Gerald E. Lang

A Critique of the Analytical Methods Used in Examining Decomposition Data Obtained From Litter Bags

The study of plant litter decomposition in terrestrial ecosystems commonly employs litter bags to compare the loss of mass among species, among sites, and under various experimental manipulations, or to investigate the process itself. Analysis of the resulting data is quite variable among investigators, and at times inappropriate. Two general analytical approaches to the examination of decomposition data are reviewed. Analysis of variance is useful if the intent is to compare treatment means, but does not directly test hypotheses regarding decomposition rates. If the intent is to determine rate constants, than fitting mathematical models to data is the more appropriate analysis. Single and double exponential models best describe the loss of mass over time with an element of biological realism. See full-text article at JSTOR

Loss of mass and chemical change in decaying boles of a subalpine balsam fir forest

Decay of balsam fir (Abies balsamea) boles was examined in an upper subalpine forest of the White Mountains, New Hampshire, USA. Fifty percent of the initial mass was lost in 23 yr; 90% was lost in 77 yr. High decay rates were attributed to the small diameters of the boles, ample moisture, and a nitrogen-rich environment. Average dead wood mass in this forest was 4.9 kg/M2, representing 25% of the sum of dead wood, live plant biomass, and forest floor organic matter. Changes in density and moisture and in the concentrations and content of various chemical com- ponents of the boles were traced over the decay sequence. Changes in the content of cellulose, lignin, carbon and sodium followed loss of mass during decay. Contents of calcium, magnesium, potassium and phosphorus decreased faster than loss of mass in the early stages of decay. Much of this initial loss was acribed to sloughing of nutrient-rich bark which in these small boles comprised 13% of dry mass. Later in decay, the loss rates of calcium, magnesium and potassium were about the same or slightly less than the loss rate of mass. After a steep initial drop, phosphorus content of the boles remained approximately constant between years 12 and 33. Thereafter the loss rate paralleled loss of mass. Nitrogen content was approximately constant in the first 33 yr after which it declined in parallel with loss of mass.

Tree Growth, Mortality, Recruitment, and Canopy Gap Formation during a 10‐year Period in a Tropical Moist Forest

All trees @>2.5 cm dbh were censused on a 1.5—ha tract of 60—yr—old tropical moist forest in 1968 and again in 1978 to determine rates of tree mortality, recruitment, dbh increment, and canopy gap formation. Species composition changed very little. The pioneer of gap species Cordia alliodora, Luehea seemanii, and Spondias radlkoferi had no recruitment and accounted for most mortality in the larger size classes. Ninety percent of all mortality was for stems <10 cm dbh. Total tree density decline 11% (from 3112 to 2781 trees/ha), but basal area increased 22% (from 25.7 to 31.4 m2/ha). Growth in diameter was highly variable, both among species and among size classes. Trees in the 30—50 cm dbh class had a mean dbh increment of 0.9 cm/yr. Gaps occurred over an area equal to 7.3% of the plot during the 10—yr period, suggesting that about 137 yr would be required for the 1.5—ha plot to be affected by tree falls.

Vegetational Patterns and Processes in the Balsam Fir Zone, White Mountains New Hampshire

Vegetation structure and dynamics of the upper subalpine or fir zone were studied in the White Mountains of New Hampshire. The fir zone extends from 1220 m, the approximate upper limit of Picea rubens occurrence, to treeline (°1450 m) where it is usually represented by a low krummholz. Live tree density in the part of the zone in which trees are >2 m tall averages 5000 stems/ha. Eighty—four percent of these are Abies balsamea, and most of the rest are Betula papyrifera var. cordifolia. Basal area averages 30 m2/ha; canopy height averages 6.8 m. Stands tend to be dominated by discrete age classes. Tree ages range up to 111 yr (average 55 yr). Fir zone vegetation is subject to a number of processes that lead to a hierarchical set of overlapping patterns. Elevation and wind exposure produce general, or first—order, patterns over the landscape, e.g., canopy height decreases with elevation and exposure. Overlying this general pattern are a series of second—order patterns. Two acute disturbance factors–hurricanes and avalanches–have stamped discrete impressions over the general pattern. Other, more endogenously generated patterns, marks the landscape with more subtle textures. These patterns include fir waves, broken gaps, strips, and glades. A conceptualization of vegetation as a hierarchical series of overlapping patterns is an extension of Watts view of vegetation dynamics and bears important ecological implications.

Forest Floor Leaching: Contributions from Mineral, Organic, and Carbonic Acids in New Hampshire Subalpine Forests

Analyses of soil water and groundwater samples from a high-elevation coniferous ecosystem in New England indicate that sulfate anions supply 76 percent of the electrical charge balance in the leaching solution. This result implies that atmospheric inputs of sulfuric acid provide the dominant source of both H+ for cation replacement and mobile anions for cation transport in subalpine soils of the northeastern region affected by acid precipitation. In soils of relatively unpolluted regions, carbonic and organic acids dominate the leaching processes.

