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Environmental Reviews

BOREALIZATION OF THE -ACADIAN : 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 , Faculty of 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

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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

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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 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 , anthropogenic fire, and boreal

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.

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54 INTRODUCTION

55 The New England-Acadian Forest (NEAF) is an ecoregion located in eastern .

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 (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

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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 . 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 ,

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

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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 (), Balsam Poplar (), Tamarack (Larix

103 Laricina), White (), Balsam (), Trembling

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 (see Neily et

122 al., 2011) and Eastern Hemlock (Tsuga canadensis), followed by Red Spruce (), the

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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). Unlike elsewhere in eastern North America,

127 Aboriginal peoples of the NEAF generally did not rely on fire for hunting or clearing land, and

128 there was very little agriculture practiced north of the Kennebec River in (Cronon, 1983).

129 In general, there is little evidence to suggest that Aboriginal peoples exerted landscape-scale

130 ecological change across the region, both owing to their low population density and hunter-

131 gatherer lifestyles (Anderson et al., 1986; Cronon, 1983; Foster et al., 1998; Loo et al., 2010).

132 Natural disturbances within the pre-settlement NEAF were primarily driven by gap- and patch-

133 scale dynamics (Fraver et al., 2009; Lorimer,Draft 2001; Seymour et al., 2002). Large-scale natural

134 disturbance, such as fire, catastrophic windstorms and insect outbreaks occurred infrequently

135 (Anderson et al., 1986; Seymour et al., 2002). As a result, at any time over the 3,000-year period

136 prior to European settlement, it is estimated that between 60-85% of the NEAF persisted in a state

137 of old-growth, which is defined here as forest >150 years old (Mosseler et al., 2003a; Lorimer &

138 White, 2003). That the pre-settlement forest was dominated by long-lived, shade tolerant tree

139 species is well-established through reviews of historical records (Lorimer, 1977; Lutz, 1996;

140 Cogbill, 2000; Blackadar, 2002; Crossland, 2006; Aubé, 2008; Dupuis et al., 2011; Thompson et

141 al., 2013; Ponomarenko et al., 2013), palynological studies (Mott, 1975; Anderson et al., 1986;

142 Green, 1987), extrapolative assessments using site classifications (Siccama, 1971; Zelazny et al.,

143 1997; Stewart et al., 2003; Sobey & Glen, 2004), and characterizations of remaining old-growth

144 (Greenidge, 1987; Chokkalingam & White, 2001; Mosseler et al., 2003a; Fraver & White; 2005;

145 D'Amato & Orwig, 2008; Fraver et al., 2009). In many historical records, trees are often described

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146 only to the genus level, such as birch (Betula spp.), pine (Pinus spp.) and spruce (Picea spp.),

147 which prevents distinguishing between predominantly boreal versus temperate species within the

148 same genus. Nonetheless, the combined approaches clearly illustrate a pre-settlement forest

149 dominated by temperate tree species, such as American (Fagus grandifolia), Sugar

150 (), Yellow Birch (), Eastern Hemlock, Red Spruce, and

151 Eastern White Cedar (Thuja occidentalis), and to a lesser extent, Eastern White Pine (Pinus

152 strobus), White Ash (Fraxinus americana), and Red Oak (Quercus rubra). The studies listed

153 above also illustrate that Balsam Fir played an important role in the pre-settlement forest, but with

154 higher proportions generally occurring in the north of the NEAF, as expected given its boreal

155 affinity. Furthermore, boreal tree species are known to have dominated under specific conditions,

156 such as in exposed coastal areas, acidicDraft wetlands, and high elevation zones (Seymour & Hunter,

157 1992; Mosseler, 2003a; Neily et al., 2017). Outside these localized conditions, tree species with

158 boreal affinities appear to have had minor compositional importance in the pre-settlement forest.

159 Lorimer (1977) suggests that, in northeastern Maine, “Shade-intolerant species, such as white

160 birch (Betula papyrifera), aspen (Populus spp.), pin cherry (Prunus pensylvanica), larch (Larix

161 laricina), and pine were of minor importance” (p. 145). Dupuis et al. (2011) found that, in eastern

162 Quebec, “…dominance of cedar, fir and spruce was strong and uniform across the study area. In

163 contrast, the dominance of maple and was patchy, especially for paper birch [White Birch]

164 …” (p. 6). In eastern New Brunswick, Crossland (2006) found that, “Shade-intolerant species,

165 such as Populus, Pinus resinosa, L. laricina, Prunus, Q. rubra (and probably B. papyrifera), were

166 only minor components of historic forest composition” (p. 121). Furthermore, within an old-growth

167 Red Spruce forest in northern Maine, Fraver & White (2005) found, “…no living or dead

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168 intolerant tree species, such as Betula papyrifera and Populus spp. ... despite their abundance in

169 the harvested landscape surrounding the Reserve” (p. 606).

170 European Settlement: 1600 – 1890

171 The period 1600–1890 marks the onset of European colonization of the NEAF. This period

172 consisted of nearly three centuries of timber harvesting and land clearing for agriculture (Keeton,

173 2006; Loo et al., 2010, Bell 1989, Parenteau 2013). Land clearing began as early as 1604-1605

174 with the first European settlements of Saint Croix Island in Maine and Port Royal in Nova Scotia

175 (Thierry, 2012). Commercial lumbering was also an important driver of forest change during this

176 period, beginning with intensive high-grading of Eastern White Pine for ship masts and ton timber

177 (Acheson, 2008; Loo et al., 2010; Crossland, 2006). Parenteau (2013) describes successive waves

178 of forest exploitation; Which species wereDraft sought, for how long, and to what extent were matters

179 closely tied to the geopolitics of Europe, as well as a variety of factors related to timber access.

