Soil, hydroperiod and bedding effects on restoring bottomland hardwoods on flood-prone agricultural lands in North Louisiana, USA

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1 Soil, hydroperiod and bedding effects on restoring bottomland hardwoods on flood-prone agricultural lands in North Louisiana, USA WILLIAM B. PATTERSON* AND JOHN C. ADAMS School of Forestry, Louisiana Tech University, Ruston, Louisiana, USA * Corresponding author. wpatter@lans.latech.edu Summary Many of the bottomland hardwood forests of the Lower Mississippi Alluvial Valley, USA have been converted to agriculture, thus constituting a sizable loss in ecological and socio-economic functions. Bottomland hardwood forest afforestation on marginal agricultural lands has grown considerably since However, many failures in bottomland hardwood afforestation have occurred for various reasons, including misunderstandings or ignoring the relationships between species, soil and hydrology. In October 1996, a 32-ha tract on an abandoned agricultural field in Catahoula Parish, Louisiana, USA was site prepared for afforestation by bedding (moulding soil in parallel ridges). The following January it was planted with seedlings of Nuttall oak (Quercus nuttallii Palmer) and green ash (Fraxinus pennsylvanica Marsh.), and direct seeded with Nuttall oak. The objective of this study was to evaluate the effects of bedding (within three soil types) on species survival and growth. Soil redox potential measurements indicated that the soils were intensely anaerobic during frequent prolonged seasonal inundation and saturation events. Bedding clayey soils significantly increased mean height of planted and direct-seeded Nuttall oak, but not that for green ash. Bedding appears to be somewhat effective in restoring site microtopography, reducing soil hydroperiod and enhancing planted Nuttall oak height growth on poorly drained, clayey soils. Introduction Over the last two centuries about three-quarters of the Lower Mississippi Alluvial Valley has been deforested for agricultural production (MacDonald et al., 1979; The Nature Conservancy, 1992). A high percentage of these deforested farmlands was marginal for agricultural production due to soil and soil/water problems. In the past 20 years a sizable number of hectares have been replanted to trees. Initial work with afforestation resulted in many failures to obtain Institute of Chartered Foresters, 2003 Forestry, Vol. 76, No. 2, 2003

2 182 FORESTRY adequate regeneration. Many of these failures were the result of poor species/site matches. Other failures resulted from a lack of understanding of the modifications of the sites, and subsequent changes in the soil water relationships, duration of inundation, and changes in flood patterns resulting from agricultural and other anthropic activities (Stanturf et al., 1998, 2001). Lockhart et al. (2003) argue that there is no single prescription for bottomland hardwood regeneration that suits all potential afforestation projects in this region. Bedding poorly drained soils should be investigated as a potential technique for increasing afforestation success. Bedding, or mounding soil in parallel ridges, is a common site-preparation practice for establishing conifer plantations on wet sites of the lower coastal plain in the south-eastern United States. Bedding is also commonly applied on peaty soils in Ireland, Scotland, Scandinavia and Canada (Paavilainen and Päivänen, 1995; Rothwell et al., 1993). Bedding a lower coastal plain wetland in South Carolina, USA lowered the overall surface water table for 2 years after stand establishment (Xu et al., 2000, 2002). Bedding also increased the depth of the water table and raised the soil redox potential, an indicator of soil aeration, on a slash pine (Pinus elliottii Engelm. var. elliottii) plantation in central Louisiana (McKee and Shoulders, 1970). Numerous studies have established that bedding usually increases early loblolly pine (Pinus taeda L.) and slash pine growth on poorly drained sites (Langdon, 1962; McKee and Shoulders, 1970; Mann and McGilvray, 1974; McKee and Wilhite, 1986). One exception was on silty soils in Louisiana, where bedding did not improve soil drainage (Haywood et al., 1990). Thus, it is possible that the benefits of bedding bottomland soils will differ according to inherent soil properties. Bottomland hardwood species productivity has been related to soil series and site conditions, including hydrologic regime or hydroperiod. For example, best site conditions for Nuttall oak (Quercus nuttallii Palmer) and green ash (Fraxinus pennsylvanica Marsh.) include silty or loamy textures, winter to spring flooding, waterlogging in winter only, water table at m depth, and concave microsite positions (Baker and Broadfoot, 1979). Average measured site index (50 year base age) for Nuttall oak on the clayey, poorly drained