Steven Archer

The University of Arizona, School of Natural Resources and the Environment, Faculty Member

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Papers by Steven Archer

Ecological Characterization as a Foundation for Prediction of Plains Village Tradition Site Locations in Central South Dakota

North American Archaeologist, Apr 1, 1983

Constraints on shrub cover and shrub–shrub competition in a U.S. southwest desert

Ecosphere, Feb 1, 2019

The cover of woody perennial plants (trees and shrubs) in arid ecosystems is at least partially c... more The cover of woody perennial plants (trees and shrubs) in arid ecosystems is at least partially constrained by water availability. However, the extent to which maximum canopy cover is limited by rainfall and the degree to which soil water holding capacity and topography impacts maximum shrub cover are not well understood. Similar to other deserts in the U.S. southwest, plant communities at the Jornada Basin Long-Term Ecological Research site in the northern Chihuahuan Desert have experienced a long-term state change from perennial grassland to shrubland dominated by woody plants. To better understand this transformation, and the environmental controls and constraints on shrub cover, we created a shrub cover map using high spatial resolution images and explored how maximum shrub cover varies with landform, water availability, and soil characteristics. Our results indicate that when clay content is below~18%, the upper limit of shrub cover is positively correlated with plant available water as mediated by surface soil clay influence on water retention. At surface soil clay contents >18%, maximum shrub cover decreases, presumably because the amount of water percolating to depths preferentially used by deep-rooted shrubs is diminished. In addition, the relationship between shrub cover and density suggests that self-thinning occurs in denser stands in most landforms of the Jornada Basin, indicating that shrub-shrub competition interacts with soil properties to constrain maximum shrub cover in the northern Chihuahuan Desert.

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Tree (Prosopis glandulosa) effects on grass growth: An experimental assessment of above- and belowground interactions in a temperate savanna

Journal of Arid Environments, Apr 1, 2008

Savanna trees can impose above-and belowground effects on the herbaceous layer by changing water,... more Savanna trees can impose above-and belowground effects on the herbaceous layer by changing water, nutrients and microclimate. Proposed mechanisms governing savanna tree-on-grass interactions include: (1) improved fertility and structure of soils below tree crowns; (2) improved water relations of shaded plants; and (3) increased competition for light, soil moisture and nutrients. To assess the relative importance and outcome of these interacting positive and negative factors, we conducted a series of field experiments that altered the presence and absence of tree canopy and tree roots at locations both immediately under trees and in interstitial locations in a mesquite (Prosopis glandulosa) savanna. Basal area, tiller density and production of the dominant C 3 grass, Nassella leucotricha, and herbaceous layer annual net primary production (ANPP) were quantified in 1998 and 1999. Annual rainfall during these 2 years was substantially below normal and most responses to treatments were neutral. However, a significant reduction in herbaceous ANPP, largely annual C 3 grasses, indicated that belowground competition rather than facilitation was the mechanism controlling tree effects on grass in this savanna. Lower than average rainfall was a potentially overriding factor. Hence, it is possible that other treeon-grass mechanisms might operate under average or above-average rainfall years.

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Growth and Physiological Responses of Tundra Plants to Defoliation

Arctic and alpine research, Nov 1, 1980

Conundrums in mixed woody-herbaceous plant systems

Journal of Biogeography, Oct 23, 2003

Aims To identify approaches to improve our understanding of, and predictive capability for, mixed... more Aims To identify approaches to improve our understanding of, and predictive capability for, mixed tree-grass systems. Elucidation of the interactions, dynamics and determinants, and identification of robust generalizations that can be broadly applied to tree-grass systems would benefit ecological theory, modelling and land management. Methods A series of workshops brought together scientific expertise to review theory, data availability, modelling approaches and key questions. Location Ecosystems characterized by mixtures of herbaceous and woody plant lifeforms, often termed ÔsavannasÕ, range from open grasslands with few woody plants, to woodlands or forests with a grass layer. These ecosystems represent a substantial portion of the terrestrial biosphere, an important wildlife habitat, and a major resource for provision of livestock, fuel wood and other products. Results Although many concepts and principles developed for grassland and forest systems are relevant to these dual life-form communities, the novel, complex, nonlinear behaviour of mixed tree-grass systems cannot be accounted for by simply studying or modelling woody and herbaceous components independently. A more robust understanding requires addressing three fundamental conundrums: (1) The ÔtreenessÕ conundrum. What controls the relative abundance of woody and herbaceous plants for a given set of conditions at given site? (2) The coexistence conundrum. How do the life-forms interact with each other? Is a given woody-herbaceous ratio dynamically stable and persistent under a particular set of conditions? (3) The net primary productivity (NPP) conundrum. How does NPP of the woody vegetation, the herbaceous vegetation, and the total ecosystem (woody þ herbaceous) change with changes in the tree-grass ratio? Tests of the theory and conceptual models of determinants of mixed woody-herbaceous systems have been largely site-or region-specific and have seldom been broadly or quantitatively evaluated. Cross-site syntheses based on data and modelling are required to address the conundrums and identify emerging patterns, yet, there are very few data sets for which either biomass or NPP have been quantified for both the woody and the herbaceous components of tree-grass systems. Furthermore, there are few cross-site comparisons spanning the diverse array of woody-herbaceous mixtures. Hence, initial synthesis studies should focus on compiling and standardizing a global data base which could be (1) explored to ascertain if robust generalizations and consistent patterns exist; and (2) used to evaluate the performance of savanna simulation models over a range of woody-herbaceous mixtures. Savanna structure and productivity are the result of complex and dynamic interactions between climate, soils and disturbances, notably fire and herbivory. Such factors are difficult to isolate or experimentally manipulate in order

