Silvo Fennica 32(3)32(3) ~~~~~w~~~~~w__l__l ~---~-_~---~-_ __~______~~~__~______~~~

Afforestation of Marginal AgriculturalLand in the Lower Mississippi RiverAlluvial Valley, U.S.A.

John A. Stanturf, Collie 1. Schweitzer and Emile S. Gardiner

Stanturf, J.A., Schweitzer, C.J. & Gardiner, E.S. 1998. Afforestation of marginal agriculturalland in the Lower Mississippi River Alluvial Valley, U.S.A. Silva Fennica 32(3): 281-297.

Afforestation of marginal agricultural land in the Lower Mississippi Alluvial Valley(LMAV) relies on native species, planted mostly in single-species plantations. Hardmast species such as oak and pecan are favored for their value to wildlife, especially onpublic land. Successful afforestation requires an understanding of site variation withinfloodplains and matching species preferences and tolerances to site characteristics, inparticular to inundation regimes. Soil physical conditions, root aeration, nutrient avail-ability, and moisture availability during the growing season also must be considered inmatching species to site. Afforestation methods include planting seedlings or cuttings,and direct-seeding. Both methods can be done by hand or by machine. If good qualityseedlings are planted properly and well cared for before planting, the chances forsuccessful establishment are high but complete failures do occur. Mortality and poorgrowth are caused by many factors: extended post-planting drought or flooding; poorplanting or seeding practices; poor quality seed or seedlings; animal depredation; orherbicide drift from aerial application to nearby cropland. More species can be planted,even on continuously flooded sites. Direct-seeding, while limited to heavy-seededspecies (oaks and hickories), costs less than 50 % of planting seedlings. Growth variesconsiderably by soil type; most bottomland hardwoods grow best on silt loam and lesswell on clay soils. Up to 200 000 ha of land in the LMAV subject to spring and earlysummer backwater flooding could be afforested over the next decade.

Keywords bottomland hardwoods, direct-seeding, Liquidumbar styraciflua, Fruxinuspennsylvanica, Populus deltoides, Quercus nuttallii, Quercus nigraAuthors’ addresses USDA Forest Service, Southern Research Station, P.O. Box 227,Stoneville, MS 38776, USAFax +l 601 686 3195 E-mail jstantur/srs_stoneville@fs.fed.usAccepted 2 July 1998

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1 Introduction

Forested wetlands in the southern United Statesmostly occur in the floodplains of major rivers andtheir tributaries within a broad coastal plain stretch-ing from Texas to Virginia. Occupying almost 13million ha in the southern United States, the impor-tance to society of these floodplain forests is welldocumented (Wharton et al. 1982). Nevertheless,the present extent of forested wetlands in theUnited States is less than one-third of their extentbefore European settlement. Two-thirds of theannual losses of wetlands in the conterminousUnited States occur in forested wetlands, prima-rily in the South (Wilen and Frayer 1990). Conver-sion to agriculture by clearing and draining hasbeen the major cause of forested wetland loss(McWilliams and Rosson 1990). Of an estimated8.5 to 9.5 million ha before 1780, only two millionha of forested wetlands remain in the floodplain ofthe lower Mississippi River (MacDonald et al.1979, Turner et al. 198 1, The Nature Conservan-cy 1992). Forested wetland losses in other parts ofthe southern U.S. are just as striking (Tansey andCost 1990, Hefner and Dahl 1993).

The Lower Mississippi Alluvial Valley(LMAV) once supported the largest expanse offorested wetlands in the United States. Rich allu-vial soils received periodic sediment additionsfrom the world’s third largest river and support-ed highly productive ecosystems (Putnam et al.1960, Harris and Gosselink 1990). Extensive ar-eas of bottomland hardwood forests were foundin the floodplains of tributaries of the Mississip-pi and other large rivers of the southeastern United

States that drained into the Gulf of Mexico andthe Atlantic Ocean. The LMAV has undergonethe most widespread loss of bottomland hard-wood forests in the United States. As much as96 % of the loss of bottomland hardwood forestsin the LMAV has been due to conversion toagriculture (MacDonald et al. 1979, Departmentof the Interior 1988).

Between the early 1800s and 1935, about one-half of the original forests were cleared. A latersurge in forest clearing for agriculture took placein the 1960s and 1970s in response to a rise insoybean prices (Stemitzke 1976). When priceseventually fell, land that was marginal for agri-culture because it was still subject to spring andearly summer backwater flooding became idle.These are the lands that are now available forafforestation.

Over the last 25 yrs, scientists at the SouthernHardwoods Laboratory in Stoneville, Mississip-pi have developed most of the artificial regener-ation methods used today in afforestation of bot-tomland hardwoods. In this paper, we provide anoverview of afforestation efforts in the LMAV.Strategies vary by landowner objectives and aredriven mainly by public programs supportingafforestation for water quality protection andwetlands restoration. We provide a summary ofpublic and private programs supporting affores-tation of economically marginal farmland anddescribe common practices of artificial regener-ation, including examples of afforestation pro-grams that have different objectives.

Afforestation primarily is occurring in theLMAV states of Louisiana, Mississippi and Ar-

Table 1. Actual and potential afforestation in the Lower Mississippi Alluvial Valley, by program and agency.

Program

Agency 2 199s

Area (ha)’

Planned to 2005 Totd

Wildlife refuges USFWS 5180 10000 15180Wetland mitigation COE 2025 9700 11725State agencies MS,LA,AR 13500 40500 54000Wetlands Reserve Program (WRP) NRCS 53000 47750 100750Total 73705 107950 181655

’ Estimates furnished by participants at the Workshop on “Artificial Regeneration of Bottomland Hardwoods: Reforestation/Restoration

’Research Needs”, held May I l-12. 1995 in Stoneville, Mississippi.USFWS=U. S. Fish and Wildlife Serwce; COE=U. S. Army Corps of Engineers; MS=Mississippi; LA=Louisiana; AR=Arkansar;NRCS=U. S. Natural Resources Conservation Service, formerly Soil Conservation Service.

