Lake pollen records of the past century in northern New Jersey and southeastern New York, U.S.A.

Abstract

Pollen records of vegetational change in northern New Jersey and adjacent southeastern New York in the past century were examined in four lake sections. Pollen data from three sites (Lake Surprise, Rockland Lake and Lake Marcia) indicate that forests were dominated by Quercus, Castanea, and Carya before the chestnut (Castanea) blight and hickory (Carya) bark beetle decimated Castanea and Carya tree populations. Afterward, Castanea and Carya pollen percentages decreased and Betula increased. Forest canopy opening following the loss of chestnut trees was indicated by a transient pollen concentration peak. An increase in Ambrosia pollen percentages and concentration preceded an increase in Gramineae percentages which reflects secondary succession. Ambrosia and Gramineae increases are not synchronous among the lakes which indicates field abandonment began at various times in different parts of the region. Three regional pollen assemblages characterize vegetation conditions and changes in the region: (1) Quercus‐Castanea‐Carya represents pre‐chestnut blight and hickory bark beetle forests, (2) Quercus‐Ambrosia‐Gramineae indicates secondary succession, and (3) Quercus‐Betula shows the continued importance of Quercus and rise of Betula in the forest after the loss of Castanea.

Ordinary least squares linear regression analysis was employed with means of section intervals encompassing three samples to ascertain trends in each lake section. Significant increasing trends in pollen records were not observed for Betula and Quercus at Rockland Lake and Lake Marcia, despite Betula population increasing regionally. Lake Surprise had increasing Betula and Quercus pollen trends which accurately followed regional changes for Betula but not for Quercus.

Historical records show that agricultural decline, tree plantings, and fossil fuel use permitted forest area to increase continuously over the past century. Increases in forested land could not be clearly related to increasing pollen concentration because of changing sedimentary and pollen deposition conditions.

Data from the one‐year section at Sheppard Pond indicated pollen concentration peaks were related to times of leaf fall, and runoff, including periods of abnormally heavy rainfall and snow melt. Percentage peaks for Quercus, Pinus, and Ambrosia occurred during the time of anthesis in the region.