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 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 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 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 ( 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 slow or moderate rates of C turnover Cordell et al. 2016). As an experiment, Liko (Table 1). Remaining species in each treat- Nä Pilina consists of a reference (invaded ment were selected by calculating the cen- forest) and four restoration treatments in troid of the four core species and then choos- which natives were left in place, all nonnative ing species (based on Euclidean distances) species were cleared, and different mixtures that were either similar (near) in trait expres- of 10 redundant or complementary species sion to the core species (Redundant) or differ- were planted. Noninvasive nonnative species ent (far) (Redundant). Four treatment com- (exotic) were combined with natives to fll binations exist: Slow Complementary, Slow ecological roles and aid in guiding site biodi- Redundant, Moderate Complementary, and versity toward species assemblages that pro- Moderate Redundant. Intact invaded refer- mote preferred ecosystem functions and ser- ence plots served as a control for comparison. vices such as slower carbon cycling rates. In Lowland [30 m above sea level (a.s.l.)] this project, we tested how species assem- wet forest portions of the Keaukaha Military blages store carbon at an early experimental Reservation (KMR, 19° 42′ 15″ N, −155° 2′ stage, leading to the following hypothesis: 40″ W) in Hilo, Hawai‘i, serve as the test The species mixture with a combination of location (Ostertag et al. 2015). The site is “Moderate” C cycling species and the “Com- located on an ‘a‘ä lava fow occurring 750– plementary” functional trait species will have 1,500 yr ago, with annual temperature aver- the highest C storage capacity as measured by age 22.7°C (Giambelluca et al. 2014) and aboveground woody biomass. Such early car- average annual rainfall 3,347 mm (Giambel- bon storage results are an important bench- luca et al. 2011). Native canopy but limited mark for comparison with later successional native tree regeneration (Cordell et al. 2009) stages when biotic and abiotic limitations may and heavy invasion by nonnative, invasive differ. and characterizes forests at KMR [approximately 45% of basal area (Ostertag et al. 2009)]. Reference treatment plots re- materials and methods ceived no management, but the four experi- Experimental Design and Study Site mental treatments were cleared before plant- ing. Experimental nonnative tree species The process of developing treatments in the clearing began in late July 2012 and ended in Liko Nä Pilina experiment is described in mid-April 2013, and native tree species were Ostertag et al. (2015) and is briefy summa- left intact. Introduced trees that were at least rized here. To choose species for the experi- 50% rooted in a plot or had a tree canopy that TABLE 1 Species in the Liko Nä Pilina Experiment, Noting Presence of Each Species in the Four Hybrid Community Treatments

Species Slow Moderate Slow Moderate Species Code Origina Scientifc Name Family Redundant Redundant Complementary Complementary Existing

ALEMOL E Aleurites moluccana Euphorbiaceae X X ANTPLA N platyphyllum X ARTALT E Artocarpus altilis Moraceae Core Core CALINO E Calophyllum inophyllum Clusiaceae Core Core CIBGLA N /glaucum Cibotiaceae X X X COCNUC E Cocos nucifera X X DIOSAN N Diospyros sandwicensis Ebanaceae X MANIND E Mangifera indica Anacardiaceae Core Core X METPOL N X MORCIT E Morinda citrifolia Moraceae X MYRLES N Myrsine lessertiana Myrsinaceae Core Core X PANTEC N Pandanus tectorius Pandanaceae Core X Core X PERAME E Persea americana Lauraceae X X PIPALB N Pipturus albidus Urticaceae X X X POLHAW N Polyscias hawaiensis Araliaceae X X PRIBEC N beccariana Arecaceae Core X Core PSYHAW N Psychotria hawaiiensis X PSYODO N odorata Rubiaceae X Core Core RHUSAN N Rhus sandwicensis Anacardiaceae X X SAMSAM E Samanea saman Fabaceae Core Core SYZMAL E malaccense Myrtaceae X TERCAT E Terminalia catappa Combretaceae X THEPOP N Thespesia populneoides Malvaceae X X

