Restoring Forests in Bottomland Fields

Research Issue 

Public land managers and private land owners have a strong interest in regenerating native oak species (Quercus spp.) on what are largely agricultural floodplains. Bottomland oak species are highly valued for timber products and wildlife habitat. They are of conservation concern because of the substantial decline in oaks from historic levels and the difficulty in regenerating them on highly productive floodplains. Much (>85%) of the original bottomland forests in Missouri have been cleared and the land put in agricultural production.

The Great Flood of 1993 inundated floodplains throughout much of the summer ruining bottomland farms and causing extensive mortality of oaks in forests along the Missouri and Mississippi Rivers. Since 1993, many abandoned bottomland crop fields have naturally regenerated to forests dominated by pioneering species such as cottonwood (Populus deltoids), silver maple (Acer saccharinum), sycamore (Platanus occidentalis) and willow (Salix nigra). These species are abundant in remnant floodplain forests, thus ensuring a local seed supply.  They are prolific annual seed producers whose seed is easily dispersed by wind and water. Seed germination is favored on mineral soils in open environments, typical of conditions following abandonment of bottomland crop fields. Their seedlings exhibit rapid juvenile growth, which makes them highly competitive on the productive bottomland soils.

Former small- to moderate-sized bottomland crop fields have developed into well-stocked sapling stands dominated by these pioneer species over the past 12 years. Cottonwood, willow, sycamore, silver maple and other early successional tree species are native to bottomlands and are considered desirable reproduction. A widespread pattern in forest succession on former bottomland crop fields is the lack of oaks and other nut-producing trees. For example, Shear and others (1996) found a lack of hard mast species in 50-year-old forests that naturally regenerated on bottomland crop fields in southwestern Kentucky. Thus, artificial regeneration of oaks is needed to increase the likelihood that oaks are present in future forests.

To-date, traditional methods of planting bareroot oak seedlings or direct seeding acorns in bottomlands have not always been successful. For example, in a survey of 4-year-old Wetland Reserve Program plantings in the Mississippi River floodplain, researchers found that only 9% of the total reforested land in 13 Mississippi counties met the Natural Resources Conservation Service requirement for at least 125 hard mast stems per acre in 3-year-old stands.  

Oak regeneration failures in bottomland crop fields are largely a result of the low competitiveness of small oak seedlings on these sites, which can producetremendous herbaceous biomass in one summer. Small oak seedlings are also less competitive than the pioneer tree species that invade abandoned crop fields. In addition, oak plantings are not often maintained by controlling competing vegetation, which makes successful oak regeneration less likely. Oak species are moderately tolerant to intolerant of shade and thus unable to persist in the heavy shade of competing vegetation.

Oak regeneration success can be improved, in part, by planting large seedlings, particularly those having well-developed root systems. Nursery managers can produce hardwood bareroot seedlings with large root systems that have 5 or more large lateral roots by undercutting the taproot, growing seedlings at lower seedbed densities, or by transplanting 1-0 seedlings for a second year. Air pruning the roots of seedlings grown in open-bottomed containers is another way to promote the growth of large lateral roots and dense fibrous root systems.

In the Midwest, several private nurseries have begun commercial production of large (e.g., 3- to 5-gallon) container seedlings that are being used in the afforestation of bottomland crop fields on public and private lands. The Forrest Keeling Nursery of Elsberry, Missouri has developed a nursery cultural technique, the Root Production Method (RPM®), to produce high-quality hardwood seedlings with large basal diameters and heights, and substantial fibrous root systems for regenerating floodplains. For the past 5 years or so, these large container seedlings have been planted in various floodplain situations throughout the Midwest. In 1999, we began a study to evaluate the performance of these seedlings in the afforestation of bottomland crop fields. This paper presents early survival and growth performance of large container seedlings compared with that of 1-0 bareroot seedlings in regenerating pin oak and swamp white oak in bottomland crop fields along the lower Missouri River. We discuss the role of large container seedlings in regenerating oaks in floodplains.

Unsuccessful regeneration may also be a consequence of not properly matching the oak species to soil nutrient and hydrological conditions.  Soils within the Missouri and Mississippi River floodplains are frequently dominated by alluvial deposits from calcareous soils throughout the Midwest resulting in high pHs.  In addition, flooding can both deposit nutrient-rich soil as well as leach nutrients from the rooting zone, especially soil nitrate nitrogen.  Duration and depth of flooding also need to be considered both when choosing which species to plant as well as the type of planting stock. Taller and larger seedlings subjected to partial inundation are more likely to survive than seedling overtopped by poorly aerated backwater.

