Analysis of colonization, growth and mortality in a maple-basswood forest restoration over 30 years

Link To Share This Poster: https://cdmcd.co/PJ9xG3

Sean R.D. Meagher, Biology, Saint Olaf College, Northfield, MN, Cullen T. Hauck, Environmental Studies, St. Olaf, Northfield, MN and Kathleen L. Shea, Biology, St. Olaf College, Northfield, MN

Background/Question/Methods
Maple-basswood forests greatly declined as land was developed for agriculture and urbanization. Restoring these forests and maintaining existing forests provides the opportunity to increase biodiversity, facilitate ecosystem resilience to environmental changes, test ecological concepts, enhance ecosystem services, serve as an educational resource, and develop management guidelines. This study aims to examine restoration methods and early growth patterns of trees in two former agricultural fields now part of the St. Olaf College Natural Lands in southeastern Minnesota, USA. Two-year old seedlings were initially planted in 1990 using species characteristic of current maple-basswood remnants, such as Acer saccharum (sugar maple), Fraxinus americana (white ash), Juglans nigra (black walnut), Quercus macrocarpa (bur oak), Quercus rubra (red oak) and Tilia americana (basswood). Trees were planted and measured for height and diameter every 2-4 years for 30 years. Colonizing trees with diameter > 2.5 cm have been measured since 2013and canopy density was measured using a densiometer in 2015 and 2020. The objectives of this study were to 1) compare tree growth and mortality patterns among species planted in 1990, 2) analyze species composition and size of colonizing woody species, and 3) make projections about future changes and maturity of the restoration.
Results/Conclusions
In 2020, F. americana was the most common tree, followed by J. nigra and Q. macrocarpa. Of original trees, Q. rubra was tallest on average (17.415m), followed by F. americana (13.933m), then T. americana (13.607m). Total mortality of original trees since 1990 was 44.09%, averaging 1.92% of original trees dying yearly. A. saccharum had higher mortality (58%), suggesting that it may survive better once canopy shade has been established. Colonizing trees make up approximately half the 1,587 trees measured and have increased overall species diversity. F. americana and Ulmus americana (American elm) were the most common colonizing trees. 42.6% of U. Americana and 40% of A. saccharum colonizers, with intermediate and high shade tolerance respectively, became established over the last three years, making them the most prolific colonizers as the forest is maturing. Canopy coverage increased from 90.6% to 96.4%. These results point to the restoration being at a turning point, about to move beyond an early successional forest composition as the canopy closes and shade intolerant trees are pushed out, supporting the effectiveness of St. Olaf’s restoration methods and the likelihood that a mature forest will become established.