and frequently flooded Alligator series was 27.1 m, and on the clayey, poorly drained Perry series, 24.7 m (Broadfoot, 1976). Average measured site index (50 year base age) for green ash on the Alligator series was 24.4 m, and 21.0 m on the Perry series (Broadfoot, 1976). Ozalp et al. (1998), in Mississippi, found Nuttall oak fifth year survival, height and diameter unaffected by soil series. Their soils included the clayey Sharkey series (Chromic Epiaquert) and loamier soils. The study site is part of a 4000-ha area that was cleared of bottomland hardwoods about 40 years ago and converted to cropland. The area was land levelled and ditched, thus altering natural drainage, and is located near the confluence of the Ouachita and Boeuf Rivers, downstream of a medium-sized metropolitan area (Monroe, LA). This study was designed to examine survival and growth of Nuttall oak and green ash on bedded and non-bedded site preparation treatments applied to three soil series impacted by altered hydrologic regimes. Methods Study site The study site was a 32-ha area of abandoned cropland located on Bouef River Wildlife Management Area, which is between the Bouef and Ouachita Rivers in northern Catahoula Parish, Louisiana (31º 56 lat., 91º 52 long.). The area has an average annual precipitation of cm, an average annual daily temperature of 18.7ºC, an average annual daily maximum temperature of 25.1ºC and an average daily minimum temperature of 12ºC (Boyd, 1986). Study establishment The study site was bedded in October 1996, using a Savannah bedding plough pulled by a rubbertyred skidder, and was planted to bottomland hardwoods in January Bare root seedlings of Nuttall oak and green ash were planted by hand on beds and non-bedded positions. Nuttall oak was also direct seeded by hand at 7 10 cm depth on both bedded and non-bedded areas. Herbicides were not applied due to prolonged

3 RESTORATION OF BOTTOMLAND HARDWOODS 183 high water. The experimental design was randomized block, with blocking on the three soil series mapped on the site. Alligator clay (veryfine, smectitic, thermic Chromic Dystraquert) occurs in the lowest elevation backswamps subjected to frequent backwater flooding. Hebert silt loam (fine-silty, mixed, active, thermic Aeric Epiaqualf) is located on the natural levee, and Perry clay (very-fine, smectitic, thermic Chromic Epiaquert) is situated in intermediate positions. Bed and non-bed rows were replicated randomly within each block (soil series). Seedlings were planted with a spacing of 3 m 3 m (1087 trees ha 1 ) on 3-m-wide rows. Nuttall oak acorns were direct-seeded at 0.5-m intervals on 3-m-wide rows. Survival on random 30 m 30 m plots (four plots per a treatment) was measured at the end of the fourth growing season. A plot of this size would allow for 10 planting spots per row for seedlings or 32 sowing spots per row for directseeded acorns. There were 10 rows in a plot. Seedling height and ground-line diameter were also measured at the end of the fourth growing season. Survival, height and diameter of planted Nuttall oak, direct-seeded Nuttall oak and planted green ash were analysed by bedding treatment within soil series using analysis of variance (ANOVA) of the General Linear Model Procedure of SAS (SAS Instititute, Inc., 1999). A US Geological Survey river stage (measured and recorded by the US Army Corps of Engineers) is located ~12 km upstream on the Boeuf River. Stage data for the period were evaluated and related to the restoration area s elevation, to determine inundation frequency and duration. Days with river stage heights at or above the sites elevation were counted as inundation events, and these events at the lower end of predicted flooding were verified in the field. To assess soil hydroperiod and onset of oxidizing and reducing conditions, soil redox potential electrodes were installed in November 1998 on beds and non-bedded sites in each of the three soils mapped on the site. For each soil type, three plots were established in which five platinum wire redox electrodes, constructed as in Faulkner et al. (1989), were installed at 15 cm and 30 cm depths for both bedded and non-bedded positions. Results and discussion During the 5-year period, the restoration area was inundated by the Boeuf River, for at least two flood events per year (Figure 1). The site was flooded up to 116 consecutive days in the winter and spring, and occasionally in the late fall, at heights up to 3 m above the backswamp soil Stage (m) /1/1997 4/1/1997 7/1/1997 Plots flooded 10/1/1997 1/1/1998 4/1/1998 7/1/ /1/1998 1/1/1999 4/1/1999 7/1/ /1/1999 Date 1/1/2000 4/1/2000 7/1/ /1/2000 1/1/2001 4/1/2001 7/1/ /1/2001 1/1/2002 Figure 1. Stage of Boeuf River at Fort Necessity, LA, USA, 12 km upstream from study area, for the period The heavy horizontal line through the graph indicates the stage at which the study site is inundated.

