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This chapter discusses controls over ecosystem structure and function, which is a complicated topic, and offers some general observations about ecosystem controls that can be used in both scientific studies and management contexts. Control is defined, and several reasons why this topic occupies a central position in ecosystem science is discussed. Also, a few of the more important conclusions that ecosystem scientists have reached about how ecosystems are controlled are covered.

Burial of aboveground plant litter by animals reduces the amount available for surface transport and places it into a different environment, affecting decomposition rates and fluxes of organic matter to adjacent ecosystems. Here we show that in a Southwestern Atlantic salt marsh the burrowing crab Neohelice granulata buries aboveground plant litter at rates (0.5–8 g m−2 day−1) comparable to those of litter production (3 g m−2 day−1). Buried litter has a low probability (0.6%) of returning to the marsh surface. The formation of burrow excavation mounds on the marsh surface is responsible for most litter burial, whereas litter trapped in burrows was an order of magnitude lower than rates of burial under excavation mounds. Crab exclusion markedly increased surface litter accumulation (3.5-fold in just 21 days). Tides with the potential to transport significant amounts of surface litter are infrequent; hence, most litter is buried before it can be transported elsewhere or decomposes on the surface. Crab litter burial can account for the observed low levels of surface litter accumulation in this ecosystem and likely drives organic matter transformation and export. The impacts of ecosystem engineering by this crab species are therefore substantial and comparable in magnitude to the large effects found for tropical crabs and other litter-burying organisms, such as anecic earthworms. Fil: Gutierrez, Jorge Luis Ceferino. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales; Argentina. Cary Institute of Ecosystem Studies; Estados Unidos. Grupo de Investigación y Educación en Temas Ambientales (GrIETA) - Estación Biológica Las Brusquitas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Jones, Clive G.. Cary Institute of Ecosystem Studies; Estados Unidos Fil: Ribeiro, Pablo Damián. Grupo de Investigación y Educación en Temas Ambientales (GrIETA) - Estación Biológica Las Brusquitas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Findlay, Stuart E. G.. Cary Institute of Ecosystem Studies; Estados Unidos Fil: Groffman, Peter M.. Cary Institute of Ecosystem Studies; Estados Unidos. City University of New York; Estados Unidos

Boom-bust dynamics - the rise of a population to outbreak levels, followed by a dramatic decline - have been associated with biological invasions and offered as a reason not to manage troublesome invaders. However, boom-bust dynamics rarely have been critically defined, analyzed, or interpreted. Here, we define boom-bust dynamics and provide specific suggestions for improving the application of the boom-bust concept. Boom-bust dynamics can arise from many causes, some closely associated with invasions, but others occurring across a wide range of ecological settings, especially when environmental conditions are changing rapidly. As a result, it is difficult to infer cause or predict future trajectories merely by observing the dynamic. We use tests with simulated data to show that a common metric for detecting and describing boom-bust dynamics, decline from an observed peak to a subsequent trough, tends to severely overestimate the frequency and severity of busts, and should be used cautiously if at all. We review and test other metrics that are better suited to describe boom-bust dynamics. Understanding the frequency and importance of boom-bust dynamics requires empirical studies of large, representative, long-term data sets that use clear definitions of boom-bust, appropriate analytical methods, and careful interpretations.

We examined whether the effects of elevated CO

The gypsy moth (Lymantria dispar L.), a major defoliator of hardwood forests in the eastern U.S., has a highly alkaline midgut pH. We hypothesized that the high pH would cause high rates of ammonia (NH3) volatilization as larvae consumed foliage, leading to potentially large losses of N from the ecosystem to the atmosphere during gypsy moth outbreaks. We measured NH3 emission during the consumption of oak foliage by larvae in the laboratory. Surprisingly, we found very low amounts of NH3 release of about 0.1% of the N consumed in foliage. We speculate that digestive mechanisms may limit NH3 production in the midgut, and that the acidic environment of the hindgut traps most of the small amount of NH3 that is produced, effectively preventing a potentially very large N loss from both larvae and ecosystem. The estimated rate of NH3 emission from a defoliated forest is small compared to other inputs and outputs of N from the ecosystem, but could potentially enhance the neutralization of atmospheric acidity during the defoliation period.

Effectively managing human pressures on tropical seascapes (mangrove forests, seagrass beds and coral reefs) requires innovative approaches that go beyond the ecosystem as the focal unit. Recent advances in scientific understanding of long-distance connectivity via extended ecosystem engineering effects and on-going rapid developments in monitoring and data-sharing technologies provide viable tools for novel management approaches that make use of positive across-ecosystem interactions (for example, hydrodynamics). Scientists and managers can now use this collective knowledge to develop monitoring and restoration protocols that are specialised for cross ecosystem fluxes (waves, sediments, nutrients) on a site-specific basis for connected tropical seascape (mangrove forests, seagrass beds and coral reefs).

Although environmental modification by ecosystem engineers influences species distributions and abundances and ecological process rates, general determinants of the environmental states of engineered landscapes are not well understood. Here we develop a general, spatially implicit model of engineered landscapes that includes parameters driving engineer populations (demographics, environmental modification) and environmental decay. We show that average environmental states and heterogeneities of landscapes are the result of a balance between parameters determining engineering rates and decay rates that can be expressed as a net engineering ratio (NER). This ratio highlights the need to include environmental decay in ecosystem engineering studies. Moreover, it defines a significant engineer as one that can alter the environment despite decay and generates expectations for different kinds of effects on the engineer, other species and ecological processes depending on ratio values. Finally, it suggests that, in general, decay places limits as to what can be inferred about engineer population dynamics from environmental dynamics and vice versa.