180 Logging and land clearing continued to expand across the NEAF as European settlements grew

181 and new timber markets were exploited. Studies comparing pre- and post-settlement impacts to

182 the forest indicate that changes to forest composition were both widespread and severe. At one

183 extreme, approximately 70% of Prince Edward Island was cleared for agriculture by 1900, and

184 what forest remained was largely subject to burning and high-grading (Glen, 1997). Cavallin &

185 Vasseur (2009) suggest the impacts of land clearing and high-grading in Prince Edward Island

186 have resulted in a forest with, “…higher frequencies of balsam fir, red maple, white spruce, white

187 birch and trembling aspen” (p. 170). Both Loo et al. (2010) and MacDougall et al. (1999) identified

188 several forest communities that have been “greatly reduced” throughout eastern Canada in part

189 due to agricultural clearing, including rich tolerant , wet calcareous mixedwood, and

190 tolerant softwood. on calcareous soils and floodplains were particularly susceptible to land

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191 clearing for agriculture, resulting in declines in Bur Oak (Quercus macrocarpa; McPhee & Loo,

192 2009), Silver Maple (Acer saccharinum; MacDougall & Loo, 2002), and upwards of a 99% loss

193 of rich hardwood forest containing Basswood (Tilia americana), Ironwood (Ostrya virginiana),

194 and Butternut (Juglans cinerea) in western New Brunswick and northeastern Maine (Betts, 1999).

195 Although Maine, New Brunswick, Nova Scotia and the Quebec portion of the NEAF were

196 generally less affected by agricultural expansion compared to southern New England and Prince

197 Edward Island, waves of commercial logging, high-grading, and human-caused fire has left little

198 of the pre-settlement forest intact (Loo et al., 2010; Cronon, 1983). Thompson et al. (2013) state

199 that, across the northeastern U.S., “…logging and agricultural clearing were initiated that

200 removed more than half of the forest cover and cut over almost all of the rest” (p. 1). Mosseler et

201 al. (2000) suggest that Red Spruce hasDraft undergone a severe decline throughout its range due to,

202 “…a long history of selective removal, particularly during the 1800s…,” (p. 929). Seymour &

203 Hunter (1992) suggest that species such as White Pine, Red Spruce, and Yellow Birch have been,

204 “…greatly reduced in certain stand types through preferential high-grading and disease” (p. 9).

205 In Kings County, New Brunswick, Lutz (1997) concluded that temperate species such as Eastern

206 Hemlock, Eastern White Cedar, and Ash (Fraxinus spp.) have all declined since European

207 settlement, and that the current frequency of Balsam Fir has more than doubled. He goes on to

208 conclude that, “…white birch, poplar and red maple increased in areas where they were absent

209 two hundred years ago” (p. 66). In eastern Quebec, Dupuis et al. (2011) also found a significant

210 decline of Eastern White Cedar since European settlement, as well as an increase in Balsam Fir,

211 White Birch, maple, and poplar. In the eastern lowlands of New Brunswick, Crossland (2006)

212 found that White Elm, Ironwood, Eastern Hemlock, Eastern White Cedar, Eastern White Pine, and

213 American Beech have all declined. She goes on to state that, “[Balsam Fir] has doubled on many

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214 sites, and Populus has become the most abundant hardwood species. [Jack Pine], nearly absent

215 ca. 1800, has become the most dominant pine species” (p. iii). In northern Vermont, Siccama

216 (1971) found upwards of a 90% decline in the abundance of American Beech, and this is also

217 supported by Thompson et al. (2013) for the entire northeast U.S., who state that, “…while climate

218 and disease (particularly beech disease) may be contributing factors, the primary cause of

219 beech reduction locally and regionally is the disruption of the forest by deforestation, logging and

220 fire” (p. 12). In the Miramichi River watershed of New Brunswick, Aubé (2008) found declines in

221 Eastern Hemlock, White Elm, Eastern White Cedar, and “…presumably Yellow Birch…” (p.

222 1179), and concluded that, “…the Acadian forest bears more resemblance to the boreal forest than

223 it used to, at least in New Brunswick” (p. 1179). Similar results were found by Blackadar (2002)

224 in southwest Nova Scotia, with significantDraft declines in Sugar Maple, Eastern Hemlock, Eastern

225 White Pine, and Red Oak. In a historical review, Loo & Ives (2003) conclude that Sugar Maple,

226 Red Spruce, Eastern Hemlock, Yellow Birch, American Beech, and Eastern White Cedar have

227 declined throughout the Maritime Provinces, while Balsam Fir, Red Maple, White Spruce, White

228 Birch, and Trembling Aspen have increased.

229 As previously eluded to, anthropogenic fire also played a significant role in influencing the forest

230 composition of the NEAF (Lorimer, 1977; Crossland, 2006), such as the Miramichi fire of 1825,

231 which burned nearly 16,000 square km of forest in New Brunswick and Maine alone (MacEachern,

232 2014). While detailed compositional changes resulting from human-caused fires are scarce,

233 Ponomarenko et al. (2013) found that, in the eastern lowlands of New Brunswick, “...Pinus

234 banksiana [Jack Pine] – a fire-dependent species that is common and widespread in the modern

235 landscape, was absent at the time of land clearance” (p. 212). Furthermore, Loo et al. (2010)

236 suggest that mixedwood communities of fire adapted species such as of Jack Pine, Trembling

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237 Aspen, and Black Spruce have increased throughout eastern Canada since European settlement.

