Plant Cover Types Research Articles

Soil microbial metabolism and nutrient status in a Mediterranean area as affected by plant cover

The Mediterranean area of Southern Italy is characterized by different natural plant covers that mainly reflect different successional stages (i.e. low maquis, high maquis, Quercus ilex wood) and managed areas with introduced plant species (such as Pinus species). Soil properties could be affected by plant cover types as well as by plant species. Our objective was to determine the relationships of plant cover types and plant species with the chemical and biological characteristics of the soil. In four neighbouring areas with different plant cover types (low maquis, pure high maquis, high maquis with pines and pinewood, with pines planted by foresters in both cases), soil samples were collected under different plant species in order to evaluate the effect of plant cover types and plant species on soil properties. Soil samples were analyzed for nutrient content, microbial biomass, soil potential respiration and enzymatic activity (phosphatase, arylsulphatase, β-glucosidase and hydrolase activities) as well as for pH, water holding capacity (WHC) and cation exchange capacity (CEC). Application of cluster analysis and principal component analysis to the data revealed that the plant cover type was the key factor influencing soil properties more than plant species. In fact, the largest differences were observed between pure high maquis soils and all other soils, with pure high maquis soils generally showing the highest values of WHC, CEC, nutrient content, organic and microbial C, soil respiration, phosphatase, arylsulphatase and β-glucosidase activities. The significantly lower values of these variables in the low maquis relative to the pure high maquis probably reflect the effect of ecological succession on soil. The high maquis with pine, differing from the pure high maquis only for the presence or absence of pine, showed values of soil physical, chemical and biological characteristics similar to those found in the low maquis, thus suggesting that the presence of pine retards soil development.

Mosquito (Diptera, Culicidae) ecology in the Iguaçu National Park, Brazil: 1 Habitat distribution

A study of the mosquito fauna in the Iguaçu National Park focused on population behavior in four biotopes with different types of plant cover inside the Park. Systematic bimonthly diurnal and nocturnal human bait and Shannon trap captures were conducted in both forest and domiciliary environments over the course of 24 months. A total of 20,273 adult mosquito specimens belonging to 44 species were collected: Ochlerotatus serratus (10.3%), Haemagogus leucocelaenus (9.7%), Mansonia titillans (9.6%), and Chagasia fajardoi (8.8%) were the most frequently captured mosquitoes. Anopheles cruzii, Runchomyia theobaldi, Wyeomyia aporonoma, and Wy. confusa were captured almost exclusively in well-preserved areas with dense forest cover. Culex nigripalpus, Oc. pennai, Oc. serratus, Sabethes purpureus, and Sa. albiprivus were captured in three essentially sylvatic biotopes. Species captured in the forest areas around a dam were: An. albitarsis s.l., An. galvaoi, An. evansae, An. fluminensis, Coquillettidia venezuelensis, Cq. juxtamansonia, Wy. quasilongirostris, and Onirion personatum, Ch. fajardoi, Cq. fasciolata, Cq nitens, and Ma. titillans were the most frequently captured species in a residential area.

Habitat and Season in Structuring Ground-Dwelling Spider (Araneae) Communities in a Shortgrass Steppe Ecosystem

We assessed habitat differences in ground-dwelling spider communities that stem from fine-scale differences in plant cover types and height in a shortgrass steppe ecosystem. The number of spiders captured in pitfall traps was used to determine habitat and temporal dynamics in the spider communities. Two habitat types were sampled, grass and mixed-grass/shrub during May, June, July, and August 1995 and 1996. Spiders in the Lycosidae (56%) and Gnaphosidae (29%) were the numerically dominant spiders collected. The Lycosidae was represented by three species and significantly more abundant in grass habitats in 1995 only. The Gnaphosidae was the most speciose family collected (15 spp). The most abundant species of Gnaphosidae exhibited consistent habitat and seasonal patterns of species turnover and abundance during the 2-yr study. Results from detrended correspondence analysis revealed significant species-specific differences in the spider communities between the two habitats. Of the 10 most abundant species, Schizocosa mccooki (Montgomery), S. mimula (Gertsch), Gnaphosa clara (Keyserling), and G. brumalis (Thorell), were more abundant in grass sites. The most abundant spiders in the mixed-grass/shrub habitat were Schizocosa spp. (immatures), Gnaphosa spp. (immatures), G. sericata (Koch), Haplodrassus signifer (Koch), Habronattus altanus (Chamberlin), and Xysticus nigromaculatus (Keyserling). Overall, the spider communities differed between grass and mixed-grass/shrub habitats in their response to seasonal change, and these differences in community composition were similar both years of the study. Our results underscore the importance of habitat selection at fine-scales and patterns of seasonal activity that translate to population and community patterns at larger spatial and temporal scales.

