Enhancing Aboveground Carbon Storage and Invasion Resistance through Restoration: Early Results from a Functional Trait-Based Experiment1 Donald D. Rayome,2,5 Rebecca Ostertag,3 and Susan Cordell 4 Abstract: One of many ecosystem services essential to land management is car- bon regulation, but presence of invasive species can infuence carbon (C) in un- desirable ways. Here we discuss early results of C accumulation from the Liko Nä Pilina hybrid wet forest restoration experiment. The focus of our project is to deliberately increase C storage through a functional trait-based approach to restoration. By choosing plant species mixes with specifc functional trait values, a novel ecosystem can be assembled that supports desired ecosystem services such as C regulation. We designed species mixtures based on species rate of C turnover (slow or moderate) and their position in trait space (complementary or redundant functional trait values). New species mixes were planted as four treat- ments (Slow Redundant, Slow Complementary, Moderate Redundant, and Moderate Complementary), with an additional unmanaged Reference treat- ment. Our objective was to compare C in aboveground woody biomass using allometric equations to determine which mixture had the greatest potential for site restoration, balancing carbon storage with the eventual goal of creating for- ests better able to resist establishment by invasion species. Initially, we predicted the Moderate Complementary treatment would have increased C storage. How- ever, we found that the Moderate Redundant treatment had the greatest C stor- age, largely driven by a few fast-growing species during early development. Even though our short-term results did not support our experimental prediction, these data serve as an important benchmark for contrasting with later results when ecological succession might favor complementary species mixes for sus- tainable biomass productivity and decreased management efforts. Rapid changes in the world’s ecosystems Anthropocene can be described as an era of from human activities (Chapin et al. 2000, ecosystem novelty, or ecosystems existing Mascaro et al. 2008, Cusack et al. 2016) have without analogues in historical or modern resulted in a new era of human-dominated reference conditions (Hobbs et al. 2009, ecosystems: the Anthropocene (Morse et al. Montoya and Raffaelli 2010, Catford et al. 2014, Lugo 2015, Bai et al. 2016). Due to un- 2012). As changing species abundances and precedented levels of human infuence, the successional patterns alter ecosystem func- 1 Funding for this work originated from Strategic project RC-2117, “Liko Nä Pilina: Developing Novel Environmental Research and Development Program Ecosystems that Enhance Carbon Storage, Native Bio- diversity, and Human Mobility in Lowland Hawaiian Forests.” Manuscript accepted 28 June 2017. 2 Northern Marianas College Cooperative Research, Pacifc Science (2018), vol. 72, no. 1:149–164 Extension, and Education Service, P.O. Box 501250 CK, doi:10.2984/72.1.10 (Includes online supplements) Saipan, MP 96950. This article was created by a U.S. government employee 3 University of Hawai‘i at Hilo, 200 Käwili Street, and is in the public domain. Public domain information Hilo, Hawai‘i. may be freely distributed and copied, but it is requested 4 Institute of Pacifc Islands Forestry, U.S. Forest Ser- that in any subsequent use the Smithsonian Institution vice, 60 Nowelo Street, Hilo, Hawai‘i. and the journal, Pacifc Science, be given appropriate 5 Corresponding author: donald.rayome@marianas acknowledgment. .edu. 149 150 PACIFIC SCIENCE · January 2018 tions and processes, consequences or potential ations, and functional changes inhibit a return benefts of novelty can be diffcult to ascertain to previously known forest types and support (Mascaro et al. 2008, Kueffer et al. 2010, a need for carbon management. Hulvey et al. 2013). The challenge of manag- One strategy to promote desired levels of ing novel landscapes and understanding their carbon accumulation and cycling is to use a effects requires new strategies that extend be- functional trait-based approach to assemble yond recovering historical compositions and plant communities that support desired ser- processes (Hobbs et al. 2011) and instead vices such as carbon storage. Functional traits focus on resulting ecosystem services (Har - relate to the expression of various morpho- borne and Mumby 2011, Hulvey et al. 2013). logical, structural, physiological, or chemical One of many ecosystem services essential traits of organisms. For example, selecting to land management is carbon regulation species with a broad range of functional trait (Vitousek, D’Antonio, et al. 1997; Vitousek, expressions may preclude species invasions if Mooney, et al. 