Kenneth W. McLeod

Flooding and salinity effects on growth and survival of four common forested wetland species

The survival, growth, and biomass of baldcypress (Taxodium distichum (L.) Rich.), water tupelo (Nyssa aquatica L.), Chinese tallow (Sapium sebiferum (L.) Roxb.), and green ash (Fraxinus pennsylvanica Marsh.) seedlings were examined in an experiment varying water levels (watered, flooded) and salinity levels (0, 2, and 10 ppt, plus a simulated storm surge with 32 ppt saltwater). All seedlings, except for those flooded with 10 ppt saltwater, survived to the end of the experiment. In 10 ppt saltwater, flooded baldcypress, water tupelo, and green ash survived two weeks whereas Chinese tallow survived for 6 weeks. However, a second set of slightly older baldcypress, water tupelo, and Chinese tallow seedlings survived eight weeks of flooding with 10 ppt saltwater. When carried through the winter to the beginning of the second growing season, flooded baldcypress and Chinese tallow seedlings from the 0 and 2 ppt treatments leafed out, but only Chinese tallow recovered from the saltwater surge treatment. The diameter and growth (height) of each species was not affected when watered with 2 ppt saltwater, except for the effects of the height growth of baldcypress. Growth was reduced for all species when watered with 10 ppt saltwater. The diameter growth of green ash was reduced by freshwater flooding. The diameter growth of baldcypress and water tupelo was greater when flooded with fresh water. Flooding with 2 ppt saltwater caused a significant reduction in diameter growth in water tupelo, green ash, and Chinese tallow, but not in baldcypress. Root and stem biomass values were not significantly different for any species between the 0 and 2 ppt salinity watering treatments. However, seedlings watered with 10 ppt saltwater had significantly lower root and stem biomass values, except for baldcypress roots and green ash stems. Baldcypress was least affected by flooding with 0 and 2 ppt saltwater, although there were slight reductions in root biomass with increasing salinity. Because of the susceptibility of the seedlings of these four species to increases in flooding and salinity, their regeneration may be limited in the future, thereby causing shifts in species composition.

Water stress in longleaf pine induced by litter removal

Abstract Forest litter layer acts as a nutrient pool to support future growth of trees and as a blanket which intercepts and absorbs rainfall and insulates soil from evaporative water loss. Litter disturbance can modify either of these functions. Soil moisture content and xylem pressure potential were determined in a longleaf pine plantation for 7 weeks following litter removal. Two weeks following treatment, xylem pressure potential of trees in control, red straw removal and total litter removal plots diverged. Trees in the total litter removal plot had the lowest xylem pressure potential (i.e. most stressed), control trees had the highest xylem pressure potential, and trees in the red straw removal plot were intermediate. Differences in xylem pressure potential among treatments were consistent throughout the season, regardless of precipitation or drought. Soil moisture content also showed different patterns based on the particular litter removal treatment. Differeces in soil water content and xylem pressure potential could explain observed growth reductions of trees in plantations where litter had been removed. Therefore consideration of the potential modification of both the hydrologic and nutrient cycles should be made prior to litter removal.

Production of short-rotation woody crops grown with a range of nutrient and water availability: establishment report and first-year responses.

Coleman, M.D., et. al. 2003. Production of Short-Rotation Woody Crops Grown with a Range of Nutrient and Water Availability: Establishment Report and First-Year Responses. Report. USDA Forest Service, Savannah River, Aiken, SC. 26 pp. Abstract: Many researchers have studied the productivity potential of intensively managed forest plantations. However, we need to learn more about the effects of fundamental growth processes on forest productivity; especially the influence of aboveground and belowground resource acquisition and allocation. This report presents installation, establishment, and first-year results of four tree species (two cottonwood clones, sycamore, sweetgum, and loblolly pine) grown with fertilizer and irrigation treatments. At this early stage of development, irrigation and fertilization were additive only in cottonwood clone ST66 and sweetgum. Leaf area development was directly related to stem growth, but root production was not always consistent with shoot responses, suggesting that allocation of resources varies among treatments. We will evaluate the consequences of these early responses on resource availability in subsequent growing seasons. This information will be used to: (1) optimize fiber and bioenergy production; (2) understand carbon sequestration; and (3) develop innovative applications such as phytoremediation; municipal, industrial, and agricultural wastes management; and protection of soil, air, and water resources.