Microbial Biomass and Community Structure in a Sequence of Soils with Increasing Fertility and Changing Land Use.

The microbial biomass and community structure of eight Chinese red soils with different fertility and land use history was investigated. Two community based microbiological measurements, namely, community level physiological profiling (CLPP) using Biolog sole C source utilization tests and phospholipid fatty acid (PLFA) profiles, were used to investigate the microbial ecology of these soils and to determine how land use alters microbial community structure. Microbial biomass-C and total PLFAs were closely correlated to organic carbon and total nitrogen, indicating that these soil microbial measures are potentially good indices of soil fertility in these highly weathered soils. Metabolic quotients and C source utilization were not correlated with organic carbon or microbial biomass. Multivariate analysis of sole carbon source utilization patterns and PLFAs demonstrated that land use history and plant cover type had a significant impact on microbial community structure. PLFAs showed these differences more than CLPP methods. Consequently, PLFA analysis was a better method for assessing broad-spectrum community differences and at the same time attempting to correlate changes with soil fertility. Soils from tea orchards were particularly distinctive in their CLPP. A modified CLPP method, using absorbance readings at 405 nm and different culture media at pH values of 4.7 and 7.0, showed that the discrimination obtained can be influenced by the culture conditions. This method was used to show that the distinctive microbial community structure in tea orchard soils was not, however, due to differences in pH alone.

A comparison of Phragmites australisin freshwater and brackish marsh environments in North America

This paper compares the available North Americanliterature and data concerning several ecologicalfactors affecting Phragmites australisin inlandfreshwater, tidal fresh, and tidal brackish marshsystems. We compare aboveground productivity, plantspecies diversity, and sediment biogeochemistry; andwe summarize Phragmiteseffects on faunalpopulations in these habitats. These data suggest thatPhragmitesaboveground biomass is higher thanthat of other plant species occurring in the samemarsh system. Available data do not indicate anysignificant difference in the aboveground Phragmitesbiomass between marsh types, nor doesthere appear to be an effect of salinity on height.However, Phragmitesstem density wassignificantly lower in inland non-tidal freshwatermarshes than in tidal marshes, whether fresh orbrackish. Studies of the effects of Phragmiteson plant species richness suggest that Phragmitesdominated sites have lower diversity.Furthermore, Phragmiteseradication infreshwater sites increased plant diversity in allcases. Phragmitesdominated communities appearto have different patterns of nitrogen cyclingcompared to adjacent plant communities. Abovegroundstanding stocks of nitrogen (N) were found to behigher in Phragmitessites compared to thosewithout Phragmites. Porewater ammonium(NH4+) did not differ among plant covertypes in the freshwater tidal wetlands, but inbrackish marshes NH4+was much higher inSpartinaspp. than in neighboring Phragmitesstands. Faunal uses of Phragmitesdominated sites in North America were found to vary bytaxa and in some cases equaled or exceeded use ofother robust emergent plant communities. In light ofthese findings, we make recommendations for futureresearch.