Our Research

In crop fields in the Missouri River floodplain, we planted large container (RPM®) and 1-0 bareroot seedlings of pin oak (Quercus palustris) and swamp white oak (Q. bicolor). We also evaluated the benefits of soil mounding and a grass (Agrostis gigantean) cover crop. RPM® oak seedlings had significantly greater survival and basal diameter increment after three years than bareroot seedlings. RPM® trees lost significantly more height during the first 3 years than bareroot seedlings due to rabbit herbivory, which was substantially greater in the natural vegetation than the redtop grass fields. Oak seedlings in redtop grass cover grew substantially more in diameter and height than oaks competing with natural vegetation. Soil mounding had no significant effect on oak survival or growth. Swamp white oak RPM® seedlings produced acorns annually the first 4 years. Planting large container seedlings in redtop grass improved early oak regeneration success, and rapidly restored acorn production. Application of slow-release nitrogen as urea or ammonium nitrate or interplanting of nitrogen-fixing shrubs failed to improve the growth of established oak saplings unless applied with iron sulfate to reduce soil pHs.   The gradual transition of the understory vegetation to native nitrogen-fixing plants further suggests soil nitrogen in these bottomland soils is not in a form available to most plants.  In cooperation with the University of Missouri Center for Agroforestry, we have evaluated differences in survival and growth both within and among hardwood seedlings subjected to partial inundation for up to 6 weeks in both stagnant and flowing flood water.  Variation in flood tolerance tends to be greater within stands than for topographic position for oak species adapted to bottomland and upland fields.

Expected Outcomes

We have identified several promising practices and seedling types that can be used to successfully restore oak to future bottomland forests when bringing marginal agricultural lands back into forest production. The potential is there in Missouri to restore forests on former agricultural bottomlands that include the desired amount of oak trees on tens of thousands of acres. In addition, many of these techniques can be used in other regions to restore bottomland oak forests, for example, on hundreds of thousands of acres in the Lower Mississippi Alluvial Valley. The principles and practices that we developed for restoring bottomland forests can be used by private landowners with small acreages, private duck hunting clubs, and public land agencies.

Research Results

Burhans, D.E.; Root, B.G.; Shaffer, T.L.; Dey, D.C. 2010. Songbird nest survival is invariant to early-successional restoration treatments in a large river floodplain. Wilson Journal of Ornithology 122(2): 307-317.

Gardiner, E.S.; Dey, D.C.; Stanturf, J.A.; Lockhart, B.R. 2010. Approaches to restoration of oak forests on farmed lowlands of the Mississippi River and its tributaries. Colombia Forestal 13(2): 223-236.

Dey, D.C.; Gardiner, E.S.; Kabrick, J.M.; Stanturf, J.A.; Jacobs, D.F. 2010. Innovations in afforestation of agricultural bottomlands to restore native forests in eastern USA. Scandinavian Journal of Forest Research 25(Suppl. 8): 25-32.

Millspaugh, J.J.; Schultz, J.H.; Mong, T.W.; Burhans, D.; Walter, W.D.; Bredesen, R.; Pritchert, Jr., R.D.; Dey, D.C. 2009. Agroforestry wildlife benefits. In: Garrett, H.E. (ed.) North American Agroforestry: An integrated science and practice, 2nd edition. Madison, WI: American Society of Agronomy: 257-286.

Dey, D.C.; Jacobs, D.F.; McNabb, K.; Miller, G.W.; Baldwin, V.C.; Foster, G.S.; Bridgwater, F. 2008. Artificial regeneration of major oak (Quercus) species in the eastern United States: a review of the literature. Forest Science 54(1): 77-106.

Ponder, F., Jr.; Kramer, M.J.; Eivazi, F.  2008.  Effect of fertilizer treatments on an alkaline soil and on early performance of two bottomland oak species.  In: Jacobs, D.F.; Michler, C.H. (eds.) Proceedings: 16th Central Hardwood Forest Conference. NRS-GTR-P-24.  Newtown Square, PA: USDA Forest Service, Northern Research Station: 552-558.

Steele, K.L.; Kabrick, J.M.; Jensen, R.G.; Wallendorf, M.J.; Dey, D.C. 2008. Analysis of riparian afforestation methods in the Missouri Ozarks. In: Jacobs, D.F.; Michler, C.H. (eds.) Proceedings, 16th Central Hardwood Forest Conference; 2008 April 8-9; West Lafayette, IN. NRS-GTR-P-24. Newtown Square, PA: USDA Forest Service, Northern Research Station: 80-90.

Walsh, M.P.; Van Sambeek, J.W.; Coggeshall, M.V.  2008. Variation in flood tolerance of container-grown seedlings of swamp white oak, bur oak, and white oak.  In: Jacobs, Douglass; Michler, Charles H. (eds.) 16th Central Hardwood Forest Conference.  Gen. Tech. Rep. NRS-P-24.  Radnor, PA: USDA Forest Service, Northern Research Station: 446-456.  