INRA, UMR AMAP, Bld de la Lironde, 34398 Montpellier Cedex 5, France IRD-Bioemco, UMR 7618, Ecole Normale Superieure, 46 Rue d’Ulm, 75230 Paris Cedex 05, France UPMC-Bioemco, UMR 7618, Ecole Normale Superieure, 46 Rue d’Ulm, 75230 Paris Cedex 05, France CNRS-Bioemco, UMR 7618, Ecole Normale Superieure, 46 Rue d’Ulm, 75230 Paris Cedex 05, France Cary Institute of Ecosystem Studies, P.O. Box AB, Millbrook, NY 12545, USA Wilma H. Schiermeier Olentangy River Wetland Research Park, The Ohio State University, 352 W. Dodridge Street, Columbus, OH 43202, USA Everglades Wetland Research Park, 110 Kapnick Center, Florida Gulf Coast University, 4940 Bayshore Drive, Naples, FL 34112, USA1

Ecological engineering is an idea and field whose time has already come, but what will it be in the future? It can be a leader in environmental sustainability, but this will not be easy to achieve. Three grand challenges need to be met and integrated into practice to accomplish this ambitious goal; they are the ethical, the relational, and the intellectual. The ethical challenge requires clearly articulating what is meant by the statement that ecological engineering integrates human society with its natural environment for the benefit of both, and what this then implies for codes of practice. The statement is open to ethical interpretation and invokes the key issue of balance amidst inevitable tradeoffs. The relational challenge is strategic. If ecological engineering seeks wide adoption it must develop and strengthen its relationships with other scientific disciplines and other segments of society. Key scientific partners are social science, management science, domain-specific science and technology, conservation and restoration science, engineering science and technology, and many areas of ‘green’ science and technology. Key social partners are business, policy, education and practitioners. The intellectual challenge requires those coming from ecological and engineering perspectives to respectively identify and fuse their key principles into a coherent, useful set that is comprehensible and accessible to all. All three challenges have to be met and integrated if ecological engineering is to significantly contribute to environmental sustainability. Given rapid environmental change, time to accomplish these tasks is limited. I call for a substantive open discourse and progress on these challenges and their integration into ecological engineering practice. If ecological engineering does not do this it risks misinterpretation, misapplication and non-acceptance, and may get lost in a sea of rapidly growing green endeavors.

While well-recognized as an important kind of ecological interaction, physical ecosystem engineering by organisms is diverse with varied consequences, presenting challenges for developing and using general understanding. There is also still some uncertainty as to what it is, and some skepticism that the diversity of engineering and its effects is amenable to conceptual integration and general understanding. What then, are the key cause/effect relationships and what underlies them? Here we develop, enrich and extend our extant understanding of physical ecosystem engineering into an integrated framework that exposes the essential cause/effect relationships, their underpinnings, and the interconnections that need to be understood to explain or predict engineering effects. The framework has four cause/effect relationships linking four components: 1. An engineer causes structural change; 2. Structural change causes abiotic change; 3. Structural and abiotic change cause biotic change; 4. Structural, abiotic and biotic change can feedback to the engineer. The first two relationships describe an ecosystem engineering process and abiotic dynamics, while the second two describe biotic consequence for other species and the engineer. The four relationships can be parameterized and linked using time-indexed equations that describe engineered system dynamics. After describing the relationships we discuss the utility of the framework; how it might be enriched; and briefly how it can be used to identify intersections of ecosystem engineering with fields outside ecology.

1. The area or size of an ecosystem affects the acquisition, storage and redistribution of energy and matter. Patch size reduction due to natural or anthropogenic habitat loss will not only modify species distribution and patch structure but also affect the ecosystem processes that are, in part, responsible for patch persistence. 2. In a fog-dependent forest ecosystem, trees and their architectures play essential roles in capturing and redistributing water from collection surfaces. In this paper, we address the question of how forest patch size and structure interact to determine fog water inputs and storage in a fog-inundated, coastal ecosystem in semi-arid Chile (30°S). 3. Six forest patches ranging in area from 0·2 to 36 ha on a coastal mountaintop of Fray Jorge National Park were characterized using 0·1 ha plots laid down at the centre of each forest patch. In each patch, we assessed tree basal area as a measure of forest structure, recorded daily air temperature and humidity, measured water influx from stemflow and throughfall (water that has passed through the forest canopy). Soil and litter gravimetric water contents were used as a measure of storage. 4. Total tree basal area per hectare was positively related to patch area, despite some variation at the species level. Mean and maximum air temperatures inside the patches were inversely related to patch size, with maximum temperatures differing by 2 °C on average. Annual fog water capture by trees within forest patches (net throughfall) was estimated in 296·1 mm after rain flux (about 122 mm) was subtracted. Throughfall volume and patch area were uncorrelated, but stemflow volume, soil and litter water contents scaled positively with patch area, showing a functional link between water interception and ecosystem retention. 5. Our study shows that ecosystem area in this mosaic of fog-dependent temperate forest patches can modify water fluxes and storage capacity of the ecosystem. This finding has important consequences for fragmented landscapes, where large continuous forests are fragmented into smaller patches, affecting not only the persistence of species but also the continuity of critical ecosystem processes.

Why do organisms make the types of chemicals that they do? Evolutionary theory tells us that individuals within populations will be subject to mutation and that some of those mutations will be enzyme variants that make new chemicals. A mutant making a novel chemical for that species will only survive in the population if the 'cost' of making the new chemical is outweighed by the benefits that result from making that molecule. The benefits, or adverse consequences, that a novel chemical X can confer to the individual organism are not a property of the simple existence of X in the cell but can be traced to one of the multiple properties that X will possess because of its molecular structure. By considering only three basic types of molecular property and by considering how selection pressures will differ for each kind of property, it is possible to account for much of the chemical diversity made by organisms. Such an evolutionary model can also explain why the properties of enzymes will differ depending on the molecular properties of the chemicals they make, and why the widely accepted terms 'primary metabolism' and 'secondary metabolism' have been so misleading and unsatisfactory.

Phenotypic plasticity in response to environmental variation occurs at all levels of organization and across temporal scales within plants. However, the magnitude and functional significance of plasticity is largely unexplored in perennial species. We measured the plasticity of leaf- and shoot-level physiological, morphological and developmental traits in nursery-grown Populus deltoides Bartr. ex Marsh. individuals subjected to different nutrient and water availabilities. We also examined the extent to which nutrient and water availability influenced the relationships between these traits and productivity. Populus deltoides responded to changes in resource availability with high plasticity in shoot-level traits and moderate plasticity in leaf-level traits. Although shoot-level traits generally correlated strongly with productivity across fertilization and irrigation treatments, few leaf-level traits correlated with productivity, and the relationships depended on the resource examined. In fertilized plants, leaf nitrogen concentration was negatively correlated with productivity, suggesting that growth, rather than enhanced leaf quality, is an important response to fertilization in this species. With the exception of photosynthetic nitrogen-use efficiency, traits associated with resource conservation (leaf senescence rate, water-use efficiency and leaf mass per area) were uncorrelated with short-term productivity in nutrient- and water-stressed plants. Our results suggest that plasticity in shoot-level growth traits has a greater impact on plant productivity than does plasticity in leaf-level traits and that the relationships between traits and productivity are highly resource dependent.