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Scale Dependence of Absorption of Photosynthetically Active Radiation in Terrestrial Ecosystems

Ecological Applications, Nov 1, 1998

Effects of simulated grazing on foliage and root production and biomass allocation in an arctic tundra sedge (Eriophorum vaginatum)

Oecologia, Apr 1, 1983

Variability in Leaf and Litter Optical Properties: Implications for BRDF Model Inversions Using AVHRR, MODIS, and MISR

Remote Sensing of Environment, Mar 1, 1998

Canopy radiative transfer models simulate the bidirec-model inversions by decreasing the number o... more Canopy radiative transfer models simulate the bidirec-model inversions by decreasing the number of observations required to retrieve canopy structural and biophysi-tional reflectance distribution function (BRDF) of vegetation covers with differing leaf and soil spectral and can-cal information from multiangle remotely sensed data. ©Elsevier Science Inc., 1998 opy structural characteristics. Numerical inversion of these models has provided estimates of vegetation structural and biophysical characteristics from multiangle, remotely * Center for the Study of Earth from Space/CIRES and Departvanced from simple light extinction algorithms to those ment of Environmental, Population and Organismic Biology, University based explicitly on scattering theory using turbid medium of Colorado, Boulder and turbid-medium/geometric-optical methods (e.g.

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Cultural Resources Reconnaissance of the Federal Lands On the East Bank of Lake Francis Case, South Dakota, Volume 2 of 2; Section II - An Ecological Characterization and Locational Model for Archeological Sites Along the Missouri River / L

Plant Communities, Mountains and Climate in Arizona ant Co

Brush management and grassland conservation: an ecosystem services perspective

Relationship between shrub cover and plant available water in a U.S. Southwest desert

Artificial intelligence advances have an important role on self-driving cars development, such as... more Artificial intelligence advances have an important role on self-driving cars development, such as assisting the recognition of traffic lights. However, when relying on images of the scene alone, little progress was observed on selecting the traffic lights defining guidance to the car. Common detection approaches rely on additional high-level decision-making process to select a relevant traffic light. This work address the problem by proposing a deep regression system with an outliers resilient loss to predict the coordinates of a relevant traffic light in the image plane. The prediction can be used as a high-level decisionmaker or as an assistant to a cheaper classifier to work on a region of interest. Results for European scenes show success in about 88% of the cases. T raining Manual annotation (Predicted) Target's Position Training imagesC amera image Learning stage Test stage

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Seed dormancy and persistence of Acacia berlandieri andLeucaena pulverulenta in a semi-arid environment

Journal of Arid Environments, 1995

Seed longevity of the leguminous shrubs Acacia berlandieri and Leucaena pulverulenta was evaluate... more Seed longevity of the leguminous shrubs Acacia berlandieri and Leucaena pulverulenta was evaluated under field conditions at the soil surface and at 3-5 cm depth. Abiotic influences on seed longevity and dormancy were investigated by comparing seeds maintained at 5°C with seeds experiencing fluctuating day/night temperatures (40°C/20°C vs. 50°C/30°C) under dry and moist conditions. Acacia seed demonstrated no dormancy and initial germinability was > 82% in the laboratory. Viability of Leucaena seed was >97%, but seed coat dormancy limited germination to < 7%. Persistence of Acacia seeds in the soil seed bank varied with depth. After 42 days the viable seed population of Acacia was reduced by 10 and 80% for surface and buried seeds, respectively, and no viable seeds were present after 3"5 months of burial. In contrast, Leucaena seeds on the soil surface exhibited no significant decline in viability over 60 days and attrition of buried seed was <11%. After 3"5, 6 and 12 months of burial, 86, 81 and 71% of the Leucaena seeds dispensed remained viable, but the hard seed coat limited germination to 5, 2 and 0%, respectively. Loss of dormancy of Leucaena seeds stored in the laboratory over 7, 30 and 78 clays was 7, 12 and 19%. Thus, the 29% attrition after 1 year of burial was probably associated with a gradual loss of seed coat dormancy. Light levels (full sun and 25% full sun) manipulated with neutral density shade cloth had no signficant influence on surface seed viability for either slaecies. Temperature and moisture interacted to influence Leucaena seed coat dormancy and embryo viability, but fluctuating temperatures under dry conditions affected neither viability nor germination. However, when moisture was available, germinability of seeds in the 40°C/20°C regime was higher (41%) than that of the control group maintained at 30°C (7%). All seeds in the 50°C/30°C regime imbibed water within 50 days, but none germinated. Low germination of buried seeds (29%) suggest that temperature/moisture combinations capable of disrupting seed coat dormancy or inducing embryo mortality were infrequent during the year of the field experiment.

