Liko Nā Pilina - The hybrid ecosystems project

What's in a name?

Loosely translated, 'liko nā pilina' means "Budding (or growing) new partnerships (or relationships)" in the Hawaiian language. We chose this name for the project because our goal is to create novel communities to restore degraded Hawaiian lowland wet forest, using both native and non-invasive, non-native species. In other words, we are creating new forests using some plants which evolved in Hawai'i and others that have come here from around the world. For example, our plots include Hawaiian ōhi'a (Metrosideros polymorpha) and kōpiko (Psychotria hawaiiensis), as well as kukui (Aleurites moluccana, also known as candlenut in Australia) which arrived in Hawai'i with the Polynesians, and mango (Mangifera indica) which is a much more recent arrival (and is originally from India). 

What are we trying to do & why? 

The Hawaiian archipelago, like other oceanic islands, is very susceptible to biological invasions. Because of the archipelago's long isolation, it became home to unique flora and fauna which evolved on the islands. Although Hawaii's native biodiversity was relatively low (especially in comparison to other tropical biomes), the rates of endemism on the islands were very high. With the arrival of humans came a variety of new species and the extinction of some native species. In particular some species which have been introduced have become invasive- that is, they thrive in their new habitat to the extent that they are detrimental to native species and ecological functioning of native ecosystems.

Lowland wet forests in Hawai'i have been hit especially hard by human activities and invasive species, to the point where there are very few of these forests left. The forest at our study site, the Keaukaha Military Reservation (KMR), is important because it still has native species in the canopy, particularly ōhi'a, lama (Diospyros sandwicensis) and kōpiko. However, the presence of a multitude of invasive species means that even though the native species are present, there is very limited recruitment of seedlings happening. In other words, while the adults are surviving and some of their seeds may persist in the soil, few-if-any seedlings are surviving into adulthood. It's a case of 'dead men standing': when the existing adults die, this forest will become wholly made up of exotic and invasive species.

Our project has two main goals, the first is to restore the forest in line with the land manager's (KMR) wishes. This means putting together a forest community that minimizes ongoing management costs and effort, maximizes carbon storage, creates an open understory and benefits native biodiversity. The second goal is to test ideas about how to go about restoring complex ecosystems (such as rain forests), and to increase our understanding about how communities assemble and persist in nature. To accomplish these goals, the first step is to remove the invasive species from our study plots. While 'weeding' sounds fairly simple and straightforward, things become a little more complicated when your weeds happen to be ~30 meters tall and have multiple trunks which are fairly entangled with other trees in the high canopy!! See photos here.

What are we doing, exactly?

The first step was to clear our plots of invasive species- this took us nearly a year to accomplish! The next, and very exciting, step was planting! See photos here. But how did we choose what species to plant? We used a system based on plant species' functional traits. That is, a series of measurements that can give you an idea of a species' functional role within a given environment. For example, data from leaf chemistry and wood density can tell you what sort of strategy (on the "live fast, die young" - "grow conservatively and slowly" spectrum) a species uses. We also collected seed data (to get an idea of reproductive output/costs/dispersal), light use and water use, etc... In total we looked at 19 traits for nearly 40 species of native and non-native, non-invasive species.

Why not use just native species for restoration? 

We are using a mix of native and non-native species because native species alone (at least in KMR) are unable to maintain their recruitment levels and keep the invasive species out. Previous work at KMR has shown that invasive species quickly recolonize plots after removal. Although maintaining plots relatively weed-free becomes a lot easier after the invasive seed bank is exhausted, this still involves hundreds of intensive people-hours in the field. This is not feasible for KMR either from an ecological or economic perspective. It's not that we don't think native species should be used... we just think restoring this site to a functional forest (which includes native species, and their seedling recruitment) is more feasible if we mix native and non-native species.  

Based on species traits, our hypothesis is that using a mixture of species will create a more diverse and complimentary "trait space", than if we just used native species. In other words, it will be harder for the invasive species to get a foothold and outcompete the rest of the plants in a "hybrid" community than in a solely native one. This means that our novel communities should be able to sustain themselves with a lot less management (after the initial push) than a community made up only of native species. An important thing to mention is that we are not even thinking of introducing new species to the Big Island! All of the species considered have been here for quite some time, have shown not to be invasive here, and, in many cases, are already found at KMR.

Who is this "we" you keep mentioning? 

Rebecca Ostertag (University of Hawai'i at Hilo), Susan Cordell (USDA Forest Service at IPIF) and Peter Vitousek (Stanford University) are the PI's (or primary researchers) working on the project. Other UHH team members include Nicole DiManno, Jodie Schulten and Corie Yanger. Other Forest Service staff include Amanda Uowolo, Taite Winthers and myself. Other Stanford people include Bill Buckley- our chainsaw-meister and artist extraordinaire. PIPES Interns include Malia Stewart, Stephen McAuliffe and Jose Ivan Martinez Martes. Funding was provided by the Strategic Environmental Research and Development Program (SERDP), which is administered by the Department of Defense (Grant # RC-2117) Here we are at work- On the news and via a UH video

Importantly, we've had an amazing group of volunteers, visitors and interns without whose help we would not have gotten as far as we have!

Links and references: 

Cordell S, et al. 2009. Evaluating barriers to native seedling establishment in an invaded Hawaiian lowland wet forest. Biological Conservation (142): 2997-3004.

- Ostertag R, et al. 2009. Ecosystem and restoration consequences of invasive woody species removal in Hawaiian lowland wet forest. Ecosystems (12): 503-515.