Forest Disturbance Types and Current Analogs for Historical Disturbance-Independent Forests

Abstract

Forest classifications by disturbance permit designation of multiple types of both old growth forests and shorter-lived forests, which auto-replace under severe disturbance, and also identification of loss of the disturbance type and associated forest. Historically, fire and flooding disturbance regimes, or conversely, infrequent disturbance, produced unique forests such as disturbance-independent forests of American beech (Fagus grandifolia), eastern hemlock (Tsuga canadensis), and sugar maple (Acer saccharum) in the Eastern United States. However, disturbance has changed to primarily frequent mechanical overstory disturbance, resulting in novel forests. To demonstrate the transition to no-analog forests after disturbance change, I compared historical tree surveys (ca. 1837 to 1857) to current surveys in the Northern Lower Peninsula of Michigan. To establish widespread disturbance change effects, I also located where beech and hemlock are currently most abundant throughout the Eastern US compared to historical distribution of beech–hemlock forests. In the Northern Lower Peninsula of Michigan, beech and hemlock historically were about 30% of all trees, but currently, beech and hemlock are 2% of all trees. Red maple (Acer rubrum) increased from 1% to 11% of all trees and aspen (Populus) increased from 2% to 13% of all trees. The squared-chord difference between historical and current surveys was 0.40, or dissimilar forests. Areas with ≥20% beech and hemlock or ≥15% of either species decreased from about 52 million to 6 million hectares, with current distribution restricted to the Northeastern US. Current forests are dissimilar to historical forests, and this transition appears to be driven by disturbance regimes without historical analogs. Disturbance change may provide perspective in forest management for climate change.

Confronting the Issue of Invasive Native Tree Species Due to Land Use Change in the Eastern United States

“…Historical forests were old-growth closed and open forests, but not successional forests (Figure 1). In addition to composition and structure, successional forests have different functions, conditions, and biodiversity than historical forests [3,31]. Indeed, some "successional" species are declining despite the presence of abundant successional forests, indicating the misattribution.…”

“…Open forests of fire-tolerant oaks dominated the central region, with localized forests of shade-tolerant American beech (Fagus grandifolia, about 5% of all trees), sometimes in conjunction with eastern hemlock Land 2022, 11, 161 2 of 9 (Tsuga canadensis) or sugar maple (Acer saccharum), which have similar traits of shade tolerance and a long lifespan. Beech forests were disturbance independent (i.e., old-growth with rare overstory and understory disturbances), but open oak and pine forests were also old-growth forests with long-lived species due to infrequent overstory disturbance [3]. Although the historical surveys may suffer from measurement bias, for example, a preference for American beech that may be over-representative in records, open oak and pine forest types maintained by low-severity surface fires, modulated by native human management, consistently emerge from the work of countless surveyors and are upheld by pollen evidence [4] and historical accounts that remain similar, regardless of location or date [5,6].…”

Surveyor and analyst biases in forest density estimation from United States Public Land Surveys

“…Without an explicit lower diameter limit, any cited density is indefinite because including smaller trees will always increase that density. In various PLS studies, a diameter limit has been assumed based on surveyor instructions (e.g., 12.7 cm [5 inches]; 1833 instructions—Bourdo, 1956; Hanberry, 2021; Hanberry, Yang, et al, 2012; Manies & Mladenoff, 2000; Rhemtulla et al, 2009; White, 1983) or reported diameters (e.g., 5–15 cm [2–6 inches]; Bourdo, 1956; Cottam & Curtis, 1949; Grimm, 1984; Liu et al, 2011; Williams & Baker, 2011). Unfortunately, these diameter limits are absolute minimums and do not account for selective bias against trees larger than that limit.…”

“…These records contain substantial surveyor choice compromising any calculation of species composition, tree density, or size frequency distribution from them (cf. Almendinger, 1996; Grimm, 1984; Hanberry, 2021; Kronenfeld, 2014; Liu et al, 2011).…”

Recovery Status and Livestock Use of a Kenyan Montane Forest a Decade after Cessation of Human Encroachment

“…Forest disturbances either human-induced or natural have the potential to shape forest systems by altering composition, structure, and functional processes [8] [9] [10] [11]. Human induced forest disturbances are multifaceted and include conversion to agricultural use, logging and other extractive wood uses, forest fires, hunting and illegal wildlife trade, fragmentation, species invasion, altered bio-geochemical cycles and climate change [12] [13] [14] which leads to deforestation and forest degradation [15].…”