Disassociating tree species associations in the eastern United States

Abstract

© iForest -Biogeosciences and Forestry IntroductionPlant ecologists have spent well over a century defining plant associations along successional pathways (Pound & Clements 1898, Schmelz & Lindsey 1970. Clements (1936) influenced plant classifications in both the United States and Great Britain (Whittaker 1978), andBraun (1950) applied Clementsian classifications throughout the eastern United States. Initial terminology for species associations and other vegetation units became elaborate with many competing terms (Moss 1910, Braun 1935. For example, a hierarchical system for the vegetation unit of formations incorporated associations, which in turn were further subdivided into fasciations, lociations, followed by societies of sociation, lamination, sation, and clan, along with seral units of associes-facies-locies-socies-lamies-saties-colony-family, and moreover, different serules (Clements 1936). Although complex terminology has fallen into disuse (due to "hopeless confusion" combined with "inadequate terminology" -Braun 1935), the term association, which is composed of a few genera or species that grow together, remains current, but also may be outdated. Further modifications of vegetation classifications tend to maintain Braun's associations, with the exclusion of oak-American chestnut (Castanea dentata), due to near extirpation of chestnut (e.g., Eyre 1980, Monk et al. 1989, Dyer 2006.Oak and hickory species are one of the predominant associations throughout the eastern United States since at least 1898 (Pound & Clements 1898, Hanson 1922, Eyre 1980, Monk et al. 1989, Dyer 2006, Tang & Beckage 2010, Pan et al. 2011, Domke et al. 2012, Elderd et al. 2013). Originally, oakhickory associations may have specified Quercus rubra-Carya ovata forests present in Missouri and in other states near grassland ecosystems, but by 1914 oak-hickory associations had been generalized throughout eastern forests (Livingston 1903, Fuller 1914, Nichols 1914, Clements 1936. Sampson (1927) stated that before 1900 over 30 well-described associations including oakhickory existed for Ohio.Oak and hickory species are more abundant in upland forest rather than floodplain forests and hydric soils; therefore, oak-hickory associations generally refer to species in upland, mesic to xeric sites (Sampson 1927, Schmelz & Lindsey 1970. The most common species of oak in the central eastern and southeastern regions (hot continental and subtropical divisions -ECOMAP 1993, USDA Forest Service - Fig. 1) of the eastern United States are white oak (Quercus alba, 4.6% of total stems -B. Hanberry unpublished data from USDA Forest Service Forest Inventory and Analysis), chestnut oak (Q. prinus, 2.3%), northern red oak (Q. rubra, 2.1%), black oak (Q. velutina, 2.0%), and post oak (Q. stellata, 1.9%). The most common species of hickories are pignut hickory (Carya glabra, 1.3%), mockernut hickory (C. tomentosa, 1.2%), shagbark hickory (C. ovata, 0.8%), black hickory (C. texana, 0.5%), and bitternut hickory (C. cordiformis, 0.4%). Because there are numerous ...