Xeric Oak Research Articles

Carbon and nitrogen cycling during old-field succession: Constraints on plant and microbial biomass

Soil C and N dynamics were studied in a sequence of old fields of increasing age to determine how these biogeochemical cycles change during secondary succession. In addition, three different late-successional forests were studied to represent possible steady state conditions. Surface soil samples collected from the fields and forests were analyzed for total C, H2O-soluble C, total N, potential net N mineralization, potential net nitrification, and microbial biomass. Above-and belowground plant biomass was estimated within each of the old field sites. Temporal changes in soil organic C, total N and total plant biomass were best described by a gamma function [y =at b e ctd +f] whereas a simple exponential model [y =a(l − e−bt ) + c] provided the best fit to changes in H2O-soluble C, C:N ratio, microbial C, and microbial N. Potential N mineralization and nitrification linearly increased with field age; however, rates were variable among the fields. Microbial biomass was highly correlated to soil C and N pools and well correlated to the standing crop of plant biomass. In turn, plant biomass was highly correlated to pools and rates of N cycling. Patterns of C and N cycling within the old field sites were different from those in a northern hardwood forest and a xeric oak forest; however, nutrient dynamics within an oak savanna were similar to those found in a 60-yr old field. Results suggest that patterns in C and N cycling within the old-field chronosequence were predictable and highly correlated to the accrual of plant and microbial biomass.

Regional variability in nitrogen mineralization, nitrification, and overstory biomass in northern Lower Michigan

Potential net nitrogen (N) mineralization, potential net nitrification, and overstory (boles and branches) biomass were measured in nine forest ecosystems commonly found within the well-drained uplands of northern Lower Michigan. The ecosystem types ranged from oak-dominated forests on coarse-textured outwash sands to mesic northern hardwood forests on sandy glacial till. Overstory biomass was calculated using species-specific allometric equations developed for Lake States hardwood species. Potential net N mineralization and potential net nitrification were measured by a 30-day aerobic laboratory soil incubation. Analyses of (co)variance were used to determine differences in potential N mineralization, net nitrification, overstory biomass, and biomass increment among the nine ecosystem types. Linear and nonlinear regression analyses were used to predict overstory biomass and biomass increment using potential net N mineralization as the independent variable. Overstory biomass ranged from 92 t•ha−1 in a xeric oak ecosystem to 243 t•ha−1 in a northern hardwood ecosystem; annual biomass production ranged from 1.3 to 3.5 t•ha−1 year−1, respectively. Potential net N mineralization was lowest in the xeric oak ecosystem (52.0 μg N•g−1) and greatest in the mesic northern hardwood ecosystem (127.8 μg N•g−1). Potential net nitrification was 45.5 μg NO3−-N•g−1 in the northern hardwood ecosystem; 10 to 230 times greater than in other ecosystems. A saturating exponential model (y = a(1–e−kx) + c) produced the smallest residual mean squares in predicting overstory biomass (R2 = 0.822) and annual biomass increment (R2 = 0.847) from potential net N mineralization. Maximum overstory biomass and biomass increment predicted from this equation were 247 t•ha−1 and 3.7 t•ha−1, respectively. In addition, laboratory net N mineralization potentials were highly correlated with annual rates of N mineralization determined by insitu incubation (r2 = 0.849). Overstory biomass and woody biomass increment were poorly correlated with potential net nitrification. The exponential function used to predict biomass increment from N mineralization suggests that the productivity of some northern hardwood forests in northern Lower Michigan is not limited by N availability.

Mating Behavior of the Grasshopper Melanoplus tequestae (Orthoptera: Acrididae)

Melanoplus tequestae Hubbell is a small, brachypterous, forb-feeding grasshopper inhabiting sand scrub and xeric oak forests of central Florida. Pair formation between silent males and females occurred when the male slowly approached the female or waited until her general activities brought her closer to him. Females raised their ventrally colored hind femora and extended their tibia to signal non-receptiveness. There was no apparent courtship before mounting, but after mounting males shook their hind femora before copulating. Mounting and copulation could last from a few hours to 1 1/2 days. Male aggressive signaling was by bursts of femur shaking.

