Observations

This experiment has achieved the goal of slowing down nutrient cycling in the forest; nutrient cycling is at least 80% lower, regardless of treatment! Moderate redundant plots have shown the most combined survival and growth of outplants. Redundant plots have the greatest native seedling recruitment. Moderate complementary plots appear to be the least resistant against invasive species.

  • Fruiting ʻieʻie
    ʻIeʻie (Freycinetia arborea) is only typically found in lowland wet forests, and is an indicator of a healthy forest. We have found ʻieʻie growing in many of our plots! 

Survival and Growth

Slow redundant plots have the greatest outplant survival over the years, with moderate redundant in second (Figure 9). However, slow redundant sees the lowest growth based on basal area, while moderate redundant plots have the greatest (Figure 10). Some outplants that did especially well in terms of survival and growth include kukui, ʻulu, mango, false kamani, neneleau, avocado, kamani, and ʻōhiʻa ʻai. On the other hand, māmaki, hame, and kōlea lau nui had very low survival.

A graph showing outplant survival (%) over the course of five years. Slow redundant had the greatest outplant survival, followed by moderate redundant. Slow complementary and moderate complementary tied for the lowest outplant survival.
Figure 9. Outplant survival (%) across the treatments for 6 census dates since the experimental start in January 2014. Values are means + SE. Letters that are different at the last timepoint in February 2018 indicate significant differences (p ≤ 0.05) among treatments.
Outplant basal area (m^2/ha) by treatment. Slow redundant had the lowest basal area, while moderate redundant had the highest. Slow complementary and moderate complementary fell in the middle, but did not differ from one another.
Figure 10. Outplant basal area across the treatments for the census date (February 2018) that represents five years of growth. Values are backtransformed least-square means +/- 95% confidence limits. Letters that are different denote statistically significant differences among the four experimental treatments.

Reproduction and Regeneration

Slow complementary plots show the greatest amount of fruiting, and moderate redundant had the second most fruiting. For all plots but moderate complementary, existing native plants have significantly more seedlings than outplants (Figure 11a). Existing native recruitment was greatest form slow redundant and moderate redundant, and lowest for moderate complimentary (Figure 11b).

Slow complementary plots showed the greatest amount of fruiting, and moderate redundant had the second most fruiting. For all plots but moderate complementary, existing native plants had significantly more seedlings than outplants. Existing native recruitment was greatest form slow redundant and moderate redundant, and lowest for moderate complimentary.
Figure 11. Mean number of fruiting outplant individuals per month compared between treatments and across five years of data collection (a). Values are means + SE. Lower case letters denote statistically significant differences among the four experimental treatments for the most recent census year. Seedling recruitment (#/m²) of native seedlings from ‘Existing’ native seed source (filled circles) and planted native/exotic seedlings from the ‘Outplant’ native/exotic seed source (open circles) recorded in 2018, across the treatments (b). Values are least-square means + 95% confidence limits. Letters denote statistically significant differences across the four experimental treatments.

Invasion Resistance

Weeding effort is greater in moderate complementary plots than all other treatments (Figure 12), suggesting it is the least resistant to invasive species encroachment.

Graph showing the weeding effort required for each treatment. Weeding time is significantly higher in moderate complementary than all other treatments.
Figure 12. Weeding effort (# person hours per plot), for the most recent 6-month maintenance interval (July 2018-Dec 2018), which represents the fifth year of the experiment. Values are backtransformed least-square means +/- 95% confidence limits. Letters denote statistically significant differences among the four experimental treatments.

Nutrient Cycling

Different functional traits modify the environment in different ways. One goal of this project was to reduce light levels in the understory as well as the rate of nutrient cycling to make the forest lest prone to invasion. A greater leaf area index equates to more leaf layers in the canopy and therefore a darker understory. Moderate redundant plots had the greatest leaf area index, whereas slow complimentary and moderate complementary plots had the lowest (Figure 13). Moderate redundant plots also had the greatest amount of nutrients released from litterfall, significantly more than slow redundant and slow complimentary plots (Figure 14).

Graph showing leaf area index (LAI, m^2 leaf/m^2 ground) by treatment. Moderate redundant plots had the greatest LAI, followed by slow redundant, and then slow complementary and moderate complementary both having the lowest.
Figure 13. Leaf area index (LAI, m^2 leaf m^-2 ground) in the four treatments. Values are backtransformed least-square means + 95% confidence limits. Letters denote statistically significant differences among the four experimental treatments.
Graph showing Nitrogen release in litterfall (g N/plot) by treatment. Moderate redundant plots had the highest N released, while slow redundant and slow complementary had the slowest N release. Moderate complementary plot did not significantly differ from any treatment, falling in the middle.
Figure 14. Nitrogen (N) released from litterfall across the four experimental community treatments (SLOW RED, MOD RED, SLOW COMP, and MOD COMP). Values are back-transformed means +/-95% confidence intervals. Letters indicate significant differences among treatments. The same patterns were seen for two other nutrients: carbon (C) and phosphorus (P).
Niu (Coconut) — Cocos nucifera Family: Arecaceae Polynesian-Introduced Habitat: Dry to mesic, coastal Elevation: Sea level to 600 m Outplanted in: Slow Redundant, Moderate Complementary Fun Fact: Not only an excellent food source, niu can also be used for oil, rope, weaving, thatching, and endless other possibilities. Ka niu peʻahi kanaka o Kaipalaoa (1502) The man-beckoning coco palms of Kaipalaoa
ʻUlu — Artocarpus altilis Family: Moraceae Polynesian-Introduced Habitat: Mesic to wet, coastal Elevation: sea level to 650 m Outplanted in: Moderate Redundant, Moderate Complementary Fun Fact: An ʻulu tree is traditionally planted when a child is born to ensure that the child has a lifetime of food. ʻAʻohe ʻulu e loaʻa i ka pōkole o ka lou (213) No breadfruit can be reached when the picking stick is too short
ʻŌhiʻa ʻai — Syzygium malaccense Family: Myrtaceae Polynesian-Introduced Habitat: Mesic to wet, high humidity Elevation: sea level to 600 m Outplanted in: Slow Redundant Fun Fact: ʻŌhiʻa ʻai, also known as mountain apple, not only has delicious fruits, but can also be used medicinally. Traditionally, the bark is used to treat sore throats and deep cuts, and the leaves can be crushed and injested as a treatment for bronchitis. ʻŌhiʻa noho malu (2362) Mountain apple in the shade (Said of a beautiful person compared to an ʻōhiʻa ʻai that ripens perfectly in the shade)
Noni — Morinda citrifolia Family: Rubiaceae Polynesian-Introduced Habitat: Dry to wet, coastal Elevation: 1 to 800 m Outplanted in: Slow Complementary Fun Fact: Noni is not known for being particularly tasty. However, it is well known for its medicinal properties, used to treat a variety of ailments. The roots and bark can also be used to create a dye for kapa. Noni is the kinolau of Kū, the Hawaiian god of war. He noni no Kaualehu, he pūhai aʻa (845) It is a noni tree of Kaualehu whose roots are in shallow ground
Milo — Thespesia populnea Family: Malvaceae Indigenous Habitat: Dry to wet forest with volcanic soil, coastal Elevation: Sea level to 150 m Outplanted in: Slow Complementary, Moderate Complementary Fun Fact: Milo flowers start out bright yellow with a maroon center in the morning, and fade to orange throughout the day. Milo is traditionally used in cordage, to produce tannin, dye, oil, medicine and gum, and also skillfully crafted into food bowls called ‘umeke ‘ai. He milo ka lāʻau, mimilo ke aloha (818) Milo is the plant; love goes round and round
Manakō (Mango) — Mangifera indica Family: Anacardiaceae Introduced Habitat: Dry to wet, coastal Elevation: Sea level to 1,200 m Outplanted in: Slow Redundant, Moderate Redundant, Slow Complementary Fun Fact: Mango was introduced to Hawaiʻi in the late 1800s. Although the fruit is delicious, you must be careful when picking it! The white sap that oozes from the fruit and stem during harvesting is toxic and can cause rashes or blistering, much like poison ivy, which is in the same family.
