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The University of Massachusetts Amherst

Interspecific competition limits the realized niche of Fraxinus nigra along a waterlogging gradient

Authors:

Christopher Looney

Anthony D'Amato

Shawn Fraver

Brian Palik

Lee Frelich

Publication Type:
Journal Article
Year of Publication:
2018
Secondary Title:
Canadian Journal of Forest Research
ISSN:
0045-5067
DOI:
10.1139/cjfr-2018-0023
Pages:
1292-1301
Volume:
48
Year:
2018
Date:
Jan-11-2018
URL:
http://www.nrcresearchpress.com/doi/10.1139/cjfr-2018-0023

Abstract

Gradient studies of wetland forests have inferred that competition from upland tree species confines waterlogging-tolerant tree species to hydric environments. Little is known, however, about competition effects on individual-tree growth along stress gradients in wetland forests. We investigated tree growth and competition in mixed-species stands representing a waterlogging stress gradient in Fraxinus nigra Marsh. (black ash) forests in Minnesota, USA. Using competition indices, we examined how F. nigra basal area increment (BAI) responded to competition along the gradient and whether competition was size-asymmetric (as for light) or size-symmetric (as for soil resources). We modeled spatial distributions of F. nigra and associated tree species to assess how variation in species mixtures influenced competition. We found that although F. nigra BAI did not significantly differ with variations in site moisture, the importance of competition decreased as waterlogging stress increased. Competition across the gradient was primarily size-asymmetric (for light). Variation in species mixtures along the gradient was an important influence on competition. Some segregation of tree species occurred at all but the most upland site, where waterlogging stress was lowest and evidence of competition was greatest, confirming that competition from upland tree species confines F. nigra and potentially other waterlogging-tolerant species to hydric environments.