Late Quaternary Vegetational History of Illinois

Pollen diagrams from the Prairie Peninsula in Illinois record the climatically related vegetation shifts that have occurred since the late Pleistocene. They indicate that the major period of prairie development started between 8500 and 7900 BP, apparently occurring first along the southern margin. These events mark the beginning of the Hypsithermal interval and are correlated with the final disintegration of the Laurentide ice sheet and the establishment of the postglacial system of atmospheric circulation over North America. The late—glacial vegetation was spruce woodland in the north and open spruce woodland/tundra in central Illinois. These vegetation communities disappeared from the state in a northward direction between 14 000 and 10 900 BP. They were followed in northern Illinois by Pinus, Abies, Betula, and Fraxinus; in central Illinois Fraxinus expanded in the lowlands while the uplands remained relatively treeless. These assemblages, which persisted longer in the south than in the north, were subsequently replaced first by a mixture of cool temperate, then warm temperate deciduous trees as climatic amelioration continued. By 9000 BP, Illinois was dominated by deciduous forest. In response to Hypsithermal climatic stress, prairie vegetation began replacing deciduous forest about 8300 BP on the uplands in central Illinois and by 7900 BP xeric oak—hickory forest became dominant in northern Illinois. This is the beginning of the Prairie Peninsula as a discrete floristic area in Illinois. About 5000 BP the southern border of the Prairie Peninsula experienced increased moisture and renewed forest development suggesting a western contraction of the prairie margins. Central Illinois, however, remained grassland to the present. Between 900 and at least 400 yr ago an indicated trend toward cooler temperatures is correlated with late stages of the Neoglacial. Pollen evidence from northern Illinois and adjacent Lake Michigan indicates the reappearance or increase in Betula, Pinus, Picea and Larix. This short cool episode appears to end prior to the beginning of large—scale historic land clearance, about 140 yr ago, as the evidence for a vegetational readjustment to warmer climate is truncated by the logging of the forests, the plowing of the prairies and the resultant dramatic increase in Ambrosia pollen.

Trail erosion patterns in Great Smoky Mountains National Park

All the maintained trails in Great Smoky Mountains National Park were surveyed for width, depth, and a variety of types of erosion. Trail erosion is related to a number of environmental variables, including vegetation type, elevation, trail slope, and section of the park. Open grass balds and spruce-fir forest are the most erosion-sensitive plant communities, and the xeric oak and pine types are the least sensitive. Trails in virgin or mature forest tend to be in poorer condition than those in successional areas. The most important physical factor is the slope of the trail.

Vegetation Record for the Last 20,000 Years from a Small Marsh on Lookout Mountain, Northwestern Georgia

Three pollen zones are found in 1 m of sediment from a small marsh on Pigeon Mountain. The oldest, which begins at 19,520 yr B.P. and ends at 10,820 yr B.P., has pollen of pine, spruce, deciduous trees, and herbs, which implies that the plateau was not forested in full-glacial time but that tree pollen was transported to the site from valleys below the plateau. The second zone of late Pleistocene or early Holocene age implies a mesic forest in which beech was a common tree. The youngest zone has pollen of oak, chestnut, sweetgum, and blackgum, representing the modern somewhat xeric oak forest. The site was a pond with water lilies and rooted and submerged aquatic plants at the time of zones P-l and P-2. Subsequently, woody wet-ground plants (such as button-bush, red maple, sweetgum, and willow) invaded the site and converted it into a marsh.

Carbon Dioxide Exchange by Several Streamside and Scrub Oak Community Species of Red Butte Canyon, Utah

Species of a xeric scrub oak community (scrub oak, Quercus gam.belii; sagebrush, Artemisia tridentata; bitterbrush, Purshia tridentata) have lower seasonal water potentials than species of a mesic streamside habitat (box elder, Acer negundo; bigtooth maple, Acer grandidentatum; creeping barberry, Berberis repens). The restriction of box elder to mesic sites is, in part, a function of its physiological responses to moisture stress. Positive net photosynthesis of box elder ceases at water potentials 10 to 15 bars higher than net photo- synthesis of the other five species, and dark respiratory rates of box elder decline more rapidly. The relative photosynthetic and dark respiratory responses to water stress of scrub oak, sagebrush, bitterbrush, bigtooth maple and creeping barberry are apparently not significant factors influencing the distribution of these species.