Examining the influences of tree-to-tree competition and climate on size-growth relationships in hydric, multi-aged Fraxinus nigra stands

• Published in: Forest ecology and management 2016-09, Vol.375, p.238-248
• Main Authors: Looney, Christopher E., D’Amato, Anthony W., Fraver, Shawn, Palik, Brian J., Reinikainen, Michael R.
• Format: Article
• Language: English
• Subjects: Climate; Competition; Fraxinus nigra; Size-growth relationship; Wetland forest
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2016.05.050

•We examined tree competition and stand-level SGR in Fraxinus nigra wetland forests.•Multi-aged F. nigra stands showed size-asymmetric distance-independent competition.•F. nigra stands displayed a consistent pattern of inverse size-asymmetric SGR.•Size-asymmetric competition/SGR suggest declining large tree production efficiency.•Combined competition/SGR results can add insight into forest growth and development. Most research on tree-tree competition and size-growth relationship (SGR – a stand-level metric that infers the relative efficiency with which different sized trees utilize available resources) has focused on upland systems. It is unclear if inferences from these studies extend to wetland forests. Moreover, no study to date has thoroughly investigated the relationship between individual tree-tree competition and SGR. To fill these research gaps, we conducted a dendrochronological study examining the relationship of tree-tree competition, SGR, and climate in late-successional Fraxinus nigra (black ash) wetland forests in northern Minnesota, USA. We took advantage of a detailed, stem-mapped dataset of 1670 trees in five late-successional, multi-aged stands to explore the following research questions: (1) how do competitive interactions, particularly size symmetry, influence individual-tree growth; (2) do late-successional F. nigra stands display inverse asymmetric SGR; and (3) do short-term variations in drought influence SGR in F. nigra wetland forests? Using neighborhood competition indices, which characterize the growth of individual trees based on the size, number, and distance of competitors, we examined the nature and strength of individual tree-tree interactions. Additionally, we used SGR to determine how tree size and individual tree contributions to stand productivity relate to changes in stand growth and competitive interactions during stand development. At the individual tree level, we found evidence of size-asymmetric competition, with larger trees disproportionately suppressing the growth of smaller trees. However, tree size was a stronger predictor of growth than competition at all sites. At the stand level, our multi-aged F. nigra sites showed consistent patterns of inverse size-asymmetric SGR (i.e., smaller individual trees growing at disproportionately higher rates relative to larger trees), which is generally consistent with previous observations of mature upland forests and supports the hypothesis that large trees decline in relat