Shrub facilitation of Quercus humilis regeneration in succession on calcareous grasslands

Abstract. In southern France, the natural invasion by Quercus humilis of calcareous grassland takes place in a mosaic of herbaceous and scrubby patches. We hypothesized that the presence of the shrubs Buxus sempervirens and Juniperus communis alter the rate and the pathway of the succession by facilitating the regeneration of Q. humilis. To infer the process of facilitation at a large scale, the spatial distribution of Q. humilis was studied in relation to acorn sources and the type of plant cover in grazed and ungrazed sites.Abundant recruitment up to 80 m from the wood margins and from isolated oak trees in grassland shows that acorns are dispersed effectively. At the three study sites, the density of Q. humilis individuals was higher under shrubs than in grassland, suggesting that facilitation may occur. This density difference was much higher in the grazed sites than in the ungrazed site. Moreover, before grazing by livestock, the distribution of first‐year seedlings is independent of vegetation cover. Thus, shrubs improve Q. humilis regeneration by protecting individuals from grazing. The high density of individuals at the northern edge of shrubs suggests that a second facilitation mechanism may exist, probably related to improved germination conditions. Facilitation by shrubs appears to be very important for Q. humilis dynamics.

Soil Carbon Inventories under a Bioenergy Crop (Switchgrass): Measurement Limitations

AbstractApproximately 5 yr after planting, coarse root (>2 mm) carbon (C) and soil organic C (SOC) inventories (0–40 cm deep) were compared under different types of plant cover at four switchgrass (Panicum virgatum L.) production field trials in the southeastern USA. There was significantly (p ≤ 0.05) more coarse root C under switchgrass (Alamo variety) and forest cover than under tall fescue (Festuca arundinacea Schreb.), corn (Zea mays L.), or native pastures of mixed grasses. Inventories of SOC under switchgrass were not significantly greater than SOC inventories under other plant covers. At some locations the statistical power associated with ANOVA of SOC inventories was low, which raised questions about whether differences in SOC could be detected statistically. A minimum detectable difference (MDD) for SOC inventories was calculated. The MDD is the smallest detectable difference between treatment means once the variation, significance level, statistical power, and sample size are specified. The analysis indicated that a difference of ≈50 mg SOC/cm2 or 5 Mg SOC/ha, which is ≈10 to 15% of existing SOC, could be detected with reasonable sample sizes (n = 16) and good statistical power (1 − β = 0.90). The smallest difference in SOC inventories that can be detected, and only with exceedingly large sample sizes (n > 100), is ≈2 to 3% (≈10 mg SOC/cm2 or 1 Mg SOC/ha). These measurement limitations have implications for monitoring and verification of proposals to ameliorate increasing global atmospheric CO2 concentrations by sequestering C in soils.

The Effects of Phragmites Removal on Nutrient Pools in a Freshwater Tidal Marsh Ecosystem

Selected nitrogen and phosphorus pools in two freshwater tidal marsh ecosystems on the lower Connecticut River were measured relative to Phragmites, Typha and mixed native wetland plant cover types. For both the Chapman Pond Preserve and Chester Creek Marsh, significant differences were found between plant cover types in porewater ammonium and phosphate for some months during the 1998 growing season; porewater nitrate was always below the detection limit. At Chapman Pond, no significant differences were detected between Phragmites and Typha for plant tissue N concentrations. The standing stock of nitrogen was higher in Phragmites stands, however, owing to its greater aboveground biomass. No significant difference was found between plant cover types for total soil N at Chapman Pond, but KCl extractable ammonium was higher in the mixed cover type than Phragmites or Typha. The results of this study suggest that Phragmites is affecting nutrient pools in freshwater tidal marshes, a result that should be considered in future management design.

Movimentação de cátions em amostras de um Latossolo Vermelho-Amarelo incubadas com duas fontes de cálcio

Estudou-se a movimentação de cátions alcalinos e alcalinos terrosos (CAAT) em colunas de solo arranjadas com amostras de Latossolo Vermelho-Amarelo, álico, coletadas a profundidade de 0 a 5cm sob dois tipos distintos de cobertura, floresta secundária e grama batatais (Paspalum notatum L.), as quais foram superpostas em potes plásticos à amostras do horizonte Bw, da mesma unidade de solo. Aplicaram-se carbonato de cálcio, sulfato de cálcio ou a mistura das duas fontes de cálcio às amostras superficiais, as quais foram colocadas a incubar e depois submetidas a sete aplicações de água destilada, na taxa de 1 volume-poro por semana, durante sete semanas consecutivas. O lixiviado foi recolhido semanalmente e analisado para cálcio, magnésio, potássio e sulfato solúveis. Nos solos, fizeram-se determinações dos teores de cálcio, magnésio e potássio trocáveis, e a determinação da acidez potencial a pH 7,0. A aplicação de sulfato de cálcio favoreceu o processo de lixiviação de potássio e magnésio, enquanto que a aplicação de carbonato de cálcio minimizou a lixiviação. Concluiu-se que a utilização de sulfato de cálcio para a correção da deficiência de cálcio em subsolos ácidos deve ser acompanhada necessariamente da aplicação de carbonato.