4 184 FORESTRY Table 1: Flooding duration and height above flood stage at the study area from 1997 to 2001, Bouef River Wildlife Management Area, LA, USA Total days Consecutive flooding Maximum flood height Year flooded periods (days) above flood stage (m) , , , 15, 11, 4, 4, , 3, , 32, 15, 7, (Alligator clay) level (Table 1). Soil oxidationpotential (redox) measurements (Figure 2) indicate that these soils have mostly oxidized with aerobic conditions from mid-summer to November, and undergo periods of moderate reduction and anaerobic conditions (redox potential 200 mv; Gambrell and Patrick, 1978; Patrick et al., 1996) before flooding, ponding and saturation induces periods of intense reduction and anaerobic conditions (redox potential 100 mv; Gambrell and Patrick, 1978; Patrick et al., 1996) lasting several months in the spring. The timing of the flooding periods indicated in Figure 1, as well as high seasonal precipitation relative to evaporation, is associated with the decline in soil redox depicted in Figure 2. Soil redox potential in the rooting zone was slightly higher on bedded sites versus non-bedded sites for extended periods, indicating less intensely anaerobic conditions. Survival Overall survival on bedded sites for all species was 61 per cent, versus 47.3 per cent on nonbedded sites. Direct-seeded Nuttall oak survival was very high regardless of bedding ( per cent). Planted Nuttall oak seedlings had a 66.6 per cent survival rate on bedded positions, versus 55.8 per cent survival on non-bedded sites. Green ash seedling survival did not differ on bedding position; survival on beds was 60.0 per cent compared with 61.6 per cent off beds. Measured survival rates for direct-seeded Nuttall oak in this study are significantly higher than those of Miwa et al. (1993) and Schweitzer et al. (1997) in Mississippi, but the latter two studies were firstyear measurements in which Nuttall oak may have delayed germination. Ozalp et al. (1998), following up Miwa et al. (1993), found a fifth year 65 per cent survival for direct-seeded Nuttall oak on the clayey Sharkey soil series in Mississippi. In the study reported here, in Louisiana, planted Nuttall oak seedlings on beds had a mean survival of 66.6 per cent compared with the 55.8 per cent survival on non-bedded sites. On a similar poorly drained clay soil in Mississippi, Schweitzer et al. (1997) measured 63 per cent survival after one growing season. Ozalp et al. (1997) had 79 per cent fifth year survival for planted Nuttall oak on similar clay soils at Lake George, Mississippi. For this study reported here, in Louisiana, green ash survival was nearly identical on beds (60.0 per cent) or on non-bedded positions (61.6 per cent). Krinard and Kennedy (1987) reported 80 per cent survival for Nuttall oak and 98 per cent survival of green ash at age 4 years on a plantation without weed control and without prolonged inundation on a cleared, clayey poorly drained Vertisol in Mississippi. The two studies in the Lower Mississippi Alluvial Valley were on soils very similar to the Alligator and Perry in this study; however, the former sites were protected from prolonged flooding by levees. Height and diameter growth On the Alligator clay soils, planted and directseeded Nuttall oak had significantly greater fourth year heights on beds than on non-bedded positions (Table 2). On Perry clay soils, however, bedding significantly increased only planted Nuttall oak height. There were no differences in height of bedded or non-bedded Nuttall oaks on the better drained and loamy Hebert silt loam, whether trees were planted or direct seeded. Bedding did not significantly increase green ash height on any of the three soils.

