The influence of microhabitat variation on seedling recruitment ofChamaecyparis thyoides andAcer rubrum

Abstract

Chamaecyparis thyoides (Atlantic white-cedar) swamps are in decline in the New Jersey Pinelands, while Aeer rubrum (red maple) swamps are increasing. One possible reason for this occurrence may be differences in seedling recruitment of the two species. Seedling establishment of different species is expected to vary with physical conditions and requirements for safe sites. This study examined differences in seedling recruitment for C. thyoides and A. rubrum in the New Jersey Pinelands. A field survey of six C. thyoides swamps found that C. thyoides seedlings occur most often under an open or C. thyoides canopy on peaty, cedar needle covered soils or on mats of Sphagnum. In contrast, A. rubrum seedlings were most often found under A. rubrum canopies on Sphagnum mats or grass-dominated bottom areas. A greenhouse experiment was conducted to determine whether differences in microhabitat occupation were related to differences in growth of C. thyoides and A, rubrum seedlings. Seedlings were grown in different soil types (Sphagnum or peat) and at different water levels (inundated, saturated, or moist soil) typical of those found in C. thyoides swamps within the New Jersey Pinelands. Chamaecyparis thyoides experienced the greatest increase in height in moist soils and the least increase in height in inundated soils. Chamaecyparis thyoides achieved greater biomass than A. rubrum in peat soil, while A. rubrum had greater biomass in Sphagnum. These results indicate that C. thyoides and A. rubrum differ in conditions that are best for their seedling growth and that different management schemes may favor one species over the other.

The role of microtopography and substrate in survival and growth of Atlantic white-cedar seedlings

“…In fact, experimental seedlings grew at least as much, and for some growth measures more, on tussock sedge substrate than on moss-litter substrate and seedling survival was similar between substrates. The weak substrate type effect on experimental seedlings was not only in contrast to the previous survey (Gengarelly and Lee, in press) but also to other AWC studies that indicate AWC prefer peat soils for establishment (Korstian and Brush, 1931;Little, 1950;Allison and Ehrenfeld, 1999). Furthermore, seedling success on the two substrate types was inconsistent with the significant differences in soil moisture and pH between the substrates.…”

“…Other studies of AWC seedlings have also shown greater frequency of occurrence or growth in organic peat soils (histosols) with moss and litter substrate than on other substrates (Little, 1950;Laderman, 1989;Allison and Ehrenfeld, 1999), although Haas and Kuser (1999) found it was possible to establish AWC seedlings on a sandy mineral soil. These conflicting results reveal uncertainty in our understanding of AWC germination and seedling establishment requirements with regard to substrate.…”

“…In fact, reports are conflicting concerning the shade tolerance of AWC (Korstian and Brush, 1931;Little, 1950;Hickman and Neuhauser, 1977;Motzkin, 1990;Stoltzfus and Good, 1998). Other limiting factors, observed at a microhabitat scale and including microtopography, soil moisture, and substrate, may better explain the lack of successful AWC recruitment in some wetlands (Ehrenfeld, 1995b;Allison and Ehrenfeld, 1999).…”

“…The decline of AWC due to inadequate recruitment has become an important management concern (Motzkin, 1990;Kuser and Zimmermann, 1995;Allison and Ehrenfeld, 1999;Mylecraine and Zimmermann, 2000). In fact, there has been much recent interest in AWC's recruitment requirements and techniques for regenerating and restoring AWC populations (Ehrenfeld, 1995b;Kuser and Zimmermann, 1995;Mylecraine and Zimmermann, 2000).…”

Response of wetland plant species to hydrologic conditions

“…Extant wetlands, in many ecoregions, represent remnants of increasingly endangered plant communities. For example, in the United States of America, the extensive wetprairie system in the Willamette Valley, OR (Noss et al 1995;Christensen et al 1996), the prairie pot-holes of the mid-west (Kantrud et al 1989;Galatowitsch and van der Valk 1994), the whitecedar forests of the Northeast (Zampella 1987;Schneider 1991, 1993;Allison and Ehrenfeld 1999), and the coastal marshes of southern California (Zedler 1991(Zedler , 1996 have all undergone major reductions in area compared to historical conditions.…”