Environmental Reviews BOREALIZATION OF THE NEW ENGLAND-ACADIAN FOREST: A REVIEW OF THE EVIDENCE Journal: Environmental Reviews Manuscript ID er-2019-0068.R1 Manuscript Type: Review Date Submitted by the 06-Feb-2020 Author: Complete List of Authors: Noseworthy, Joshua; University of New Brunswick, Faculty of Forestry and Enviromental Management Beckley, Thomas; University of New Brunswick, Faculty of Forestry and EnviromentalDraft Management Is this manuscript invited for consideration in a Special Not applicable (regular submission) Issue? : Borealization, New England, Maritimes, Acadian Forest, Forest Keyword: Composition https://mc06.manuscriptcentral.com/er-pubs Page 1 of 42 Environmental Reviews 1 2 3 4 5 6 7 8 BOREALIZATION OF THE NEW ENGLAND-ACADIAN FOREST: A REVIEW OF THE 9 EVIDENCE 10 11 12 13 JOSHUADraft NOSEWORTHY 14 GLOBAL CONSERVATION SOLUTIONS 15 AND 16 THOMAS M. BECKLEY* 17 UNIVERSITY OF NEW BRUNSWICK 18 19 20 21 22 23 24 *CORRESPONDING AUTHOR: 25 FACULTY OF FORESTRY AND ENVIRONMENTAL MANAGEMENT 26 UNIVERSITY OF NEW BRUNSWICK 27 P.O. BOX 4400 28 FREDERICTON, NB CANADA E3B 5A3 29 EMAIL: [email protected] 30 506-453-4917 1 https://mc06.manuscriptcentral.com/er-pubs Environmental Reviews Page 2 of 42 31 TITLE: BOREALIZATION OF THE NEW ENGLAND-ACADIAN FOREST: A REVIEW OF THE 32 EVIDENCE 33 34 ABSTRACT 35 The New England-Acadian Forest (NEAF) is an ecoregion spanning 24 million hectares of the 36 northeastern U.S. and eastern Canada. The region is characterized as a transitional forest naturally 37 composed of both boreal and temperate species. The term “borealization” is sometimes used to 38 describe various processes driving the NEAF toward a more boreal character at the expense of its 39 temperate forest species and ecological communities. That the NEAF has undergone significant 40 landscape-scale change in the last four centuries since European settlement is well understood. 41 The purpose of this manuscript is to reviewDraft the literature on the forest composition and dynamics 42 of this region to investigate whether past, current, and/or predicted future processes of change are 43 indeed driving the forest toward a more boreal character. We examine studies on the historical 44 forest composition, impacts of past and current land-use practices, as well as indirect 45 anthropogenic changes that are predicted to influence future forest compositions of the NEAF. We 46 review over 100 peer-reviewed scientific journal articles and government reports related to this 47 issue. We find ample evidence to suggest that, at the landscape scale, there has been widespread 48 replacement of temperate tree species by boreal species since European settlement. Five primary 49 drivers have facilitated borealization across the NEAF: logging and high-grading, natural 50 reforestation of abandoned farmland, industrial clearcutting, anthropogenic fire, and boreal conifer 51 plantations. Furthermore, the borealization of the NEAF has continued to occur in direct contrast 52 to the predicted impacts of climate change. We encourage future scholarship to tackle these aspects 53 of borealization in the NEAF, including its social, economic, and ecological implications. 2 https://mc06.manuscriptcentral.com/er-pubs Page 3 of 42 Environmental Reviews 54 INTRODUCTION 55 The New England-Acadian Forest (NEAF) is an ecoregion located in eastern North America. 56 Although geographic interpretations of the NEAF differ among sources, it can generally be 57 described as spanning the majority of New England (USA), the three Maritime Provinces of 58 Canada (with the exception of the highlands of New Brunswick and Nova Scotia), and 59 portions of southeastern Quebec (Figure 1). The NEAF is characterized as a transitional 60 forest composed of both northern boreal and southern temperate tree species. We are 61 interested in the long-term trend and trajectory of the forest composition of this region. The 62 term “borealization” is increasingly used to describe both current and historic land-use 63 practices that have driven the NEAF toward a more boreal character at the expense of 64 temperate tree species and forest communities.Draft Although landscape-scale changes since the 65 onset of European settlement are well documented across the NEAF, this paper addresses 66 whether these changes truly reflect a shift toward a more boreal tree species composition. 67 In order to proceed with this investigation, we first define borealization in the specific 68 context of the NEAF. Concurrently with the review of tree species compositional changes, we 69 summarize the key drivers of change that led to the current composition of the NEAF. In the 70 discussion section, we speculate about possible future trajectories for the NEAF given 71 climate change, as well as identify other distinct but related structural changes to the NEAF 72 that warrant further investigation. 