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Net changes in regional woody vegetation cover and carbon storage in Texas Drylands, 1937-1999

Global Change Biology, Mar 1, 2003

Although local increases in woody plant cover have been documented in arid and semiarid ecosystem... more Although local increases in woody plant cover have been documented in arid and semiarid ecosystems worldwide, there have been few long-term, large-scale analyses of changes in woody plant cover and aboveground carbon (C) stocks. We used historical aerial photography, contemporary Landsat satellite data, field observations, and image analysis techniques to assess spatially specific changes in woody vegetation cover and aboveground C stocks between 1937 and 1999 in a 400-km 2 region of northern Texas, USA. Changes in land cover were then related to topo-edaphic setting and historical land-use practices. Mechanical or chemical brush management occurred over much of the region in the 1940±1950s. Rangelands not targeted for brush management experienced woody cover increases of up to 500% in 63 years. Areas managed with herbicides, mechanical treatments or fire exhibited a wide range of woody cover changes relative to 1937 (275% to + 280%), depending on soil type and time since last management action. At the integrated regional scale, there was a net 30% increase in woody plant cover over the 63-year period. Regional increases were greatest in riparian corridors (33%) and shallow clay uplands (26%) and least on upland clay loams (15%). Allometric relationships between canopy cover and aboveground biomass were used to estimate net aboveground C storage changes in upland (nonriparian) portions of regional landscapes. Carbon stocks increased from 380 g C m 22 in 1937 to 500 g C m 22 in 1999, a 32% net increase across the 400 km 2 region over the 63-year period. These plant C storage change estimates are highly conservative in that they did not include the substantial increases in woody plant cover observed within riparian landscape elements. Results are discussed in terms of implications for`carbon accounting' and the global C cycle.

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A prairie dog (Cynomys ludovicianus) colony with a known history of habitation was studied to qua... more A prairie dog (Cynomys ludovicianus) colony with a known history of habitation was studied to quantify the effects of herbivory on plant species composition, dominance, stature and diversity in a North American mixed-grass prairie. Gradient analysis was used to quantify the relationship between plant community structure, prairie dog density, burrow density and habitation history and to document community-level r sponses of plants ubjected to heavy grazing pressure. The results quantify the type, rate and extent of change which plant populations and communities may undergo in response tothe differential grazing of plants variously tolerant of defoliation. Detrended correspondence analysis indicated that 69 % of the between-sample floristic variance on the site was attributable toprairie dog habitation. Perennial grasses were rapidly displaced from the site within 3 yr of colonization and were replaced by annual forbs. The net result was an increase in species richness and diversi-ty ...

T Re e S in GR a S S L a N D S : Bio Ge O C Hemic a L C O N Se Q Ue N C Es O F W O O Dy PL a N T Exp a N Sio N

Understanding and managing rangeland plant communities

Global rangelands: progress and prospects. VI International Rangeland Congress on 'People and Rangelands: Building the Future', Townsville, Australia, 1999, 2002

Contrasting perspectives on rangeland community organization such as limiting factors (water vs. ... more Contrasting perspectives on rangeland community organization such as limiting factors (water vs. nitrogen), species interactions (competition vs. facilitation), main effects vs. interactions, and description vs. experimentation, are discussed. Problems regarding field experiments, and hierarchical and future perspectives are presented.

Aggregation of Species Properties for Biogeochemical Modeling: Empirical Results

Linking Species & Ecosystems, 1995

... is however consistent between adjacent individuals of the different dominant species, We have... more

Vegetation Dynamics in Changing Environments

The Rangeland Journal, 1993

Human-induced changes in atmospheric chemistry and meteorology have the potential to alter a broa... more Human-induced changes in atmospheric chemistry and meteorology have the potential to alter a broad array of ecosystem processes over a range of temporal and spatial scales. These may have direct and indirect effects that could influence management strategies and landscape response to disturbances associated with natural events and land use. The extent to which forecasted global changes are effective in altering local ecosystem properties will depend upon a variety of factors. In this paper, I address species life history traits and community and landscape properties that can be used by land managers to evaluate potential manifestations of global change on a local scale.

A tool for estimating impacts of woody encroachment in arid grasslands: Allometric equations for biomass, carbon and nitrogen content in Prosopis velutina

Journal of Arid Environments, 2013

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

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