Effects of flooding and salinity on photosynthesis and water relations of four Southeastern Coastal Plain forest species

The influence of flooding and salinity on photosynthesis and water relations was examined for four common coastal tree species [green ash (Fraxinus pennsylvanica Marshall), water tupelo (Nyssa aquatica L.). Chinese tallow (Sapium sebiferum (L.) Roxb.), and baldcypress (Taxodium distichum (L.) Richard)]. Both chronic (as might be associated with sea level rise) and acute (similar to hurricane storm surges) exposures to these stresses were examined. Chronic freshwater flooding of green ash, water tupelo, and Chinese tallow seedlings reduced photosynthesis (A) relative to that of watered seedlings, while baldcypress was unaffected. Chinese tallow A declined with increasing length of flooding. A salinity increase of the floodwater to 2 ppt decreased A of baldcypress and water tupelo, but not A of green ash and Chinese tallow, which was already severely reduced by freshwater flooding. All seedlings of the four species died within 2 to 6 weeks when flooded with 10 ppt saltwater. Photosynthesis of all four species did not differ between 0 and 2 ppt watering. Watering with 10 ppt salinity initially reduced A of all four species, but the seedlings recovered over time. Photosynthesis was severely decreased for all species when flooded with 21 ppt salinity for 48 hours. Reduced A continued following the treatment. Photosynthesis of only green ash and water tupelo was reduced by watering with 21 ppt salinity for 48 hours. Flooding of low-lying areas with increased salinity would lead to shifts in species composition of coastal forests due to these differential tolerances.

Response of longleaf pine plantations to litter removal

Abstract Potential impact of litter removal in longleaf pine (Pinus palustris Mill.) plantations includes disruption of both hydrologic and macronutrient cycles. Both could cause growth reduction of plantation trees. In longleaf pine plantations on the Savannah River Plant which were examined 2 or 3 years following litter removal, growth (as determined by ring analysis) was reduced in the first year following removal. Growth reduction may also continue through the second year. Due to the rapid response to litter removal, disruption of the hydrologic cycle seems most probable. No differences were found in macronutrient concentration of foliage or litter components between treatments. The economic benefit of this practice must be evaluated in light of the observed growth reduction to determine the overall costs of this practice.

Flood and salinity stress of wetland woody species, buttonbush (Cephalanthus occidentalis) and swamp tupelo (Nyssa sylvatica var.biflora)

Buttonbush (Cephalanthus occidentalis) and swamp tupelo (Nyssa sylvatica var.biflora) seedlings were exposed to flooding and salinity conditions simulating the chronic exposure of sea-level rise and the acute exposure of hurricane storm surge. Chronically exposed seedlings were either watered or flooded with 0, 2, or 10 ppt salinity. Those in the acute experiment were watered or flooded with freshwater until exposed to a 21-ppt salinity surge for 48 hours. Freshwater flooding reduced photosynthesis (A), water pressure potential (Ψ), height, and stem and root biomass for swamp tupelo while biomass of buttonbush roots decreased and stem increased. Chronic watering with 2 ppt salinity reduced height, basal diameter, and stem and root biomass for swamp tupelo but did not significantly affect buttonbush. Both species were negatively affected by watering with 10 ppt salinity, with total mortality of swamp tupelo. Flooding with 2 ppt salinity also caused a 100% mortality for swamp tupelo. All buttonbush seedlings survived with reducedA, Ψ, and stem and root biomass. Plants chronically flooded with 10 ppt salinity were more affected, with drastically decreasedA, stomatal conductance (gs), and Ψ within the first day of treatment and all dying within three weeks. Watering with 21 ppt salinity reducedA andg, of both species during the second day of the surge, but buttonbush recovered within the next 20 days. Flooding with 21-ppt saline water also greatly impacted buttonbush, which did not recover as when watered with 21 ppt salinity. Swamp tupelo was already stressed due to flooding and showed no further reduction in A orgs due to the 21-ppt salinity flood surge. Buttonbush seedlings were more tolerant of salinity and flooding conditions than swamp tupelo seedlings, although it is unlikely that either species could survive long-term exposure to 10-ppt salinity flooding.

ELEVATION, COMPETITION CONTROL, AND SPECIES AFFECT BOTTOMLAND FOREST RESTORATION

This experiment examined how elevation and control of early successional vegetation would affect the growth and survival of tree species used in restoration. Vegetation was controlled by either mowing or spraying with Accord [glyphosate,-(phosphononomethyl)glycine, in the form of its isopropylamine salt] herbicide. These control methods were applied to either the entire plot or a narrow 1-m strip where seedlings were to be planted. A fifth treatment (control) had seedlings planted into the existing vegetation. Species planted were baldcypress (Taxodium distichum), water tupelo (Nyssa aquatica), willow oak (Quercus phellos), Nuttall oak (Q. nuttallii), overcup oak (Q. lyrata), and cherrybark oak (Q. falcata var. pagodaefolia). Seedlings were randomly planted in late April 1993 with six rows in each plot and six trees per row on a 2×2 m spacing with five replicate plots per treatment. Survival was not enhanced by any competition control treatment, but survival among species differed. All six species had overall survival>90% in autumn 1993. Species survival was affected by several summer floods during 1994. Baldcypress and overcup oak survival was greater than 89%, while water tupelo, Nuttall oak, and willow oak were all approximately 70%, and cherrybark oak was only 29%. By the end of 1995, survival of all species decreased further, but the species groupings remained the same. Survival and height growth of baldcypress and water tupelo were greatest at lower planting elevations. At higher elevations, survival of cherrybark oak and willow oak were greatest, while overcup oak and Nuttall oak were unaffected by elevation. Thus, controlling the herbaceous vegetation did not affect survival or growth as much as relative planting elevation due to site flooding and the flood tolerance of the species. All of the species in this experiment except cherrybark oak were successfully established.

