Using plant functional traits to restore Hawaiian rainforest

Abstract

Ecosystem restoration efforts are carried out by a variety of individuals and organizations with an equally varied set of goals, priorities, resources and time-scales. Once restoration of a degraded landscape or community is recognized as necessary, choosing which species to include in a restoration programme can be a difficult and value-laden process (Fry, Power & Manning 2013; Jones 2013). Species choice in restoration is often carried out with limited ecological information, particularly in regard to species interactions, successional processes and resource-use patterns. Selecting species can be particularly problematic in systems where there is no available baseline data on historical communities, or when restoration to a historic state is not feasible for ecological, logistic or economic reasons. In such cases, it may be preferable to focus on restoring site 'functionality' rather than returning to a historic baseline composition. We present a method for species selection in restoration, based on the collection of plant functional trait data. Using this method, managers can develop species mixtures with desired properties, including expected predictions of interspecific interactions and potential changes in biotic and abiotic conditions. To illustrate this approach, we present a case study in Hawaiian lowland wet forests (HLWF) in which plant species for a restoration project were chosen based on their functional traits, in order to help land managers achieve their restoration goals while at the same time allowing researchers to better understand invasion resistance and ecosystem functioning. In our case, our choices led to the development of hybrid ecosystems including both native and introduced species. However, the approach that we present is not limited to novel or hybrid ecosystem creation, because the candidate species examined and functional traits measured are determined by the user. Whereas restoration usually implies a return to historic conditions, there is also growing attention to what some authors have called 'intervention ecology' (sensu Hobbs et al. 2011). This view emphasizes maintaining ecosystem services and functions (Hobbs et al. 2011). The contrast between these frameworks has been widely debated in the literature, and we do not intend to advocate the merit of one view over the other here. Rather, we present the logic behind a functional trait approach, describe why its use is feasible in a Hawaiian lowland forest and present a step-by-step approach to the method that can be applied to a wide variety of ecological systems. While we readily acknowledge that in our study system, we cannot return to a pre-human state, we still consider our approach ‘restoration’ in a broad sense.

Citation

Ostertag, Rebecca; Warman, Laura; Cordell, Susan; Vitousek, Peter M.; Lewis, Owen. 2015. Using plant functional traits to restore Hawaiian rainforest. Journal of Applied Ecology. 52(4): 805-809.