The persistence of rainforest patches at Fray Jorge National Park (FJNP) in semiarid Chile (30°40'S), a region receiving approximately 147 mm of annual rainfall, has been a source of concern among forest managers. These forests are likely dependent on water inputs from oceanic fog and their persistence seems uncertain in the face of climate change. Here, we assessed tree radial growth and establishment during the last two centuries and their relation to trends in climate and canopy disturbance. Such evaluation is critical to understanding the dynamics of these semiarid ecosystems in response to climate change. We analyzed forest structure of six forest patches (0.2-22 ha) in FJNP based on sampling within 0.1 ha permanent plots. For the main canopy species, the endemic Aextoxicon punctatum (Aextoxicaceae), we used tree-ring analysis to assess establishment periods, tree ages, growing trends and their relation to El Nifio Southern Oscillation (ENSO), rainfall, and disturbance. The population dynamics of A. punctatum can be described by a continuous regeneration mode. Regeneration of A. punctatum was sensitive to different canopy structures. Growth release patterns suggest the absence of large scale human impact. Radial growth and establishment of A. punctatum were weakly correlated with rainfall and ENSO. If water limits forests patch persistence, patches are likely dependent on the combination of fog and rain water inputs. Forest patches have regenerated continuously for at least 250 years, despite large fluctuations in rainfall driven by ENSO and a regional decline in rainfall during the last century. Because of the positive influence on fog interception, forest structure should be preserved under any future climate scenario. Future research in FJNP should prioritize quantifying the long-term trends of fog water deposition on forests patches. Fog modeling is crucial for understanding the interplay among physical drivers of water inputs under climate change.

Apterous populations of Chaitophorous populicola Thomas (Homoptera: Aphididae) appear to track Eastern cottonwood (Populus deltoides Bartr.) leaf development. Few aphids occur on mature leaves. Marked individual aphids on leaves of different developmental stages were observed through a period of new leaf initiation. Nymph and adult C. populicola frequently track leaf development by moving up to younger leaves. A comparison of phloem sap constituents and leaf toughness among leaf developmental stages revealed some differences that could be used by C. populicola to determine leaf age. Phloem sap exudates, collected from P. deltoides leaves of different developmental stages, were analyzed by high-performance liquid chromatography for free amino acids and the phenolic glycoside salicin. Sucrose concentration in exudates, indicative of phloem sap exudation rate, was uniform among leaf stages. Of 20 amino acids examined, only aspartic acid and γ-amino-n-butyric acid (GABA) concentrations differed significantly between leaf stages. Forward stepwise discriminant function analysis showed that seven of the amino acids analyzed are useful for classifying leaf maturity groupings. Aphid-infested cottonwoods had lower cystine concentrations in phloem sap than aphid-free plants. Salicin concentration was significantly higher in new leaves. Leaf toughness was assessed by lignin density and distance measurements in petiole cross-sections. Rapidly expanding leaves had significantly less lignification and new leaves had shorter distances to the vascular bundles than senescent leaves. These physiological and phytochemical differences among P. deltoides leaf developmental stages may contribute to the leaf stage selection patterns exhibited by the aphid, C. populicola.

Organisms in highly suitable sites generally produce more offspring, and offspring can inherit this suitability by not dispersing far. This combination of spatial selection and spatial inheritance acts to bias the distribution of organisms toward suitable sites and thereby increase mean fitness (i.e., per capita population increase). Thus, population growth rates in heterogeneous space change over time by a process conceptually analogous to evolution by natural selection, opening avenues for theoretical cross-pollination between evolutionary biology and ecology. We operationally define spatial inheritance and spatial selective differential and then combine these two factors in a modification of the breeder's equation, derived from simple models of population growth in heterogeneous space. The modified breeder's equation yields a conservative criterion for persistence in hostile environments estimable from field measurements. We apply this framework for understanding gypsy moth population persistence amidst abundant predators and find that the predictions of the modified breeder's equation match initial changes in population growth rate in independent simulation output. The analogy between spatial dynamics and natural selection conceptually links ecology and evolution, provides a spatially implicit framework for modeling spatial population dynamics, and represents an important null model for studying habitat selection.

Spatial and temporal variation in interactions among plants, other species and the abiotic environment create context-dependency in vegetation pattern. We argue that we can enhance understanding of context-dependency by being more explicit about the kinds of direct interactions that occur among more than two living and non-living entities (i. e., third through nth parties) and formalizing how their combinations create context-dependency using simple conceptual models. This general approach can be translated into field studies of context-dependency in communities by combining: progres- sive sampling of local variation in vegetation pattern that encompasses variation in combinations of direct interactions; spatial and temporal measures of these direct interactions; locally parameterized versions of the conceptual models; and appropriately scaled experiments.

The ecosystem engineering concept focuses on how organisms physically change the abiotic environment and how this feeds back to the biota. While the concept was formally introduced a little more than 10 years ago, the underpinning of the concept can be traced back to more than a century to the early work of Darwin. The formal application of the idea is yielding new insights into the role of species in ecosystems and many other areas of basic and applied ecology. Here we focus on how temporal, spatial and organizational scales usefully inform the roles played by ecosystem engineers and their incorporation into broader ecological contexts. Two particular, distinguishing features of ecosystem engineers are that they affect the physical space in which other species live and their direct effects can last longer than the lifetime of the organism – engineering can in essence outlive the engineer. Together, these factors identify critical considerations that need to be included in models, experimental and observational work. The ecosystem engineering concept holds particular promise in the area of ecological applications, where influence over abiotic variables and their consequent effects on biotic communities may facilitate ecological restoration and counterbalance anthropogenic influences.

Understanding biotic influences on soil processes is a major research frontier made challenging by organismal diversity, variation in distribution, and variety of interactions. Nevertheless, two fundamental influences can be recognized: assimilation/dissimilation (uptake, metabolism, wastes, death) and physical ecosystem engineering (non-assimilatory/dissimilatory, organismally-induced, structurally-mediated changes in energy and materials in the abiotic environment). Because many organisms can engineer soils, predicting their effects is particularly challenging. Here we use Hans Jenny’s State Factor Equation as a flexible, integrative tool for understanding these effects. We distinguish organismal influences via engineering from those of assimilation/dissimilation, explicitly placing engineers into the equation as independent state factors. We then ask: What abiotic state factors does an engineer affect? What relationships among state factors does it change? How does this affect soil processes? Using examples from our work, we illustrate use of this conceptual framework for a physical process—soil erosion; a chemical process—desalination; and a biogeochemical process—denitrification. We show that the framework can be used to: Identify conditions for small or large engineering effects on soil processes; assess engineer impacts on multiple soil processes; compare effects of different engineers on a given soil process; and integrate effects of multiple engineers on a single soil process.