Control of carbon mineralization to CH4 and CO2 in anaerobic, Sphagnum-derived peat from Big Run Bog, West Virginia

The mineralization of organic carbon to CH4 and CO2 inSphagnum-derived peat from Big Run Bog, West Virginia, was measured at 4 times in the year (February, May, September, and November) using anaerobic, peat-slurry incubations. Rates of both CH4 production and CO2 production changed seasonally in surface peat (0–25 cm depth), but were the same on each collection date in deep peat (30–45 cm depth). Methane production in surface peat ranged from 0.2 to 18.8 μmol mol(C)−1 hr−1 (or 0.07 to 10.4 μg(CH4) g−1 hr−1) between the February and September collections, respectively, and was approximately 1 μmol mol(C)−1 hr−1 in deep peat. Carbon dioxide production in surface peat ranged from 3.2 to 20 μmol mol(C)−1 hr−1 (or 4.8 to 30.3 μg(CO2) g−1 hr−1) between the February and September collections, respectively, and was about 4 μmol mol(C)−1 hr−1 in deep peat. In surface peat, temperature the master variable controlling the seasonal pattern in CO2 production, but the rate of CH4 production still had the lowest values in the February collection even when the peat was incubated at 19°C. The addition of glucose, acetate, and H2 to the peat-slurry did not stimulate CH4 production in surface peat, indicating that CH4 production in the winter was limited by factors other than glucose degradation products. The low rate of carbon mineralization in deep peat was due, in part, to poor chemical quality of the peat, because adding glucose and hydrogen directly stimulated CH4 production, and CO2 production to a lesser extent. Acetate was utilized in the peat by methanogens, but became a toxin at low pH values. The addition of SO42− to the peat-slurry inhibited CH4 production in surface peat, as expected, but surprisingly increased carbon mineralization through CH4 production in deep peat. Carbon mineralization under anaerobic conditions is of sufficient magnitude to have a major influence on peat accumulation and helps to explain the thin (< 2 m deep), old (> 13,000 yr) peat deposit found in Big Run Bog.

Methane production in contrasting wetland sites: response to organic-chemical components of peat and to sulfate reduction.

Abstract We used methane‐production measurements of slurried peat to study controls of methane production in six contrasting Appalachian wetland sites. The sites differed widely in plant‐community composition and in rates of methane production, which varied from 3 μmol/L/day in slurried‐peat samples from a shrub‐dominated bog to 216 μmol/L/day in peat from a spruce‐forested wetland. Three controlling factors of methane production were examined: organic‐chemical components of the peat (e.g., hot‐water soluble, sulfuric acid soluble, sulfuric acid insoluble), concentrations of dissolved organic carbon, and rates of sulfate reduction. Peats from shrub‐dominated sites contained mostly acid‐insoluble organic matter, which was presumably recalcitrant to microbial decomposition. In contrast, peats from moss‐and sedge‐dominated sites contained mostly acid‐soluble organic matter, which was presumably labile. Differences of organic‐chemical components of the peat could explain about 50% of the variation in rates of...

Methane consumption in two temperate forest soils

Forest soils are thought to be an important sink for atmospheric methane. To evaluate methane consumption,14C-labeled methane was added to the headspace of intact soil cores collected from a mixed mesophytic forest and from a red spruce forest located in the central Appalachian Mountains. Both soils consumed the added methane at initially high rates that decreased as the methane mixing ratio of the air decreased. The mixed mesophytic forest soil consumed an average of 2 mg CH4 m−2 d−1 versus 1 mg CH, m−2 d−1 for the spruce forest soil. The addition of acetylene to the headspace completely suppressed methane consumption by the soils, suggesting that an aerobic methane-consuming microorganism mediated the process. At both forest sites, methane mixing ratios in soil air spaces were greater than that in the air overlying the soil surface, indicating that these soils had the ability to produce methane. Models of methane emission from forest soils to the atmosphere must represent methane flux as the balance between production and consumption of methane, which are controlled by very different factors

Methane consumption in decomposing Sphagnum-derived peat

Abstract Methane production and CH 4 consumption by moss-derived peats were measured and related to CH 4 emission from the same peats to the atmosphere. Peat samples (0–40 cm depth) maintained under anoxic conditions at 19 C for 40 h produced CH 4 at rates ranging from 0.5 to 1.0 μmol 1 peat −1 h −1 .The same peat samples exposed to aerobic conditions consumed CH 4 without showing a lag between production and consumption, suggesting that an active population of aerobic CH 4 -consuming microorganisms was present in the mostly anoxic peat. However, anaerobic CH 4 oxidation could not be ruled out completely. Rates of methane consumption ranged from 1.6 to 0.2μmol 1 peat −1 h −1 . Consumed CH 4 -C was converted to CO 2 rather than biomass, indicating that the consumers used CH 4 as an energy source. The difference between integrated rates of CH 4 production (6.8 mmol m −2 day −1 ) and CH 4 consumption (5.4 mmol m −2 day −1 ) represented the available amount of CH 4 for atmospheric emission. This estimate agreed with measured emission values from intact peat cores (0.2–0.7 mmol m −2 day −1 ). The results of these studies emphasize the importance of CH 4 consumption in controlling CH 4 emissions from peatlands to the atmosphere.

Fe, Al, Mn, and S chemistry of Sphagnum peat in four peatlands with different metal and sulfur input

Comparisons among 4 peatland sites representing a gradient of increasing Fe, Al, Mn, and S loading revealed significant accumulation of total Fe, Al, and S, but not Mn, in surface (0 to 20 cm deep) peat along the gradient. Iron and Al accumulation were contributed mainly by organically bound fractions, with oxides contributing to a lesser extent. Although SO42− and Fe sulfides showed significant increases in concentration along the gradient, most of the accumulation of total S was contributed by organic, rather than inorganic S. Laboratory studies of Fe2+ adsorption by peat indicated that increasing the pH of added Fe2+ solutions (pH values of 3, 4, 5, and 6) did not significantly affect Langmuir equation estimates of either maximum Fe2+ adsorption capacity or the affinity of peat for Fe2+. Regardless of the pH of the added Fe2+ solutions, final solution pH values were relatively uniform, averaging about 3.4, reflecting a considerable bufferring capacity of Sphagnum peat. Factors affecting the accumulation of metals and S in peat remain topics for further investigation.