Drought, salinity, and alkaline soils are common problems faced by many arborists, urban foresters, landscapers, and homeowners. Kelsey and Hootman (1990) found that many urban street tree planter soils could be classified as saline or sodic, soil types that usually occur in arid or semiarid areas with a higher evapotranspiration than precipitation rate. In many parts of the United States, drought and irrigation restrictions are becoming more common (Beeson et al., 2004). The combination of these problems necessitates the selection and use of more adapted tree species and genotypes in urban areas.
Taxodium distichum is a widely adaptable tree species for landscape use, tolerating both wet and dry soils and air pollution (Cox and Leslie, 1988; Wasowski and Wasowski, 1997). Watson (1983) reports tolerance to varying nutrient availability conditions, a wide range of soil aeration levels, and somewhat extreme pH levels. It is fast growing, has reliable feathery foliage, and a nice form (Arnold, 2002; Cox and Leslie, 1988). Two varieties, T. distichum var. distichum (baldcypress) and T. distichum var. imbricarium (Nutt.) Croom (pondcypress), have good fall color in some areas, whereas T. distichum var. mexicana Gordon (Montezuma cypress) remains semievergreen (Arnold, 2002). It is an extremely long-living tree with a lifespan of up to 700 years (Cox and Leslie, 1988). All of these factors allow T. distichum to tolerate many environmental stresses, making this species a promising choice for urban landscapes. However, there are a few limitations to this species. Although it is tolerant of substantial soil salt levels, it tends to defoliate when leaves come into contact with saline irrigation water, develop chlorosis on sites with high pH soils, and “brown out” in periods of extended or severe drought (Arnold, 2002).
Arnold (2002) defines ecotypic variation as “a distinct morphological or physiological form, or population, resulting from (natural) selection by a distinct ecological condition.” It is the entire basis for provenance studies (Arnold, 2002). Zobel and Talbert (1984) define a provenance as “the original geographic area from which seed or other propagules were obtained” and equate it to the concepts of geographic source and geographic race. They also present a more useful definition of the concept as “a subdivision of a species consisting of genetically similar individuals, related by common descent, and occupying a particular territory to which it has become adapted through natural selection” (Zobel and Talbert, 1984). Provenances can be determined by numerous characteristics of the geographical origin, including latitude, altitude, precipitation, temperature, soil, and daylength (Zobel and Talbert, 1984). The identification of adapted provenances allows industry professionals to more closely tailor their plant selections to specific situations and can offer “the largest, cheapest and fastest gains” in tree improvement programs seeking an improved product for use in difficult ecophysiographic situations (Zobel and Talbert, 1984).
In forest management, the concept of seed source and provenance is widely recognized and used (Zobel and Talbert, 1984). However, in landscape horticulture and urban forestry, it is less widely used (Arnold, 2002). Some of the taxa studied in provenance research in this field include maple (Acer L.) spp. (St. Hilaire and Graves, 2001; Zwack et al., 1999), seaside alder [Alnus maritima (Marsh.) Muhl. ex Nutt.] (Schrader and Graves, 2000), pecan [Carya illinoinensis (Wangenh.) K. Koch] (Wood et al., 1998), Atlantic whitecedar [Chamaecyparis thyoides (L.) B.S.P.] (Jull et al., 1999), Amur maackia (Maackia amurensis Rupr.) (Pai and Graves, 1995), and sycamore (Platanus occidentalis L.) (Shoemake, 1996; Shoemake and Arnold, 1997).
The purpose of this study was to determine if there is a geographic basis for alkalinity tolerance in Taxodium distichum and to evaluate provenances in an effort to select those that could yield individuals that are most adaptable/tolerant to this environmental stress.
Arnold, M.A. , McDonald, G.V. , Bryan, D.L. , Denny, G.C. , Watson, W.T. & Lombardini, L. 2007 Below-grade planting adversely affects survival and growth of tree species from five different families Arboriculture and Urban Forestry 33 64 69
Beeson R.C. Jr , Arnold, M.A. , Bilderback, T.E. , Bolusky, B. , Chandler, S. , Gramling, H.M. , Lea-Cox, J.D. , Harris, J.R. , Klinger, P.J. , Mathers, H.M. , Ruter, J.M. & Yeager, T.H. 2004 Strategic vision of container nursery irrigation in the next ten years J. Environ. Hort. 22 113 115
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Beeson R.C. Jr Arnold, M.A. Bilderback, T.E. Bolusky, B. Chandler, S. Gramling, H.M. Lea-Cox, J.D. Harris, J.R. Klinger, P.J. Mathers, H.M. Ruter, J.M. Yeager, T.H. 2004 Strategic vision of container nursery irrigation in the next ten yearsJ. Environ. Hort. 22 113 115
Denny, G.C. & Arnold, M.A. 2007 Taxonomy and nomenclature of baldcypress, pondcypress and montezuma cypress: One, two or three species? HortTechnology 17 125 127
Jull, L.G. , Ranney, T.G. & Blazich, F.A. 1999 Heat tolerance of selected provenances of Atlantic white cedar J. Amer. Soc. Hort. Sci. 124 492 497
Marcar, N.E. , Zohar, Y. , Guo, J. & Crawford, D.F. 2002 Effect of NaCl and high pH on seedling growth of 15 Eucalyptus camaldulensis Dehnh. provenances New For. 23 193 206
Pai, J.G.B. & Graves, W.R. 1995 Seed source affects seedling development and nitrogen fixation of Maackia amurensis J. Environ. Hort. 13 142 146
Schrader, J.A. & Graves, W.R. 2000 Seed germination and seedling growth of Alnus maritima from its three disjunct populations J. Amer. Soc. Hort. Sci. 125 128 134
Shoemake, L.J. 1996 Effects of half-sib family selection on the root regeneration potential and initial landscape establishment of container-grown sycamore, Platanus occidentalis L Texas A&M Univ College Station, TX MS Thesis.
Shoemake, L.J. & Arnold, M.A. 1997 Half-sib family selection improves container nursery and landscape performance of sycamore J. Environ. Hort. 15 126 130
St. Hilaire, R. & Graves, W.R. 2001 Stability of provenance differences during development of hard maple seedlings irrigated at two frequencies HortScience 36 654 657
Zwack, J.A. , Graves, W.R. & Townsend, A.M. 1999 Variation among red and freeman maples in response to drought and flooding HortScience 34 664 668