a E, exotic; N, native. Note: Each experimental treatment had four core species that were chosen for either their slow or moderate rates of C turnover, and six additional species that had functional traits that were either redundant or complementary to the core species. Also noted are existing native species not removed from the experimental plots. Enhancing Aboveground Carbon Storage through Restoration · Rayome et al. 153 fell more than halfway into the buffer zone Data Collection (2.5 m) were removed. Herbicide (30% Gar- lon 4 Ultra, mixed with 70% crop oil) was Experimental measurements commenced in sprayed immediately onto cut stumps to pre- January 2014 after all individuals had been vent resprouting. Planting density was based planted and tagged for long-term monitoring. on data from other Hawaiian lowland wet for- Carbon values in this article focus on summed ests that have maintained a greater abundance aboveground biomass data collected in April of native species (Zimmerman et al. 2008), and May 2016, which integrate the growth of as well as the mature plant size. Total planted outplanted individuals and recruits (seedlings individuals per plot were as follows: 125 for of existing or outplant species) during 2 yr of Slow Complementary, 130 for Moderate experimental conditions. Data originate from Complementary, and 120 for the two Redun- individual on-site woody species but exclude dant treatments. We identifed four separate biomass removed from study plots, below- areas (blocks) with appropriate conditions ground biomass, and herbaceous species bio- while using surveying equipment to lay out mass. Data collected for carbon analysis were fve plots in each block (Figure 1). Assignment plant height and diameter at breast height of treatments to plots was random, with 20 (DBH) at 1.3 m for all stems ≥1.0 cm diam- plots measuring 20 m by 20 m and a 5 m pe- eter. Species were grouped in one of three rimeter buffer. We aimed for a 10 m distance categories: existing, outplants, and recruits. between the buffers for each plot, but actual Existing species were trees left in situ after distances depended on terrain and avoidance commencing experimental treatments (also of gullies and treefall gaps. inclusive of initial trees present in reference To evenly distribute the across each plots). Outplants refer to those species meant plot we set up a grid across each planting area to defne experimental treatment mixtures with the number of quadrats depending on (i.e., all native and nonnative plants installed the number of large tree species designated in cleared experimental plots). Recruits are for that treatment. These large tree species defned as all new growth originating during served as foci, with other species planted the experiment from either existing pools around them in a stratifed random design or reproducing outplants. (see Figure 1 for spatial confguration in each We also wanted to determine if abiotic treatment). Plant spacing was based on adult variables (light, soil nutrients, soil pH) might plant size, such that large plants were placed contribute to outplant and recruit C storage, 2 m away from their nearest neighbor, and regardless of treatment. Before the experi- medium and small plants were placed 1.5 m ment (2012) and again during outplanting and 1 m away, respectively. Planting was done (2014), we took hemispherical photos to esti- in stages from April 2013 to January 2014 be- mate percentage canopy cover. The photos cause different species were ready for transfer were taken with a Canon EOS 5D camera and at different times. All outplants were grown Canon EF 15 mm fsheye lens before analysis on Hawai‘i Island from locally available prop- using WinsCanopy software (Regent Instru- agules. When a preexisting native tree was ments, Inc., Quebec City, Canada). In July located where an outplant was supposed to be 2012 soils were sampled no deeper than 10 cm planted we relocated the outplants, making using trowels (n = 4 per plot, with one sample sure that no plant was placed <1 m from any in each subplot). Volumetric soil core data are other plant. Plots were weeded before plant- not expressed on an area basis due to diffcul- ing because several months had passed after ties associated with the extremely rocky ter- clearing, and new nonnative seedlings had rain. Roots and debris were handpicked out of popped up after the disturbance. After plant- soil samples to maintain soil aggregates, dried ing, plots were weeded at 4- to 6-month in- at 60°C, and ground. Soils were analyzed for tervals; native species plantings and recruits carbon (C) and nitrogen (N) in a Costech were left intact and invasive species were 4010 Elemental Analyzer (Costech Analytical removed. Technologies, Valencia, California), and for Figure 1. Map of the study site and Liko Nä Pilina experimental locations. Reference treatments include plots 1, 7, 12, and 19. Slow Redundant