Jim L. Chambers

Intraspecific variation in the response of Taxodium distichum seedlings to salinity

Abstract Seedlings of 15 open-pollinated families of baldcypress ( Taxodium distichum ) were tested for their tolerance to combined salinity and flooding strees. Ten of the families were from coastal locations in Louisiana or Alabama, USA, that were slightly brackish. The other families were from locations not affected by saltwater intrusion. Five salinity levels were investigated — 0, 2, 4, 6, and 8 g l −1 artificial seawater—all with flooding to approximately 5 cm above the soil surface. Survival, height growth, leaf area and total biomass all declined with increasing salinity. Significant variation was found among salinity levels, families, and salinity×family interactions for leaf area and total biomass. Two tolerance indices were also developed to compare family response with salinity. In generalm families from brackish sources had greater total biomass, leaf area, and tolerance index values than families from freshwater sources at the higher salinity levels. A selection and breeding program designed to develop moderately salt-tolerant baldcypress seedlings for use in wetland restoration projects and other applications appears to be well-justified.

Effects of salinity on baldcypress seedlings: Physiological responses and their relation to salinity tolerance

Growth and physiological responses of 15 open-pollinated families of baldcypress (Taxodium distichum var.distichum) subjected to flooding with saline water were evaluated in this study. Ten of the families were from coastal sites in Louisiana and Alabama, USA that have elevated levels of soil-water salinity. The other five families were from inland, freshwater sites in Louisiana. Seedlings from all families tolerated flooding with water of low (2 g 1−1) salinity. Differences in biomass among families became most apparent at the highest salinity levels (6 and 8 g 1−1). Overall, increasing salinity reduced leaf biomass more than root biomass, which in turn was reduced more than stem biomass. A subset of seedlings from the main greenhouse experiment was periodically placed indoors under artificial light, and measurements were made of gas exchange and leaf water potential. Also, tissue concentrations of Cl−, Na+, K+, and Ca2+ were determined at the end of the greenhouse experiment. Significant intraspecific variation was found for nearly all the physiological parameters evaluated, but only leaf concentrations of Na+ and Cl− were correlated with an index of family-level differences in salt tolerance.

Understory light levels in mature hardwood stands after partial oversotry removal

Abstract Understory light levels have significant effects on the type and amount of advance regeneration in natural hardwood stands. This study was initiated to look at the effects of partial overstory removal on understory light levels and to develop regression equations to predict understory light levels from stand characteristics and felling levels. Understory light levels were measured in five types of relatively mature, unmanaged, bottomland hardwood stands in southeastern Louisiana. Study plots were selected within each stand type to encompass a broad range of initial basal areas. Each stand type was then subjected to six levels of overstory removal. Percent basal area removed, and percent crown cover, had higher correlations with relative understory light levels than eight other stand characteristics, accounting for 71% of the variation in relative understory light level across all stand types. Regression equations presented provide a means by which relative understory light levels can be replicated even when initial stand basal areas very among treatment plots. This has important implications for further study of natural hardwood regeneration by encouragement of advance regeneration.

Salinity effects and differential germination of several half-sib families of baldcypress from different seed sources

Saltwater intrusion is responsible for the destruction of large expanses of baldcypress swamps along the Gulf of Mexico in the southern United States. Recent restoration efforts have focused on the identification, and subsequent planting, of moderately salt-tolerant plant material within these “ghost forests.” The long-term persistence of cypress swamps in these areas, however, will ultimately depend on the germination of seeds from the improved parent trees. This study investigates the germination capacity of seeds collected from baldcypress parent trees, located in both freshwater and brackish water environments. Seeds were tested at four different salinity levels under controlled conditions for a period of 65 days. Mean germination under the 0, 2, 4, and 6 g l-1 seawater treatments was 26.3, 22.9, 15.4, and 10.2%, respectively. Although none of the eight families used in this study had a germination greater than 50%, three families demonstrated superiority in their germination capacity under all four salinity treatments. In general, brackish water seed sources had greater germination success than the two families from freshwater sources. Results indicate that families previously identified as moderately salt-tolerant based on physiological and morphological parameters may be equally successful in seed germination capacity under moderately saline conditions.

Temporal and spatial patterns of net photosynthesis in 12-year-old loblolly pine five growing seasons after thinning

Physiological parameters were measured under natural light conditions and needle orientation from towers and walkways erected in the canopy of a loblolly pine (Pinus taeda L.) plantation. Four silvicultural treatments were randomly assigned to the twelve plots in the fall of 1988. Plots were thinned to a density of 731 trees per hectare or left unthinned, at a density of 2990 trees per hectare. The plots were left unfertilized or fertilized with 744 kg/ha of diammonium triple superphosphate was applied. During the fifth growing season (1993) following thinning and fertilization, needle level physiology was not different with respect to the thinning treatment for fertilized or unfertilized plots. In contrast, upper crown levels within the fertilized and unfertilized plots had significantly higher light levels and photosynthetic rates than lower crown foliage. Light levels were greater in the thinned, fertilized plots than in the unthinned, fertilized plots. In contrast, no effect of thinning on canopy light levels was found in the unfertilized plots. Within crown variation in photosynthesis was strongly dependent on canopy light levels. A strong interaction of canopy level with thinning was apparent for net photosynthesis. Loblolly pine, being a shade intolerant species, showed only small physiological differences between needles from different parts of the crown. Because of the variability found in this study, more extensive sampling is needed to correctly describe the physiology of a forest canopy with adequate precision.