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Stanturf. Schweitzer and Gardiner Afforestation of Morainol Aaritultural Land in the lower Mississiooi River . . .

River Base Level

4

Fig. I. Cross-section of a typical floodplain, showing the approximate relationship betweensite types.

kansas, although restoration is taking placethroughout the South. Afforestation in the LMAVis driven primarily by acquisition of land by pub-lic agencies to enlarge federal wildlife refuges andto mitigate or offset wetland losses due to con-struction for flood control; by state programs; andby public policy initiatives such as the WetlandsReserve Program (WRP) on private land.Through 1995, approximately 74 000 ha are underafforestation plans, mostly on private land (Table1). Afforestation will increase over the next 10years, so that 182 000 ha should be in afforesta-tion schemes in the LMAV, primarily in the statesof Mississippi, Louisiana, and Arkansas.

2 Site and Species

2.1 Species/Site Relationships

Successful afforestation of marginal farmland inthe LMAV requires an understanding of site var-iation within floodplains and site requirementsof the species to be used. Although most affores-tation areas are flat, large differences in site qual-ity exist, and many afforestation efforts havefailed because these differences were ignored.Elevational changes of only a few inches canhave a marked effect on the site and therefore onspecies occurrence and development (Hodges andSwitzer 1979). Differences in hydrology, partic-ularly drainage and soil moisture, are clearlyassociated with these minor elevational differ-ences. Other factors also vary according to ele-vation, such as soil type, texture, structure, and

pH. All these factors affect which species aresuitable for the site.

2.2 Site Characteristics

The origin and development of floodplain geo-morphic features were discussed by Hodges(1994) and detailed descriptions, including rela-tive elevation, soil types, drainage class, andproductivity are given in Hodges and Switzer(1979) and Hodges (1997). In summary, the frontsand ridges (former fronts) are the highest, bestdrained, and most productive sites within thefloodplain (Fig. 1). Soils are generally sandy orsilty loams. Soils on the flats are predominantlyclays and the sites are poorly to somewhat poor-ly drained. Sloughs and swamps arise from oldstreambeds that are filling with sediment. Thesoils are usually fine-textured and drainage ispoor. Standing water may be present in theswamps except in extremely dry years. Most ofthe land available for afforestation is on the flats;sloughs and swamps were seldom cleared, andfronts and ridges continue to support active agri-culture. Because of the great spatial variabilityin floodplains, however, sites are often inter-mixed so that an area to be afforested is likely toinclude several site conditions.

2.3 Species Tolerances to Flooding

For successful regeneration, species preferencesand tolerances must be matched to site charac-teristics, in particular to inundation regimes. Rel-

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Table 2. Species tolerance in relation to flooding time and duration.

Continuous flooding

January-June January-May January-May

Periodic flooding

January-April

Taxodium Diospyros Liquidambardistichum L. virginiana L. styra+ua L.(Baldcypress) (Persimmon) (Sweetgum)

Quercus Fraxinus Quercuslyrata Walt. pennsylvanica Marsh. nigra L.(Overcup oak) (Green ash) (Water oak)

Platanus Quercusoccidentalis L. shumardii Buck1(Sycamore) (Shumard oak)

Populus Quercus falcatadeltoides Bartr. ex. var. pagodifolia El1Marsh. var. deltoides (Cherrybark oak)(Eastern cottonwood)

Carya Quercusaquatica laurifolia Michx.(Michx. f.) Nutt. (Swamp laurel oak)(Water hickory)

Nyssa aquatica L. Quercus(Water tupelo) nuttallii Palmer

(Nuttall oak)

Salix nigra L.(Black willow)

Quercusphellos L.(Willow oak)

Carya Quercusillinoensis Wangenh. michauxii Nutt.(Sweet pecan) (Swamp chestnut oak)

Celtislaevigata willd.(Sugarberry)

ative flood tolerance of bottomland trees is sum-marized in Table 2 (see McKnight et al. 198 1 fora more complete compilation). Few species cantolerate continuous flooding, especially if it ex-tends into the growing season. Baldcypress (Tux-odium distichum L.) and water tupelo (Nyssaaquatica L.) can survive extended flooding oftheir roots to a greater extent than other species.After leafout, seedlings can withstand limitedsoil inundation if their leaves are not submerged(Hook 1984). The choice of species is greater ifflooding is periodic, as is true on most bottom-land sites in most years.

Inundation regime is more complex, however,than whether a site floods or not, and seedlingsare more susceptible than mature trees. Depth,time, and duration of flooding must be consid-ered, and the state of the floodwater, particularlyflowing versus stagnant (Hook and Scholtens1978). Inundation regime is difficult and time-consuming to measure, and natural regimes fre-quently have been altered. An indicator of flood-ing regime is published in soil surveys, and near-by landowners often know of alterations due todrainage and other factors not reflected in soilsurveys. A flood history for at least the previousfive years is recommended, to select suitable

species. The choice of species should be guidedby the upper, rather than the lower, level offlooding. Most flood tolerant species can be plant-ed on drier sites. but not the reverse.