Badano, E. I., Jones, C. G., Cavieres, L. A. and Wright, J. P. 2006. Assessing impacts of ecosystem engineers on community organization: a general approach illustrated by effects of a high-Andean cushion plant. � Oikos 115: 369 � 385. Comparative and integrative tools are of fundamental value in ecology for understanding outcomes of biological processes, and making generalizations and predictions. Although ecosystem engineering has been shown to play a fundamental role in community organization, there are no standardized methods to measure such effects. We present a framework and methodology for assessing the impact of physical ecosystem engineers on three general features of community organization: (1) species richness and composition, (2) stability of richness over time, and (3) dominance patterns of species assemblages. We then apply the framework and methodology to assess the effects of the cushion plant Azorella monantha on high-Andean plant communities on two mountaintops. Substrate temperatures, soil moisture and the availability of mineral nutrient resources were compared between A. monantha and surrounding open areas to ascertain whether cushions altered abiotic environmental conditions, while community analysis assessed changes in species richness, composition and abundances at patch and landscape levels. Cushions thermally buffered temperature extremes and increased soil moisture, but had no detectable effect on soil mineral nutrients. Cushion habitat was not more species rich than surrounding areas, but cushions added new species into the community, altering species composition and markedly enhancing landscape-level richness. Cushions also showed potential for stabilizing species richness over time, and changed patterns of species dominance. Findings were consistent across mountaintops. We evaluate the general utility of the framework and call for its application in other systems as a means to generate comparative data sets for assessing the general effects of ecosystem engineers on community organization.

Tree presence in semiarid ecosystems is generally constrained by insufficient annual rainfall. However, in semiarid Chile, rainforest patches dominated by Aextoxicon punctatum are unexpectedly found on coastal mountaintops (450–600 m) at 30°S, surrounded by a xerophytic vegetation matrix that receives only 147 mm of annual precipitation. It has been proposed that these forests persist as a result of fog-water inputs. If so, then because fog-water deposition is spatially heterogeneous and shows strong edge effects, the potential environmental gradient created by the direction of fog input should determine forest structure and tree regeneration patterns. To investigate this hypothesis, we measured fog inputs, forest structural attributes (age and size distribution, basal area, and coarse woody debris), and tree regeneration in three different habitats: the windward edges (WE), leeward edges (LE), and the interior (center) of rainforest patches varying in area from 0.2 to 22 ha. Mean fog-water input was estimated from passive collectors over 1 year in WE and LE of patches. Tree regeneration was greater in the WE and forest interior (FI) and decreased toward the LE of patches, following a marked pattern of decline in fog inputs. Older trees and coarse woody debris were concentrated in the FI and LE of patches. Tree regeneration and patch structure appear to be largely controlled by fog-input direction and edge effects. We propose that forest patches may be slowly growing toward the incoming fog edge, while dying at the opposite edge.

Geomorphology, vegetation and tidal fluxes are usually identified as the factors introducing variation in the flushing of particulate organic matter (POM) from tidal marshes to adjacent waters. Such variables may, however, be insufficient to explain export characteristics in marshes inhabited by ecosystem engineers that can alter the quantity and quality of POM on the marsh surface that is subject to tidal flushing. In this study we evaluated the balance between transfer of buried sedimentary organic carbon (C) to the marsh surface due to crab excavation (measured from the mounds of sediment excavated from burrows) and outputs of C from the surface due to sediment deposition within crab burrows (estimated from sediment deposited within PVC burrow mimics), in a Southwestern Atlantic salt marsh supporting dense (approximately 70 ind m−2) populations of the crab Chasmagnathus granulatus. C excavation by crabs was much greater than deposition of C within crab burrow mimics. Per area unit estimates of the balance between these two processes indicated that crabs excavated 5.98 g m−2 d−1 and 4.80 mg m−2 d−1 of total and readily (10 d) labile C, respectively. However, sediments excavated by crabs showed a significantly lower content of both total and readily-labile C than sediment collected in burrow mimics. This indicates that ecosystem engineering by burrowing crabs causes a net decrease in the concentration of C in the superficial sediment layers and, thus, an overall decrease in the amount of C that can be washed out of the marsh by tidal action. Incorporating the in situ activities of ecosystem engineers in models of marsh export should enhance understanding of the function of marshes in estuarine ecosystems.

Summary 1 The effect of physical ecosystem engineering – structurally mediated modification of the abiotic environment by organisms – on species richness and composition probably depends on the area of observation and environmental context. 2 We develop specific hypotheses to evaluate how such effects will vary with spatial scale and environmental variability, and test these hypotheses by examining the effects of shrub mounds on the diversity of annual plant communities in the Negev Desert, Israel. 3 We find that previously reported increases in species richness at small spatial scales as a result of shrub mounds are maintained at large spatial scales because shrub mounds host a number of species never found in adjacent crust patches. 4 We find that the magnitude of this effect is dependent on annual precipitation, with shrub mounds having a smaller effect in years with higher precipitation. 5 The results generally support our hypotheses. Given the ubiquity of ecosystem engineering, these results have the potential to explain variation in patterns of ecosystem engineer-induced diversity across ecosystems and environmental gradients. In general, understanding the interactions between resources modified by an ecosystem engineer and the availability of these resources in unmodified habitats aids prediction of the magnitude of the effects of an ecosystem engineer on diversity.

Predation is an important factor in the dynamics of gypsy moth (Lymantria dispar L.) populations, yet predation rates can be difficult to estimate accurately in the field. Biased estimates can result from spatial heterogeneity in risk or from artifacts associated with deploying prey. Here we compare predation rates on freeze-dried gypsy moth pupae affixed with beeswax to pieces of burlap with predation rates on naturally occurring live pupae in the same sites. Daily predation rates, primarily by small mammals, were two to eight times greater for freeze-dried deployed pupae than natural pupae, depending on the year. These results indicate apparent predation rates can be substantially biased by artifacts associated with deployed prey, such as human scent, artificial substrates, or freeze drying. Results from studies using similar methods may provide qualitative comparisons of relative predation risk, but their estimates of absolute predation rates should be interpreted with caution, and attempts should be made to quantify and correct for any resulting bias.

