Fluctuations in the population density and biomass of Gnathamitermes tubiformans (Buckley) in the upper 30.2 cm of soil were determined over a 2—yr period in a shortgrass community in Garza County, Texas. Linear stepwise multiple regression was used to determine the relationships of termite population densities with environmental factors in this soil increment. Termites were not present in the upper 30.2 cm when the soil temperature at 15 cm was < 9 degrees C. Termite population densities in the upper 30.2 cm of soil varied significantly between years as a function of air and soil temperatures, precipitation and soil moisture. Consideration of data from relatively short time periods alleviated many difficulties in identifying biologically important causal factors. In a year of above—normal precipitation, temperature was the most important factor affecting desert termite population densities, whereas during a year of below—normal precipitation, soil moisture was the most important factor. Biomass of desert termites in the upper 30.2 cm of soil averaged 5.83 g/m² (live—weight) over the 2—yr period and reached a peak of 23.03 g/m² during September 1972. The abundance of tunnels and chambers of G. tubiformans decreased with depth in the soil profile. Termites migrated below 124 cm in subterranean galleries to avoid soil temperatures < 10 degrees C.

Nodulation, N accretion, and above-ground biomass production were investigated in Ceanothus velutinus (snowbrush) stands developing following wildfire and salvage logging in second growth ponderosa pine (Pinus ponderosa Laws) and logging and slash burning in old growth Douglas-fir stands [Pseudotsuga menziesii (Mirb.) Franco]. In the pine site 82% of the Ceanothus plants were nodulated the first year, whereas in the fir site only 42% were nodulated. Above-ground snow-brush biomass production at the end of 10 years was 48,000 and 54,000 kg/ha, respectively, for the pine and fir sites. Nitrogen accretion in biomass, litter, and soil for the 10-year period was 715 and 1,080 kg/ha, respectively, for the pine and fir sites. The higher accretion in the fir site despite slower nodulation is due to more favorable temperature and moisture conditions at the fir site than at the pine site.

Nitrogen concentration profiles in soil columns with associated microbial distributions have been used in the past to deduce the kinetics of nitrogen transformations during steady leaching. Owing to the many factors which control microbial reaction kinetics in continuous flow systems, the effect of biomass variation and order of reaction cannot be separated by simply measuring steady-state concentrations profiles. It is shown here that in practice these measurements only lead to some average kinetics for the system observed, even when the microbe distribution is measured independently. Previously published experimental data in conjunction with a derived expression are used to illustrate the point.

Plant standing crop and productivity relations were examined for an extensive marsh complex in southern Quebec, Canada. Forty—five 1—m² plots were sampled for dry weight shoot biomass, species composition, structure (species density, diversity, height), and soil parameters including nutrient concentrations. (Ca, K, Mg, Na, N, P), pH, organic matter, and water depth. Shoot net productivity and decomposition rates were computed for 20—day intervals across the growing season. Relationships between all parameters were examined by principal components analysis. Dominant emergent species included Scirpus fluviatilis, Equisetum fluviatile, Scirpus validus, Phragmites communis, and Eleocharis palustris. For a 150—day interval, shoot net productivity averaged 6.10 g·m⁽—2) · day⁽—1) and terminal standing crop was 845 g/m². Seasonal productivity showed a strong bimodal pattern with peaks in late July (12.90 g°m⁽—2) · day⁽—1) and midSeptember 4.73 g°m⁽—2) · day⁽—1). Species typical of deep water showed much earlier and higher peak productivity than this general pattern but net shoot productivity as of short duration. Two—thirds of annual litter production was lost by export. Complete decomposition of remaining litter occurred within the next growing season. Temperature and decomposition rate maxima coincided with peak productivity in July and decreased exponentially through October. Among edaphic parameters, soil K had the highest correlation (r = 0.49**) with standing crop while soil N had the highest correlation with shoot net primary production (r = 0.39**). Soil P correlated negatively with all production and soil nutrient parameters except soil Mg levels. It was the only nutrient with a soil concentration maximum in shallow water. Other nutrients attained maximum levels at an intermediate point on the water depth gradient. Maximum litter standing crop occurred at this point, coinciding closely with changes in soil cation levels. While shoot density and standing crop followed these trends, they coincided more closely with changes in soil anion concentrations (nitrogen, hydrogen). Sedimentation and nutrient uptake associated with high stem density and standing crop were shown to be important factors in site enrichment. Shoot net primary productivity and standing crop correlated negatively with all measures of species diversity. Variety and equitability decreased from 8.00 species and 0.96 bits/m² in Scirpus validus stands of deep water to 2.00 species and .01 bits/m² in shallow stands of S. fluviatilis. Sparse canopy cover and high levels of disturbance in S. validus stands made possible the coexistence of a rich variety of aquatic life forms not possible under conditions of intense competition typical of S. fluviatilis.

Plant and soil scientists have devised many methods with varying degrees of success to determine the density of vegetative cover. Canopy density is important in estimating yield of biomass, characterizing vegetative stress, predicting soil losses from erosion, and planning resource management programs. The objective of this investigation was to examine quantitatively the relationship between the densities of maize (Zea mays L.) canopies and the energy reflected by them. Spectral and spatial data were obtained from color and color infrared (IR) photographs from 10 m above field plots of four growth stages of maize on dark and light-colored soils. Leaf area index (LAI) measurements were made in the field. Photographs were used for determining percent ground cover 1) by a point grid technique and 2) by microdensity scanning of the three separate emulsion layers of the color photographs and digital analysis of the resulting data. A statistical pattern recognition computer program was used to determine the spectral separability of the digitized photographic data and to classify the data into two categories—green vegetation and soil. Of the emulsion layers of the color IR photographs, classification of the digitized infrared wavelength band best represented the actual percent ground cover. A plot having an LAI of 4.44 had a ground cover of 96.5% as determined by the point grid method and 93.2% by digital analysis of IR data. Classification of data from the visible red (0.59 to 0.71 μm) overestimated percent ground cover and from the green (0.47 to 0.61 μm) underestimated percent ground cover.

Polygonum pensylvanicum and Abutilon theophrasti, components of old—field communities in central Illinois were grown on a controlled soil moisture gradient to determine whether they exhibit different response centers. Germination response of a constant number of seeds per six moisture resource states, height, biomass, and reproductive response of initially constant numbers of plants per state were monitored. States, ranging from saturation down to 13.61 ± 5.53% moisture, are numbered in order of increasing drought. Maximum height of Polygonum occurred in states 4 and 5, and of Abutilon in 4, 5, 6. Vegetative and reproductive biomass maxima of Polygonum and Abutilon occurred in states 5 and 6, respectively. Abutilon reproduced only in states 5 and 6 where it overtopped the Polygonum canopy, while Polygonum reproduced in all states. Polygonum performance declined sharply in state 6. Thus, Polygonum and Abutilon response centers are displaced toward the wetter and drier ranges of the gradient, respectively. On a within—community level, Abutilon reproduces in less mesic resource states where Polygonum canopy height is reduced. In general, Abutilon reproduction may occur throughout the gradient when the Polygonum canopy opens. The performance of these species is strongly influenced by both physical and biotic conditions. Previously investigated adaptations, including drought resistance and rooting patterns in space and time, appear to underlie divergence along the moisture gradient. The response patterns found here are broad and exhibit considerable overlap as expected in fugitive strategies. The patterns of divergence shown on point and gradient scales in this and our previous work reflect a related complex of adaptations and strongly suggest that competitive divergence occurs in early successional communities.