2.4 Soil Characteristics

Soil physical conditions, root aeration, nutrientavailability, and moisture availability during thegrowing season are other important factors toconsider in matching species to site (Stone 1978,Baker and Broadfoot 1979). Bottomland soils ofsilt loam texture generally suggest a moist, well-drained site. Clay textured soils usually indicatea low-lying site that is periodically inundated.Medium-textured soils are suitable for most bot-tomland hardwood species, with three possibleexceptions. Survival and growth of red oak spe-cies are limited by high pH (more than 7.0),although Shumard oak (Quercus shumardiiBuckl.) does well over pH 7.5 (Kennedy 1984,Kennedy and Krinard 1985). On former crop-land, plow pans can occur at 20 cm to 30 cmdepth that will limit root development. Inade-quate rooting will affect survival, growth, andwindfirmess. Plow pans can be broken up by

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Stanturf, Schweitzer and Gardiner Afforestotion of Morginal Agricultural land in the lower Mississippi River . . .

subsoiling before planting or direct seeding. Onformer agricultural land or engineered sites, min-eral toxicities or nutrient deficiencies may occur,but they can be diagnosed by soil analyses andcorrected. Clay soils tend to be very wet in win-ter and spring and very dry in mid to late sum-mer, presenting fewer options for selecting suit-able species. Green ash (FraxinuspennsylvanicaMarsh.) and Nuttall oak (Quercus nuttallii Palm-er) both tolerate periodic flooding and grow bet-ter than other species when available water islow.

Broadfoot developed two methods for evalu-ating sites based upon soil characteristics. Oneapproach requires knowing which soil series arepresent and consulting either Broadfoot (1976)or recently published soil survey reports thatinclude woodland suitability interpretations(Francis 1985). A more complicated approachinvolves estimating site index, a measure of po-tential productivity based upon a tree’s heightgrowth over time (Baker and Broadfoot 1979).Advantages of this approach include widespreadapplicability throughout the southern U.S., iden-tification of soil series is not required, and guide-lines for ameliorative treatments such as fertili-zation are included (Baker and Broadfoot 1979).Disadvantages include the need for users to esti-mate soil conditions such as texture, compac-tion, water table depth, organic matter content,and pH (Francis 1985). On the other hand, mostsoil scientists and many foresters can make fieldestimates of these properties that produce siteindex estimates of sufficient accuracy for mostreforestation projects. While site index is a use-ful guide to inherent productivity, there is nofixed rule for applying productivity measures tojudge afforestation potential for wildlife and otherpurposes. We have suggested that a site be atleast minimally acceptable for a species, as de-termined by Baker and Broadfoot (1979). Thismeans growth on a site is likely to range from54 % to 63 % of the maximum productivity levelfor that species (Stanturf 1993).

3 Afforestation Methods

3.1 General

Two major afforestation methods are plantingseedlings or cuttings, and direct-seeding. Bothmethods can be done by hand or by machine.Suitability of afforesting several species withthese stock types is summarized in Table 3. Ifgood quality seedlings are planted properly andwell cared for before planting, the chances forsuccessful establishment are high (Kennedy 1984,Kennedy et al. 1987, Allen and Kennedy 1989,Allen et al. in press). Planting has the advantagesthat more species can be planted, and it can bedone even on continuously flooded sites. Direct-seeding, while limited to heavy-seeded speciessuch as the oaks (Quercus spp.) and hickories(Carya spp.), costs less than 50 % of the cost ofseedling planting (Bullard et al. 1992). Direct-seeding has been successful in every month

Table 3. Suitable artificial regeneration methods andstock types for major bottomland hardwood spe-cies.

Species

Planting Direct-Seeding

Seedlings Cuttings

Carya illinoensis X X

Carya aquatica X X

Celtis laevigata X

Diospyros virginiana X

F r a x i n u s pennsylvanica xx1 X

Liquidambar styraciflua xx X

Nyssa aquatica X

Platanus occidentalis xx X

Populus deltoides X x x

Quercus falcata X X

var. pagodifoliaQ. laurifolia X X

Q. lyrata X X

Q. michauxii X X

Q. nigra X XQ. nuttallii X X

Q. phellos X X

Q. shumardii X X

Salix nigra X

Taxodium distichum X

’ xx = preferred stock type.

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(Johnson 1983), and operationally it can be donefor a month or longer beyond the time whenplanting is recommended.

3.2 Site Preparation

The best site preparation on marginal cropland isto continue farming the site until it is afforested.Normal farming operations will control woody andherbaceous weeds so that often no site preparationis needed. If a plow pan has developed, diskingwith a heavy disk at least twice in late summerbefore planting breaks up the plow pan and con-trols weeds. If a heavy weed cover has been al-lowed to develop from fallowing, disking is advis-able to reduce cover for rodents. Planting or direct-seeding by machine will be aided by site prepara-tion and generally result in greater survival.

3.3 Seedlings

Suitable bare-root hardwood seedlings are largerthan the typical pine seedling planted in the south-ern U.S. Bare-root hardwood seedlings are usu-ally 1-O stock. Recommended size is at least 45cm top length with at least 1 cm root collardiameter (Kennedy 1993). Root systems shouldbe well-developed with several lateral roots, andcan be pruned to 20 cm length to make plantingeasier.

While bare-root seedlings are generally pre-ferred, container stock can be planted later in theseason and thus extend the planting season. Thismay allow sites that flood into the growing sea-son to be planted successfully with containerstock after flood waters recede, later in the sea-son than is feasible for bare-root stock. Oak seed-lings grown in pots may have higher survival on“harsher” sites such as heavy clay soils withvertic (shrink-swell) properties (Allen et al. inpress). Container grown Nuttall oak seedlingssurvived flooding better than bare-root seedlingsafter out planting in one trial (&mphrey 1994).Containerized seedlings are more expensive thanbare-root seedlings, heavier, and more difficultto transport and plant.

Additional research, including side-by-sidecomparisons of bare-root and container stock, is

286

needed before definitive recommendations canbe given. The ability to extend the planting win-dow to include fall, late spring and early summerplantings will probably make container stockcost-effective for some public agencies (J. Kiser,Corps of Engineers-Vicksburg District, pers.comm., May 1995).

Bare-root seedlings survive best if they areplanted while dormant in moist soil. These con-ditions are obtained in the southern U.S. fromJanuary through mid-March. Planting can beginas early as November if antecedent precipitationhas recharged soil moisture (Kennedy 1979). Ifseedlings are kept dormant in cold storage, plant-ing may be extended into May (Allen andKennedy 1989). The most frequent limitationson planting are excessive cold and flooding. Sub-freezing temperatures cause root death, resultingin low survival. While flood tolerant species canbe planted in standing water, even hand-plantingis easier if soils are moist but not flooded.