treatments include plots 2, 6, 15, and 16. Moderate Redundant treatments include plots 3, 9, 11, and 18. Slow Complementary treatments include plots 4, 8, 13, and 17. Moderate Complementary treatments include plots 5, 10, 14, and 20. Enhancing Aboveground Carbon Storage through Restoration · Rayome et al. 155 phosphorus (P) on a Technicon AutoAnalyzer .bioone.org/toc/pasc/current) and Project AAI with parts from Pulse Instrumentation MUSE (http://muse.jhu.edu/journal/166). (Mequon, Wisconsin) after a modifed Truog extraction. Cations (Mg, Ca, K, Na) were an- Statistical Analysis alyzed after ammonium acetate extraction on a Varian Vista MPX ICP-OES (Varian Ana- Statistics were examined using R 3.1.2 (R lytical Instruments, Walnut Creek, Califor- Core Team 2014) and JMP 11.2.0 (SAS nia). All laboratory analyses were done at the 2013). To examine the effects of experimental Analytical Laboratory at University of Hawai‘i planting, we compared the C amount in the at Hilo. outplants plus recruits as the response vari- able because this biomass represents growth in response to the experimental conditions. Calculations We focused on the plot level rather than the Carbon in aboveground biomass was calcu- individual level because C in the plots inte- lated for outplanted and recruit trees and grate survival and growth. C values were ln compared among all treatments. Calculations transformed to achieve normality and equal were completed using allometric equations variances. To examine the effects of the hy- for individual species or those generally ap- brid community treatments, we ran a com- plicable for species in wet tropical forests as plete randomized block analysis of variance described in past studies and the literature (ANOVA), based on procedures by Logan (Asner et al. 2011) (Supplemental Table S1). (2010), followed by Tukey’s tests to com- These equations use DBH, wood density, and pare among the treatments. To examine dif- height as independent variables. For most ferences in C across species, we examined the species, aboveground biomass was determined outplants and recruits separately, because it by diameter-to-biomass equations, supple- was a fairer comparison across species. Only mented with additional diameter-to-height a few species had recruits, and these were equations as needed. For all individuals with a generally small individuals with small amounts measureable DBH, the General Wet Forest of C. We ran one-way ANOVA tests for the equation (Chave et al. 2014), Hawai‘i-derived outplants and the recruits; we did not test equations (Asner et al. 2011), or more species- for a treatment effect here because we previ- appropriate equations (Donato et al. 2012, ously had verifed by two-sample t tests that Hung et al. 2012, Goodman et al. 2013) were all the species found in multiple treatments utilized. Tree heights were determined as (see Table 1) were not signifcantly different needed via Asner et al. (2011) or feld data in C amounts. when available. Where required, wood den- We suspected that environmental variables sity estimates originated from Asner et al. also infuenced C gain and chose several ad- (2011), Chave et al. (2009), the Global Wood ditional analyses to assess this potential con- Density database (Little and Wadesworth nection. First, we utilized one-way ANOVA 1964, Anon. 1974, Benthall 1984, Chundoff for pretreatment soil and light variables to 1984, Oey 1990, Flynn and Holder 2001, test possible treatment differences before ex- Tree Talk 2005), or previous feld measures perimental manipulation. Among treatments, (R. Ostertag and feld assistants, unpubl. there was no signifcant difference in canopy data). Calculations include all stems ≥1 cm openness, soil pH, or nutrients (C, N, P, Mg, DBH, but exclude secondary growth such as Ca, Na, K). To test whether these abiotic branches below breast height. Biomass to variables infuence C storage in outplants C-equivalent conversions followed wood pro- (independent of assigned treatment), we ran duction industry standards (Alabama Forestry Pearson correlation tests between outplant C Commission 2016; D. D. Rayome, R. Oster- and seven environmental variables: soil pH, tag, and S. Cordell, unpubl. data). C, N, P, Mg, K, and canopy openness in 2014 Authors’ Note: Supplemental materials at the start of the experiment. We omitted available online at BioOne (http://www some variables from the analysis that were 156 PACIFIC SCIENCE · January 2018 highly correlated (r > 0.8) to other soil vari- varied signifcantly in their C. Total experi- ables and would have been redundant (i.e., Ca mental C value ranged greatly (Table 2, Fig- was omitted because it was correlated with ure 3). For most cases, the differences in Mg, and Na was omitted because it was cor- treatments can be explained by responses of related with C). individual species therein. For outplants, Ar- tocarpus altilis, Cibotium glaucum, Terminalia