Root and shoot responses of Taxodium distichum seedlings subjected to saline flooding

Abstract Variation among progeny of five half-sib family collections of baldcypress ( Taxodium distichum ) from three freshwater and two brackish-water seed sources subjected to saline flooding was evaluated. Mini-rhizotrons (slant tubes) were used to monitor root elongation for a period of 99 days. Salinity level produced significant effects across all baldcypress half-sib families, with root elongation averaging 1594.0, 956.8, and 382.1 mm, respectively, for the 0, 4, and 6 g l −1 treatments. Combined mean root elongation for families from brackish-water seed sources was greater (1236.7 mm) than for families from freshwater seed sources (794.6 mm). Considerable variation occurred at the highest salinity treatment, however, with one freshwater family maintaining more than 28% more root growth than the average of the two brackish-water collections. Hence, results indicate that short-term evaluation of root elongation at these salinity concentrations may not be a reliable method for salt tolerance screening of baldcypress. Species-level effects for height and diameter, which were measured at day 62, were significant for both parameters. Height increment in the control (7.4 cm), for example, was approximately five times greater than height increment in the 6 g l −1 salinity treatment (1.5 cm). Family-level variation was significant only for diameter, which had an incremental range of 0.2 to 1.5 mm across all salinity levels.

Selection for Salt Tolerance in Tidal Freshwater Swamp Species: Advances Using Baldcypress as a Model for Restoration

Worldwide, the intrusion of salinity into irrigated and natural landscapes has major economic and cultural impacts and has resulted in large reductions in crop yields (Epstein et al. 1980; Flowers 2003). Losses have prompted wide-scale programs to improve the salt tolerance of many agronomic species or to identify crop species that can tolerate lands affected by low levels of salinity. Few historic research efforts have considered forest tree species in the United States, especially in nonurban areas. Newer programs have focused on identifying salt tolerance in forest tree species but have mainly limited these efforts to compiling lists of salt tolerant species to be used in afforestation projects (Gogate et al. 1984; Shrivastava et al. 1988; Beckmann 1991; Bell 1999). Gogate et al. (1984), for instance, listed 26 potential species from Australia with silvicultural application to salt affected lands in India. More comprehensive efforts have considered species lists along with specific site requirements (Bell 1999); species tolerant to saline irrigation waters on dry land, for example, will not often be tolerant of salinity increases in wetland settings. Similar ideas

Ecophysiological Response of Managed Loblolly Pine to Changes in Stand Environment

Anticipated shifts in our global climate may expose southern pine ecosystems to such environmental stimuli as elevated carbon dioxide and water and nutrient deficiencies (Hansen et al., 1988; Kirschbaum et al., 1990; Peters, 1990). Global climate change may also increase the degree of stress to which trees are presently exposed (Kirschbaum et al., 1990; Peters, 1990). For example, the western extent of loblolly pine (Pinus taeda L.), now dictated by moisture availability for seedling establishment, is predicted to shift eastward with temperature and precipitation changes that may occur with global climate change (Miller et al., 1987).

Conservation and Use of Coastal Wetland Forests in Louisiana

U.S. Geological Survey, National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, LA 70506 School of Renewable Natural Resources, Louisiana State University Ag Center, Renewable Natural Resources Building, Baton Rouge, LA 70803 Baruch Institute of Coastal Ecology and Forest Science, Clemson University, Department of Forestry and Natural Resources, PO Box 596, Georgetown, SC 29442 Department of Oceanography and Coastal Sciences and Coastal Ecology Institute, School of the Coast & Environment, Louisiana State University, Baton Rouge, LA 70803 Center for Bottomland Hardwoods Research, USDA-Forest Service Southern Hardwoods Laboratory, PO Box 227, Stoneville, MS 38776 USGS Louisiana Cooperative Fish and Wildlife Research Unit, Louisiana State University Ag Center, School of Renewable Natural Resources, Baton Rouge, LA 70803 Savannah River Ecology Laboratory, PO Drawer E, Aiken, SC 29802 Department of Biological Sciences, Southeastern Louisiana University, Box 10736, Hammond, LA 70402

Performance measures for a Mississippi River reintroduction into the forested wetlands of Maurepas Swamp

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