73 DEFINING BOREALIZATION 74 Outside of North America, the term borealization has been used in several contexts, such as a 75 turnover in Arctic fish populations as a result of climate change (Fossheim, et al., 2015), to describe 76 the process of soil acidification due to the impacts of acid deposition and industrial conifer 3 https://mc06.manuscriptcentral.com/er-pubs Environmental Reviews Page 4 of 42 77 plantations (Emmer et al., 1998), and most frequently, to describe declines in temperate tree 78 species due to land-use practices that directly or indirectly favour boreal tree species (Jedrzejewska 79 et al., 1994; Fanta, 1997; Emmer et al., 2000; Lindbladh et al., 2014). Ideally, a wholistic and 80 comprehensive assessment of borealization would include examination of a range of biotic and 81 abiotic factors; However, historical forest scholarship in the region almost exclusively focuses on 82 trees. As such, we confine our definition of borealization to refer to forest tree species composition, 83 which is also the definition most often used when cited in the context of the NEAF (see Loo et al., 84 2005; Diamond, 2008; Taylor et al., 2017; Lahey, 2018). With this in mind, it is important to 85 distinguish between native boreal and temperate tree species that occur within the NEAF for 86 comparison. The boreal forest is often characterized as coniferous and the temperate as deciduous, 87 but these generic associations do not reflectDraft the true nature of tree species distributions. Coniferous 88 and deciduous tree species occur in both boreal and temperate biomes, and as such, to determine 89 whether changes across the NEAF constitute borealization, a species-specific approach is required. 90 To establish a baseline for comparison, we conducted a spatial assessment to categorize the boreal 91 and temperate affinities of 30 tree species native to the NEAF, as presented in Burns & Honkala 92 (1990). Using a Geographic Information System (GIS), we calculated the proportion of each 93 species’ native range (spatially delineated by Little, 1971; 1976; 1977) that overlaps the North 94 American boreal zone as delineated by Brandt (2009). Tree species with >50% of their native 95 range overlapping the North American boreal zone were assumed to have a stronger boreal affinity 96 and were categorized as such. Incidentally, the results of this assessment align with the species 97 identified by Brandt (2009) as boreal, as well as other studies that identify boreal tree species in 98 North America (see Greene et al., 1999; Chen & Popadiouk, 2002; Taylor & Chen, 2011; 99 Nienstaedt & Zasada, 1990). Based on these results (Figure 2), if borealization is a true 4 https://mc06.manuscriptcentral.com/er-pubs Page 5 of 42 Environmental Reviews 100 phenomenon, we would expect two outcomes from the literature review: (1) evidence of a general 101 increase in one or more of the following species: Jack Pine (Pinus banksiana), White Spruce (Picea 102 glauca), Black Spruce (Picea mariana), Balsam Poplar (Populus balsamifera), Tamarack (Larix 103 Laricina), White Birch (Betula papyrifera), Balsam Fir (Abies balsamea), Trembling Aspen 104 (Populus tremuloides), Pin Cherry (Prunus pensylvanica); and (2) evidence of a general decline 105 in one or more of the remaining species listed in Figure 2. In the following sections, we summarize 106 our findings from the literature review, which are structured across three time periods: pre- 107 European Settlement (pre-1600), European Settlement (1600-1890), and post-European 108 Settlement (1890 – 2019). 109 LITERATURE REVIEW 110 Pre-European Settlement Draft 111 In order to determine whether there has been a change in tree species composition in the NEAF, 112 we need to establish a baseline. Betts and Loo (2002) contrast two methods for setting a pre- 113 European settlement baseline for the NEAF - the Witness Tree and Potential Forest methods. Each 114 has its strengths and weaknesses, but taken together, such methods can provide a partial view of 115 tree species distributions and community types prior to 1600 AD. The processes that led to the 116 current landscape of the NEAF began approximately 12,000 years ago following the last glaciation 117 event. As the Laurentide Ice Sheet retreated, the exposed substrate was first colonized by tundra 118 vegetation, which was then replaced by boreal forest as the climate warmed over time (Anderson, 119 1980; Anderson et al., 1986). Tree species with temperate affinities began colonizing the region 120 approximately 9,600 years ago, and the NEAF as first encountered by Europeans came into being 121 approximately 3,000 years ago, coinciding with an increase in tolerant hardwoods (see Neily et 122 al., 2011) and Eastern Hemlock (Tsuga canadensis), followed by Red Spruce (Picea rubens), the 5 https://mc06.manuscriptcentral.com/er-pubs Environmental Reviews Page 6 of 42 123 so-called “signature” species of the NEAF (see Lorimer, 2001; Loo et al., 2010). The region has 124 been inhabited by humans for at least 10,000 years, albeit initially in relatively low densities, with 125 an estimated population between 90,000 – 120,000 at the time of European contact (Cronon, 1983; 126 American Friends Service Committee, 1989).