Fatores envolvidos na supressividade a Rhizoctonia solani em alguns solos tropicais brasileiros

O experimento foi realizado em condições de casa de vegetação, na Universidade Federal de Uberlândia, no período de março a agosto de 1995, visando determinar, em sete classes de solo, a supressividade ao fungo Rhizoctonia solani e estudar o possível relacionamento dessa característica com a mineralogia, propriedades físicas e químicas e populações de fungos do solo. Após proceder à inoculação dos solos com R. solani, multiplicada em grãos de sorgo autoclavados, observou-se que o índice de doença em plântulas de soja aumentou em todos eles. Tal índice foi sempre maior na camada de 0-20 cm, associando-se com o maior teor de matéria orgânica, com exceção do Solo Orgânico eutrófico (SOe), o qual apresentou um índice de doença similar nas duas profundidades (0-20 e 20-40 cm). O efeito supressivo a R. solani, observado no material do Plintossolo distrófico (PTd) e no Latossolo Vermelho-Escuro álico (LEa), relacionou-se com a textura muito argilosa, com a alta saturação por alumínio e com a vegetação (fase cerrado), mesmo com a ausência de Trichoderma spp. Os materiais do Solo Orgânico eutrófico (SOe), do Latossolo Roxo distrófico (LRd) e da Terra Roxa Estruturada eutrófica (TRe) apresentaram maior conducividade a R. solani , possivelmente relacionada com o caráter eutrófico e com o teor da matéria orgânica, decorrente do tipo de cobertura vegetal (fase vegetação). O material do Latossolo Vermelho-Escuro álico textura média (LEam) e o do Latossolo Vermelho-Amarelo álico (LVa) mostraram comportamento intermediário. O índice de doença correlacionou-se negativamente com a saturação por alumínio e teor de argila e positivamente com a saturação de bases (V) e com o pH. A mineralogia parece não ter influência direta na supressividade ou conducividade dos solos estudados, provavelmente por variar apenas no que se refere às formas de óxidos de ferro.

A simple technique for measuring rainfall interception by small shrub: “interception flow collection box”

Abstract: In this paper a simple technique for field measurement of rain water loss arising from interception and waterflows associated with species of small Mediterranean shrub is described: the ‘interception flow collection box’.This technique solves the problem of installing devices to control stemflow in species with a multiple trunk anddemonstrates its e†ciency through the results obtained from the data observed for three species of semi-aridMediterranean shrub: Juniperus oxycedrus, Rosmarinus o†cinalis and Thymus vulgaris. Finally, the empiricalequations for the prediction of throughfall, stemflow and rain water loss through interception are presentedfor the three selected species and the validity of the technique employed is established. #1998 John Wiley S drainage; stemflow; interception; small shrub INTRODUCTION AND OBJECTIVESInitial studies of interception arose from the idea that large areas of forest retain and evaporate a significantpart of the rainfall they receive, at the same time reducing the water resources available to the forest floor.These studies, essential to the research of water balance in wooded areas, are very important at a local andregional level, in addition to contributing to knowledge of the processes in a wide range of structurallycomplex forest covers.Following the initial work of Horton (1919), hundreds of experiments have been carried out in this area(for example, Haynes, 1940; Kittredge et al., 1941; Law, 1957; Rutter, 1963; Helvey and Patric, 1965;Leonard, 1966; Gash and Morton, 1978). However, the majority of these have been carried out in forests,with very few paying attention to other types of plant cover, such as shrubland, grassland, etc. (Burgy andPomeroy, 1958; Slatyer, 1965; Crouse et al., 1966; De Ploey, 1982; Tromble, 1988; Navar and Bryan, 1990).In forests, the procedures used to measure the water that passes through the cover and reaches the soil(throughfall) are various: ranging from a dense networkof pluviometers uniformly distributed around atree(Ford and Deans, 1978; Durocher, 1990; Belmonte Serrato and Romero Di´az, 1992), to a network ofpluviometers that are moved periodically (Aussenac, 1970) or maintained in their original, randomly chosenpositions (Veneklaas and Van Ek, 1990). Also, large surface pluviometers (Rutter et al., 1971; Massman,1983; Mulder, 1985) or ‘net rain water pluviometers’ (Calder and Rosier, 1976) have been used, althoughtheselatterdevicespresenttheproblemofsummingtheflowsofthroughfallandstemflow(waterthatreaches