Species selection trials and silvicultural techniques for the restoration of bottomland hardwood forests.

From 1992 to 1994, species trials were initiated in the Fourmile Branch delta to investigate the best methods of re-establishing tree species in a severely disturbed, thermally affected stream delta. Treatments examined included planting stock type, habitat, tree shelters, root pruning, and competition controls. Survival of most species, as determined in 1994 or 1996 and 2003, changed little over the past decade and was not strongly affected by the treatments within a trial, except for root pruning. Trees in many treatments have grown tremendously, but individuals with no competition controls generally grew more slowly. For example, Taxodium distichum Richard has had a high survival rate, regardless of whether planted as bareroot or balled-and-burlapped saplings, and have grown to 8 to 12 m in height. Quercus lyrata Walter, Carya aquatica (Michaux f.) Nuttall, Q. nuttallii Palmer, and Q. phellos L. planted in later trials also had adequate survival rates and have grown to 5+ m. Low mortality rates after the initial 3 to 4 years suggests that these species are appropriate for restoration. In contrast, survival of Nyssa aquatica L. and Fraxinus pennsylvanica Marshall have continually declined over time.

INFLUENCE OF A WILLOW CANOPY ON TREE SEEDLING ESTABLISHMENT FOR WETLAND RESTORATION

Black willow (Salix nigra) is a well-known pioneer species of disturbed riparian areas. It competes for nutrients, light, and water, but it may also act as a “nurse” crop, providing shelter for other species from high light and temperature; so, the overall effect on species planted under a willow canopy could be positive or negative. This experiment examined the response of container-grown seedlings of four tree species outplanted into three habitats: 1) an existing willow stand, 2) a similar habitat, but with the willow canopy removed, and 3) an adjacent grass-dominated area free of willow. After three years, survival rates of overcup oak (Quercus lyrata), baldcypress (Taxodium distichum), and water hickory (Carya aquatica) were not reduced under the willow canopy relative to the other two treatments. Laurel oak (Q. laurifolia) was killed by several floods during the first growing season. Height of baldcypress seedlings planted under a willow canopy was less than for seedlings where the willow had been removed. Water hickory and overcup oak height were not affected by the willow canopy. Elevation of the planting sites, indicating probable soil wetness, was a good indicator of survival when used in conjunction with the species flood-tolerance. The existing willow stand was not detrimental to survival of three of the outplanted tree species. Thus, willow removal is unnecessary for successful outplanting, saving time and money.

Photosynthesis and water relations of four oak species: impact of flooding and salinity

Abstract As global climate changes, sea level rise and increased frequency of hurricanes will expose coastal forests to increased flooding and salinity. Quercus species are frequently dominant in these forest, yet little is known about their salinity tolerance, especially in combination with flooding. In this study, 1-year-old seedlings of Quercus lyrata Walt. (overcup oak), Q. michauxii Nutt. (swamp chestnut oak), Q. nigra L. (water oak), and Q. nuttallii Palmer (Nuttall oak) were chronically (simulating sea level rise) and acutely (simulating hurricane storm surge) exposed to increased flooding and salinity, individually and in combination. The four species demonstrated two response patterns of photosynthesis (A), conductance, and leaf water potential, apparently related to their relative flood tolerance. In Q. lyrata, Q. nuttallii, and Q. nigra (moderately flood-tolerant), A was not immediately reduced after the initiation of the freshwater flooding, but was reduced as the duration of flooding increased. In the second pattern, demonstrated by the weakly flood-tolerant Q. michauxii, A was immediately reduced by freshwater flooding with an increasing impact over time. Watering with 2 parts per thousand (ppt) saline water did not consistently reduce A, but flooding with 2 ppt reduced A of all species, similar to the response with freshwater flooding. Photosynthesis of all species was reduced by 6 ppt watering or flooding, with the latter treatment killing all species within 8 weeks. When acutely exposed to 30 ppt salinity, A was quickly and severely reduced regardless of whether the seedlings were watered or flooded. Acutely flooded seedlings exposed to high salinity died within 2 weeks, but seedlings watered with 30 ppt saline water recovered and A was not reduced the following spring. As saline flooding of coastal areas increases due to sea level rise, photosynthesis of these species will be differentially affected based primarily on their flood tolerance. This suggests that increased flooding associated with sea level rise will impact these tree species to a greater extent than small increases in soil salinity. High salinity accompanying storm surges will be very harmful to all of these species.