238 Fobes (1948) claims that, as forest was cleared for agriculture across Maine, “…fires increased in

239 number and extent to change markedly even the character of the original forest” (p. 269). He goes

240 on to suggest that much of the original spruce-fir and tolerant hardwood forest was replaced by,

241 “…light-seeded hardwoods such as aspen, grey and white birch and cherry” (p. 269).

242 While the bulk of evidence points towards a general decline in abundance of temperate tree

243 species, there is also evidence that several temperate species have benefitted from European

244 settlement. Abrams (1998) suggests that Red Maple was historically restricted to poorly drained

245 soils but has since become ubiquitous across the landscape due to land clearing, and this is

246 supported by several studies (Lees, 1978; Lutz, 1997; Loo & Ives, 2003; Cavallin & Vasseur,

247 2008). Although not stated explicitly Draft in the literature, numerous studies make reference to

248 increases in “poplar”, which would undoubtedly include Large-tooth Aspen. At the northern limit

249 of the NEAF, Dupuis et al. (2011) found that Sugar Maple increased in abundance since European

250 settlement, which is attributed to its ability to colonize cutover land and potentially due to climate

251 change. Nonetheless, with the exception of Red Maple, the available evidence demonstrates an

252 overall decline in temperate tree species throughout the NEAF due to widespread forest clearing

253 during the period of European colonization.

254 Post-European Settlement: 1890 – Present Day

255 The late 19th Century marked an increase in forest cover throughout New England and Maritime

256 Canada as a result of farmland abandonment (Census of Agriculture, 1971; Bell 1989), which was

257 followed by the rapid industrialization of forest harvesting in the mid-20th Century (Thompson et

258 al., 2013; Cronon, 1983). The previous centuries of high-grading and forest clearing not only

259 altered the abundance and diversity of tree species across the landscape, but as stated by Cronon

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260 (1983), created a new suite of growing conditions that were, “…sunnier, windier, hotter, colder,

261 and drier than they had been in their former state” (p. 123). As a result, pioneer and early

262 successional tree species became much more abundant (Thompson et al., 2013). Many boreal

263 species flourished under these new conditions, such as White Spruce, which Nienstaedt & Zasada

264 (1990) suggest is, “confined to abandoned fields in New England and the Maritime Provinces…”

265 (p. 207). In an early government report, Drinkwater (1957) suggested that White Spruce likely

266 occupied 500,000 acres (202,340 hectares) of abandoned farmland across Nova Scotia. Neily et

267 al. (2011) suggest that old-field forests in Nova Scotia today are, “typically dominated by White

268 Spruce, Tamarack, White Pine or Balsam Fir” (p. 109), and this is also supported by Simmons et

269 al. (1984). Old-field White Spruce is now one of the dominant forest communities across Prince

270 Edward Island due to farmland abandonmentDraft (Loo & Ives, 2003). The species is also known to

271 colonize old fields in Maine (Seymour, 1992), and is commonly associated with abandoned

272 farmland in New Brunswick alongside, “…poplar, white birch, grey birch and …” (Zelazny

273 et al., 2007; p. 45). Betts & Loo (2002) suggest that, “…White Spruce, poplar, Balsam Fir, and

274 White Birch are predominant species on old fields in the Maritimes” (p. 424). Although “poplar”

275 can refer to both Trembling Aspen and Largetooth Aspen (), both of which

276 are known to colonize old fields, the former generally appears to be more common (D’Orangeville

277 et al., 2008; Neily et al., 201l; D’Orangeville et al., 2011).

278 Although boreal tree species dominate abandoned farmland in the Maritime Provinces and

279 northern Maine, temperate species can also dominate abandoned farmland throughout the NEAF,

280 particularly in southern New England (Hibbs, 1983; Loo et al., 2010). This is particularly the case

281 for Eastern White Pine, which Abrams (2001) suggests may be more abundant in New England

282 today than prior to European settlement due to its ability to colonize abandoned farmland. In

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283 northern Vermont, Siccama (1971) found that, “The present success of pine (mostly white pine),

284 hardhack [Tamarack] and poplar is related to their role in secondary succession on abandoned

285 farmlands” (p.170). It is also worth noting that both Red Spruce and Eastern White Cedar are

286 known to colonize old fields, although these tend to occur under specific localized conditions and

287 are uncommon (Seymour, 1992; Cavallin & Vasseur, 2009; Curtis, 1946).

288 In addition to farmland abandonment and natural reforestation, forest harvesting – in a variety of

289 forms - has also influenced the present-day forest composition in the NEAF. While logging and

290 high-grading have been ongoing since European settlement, commercial- and industrial-scale

291 clearcutting in the NEAF began in the mid-1900s (Seymour et al., 2006; Nelson et al., 2012a). The

292 large forest openings created by clearcutting continue to perpetuate the growing conditions

293 previously listed by Cronon (1983), andDraft as stated by Salonius (2007), “…has led to increasing

294 representations of formerly rare, large-opening opportunist species […] that are more common in

295 boreal ecosystems” (p. 91). studies have consistently shown that clearcutting favours

296 early successional species, namely intolerant hardwoods and Balsam Fir (Saunders & Wagner,

297 2008; Weaver et al., 2009; Olson & Wagner, 2010; Arseneault et al., 2011; Nelson et al., 2012a;