We conducted field experiments in 2002 and 2003 to determine whether the functional response of white-footed mice (Peromyscus leucopus) to gypsy moth (Lymantria dispar) pupae is decelerating (e.g. type 2) or accelerating (e.g. type 3) at low pupal density. In both experiments, live gypsy moth pupae were deployed in June (prior to the appearance of natural pupae) at densities of approximately 1, 8, and 35 pupae per mouse home range in oak-forest grids in upstate New York and monitored over 10 days for signs of predation. Pupae were deployed 1.5-m high on tree boles in 2002, whereas in 2003 the three density treatments were crossed with a height treatment: ground level vs 1.5-m high. The relationship between daily predation rate (proportion of pupae eaten/day) and pupal density was significantly positive in both years, indicating an accelerating functional response. Daily predation rates on ground-level pupae were substantial in the lowest density treatment, suggesting that dense mouse populations could drive gypsy moths to extinction despite an accelerating functional response. Daily predation rates on elevated pupae increased over several days in the medium and high density treatments, suggesting a lagged shift from ground- to tree-level foraging by mice. Within the high-density treatments, predation rates on pupae showed no apparent relationship with the number of pupae on a tree. Our results disagree qualitatively with simple models of type 3 functional response, in which predation rate of prey approaches zero as prey approach extinction, and support the contention that an accelerating functional response alone may be insufficient to prevent prey extinction.

Ecosystem engineering—the physical modification of habitats by organisms—can create patches with altered species richness relative to adjacent, unmodified patches. The effect of ecosystem engineering on patch-scale species richness is likely to be difficult to predict from the identity of the engineer, the resources altered as a result of engineering, or the identities of the affected species. Here we develop a simple conceptual model that predicts the effects of ecosystem engineers on species richness based on how the habitat modifications caused by engineers affect primary productivity, assuming a hump-shaped relationship between productivity and species richness. We review data from 35 studies that contained 60 comparisons of species richness on patches that had been modified by ecosystem engineers vs. unmodified patches. We found no general patterns in whether species richness at the patch scale was increased or decreased by ecosystem engineering. However, 14 of these studies also contained data on pr...

Ecosystem engineers, organisms that modify the environment, have the potential to dramatically alter ecosystem structure and function at large spatial scales. The degree to which ecosystem engineering produces large-scale effects is, in part, dependent on the dynamics of the patches that engineers create. Here we develop a set of models that links the population dynamics of ecosystem engineers to the dynamics of the patches that they create. We show that the relative abundance of different patch types in an engineered landscape is dependent upon the production of successful colonists from engineered patches and the rate at which critical resources are depleted by engineers and then renewed. We also consider the effects of immigration from either outside the system or from engineers that are present in non-engineered patches, and the effects of engineers that can recolonize patches before they are fully recovered on the steady state distribution of different patch types. We use data collected on the population dynamics of a model engineer, the beaver, to estimate the per-patch production rate of new colonists, the decay rate of engineered patches, and the recovery rate of abandoned patches. We use these estimated parameters as a baseline to determine the effects of varying parameters on the distribution of different patch types. We suggest a number of hypotheses that derive from model predictions and that could serve as tests of the model.

There is considerable interest in determining whether the species richness of communities is determined by forces controlling dispersal into patches that operate at the landscape scale, or forces controlling persistence that act at the local scale. Understanding the relative importance of these two classes of factors in controlling within-patch species richness is particularly important when patches are created via ecosystem engineering. In such cases, factors affecting the population dynamics or behavior of a single species could indirectly affect species richness if richness is controlled primarily by landscape-level factors. We used a combination of experimental mesocosms and field observations to determine whether species richness in beaver wetlands in the Adirondack Mountains (New York) is more strongly controlled by the position of the wetland in the landscape or by within-wetland hydrology. Drainage rate had a significant effect on both richness and composition in mesocosms, with well-drained treatments having significantly higher richness than poorly drained treatments. Seed germinated from the seed bank in sediments collected from different ponds showed relatively small differences in richness or community composition in mesocosms, suggesting a comparatively small effect of dispersal limitation on species richness. Experimental results were mirrored in a survey of 14 meadows over two years, which indicated that variability in water table depth was consistently a significant predictor of species richness, while meadow area and isolation showed little relation to richness. The survey also suggested that the number of years since beaver had abandoned a site was a significant predictor of the number of species found in beaver meadows. The results indicate that species richness in beaver meadows is strongly controlled by local factors, but that the population dynamics of beaver could also potentially affect species richness by altering the age distribution of meadows across the landscape.

Plants in urban ecosystems are exposed to many pollutants and higher temperatures, CO2 and nitrogen deposition than plants in rural areas. Although each factor has a detrimental or beneficial influence on plant growth, the net effect of all factors and the key driving variables are unknown. We grew the same cottonwood clone in urban and rural sites and found that urban plant biomass was double that of rural sites. Using soil transplants, nutrient budgets, chamber experiments and multiple regression analyses, we show that soils, temperature, CO2, nutrient deposition, urban air pollutants and microclimatic variables could not account for increased growth in the city. Rather, higher rural ozone (O3) exposures reduced growth at rural sites. Urban precursors fuel the reactions of O3 formation, but NO(x) scavenging reactions resulted in lower cumulative urban O3 exposures compared to agricultural and forested sites throughout the northeastern USA. Our study shows the overriding effect of O3 despite a diversity of altered environmental factors, reveals 'footprints' of lower cumulative urban O3 exposures amidst a background of higher regional exposures, and shows a greater adverse effect of urban pollutant emissions beyond the urban core.

Mollusk shells are abundant, persistent, ubiquitous physical structures in aquatic habitats. Using an ecosystem engineering perspective, we identify general roles of mollusk shell production in aquatic ecosystems. Shells are substrata for attachment of epibionts, provide refuges from predation, physical or physiological stress, and control transport of solutes and particles in the benthic environment. Changes in availability of these resources caused by shell production have important consequences for other organisms. Colonization of shelled habitat depends on individual shell traits and spatial arrangement of shells, which determine access of organisms to resources and the degree to which biotic or abiotic forces are modulated. Shell production will increase species richness at the landscape level if shells create resources that are not otherwise available and species are present that use these resources. Changes in the availability of resources caused by shells and the resulting effects on other organisms have both positive and negative feedbacks to these engineers. Positive feedbacks appear to be most frequently mediated by changes in resource availability, whereas negative feedbacks appear to be most frequently mediated by organisms. Given the diversity of species that depend upon resources controlled by shells and rapid changes in global shell production that are occurring due to human activities, we suggest that shell producers should not be neglected as a targets of conservation, restoration and habitat management.