5 RESTORATION OF BOTTOMLAND HARDWOODS 185 (A) ph 7 (mv) Bedded Non-bed 0 12/1/1998 2/1/1999 4/1/1999 6/1/1999 8/1/ /1/ /1/1999 2/1/2000 Date 4/1/2000 6/1/2000 8/1/ /1/ /1/2000 (B) ph 7 (mv) /1/1998 2/1/1999 4/1/1999 6/1/1999 8/1/1999 Bedded Non-bed 10/1/ /1/1999 2/1/2000 Date 4/1/2000 6/1/2000 8/1/ /1/ /1/2000 Figure 2. Soil redox potential (adjusted to ph 7) for bedded and non-bedded positions on Alligator clay soils in the study area, Bouef River Wildlife Management Area, LA, USA. (A) Soil redox potential at 15 cm depth; (B) soil redox potential at 30 cm depth. Nuttall oak height after 4 years in the Mississippi study on Sharkey clay was 90 cm on clay sites without weed control (Krinard and Kennedy, 1987). Fifth year heights of Nuttall oak on Sharkey clay at Lake George, Mississipppi averaged 177 cm (Ozalp et al., 1998). Those height measurements are much greater than that reported in this study in Louisiana, which was unprotected by levees and subject to long and frequent inundation. Schweitzer et al. (1997) found Nuttall oak seedlings averaged 40 cm tall after 1 year on a similar poorly drained clay soil. On the more poorly drained Alligator and better drained Hebert soils, bedding did not affect planted Nuttall oak mean diameter (Table 2). Bedding significantly increased direct-seeded Nuttall oak diameters only on the Alligator soil. On the Perry soil, only planted Nuttall oak had significantly greater mean diameter on beds compared with that on non-bedded sites. Fifth year diameter of Nuttall oak on Sharkey soil at Lake George, Mississippi was 27 mm (Ozalp et al., 1998). Green ash did not have significant mean diameter differences between bedded and nonbedded sites on any of the three soils. Krinard and

6 186 FORESTRY Table 2: Fourth year heights and ground-line diameters of seedlings on bedded and non-bedded site positions for three soils, Bouef River Wildlife Management Area, LA, USA in 2000 (A) Mean heights with standard errors for species planted or seeded on bedded and non-bedded site positions are compared within each soil series Mean height (cm) Alligator clay Perry clay Hebert silt loam Species Bedded Non-bedded Bedded Non-bedded Bedded Non-bedded Nuttall oak, planted 57.6 ± 2.6* 43.7 ± 2.7* 86.5 ± 6.3* 36.8 ± 6.2* 83.3 ± ± 5.4 Nuttall oak, direct seeded 36.8 ± 1.8** 23.8 ± 2.2** 45.2 ± ± ± ± 5.1 Green ash, planted 29.1 ± ± ± ± ± ± 2.0 (B) Mean diameters with standard errors for species planted or seeded on bedded and non-bedded site positions are compared within each soil series Mean height (cm) Alligator clay Perry clay Hebert silt loam Species Bedded Non-bedded Bedded Non-bedded Bedded Non-bedded Nuttall oak, planted 12.4 ± ± ± 1.0* 5.3 ± 1.5* 15.3 ± ± 0.9 Nuttall oak, direct seeded 6.4 ± 0.4** 4.1 ± 0.3** 7.8 ± ± ± ± 0.5 Green ash, planted 6.4 ± ± ± ± ± ± 0.9 * P-value < 0.05, ** P-value < 0.01 (significance level attained in ANOVA). Comparisons are between bedded and non-bedded positions within soil for each species/regeneration technique. Kennedy (1987) measured green ash height of 2.3 m at 4 years in Mississippi on clay soils without weed control. Bedding effects on Nuttall oak height and diameter were significant only on the poorly drained Alligator and Perry clays, and not on the somewhat poorly drained Hebert silt loam. Similar results were found with loblolly pine heights and diameters on bedded south-eastern US