Our Living Rfstnirres — Terrestrial Ecosystems 



225 



Coring a small pond at Pictured Rocks National 

 Lakeshore. 



{Lycaeides melissa samiielis). Although this site 

 has experienced more disturbances than any of 

 the others described here, it is a most valuable 

 site because of its many species (Wilhelm 1990) 

 and its tall-grass prairie vegetation that has been 

 nearly eliminated elsewhere. 



The many historical impacts to this area 

 make it a good source for studying past 

 changes. Past amounts of pollen from the pri- 

 mary plant taxa are illustrated in Fig. 2. Many 

 changes occurred before settlement, but more 

 rapid changes occurred in the last 140 years. 



Past rates of change in vegetation can be 

 measured by summing the relative change in 

 each plant type between successive samples and 

 then dividing by the number of years between 

 samples. The technique is similar to that used 

 by Jacobson and Grimm (1986). 



Although these changes had been occurring 

 throughout the last 4.500 years, the postsettle- 



l^xpcnmcntal prairie fire at Indiana Dunes National 

 Lakeshore. 



ment rates of change are at least 10 times 

 greater than the presettlement rates of change 

 (Fig. 3a). The rates of change have been declin- 

 ing over the last 50 years, but are still far greater 

 than the presettlement rates of change. 



Northern Michigan Forest 



A similar analysis was carried out on pollen 

 from a sinall bog (unofficial name: 12-Mile 

 Bog) surrounded by pine forest along the south- 

 em shore of Lake Superior (Fig. 3b). This site, 

 within Pictured Rocks National Lakeshore, was 

 more severely affected by logging and slash 

 burning in the 1890"s than by the periodic wild- 

 fires that characterized this forest earlier, but it 

 has been protected for the last 80 years. The 

 magnitude of change caused by the crude log- 

 ging and slash burning of the logging era was 

 far greater than any recorded during the 2.500 

 years since Lake Superior receded to create the 

 forest of white and red pine iPlmis strobiis and 

 P. resinosa). 



As in the Indiana Dunes, rates of change 

 have declined during the last 60 years, and the 

 forest is now very similar to the forest of 2,000 

 years ago. Thus, although the area is still chang- 

 ing at a rate far above normal, it has begun to 

 recover through protection. 



■1,000 



•2,000 'S. 



3,000 



4,000 



20 40 60 

 Pine 



20 40 60 20 20 40 20 40 20 20 20 20 40 20 40 1,000 200 



Oak Maple Hickory Aspen Walnut Birch Beech Grasses Ragweed Charcoal Fly ash 



Pollen (%) 



Fig. 2. Selected ta.\a of fossil 

 pollen recorded from Howes 

 Praine in the Indiana Dunes. The 

 percentage of total pollen repre- 

 senting each plant is graphed 

 along a vertical time axis. The 

 dotted line shows the sedimentary 

 horizon representing settlement of 

 the region (about A.D. 1850). 

 Major changes indicated by let- 

 ters: A — decline in pine and 

 increases in oak and grasses due 

 to plant succession and climate 

 change; B — decline in pine due 

 to logging of white pine in mid- 

 1800's; C — increase in ragweed 

 from cleared farm fields and 

 increase in fly ash from the devel- 

 opment of the steel industry in 

 Gary. IN (22 km away) in the late 

 1800's (Cole et al. 1990); D — 

 increase in charcoal particles as 

 steam railroads ignite nearby 

 drained wetlands and subsequent 

 decline in charcoal as steam 

 power ends and wildfires are con- 

 trolled; and E — decline in oak as 

 frequent fires top-kill mature trees 

 followed by increase in oak as 

 periodic prairie fires are extin- 

 guished. 