Classification and Its Mapping of Plant Cover from a Datafile Containing Information on Plant Communities and the Degree of Influences of Human Activity on Primeval Vegetation.

An attempt was made to classify plant cover from a datafile developed by the Japan Environment Agency. This datafile has two kinds of information, codes of plant communities and the degree of influences of human activity on primeval vegetation in the center of a cell. A lookup-table for plant communities and corresponding plant cover types was constructed after alpha-numeric conversion of the plant community code and sorting. These plant cover codes in the table were applied to plant community codes in the above file, and a plant cover datafile was developed. To overlay the plant cover on other elements, precise spatial coordination of data sampling points was examined using two datafiles with different cell sizes, such as a 1km interval for the plant cover and a 250m grid system for a digital terrain model (DEM) in which altitudes above sea level were sampled at 250m intervals. This study confirmed that the plant cover derived from the above datafile is sufficiently useful for ground truth in satellite remote sensing, and for careful overlaying of other environmental elements.

A comparative modeling study of soil water dynamics in a desert ecosystem

We compared three different soil water models to evaluate the extent to which variation in plant growth form and cover and soil texture along a topographic gradient interact to affect relative rates of evaporation and transpiration under semiarid conditions. The models all incorporated one‐dimensional distribution of water in the soil and had separate functions for loss of water through transpiration and soil evaporation but differed in the degree of mechanism and emphasis. PALS‐SW (Patch Arid Lands Simulator‐Soil Water) is a mechanistic model that includes soil water fluxes and emphasizes the physiological control of water loss by different plant life forms along the gradient. 2DSOIL is a mechanistic model that emphasizes the physical aspects of soil water fluxes. SWB (Soil Water Budget) is a simple water budget model that has no soil water redistribution and includes simplified schemes for soil evaporation and transpiration by different life forms. The model predictions were compared to observed soil water distributions at five positions along the gradient. All models predicted soil water distributions reasonably well and, for the most part, predicted similar trends along the transect in the fractions of water lost as soil evaporation versus transpiration. Transpiration was lowest (about 40% of total evapotranspiration (ET)) for the creosote bush community, which had the lowest plant cover (30% peak cover). The fraction of ET as transpiration increased with increasing plant cover, with 2DSOIL predicting the highest transpiration (60% of total ET) for the mixed vegetation community (60% peak cover) on relatively fine textured soil and PALSr SW predicting highest transpiration (69% of total ET) for the mixed vegetation community (70% peak cover) on relatively coarse textured soil. The community type had an effect on the amount of water lost as transpiration primarily via depth and distribution of roots. In this respect, PALS‐SW predicted greatest differences among stations as related to differences in plant community types. However, since PALS‐SW did not provide as good of fit with the soil moisture data as did 2DSOIL, the differences in the morphology and physiology of the life‐forms may be secondary to the overall control of water loss by the primary factors accounted for in 2DSOIL: vertical distribution of soil moisture, degree of canopy cover, and evaporative energy budget of the canopy. Soil texture interacted with the amount and type of plant cover to affect evaporation and transpiration, but the effect was relatively minor.