soils (Mann and McGilvray, 1974; McKee and Wilhite, 1986), where bedding benefited pine growth on poorly drained soils, but not somewhat poorly drained or moderately well-drained soils. Conclusions Frequent, high and prolonged flooding and long periods of anaerobic conditions on this site make bottomland hardwood restoration a challenge. Although the growth results are not spectacular, mean fourth year height for a major desirable species (Nuttall oak) was increased by bedding these low, clayey backswamp Vertisols. We conclude that bedding on the more poorly drained and clayey soils, such as Alligator clay, benefits the height growth of planted Nuttall oak more than bedding on loamier somewhat poorly drained soils such as Hebert. Neither green ash height nor diameter growth is benefited by bedding on any of these three soils. Bedding was, however, effective in increasing overall species survival. Bedding helps restore soil and site micro-topography, and influences the local hydrological regime, but the massive changes made by humans are difficult to mediate and are certainly a challenge for the land manager working in heavily impacted areas. Bedding frequently flooded, poorly drained, clayey soil should be considered a potential practice to benefit Nuttall oak seedling growth when

7 RESTORATION OF BOTTOMLAND HARDWOODS 187 planning forest restoration plantings on former agricultural fields. Acknowledgements This study was funded in part by the Utility Forest Carbon Management Program, Edison Electric Institute and the McIntire-Stennis Forestry Cooperative Research Program. References Baker, J.B. and Broadfoot, W.M A practical field method of site evaluation for commercially important southern hardwoods. US Dept of Agriculture, Forest Service Gen. Tech. Rep. SO-26. Southern Forest Experiment Station, New Orleans, LA. Boyd, W.H Soil Survey of Catahoula Parish, Louisiana. US Dept. of Agriculture, Soil Conservation Service, in cooperation with Louisiana Agricultural Experiment Station and Louisiana Soil and Water Conservation Committee. Broadfoot, W.M Hardwood suitability for and properties of important midsouth soils. US Dept of Agriculture, Forest Service Research Paper SO-127. Southern Forest Experiment Station, New Orleans, LA. Faulkner, S.P., Patrick, W.H. Jr and Gambrell, R.P Field techniques for measuring wetland soil parameters. Soil Sci. Soc. Am. J. 53, Gambrell, R.P. and Patrick, W.H. Jr 1978 Chemical and microbiological properties of anaerobic soils and sediments. In Plant Life in Anaerobic Environments. D.D. Hook and R.M.M. Crawford (eds). Ann Arbor Science Publishers, Ann Arbor, MI, pp Haywood, J.D., Tiarks, A.E. and Shoulders, E Loblolly and slash pine height and diameter are related to soil drainage in winter on poorly drained silt loams. New Forests 4, Krinard, R.M. and Kennedy, H.E. Jr 1987 Planted hardwood development on Sharkey clay soil without weed control through 16 years. USDA Forest Service Southern Forest Experiment Station Research Note SO-343. Langdon, O.G Ridge planting improves early growth of south Florida slash pine. J. For. 60, 487. Lockhart, B.R., Keeland, B., McKoy, J. and Dean, T.J Comparing regeneration techniques for afforesting previously farmed bottomland hardwood sites in the Lower Mississippi Alluvial Valley, USA. Forestry 76, MacDonald, P.O., Frayer, W.E. and Clauser, J.K Documentation, Chronology, and