Mixedwood silviculture in North America: the science and art of managing for complex, multi-species temperate forests

Abstract

Temperate mixedwoods (hardwood – softwood mixtures) in central and eastern U.S. and Canada can be classified into two overarching categories: those with shade-tolerant softwoods maintained by light to moderate disturbances and those with shade-intolerant to mid-tolerant softwoods maintained by moderate to severe disturbances. The former includes red spruce (Picea rubens Sarg.), balsam fir (Abies balsamea (L.) Mill.), or eastern hemlock (Tsuga canadensis (L.) Carr.) in mixture with northern hardwood species; the latter includes pine (Pinus) – oak (Quercus) mixtures. Such forests have desirable socio-economic values, wildlife habitat potential, and/or adaptive capacity, but management is challenging because one or more softwood species in each can be limited by depleted seed sources, narrow regeneration requirements, or poor competitive ability. Appropriate silvicultural systems vary among mixedwood compositions depending on shade tolerance and severity of disturbance associated with the limiting softwoods, site quality, and level of herbivory. Sustainability of mixedwood composition requires that stand structure and composition be managed at each entry to maintain vigorous trees of species with different growth rates and longevities and to encourage development of advance reproduction or seed-producing trees of desired species. Regardless of silvicultural system, maintaining seed sources of limiting softwoods, providing suitable germination substrates, and controlling competition are critical. Here, we describe commonalities among temperate mixedwoods in central and eastern North America, and present a framework for managing them.

Insect infestations and the persistence and functioning of oak-pine mixedwood forests in the mid-Atlantic region, USA

“…Finally, our study provides some insight into the value of incorporating oak-pine mixedwoods into management strategies for forests in the mid-Atlantic region. Although mixed composition stands are typically more expensive to manage, they provide a greater variety of forest products when harvested selectively or thinned [20,83]. As these forests age, simulating natural successional processes (e.g., forest thinning, mortality, regeneration) or delaying them through the use of prescribed fire and other silvicultural management practices would create more resistant forests [84][85][86].…”

Ecological memory and regional context influence performance of adaptation plantings in northeastern US temperate forests

“…The ability to respond to dieback permitted climate-maladapted ARE species such as C. dentata and B. lenta to persist despite injury to terminal shoots and sensitive plant structures from cold winter conditions, a pattern by which seedling growth forms become increasingly shrub-like over time (Gurney et al, 2011). P. strobus performed well across sites, likely due to the species' rapid growth rates combined with intermediate tolerance for competition and light stress, although this species has been shown to be outcompeted by hardwoods on nutrient rich sites, likely requiring subsequent release treatments (Hibbs, 1982;Kenefic et al, 2021). Some species with rapid initial growth such as P. grandidentata and P. serotina in growth rates, whereby suppressed individuals may survive long periods without growth (Closset-Kopp et al, 2007).…”

Proceedings of the 21st Biennial Southern Silvicultural Research Conference

“…Although OH stems were present in the largest size class, relative abundance was low, highlighting the need to conduct silvicultural treatments (chemical or mechanical cleaning or release treatments) that encourage the regeneration and recruitment of both shortleaf pine as well as oak and hickory species. If shortleaf pine seedlings are suppressed beyond 5 to 8 years (Kenefic andothers 2021, Lyczak 2019) and oak seedlings beyond 8 years (Weigel and Johnson 2000), mortality significantly increases.…”