1997; Foley et al. 2005). Land the chosen functional traits are already repre- managers are likely to be interested in carbon sented in the community (Pokorny et al. 2005, storage from economic and legal standpoints Funk et al. 2008). Because plant functional and as a powerful complement to restoration traits relate to resource capture and process- (Huston and Marland 2003, Lubowski et al. ing ability, it is likely that a plant species’ posi- 2005, Torres et al. 2010, Evans et al. 2015, tion in trait space infuences its ability to cycle Asner et al. 2016). Humans often diminish carbon in ways that affect long-term storage. the capacity of terrestrial ecosystems to store Complementary assemblages of species in a carbon through utilization, degradation, and community are hypothesized to increase eco- biological invasion (Ciccarese et al. 2009). As system service variety, species performance, a result, many ecosystems greatly affected by and invasion resistance, and redundant assem- humans tend to release more carbon than blages likely concentrate services (Hooper they store (Foley et al. 2005, Fargione et al. 1998, Funk et al. 2008). Traits associated 2008, Pongratz et al. 2009). However, there with slower C cycling place many natives in a are several examples of management activities trait space that is at a disadvantage when com- such as reforestation and ecosystem service peting with invasives, especially where traits restoration that can help to reduce carbon loss that promote faster C cycling overlap with (Albrecht and Kandji 2003, Chazdon 2008, traits that promote weediness or inhibit na- Ciccarese et al. 2009). tive species recovery (Cardinale et al. 2011). Rates of carbon accumulation and cycling As succession progresses, functional traits are strongly infuenced by climate such that that allow a given species to take advantage of tropical forests often contain the highest car- fuctuating environmental conditions likely bon pools (FAO 2010, Raunikar et al. 2010, become less infuential. Rather, traits that Payn et al. 2015). Land managers working in promote successful competition and resource tropical ecosystems can use these high rates to co-opting become more pertinent (Lohbeck their advantage. Hawaiian forests store sub- et al. 2014), with highly productive or other- stantial amounts of carbon, comparing favor- wise infuential species often driving ecosys- ably with their global tropical counterparts tem performance measures (Cardinale et al. (Asner et al. 2011, Ostertag et al. 2014) even 2011). Thus reducing interspecifc competi- with proportionally fewer native tree species, tion through more complementary functional and thus present a unique opportunity to composition (Suding et al. 2008, Hooper examine carbon cycling in a simplifed con- and Dukes 2010) becomes important when text. Further, species invasions, disease, and assessing the trade-offs necessary to meet other anthropogenic pressures (Hughes and ecosystem management objectives. However, Denslow 2005, Asner et al. 2016, Crow et al. complementary species mixes may not be 2016) impact forests on all islands. Resulting advantageous at all stages of restoration be- novel species compositions, structural alter- cause early stages may require species with Enhancing Aboveground Carbon Storage through Restoration · Rayome et al. 151 fast rates of growth that quickly yield suit- ment, we investigated 15 functional traits of able microclimatic conditions within a site native and exotic candidate species that could (Sonnier et al. 2012, Fry et al. 2013, Ostertag be found living in the lowland wet forest com- et al. 2015). munity in East Hawai‘i Island. Species were Functional trait-based restoration has classifed as exotic as opposed to invasive rarely been tested in most forested ecosys- based primarily on the Hawai‘i Weed Risk tems (Lavorel 2013, Ostertag et al. 2015). Assessment score [Daehler et al. 2004 (see The Liko Nä Pilina hybrid lowland wet forest www.botany.hawaii.edu /faculty/daehler/ restoration experiment addresses functional wra/)]. To focus on C, we ran a Principal trait effects in terms of complementary versus Component Analysis (PCA) on a subset of redundant experimental plant communities, traits related to C allocation (leaf mass per acknowledging both the need for support- area, foliar C : N, stem specifc gravity, maxi- ing native species integrity as well as the reali- mum height, stature in the feld, and inte- ties of restoring in areas subject to constant grated water-use effciency) to calculate spe- invasion pressure and human use. Carbon is cies arrangement in trait space. We identifed an ecosystem variable readily assessed over core species that had sets of traits that can lead a shorter time frame (Ostertag et al. 2009, to either