Future Projections of Bottomland Hardwood Habitat Losses in the Lower Mississippi River Alluvial Plain. Vols 1 and 2. US Department of the Interior, Fish and Wildlife Service, Washington, DC. McKee, W.H. Jr. and Shoulders, E Depth of water table and redox potential of soil affect slash pine growth. For. Sci. 16, McKee, W.H. Jr and Wilhite, L.P Loblolly pine response to bedding and fertilization varies by drainage class on Lower Atlantic Coastal Plain sites. South. J. Appl. For. 10, Mann, W.F. Jr and McGilvray, J.M Response of slash pine to bedding and phosphorus application in southeastern flatwoods. USDA Forest Service Research Paper SO-99. Southern Forest Experiment Station, New Orleans, LA. Miwa, M., Schoenholtz, S.H., Hodges, J.D. and Kennedy, H.E First year results of bottomland oak reestablishment in alluvial soils of the lower Mississippi valley. In Proceedings of the Seventh Biennial Southern Silvicultural Research Conference, J.C. Brisette (ed.). US Dept of Agriculture, Forest Service General Technical Report SO-93, pp Ozalp, M., Schoenholtz, S.H., Hodges, J.D. and Miwa, M Influence of soil series and planting methods on fifth-year survival and growth of bottomland oak re-establishment in a farmed wetland. In Proceedings of the Ninth Biennial Southern Silvicultural Research Conference, T.A. Waldrop (ed.). US Dept. of Agriculture, Forest Service General Technical Report SRS-20. Southern Research Station, Asheville, NC, pp Paavilainen, E. and Päivänen J Peatland Forestry: Ecology and Principles. Springer-Verlag, New York, 270 pp. Patrick, W.H. Jr, Gambrell, R.P. and Faulkner, S.P Redox measurements of soils. In Methods of Soil Analysis. Part 3. Chemical Methods. D.L. Sparks et al. (eds). Soil Science Society of America, Inc., Madison, WI, pp Rothwell, R.L., Woodard, P.M. and Rivard, P.G The effect of peatland drainage and planting position on the growth of white spruce seedlings. North. J. Appl. For. 10, SAS Institute, Inc SAS/STAT User s Guide Version 8. SAS Institute, Inc., Cary, NC. Schweitzer, C.A., Stanturf, J.A., Shepard, J.P., Wilkins, T.M., Portwood, C.J. and Dorris, L.C. Jr 1997 Largescale comparison of reforestation techniques commonly used in the Lower Mississippi Alluvial Valley: first year results. In S.G. Pallardy, R.A. Cecich, H.G. Garrett and P.S. Johnson (eds). Proceedings of the Eleventh Central Hardwood Forest Conference, Columbia, MO, March 1997, pp Stanturf, J.A., Schweitzer, C.J. and Gardiner, E.S Afforestation of marginal agricultural land in the Lower Mississippi River Alluvial Valley, U.S.A. Silva Fenn. 32,

8 188 FORESTRY Stanturf, J.A., Schoenholtz, S.H., Schweitzer, C.J. and Shepard, J.P Achieving restoration success: myths in bottomland hardwood forests. Restor. Ecol. 9, The Nature Conservancy 1992 Restoration of the Mississippi River Alluvial Plain as a Functional Ecosystem. The Nature Conservancy, Baton Rouge, LA. Xu, Y.J., Burger, J.A., Aust, W.M. and Patterson, S.C Responses of surface hydrology and early loblloly pine growth to soil disturbance and site preparation in a lower coastal plain wetland. N. Z. J. For. Sci. 30, Xu, Y.-J., Burger, J.A., Aust, M.W., Patterson, S.C., Miwa, M. and Preston, D.P Changes in surface water table depth and soil physical properties after harvest and establishment of loblolly pine (Pinus taeda L.) in Atlantic coastal plain wetlands of South Carolina. Soil Tillage Res. 63,