Monkeypod — Samanea saman Family: Fabaceae Introduced Habitat: Dry to wet forest, riparian corridors Elevation: Sea level to 300 m Outplanted in: Moderate Redundant, Moderate Complementary Fun Fact: Native to South and Central America, monkeypod trees are stars when it comes to carbon sequestration. One mature tree can absorb 28.5 tons of carbon per year!
Pea (Avocado) — Persea americana Family: Lauraceae Introduced Habitat: Mesic to wet forest, well drained soils Elevation: Sea level to 2,500 m Outplanted in: Moderate Redundant, Slow Complementary Fun Fact: There are 107 varieties of avocado grown on Hawaiʻi Island. Not only are they delicious, but you can also use the pits and skins to make a dusty-rose colored dye.
Kukui — Aleurites moluccanus Family: Euphorbiaceae Polynesian-Introduced Habitat: Mesic to wet forest, gallery forests Elevation: Sea level to 800 m Outplanted in: Slow Complementary, Moderate Complementary Fun Fact: Kukui has an abundance of uses, from creating lei with the leaves and nuts, to spreading the oil over the surface of the sea to allow fishermen to see the fish more clearly. The most well-known use, which Kukui gets its name from, is lighting the oily nuts to use as a light source. Ka malu hālau loa o ke kukui (1474) The long shelter of the kukui trees
False Kamani — Terminalia catappa Family: Combretaceae IntroducedHabitat: Mesic to wet forest, coastal Elevation: Sea level to 400 m Outplanted in: Moderate Redundant Fun Fact: False kamani was introduced by the first European settlers for shade and as an ornamental. It is native to southeast Asia and the Pacific.
Kamani — Calophyllum inophyllum Family: Calophyllaceae Polynesian-Introduced Habitat: Dry to mesic to wet forest, coastal Elevation: Sea level to 200 m Outplanted in: Slow Redundant, Slow Complementary Fun Fact: Kamani was brought to Hawaiʻi by early Hawaiians for the utility of the wood, which could be fashioned into waʻa, ʻumeke, and food vessels. In kapa making, the fruit can be used for dye, the flowers for scenting, and the oil for waterproofing.
Hame — Antidesma platyphyllum Family: Phyllanthaceae Endemic Habitat: Mesic to wet forest Elevation: 500 to 1,100 m Outplanted in: Slow Redundant ** No longer present in the plots due to high mortality Fun Fact: Hame has edible fruits that can also be used to make a red dye. The wood is traditionally used as an anvil to prepare wauke fibers for kapa.
Loulu — Pritchardia beccariana Family: Arecaceae Endemic Habitat: Dry to mesic to wet forest, coastal Elevation: 300 to 1,270 m Outplanted in: Slow Redundant, Slow Complementary, Moderate Complementary Fun Fact: In Molokaʻi moʻolelo, a person could use loulu leaves as wings to glide on the wind from Molokaʻi to Maui. However, they would only succeed if they were good with their naʻau and ʻaumakua.
Kōlea lau nui — Myrsine lessertiana Family: Primulaceae Endemic Habitat: Mesic to wet forests Elevation: 300 to 2,290 m Outplanted in: Moderate Redundant, Moderate Complementary Fun Fact: A red dye made from the sap of Kōlea is traditionally used to dye kapa. Evidence of Kōlea char in ancient oceanside fire bits on Oahu show that it once grew at much lower elevations than it is found at today.
Hāpuʻu — Cibotium spp. Family: Cibotiaceae Endemic Habitat: Mesic and wet forest Elevation: 250 to 1,700 m Outplanted in: Slow Redundant, Moderate Redundant Fun Fact: Our plots have two endemic species of hāpuʻu: hāpuʻu pulu (C. glaucum), which is known for the golden hairs at the base of the fronds, and hāpuʻu iʻi (C. menziesii) which is characterized by black hairs at the base of the fronds. Hapuʻu is considered a famine food because it takes so long to prepare. He hāpuʻu ka ʻai he ʻai make (568) If the hāpuʻu is the food, it is the food of death
