Integrating ecology and economics to facilitate effective seabird restoration: Hawaii case study
I. Nutrient Cycling
Abstract:
Allochthonous nutrient flow from marine sources via seabirds to the terrestrial habitats where they nest can impact resident organisms and neighboring ecosystems. Seabird populations are decreasing both in Hawai‘i and globally, yet little is known about what is being lost from the ecosystems where they traditionally nested in large numbers. Given the marked decline in seabirds, we hypothesized that current sparsely populated seabird colonies in wet montane ecosystems of Hawai‘i contribute minimally to nutrient availability, but that this small contribution should still be reflected in vegetative uptake of soil N and in plant community composition. Soil nutrient availability on Kaua‘i was assessed using ion-exchange resin probes. Plant and soil uptake of marine-derived nitrogen was determined using δ 15N values in soil and foliage of the two dominant species using a two-end member N isotope mass balance mixing model. To determine if the added nutrients impacted the plant community, we also compared canopy cover (total and by dominant species) and species richness between treatments. Soil in seabird areas had more available ammonium, but nitrate and total inorganic N did not differ between sites. The dominant canopy tree, Metrosideros polymorpha, derived 28% of foliar N from marine sources; this value was 15% for the dominant understory plant, Dicranopteris linearis. Plant species composition was not influenced by presence or absence of seabirds. Because N plays a large role in net primary productivity, use of marine-derived N by native plants under even limited seabird populations is likely important to functioning of these ecosystems.
Abstract:
Allochthonous nutrient flow from marine sources via seabirds to the terrestrial habitats where they nest can impact resident organisms and neighboring ecosystems. Seabird populations are decreasing both in Hawai‘i and globally, yet little is known about what is being lost from the ecosystems where they traditionally nested in large numbers. Given the marked decline in seabirds, we hypothesized that current sparsely populated seabird colonies in wet montane ecosystems of Hawai‘i contribute minimally to nutrient availability, but that this small contribution should still be reflected in vegetative uptake of soil N and in plant community composition. Soil nutrient availability on Kaua‘i was assessed using ion-exchange resin probes. Plant and soil uptake of marine-derived nitrogen was determined using δ 15N values in soil and foliage of the two dominant species using a two-end member N isotope mass balance mixing model. To determine if the added nutrients impacted the plant community, we also compared canopy cover (total and by dominant species) and species richness between treatments. Soil in seabird areas had more available ammonium, but nitrate and total inorganic N did not differ between sites. The dominant canopy tree, Metrosideros polymorpha, derived 28% of foliar N from marine sources; this value was 15% for the dominant understory plant, Dicranopteris linearis. Plant species composition was not influenced by presence or absence of seabirds. Because N plays a large role in net primary productivity, use of marine-derived N by native plants under even limited seabird populations is likely important to functioning of these ecosystems.
II. Modeling Seabirds of the past, what would they have contributed to the Hawaiian ecosystem in the pre-human past?
In the past Hawaii was host to over 20 seabird species. Currently only six breed in the main Hawaiian Islands. Bird populations have declined due to predation by introduced predators, loss of nesting habitat to development, loss of habitat due to trampling and rooting by ungulates, fall out from collisions with power lines and man made structures, and fallout from light pollution. With the drastic seabird loss since the arrival of people 1500 years ago, what does this mean for the ecosystem services that the seabirds once provided? With the seabirds at a fraction of the density of historical numbers, what does the nutrient loss mean for the ecosystems where they were once found?
III. Economic assessment of seabird restoration action in Hawaii
Another piece to the puzzle is restoration of seabirds to nesting areas. With this assessment, I am investigating the different seabird restoration actions currently employed in Hawaii and assessing the costs as well as the primary and secondary ecosystem services benefits that come along with the different actions. This project is a work in progress, but will be posted here as soon as possible.
III. Economic assessment of seabird restoration action in Hawaii
Another piece to the puzzle is restoration of seabirds to nesting areas. With this assessment, I am investigating the different seabird restoration actions currently employed in Hawaii and assessing the costs as well as the primary and secondary ecosystem services benefits that come along with the different actions. This project is a work in progress, but will be posted here as soon as possible.
Predator proof fence at Kaena point, Oahu rodent control - in use in Maui and Kauai Ungulate fencing in Upper Limahuli, Kauai