Development of microtopography in a semi-arid grassland: Effects of disturbance size and soil texture

Our objective was to evaluate effects of disturbance size and soil texture on the development of microtopography for a shortgrass plant community in north central Colorado USA. Disturbances, defined as the death of individual plants, were created in 1984 and 1985 to evaluate development through time of the small-scale pattern of perennial bunchgrasses and bare soil openings that characterize this semiarid grassland. Disturbed plots of three sizes (50, 100, 150 cm-diameter) comparable in size to naturally-occurring disturbances were produced by killing plants at two sites differing in soil texture (sandy loam, clay loam). Disturbed plots were not manipulated after being created. In 1993, a laser surveying instrument was used to measure heights of crowns of individual plants of the dominant species, the perennial bunchgrass Bouteloua gracilis ([H.B.K.] Lag. ex Griffiths), and bare soil openings between plants for two locations: within each disturbance and in the surrounding undisturbed landscape. Differences between crown heights of plants and bare soil openings were comparable for both the undisturbed landscape and inside disturbances indicating that small-scale microtopography had recovered within nine years after disturbance occurred. However, complete recovery to the undisturbed state had not occurred since crown heights of plants relative to bare soil openings were significantly less on disturbed than undisturbed locations. Differences in height between plant crowns and bare soil openings on disturbed plots increased as disturbance size increased, indicating greater soil redistribution with increasing plot size. Larger differences in height were also found on plots on the fine- than the coarse-textured soil, indicating the importance of soil particle size and plant cover type to the development of microtopography. Differences in height between microsites on disturbed plots were positively related to total plant cover and negatively related to cover of B. gracilis indicating the importance of this species to reducing erosion on disturbed areas. In this semiarid grassland, patterns in microtopography were heterogeneous, likely as a result of the small-scale redistribution of soil between bare soil openings and B. gracilis plants through time. Our results indicate that this redistribution of soil is affected by disturbance size, soil texture, and patchy plant cover. The major effect of small-scale disturbances on patterns in microtopography of the shortgrass steppe are causing plant death and exposing soil to erosional and depositional processes.

Spatial Variability in the Potential for Symbiotic N 2 Fixation by Woody Plants in a Subtropical Savanna Ecosystem

1. Root infection by symbiotic N 2 -fixing Frankia and Rhizobium strains was quantified in relation to light and soil properties for seedlings of 12 woody species from a subtropical savanna in southern Texas, USA. 2. None of four rhamnaceous species nodulated, despite the fact that bioassays with a known actinorhizal species yielded 13 nodules per seedling. Celtis pallida (Ulmaceae), Acacia greggii and Acacia berlandieri (Leguminosae) also failed to nodulate even though field populations of these species were characterized by high (2.7-4.2%) foliar nitrogen concentration. 3. Infective rhizobia occurred in all soils studied regardless of soil depth, distance from a host plant or type of plant cover. Plant growth in N-free media and acetylene reduction activity suggested that all nodules were capable of N 2 -fixation. 4. The extent of nodulation varied by species. However, nodulated seedlings were taller, produced more biomass and allocated less biomass to root systems than their non-nodulated counterparts. 5. Numbers of nodules on seedlings of Prosopis glandulosa, the dominant woody species in this subtropical savanna and throughout the south-western USA, were reduced by low light (15% full sunlight) regardless of soil N level; at medium and full sunlight nodule biomass expressed as a fraction of whole plant biomass decreased with increasing soil N. Nodulation of field-grown P. glandulosa appears to be ephemeral, apparently varying with changes in soil moisture. 6. Nodulation and N 2 fixation among woody legumes in subtropical savannas can occur across a broad range of soil conditions and depths with significant impacts on local and regional N-cycles. 7. Field levels of foliar N in species that failed to nodulate in the laboratory were comparable to or greater than those in species capable of nodulation, suggesting that leaf N is not a reliable indicator of N 2 fixation.

