|Title||Natural regeneration of eastern white pine (Pinus strobus L.) and red pine (Pinus resinosa Ait.)|
|Year of Publication||1993|
|Degree||Doctor of Philosophy|
|Number of Pages||192 pp.|
|University||Michigan Technological University|
Natural regneration is of considerable importance to any future development of plant populations. It is also the most critical and precarious period in the life history of a plant. and most mortality occurs during this period. It is considered a significant "bottleneck" from a demographic standpoint. This research is designed (1) to investigate the natural regeneration patterns of eastern white pine (Pinus strobus L.) and red pine (P. resinosa Ait.) on various sites in northern Lower Michigan, and (2) to experimentally compare the regeneration strategies of these two species at the seedling emergence and seedling establishment stages in both the field and laboratory. To characterize the natural regeneration patterns of eastern white pine and red pine along a resource-availability gradient in northern Lower Michigan. 46 800-m2 plots containing either eastern white pine, red pine or both were selected and sampled to represent the variety of sites occupied by these species in the presettlernent forests. The 46 plots were classified into seven groups or ecological site units. Natural regeneration patterns of eastern white pine and red pine were compared between time groups based on the size structures of their populations. Eastern white pine exhibited abundant regeneration and stable or expanding populations over a wide range of sites, including the mesic and nutrient-rich northern hardwood sites. In contrast, red pine appeared to be decreasing on better sites because of a lack of established seedlings, and to be maintaining itself in small populations on relatively dry sites where its regeneration rates were low. The size-class distribution of red pine populations was significantly different among sites, especially in the regeneration stage. Both eastern white pine and red pine had significantly higher seedling emergence rates in old stands than in young stands. Natural substrates significantly affected seedling emergence rates of these two species with moss patches and decayed wood being the most favored substrates. Seed predation of eastern white pine was significantly higher than that of red pine, probably due to the relatively large seed size of eastern white pine. High temperature (30 deg. C) favored seed germination of red pine, but not eastern white pine. Red pine showed a wider range of adaptation to temperature and understory light conditions than did eastern white pine at their seedling emergence stage. Soil moisture (upper 15 cm) apparently was not as critical as temperature for seedling emergence in either species, except under very high temperature conditions. Compared to eastern white pine, seedling emergence in red pine was rapid and synchronous, which may be one of the critical factors in the high mortality of this species during the establishment phase. Eastern white pine had significantly higher seedling survival rates than red pine in all experiments. This difference in survival rates between the two species may be due to the large size of seedlings in eastern white pine compared to red pine, rendering them less vulnerable to environmental stress. Neither understory light conditions nor substrate type had a significant effect on seedling survival rates in either species. Likewise mammalian herbivores did not significantly reduce seedling survival of both species in the field experiments. In contract, precipitation was very important for seedling survival in both species. High precipitation, particularly in the early growing season, can significantly improve seedling survival. Early emerging seedlings suffered higher mortality than later emerging seedlings due to unfavorable environmental conditions. In summary, the results of this study indicate that: (1) the natural regeneration pattern of eastern white pine is significantly different from that of red pine: (2) the amount of precipitation in early spring is critical for the seedling emergence in both species; and (3) compared to eastern white pine the highly synchronous pattern of seedling emergence and the increased requirement for light in red pine h increase in age may currently limit the natural regeneration of this species in northern Lower Michigan in the absence of disturbance, particularly fire, and thus account for the increasing dominance of eastern white pine over red pine in landscape where the two species co-occur.