Determining influences of stream channelization and an invasive species on rate of canopy tree growth in an urban park

2012 | Travis Marsico, Arkansas State University

Tree health and regeneration is deteriorating in urban forests throughout the southeastern United States. Shelby Farms Park in Memphis, Tennessee, one of the largest urban parks in the U.S currently plans to plant 1,000,000 trees over the next 20 years; however, poor natural regeneration and health of many trees suggests that the intensive planting strategy may have a high rate of failure without additional habitat management. Preliminary data indicate that riparian tree growth rates are reduced by low water levels in the channelized neighboring Wolf River, and the health of trees in Chinese privet-invaded forests is significantly lower than in non-invaded forests in Shelby Farms Park. We hypothesize that stream channelization resulted in novel conditions in which the established tree species could not thrive, inviting the invasion of privet, which further reduced forest health. Using the technique of dendrochronology, we will determine the effects of stream flow and privet invasion on the growth rate of native oaks and hickories that dominate the forest canopy. We will also conduct a field survey in invaded/channelized (INV), non-invaded/channelized (NON), and non-invaded/unchannelized regions (REF) to investigate differences in community structure, community composition, and tree health. Ultimately, well-constructed management plans will be devised and supplied to local conservation agencies, and the information collected will be invaluable for many urban forests of the Southeast.

Study Results

Channelization promoted faster canopy oak growth in all sites. Spring drought significantly slowed growth in NON, while summer precipitation promoted wood production in NON. Investigation of Chinese privet impact on tree growth revealed a significant effect, such that trees in INV grew slower after invasion than trees in the non-invaded control sites (NON and REF).

Faster growth after channelization may be a consequence of increased aerobic conditions, by enabling higher oxygen availability to tree roots. However, many of the obligate bottomland tree species struggle to regenerate in drier, post-channelized conditions. Thus, native drought-tolerant species may have an advantage in the sub-canopy and regeneration layers of these altered forests. Instead, Chinese privet, an invasive and drought-tolerant species, has invaded most locations adjacent to the channelized portion of the Wolf River. Chinese privet presence reduces the channelization advantage by slowing growth of canopy oaks and possibly contributing to accelerated mortality.

These results suggest an emerging shift to a commonly held paradigm with respect to invasive shrub species. Not only do invasive shrubs crowd out other small woody species and herbaceous plants, but they also have the ability to impact the structure of the forest canopy.

Year: 2012

Funding Duration: 1-3 years

Grant Program: Jack Kimmel International Grant

Grant Title: Determining influences of stream channelization and an invasive species on rate of canopy tree growth in an urban park

Researcher: Travis Marsico

Key words: Bottomland hardwood forests; Channelization; Chinese privet; Dendrochronology; Flood pulses; Forested wetlands; Hydrology; Ligustrum sinense; Riparian forests; Tree ring dating; Woody invasive species

Peer Reviewed Publications from Grant:

• Foard, M., Burnette, D. J., Burge, D. R. L., Marsico, T. D. (2016), Influence of river channelization and the invasive shrub, Ligustrum sinense, on oak (Quercus spp.) growth rates in bottomland hardwood forests. Applied Vegetation Science, 19: 401–412. doi: 10.1111/avsc.12240. View the Publication >

General Audience/Trade Publications:

Presentations:

For more information on this project, contact the researcher via TREE Fund at treefund@treefund.org.