Factors understood to be facilitating a shift toward increased dominance of competing species in the oak forests of Eastern North America include fire suppression and land use across the region, a long-term increase in wetter conditions, and herbivory (Nowacki & Abrams 2008, McEwan et al. 2011, Knott et al. 2019). The tree species that are becoming more dominant in some eastern oak forests as a result of these factors include sugar and red maple, birch, hemlock and American beech (Nowacki & Abrams 2008, Knott et al. 2019).

Fire suppression in oak-dominated forests is considered one of the major drivers of this shift. Evidence from early town proprietor surveys indicates that prior to colonization, more mesic species were rare within the oak- and chestnut-dominated forests of southern New England, with the exception of areas near rivers, lakes or the coast (Cogbill et al. 2002). There is evidence that fire was used as a land management tool by Native Americans in eastern deciduous forests, and that fire was also common on the landscape during early European colonization; however, frequent fires were effectively eliminated around 1940, coinciding with the start of a period of intense maple establishment (McEwan et al. 2011).  Without the canopy-opening fire disturbances that are historically characteristic for oak-dominated forests of eastern North America, species less tolerant of fire are better able to proliferate. Red maple, in particular, has been found to alter forest hydrology and nutrient cycling in a way that reduces the overall flammability of the forest and perpetuates conditions more conducive to other mesic, shade-tolerant species (Alexander & Arthur 2014).

Despite the fact that species distribution projections indicate that oak will generally be favored under climate change scenarios (Iverson et al. 2017), certain climate change impacts could create conditions that contribute to a successional transition toward more shade-tolerant species. The substantial increase in precipitation in the Northeast over the last century has already contributed to the establishment of more mesic species in oak forests (McEwan et al. 2011), and annual precipitation is expected to continue increasing, though soil moisture patterns will ultimately depend on location as well as the impacts of increasing drought (Easterling et al. 2017). More physical disturbances to the overstory due to extreme storm events associated with climate change could also release more mesic, shade-tolerant species that may have come to dominate the understory (Janowiak et al. 2018).

Certain land uses have been identified as contributing to the transition of oak-pine forests toward shade-tolerant species. Frequent and intensive overstory tree removal allows for red maple, which establishes competitively after harvest, to monopolize growing space (Hanberry 2019). However, the extent to which shade-tolerant species could ultimately populate the overstory of oak-dominated forests is ultimately still uncertain. Because harvesting in the Northeast typically occurs at least every 100 years or less, shade-tolerant species are less likely to become dominant (Hanberry 2019). However, the extent to which shade-tolerant species could ultimately populate the overstory of oak-dominated forests is ultimately still uncertain, and will depend on the frequency and intensity of harvest, as well as management decisions related to fire.