Theor Ecol DOI 10.1007/s12080-015-0286-4 ORIGINAL PAPER Optimal harvesting strategies for timber and non-timber forest products in tropical ecosystems Orou G. Gaoue 1,2 · Jiang Jiang 3 · Wandi Ding 4 · Folashade B. Agusto 5 · Suzanne Lenhart 3 Received: 20 August 2015 / Accepted: 12 November 2015 © Springer Science+Business Media Dordrecht 2016 Abstract Harvesting wild plants for non-timber forest products (NTFPs) can be ecologically sustainable–without long-term consequences to the dynamics of targeted and associated species–but it may not be economically satisfy- ing because it fails to provide enough revenues for local people over time. In several cases, the same species can be harvested for NTFP and also logged for timber. Three decades of studies on the sustainability of NTFP harvest for local people’s livelihood have failed to successfully inte- grate these socio-economic and ecological factors. We apply optimal control theory to investigate optimal strategies for the combinations of non-lethal (e.g., NTFP) and lethal (e.g., timber) harvest that minimize the cost of harvesting while maximizing the benefits (revenue) that accrue to harvesters and the conservation value of harvested ecosystems. Opti- mal harvesting strategies include starting with non-lethal NTFP harvest and postponing lethal timber harvesting to begin after a few years. We clearly demonstrate that slow  Orou G. Gaoue ogaoue@hawaii.edu 1 Department of Botany, University of Hawaii at Manoa, Honolulu, HI 96822, USA 2 Universite de Parakou, 123, Parakou, Benin 3 National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN 37996, USA 4 Department of Mathematical Sciences and Computational Science Program, Middle Tennessee State University, Murfreesboro, TN 37132, USA 5 Department of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA growth species have lower optimal harvesting rates, objec- tive functional values and profits than fast growth species. However, contrary to expectation, the effect of species lifes- pan on optimal harvesting rates was weak suggesting that life history is a better indicator of species resilience to har- vest than lifespan. Overall, lethal or nonlethal harvest rates must be <40 % to ensure optimality. This optimal rate is lower than commonly reported sustainable harvest rates for non-timber forest products. Keywords Differential equations model · Harvest model · Life history · Lifespan · Non-timber forest products · Optimal control theory · Sustainable timber harvest Introduction Identifying sustainable harvest limits for renewable resources and how these limits are constrained by socio- economic and environmental factors represent some of the most debated issues in conservation biology. Non-timber forest products (NTFPs) such as fruits, leaves, and resins are increasingly harvested from wild populations as source of food and medicine to local people worldwide and are part of a growing interest from pharmaceutical firms (Bawa et al. 2004). Harvesting NTFP provides a range of benefits for local people and can contribute to poverty alleviation (Shackleton and Shackleton 2004; Shackleton et al. 2011). In developing countries, more than 80 % of the population relies on medicinal plants for primary healthcare (Hamilton 2004), and 72,000 species of medicinal plants are used regularly by local people with 3000 species as part of the international trade (Schippmann et al. 2003, 2006). During the dry season when agricultural products are scarce and herbaceous pasture burned, several fruits are harvested for Author's personal copy