results catappa, Rhus sandwicensis, and Persea ameri- cana all had high C contributions (Table 2, After 2 yr of experimental treatment condi- Figure 3). Of these, the overwhelming major- tions, our results indicate support for “Mod- ity of new outplant C originated from the erate” C cycling species mixtures but lack of 622 kg contribution of A. altilis. Further, Al- support for “Complementary” mixtures. Ex- eurites moluccana, Morinda citrifolia, Samanea isting native C totals in treatment plots ranged saman, Syzygium malaccense, and Mangifera from 0.10 kg to over 6,200 kg, and reference indica all had notable contributions in at least plots that included invasives ranged from one treatment type. In contrast, recruit bio- 0.14 kg to 5,652.01 kg. The hybrid commu- mass was most heavily infuenced by contri- nity treatment type signifcantly infuenced butions from R. sandwicensis, Pipturus albidus, C storage in outplants (F = 19.8; df = 3, 9; and C. glaucum (Table 2, Figure 3). Of these, P < .0003), but the block effect was not sig- R. sandwicensis contributed the majority of nifcant (F = 0.813; df = 3, 9; P = .81). The new recruit C, over 30.39 kg. Further, envi- Moderate Redundant treatment had signif- ronmental conditions had little infuence on cantly more C than the other three treatments the aboveground C values. Before experi- (Figure 2). mental conditions, there were no signifcant C measures at the treatment level were differences in canopy openness, soil pH, or driven by a handful of species. Outplants nutrients (C, N, P, Mg, Ca, Na, K). The only (F = 63.03; df = 15, 715; P < .0001) and re- signifcant effect of environmental condi- cruits (F = 6.09; df = 3, 204; P = .0005) species tions was that plots with lower soil P had sig- nifcantly more outplant C (r = −0.5239, P = .0373), but none of the other environmental variables had any signifcant differences. In addition, none of the environmental variables was related to the existing tree density of basal area before the start of the experiment (data not shown).

discussion We predicted that the treatment composed of species with moderate C cycling traits and more complementary functional trait values would have increased C storage when com- pared with treatments of species having slower C cycling traits or more redundant Figure 2. Mean (and standard error, n = 4) C found in functional traits. However, as shown by our the biomass across the four Liko Nä Pilina hybrid com- munity treatment types. Only the Moderate Redundant results after 2 yr of Liko Nä Pilina experi- treatment type differed signifcantly in C measures. Non- mental conditions, the Moderate Redundant transformed values for treatments are 0.82 (standard treatment had higher C storage than the error 0.89) for Slow Redundant, 3.62 (standard error other three treatments (Figure 2). Contrary 3.76) for Moderate Redundant, 0.90 (standard error 0.88) for Slow Complementary, and 1.22 (standard error 2.84) to our expectations, core species in the two for Moderate Complementary. Statistically different Moderate treatments, although chosen in treatments are denoted a and b. part to have trait values related to increased TABLE 2 Aboveground Carbon Mass for the Four Hybrid Treatments and Reference in the Liko Nä Pilina Experiment

Hybrid Species Treatments/ kg/ kg/ Code Reference Existing Survived kg/plant Outplant Survived plant Recruit Survived plant

ALEMOL Slow Comp 0 0 0 94.43 20 4.72 0 0 0 Mod Comp 0 0 0 83.32 20 4.17 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0 ANTPLA Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 1.35 7 0.19 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0 ARTALT Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 488.35 21 23.25 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 622.08 20 31.10 0 0 0 Ref 0 0 0 0 0 0 CALINO Slow Comp 0 0 0 10.85 19 0.57 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 12.97 20 0.65 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0 CIBGLA Slow Comp 317.06 18 17.61 0 0 0 0 0 0 Mod Comp 151.88 9 16.88 0 0 0 0 0 0 Slow Red 0 0 0 269.06 72 3.74 0 0 0 Mod Red 27.78 2 13.89 300.74 70 4.30 0 0 0 Ref 86.49 4 21.62 0 0 0 CIBMEN Slow Comp 43.32 4 10.83 0 0 0 0 0 0 Mod Comp 100.25 10 10.03 0 0 0 0 0 0 Slow Red 9.09 2 4.54 0.94 1 0.94 0 0 0 Mod Red 19.67 3 6.56 3.33 1 3.33 0 0 0 Ref 623.05 16 38.94 0 0 0 DIOSAN Slow Comp 6306.52 22 286.66 0 0 0 0 0 0 Mod Comp 5087.85 17 299.29 0 0 0 0 0 0 Slow Red 786.48 14 56.18 0 0 0 0 0 0 Mod Red 834.37 8 104.29645 0 0 0 0 0 0 Ref 2383.90 18 132.44 0 0 0 MANIND Slow Comp 0 0 0 21.65 15 1.44 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 33.87 16 2.12 0 0 0 Mod Red 0 0 0 49.97 19 2.63 0 0 0 Ref 0 0 0 0.78 1 0.78 METPOL Slow Comp 28252.29 21 1345.35 0 0 0 0 0 0 Mod Comp 43376.90 23 1885.95 0 0 0 0 0 0 Slow Red 47778.93 38 1257.34 0 0 0 0 0 0 Mod Red 46349.04 26 1782.66 0 0 0 0 0 0 Ref 40395.35 27 1496.1242 0 0 0 MORCIT Slow Comp 0 0 0 66.98 40 1.67 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0 MYRLES Slow Comp 0 0 0 0 0 0 1.11 4 0.28 Mod Comp 164.72 1 164.72 0 0 0 0 0 0 Slow Red 573.06 2 286.53 0 0 0 0.55 1 0.55 Mod Red 2.92 2 1.46 0 0 0 1.73 3 0.58 Ref 615.57 5 123.11 0.29 2 0.15 TABLE 2 (continued)

Hybrid Species Treatments/ kg/ kg/ Code Reference Existing Survived kg/plant Outplant Survived plant Recruit Survived plant

PANTEC Slow Comp 44.70 1 44.70 0 0 0 0 0 0 Mod Comp 270.12 10 27.01 0 0 0 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0 PERAME Slow Comp 0 0 0 57.33 22 2.61 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 121.13 22 5.51 0 0 0 Ref 0 0 0 0 0 0 PIPALB Slow Comp 0 0 0 2.35 5 0.47 22.34 30 0.74 Mod Comp 0 0 0 3.48 9 0.39 21.74 40 0.54 Slow Red 0 0 0 0 0 0 9.81 15 0.65 Mod Red 0 0 0 0 0 0.00 14.77 25 0.59 Ref 0 0 0 0 0 0 PSYHAW Slow Comp 1429.24 53 26.97 0 0 0 3.35 17 0.20 Mod Comp 1680.47 63 26.67 0 0 0 5.18 13 0.40 Slow Red 1670.13 93 17.96 0 0 0 2.49 8 0.31 Mod Red 1173.10 88 13.33 0 0 0 4.59 8 0.57 Ref 1284.75 56 22.94 2.78 4 0.70 PSYODO Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 1.38 6 0.23 0 0 0 Slow Red 0 0 0 1.01 6 0.17 0 0 0 Mod Red 0 0 0 3.88 10 0.39 0 0 0 Ref 0 0 0 0 0 0 RHUSAN Slow Comp 0 0 0 192.88 74 2.61 5.93 16 0.37 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 280.32 79 3.55 30.39 28 1.09 Ref 0 0 0 0 0 0 SAMSAM Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 53.15 20 2.66 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 55.19 19 2.90 0 0 0 Ref 0 0 0 0 0 0 SYZMAL Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 54.01 32 1.69 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0 TERCAT Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 287.02 40 7.18 0 0 0 Ref 0 0 0 0 0 0 TETHAW Slow Comp 0 0 0 0 0 0 0 0 0 Mod Comp 0 0 0 0 0 0 0 0 0 Slow Red 0 0 0 20.33 12 1.69 0 0 0 Mod Red 0 0 0 17.49 14 1.25 0 0 0 Ref 0 0 0 0 0 0 THEPOP Slow Comp 0 0 0 5.70 5 1.14 0 0 0 Mod Comp 0 0 0 4.94 6 0.82 0 0 0 Slow Red 0 0 0 0 0 0 0 0 0 Mod Red 0 0 0 0 0 0 0 0 0 Ref 0 0 0 0 0 0

