Determining drivers of floodplain forest regeneration success and failure on the Upper Mississippi River in Minnesota and Wisconsin

The floodplain forests of the Upper Mississippi River (UMR) Basin play a critical role in maintaining water quality, wildlife habitat, and recreational opportunities. However, these forests systems are not static. Interactions among shifting climatic patterns, invasive species (especially reed canarygrass (Phalaris arundinacea)), forest health (e.g. Dutch elm disease and emerald ash borer), herbivores, low tree species diversity, and aging stands with limited regeneration are threatening to push these forest communities past critical ecological “tipping points.” These tipping points lead to drastic shifts in community composition and structure (e.g. conversion to non-forest conditions), making ecosystem restoration and rehabilitation significantly more difficult and greatly reducing the resilience of these systems. Within the UMR floodplain in Minnesota, Wisconsin and northeast Iowa (UMR Pools 1-10), this problem is particularly acute – current forest inventory data indicates that forest regeneration is completely absent over 57% of inventory plots and of the areas. Of the remaining plots with documented regeneration, almost 25% of plots are dominated by ash or elm regeneration, but both of these species have minimal potential for long-term survival on the sites due to insects and diseases. Without viable regeneration, these forests will convert to non-forest cover types in coming decades as current canopy trees begin to die. Proactive management actions can aid in reducing the chance of future forest loss, but there is limited research or institutional knowledge along the Upper Mississippi available on the mechanisms driving regeneration of key floodplain forest tree species and, therefore, management actions to promote regeneration of trees often result in failure. The current study aims to identify key drivers of regeneration for a handful of currently widespread floodplain forest tree species and to test a set of management techniques to promote the establishment of regeneration from seed. This information is critical for developing management strategies to ensure long-term viability of UMR Floodplain Forests.

The primary goal of this research is to identify factors in existing floodplain forests on the Upper Mississippi River in Minnesota, Wisconsin and northeast Iowa that are associated with establishment and growth of regeneration from seed and planted tree seedlings in the most northern reach of the navigable portion of the Upper Mississippi River. Understanding dynamics of light-seeded species, primarily eastern cottonwood (Populous deltoides), silver maple (Acer saccharinum) and river birch (Betula nigra) is critical to this study, but other floodplain species may be incorporated as well. The research will also aim to test a set of silvicultural approaches for promoting natural regeneration in this region based on the current understanding of the silvics of these species. Because light availability, flood inundation, and soil saturation are key drivers of tree species distribution in these floodplains, the research will focus on assessing regeneration conditions across gradients of these drivers. In particular, this study will focus on the following objectives:

Objectives:

1. Develop relationships between tree seedling survival and growth for key tree species across a gradient of site-level physical conditions that drive floodplain forest regeneration: light availability, flooding and soil moisture. These relationships should incorporate seedling size as a component of seedling growth and survival.

2. Evaluate chemical and mechanical site preparation as a means to facilitate the establishment of light-seeded floodplain species from seed (natural and hand-seeded) across the same site-level gradients in Objective 1 and quantify the density of seed-origin regeneration. Establish long-term monitoring plots is study sites to develop baselines for development of stands of light-seeded species from stand initiation through stem exclusion.

Desired Outcomes:

Objective 1:

1. A set of preliminary quantitative guidelines for identifying suitable physical conditions for successful regeneration of key floodplain forest species in Pools 1 – 10 of the Upper Mississippi River

2. Quantitative relationships between tree seedling size, survival and growth across the assessed physical gradients to inform future development of target seedling characteristics for floodplain forest regeneration

Objective 2:

1. An assessment of the viability of mechanical and chemical silvicultural site preparation treatments in Upper Mississippi River floodplains to promote natural regeneration of light-seeded species across light and hydrologic gradients

2. Baseline data for potential tree seedling densities and early growth rates for floodplain forest stands originating from seed.

Objective 1 will focus on planting of seedlings of the key floodplain tree species across gradients of light availability, flooding and soil moisture. Survival and growth of these seedlings will be documented at multiple intervals across multiple growing seasons and across the environmental gradients to develop relationships between site conditions and seedling establishment. Particular emphasis will be placed on quantification of biophysical interactions associated with saturated soils within the rooting zone of tree seedlings to describe soil conditions necessary for seedling survival and growth. This portion of the research will focus on understanding basic seedling-site relationships. Resulting data will inform future development of management recommendations for site selection and target seedling characteristics for the key floodplain forest tree species.

Objective 2 will be more applied and will directly test silvicultural site preparation treatments to create seedbeds for natural regeneration, with these treatments applied across the same gradients as in Objective 1. Treatments will include chemical site prep using herbicide, mechanical site prep to break up the soil surface, and a combination of chemical and mechanical site prep. Supplemental seeding of light-seeded species will also be implemented following site prep treatments. In this component of the research, monitoring will be focused on comprehensive vegetative assessments of the treatment areas rather than detailed measurements of individual seedlings as in Objective 1. Within each treatment area, an adequate number of plots will be established to assess tree seedling density by age and size classes and cover of other vegetation. Seedling density will then be evaluated in the context of site-level gradients and silvicultural treatment to determine the effectiveness of these treatments across light and hydrologic gradients.

Field data will be collected over a minimum of three growing seasons for both components of the project. It is expected that interim data results will be analyzed, but final analyses will be conducted during the fourth year of the project.

This opportunity is restricted to non-federal partners of the Great Lakes / Northern Forest Cooperative Ecosystems Studies Unit (CESU). Disclosures of current and pending support made in this application may render an applicant ineligible for funding. Prior to award and throughout the period of performance, ERDC may continue to request updated continuing and pending support information, which will be reviewed and may result in discontinuation of funding. Religious organizations are entitled to compete on equal footing with secular organizations for Federal financial assistance as described in E.O. 13798, “Promoting Free Speech and Religious Liberty.”