Low-molecular organic acids in the rhizosphere soil solution of beech forest ( Fagus sylvatica L.) cambisols determined by ion chromatography using supported liquid membrane enrichment technique

Soil solution from the A-horizon (0–5 cm) beneath six different plant cover types of beech forest Dystric Cambisols, south Sweden, was expelled by high-speed centrifugation using freshly sampled soil at field moisture. Concentrations of low molecular weight organic acids (LOAs) were determined by an application of ion chromatography using a supported liquid membrane enrichment technique. This method facilitates the detection of LOAs at 60–200 nM in complex matrices and (most important in acid soil solutions) minimizes interferences from Al and Fe. To test the capacity of soils to immobilize LOAs from solution, the recovery of added LOAs was also studied. Between 8 and 10 LOAs were detected in measurable concentrations in most soil solutions. Monocarboxylic acids (acetic, lactic and formic acid) were the most abundant, though rather consistent differences were measured in several acids among the vegetation types, partly related to vascular plant species and soil acidity. There were also consistent differences between seasons (late spring and summer). However, recovery tests (20 min) with several of the soils clearly demonstrated that added LOAs were to a great extent rapidly immobilized, with the exception of acetic and lactic acid, probably a main reason for the high share of these monocarboxylic acids in soil solutions. The ecological relevance of determining LOAs in soil solutions is discussed briefly.

Simulating vegetation dynamics and land use in a mire landscape using a Markov model

The paper consists of a dynamical approach to mire-related vegetation and land use development. Investigations were carried out on two different study levels. First, successions of mire plant communities (community or C-level), based on stratigraphical core sample data, and, second, dynamics of plant cover and land use (PC&LU) types of mire landscapes (landscape or L-level), based on sequential aerial photographs (AP), were studied.The first reveals mainly autogenic successions of plant communities over several thousand years, the second, natural and anthropogenic successions of PC&LU types over a 30 year time span.The source data for the quantitative analysis on the basis of Markov model (MM) were provided by 17 peat types as the representatives of corresponding plant communities, taken from cores through the genetic centres of mires (C-level). Nineteen PC&LU types as the representatives of hybrid systems, were deduced from AP of three time periods (L-level).The first order MM, mainly used in ecological modelling, was also applied in addition to the C-level treatment, to a more complicated investigation, i.e. L-level.As an extension of the first order MM, second order effects were modelled. For ease of analysis of three-dimensional matrices, three states of succession (after reduction 17- and 19-element classification schemes to 3 element) only were used.The treatment represented has been used to reconstruct historical development of mire plant communities and PC&LU types in mire landscapes and analyse the future development of the corresponding types. The analysis of the first and second order models and predictions made on this basis are given.