Note: Rows indicate total carbon mass in kilograms, number of surviving plants, and average plant mass for existing, outplant, and recruited individuals. See Table 1 for species codes. Cocos nucifera and Prichardia beccariana were excluded from analysis. Enhancing Aboveground Carbon Storage through Restoration · Rayome et al. 159

example, A. altilis is successfully naturalized or cultivated in almost all suitable terrestrial ecosystems due in part to its ease of manage- ment, vigorous growth habit, and versatility in use ( Janick and Paull 2008, Breadfruit Institute 2016). Although the functional trait approach used in this experiment may not be best for all species types or successional stages, it is important to report and under- stand early results for comparison with later successional stages that may favor comple- mentarity for sustainable productivity and in- vasion resistance. Figure 3. Mean (and standard error, n = 16) C found in We found that measuring C storage in out- the biomass across Liko Nä Pilina hybrid community planted individuals and recruits was an appro- treatment outplanted species. Species codes in bold type priate metric for evaluating effects on above- indicate native species (see Table 1 for species codes). Of ground C in restoration approaches. It has contributing species, Artocarpus altilis had the most infu- been shown in these forests that once invaded, ence on C measures. Species values in individual treat- ments are displayed in Table 2. Species included here are C cycling and storage is altered and no longer outplants only; there was no signifcant difference be- benefts C storage in the long term due to de- tween treatments with respect to carbon accumulation. creased longevity of invasives (Hughes and Denslow 2005, Mascaro et al. 2012, Asner et al. 2016). Indeed, shifting C in a deliberate rates of C cycling, were in some cases sur- way toward native and noninvasive exotic spe- passed in growth in the feld by “noncore” cies has implications for structural and sub- species. Further, Redundant species mixtures sequent ecosystem process changes. Current composed of fast-growing and high carbon- reference plots as well as that from both pre- accumulating species might provide a beneft experimental conditions and nearby lowland to a restoration project earlier, whereas Com- sites indicates that increased invasive C de- plementary mixes might support long-term tracts from native species recovery (Cordell carbon accumulation. In our system, the level et al. 2016). These new C cycling regimes of weeding required was high; therefore the may affect overall integrity and long-term re- Moderate Redundant treatment has the ad- silience, especially when dwindling forests vantage of being more likely to obtain quick face continued pressure from impacts of con- canopy closure and aid in preventing addi- tinued global change. tional maintenance. Our experimental mixes Our experimental work emphasizes the were selected based on functional trait expres- potential of Hawaiian forests as a simple and sion of adult specimens, and the results after unique perspective for examining C, with spe- 2 yr may not represent mature trees. It is cies invasions, human impacts, and manage- therefore important in restoration planning ment interventions all occurring simulta- to recognize the importance of emphasizing neously (Friday et al. 2015, Ostertag et al. growth trajectories within the greater scope 2015, Asner et al. 2016). Carbon content of species life history when prescribing resto- varies among tropical tree species (Martin ration designs. Discarding the value of Mod- and Thomas 2011, Orihuela-Belmonte et al. erate Complementary mixtures would be 2013), yet the relatively few species in his- unwise without contextualizing results at the toric Hawaiian lowland wet forests store C species level. Outplant and recruit species comparably to that of more biodiverse forests including A. altilis, C. glaucum, T. catappa, R. in other regions. Similarly invaded mature sandwicensis, and P. americana are indeed infu- Hawaiian wet lowland forests store 72.8 Mg encing C, but they are growing at the same C ha−1 (Asner et al. 2016), and the man- rate regardless of treatment (Figure 3). For aged density of our experiment allows up to 160 PACIFIC SCIENCE · January 2018