Coggeshall, Mark V.; Van Sambeek, J. W.; Schlarbaum, Scott E.  2007.  Genotypic variation in flood tolerance of black walnut and three southern bottomland oaks.  In: Buckley, D.S.; Clatterbuck, Wayne K. (eds.) Proceedings: 15th Central Hardwood Forest Conference.  SRS-GTR-101.  Ashville, NC: USDA Forest Service, Southern Research Station: 629-637.

He, H.S.; Dey, D.C.; Fan, X.; Hooten, M.B.; Kabrick, J.M.; Wikle, C.K.; Fan, Z. 2007. Mapping pre-European settlement vegetation at fine resolutions using a hierarchical Bayesian model and GIS. Plant Ecology 191: 85-94.

Kabrick, J.M.; Dey, D.C.; Motsinger, J.R. 2007. Evaluating the flood tolerance of bottomland hardwood artificial reproduction.  In: Buckley, D.D.; Clatterbuck, W.K. (eds.) Proceedings: 15th central hardwood forest conference. SRS-GTR-101. Asheville, NC: USDA Southern Research Station:  727-733. 

Van Sambeek, J. W.; McGraw, Robert L.; Kabrick, John M.; Coggeshall, Mark V.; Unger, Irene M.; Dey, Daniel C.  2007.  Developing a field facility for evaluating flood tolerance of hardwood seedlings and understory ground covers.   In: Buckley, David S.; Clatterbuck, Wayne K. (eds.) Proceedings: 15th Central Hardwood Forest Conference. SRS-GTR-101.  Ashville, NC: USDA Forest Service, Southern Research Station:  727-733.  

Dey, D.C.; Kabrick, J.M.; Gold, M. 2006. The role of large container seedlings in afforesting oaks in bottomlands. P. 218-223 In Connor, K.F., ed. Proc. 13th Biennial southern silvicultural research conf. USDA Forest Service Gen. Tech. Rep. SRS-92.

Kabrick, J.M.; Dey, D.C.; Van Sambeek, J.W.; Wallendorf, M.; Gold, M.A. 2005. Soil properties and growth of swamp white oak and pin oak on bedded soils in the lower Missouri River floodplain. Forest Ecology and Management 204: 315-327.

Van Sambeek, J.W.; Coggeshall, Mark V.  2005. Evaluating physiological response and genetic variation of oak species for flood tolerance. Missouri Forestry Newsletter 20(2): 3-4. [pdf - You may download a free pdf readerfrom Adobe.]

Dey, D.C.; Lovelace, W.; Kabrick, J.M.; Gold, M.A. 2004. Production and early field performance of RPM seedlings in Missouri floodplains. In: Michler, C.H.; Pijut, P.M.; Van Sambeek, J.; Coggeshall, M.; Seifert, J.; Woeste, K.; Overton, R. (eds.) Black walnut in a new century. Pproceedings of the 6th Walnut Council research symposium; 2004 July 25-28; Lafayette, IN. NC-GTR-243. St. Paul, MN: USDA Forest Service, North Central Research Station: 59-65.

Dey, D.; Kabrick, J. 2004. Regenerating oaks in Missouri’s bottomlands. Missouri Conservationist 65(7): 18-22.

Dugger, S.; Dey, D.C.; Millspaugh, J.J. 2004. Vegetation cover effects mammal herbivory on planted oaks and success of reforesting Missouri River bottomland fields. In" Connor, K.F. (ed.) Proceedings: 12th Biennial Southern Silvicultural Conference. 24-28 February 2003. Biloxi, MS. SRS-GTR-71. Asheville, NC: USDA Forest Service, Southern Research Station. 3-6. 

Research Participants 

Principal Investigators

• Daniel C. Dey, Research Forester, US Forest Service, Northern Research Station 
• John M. Kabrick, Research Forester, US Forest Service, Northern Research Station 
• Jerry Van Sambeek, Research Physiologist, US Forest Service, Northern Research Station 
• Felix Ponder, Jr., Research Soil Scientist, US Forest Service, Northern Research Station 

Research Partners

• Lincoln University 
• University of Missouri Center for Agroforestry 
• Missouri Department of Conservation 
• U.S. Department of the Interior, Fish and Wildlife Service
• U.S. Army Corps of Engineers
• USDA Agricultural Research Service 
• Forrest Keeling Nursery

For further information log on website:
http://www.nrs.fs.fed.us/sustaining_forests/conserve_enhance/timber/herbicides/