298 Salmon et al., 2016). Seymour (2005), states that, “...typical stand compositions have shifted from

299 the slower-growing, late-successional species to those that are favored by frequent harvest

300 disturbance, such as red maple, paper birch (Betula papyrifera Marsh.), aspen (Populus spp.),

301 and balsam fir” (p. 42). According to Butler (2017), Balsam Fir accounts for 36% of all the trees

302 in Maine, which is three times more than any other species. Clearcutting has also been attributed

303 to the reduction of several forest communities throughout eastern Canada, including wet

304 calcareous mixedwood forests composed of Eastern White Cedar, Black Ash, and Red Maple, and

305 tolerant softwood composed of Red Spruce, White Pine, and Eastern Hemlock (Loo et al., 2010;

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306 MacDougall et al., 1998). Both high-grading and clearcutting are attributed to the severe decline

307 of Red Spruce throughout the Maritime provinces (Major et al., 2003; Dumais & Prévost, 2007;

308 Mosseler et al., 2003a; 2003b; Loo et al., 2010), and Fraver & White (2005) conclude that, “Only

309 0.02% of the pre-settlement [Red Spruce]-dominated forests remains unharvested in the

310 northeastern USA” (p. 598).

311 While abandoned farmland and clearcutting have directly favoured boreal tree species at the

312 expense of temperate ones, as stated by Salonius (2007), “Plantation silviculture with boreal

313 to enhance softwood fiber production has hastened such species transitions” (p. 91).

314 Although industrial conifer plantations are generally uncommon in the New England portion of

315 the NEAF (Seymour & Hunter, 1992), there has been considerable focus on plantation forestry in

316 the Maritimes, particularly in New BrunswickDraft (Ross-Davis & Frego, 2002; MacDougall et al.,

317 1998; Salmon et al., 2016). According to the National Forestry Database (2018), over 778,200

318 hectares (1.92M acres) of conifer plantations have been established in the Maritime Provinces

319 between 1990 and 2016, 67% of which were in New Brunswick.

320 Plantation forestry has traditionally relied on a handful of fast-growing tree species that are

321 exposure-tolerant, such as Tamarack, Jack Pine, White Pine, Red Pine and White Spruce

322 (McWilliams et al., 2005; Nelson et al., 2012b; Etheridge et al., 2005). Norway Spruce (Picea

323 abies) – a Eurasian boreal species, was also commonly planted in the 1970s and ‘80s and is

324 considered the most widely planted exotic tree in eastern North America (NS DLF, 1990). While

325 industrial pine plantations are generally found in southern New England (Fisher, 1928), Jack Pine

326 has been planted extensively in New Brunswick, which Erdle & Pollard (2002) state is, “…three

327 times more abundant in plantations than in the replaced natural forest” (p. 816). In contrast, Red

328 Spruce, “…comprises 1% of plantation volume in contrast to the 14% it made up in natural forest

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329 replaced by plantations” (p. 816). Throughout the Maritime Provinces, Freedman et al. (1994)

330 makes reference to “…the widespread establishment of white spruce in intensively managed

331 plantations up until the mid-1980s” (p. 43). In a compositional review of a 189,000-hectare

332 land base in northwestern New Brunswick, Etheridge et al. (2006) state that, “Although the

333 overall amount of softwood was similar in 1945 and 2002, nearly all of this area (88%) was

334 comprised of plantations in 2002. These included 56% black spruce, 30% white spruce, 9%

335 Norway spruce….” (p. 513). Black, White, and Norway Spruce were also cited by Boucher et

336 al. (2009) as covering 22% of a 117,000-hectare land base in eastern Quebec.

337 While it is difficult to ascertain to what degree plantations have replaced temperate forest 338 communities across the NEAF, activeDraft conversion of hardwood forest to conifer plantation was 339 common in the Maritimes prior to the early 1990s (Salmon et al., 2016). Loo et al. (2010) also

340 identified several forest communities that have been impacted by plantation establishment in the

341 region, including ridge-top hardwoods composed of Sugar Maple, Beech, Yellow Birch, White

342 Ash, and Ironwood, as well as upland mixedwoods composed of Sugar Maple, Yellow Birch, Red

343 Spruce, Beech, Balsam Fir, White Pine, Eastern Hemlock, and Eastern White Cedar. While it is

344 clear that plantations have at least partially contributed to the decline of temperate tree species and

345 communities in the NEAF, it should be noted that this is not always the case. In many instances,

346 forest communities replaced by plantations were already largely comprised of boreal species

347 as a result of past land use practices and anthropogenic fire (see Etheridge et al., 2005).

348 Additionally, temperate tree species such as Red Spruce, Eastern White Cedar, and White Pine

349 are increasingly being used in mixed conifer plantations (Erdle & Pollard, 2002; Dumais &

350 Prévost, 2007), although the ratio of temperate to boreal species planted across the NEAF is

351 currently unknown.