291 Mg C ha−1. This total includes reference hensive C effects allows for more informed conditions as well as existing trees, 4.02 Mg C restoration planning and increased likelihood ha−1 in outplanted individuals, and 0.19 Mg C of successful interventions (Pokorny et al. ha−1 in recruits. Comparable tropical wet for- 2005, Cordell et al. 2016). The vital snapshot ests in Bolivia store approximately 67.5 Mg C of early C values in this study will be useful ha−1, and those in Brazil store 90 Mg C ha−1 for contrasting with later results when the ( Jespen 2006). trade-offs between rate of C accumulation and functional redundancy are realized. conclusions acknowledgments Overall, we consider our experiment an im- portant contribution to the growing literature We recognize staff, students, and interns on including C aspects in restoration as well from the University of Hawai‘i, the USDA as the importance of increasing stored C in Forest Service Institute of Pacifc Islands For- forests globally (FAO 2010, Raunikar et al. estry, and Stanford University for logistical 2010, Hurmekoski and Hetema¨ki 2013, Payn and technical support. We also express appre- et al. 2015). Our experiment supports the ciation for work underlying this analysis per- fnding that mixed species plantings beneft formed by Amanda Uowolo, Laura Warman, C balances with peripheral benefts for other Nicole DiManno, Céline Jennison, and Palani ecosystem services (Lindenmayer et al. 2012, Akana. We thank our partners in the Hawai‘i Hulvey et al. 2013). We have previously Army National Guard Environmental Offce shown the approach to be both appropriate (Angela Kieran-Vast, Craig Blaisdell, and and cost-effective for the Hawaiian lowland Kristine Barker) and staff at Keaukaha Mili- wet forest context [Cordell et al. 2016; D. D. tary Reservation for facilitating the establish- Rayome, R. Ostertag, and S. Cordell (unpubl. ment of the Liko Nä Pilina project. data)]. It is important to note that our experi- mental forest is still developing: canopy clo- Literature Cited sure has not yet occurred, nor have several other factors commonly associated with a ma- Alabama Forestry Commission. 2016. Carbon ture wet tropical forest. Changing experi- sequestration, http://www.forestry.state.al mental and environmental conditions con- .us/HowMuchCarbonHaveYourTrees tinue to infuence overall forest ecology, and Stored.aspx?bv=5&s=0. we expect treatments to continue positive Albrecht, A. and S. T. Kandji. 2003. Carbon C cycling as plots mature and more-complex sequestration in tropical agroforestry sys- forest dynamics begin to unfold. We expect tems. Agric. Ecosyst. Environ. 99:15– C and other services to vary after maturity 27. as well, providing a basis for treatment com- Anonymous. 1974. Standard nomenclature of parison well into the coming decades. Longer- forest plants, Burma, including commer- lived species will likely affect C through their cial timbers. Forest Research and Training growth, and more prolifc species or those Circle, Forest Department, Burma. with traits more useful for survival will affect Asner, G. P., R. F. Hughes, J. Mascaro, A. L. C dynamics in ways that support competition- Uowolo, D. E. Knapp, J. Jacobson, T. driven C balances (Lusk et al. 2008, Suding Kennedy-Bowdoin, and J. K. Clark. 2011. et al. 2008). Finally, we understand that a High-resolution carbon mapping on the more comprehensive understanding of C million-hectare Island of Hawaii. Front. would beneft from inclusion of belowground Ecol. Environ. 9:434–439. C and not measured aboveground biomass Asner, G. P., S. Sousan, D. E. Knapp, P. C. (herbaceous and immature plant matter, Selmants, R. E. Martin, R. F. Hughes, and snags, and other coarse woody debris; on-site C. P. Giardina. 2016. Rapid forest carbon carbon cycling through leaf detritus and con- assessments of oceanic islands: A case study nected trophic webs). Focus on more compre- of the Hawaiian archipelago. Carbon Enhancing Aboveground Carbon Storage through Restoration · Rayome et al. 161

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