A lack of ecological diversity in forest nurseries limits the achievement of tree-planting objectives in response to global change

Abstract

Tree planting is increasingly being adopted as a strategy to address global change, including mitigation, adaptation, and restoration. Although reforestation has long been central to forest management, the desired outcomes of traditional and emerging tree-planting strategies face barriers linked to a lack of ecological diversity in forest nurseries. In the present article, we outline how insufficient diversity in nursery seedlings among species, genotypes, and stock types has impeded and will continue to hinder the implementation of diverse ecological or climate-suitable planting targets, now and into the future. To support this, we demonstrate disparities in seedling diversity among nursery inventories, focusing on the northern United States. To overcome these challenges, we recommend avenues for improving policy and financing, informational resources and training, and research and monitoring. Absent these advances, current seedling production and practices will fall short of ambitious tree-planting goals proposed for forest restoration and global change mitigation and adaptation.

‘Mind the Gap’—reforestation needs vs. reforestation capacity in the western United States

“…The national discourse on how best to overcome barriers to increasing reforestation capacity has largely focused on seedling production capacity through nursery development and increasing seed availability through scaling collections (Fargione et al, 2021;Klein, 2021;American Forests, 2023;Clark et al, 2023;Kildisheva et al, 2023). Further innovation will require attention to a wider range of activities in the reforestation pipeline that are often overlooked (Figure 5).…”

“…Field trials indicate that seedlings planted outside of appropriate seed zones are maladapted and perform poorly in terms of growth and survival because of climatic differences between seed sources and planting sites (Leimu and Fischer, 2008;Alberto et al, 2013). Additionally, the broadening objectives of reforestation from timber production toward ecological services and function, climate mitigation, and resilience requires a wider array of species and seed sources to be considered for reforestation (Crowe and Parker, 2008;Clark et al, 2023;Warner et al, 2023). Many non-timber species (specifically native angiosperms, e.g., Quercus sp., Acer sp., Populus sp., etc.)…”

“…Consequently, recent studies have examined reforestation, afforestation, and increased stocking scenarios for the U.S. aimed at meeting climate mitigation goals (Cook-Patton et al, 2020;Domke et al, 2020;Fargione et al, 2021). Beyond climate change mitigation, there is also considerable interest in reforestation for a broader set of objectives (Clark et al, 2023), including diversifying and restoring ecosystem function in degraded forests (Stanturf et al, 2014), engineering structural and landscape heterogeneity (North et al, 2009;Safford and Vallejo, 2019), and developing climate-adaptive strategies designed to anticipate shifting species and climatic stressors (Palik et al, 2022). Forests are also critical for myriad co-benefits that stem from intact ecosystems.…”

“…The challenges for scaling the reforestation pipeline are many (Fargione et al, 2021;Clark et al, 2023;Kildisheva et al, 2023), but emerging opportunities for collective action exist. The reforestation pipeline in the western U.S. is principally supported by "compliance" forestry needs -restocking harvested areas in accordance with statespecific forest practice regulations.…”

Bad science and good intentions prevent effective climate action

“…To remove sufficient CO2 from the atmosphere to meet the Paris targets it will be necessary to create a new carbon sink on the scale of the ocean sink . Additional problems are that the potential capacity of many CDR measures is constrained by available land, water and nutrients and by environmental concerns (e.g., Kramer, 2020;Heck et al, 2018;Dooley et al, 2021;Clark et al, 2023). Another major obstacle is cost .…”