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352 DISCUSSION:

353 Throughout the world, the term borealization is increasingly being used to describe

354 anthropogenic ecosystem changes that directly or indirectly favour boreal species at the expense

355 of non-boreal ones. This study was undertaken to determine whether these claims hold true for the

356 NEAF. While we recognize that forests are composed of many biotic and abiotic elements, and

357 are thus considerably more complex than the composition of trees alone, trees play an outsized

358 role in both the structure and function of forest communities, and for this reason, we have limited

359 the scope of this work to focus on changes to tree species compositions. Within this scope, our

360 research suggests that borealization is an accurate descriptor of what has occurred across the region

361 since European settlement, as the two definition criteria have been met: (1) evidence of a

362 significant decline in temperate tree speciesDraft that once dominated the landscape, such as Red

363 Spruce, Sugar Maple, Yellow Birch, Eastern Hemlock, Beech and several other species considered

364 rare or uncommon today, and (2) evidence of a significant increase in boreal tree species, including

365 Balsam Fir, White Birch, Jack Pine, Black Spruce, Trembling Aspen and White Spruce. While the

366 primary drivers are varied and often layered, in its simplest form, borealization is the product of

367 opening up what was previously a closed- forest, allowing exposure-adapted boreal species

368 to colonize. In the first several centuries of European settlement, this occurred as a result of high-

369 grading for commercial and subsistence purposes and clearing to convert forested land to

370 agriculture. The novel conditions that resulted from opening up the forest allowed both accidental

371 and intentional fires to burn massive swaths of the region, thus further promoting the colonization

372 of boreal tree species. Although farmland abandonment near the turn of the 20th century increased

373 the overall forest cover, this was also to the benefit of boreal tree species, particularly in the

374 northern half of the NEAF. Modern-day forestry practices, such as clearcutting and intensive

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375 conifer-based silviculture, have perpetuated the growing conditions favourable to boreal tree

376 species, and continue to do so today. While our study shows that borealization has occurred

377 throughout the NEAF in response to these drivers, it appears that borealization is “truer” as one

378 moves north, which stands to reason given the north-south climate gradient of boreal-temperate

379 biomes.

380 The current research, although anecdotal in places, clearly illustrates that the NEAF has indeed

381 undergone borealization over the past 400 years. However, given the many challenges and

382 limitations to this work, we are unable to state with any confidence the actual percentages or total

383 area of land that has been impacted. The NEAF straddles two nations and more than half a dozen

384 states and provinces, and very few studies include both Canadian and U.S. sources. Additionally,

385 the supporting evidence varies significantlyDraft in its methods and spatial and temporal scales, making

386 it nearly impossible to assess the extent of borealization in its entirety. The degree to which we

387 can rely on any single study to accurately characterize species-specific forest compositions within

388 a defined geography is directly related to how far back in time the study aims to reveal; pre-

389 settlement forest characterizations are generally less reliable than those following European

390 settlement, which in turn are less reliable than modern silvicultural studies and characterizations

391 of remaining old growth. While the combined evidence plainly demonstrates an increase in boreal

392 tree species at the expense of temperate ones, quantifying this change over a period of 400 years

393 is near impossible. Nonetheless, summarising the available evidence at an ecoregional scale is a

394 significant contribution to this body of work. Furthermore, doing so has led to several interesting

395 findings that warrant further investigation. Firstly, it is clear that much of the NEAF has undergone

396 two or more successive rounds of high-grading, clearing for agriculture, fire and/or harvesting

397 since European settlement. Even within what we characterize as the modern period (1890 –

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398 present), a significant proportion of the region has been harvested multiple times, albeit under

399 different silvicultural regimes. For example, softwood high-grading would have been common

400 practice prior to the collapse of the sawmill industry in the post -WWI era. If harvested again in

401 the post-WWII era, it was likely clearcut and allowed to regenerate naturally. If harvested again in

402 the last 50 years, clearcutting was likely followed by one or more silvicultural treatments that

403 favoured boreal conifers, such as planting, thinning or herbicide application. Each successive wave

404 of high-grading, clearing and/or harvesting had the compounding effect of both promoting the

405 regeneration of boreal species, while simultaneously decreasing the available source of

406 temperate tree species (with notable exceptions, such as Red Maple and Large-toothed Aspen),

407 and thus limiting their ability to recover.

408 In addition to borealization, our researchDraft also reveals two distinct but related forest processes that

409 have also taken place across the NEAF over the last 400 years. The first we term “forest

410 infantization”, which refers to both the perpetually young state of the forest due to the short harvest

411 rotations that became commonplace following the pulp and paper era of the 1930s, as well as the

412 hyperabundance of pioneer and early-successional tree species, regardless of their boreal or

413 temperate affinity. As shown previously, the drivers of borealization also tend to favour early

414 successional temperate species such as Red Maple and Large-tooth Aspen, providing further

415 evidence for the wide-scale replacement of long-lived, shade-tolerant (i.e. late-successional) tree

416 species. In a status review of northeastern forests, Anderson & Olivero-Sheldon (2011) suggest

417 that, “…our forests are overwhelmingly similar in age...” (p. 4-19), with an average cutting

418 rotation of 60 years or less. Furthermore, it is well established that old forest is rare throughout the

419 NEAF and is widely recognized as a conservation concern (Mosseler et al., 2003a; Davis, 1996).

420 The second process we term “forest bifurcation”, which describes a transition away from natural

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421 mixedwood communities toward pure hardwood or softwood. The former is a result of the

422 common past practice of high-grading softwoods such as White Pine, Red Spruce and Eastern

423 Hemlock from tolerant hardwood and mixedwood stands (Kelty & D'Amato, 2006), whereas the

424 latter is a product of conifer-based silvicultural practices involving planting, thinning, and

425 herbicide application that have directly favoured softwoods to the exclusion of hardwoods

426 throughout the NEAF (see Etheridge et al., 2005; 2006). Combined, these processes illustrate a

427 400-year trend towards a more simplified forest structure and composition at the landscape scale.

428 However, similar to borealization, actual percentages or total area of impacted land is unknown

429 for each of these processes. Regardless of this uncertainty, these processes warrant further

430 investigation, both individually and in combination with borealization, as they undoubtedly have

431 both economic and biodiversity implicationsDraft that are not currently understood.

432 While our objective was simply to review past scholarship to better understand changes in tree

433 species over time, we were also naturally led to speculate about the future of the NEAF,

434 particularly in the context of climate change. As asserted by Salonius (2007), “… short-lived,

435 exposure-tolerant, boreal tree species that regenerate in large forest openings are believed to be

436 less able, than the late-successional Acadian species they replace, to adapt to the climate warming

437 expected during the next forest rotation” (p. 91). Among predictive studies that covered the NEAF,

438 we found general consensus that boreal tree species will decline in the face of climate change, and

439 that temperate species will increase (Iverson & Prasad, 1998; Bourque & Hassan, 2008; Taylor et

440 al., 2017). Bourque and Hassan (2008) predict declines in Black Spruce and Balsam Fir due to

441 climate change, while species such as Yellow Birch, White Pine and Red Oak are predicted to

442 increase. Taylor et al. (2017) support these findings, and state that, “…under rapid 21st century

443 warming, Canada’s Acadian Forest Region will begin to lose its boreal character (i.e.,

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444 “deborealize”) as key tree species fail to regenerate and survive” (p. 1). While there is general

445 agreement among these studies that boreal tree species will likely decline as a result of climate

446 change, whether these predicted impacts apply to high-input plantations composed of boreal

447 conifers is to be seen. None of the predictive studies account for the effects of intensive

448 competition control, and it is conceivable that the combined effects of intensive management

449 coupled with a warmer and wetter climate may in fact increase the productivity of boreal conifer

450 plantations.

451 The results of this study, while somewhat generalized, have significant management

452 implications, not least of which relate to the “shifting baseline syndrome” that is pervasive in

453 natural resource management (Papworth et al., 2009; Vera, 2010; Soga & Gaston, 2018). This

454 phenomenon occurs as each successive Draftgeneration of scientists and managers tend to perceive the

455 environment at the beginning of their careers as the unaffected baseline condition against which

456 changes are compared. Soga & Gaston (2018) suggest that this gradual trend results in three

457 consequences: (1) an increased tolerance of ecological degradation over time, (2) an altered sense

458 of what is “desirable” or “good” from a management perspective, and (3) the setting of

459 inappropriate management targets based on reference conditions that have already been drastically

460 degraded. The NEAF has not been immune to these consequences, and we hope that this body of

461 work can assist in combatting them. Given that many temperate tree species in the NEAF are of

462 conservation concern due to past land use practices, and that the same species are generally

463 predicted to fare well in the face of climate change, we provide the following four

464 recommendations: (1) forest conservation efforts should focus on protecting remaining examples

465 of temperate forest communities in the NEAF, with priority going towards those that have

466 witnessed severe declines. Not only are they important from a biodiversity conservation

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467 perspective, but also from a climate-adaptation one, as they will likely serve as important seed

468 sources as the forest transitions to a more temperate nature in response to climate change; (2) forest

469 managers should consider transitioning to silvicultural practices that reverse borealization and

470 promote the regeneration of temperate tree species. This holds true for ecological restoration to

471 support the recovery of uncommon temperate forest communities and the wildlife that depend on

472 them, and may also hold true for commercial and industrial forestry operations. Given the risks

473 associated with climate change and the lengthy timeframes required to realize a return on

474 investment (whether ecological or economic), the opportunity costs of a climate-adapted

475 management strategy cannot be overlooked or ignored; (3) forest education programs, both formal

476 and informal, should focus on promoting firsthand experiences with remaining old-growth forests

477 across the NEAF. The shifting baselineDraft will continue to shift unless forest managers and

478 conservationists are able to recognise the differences between past and current forest conditions,

479 and this requires directly interacting with those conditions; (4) further research on the broader

480 social, ecological and economic impacts of borealization in the NEAF is warranted, including

481 research that expands the scope of borealization to non-tree biodiversity. We advocate for

482 silviculture trials aimed at reversing borealization and regenerating temperate species, as well as

483 trials designed to assess whether the predicted effects from climate change hold true for intensively

484 managed conifer plantations. Given the rate of climate change and biodiversity loss, we

485 recommend adopting an applied-science model for these studies, so that lessons can quickly be

486 translated into management.

487 CONCLUSION

488 There have been numerous published references and anecdotal claims that the New England –

489 Acadian Forest has undergone “borealization” as a result of past land use practices. While the

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490 amount and degree is impossible to discern with any precision, our review concludes

491 unequivocally that borealization has occurred throughout the New England Acadian Forest over

492 the last 400 years. The main drivers which have contributed` to borealization are high-grading,

493 clearing and subsequent abandonment of agricultural land, anthropogenic fire, clearcutting and

494 preferential conifer silviculture that directly favours boreal species. As a result of these practices,

495 many temperate forest communities are of conservation concern today. However, climate change

496 is generally predicted to favour temperate species over boreal ones, providing opportunity for

497 rebalancing historic tree species distributions and forest stand composition as well as improved

498 forest conservation, restoration and commercial management practices.

499

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753 McWilliams WH, Butler BJ, Caldwell LE, Griffith DM, Hoppus ML, Laustsen KM, Lister AJ,

754 Lister TW, Metzler JW, Morin RS, Sader SA, Stewart LB, Steinman JR, Westfall JA, Williams

755 DA, Whitman A, Woodall CW (2005) The forests of Maine: 2003. Resour Bull NE-164. US

756 Department of Agriculture, Forest Service, Northeastern Research Station. Newtown Square

757

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758 Mosseler, A., Lynds, J. A., & Major, J. E. (2003a). Old-growth forests of the Acadian Forest

759 Region. Environmental Reviews, 11(S1), S47-S77.

760

761 Mosseler, A., Major, J. E., & Rajora, O. P. (2003b). Old-growth red spruce forests as reservoirs

762 of genetic diversity and reproductive fitness. Theoretical and Applied Genetics, 106(5), 931-

763 937.

764

765 Mosseler, A., Major, J. E., Simpson, J. D., Daigle, B., Lange, K., Park, Y. S., ... & Rajora, O. P.

766 (2000). Indicators of population viability in red spruce, Picea rubens. I. Reproductive traits and

767 fecundity. Canadian Journal of Botany, 78(7), 928-940.

768 Draft

769 Mott, R. J. (1975). Palynological studies of lake sediment profiles from southwestern New

770 Brunswick. Canadian Journal of Earth Sciences, 12(2), 273-288.

771

772 National Forestry Database. (2018). 6.2.2 Area planted by jurisdiction, tenure and species group.

773 Canadian Council of Forest Ministers. Accessed Feb 6, 2019. Online:

774 http://nfdp.ccfm.org/en/terms.php

775

776 Neily, P., Basquill, S., Quigley, E & Keys, K. (2017). Ecological Land Classification for Nova

777 Scotia. Nova Scotia Department of Natural Resources, Renewable Resources Branch. REPORT

778 FOR 2017–13.

779

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780 Neily, P., Basquill, S., Quigley, E., Stewart, B. & Keys, K. (2011). Forest Ecosystem Classification

781 for Nova Scotia. Part I: Vegetation Types (2010). Nova Scotia Department of Natural Resources,

782 Renewable Resources Branch.

783

784 Nelson, A. S., Wagner, R. G., Saunders, M. R., & Weiskittel, A. R. (2012a). Influence of

785 management intensity on the productivity of early successional Acadian stands in eastern Maine.

786 Forestry, 86(1), 79-90.

787

788 Nelson, A. S., Saunders, M. R., Wagner, R. G., & Weiskittel, A. R. (2012b). Early stand production

789 of hybrid poplar and white spruce in mixed and monospecific plantations in eastern Maine. New

790 forests, 43(4), 519-534. Draft

791

792 Nienstaedt, H., & Zasada, J. C. (1990). White Spruce. In: Burns, R.M., & Honkala, B.H. (eds.).

793 Silvics of north America (Vol. 1). Washington, DC: United States Department of Agriculture.

794 pp389-442.

795

796 NS DLF (Nova Scotia Dept. of Lands and Forests). (1990). Norway Spruce: Growth Potential

797 for Nova Scotia. Forest Research Report. Online:

798 https://novascotia.ca/natr/library/forestry/reports/REPORT24.PDF

799

800 Olson, M. G., & Wagner, R. G. (2010). Long-term compositional dynamics of Acadian

801 mixedwood stands under different silvicultural regimes. Canadian journal of forest research,

802 40(10), 1993-2002.

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803

804 Olson, D.M., E. Dinerstein, E.D. Wikramanayake, N.D. Burgess, G.V.N. Powell, E.C.

805 Underwood, J.A. D'Amico, I. Itoua, H.E. Strand, J.C. Morrison, C.J. Loucks, T.F. Allnutt, T.H.

806 Ricketts, Y. Kura, J.F. Lamoreux, W.W. Wettengel, P. Hedao, and K.R. Kassem. (2001).

807 Terrestrial Ecoregions of the World: A New Map of Life on Earth. BioScience 51:933-938.

808

809 Papworth, S. K., Rist, J., Coad, L., & Milner-Gulland, E. J. (2009). Evidence for shifting

810 baseline syndrome in conservation. Conservation letters, 2(2), 93-100.

811

812 Parenteau, B. (2013). Looking Backward, Looking Ahead:: History and Future of the New

813 Brunswick Forest Industries. Acadiensis,Draft 42(2), 92-113.

814

815 Ponomarenko, E. V., Crossland, D., & Loo, J. (2013). Reconstructing tree species composition at

816 the time of land clearance: two approaches compared. In Charcoal and microcharcoal. Continental

817 records. F. Damblon, ed., Acts of the 4th International Meeting of Anthracology. Proceedings of

818 the 4th International Meeting of Anthracology. BAR International Series (Vol. 2486, pp. 203-214).

819

820 Ramovs, B. V., & Roberts, M. R. (2005). Response of plant functional groups within plantations

821 and naturally regenerated forests in southern New Brunswick, Canada. Canadian Journal of Forest

822 Research, 35(6), 1261-1276.

823

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824 Ross-Davis, A. L., & Frego, K. A. (2002). Comparison of plantations and naturally regenerated

825 clearcuts in the Acadian Forest: forest floor bryophyte community and features. Canadian

826 Journal of Botany, 80(1), 21-33.

827

828 Salmon, L., Kershaw Jr, J. A., Taylor, A. R., Krasowski, M., & Lavigne, M. B. (2016). Exploring

829 factors influencing species natural regeneration response following harvesting in the Acadian

830 forests of New Brunswick. Open Journal of Forestry, 6(03), 199.