Seedlings can be hand planted using a dibblebar or shovel, or machine planted. Planting ma-chines work well in moist sandy and loamy soils,but clay soils adhere to parts of the planter andhinder movement (Allen and Kennedy 1989).An experienced hand planter can plant up to 800seedlings in a day under ideal conditions. Anexperienced two- or three-person machine plant-ing crew can plant 4000 to 8000 seedlings perday (Allen and Kennedy 1989).

3.4 Cuttings

Planting unrooted cuttings of five species hasproven successful (Table 3), and is the most com-mon method of afforesting Eastern cottonwood(Populus deltoides Bartr., ex Marsh. var. del-toides). One advantage of cuttings over otherstock types is the ability to plant genetically supe-rior clonal material. Presently this is important forcottonwood only, but likely to increase in impor-tance for other species (R. Rousseau, WestvacoCorp., pers. comm., May 1995). Cottonwood cut-tings are produced from wands, which are them-selves produced in stool beds. Wands can be pro-duced from root stock for three to four years, thenthe nursery must be re-established (McKnight1970). Under good nursery conditions, wands will

Stonturf Schweitzer and Gardiner--..-!-_---Afforesiation of Marginal Agricultural Land in the lower Mississippi River . . .

l_l____l__ll____-_--_-_-~--_-_,--_-~-_-_~~-~~”~---~

reach heights of up to 5 m in one year. Cuttings 5 1cm long are produced from dormant wands. Cut-tings should be at least 6 mm diameter at the top(small) end. Research on survival and plantingtechniques has shown that cuttings longer than 5 1cm do not increase survival, but they do increasecosts (McKnight 1970).

Planting options for cottonwood cuttings aresimilar to options for bare-root seedlings. Theplanting window for dormant cuttings is Decem-ber through March, and cuttings can be hand- ormachine-planted. Cuttings are planted about 45cm deep, with 5 cm aboveground. Leaving onlya small amount of the cutting aboveground re-duces the likelihood of developing multiple-stems(M&night 1970). Additional information on cot-tonwood culture is given below.

Green ash has been successfully regeneratedfrom both horizontal and vertical cuttings(Kennedy 1977) but only from cuttings madefrom 1-O nursery grown seedlings. Horizontalplanting of cuttings 25 cm to 36 cm long in slits2.5 cm to 5.0 cm deep, or vertical planting of 38cm long cuttings has been suggested as an alter-native to planted seedlings (Kennedy 1977).However, where there is a danger of long peri-ods of standing water, seedlings are better thancuttings. Seedlings were larger after one grow-ing season than either horizontal or vertical cut-tings, although all material grew the same amount.

3.5 Direct-Seeding

Direct-seeding is a widely used method of affor-estation in the LMAV. Only heavy-seeded spe-cies of Quercus spp. and Carya spp. can bedirect-seeded with a strong likelihood of suc-cess. Many early tests were with Nuttall oak andit continues to be the most popular species todirect-seed. At least six other red oak species(Erythrobalanus) and four white oak species(Leucobalanus) have been direct-seeded success-fully (Table 3). Most attempts at direct seedinglight-seeded species (Fruxinus spp., Ulmus spp.,Liquidumbar styruci$kz) have failed (Allen etal. in Press). Failures have been attributed todrought stress shortly after germination, flood-ing after germination, or predation by birds androdents.

Initial trials with direct-seeding were conduct-ed in natural stands under a complete canopyand in small openings (< 0.004 ha) created byremoving single large trees. These trials general-ly resulted in complete failure because of rodentdepredation (Johnson and Krinard 1987). Fur-ther research with larger openings has estab-lished that openings greater than one ha can besuccessfully regenerated by direct-seeding (John-son and Krinard 1987). Competing vegetationmay pose more of a threat to new germinants, asoaks are notoriously slow to develop above-ground. Germination and survival as high as 80percent has been attained in research trials, but35 percent germination is more typical for com-mercial sowings. Recommended rates are 1730to 2470 sound acorns ham’ on most sites. On sitesthat have lain fallow for a few years, are weedinfested and likely to have high rodent popula-tions, the rate should be higher: 2964 to 3705acorns ha-l (Allen et al. in press). This shouldproduce 741 to 1235, l-year-old trees ha-‘, anumber sufficient for most objectives.

Seed collection is the greatest challenge indirect-seeding (Kennedy 1993). Collections mustbe made between October and February, afteracorns have fallen. Acorns of red oak speciescan be stored up to five years in cold storage(Bonner 1973, Bonner and Vozzo 1987, Bonneret al. 1994). Generally, acorns of white oak spe-cies cannot be stored longer than four months, asthey naturally germinate after falling.

Direct-seeding can be conducted from Novem-ber through June, depending upon site floodingfrequency. While direct-seeding of Nuttall oakhas been successful in every month, July throughOctober are usually too hot and dry (Johnsonand Krinard 1987, Wittwer 1991). Seeds thatgerminate in cold storage can still be sown andwill produce suitable seedlings, even if their radi-cles are broken off (Bonner 1982). Seeds sown2.5 cm to 15 cm deep will germinate and pro-duce seedlings, although 5 cm is the recom-mended depth. Deeper sowing may be worth-while when surface drying or rodent pilferage islikely. Normal spacing is rows 3 m to 3.6 mapart and acorns 1 m to 1.5 m apart within rows.

Mechanical planting and sowing are faster onclean sites with slopes less than 10 %. Modifiedagricultural planters have been used successfully

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Silva Fennico 32( 3) review articles

Table 4. Comparison of the cost of direct-seeding versus planting seedlings of oaksin the LMAV. (Source: Data are from Bullard et al. 1992 and shown in 1989dollars).

