Effect of various monotypic forest canopies on earthworm biomass and feral pig rooting in Hawaiian wet forests Noa Kekuewa Lincoln ⇑ Ngai Tahu Research Centre, University of Canterbury, Christchurch, New Zealand article info Article history: Received 30 May 2014 Received in revised form 28 July 2014 Accepted 28 July 2014 Keywords: Forestry Forest ecology Feral pigs Earthworms Hawai‘i abstract Forestry plantations are functioning ecosystems, and although they differ from natural ecosystems in many important ways they are governed by the same mechanisms and can provide similar ecological habitats and ecosystem services. In this sense, forestry plantations can be viewed as simple forest ecosys- tems, allowing us to better isolate and understand the mechanisms that drive forest function, structure, and biodiversity. On Hawai‘i Island, 68 forest stands representing 12 species of monotypic forestry plan- tations, in addition to stands of native forest and grass pastures, were surveyed at three sites to observe the effects of monotypic canopies on earthworm biomass and occurrence of rooting by feral pigs. The can- opy species strongly influenced earthworm biomass at each site (r 2 = 0.98, 0.99, 0.92; p < 0.001). Earth- worm biomass was strongly correlated to underlying soil age when examined by individual canopy species (r 2 = 0.96–0.98; p < 0.001). Earthworm biomass was highly correlated to the occurrence of rooting by feral pigs at each site (r 2 = 0.92, 0.94, 0.64; p < 0.001). Each site exhibited a different sensitivity of pig rooting in response to earthworms. Canopy and site data could thus be used to estimate total soil distur- bance by feral pigs, and inform aspects of forest management regarding soil erosion, biodiversity habitat, and hunting or trapping of feral pigs. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Forestry plantations are functioning ecosystems, and although they differ from natural ecosystems in many important ways they are governed by the same mechanisms and can provide similar ecosystem services (Kareiva and Marvier, 2007). In this sense, for- estry plantations can be viewed as simple forest ecosystems that allow us to isolate and better understand the mechanisms that drive forest function, structure and biodiversity, and therefore may advance better management of natural, novel, and managed forests and forestry plantations for increased economic, environ- mental or social benefit. The impact of plantations on forest func- tion, such as ecosystem services and habitat development, has been well studied (e.g. Ecological Society of America, 2010; Bauhus et al., 2010). Most often observations have focused on a single forestry species relative to nearby natural or novel ecosystems. The opportunity to examine how individual canopy species compare to each other in their influence on the subcanopy ecosys- tem is an underutilized tool in forest ecology. The species used in forestry plantations impact the understory ecosystem directly through physical and biogeochemical pathways, and indirectly through cascading ecological effects and species interactions, such as altering predator–prey relationships, or relationships of pollina- tion or seed dispersal (e.g. Harrington and Ewel, 1997; Leibold et al., 2004; Shea and Chesson, 2002; Strong et al., 1984). Through these interactive mechanisms of community ecology, canopy spe- cies may ultimately be driving seemingly unrelated aspects of for- est communities in human-established monotypic plantations. Species composition and behavior influences the usage and value of forests to the local community (Bauhus et al., 2010), and may cause tensions around forest management at the local level. In Hawai‘i, feral pigs (Sus scrofa) define the tensions of contempo- rary forest management, which tends to be divided between those who value Hawaiian forests for their natural sake and those who value the forests as a resource to be utilized (Tummons, 2006). Feral pigs are desired by some for hunting and traditional values (Tummons, 2006), while opposed by others seeking to preserve biodiversity and watershed function (Nogueira-Filho et al., 2009). Despite the impacts, values, and tensions associated with feral pigs in Hawaiian forests, very little work has been conducted to under- stand how they interact with forest ecology to improve manage- ment, land use designation, and capture techniques (Nogueira et al., 2007). http://dx.doi.org/10.1016/j.foreco.2014.07.034 0378-1127/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Address: Private Bag 4800, Christchurch 8140, New Zealand. Tel.: +64 808 217 7710. E-mail address: nlincoln@alumni.stanford.edu Forest Ecology and Management 331 (2014) 79–84 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco