Presettlement forests of North America

These forests covered an enormous area and few remain in anything like their original condition, but Friedman et al. (2001) have used data collected during the General Land Office Survey (GLO) between 1853 and 1917 to throw light on the north-east Minnesota southern or hemiboreal presettlement forest in a landscape which occupied 32 000 km2. The mapping scheme employed dated from as long ago as 1785; it involved the collection of data at intersecting points (marked by trees or cairns) within a nested mapping scheme for the 64 years before the initiation of logging and local settlement. This involved the identification of the tree species present, of which there were 40, and recording individuals in size classes. Black spruce Picea mariana was by far the most abundant tree and in some cases was not properly distinguished from the much less abundant white spruce P. glauca. White and red pines (Pinus strobus and P. resinosa) were by far the largest trees and together accounted for 9% of the trees present, with white pine having 20.1% and red pine 7.3% of the total basal area of all trees.

Arrowhead Identification Region
Figure 9.5 Physiographic zones of the Arrowhead Region, north-east Minnesota, USA, used in Fig. 9.6. (Redrawn from Friedman et al. 2001. Journal of Ecology 89, Blackwell Publishing.)

Figure 9.5 shows the eight physiographic zones present in this heavily glaciated area, while Fig. 9.6 indicates the distributions of the nine most abundant tree species. Most of the Arrowhead region is covered by moraine, but Holocene peats form the dominant geological material in the Glacial Lakes Upham and Aitkin zone, where larch accounted for 43.2% of tree species composition and 31.9% basal area. The Toimi and the Brainerd Autoinba zones are both occupied by drumlins, streamlined ridges with their long axes parallel to the flow of the glacial ice that moulded them from soft sediment. The eight zones supported different compositional mixes of the nine tree species which each accounted for more than 1% of the total tree population; the other 31 species accounted for only 6.1% between them. Spruce had a relatively even distribution in most of the Arrowhead region.

Landscape patterns of the tree species were measured at two spatial scales: 1-10 km and 5-50 km. This investigation shows how spatial patterns of forest trees were influenced on local to landscape scales by particular environmental factors, disturbance events and regeneration strategies.

Factor Tree For 140 Map Arrowhead Region

Figure 9.6 Distribution maps of the nine most abundant tree species (during the period 1853 and 1917) in the Arrowhead region, north-east Minnesota. Dots on these maps indicate plots in which three or four individuals of the same species occurred. Colonization patterns of these southern boreal species after stand-killing fires involved different regeneration strategies. Species dependent on seeds from surrounding unburnt trees included (b) white pine Pinus strobus, (c) northern white cedar Thuja occidentalis, (d) red pine Pinus resinosa, (f) balsam fir Abies balsamea, (i) larch Larix laricina (a late-successional larch) and (not shown) white spruce Picea glauca. Trees of (a) jack pine Pinus banksiana, (e) aspen Populus tremuloides and (h) black spruce Picea mariana burn and then regenerate vegetatively or from seeds in canopy-stored serotinous cones (see Section 3.7.1). Paper birch (g) Betula papyrifera regenerates from both fire-damaged stumps and blown seed from adjacent stands. (From Friedman et al. 2001. Journal of Ecology 89, Blackwell Publishing.)

Map East Mariana Basin

Figure 9.6 Distribution maps of the nine most abundant tree species (during the period 1853 and 1917) in the Arrowhead region, north-east Minnesota. Dots on these maps indicate plots in which three or four individuals of the same species occurred. Colonization patterns of these southern boreal species after stand-killing fires involved different regeneration strategies. Species dependent on seeds from surrounding unburnt trees included (b) white pine Pinus strobus, (c) northern white cedar Thuja occidentalis, (d) red pine Pinus resinosa, (f) balsam fir Abies balsamea, (i) larch Larix laricina (a late-successional larch) and (not shown) white spruce Picea glauca. Trees of (a) jack pine Pinus banksiana, (e) aspen Populus tremuloides and (h) black spruce Picea mariana burn and then regenerate vegetatively or from seeds in canopy-stored serotinous cones (see Section 3.7.1). Paper birch (g) Betula papyrifera regenerates from both fire-damaged stumps and blown seed from adjacent stands. (From Friedman et al. 2001. Journal of Ecology 89, Blackwell Publishing.)

9.1.6 Presettlement forests of the Amazon Basin

It should be mentioned here that what appear to be pristine forests might hide a different past. Over recent years the idea has been taking hold that the Amazon basin was not covered in pristine natural forest when the first post-Columbus colonists arrived after 1492. Rather, Amerindians who had been there for thousands of years may have developed a very highly modified landscape consisting of earthworks many kilometres long, major roads, big settlements, agricultural fields associated with terrapreta soils (Section 2.5.1), and a variety of wetland features such as bridges, causeways, canals and fishing ponds (Heckenberger et al, 2003). In fact, some people believe that in 1491 more people lived in the Americas than in Europe (Crosby, 1972). The reason why we do not see this now, some anthropologists argue, is due to the widespread and catastrophic post-Colombian depopulation from introduced disease, similar to that which happened in North America. Others disagree (e.g. Meggers, 1996) and suggest that the poor soils can never have supported more than small, often shifting populations. There is still no hard and fast consensus but the evidence does seem to be leaning towards the apparently pristine forests really being lush secondary growth following abandonment.

Similar but more recent (and thus documented) depopulation is known to have happened along the eastern seaboard of the USA - see Section 9.4.2 below.

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