Activity Costs, dollars ha-’

Direct-Seeding Planting

Site preparation (bush-hogging or disking)Seeding/PlantingAcorn/Seedling materialTotal costs

12.35 12.3586.45 86.4561.75 284.05

$160.55 $382.85

for direct seeding, although some new equip-ment has been developed for acorns. Machinesused for direct-seeding are modified one- andtwo-row grain planters. Some drop acorns auto-matically, others require an operator who dropsacorns at specified distances. A broadcast seederhas been used in trials in Louisiana (Allen et al.in press). Aerial seeding has been shown in smalltrials to have potential, although more work needsto be done to optimize the delivery system andthe method of burying acorns after sowing (Al-len et al. in press). Typical rates of direct-seed-ing are 12 to 16 ha per day for a three-personcrew using machines, to 2 ha per day for oneperson sowing by hand.

Success rates with direct-seeding have beengood. Failures are usually due to poor handlingof acorns, or to adverse field environments fol-lowing sowing. Flooding and high water tem-peratures are a deadly combination for newlygerminated acorns (Johnson and Krinard 1985)such as occur during May or June flooding. Thismay follow a dry March and April, during whichacorns have successfully germinated. On siteswhere extended flooding is likely during the ear-ly portion of the growing season, acorns shouldbe kept in cold storage and sown after floodwaters recede (Johnson and Krinard 1987).

3.6 Direct-Seeding Versus Planting Seed-lings

Advantages of planting seedlings include a wid-er range of species and a wider range of sites andconditions can be tolerated. While extended post-planting flooding damages most seedlings, taller

288

planted seedlings may extend above floodwatersand survive. On the other hand, the plantingwindow for seedlings is narrower in the Souththan for direct-seed.

The main advantage of direct seeding is poten-tially lower costs (Bullard et al. 1992, Allen etal. in press). This comes about in two ways: allthe costs of growing and handling seedlings areavoided, and planting acorns is usually less time-consuming than seedlings. The major disadvan-tages of direct seeding are that the plants are inmore vulnerable stages of development longer,so that the risk of poor survival and possiblefailure is greater. Bullard et al. (1992) comparedthe economics of direct-seeding and planting oakson afforested sites. The significant advantage ofdirect-seeding was the lower cost for material(Table 4). Although direct-seeding is quickerand easier than planting seedlings, the techniqueis relatively new to contractors and no price dif-ferential was offered (Bullard et al. 1992). Theyconcluded that the primary advantage of plant-ing seedlings was that in a given year, the overallprobability was greater of achieving an adequate-ly stocked stand. Allen (1990) reached a similarconclusion from his survey of oak planting anddirect-seeding on wildlife refuges.

4 Growth and Production

4.1 General

Establishment problems will be apparent withinthe first two years on afforestation sites. Com-plete failures do occur. Mortality and poor growth

Statatehweitzer and Gordiner Afforestation of Marginal Agricultural Land in the lower Mississippi River . . .

8

6 ,

4

“ 2 4 6 8

Age, yr

+WOl +wo2 f NO1 fl NO2

+CBOl x CB02 *SC01 =-SC02

10

Fig. 2a. Height growth of four oak (Quercus) speciesplanted at two spacings on a minor bottom site.(WO = Q. nigra, NO = Q. nuttullii, CBO = Q.fal-cata var. pagodifolia, SC0 = Q. michauxii;1 = spacing of 2.44 m by 2.44 m and 2 = spacingof 3.66 m by 3.66 m. Source: Kennedy et al. 1988,p. 84).

are caused by many factors: extended post-plant-ing drought or flooding; poor planting or seed-ing practices; poor quality seed or seedlings;animal depredation; or herbicide drift from aeri-al application to nearby cropland (Kennedy 1993).

Sometimes the slow initial growth, especially ofoaks, gives the appearance of failure becauseseedlings are hidden by profuse stands of tallweeds.

Early weed control, mechanical or chemical,may increase survival and speed early growth ofseedlings, but benefits may not justify costs. Kri-nard and Kennedy (1987a) compared growth ofsix hardwood species on a formerly forested Shar-key clay soil (very-fine, montmorillonitic, non-acid, thermic, vertic Haplaquepts) that wasmowed or disked to control weeds. Plots weretreated three to five times annually the first 5years. Mowing provided no advantage over noweed control for the first 4 years (Kennedy 1981)and there was no difference between mowed ordisked treatments after 15 years (Krinard andKennedy 1987a). Because competitors on old-field sites differ significantly, these results serve

8

10

Year

-sControl +-Mow +Disk

Fig. 2b. Height growth of Nuttall oak (Q. nuttullii ) ona Sharkey Clay soil; control plots measured at age4 and at age 16; mowed and disked plots meas-ured at ages 5, 10 and 15 years. (Source: Krinardand Kennedy 1987a, p. 2; Krinard and Kennedy1987b, p. 2).

only to caution that expenditures for weed con-trol may not be warranted.

Intensive cultivation is recommended for thefirst year in cottonwood plantations (McKnight1970). High survival and best growth of syca-more was obtained with clear cultivation for 1 or2 years, although it is possible to successfullyestablish sycamore plantations without weed con-trol (Briscoe 1969). Disking often produces sig-nificantly greater growth than mowing (Aird1962, Fitzgerald et al. 1975, Kennedy 1984).

4.2 Oak Plantings

Most species of bottomland oaks grow slowlythe first several years, typically 30 cm to 60 cmin height growth annually. If seedlings are notovertopped, height growth will increase to over1 m annually (Kennedy 1993). Four oak species(Kennedy et al. 1988) established with 1-O bare-root seedlings ranged in height from 4 m forswamp chestnut oak (Q. michaunii Nutt.), to 8.1m for water oak (Q. nigru L.) at age 10 (Fig. 2a).

