the first Superintendent of Forestry of the Territory of Hawai‘i (NPS, 2019). However, there are still several native plant and animal communities surrounding this area, as current forest managers attempt to contain the non-native species within Hosmer Grove (Loope et al., 1992). Native plant species include Santalum haleakalae (‘Iliahi), Sophora chrysophylla (Māmane), and Osteomeles anthyllidifolia (‘Ūlei), all of which are shrubs or small trees that have bright blooms (NPS, n.d.). The native animals in the area are primarily birds, including several species of endemic honeycreeper birds (NPS, 2020), such as Loxops coccineus (‘Akepa )(FWS, n.d.a). Hawaiian honeycreepers are birds that are typically brightly colored, and as their name suggests, they rely on flower nectar as their main source of food (NPS, 2020).

  

Loxops coccineus species range (FWS, n.d.a) and photo (USGS, 2016).

  

Eucalyptus globulus Labill. species range (USDA, n.d.a) and photo (PFAF, n.d.).

Makena Biotic Communities 

     On the leeward side of Mt. Haleakala, near the southern coast, tropical dry savanna dominates the landscape (Cuddihy, 1988). This area around the Makena NOAA station typically receives little rainfall, so vegetation is adapted to low water conditions (Cuddihy, 1988). However, much of the lowland dry savanna has been invaded by non-native grasses that are adapted to fire, as fires are becoming a more frequent disturbance in this area due to anthropogenic influence (Cuddihy, 1988). Additionally, few trees can be supported in this landscape, but Schefflera actinophylla (Octopus Tree), a non-native ornamental tree, can be seen in the area and through many other parts of Hawaii (USDA, n.d.b). There are many shrubs in the area, often dense and flowering with fruits, such as Dodonaea viscosa and Wikstromeia oahuensis, an endemic species (Cuddihy, 1988). This area also has a rich bird community, with species such as Pterodroma sandwichensis (Hawaiian Petrel), an endangered, endemic coastal bird (NPS, 2020). Additionally, Hawaii’s only reptile, Chelonia mydas (Green Sea Turtle), can also be found along the beaches of Makena (NOAA, n.d.a).


Schefflera actinophylla species range (USDA, n.d.b) and photo (Sorge, 2019).



Chelonia mydas species range (NOAA, n.d.a) and photo (The Nature Conservancy, 2020).

‘Ohe‘o Gulch Biotic Communities

    The area near ‘Ohe‘o Gulch is tropical rainforest and coastal. Since it is on the windward side of Mt. Haleakala, ‘Ohe‘o Gulch receives an abundance of rainfall (NOAA, n.d.b.). There are several unique freshwater animal species in the streams of the gulch, such as Sicyopterus stimpsoni (rock-climbing goby) and Macrobrachium grandimanus (Hawaiian prawn) (NPS, 2020b). There is also a rich diversity of plant communities in ‘Ohe’o Gulch, consisting of tropical trees, shrubs, flowing plants, fruit trees, epiphytes, coastal grasses, etc., (NPS, 2015a). One such shrub, Scaevola sericea (Naupaka), is very salt-tolerant with thick leaves and is one of a few species that are able to grow in the salt spray zone (NPS, 2015a). A common flowering plant, Hibiscus furcellatus, typically grows in wet, disturbed areas, and Asplenium nidus (Ēkaha) is an indigenous epiphyte that typically grows in dark rainforests (NPS, 2015a). Additionally, one uncommon indigenous tree, Pisonia umbellifera, has sticky fruits and were used by native Hawaiians to catch birds (Kuo et al., 2011; NPS, 2015a).

Scaevola sericea species range (USDA, n.d.c; *note that this data is not complete for Maui County, and the actual species range would be more restricted to coastal areas) and photo (National Parks Board, 2020).

Pisonia umbellifera species range (USDA, n.d.b) and photo (Geiger, 2016).

Mount Haleakala Disturbances

        Mount Haleakala National Park has had non-native vegetation, specifically trees, since 1909 when Ralph Hosmer planted his experimental plots (NPS, 2019). Hosmer was interested in exploring ways to boost Hawaii's economy via the timber industry, and his experiment was aimed at understanding what types of trees would grow at higher elevations (NPS, 2019). These non-native trees, including eucalyptus, pines, spruce, cedar, etc., established well in the area but started to outgrow native plant communities (NPS, 2019). Trees exceeding the bounds of the experimental zone were removed, and the NPS chose to make Hosmer's Grove a campsite and educational trail (NPS, 2019). The NPS now must closely monitor these invasive species and manage them so they do not become a disturbance again (NPS, 2019). 