Isoprene is emitted from numerous plant species and profoundly influences tropospheric chemistry. Due to the short lifetime of isoprene in the atmosphere, developing an understanding of emission patterns at small time scales is essential for modeling regional atmospheric chemistry processes. Previous studies suggest that diurnal fluctuations in iso- prene emission may be substantial, leading to inaccuracies in emission estimates at larger scales. We examined diurnal patterns in the basal emission rate of isoprene in red oak (Quercus rubra), eastern cottonwood (Populus deltoides), and eucalyptus (Eucalyptus sal- igna) and the influence of light and temperature on the magnitude of these diurnal patterns. Maximum diurnal increases in isoprene emission were large in cottonwood (45%) and oak (25%), with increases exceeding 100% in 1-yr-old cottonwoods. Eucalyptus showed no diurnal variation in emission. All species showed diurnal declines in photosynthesis. Across species, there was a positive correlation between maximum diurnal change in both isoprene emission and photosynthesis. The magnitude of diurnal increase in isoprene emission varied when individual cottonwoods were sampled repeatedly over three days. Temperature and light history, integrated from 1 to 48 hours prior to measurement, did not explain these variations in diurnal emission. Diurnal increases in emission were present when plants were shaded to

It is well recognized that host-specialized folivores prefer to feed on young in com- parison to old leaves. However, the capacity of young leaf feeders to track speciÞc leaf developmental stages has not been clearly demonstrated. Using three insect folivores and two plant species, we show that nitrogen (N) fertilization changes leaf development and that herbivores track these changes in leaf development. Nicotiana tabacum L. and Populus deltoides Bartram were fertilized at two and three rates of N addition, respectively. Plants with high rates of N supply had faster growth, greater leaf area, and faster leaf initiation rates than plants receiving low rates of N supply. Most important, all N addition treatments changed the position on the stem where leaves reached 95% full expansion; with leaves on plants receiving high rates of N addition reaching 95% full expansion further from the stem apex (e.g., leaf position 5 versus leaf position 3). Feeding assays with Trichoplusia ni Hubner on N. tabacum, and Plagiodera versicolora Laicharting and Chrysomela scripta F. on P. deltoides showed that these insect species preferred to feed on leaves at a speciÞc degree of leaf expansion. This preference was exhibited independent of leaf position and N addition rate.

All living organisms modify their biotic and abiotic environment. Niche construction theory posits that organism-mediated modifications to the environment can change selection pressures and influence the evolutionary trajectories of natural populations. While there is broad support for this proposition in general, there is considerable uncertainty about how niche construction is related to other similar concepts in ecology and evolution. Comparative studies dealing with certain aspects of niche construction are increasingly common, but there is a troubling lack of experimental tests of the core concepts of niche construction theory. Here, we propose an operational framework to evaluate comparative and experimental evidence of the evolutionary consequences of niche construction, and suggest how such research can improve our understanding of ecological and evolutionary dynamics in ecosystems. We advocate for a shift toward explicit experimental tests of how organismmediated environmental change can influence the selection pressures underlying evolutionary responses, as well as targeted field-based comparative research to identify the mode of evolution by niche construction and assess its importance in natural populations. © 2014 by the Ecological Society of America. ispartof: Ecological Monographs vol:84 issue:2 pages:245-263 status: published

Why do microbes make secondary products? That question has been the subject of intense debate for many decades. There are two extreme opinions. Some argue that most secondary metabolites play no role in increasing the fitness of an organism. The opposite view, now widely held, is that every secondary metabolite is made because it possesses (or did possess at some stage in evolution) a biological activity that endows the producer with increased fitness. These opposing views can be reconciled by recognizing that, because of the principles governing molecular interactions, potent biological activity is a rare property for any molecule to possess. Consequently, in order for an organism to evolve the rare potent, biologically active molecule, a great many chemical structures have to be generated, most of which will possess no useful biological activity. Thus, the two sides of the debate about the role and evolution of secondary metabolism can be accommodated within the view that the possession of secondary metabolism can enhance fitness, but that many products of secondary metabolism will not enhance the fitness of the producer. It is proposed that secondary metabolism will have evolved such that traits that optimize the production and retention of chemical diversity at minimum cost will have been selected. Evidence exists for some of these predicted traits. Opportunities now exist to exploit these unique properties of secondary metabolism to enhance secondary product diversity and to devise new strategies for biotransformation and bioremediation.

Summary Experiments were carried out to determine the effects of elevated atmospheric carbon dioxide (CO2) on phenolic biosynthesis in four plant species growing over three generations for nine months in a model plant community. Results were compared to those obtained when the same species were grown individually in pots in the same soils and controlled environment. In the model herbaceous plant community, only two of the four species showed any increase in biomass under elevated CO2, but this occurred only in the first generation for Spergula arvensis and in the second generation for Poa annua. Thus, the effects of CO2 on plant biomass and carbon and nitrogen content were species- and generation-specific. The activity of the principle phenolic biosynthetic enzyme, phenylalanine ammonia lyase (PAL), increased under elevated CO2 in Senecio vulgaris only in Generation 1, but increased in three of the four plant species in Generation 2. There were no changes in the total phenolic content of the plants, except for P. annua in Generation 1. Lignin content decreased under elevated CO2 in Cardamine hirsuta in Generation 1, but increased in Generation 2, whilst the lignin content of P. annua showed no change, decreased, then increased in response to elevated CO2 over the three generations. When the species were grown alone in pots, elevated CO2 increased PAL activity in plants grown in soil taken from the Ecotron community after nine months of plant growth, but not in plants grown in the soil used at the start of the experiment (‘initial' soil). In P. annua, phenolic biosynthesis decreased under elevated CO2 in initial soil, and in both P. annua and S. vulgaris there was a significant interaction between effects of soil type and CO2 level on PAL activity. In this study, plant chemical composition altered more in response to environmental factors such as soil type than in response to carbon supply. Results were species-specific and changed markedly between generations.

We examined whether the eAects of elevated CO2 on growth of 1-year old Populus deltoides saplings was a function of the assimilation responses of particular leaf developmental stages. Saplings were grown for 100 days at ambient (approximately 350 ppm) and ele- vated (ambient + 200 ppm) CO2 in forced-air green- houses. Biomass, biomass distribution, growth rates, and leaf initiation and expansion rates were unaAected by elevated CO2. Leaf nitrogen (N), the leaf C:N ratio, and leaf lignin concentrations were also unaAected. Carbon gain was significantly greater in expanding leaves of saplings grown at elevated compared to ambient CO2. The Rubisco content in expandingleaves was not aAected by CO2 concentration. Carbon gain and Rubisco content were significantly lower in fully expanded leaves of sap- lings grown at elevated compared to ambient CO2, indi- cating CO2-induced down-regulation in fully expanded leaves. Elevated CO2 likely had no overall eAect on bio- mass accumulation due to the more rapid decline in car- bon gain as leaves matured in saplings grown at elevated compared to ambient CO2. This decline in carbon gain has been documented in other species and shown to be related to a balance between sink/source balance and acclimation. Our data suggest that variation in growth responses to elevated CO2 can result from diAerences in leaf assimilation responses in expanding versus expanded leaves as they develop under elevated CO2.

