Promote species and structural diversity to enhance carbon capture and storage efficiency

Species are vulnerable to stressors at different stages of their life cycle, such that even-aged stands are often more vulnerable to disturbances such as insect pests and disease. Likewise, greater compositional diversity may reduce vulnerability to disturbances. As one or more species are at risk for a given stressor, greater diversity reduces the likelihood that the entire systems will decline (Duveneck et al. 2014). Even as greater species and structural diversity confer reduced vulnerability to carbon losses from disturbance, particularly under a changing climate (see review by O’Hara and Ramage 2013), these characteristics can also increase carbon density in forest ecosystems. Higher rates of carbon storage and annual carbon sequestration can result from resource-use efficiencies from increased diversity of tree species (Ammer 2018; Curtis and Gough 2018; Lui et al. 2018; Ruiz-Benito et al. 2014; van der Sande et al. 2017), while increased carbon stocks can be supported with a greater diversity of age classes and more vertical and horizontal structural complexity (Gunn et al. 2014; Ford and Keeton 2017; McGarvey et al. 2015). Results from both modeling and experimental studies suggest that over longer time scales (e.g. 50-100 years) silvicultural practices that promote uneven-aged management in forests promote greater carbon stocks in forests (D’Amato et al. 2011; Duveneck and Scheller 2015; Li et al. 2007; Mika and Keeton 2015). Carbon stocks in forests managed for increased structural and species diversity may increase over long temporal scales despite short-term reductions in carbon.

Climate change is projected to increase the potential for severe disturbance events that reduce forest ecosystems carbon stocks (Williams et al. 2016), while additionally affecting the growth and regeneration of extant species. Many forest management decisions aim to limit the negative impacts of disturbances while enhancing the growth of residual trees and the regeneration of desired species that represent the current and future capacity of the ecosystem to sequester carbon (McKinley et al. 2011). Often these management actions aim to enhance existing forest conditions, such as species composition and stand structural diversity that are key to the desired services provided by the forest. Slight adjustments in forest conditions can improve the retention of carbon within various forest carbon pools or enhance the rate of recovery following a disturbance event without dramatically altering the character of forest ecosystems.