        The area around Makena, as aforementioned, receives little rainfall and is now becoming a fire-controlled system due to anthropogenic influence (Cuddihy, 1988). Many native plants are only adapted to low water, thus allowing fire-adapted invasive species to establish and further dominate the landscape (Cuddihy, 1988). There is little undisturbed, native vegetation remaining in the area (Cuddihy, 1988). These two disturbances--fire-adapted invasive species and increased fires--likely help to perpetuate one another. The seeds from non-native vegetation can easily germinate and regrow, and the plants themselves may also promote fire (Smith & Tunison, 1992). In turn, fire is encouraged, and native species that were not fire-adapted may have a much harder time reestablishing (Smith & Tunison, 1992).

        Several areas around Mt. Haleakala have suffered from ungulate threats, but 'O'heo Gulch has suffered more than many other areas (NPS, 2015b). Ungulates, hoofed animals, are not native to Hawaii and have caused major defoliation and soil disturbances since they were introduced (Weller et al., 2010). Continual defoliation of vegetation has caused some irreversible damage to individual plants, which evolved with no way to protect against this type of disturbance (NPS, 2015b). In attempts to keep ungulates from several threatened, endangered, or otherwise endemic species, the NPS fenced in the upper elevations of the park to avoid the ungulates defoliating and disturbing those vegetation communities (NPS, 2015b). However, areas such as 'O'heo Gulch are still at risk of defoliation (NPS, 2015b).

Invasive eucalyptus trees that are a carefully managed tourist attraction (Shute, 2018).

2019 fires in South Maui County, near Makena (Maui News, 2019).

Defoliation and soil disturbance by feral hogs. Image taken only six months after the fence was built (Litton, n.d.).

Mount Haleakalā Stressors and Management

Anthropogenic Stressors

Several human-caused stressors threaten Mt. Haleakalā, and these stressors can be detrimental to the surrounding ecosystem. First, Mt. Haleakalā National Park is faced with acidification of the soil (NPS, 2019b), determined to be primarily due to anthropogenic air pollution and exasperated with volcanic eruptions (NPS, 2020a). The non-native tree community within Hosmer Grove has many species sensitive to acid deposition (NPS, n.d.). All of the species listed as sensitive are either pines, cedars, or firs and none are native to Mt. Haleakalā (NPS, n.d.), and the Eucalyptus globulus Labill. may also be affected due to its reliance on the soil. Almost every species exhibits reduced growth and/or survival due to acid deposition of sulfur and nitrogen in the area (NPS, n.d.). The response of species to acid deposition depends on the amount and cause of the deposition (Horn et al., 2018), and in the state of Hawaii, Mt. Haleakalā is ranked highest in terms of ecosystem sensitivity and risk (Sullivan et al., 2011). Second, as aforementioned, ‘O’heo Gulch struggles with non-native ungulates threatening native plant and animal populations (NPS, 2015c). Accidental and purposeful spread of these ungulates to Maui has promoted the threat (NPS, 2015c), and some management strategies have allowed ecosystems to recover to varying degrees (Stone et al., 1992). Native plants without any defoliation defense strategies are often eaten (NPS, 2015c), and many diseases have been introduced from the ungulates, one of the major threats to endangered honeycreepers (Audubon Society, 2018). It is more likely that ungulates threaten Scaevola sericea because the sticky sap of Pisonia umbellifera may act as a deterrent to the ungulates. Finally, the marine life in the beaches of Makena is threatened by anthropogenic degradation of watersheds and nutrient pollution (Maynard et al., 2019). There are higher than average amounts of nitrogen and phosphorus in the beaches around Makena, as well as higher levels of sedimentation (Maynard et al., 2019). However, the marine ecosystems on the leeward side of Maui have been classified as medium-high to high resilience systems, letting these systems recover quickly after instances of eutrophication and pollution (Maynard et al., 2019). Because it is primarily marine species affected by the water quality threats, it is more likely the Green Sea Turtle is negatively impacted than the Schefflera actinophylla.

Leaf damage to a macadamia tree after heavy smog exposure (Duff, 2018).

A non-native feral hog that arrived on Maui via human transport that defoliates native vegetation (Litton, n.d.).

Coral reef degradation in a dead zone that occurred from nutrient pollution (Coastal Care, 2017).