Isoprene emission from plants is one of the principal ways in which plant processes alter atmospheric chemistry. Despite the importance of this process, few long-term controls over basal emission rates have been identified. Stress-induced changes in carbon allocation within the entire plant, such as those produced by defoliation, have not been examined as potential mechanisms that may control isoprene production and emission. Eastern cottonwood (Populus deltoides) saplings were partially defoliated and physiological and growth responses were measured from undamaged and damaged leaves 7 days following damage. Defoliation reduced isoprene emission from undamaged and damaged leaves on partially defoliated plants. Photosynthetic rates and leaf carbon and nitrogen pools were unaffected by damage. Photosynthetic rate and isoprene emission were highly correlated in undamaged leaves on undamaged plants and damaged leaves on partially defoliated plants. There was no correlation between photosynthetic rate and isoprene emission in undamaged leaves on partially defoliated plants. Isoprene emission was also highly correlated with the number of source leaves on the apical shoot in damage treatments. Increased carbon export from source leaves in response to defoliation may have depleted the amount of carbon available for isoprene synthesis, decreasing isoprene emission. These results suggest that while isoprene emission is controlled at the leaf level in undamaged plants, emission from leaves on damaged plants is controlled by whole-branch allocation patterns.

The carbon–nutrient balance hypothesis (CNBH) predicts that shading should increase leaf palatability to herbivores by decreasing concentrations of carbon (C) -based chemical defenses and increasing nitrogen (N). We measured cottonwood (Populus deltoids) growth, leaf chemistry, and beetle (Plagiodera versicolora) feeding preferences on saplings grown in either continuous high (HH) or low (LL) light, and saplings switched from high to low (HL) or low to high (LH) light for nine days. As expected, based on the CNBH, shading increased total N and decreased total phenol glycoside (C-based secondary metabolites) concentrations in plants from all shade treatments (LL, HL, and LH), relative to HH plants, with plant growth and gross leaf chemistry being affected by initial and final light regime. In contrast, while specific phenol glycoside concentrations were affected by the initial and final light regime, they also showed an initial × final light interaction. Beetles tended to prefer LL to HH plants. Beetles unexpectedly preferred HH to either HL or LH switched plants, most likely because high concentrations of a specific phenol glycoside – salicin – occurred in both switched treatments and inhibited beetle feeding. Plant chemical allocation during light acclimation led to unpredictable changes in specific C-based compounds, even though plant growth and gross chemistry conformed to expectations for shading effects and the CNBH. The response of this herbivore to altered concentrations of a specific compound confounded predictions based on average dynamics of suites of chemicals. Our findings may help explain why relationships between light availability and herbivory in field studies, where light varies on many time scales, can differ from those predicted by the CNBH. Understanding both dynamic plant chemical responses to altered resource availability and controls over allocation to specific compounds would likely enhance future predictability of specific environment-plant-herbivore interactions.

In eastern U.S. oak forests, defoliation by gypsy moths and the risk of Lyme disease are determined by interactions among acorns, white-footed mice, moths, deer, and ticks. Experimental removal of mice, which eat moth pupae, demonstrated that moth outbreaks are caused by reductions in mouse density that occur when there are no acorns. Experimental acorn addition increased mouse density. Acorn addition also increased densities of black-legged ticks, evidently by attracting deer, which are key tick hosts. Mice are primarily responsible for infecting ticks with the Lyme disease agent. The results have important implications for predicting and managing forest health and human health.

Lyme disease and gypsy moth outbreaks plague many temperate oak forests. Over the past decade, we have developed models and hypotheses designed to allow us to predict irruptions of both gypsy moths and the tick vector of Lyme disease. We have documented a web of connections involving mast production by oak trees, population responses by white-footed mice, habitat selection by white-tailed deer, and population dynamics of both tick parasites and defoliating insects. In patchy landscapes typical of the northeastern U.S., dispersal by mice, deer, and attached ticks between oak and nonoak forests creates dynamics that would not be predictable by focusing on a single patch type. We would not have uncovered these interactions without adopting a research approach that comprised: (1) the inclusion of diverse taxa of animals, plants, and microbes; (2) the integration of individual, population, community, and ecosystem levels of organization; (3) the incorporation of more than one patch type in a heterogeneous landscape; and (4) a combination of long-term monitoring and manipulative field experiments.

International audience; Ecosystem engineering, the physical modification of the environment by organisms, is a common and often influential process whose significance to food web structure and dynamics is largely unknown. In the light of recent calls to expand food web studies to include non-trophic interactions, we explore how we might best integrate ecosystem engineering and food webs. We provide rationales justifying their integration and present a provisional framework identifying how ecosystem engineering can affect the nodes and links of food webs and overall organization; how trophic interactions with the engineer can affect the engineering; and how feedbacks between engineering and trophic interactions can affect food web structure and dynamics. We use a simple integrative food chain model to illustrate how feedbacks between the engineer and the food web can alter 1) engineering effects on food web dynamics, and 2) food web responses to extrinsic environmental perturbations. We identify four general challenges to integration that we argue can readily be met, and call for studies that can achieve this integration and help pave the way to a more general understanding of interaction webs in nature. Synthesis All species are affected by their physical environment. Because ecosystem engineering species modify the physical environment and belong to food webs, such species are potentially one of the most important bridges between the trophic and non-trophic. We examine how to integrate the so far, largely independent research areas of ecosystem engineering and food webs. We present a conceptual framework for understanding how engineering can affect food webs and vice versa, and how feedbacks between the two alter ecosystem dynamics. With appropriate empirical studies and models, integration is achievable, paving the way to a more general understanding of interaction webs in nature.

