A multiproxy environmental investigation of Holocene wood from a submerged conifer forest in Lake Huron, USA

Remains of a Holocene drowned forest in southern Lake Huron discovered in 12.5 m of water (164 m above sea level), 4.5 km east of Lexington, Michigan USA (Sanilac site), provided wood to investigate environment and lake history using several proxies. Macrofossil evidence indicates a forest comprised primarily of conifers equivalent to the modern “rich conifer swamp” community, despite generally low regional abundance of these species in pollen records. Ages range from 7095 ± 50 to 6420 ± 70 14C yr BP, but the clustering of stump dates and the development of 2 floating tree-ring chronologies suggest a briefer forest interval of no more than c. 400 years. Dendrochronological analysis indicates an environment with high inter-annual climate variability. Stable-carbon isotope composition falls within the range of modern trees from this region, but the stable-oxygen composition is consistent with warmer conditions than today. Both our tree-ring and isotope data provide support for a warmer environment in this region, consistent with a mid-Holocene thermal maximum. This drowned forest also provides a dated elevation in the Nipissing transgression at about 6420 14C yr BP (7350 cal yr BP) in the southern Lake Huron basin, a few hundred years before reopening of the St. Clair River drainage.

Postglacial history of a marl fen: vegetational stability at Byron-Bergen Swamp, New York

Byron-Bergen Swamp, an 800-ha mire complex in western New York, is a mosaic of hardwood–conifer forest, white cedar swamp, and open nonforested fens dominated by sedges, other herbs, and shrubs. The mire is a sloping, spring-fed rich fen in which marl deposition occurs in the open fens but not under forest. Two cores, 120 m apart, one in a marl fen and the other in a hardwood–conifer swamp, were taken to investigate the history of the mire. Sediment, pollen stratigraphy, and 14C chronology show that the Holocene record of local vegetation at each coring site was very different. One site was first a shallow marl pool (10 700 – 5600 years BP), then an open shrub–conifer vegetation, and finally a closed hardwood–conifer swamp. The other site progressed from a pine–spruce–tamarack swamp (10 700 – 8000 years BP) to a white cedar swamp (7500–3500 years BP) and then to a marl sedge fen (3500 years BP – present). The spatial arrangement of swamp forest and marl fen changed through time, responding to marl accumulation and lateral shifts in drainage pathways. Marl deposition occurred continuously at each site, although at different times, for several thousand years. The pattern of vegetation change that we found is not congruent with that predicted from classical hydrarch succession.Key words: marl, mire development, pollen stratigraphy, rich fen.

Seasonal growth and foliar nutrients of Larix laricina in three wetland ecosystems

Levels of N, P, Ca, Mg, K, Al, Fe, Zn, Mn, and B were determined in foliage from tamarack (Larix laricina (DuRoi) K. Koch) in a bog, conifer swamp, and fen from budbreak to leaf abscission. Elongation of needles and lateral shoots as well as dry and ash weight of needles were determined. Expansion of needles and shoots ceased at similar dates for all sites, but trees in the fen had significantly longer needles and lateral shoots.On August 13, foliar concentrations of N, Ca,and Mg were higher in the fen than in the conifer swamp or bog, while concentrations of Al, Fe, Zn, Mn, and B were higher in the bog than the other two sites. Phosphorus concentrations in foliage were similar on this date in the fen and conifer swamp but were lower in the bog site. Despite significant between-site variation for certain foliar elements, two patterns of seasonal variation in nutrient concentrations were discerned. Significant between-site differences in the amounts and rates of needle and shoot elongation, foliar nutrient concentrations at a single sampling time, and patterns of certain foliar elements were associated with variations in nutrient status and moisture–aeration conditions of the study sites.