831

832 Salonius, P. (2007). Silvicultural discipline to maintain Acadian forest resilience. Northern Journal

833 of Applied Forestry, 24(2), 91-97.

834 Draft

835 Saunders, M. R., & Wagner, R. G. (2008). Long-term spatial and structural dynamics in Acadian

836 mixedwood stands managed under various silvicultural systems. Canadian Journal of Forest

837 Research, 38(3), 498-517.

838

839 Seymour, R.S. (1992). The red spruce-balsam fir forest of Maine: evolution of silvicultural practice

840 in response to stand development patterns and disturbances. In: Kelty, M. J., Larson, B. C., &

841 Oliver, C. D. (eds.) The ecology and silviculture of mixed-species forests. Springer, Dordrecht.

842

843 Seymour, R.S. (2005). Integrating natural disturbance parameters into conventional silvicultural

844 systems: experience from the Acadian forest of northeastern North America. United States

845 Department of Agriculture Forest Service General Technical Report Pnw, 635, 41.

846

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847 Seymour, R. S., Guldin, J., Marshall, D., & Palik, B. (2006). Large-scale, long-term silvicultural

848 experiments in the United States: historical overview and contemporary examples. Allgemeine

849 Forst und Jagdzeitung. 177: 104-112.

850

851 Seymour, R. S., & Hunter, M. L. (1992). New forestry in eastern spruce-fir forests: principles and

852 applications to Maine (Vol. 716). College of Forest Resources, University of Maine.

853

854 Seymour, R.S., White, A.S. & deMaynadier, P.G. (2002). Natural disturbance regimes in

855 northeastern North America—evaluating silvicultural systems using natural scales and

856 frequencies. Forest Ecology and Management, 155(1-3), 357-367.

857 Draft

858 Siccama, T. G. (1971). Presettlement and present forest vegetation in northern Vermont with

859 special reference to Chittenden County. American Midland Naturalist, 153-172.

860

861 Sobey, D. G., & Glen, W. M. (2004). A mapping of the present and past forest-types of Prince

862 Edward Island. The Canadian Field-Naturalist, 118(4), 504-520.

863

864 Soga, M., & Gaston, K. J. (2018). Shifting baseline syndrome: causes, consequences, and

865 implications. Frontiers in Ecology and the Environment, 16(4), 222-230.

866

867 Stewart, B. J., Neily, P. D., Quigley, E. J., & Benjamin, L. K. (2003). Selected Nova Scotia old-

868 growth forests: age, ecology, structure, scoring. The Forestry Chronicle, 79(3), 632-644.

869

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870 Taylor, A. R., Boulanger, Y., Price, D. T., Cyr, D., McGarrigle, E., Rammer, W., & Kershaw, J.

871 A. (2017). Rapid 21st century climate change projected to shift composition and growth of

872 Canada’s Acadian Forest Region. Forest Ecology and Management, 405, 284-294.

873

874 Taylor, A. R., & Chen, H. Y. (2011). Multiple successional pathways of boreal forest stands in

875 central Canada. Ecography, 34(2), 208-219.

876

877 Thierry, E. (2012). French Settlement, 1604-1613. In: Pendery, S. (ed.) Saint Croix Island, Maine:

878 History, Archaeology, and Interpretation. Occasional Publications in Maine Archaeology, No. 14.

879 Maine Historic Preservation Commission and the Maine Archaeological Society, Augusta. 310 pp.

880 Draft

881 Thompson, J. R., Carpenter, D. N., Cogbill, C. V., & Foster, D. R. (2013). Four centuries of change

882 in northeastern United States forests. PLoS One, 8(9), 40.

883

884 Vera, F. (2010). The shifting baseline syndrome in restoration ecology. In Restoration and

885 History (pp. 116-128). Routledge.

886

887 Weaver, J. K., Kenefic, L. S., Seymour, R. S., & Brissette, J. C. (2009). Decaying and tree

888 regeneration in the Acadian Forest of Maine, USA. Forest Ecology and Management, 257(7),

889 1623-1628.

890

891 Zelazny, V. F., Martin, G. L., Toner, M., Gorman, M., Colpitts, M., Veen, H., ... & Roberts, M.

892 (2007). Our landscape heritage: the story of ecological land classification in New Brunswick.

39 https://mc06.manuscriptcentral.com/er-pubs Environmental Reviews Page 40 of 42

893 New Brunswick Department of Natural Resources, Hugh John Fleming Forestry Centre,

894 Fredericton, NB E3C 2G6, Canada.

895

896 Zelazny, V., H. Veen & M. Colpitts. (1997). Potential Forests of the Fundy Model Forest.

897 Department of Natural Resources and Energy, Fredericton, N.B.

Draft

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Draft

899

900 Figure 1. The New England – Acadian Forest Region; Map created by Josh Noseworthy in ArcMap

901 10.3 (ESRI, 2015). Ecoregional boundary adapted from the Terrestrial Ecoregions of the World

902 (Olson et al., 2001).

41 https://mc06.manuscriptcentral.com/er-pubs Environmental Reviews Page 42 of 42

Draft

903 Figure 2. The proportion of 30 native tree species ranges’ that occur within the North American

904 boreal region. Proportions were calculated in a GIS using United States Forest Service range maps

905 for each species (Little, 1971; 1976; 1977) overlaid on the North American Boreal Zone as

906 delineated by the Canadian Forest Service (Brandt, 2009). Species were considered boreal if >50%

907 of their range fell within the North American Boreal Zone.

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