Climate Change

        Due to global climate change, small Pacific islands like Hawaii are projected to be highly impacted by temperature changes and rising sea levels (Christensen et al., 2018). In the A1B scenario, the temperature change of small, Pacific islands is expected to increase an average of 1.8°C, lower than the global mean (Christensen et al., 2018). Because Hawaii has high amounts of topographical change, it is expected that orographic rainfall will have dramatic variability (Christensen et al., 2018). On average, warm seasons are projected to increase by 100%, wet seasons will increase by 40%, and dry seasons will increase by 3% (Christensen et al., 2018). Because the Hawaiian Islands are small relative to global comparisons, it was challenging to find predictions for variability for specific locations on Mt. Haleakalā. However, there were some general predictions for the windward, leeward, and upper elevations of the island of Maui. Primarily on the windward side of Maui, from sea level elevations to the summit, rainfall has decreased by about 2% to 4% per decade since the 1920s (USGCRP, 2018). This includes both ‘O’heo Gulch and the National Park location. Additionally, areas on the leeward side of Mt. Haleakalā, including Makena, are projected to have up to 60% decreased rainfall according to the RCP8.5 scenario (USGCRP, 2018). Makena’s disturbance regime of fire and fire-adapted invasives will likely be exacerbated by climate change. The decreased rainfall could increase the frequency and intensity of fires, making them more challenging to manage while also promoting the fire adapted-invasives. In this instance, it is more likely that the terrestrial plant species Schefflera actinophylla will be negatively impacted. Because the ungulate disturbances in ‘O’heo Gulch are biotic, the ungulates may begin to move upwards in elevation as temperatures warm and shores are inundated. However, it is also possible that the native plants will also move up Mt. Haleakalā. Both example plant species are likely to suffer from the effects of climate change. Similarly, the invasive species in Hosmer Grove are also biotic disturbances, so they may also move up in elevation. However, many large abiotic factors change with elevation, such as increased rocky soils. This makes it difficult to predict how they will be influenced by climate change. The endangered honeycreeper will likely suffer more due to climate change because of the increased stressors. 

Conservation Plan

        In ‘O’heo Gulch, I recommend conservation of native species that are threatened by ungulates. This includes both plant species that are defoliated and the animals impacted by the spread of diseases. Additionally, I believe that it is also crucial to consider how the soil is impacted and degraded by ungulate traffic and rooting. With the removal of vegetation, there is also the potential for soil to erode into watersheds (Leopold & Hess, 2017; Stone et al., 1992). Plans to manage the population sizes of ungulate species or removal of them altogether should also be considered, although this can be expensive (Stone et al., 1992). Ungulate management could include expanding the fenced-in section of Mount Halakalā National park to include ‘O’heo Gulch. The recovery extent of these ecosystems impacted by ungulates varies, especially when considering the extent to which non-native species invade following defoliation and vegetation disturbances (Leopold & Hess, 2017). For this reason, restoration in these ecosystems may also be necessary to promote health and recovery (Leopold & Hess, 2017).
        The ecosystems surrounding Hosmer Grove in Mt. Haleakalā National Park are already carefully managed to prevent the spread of the invasive plant species. However, climate change may begin to cause the invasive species to disperse to higher elevations. This may also mean that the native plant and animal populations will suffer from increased habitat loss, and several of these native species are already endangered, threatened, or endemic to Hawai’i (NPS, 2015a). The NPS urges visitors to have safe practices when visiting the park in order to prevent the spread of invasives and destruction of native habitats (NPS, 2015a). This includes practices such as reminders to brush off seeds from hiking boots before entering and exiting the park and staying on designated trails (NPS, 2015a). In the future, it will be essential to monitor how climate change impacts the species range of invasives, as well as prevent rising threats to endangered and endemic species.
        Makena faces several stressors, many anthropogenic stressors, and includes both marine and terrestrial ecosystem threats. First, terrestrial threats are primarily due to invasives and fire (Cuddihy, 1988). These threats may be particularly difficult to manage because they likely promote each other. Fire clears away native species that are not adapted to fire and allows fire-adapted invasives to quickly establish and dominate the landscape (Smith & Tunison, 1992). In turn, the fire-adapted invasives likely have strategies to promote fire because it is favorable to them (Smith & Tunison, 1992). I suggest removing the invasives, better management of the fires, and restoration of the native species driven out by this disturbance regime. Second, marine threats such as nutrient pollution and sedimentation are causing instances of coral reef bleaching and degradation and promoting dead zones in the immediate ocean area (Maynard et al., 2019). I propose stricter management of nutrient usage, especially in areas in immediate proximity to a watershed. Runoff into the water systems ends up in the ocean, causing eutrophication to occur (Maynard et al., 2019). Increased monitoring and regulations are vital in the future to protect the health of marine ecosystems. 
When comparing each location, I believe that Makena is in the greatest need of management and conservation. Both ‘O’heo Gulch and the Hosmer Grove fall within the borders of Mt. Haleakalā National Park, granting them more management and monitoring by the NPS. Additionally, Makena faces both marine and terrestrial ecosystem threats due to anthropogenic stressors and disturbances. Further, how climate change will affect existing stressors in Makena are more straightforward than they are in the other two locations. Fires and fire-adapted invasive species will likely be exacerbated by climate change, and increases in ocean temperature will add increased stress on marine ecosystems already struggling with nutrient pollution and sedimentation. 

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