2 8 9

Silvo Fennita 32(3) review articles__~“__II_II^__~X__~__-_-___-~___.~_,~~_.~~~”~~_-~~~~~~I1I -_l_,~--- __l-ll- -”

Diameter, cmHeight, m Volume, m” ha-’

200

2 0

150

1s

100

10

505

0 0Sharkey Sharkey Sharkey

Commerce Commerce CommerceSoil type

Fig. 3a. Eighteen-year average diameter, height, andvolume for sweetgum (Liquidumbar styruciflua)grown on two soil types in Mississippi. (Source:Krinard and Johnson 198.5, p. 7).

The site was a relatively infertile, minor bottomin Arkansas but growth was good. Swamp chest-nut oak was the slowest growing in the first 6years, probably due to the small seedlings thatwere available for planting (Kennedy et al. 1988).

On a Sharkey clay soil, Nuttall oak planted at3 m x 3 m spacing and no weed control averaged8 1 percent survival after 16 years. Height growthwas only 6 m (Fig. 2b), as opposed to the bettergrowth on the Arkansas site after only 10 years(Fig. 2a). On the Sharkey clay (Fig. 2b), mowingbetween the rows annually for 5 years increasedheight growth of Nuttall oak to 7.9 m at age 15years (Krinard and Kennedy 1987a,b).

Nuttall oak was direct-seeded on an intensive-ly prepared Sharkey clay soil at the Delta Exper-imental Forest near Stoneville, MS (Johnson1983). Germination averaged 36 percent. Initialspacing between planting spots was 0.6 m (5380acorns ham’). Of the trees alive at the end of thefirst year, 96 percent were still alive at the end of11 years. Many of the trees were overtopped but1360 Nuttall oak seedlings per hectare were in afree-to-grow position at age 11 years. Diameterat breast height ranged from 4 cm to 7 cm, andaverage height was 5.1 m.

Height, m

1”

n C0ntr0l

m Disked

PWXll Sweetgum GIreen ash Sycamore Cottonwood

Fig. 3b. Average height of four hardwood species grow-ing on a Sharkey Clay soil. Treatment was diskingannually for the first five years. Control plots meas-ured at age 16 and disked plots at age 15 years.Sweet pecan could not be measured reliably dueto the number of water hickory (Carya aquatica(Michx. f.) Nutt.) sprouts present, but survival wasprobably low. (Source: Krinard and Kennedy1987a, p. 2; Krinard and Kennedy 1987b, p. 2).

4.3 Sweetgum Plantings

Growth varies considerably by soil type; mostbottomland hardwood species grow best on me-dium textured soils such as Commerce silt loam(fine-silty, mixed, nonacid, thermic aeric Fluva-quents) and less wells on clay soils such as Shar-key. A comparison of two sweetgum plantationsin Mississippi illustrates these differences. At thesame stocking, sweetgum on the Commerce soilwas 75 percent taller, and nearly five times morevolume and weight (Figure 3a; Krinard and John-son 1985, Krinard 1988). Thinning at age 12 re-duced stocking in the clay soil to 4.25 m x 4.25m. The stand on the silt loam soil was thinnedtwice. Alternate diagonal rows were removed atage 6, and half the remaining trees were removedat age 30, leaving a spacing of 6 m x 6 m. Re-measurement after 3 1 years shows greater basalarea on fewer trees on the more productive Com-merce silt loam soil (Table 5).

9yElf, SchweitzEJnd Gardiner Afforestotion of Marginal Agricultural Land in the lower Mississippi River ..~ _,-- _Il-,“-_l”_*._X_II_~-.-~,~~-~~~ ~_l__~~~_~“-*--,~_I*c.~II~~II1ll~

4.4 Green Ash Plantings

Green ash is a valuable bottomland hardwoodspecies for timber but has not been favored inafforestation for wildlife. Krinard (1989) com-pared three green ash plantings of different agesplanted on Sharkey (clay), Commerce (silt loam),and Tunica-Bowdre (clayey over loamy,montmorillonitic, nonacid, thermic vertic Hap-laquepts and thermic fluvaquentic Hapludolls)soils. All plantings were at 3.67 m by 3.67 mspacings except the Sharkey planting was 3.05m by 3.05 m spacing and thinned at age 10.Plantings on the Commerce and Tunica-Bowdresoils grew the fastest. Mean annual incrementsof average diameter and height growth were about12.5 mm yrl and 1.22 m yrl (Table 6). Meanannual increment values for the Sharkey soilwere lower, 7.6 mm yri in diameter growth and0.76 m yrl in height growth. Survival exceeded80 percent on all sites. Krinard (1989) concludedthat spacings wider than 3.67 m by 3.67 m werenot advisable for green ash because of forkingproblems.

Table 5. Comparison of growth of sweetgum(Liquidambar styruci~ua) plantations on two soiltypes after 31 years. (Source: J. Goelz, unpub-lished data on file at Southern Hardwoods Lab.).

Density Basal Area DBH (Dq)stems ha-’ m* ha-t cm

Commerce Silt Loam 221 24.4 37.1Sharkey Clay 505 15.8 19.8

4.5 Comparisons of Several Species

Relative growth rates among species planted onthe same soil type and receiving similar culturaltreatments illustrate adaptations to soil types.Growth on the clay soils that are available forafforestation is lower than growth on mediumtextured soils, thus these sites may not be suit-able for timber production alone. Krinard andKennedy (1987a) reported on five hardwood spe-cies planted on a Sharkey clay soil, disked forthe first 5 years to control weeds, and selectivelythinned after 5 years to double the original plant-ing spacing. By age 15, average height was inthe order sweet pecan (Carya illinoensis L.) <sweetgum < green ash < sycamore < cottonwood(Fig. 3b). At age 16, trees growing on controlplots (no weed control, no thinning) were small-er but height growth ranking was the same (Kri-nard and Kennedy 1987b).

5 Afforestation Programs andStrategies

5.1 Public Programs

In 1987, the United States Fish and WildlifeService (FWS) began an aggressive program inthe LMAV to restore bottomland hardwood eco-systems (Haynes et al. 1993). This effort was notlimited to existing wildlife refuges, and includedreforestation of private lands and foreclosed farm-land transferred to the FWS from the FarmersHome Administration, another federal agency.The FWS strategy has been to afforest the mostland, at the lowest unit cost per hectare. Site

Table 6. Stand parameters of three green ash (Fraxinus pennsylvanicu Marsh.) plantings onrepresentative soil types in the LMAV. (Source: Krinard 1989, Table 1).

Soil Type Age Dbhyrs cm

Htm

Basal Area Cubic Volume Trees ha-’m2 ha-’ m3 ha-’

Sharkey 15 11.9 11.2 6.0 31.9 504Commerce 13 16.0 15.7 13.3 101.2 635Tunica-Bowdre 11 15.7 13.6 14.7 78.4 102

291

Silvo Fennico 32(3) review articles

preparation is minimal; weeds on fallow sitesare reduced using a bush hog or fire plow, fol-lowed by disking once or twice just before plant-ing (Haynes et al. 1993). Spacing may be greater(7.32 m by 7.32 m), the goal is to guarantee thehard mast component. Allen (1990) reviewedoperational planting and direct-seeding on tensites on federal wildlife refuges and concludedthat planting seedlings is preferred over direct-seeding if the objective is to quickly afforest oldfields. A summary of afforestation efforts byagency is given in Table 1.

The Army Corps of Engineers is restoring bot-tomland hardwood forests to mitigate fish andwildlife habitat losses caused by water resourcesprojects, primarily construction for flood con-trol. One ambitious mitigation project is the LakeGeorge property in the Yazoo River Basin inMississippi (Corps of Engineers 1989). The siteis characterized by Sharkey-Forestdale Associa-tion soils, backwater flooding in winter andspring, and poor drainage. The agency’s strategyhas been to treat the wettest sites first, leavingdrier sites in active agriculture to lower overallproject costs by revenue from leasing, and tocontrol weeds (lower site preparation costs). Bare-root seedlings (sweet pecan, willow oak, Shu-mard oak, cherrybark oak (Q. falcatu var. pa-godifolia Ell.) are planted at 3.66 m by 3.66 mspacing, and container seedlings (water tupeloand water oak) at 4.27 m by 4.27 m spacing.Only 5 % of the area will be direct-seeded.

State government agencies such as the Louisi-ana Department of Wildlife and Fisheries andthe Mississippi Department of Wildlife, Fisher-ies and Parks also have undertaken ambitiousrestoration projects. More than 2000 ha nearMonroe, Louisiana are being restored by the Loui-siana Department of Wildlife and Fisheries (Sav-age et al. 1989, Newling 1990). The MississippiDepartment of Wildlife, Fisheries and Parks isrestoring more than 400 ha near Greenwood, MS(Newling 1990). Participants at a recent work-shop estimated a total of 54 000 ha are sched-uled for afforestation by state agencies in Mis-sissippi, Arkansas, and Louisiana (Stanturf, un-published data, Table 1).

The federal Conservation Reserve Program(CRP) in 1980 began to subsidize establishingpermanent vegetative cover on erodible crop-

292

land. When reauthorized by Congress as part ofthe 1985 Food Security Act (popularly known asthe Farm Bill), the CRP included wetlands con-verted to cropland (Kennedy 1990). A landown-er participating in CRP reserves the land for 10years in return for reimbursement of some affor-estation costs and an annual payment, per hec-tare. By the ninth enrollment year (1989), morethan 20 000 ha of wetlands in the LMAV wereplaced into the CRP (The Nature Conservancy1992). An unknown portion of this land wasafforested, thus Table 1 does not include an esti-mate of CRP land.

The Wetland Reserve Program (WRP) wasincluded in the 1990 Farm Bill and set a maxi-mum sign up of 400 000 ha nationwide. A pilotprogram in 1992 in eight states was expanded to20 states in 1994. Three states in the LMAV,Mississippi, Arkansas, and Louisiana, were in-cluded. More land was submitted in these threestates (200 000 ha) than could be accepted be-cause of financial limitations on the program. In1995, Congress authorized an additional $92 mil-lion. The federal Natural Resources Conserva-tion Service administers the program and ex-pects a total of 100 750 ha to be afforested in theLMAV by 2005 (Table 1). In return for a perma-nent easement that removes the land from agri-cultural production, the government shares thecost of afforestation and provides a one-timepayment based upon the fair market agriculturalvalue of the land. The WRP will only reimburseafforestation costs for 741 stems ha-l, which isinsufficient for commercial forest management.Discussion of incorporating timber managementinto WRP has begun to remove some of theuncertainty surrounding future management op-tions.

5.2 Other Private Efforts

Many private efforts that do not depend on fed-eral cost-sharing programs have focused on hard-wood plantations for producing fiber. Fitler Man-aged Forest near Onward, Mississippi comprises4000 ha of eastern cottonwood plantations. Fit-ler is owned by Crown Vantage (formerly JamesRiver Timber Corp.) and intensively managedfor pulpwood production. Intensive plantation

Stanturf, Schweitzer and Gordiner Affor,estation of Morainal Agricultural Land in the lower Mississippi River . .

Table 7. Financial analysis for a private landowner of acottonwood plantation on a lo-year pulpwood ro-tation. (Source: J. Portwood, Crown Vantage Corp.,pers. comm., July 1995).

Contract’ No Contract

Yield 1122 112 Ton ha-‘(green)Stumpage 17.243 13.24 $US Ton-’ (green)Expenses 274 27 SUSCapital Costs 39@ 583 $US ha-’

Gross Income 1483 1483 $US ha-’Net Income 1058 873 $US ha-’Internal Rateof Return 10% 4%

1 If a landowner enters into a contract with Crown Vantage, tooffer first rights on stumrae at fair market value. CrownVantage p&ides cuttin& at no cost. Otherwise, market price for

2cuttings is $US 250 for 1000 cuttings.Yield on a medium-textured soil such as Tunica-Bowdre.