Alaheʻe — Psydrax odoratus Family: Rubiaceae Indigenous Habitat: Dry shrubland, dry to mesic forest, sometimes wet forest Elevation: 10 to 860 m Outplanted in: Slow Redundant, Moderate Redundant, Moderate Complementary Fun Fact: Alaheʻe is the kinolau of Kanaloa. Its leaves can be used to create a black dye, resembling the ink of its ocean counterpart, the heʻe (octopus). The dense wood is often used to create fishing implements.
Hala — Pandanus tectorius Family: Pandanaceae Indigenous Habitat: Coast or slopes of mesic valleys Elevation: Sea level to 600 m Outplanted in: Slow Redundant, Slow Complementary, Moderate Complementary Fun Fact: Lei hala are traditionally used for funerals and to honor the dead. The leaves are often used for weaving; people once demonstrated their wealth based on how many woven hala mats they had stacked in their home. He iki hala au no Keaʻau, ʻaʻohe pōhaku ʻalā e nahā ai (624) I am a small hala fruit of Keaʻau but there is no rock hard enough to smash me
Māmaki — Pipturus albidus Family: Urticaceae Endemic Habitat: Mesic to wet forest Elevation: 70 to 1,870 m Outplanted in: Slow Complementary, Moderate Complementary Fun Fact: Māmaki can be made into a tea that is both calming and good for the circulatory system. The fruit is traditionally eaten by women to aid in child birth. Māmaki is the host plant for the increasingly rare King Kamehameha butterfly.
Neneleau — Rhus sandwicensis Family: Anacardiaceae Endemic Habitat: Dry to wet disturbed areas Elevation: 150 to 750 m Outplanted in: Moderate Redundant, Slow Complementary Fun Fact: Neneleau was one of few native plants that was able to re-colonize old sugar cane fields in which the soil had been severely degraded and contaminated with toxins like arsenic. Pua ka neneleau, momona ka wana (2696) When the neneleau blooms, the sea urchin is fat
Hawaiʻi ʻOhe — Polyscias hawaiensis Family: Araliaceae Endemic Habitat: Mesic to wet forest Elevation: 150 to 800 m Outplanted in: Moderate Redundant Fun Fact: The ʻOhe is among trees at Maunaloa, Molokaʻi posessed by the poison gods, Kāneikaulanaʻula and Kahuilaokalani, and the goddess Kapo. To tamper with the wood is to invite serious trouble. The berries are traditionally eaten by mothers to help produce milk that improves the growth and health of their baby.
Lama — Diospyros sandwicensis Family: Ebenaceae Endemic Habitat: Dry to mesic forest Elevation: 5 to 1,220 m Lama was already present at the project site and was left during clearing; it is therefore found in all treatments though none were outplanted. Fun Fact: The wood of lama is traditionally used medicinally and to fence off areas that are kapu such and for heiau construction. The small, red fruits are edible when ripe! Lama translates to “light”, as the plant is associated with enlightenment.
Kōpiko — Psychotria hawaiiensis Family: Rubiaceae Endemic Habitat: Dry, mesic, to wet forest Elevation: 150 to 1,590 m Kōpiko was already present at the project site and was left during clearing; it is therefore found in all treatments though none were outplanted. Fun Fact: Kōpiko has a hard, dense wood that is traditionally used for beating kapa. Kōpiko is named for the the distinctive line of glands along the bottom of the central vein (piko) of each leaf. Ke kōpiko i ka piko o Waiʻaleʻale (1756) A kōpiko tree on the summit of Waiʻaleʻale (A boast about an outstanding person)
‘Ōhi‘a lehua — Metrosideros polymorpha Family: Myrtaceae Endemic Habitat: Dry, mesic, to wet forest Elevation: Sea level to 2,500 m ‘Ōhiʻa was already present at the project site and was left during clearing; it is therefore found in all treatments though none were outplanted. Fun Fact: While in a jealous rage, Pele transformed her romantic interest, ʻŌhiʻa, into this gnarled tree. The lover of ʻŌhiʻa, Lehua, asked her ʻaumakua for help, so they transformed her into the flower to keep the lovers together. It is said that if you pick the lehua, it will rain because the lovers mourn their separation. Welehu ka malama, liko ka ʻōhiʻa (2932) Welehu is the month the ʻōhiʻa put forth leaf buds