Figure 7. Atlantic white cedar logs in exposed freshwater peat underlying a salt marsh on Buzzard's Bay, 

 Massachusetts. Note that many trunl<s and roots remain as they grew in the forest floor. Photo by I . Laderman. 



1 .4.3 Time and Path of Migration 



Atlantic white cedar appears to have moved 

 southward to refugia on the Gulf Coastal Plain during 

 full glaciation (Belling 1977; Delcourt and Delcourt 

 1977). It probably began its northward migration 

 from the Gulf refugia during the late glacial period, 

 between 17,000 and 10,000 years B.P (Belling 1977 

 and unpubl.). Some evidence for this view is that 

 cedar (Cupressaceae) pollen grains are found in 

 North Carolina sediments that predate the most 

 recent glaciation (25,000 yrs B.P), but are absent 

 during the glacial epoch (21,000 to 10,000 yrs B.P). 

 Cupressaceae pollen reappears there at 10,000 yrs 

 B.P (the beginning of the present interglacial period), 

 and is continuously recorded in the peats until the 

 present time (Whitehead 1981). 



Dated macrofossils of Atlantic white cedar 

 from as early as 9500 yrs B. P (Watts 1 979) and 7700 

 yrs B.P (Psuty et al. 1983) were recorded from un- 

 glaciated sites (Table 1; Figure 8). Most 

 palynologists do not distinguish between the pollen 

 grains of Thuja, Juniperus, and Chamaecyparis, 

 which are all in the family Cupressaceae and are very 

 similar in pollen morphology (see Figures 2 and 3). 

 Belling (1977 and unpubl.) uses macrofossil 

 evidence in conjunction with pollen data to separate 

 the three genera and outlines a probable sequence 

 of cedar migration in the glaciated region. Arrival of 

 the species at specific sites during postglacial time 

 was determined by radiocarbon dating results for 



peats containing both macrofossil and pollen evi- 

 dence. Belling (unpubl.) postulates that northward 

 movement of Atlantic white cedar was influenced 

 more by the distance from the nearest refugium (i.e., 

 the seed source) and the availability of suitable 

 growth sites than solely by warmer climate. The 

 most suitable sites are those with a favorable water 

 regimen (discussed in Section 3.2 [silvical habits] 

 and Section 4.1 [hydrology]) and a consolidated 

 peat substrate . 



Basin depths range from 3 to 9 m in glacial 

 sites; the build-up of peat is evidence of the rise in 

 water tables throughout the region. Belling (1977 

 and unpubl.) noted that Atlantic white cedar was vir- 

 tually continuous in all sampled glaciated sites from 

 the time of its establishment to the present. 



1.4.4 Sediment Stratigraphy 



Peat contains an excellent record of events 

 and biological succession. Sediment cores from 

 cedar bogs in the glaciated region reveal a well- 

 defined vertical stratigraphy (Figure 9). At most sites, 

 the overlying organic layer consists, in descending 

 sequence, of woody cedar peat, woody-fibrous or fi- 

 brous shrub peat, sedge peat, mossy peat (rarely), 

 and finally gyttja formed from benthic and planktonic 

 lake flora and fauna. The inorganic basal sediments 

 are composed of sand and/or clay. Water layers may 

 interrupt the sediments. 