34

Pulpwood stumpage, inflated 26% over summer 1995 values.Annual costs such as taxes, estimated as $1 ha-’ over an 11 -year

5period.Cost difference between contract and no contract is the price ofcuttings at planting density of 747 stems ha-‘.

establishment includes two-pass disking, 3.7 m

row marking, application of liquid nitrogen ferti-lizer (50/50 ammonium nitrate and urea, 112kg-N ha-l), hand planting of improved clonalcuttings and the application of pre-emergentherbicides. Mechanical cultivation includes asmany as three two-pass diskings the first year,and insecticides and additional mechanical culti-vation the second year. Total establishment costsare $583 ha-l. Landowners interested in theCrown Vantage cost-sharing program may useafforestation to create wildlife habitat, in addi-tion to fiber production. The company pays forthe cuttings (about $185 ha-l), and landownersagree to give first right of refusal for the timberat rotation (10 years), at market value. A finan-cial analysis for cottonwood on former agricul-tural land is given in Table 7. Net income from alo-year rotation is $873 ha-l, with no contract;and $1085 ha-’ under contract. internal rates ofreturn are 4 % and 10 %. All costs are estimatesof what a private landowner would have to payto contract for silvicultural operations.

5.3 Afforestation Strategies

Afforestation on marginal agricultural land inthe LMAV relies on using native species, plant-ed mostly in single-species plantations. Choiceof species on a site is guided by landowner ob-jectives, species tolerance to flooding, and soils.Hard mast producing species such as oaks andsweet pecan are favored for their value to wild-life, especially on public land. Oak plantings arewidely spaced, to allow natural invasion of otherspecies. Wind and water dispersal are relied uponto establish soft mast producers such as sweet-gum, sycamore, the ashes, and the elms. Whilegenerally successful, sites that do not flood oftenand are more than 100 m from a seed source maynot seed in with light seeded species (Allen andKennedy 1989, Allen 1990). This strategy canbest be described as extensive, or least-cost. In-creasingly, it is called into question on two counts:could a more intensive approach provide a morediverse landscape more quickly, and is this ap-proach appropriate if a landowner’s objectivesinclude timber production? While we cannot an-swer these questions definitively with our cur-rent knowledge of the growth and developmentof plantations, they can be examined within thecontext of specific examples, recognizing thatland ownership (public or private) is an impor-tant factor in determining landowner objective.

6 Future Directions

Up to 200 000 ha of marginal agricultural landin the LMAV could be afforested over the nextdecade. Recent modifications to the WRP, pro-viding for a 30-year term instead of a perpetualeasement, could make the program even moreattractive (Shepard 1995). Rising stumpage pric-es for hardwoods and changes in agriculturalprice supports might tip the balance in favor ofprivate afforestation on marginal farmland, par-ticularly if economic incentives for carbon se-questration could be captured by landowners(Shepard 1995). Experience with the Conserva-tion Reserve Program argues that an aggressivetechnology transfer program will be needed toprovide landowners with information on grow-

2 9 3

Silvo Fennica 32(31 review articles

ing and marketing trees (Essek et al. 1992).Scant provision has been made for manage-

ment of afforested areas, on public and also onprivate land. Wildlife managers believe the ex-tensive, low-cost strategy described above issufficient to meet their objectives. However, man-agers will have few options for manipulatingthese understocked stands to further enhancewildlife habitat.

Private landowners who utilize WRP to affor-est their marginal cropland with the intention ofgenerating income through future timber har-vesting will be disappointed, unless they are pre-pared to invest in denser planting. The stockingthat will result from typical WRP afforestationschemes will not be sufficient to support a pulp-wood thinning at age 20 or 30 (J. Goelz, U.S.Forest Service, pers. comm., May 1995). Fur-thermore, it is uncertain whether landowners willbe allowed to harvest WRP plantings. Althoughan “official” interpretation of the language of theeasement has not been made, public opinion inthe United States is not generally supportive ofharvesting and vegetation manipulation.

Concerns for restoration of wetland functionswill play an increasing important role in affores-tation programs. Overstory species diversity inpredominantly oak plantings is expected fromdispersal of light-seeded species by naturalagents. Observations suggest, however, that dis-persal into plantings more than a hundred metersfrom natural stands is ineffective (Allen 1990).Thus one response to the artificial appearance ofplantings has been to plant in wavy lines, thusavoiding the regularity of straight rows.

Modifications to establish mixed species stands,with a canopy structure that approximates natu-ral stands, have been suggested. Recommenda-tions for establishing mixed stands have been toplant species with similar flood tolerance, soilpreferences, and height growth rates. Such mix-tures include cherrybark and Shumard oaks; Nut-tall and overcup (Q. lyrutu Walt.) oaks; syca-more and green ash; sweetgum ahd water oak;and cypress, green ash, overcup oak, and Nuttalloak. Most plantings following these recommen-dations have been block plantings or single spe-cies rows. This species clumpiness, however,does not mimic natural conditions.

Establishing understory and midstory species

294

in afforestation programs is easy, in principle,but practical guidelines are unavailable. Meth-ods for establishing true mixtures of shade toler-ant understory and midstory species, along withintolerant overstory species, requires informa-tion on how species compete with each otherduring early stand development. In addition toinherent growth rates, competitive ability is great-ly affected by soil properties and flooding fre-quency and duration.

Most afforestation work occurs in small patch-es, except for a few large public projects. Whilethere has been much discussion of the effects offorest fragmentation on wildlife, particularly area-sensitive, interior dwelling neotropical migratorybirds (Robbins et al. 1989), there have been fewopportunities to examine the benefits of reforest-ing in large blocks. The Lake George Mitigationsite provides an opportunity to examine this andthe related question of whether travel corridorsbetween large patches of existing natural forest isa net gain or loss for wildlife diversity.

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