Two Lesquerellas (Cruciferae) of South Central and Western Montana

Two heretofore unknown species of Lesquerella are described. These occur in limited areas in the mountains of central and western Montana. Both species, here named L. lesicii and L. pulchella, occur in patches of limestone-derived soils and rubble that are conspicuously barren of trees and shrubs and other types of plant cover, or on the borders of such areas where the limestone detritus meets soils and rubble of crystalline rocks. Also, they are often found in open areas in sparse stands of low-growing trees or shrubs. Recent samplings of populations of Lesquerella in Montana show that species diversity in this genus goes somewhat beyond that previously recognized in monographic treatments (Payson, 1922; Rollins & Shaw, 1973; Rollins, 1993). What has been known for the area is that species of Lesquerella are often abundant and are an important component of the flora of specialized habitats, especially where limestone or derivatives of limestone are involved. The nature of some of these habitats is well shown in Figures 1 and 2, where the highly reflective limestone-derived soil and rubble contrast with the more vegetated surrounding areas. These windswept whitish areas are the places where L. pulchella grows. Also known is that a high degree of complexity exists within some species, such as L. alpina (Nuttall ex Torrey & A. Gray) S. Watson, which is frequently encountered in the general region. But now we see that there are existing taxa not previously recognized, and these have complicated relationships with species south of Montana in Idaho and Wyoming. The main purpose of this paper is to describe two new species of Lesquerella and explain their relationships to previously known taxa. It is somewhat ironic that I had only recently (Rollins, 1993) completed a review of Lesquerella as it occurs in North America when these two species showed up too late to be included in my treatment. Lesquerella lesicii Rollins, sp. nov. TYPE: U.S.A. Montana: abundant in gravelly limestone-derived soil at edge of limber pine woodland on the ridge W of Layout Creek, '/ mi. S of Mystery Cave, Pryor Mountains, Carbon County, 7500 ft., T85, R28 E, S21, SW '4, with Shoshonea pulvinata, Astragalus aretoides, and A. miser, 20 June 1992, Peter Lesica 5707 and Rob DeVelica (holotype, GH). Herba perennis, caudicibus simnplicibus, folia basibus erectis dense stellatis argenteis 0.5-1 cm longis, caulis erectis vel decumbentibus gracilibus 1-1.5 dm longis, petalis aureis spathulatis vel lingulatis 6-7 mm longis, pedicellis fructiferis recurvatis vel divaricatis 5-10 mm longis, siliquis globosis vel subglobosis 3-4 mm diametro pilis stellatis adspersus, loculis 3-5 ovulatis. Delicate perennial; caudex simple, sometimes elongated and with old leaf bases; basal leaves erect, usually fewer than 10, entire, 1.5-3 cm long, petioles slender, abruptly expanded to blade, 1-2.5 cm long, blades broadly ovate to elliptical, 0.5-1 cm long, silvery from a dense cover of stellate trichomes; leaf trichomes small, ca. 0.02 mm diam., ray tips 15-25, each primary ray forked near its base; flowering stems very slender, mostly filiform, simple, erect to decumbent, 1-1.5 dm long; cauline leaves few, remote, ? spatulate, lower somewhat petiolate, upper cuneate at base; inflorescences lax, rarely nodding, usually with fewer than 10 flowers; sepals erect, densely pubescent, oblong, nonsaccate and without scarious margins, 3.5-4 mm long; petals yellow, often fading to light purple toward their tips, spatulate to nearly lingulate, 6-7 mm long; stamens strongly tetradynymous; infructescences lax, greatly elongated; fruiting pedicels filiform, recurved in a single arch to widely spreading, 5-10 mm long; siliques globose or subglobose, spreading at right angles to rachis to pendent, 3-4 mm diam., + densely pubescent on exterior, valves glabrous on the interior; styles ca. 1.5 mm long, glabrous or NovoN 5: 71-75. 1995. This content downloaded from 207.46.13.38 on Fri, 20 May 2016 08:54:19 UTC All use subject to http://about.jstor.org/terms

An evaluation of the regional acid deposition model surface module for ozone uptake at three sites in the San Joaquin Valley of California

Plants and soils act as major sinks for the destruction of tropospheric ozone, especially during daylight hours when plant stomata open and are thought to provide the dominant pathway for the uptake of ozone. The present study, part of the California Ozone Deposition Experiment, compares predictions of the regional acid deposition model ozone surface conductance module with surface conductance data derived from eddy covariance measurements of ozone flux taken at a grape, a cotton, and a grassland site in the San Joaquin Valley of California during the summer of 1991. Results indicate that the model (which was developed to provide long‐term large‐area estimates for the eastern United States) significantly overpredicts the surface conductance at all times of the day for at least two important types of plant cover of the San Joaquin Valley and that it incorrectly partitions the ozone flux between transpiring and nontranspiring components of the surface at the third site. Consequently, the model either overpredicts or inaccurately represents the observed deposition velocities. Other results indicate that the presence of dew does not reduce the rate of ozone deposition, contradicting to model assumptions, and that model assumptions involving the dependency of stomata upon environmental temperature are unnecessary. The effects of measurement errors and biases, arising from the presence of the roughness sublayer and possible photochemical reactions, are also discussed. A simpler model for ozone surface deposition (at least for the San Joaquin Valley) is proposed and evaluated.

Scale Effects of Vegetation on Forager Movement and Seed Harvesting by Ants

The responses of animals to patch structure at different spatial scales influence how processes such as foraging and species interactions vary with spatial scale or translate across levels of organization. We investigated how seed harvesting by the western harvester ant (Pogonomyrmex occidentalis) was affected by vegetation structure in a shortgrass steppe ecosystem at levels of organization ranging from individual ants to populations and at spatial scales from 0.1 m 2 to 15 ha. In the first of two experiments, we used a hierarchical experimental design to assess the magnitude and variation in seed harvesting (1) among ant colonies in three pastures differing in livestock grazing intensity, (2) among colonies within pastures, and (3) among plant cover types within colonies