Herbaceous and woody plant establishment across hydrologic gradients in bottomland reforestation sites

Krzywicka, Adrianna Ewa

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https://hdl.handle.net/2142/89029 Copy

Description

Title

Herbaceous and woody plant establishment across hydrologic gradients in bottomland reforestation sites

Author(s)

Krzywicka, Adrianna Ewa

Issue Date

2015-12-01

Director of Research (if dissertation) or Advisor (if thesis)

Matthews, Jeffrey W.

Department of Study

Natural Resources & Environmental Sciences

Discipline

Natural Resources & Environmental Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Passive restoration
• active restoration
• hydrologic gradients
• soil magnetic susceptibility (MS)

Abstract

Flooding is an important determinant of plant establishment, as well as planted tree survival and growth, in restored floodplain forests. Thus, community assembly in a restored floodplain and, ultimately, restoration outcomes are likely constrained by the site’s hydrologic regime, along with other abiotic factors including light availability and the distance from potential colonization sources. However, trees are often planted in restorations without regard to the site’s hydrologic context and do not survive. Therefore, there is a need to understand the relative importance of abiotic factors on tree and herbaceous species establishment and growth, and there is a need for improved tools for identifying critical abiotic factors during pre-restoration planning. In order to determine the effect of hydrology and other abiotic conditions on plant community assembly, I surveyed plant communities within restored floodplain areas of three different ages. I assessed the density and composition of naturally colonizing tree species and the cover of herbaceous-layer plant species. I evaluated the relationship between tree and herbaceous species establishment and light availability, distance from a nearby seed source, elevation and flood regime. In order to determine the effect of hydrology on planted tree survival, I planted 400 bareroot tree seedlings of four commonly planted species along a hydrologic gradient in a recently restored floodplain. I evaluated the effect of exposure to flooding on planted tree survival and growth. I also evaluated the use of soil magnetic susceptibility (MS), a proxy for soil drainage (other factors being equal), as an easily measured, quantitative predictor of planted tree survival and growth. Lower values of soil MS result from long-term reducing (or anaerobic) soil conditions, and so soil MS might provide a guide to match individual tree species with site-specific soil moisture regimes during restoration planning. Despite the presence of an adjacent mature floodplain forest, passive tree seedling colonization in the restored areas was minimal. In the oldest restored area, tree seedling density increased with increasing elevation and decreased with distance from the seed source, suggesting that tree colonization was limited by both flooding and dispersal. The responses of herbaceous understory species composition to site abiotic conditions varied among the three restored areas, but hydrology was the most important predictor of species composition in all areas. In the first year, the overall survival rate of the planted tree seedlings was 55%. After two growing seasons, the overall survival rate was reduced to 24%. Of the four species planted, Quercus bicolor had the highest survival rate, followed by Quercus palustris and Carya illinoensis. None of the Juglans nigra seedlings survived to the end of the study. Elevation, along with time and species identity, were important predictors of planted tree survival; as elevation increased, probability of survival for each of the four species increased. For growth, flood exposure and species identity were the best predictors of changes in planted tree height, whereas planted tree diameter was not well explained by the measured predictor variables. Soil MS was significantly correlated to both total flood duration and elevation. Soil MS was able to predict planted tree survival, with more flood-tolerant species such as Quercus bicolor surviving in areas with a low soil MS reading, corresponding to poorly drained soils. Understanding how tree colonization, planted trees, and herbaceous understory vegetation respond to abiotic factors such as flood duration and distance from colonization sources, as well as developing tools for identifying critical abiotic factors, will allow for more accurate predictions of restoration outcomes and more targeted planting in floodplain restorations.

Graduation Semester

2015-12

Type of Resource

text

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http://hdl.handle.net/2142/89029

Copyright and License Information

Copyright 2015 Adrianna Krzywicka

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