Fluxes of energy, materials and organisms among ecosystems are consequences of their openness to exchange and lead to the consideration of reciprocal connections among adjacent ecosystems. Reciprocal connectivity may have implications for ecosystem functioning and manage- ment but it is generally studied only for a single factor, rather than for multiple factors. We examined the extent to which these fluxes may apply at the landscape scale for 3 ecosystems: mangrove forests, seagrass beds and coral reefs. From a literature review and analysis, we semi- quantitatively assessed fluxes based on attenuation of wave height and exchanges of sediments, nutrients and al- givores. We found that coral reefs and seagrass beds significantly attenuated wave height and that this effect depended on specific physical conditions. In the case of coral reefs, the attenuation ca- pacity depended on the section of the reef the wave breached, whilst for seagrass beds, we hypoth- esised that the density of the plants was the controlling factor. Mangrove forests' ability to reduce sediment fluxes was related to the mangrove forest area. Seagrass plants have a capacity to decrease sediments in the water column. Both mangrove forests and seagrass beds retained nutri- ents within the ecosystems, which was a positive interaction. Isolated reefs showed a decrease (30 to 95%) in algivore biomass compared to situations where the 3 habitats were in proximity to each other. The findings show that there is potential for reciprocal connections among coastal eco- systems. Our results indicate that these exchanges at the ecosystem scale can be placed into the context of facilitation in the field of community ecology. Future research should focus on which natural and anthropogenic factors determine reciprocal facilitation between these ecosystems and determine how ecosystem-based management can be improved with this knowledge. The consid- erable potential for reciprocal facilitation implies that ecosystem managers may need to place greater emphasis on the landscape scale.

Progress in the study of ecosystem impacts of invasive species can be facilitated by moving from the evaluation of invasive species impacts on particular processes to the analysis of their overall effects on ecosystem functioning. Here we propose an integrative ecosystem-based approach to the analysis of invasive species impacts that is based on an understanding of the general mechanistic links between biotic factors, abiotic factors, and processes in ecosystems. Two general kinds of biotic mediation – direct and indirect – and two general mechanisms of invasive species impact – assimilatory–dissimilatory (uptake and release of energy and materials) and physical ecosystem engineering (physical environmental modification by organisms) – are most relevant. By combining the biotic mediation pathways and the general mechanisms, four general situations emerge that characterize a great many of the impacts invasive species can have on ecosystem processes. We propose ways to integrate these distinctive impacts into general mechanistic representations that link ecosystem processes with changes in biotic and abiotic states (changes in structure, composition, amount, process rates, etc.). In turn, these help generate predictions about the interplay of invasive species and other drivers of ecosystem processes that are of particular relevance to ecosystems where invasive species co-occur with other anthropogenic impacts., We thank Financial support from CONICET, Argentina (PIP112-200801-00732; JLG), the Cary Institute of Ecosystem Studies (CGJ, JLG), the Portuguese Foundation for the Science and the Technology (RS) and COMPETE funds through the Project ECOIAS (PTDC/AACAMB/116685/2010) (RS). Contribution to the programs of GrIETA and the Cary Institute of Ecosystem Studies.

Physical ecosystem engineers are organisms that directly or indirectly control the availability of resources to other organisms by causing physical state changes in biotic or abiotic materials. Physical ecosystem engineering by organisms is the physical modification, maintenance, or creation of habitats. Ecological effects of engineers on many other species occur in virtually all ecosystems because the physical state changes directly create nonfood resources such as living space, directly control abiotic resources, and indirectly modulate abiotic forces that, in turn, affect resource use by other organisms. Trophic interactions and resource competition do not constitute engineering. Engineering can have significant or trivial effects on other species, may involve the physical structure of an organism (like a tree) or structures made by an organism (like a beaver dam), and can, but does not invariably, have feedback effects on the engineer. We argue that engineering has both negative and positive effects on species richness and abundances at small scales, but the net effects are probably positive at larger scales encompassing engineered and nonengineered environments in ecological and evolutionary space and time. Models of the population dynamics of engineers suggest that the engineer/habitat equilibrium is often, but not always, locally stable and may show long-term cycles, with potential ramifications for community and ecosystem stability. As yet, data adequate to parameterize such a model do not exist for any engineer species. Because engineers control flows of energy and materials but do not have to participate in these flows, energy, mass, and stoichiometry do not appear to be useful in predicting which engineers will have big effects. Empirical observations suggest some potential generalizations about which species will be important engineers in which ecosystems. We point out some of the obvious, and not so obvious, ways in which engineering and trophic relations interact, and we call for greater research on physical ecosystem engineers, their impacts, and their interface with trophic relations.

popular characterization of ecological systems is that everything is connected to everything else. Although in some metaphysical sense it may be true that influences experienced by a particular species are transmitted to all other species in the ecosystem, such pervasive connections have not been demonstrated scientifically. Instead, the focus of community ecology has been on pairwise interactions between species. The paradigm has been that the determinants of community structure can be elucidated by studies of direct effects of populations on one or a few other populations (Kareiva 1994). To identify the role of predation or competition in structuring ecological communities, typically a predator or competitor is removed, and the responses of prey or other competitors are monitored (Connell 1983, Menge and Sutherland 1976, Schoener 1983, Sih et al. 1985). These studies reveal the importance of direct effects in ecological communities. However, such experiments often produce unexpected results, In oak forests, both

We developed a fertilization technique that results in the control, and maintenance at defined rates and levels, of growth and tissue composition of plants of different sizes and developmental stages growing at exponential and nonexponential rates in solid media under naturally fluctuating light and temperature regimes. Clonal cottonwood (Populus deltoides Bartr.) saplings were grown in sand. Low concentrations of nutrient solution were added daily at different constant exponentially increasing rates for 20-30 days to produce plants with different growth rates and tissue nutrient composition. Matching nutrient supply to measured growth demand by bootstrapping, where bootstrapping is the use of an iterative equation that calculates demand from either actual or desired growth rates, maintained these differences for 20-40 days. Nutrient additions controlled growth of saplings with growth rates between 2.0 and 4.0% day(-1), heights between 13.9 and 37.5 cm, dry weights between 0.70 and 3.90 g, leaf nitrogen contents between 1.2 and 3.9%, and leaf carbon/nitrogen ratios between 42.1 and 12.5. The technique was reproducible in a greenhouse without temperature, humidity, or light control, and is easily modified to suit different plant species, plants of various sizes, and various growing conditions.

The leaves of plants in nature are commonly subjected to damage from a wide variety of agents, including herbivory, air pollutants, and simple physical damage. Despite the attention paid to damage effects on living plants, the potential effects on the quality of litter derived from damaged leaves has not been considered. We used controlled laboratory assays of decomposition to show that both ozone (0.2 mL/m3, 4 h) and mite damage, but not ultraviolet radiation (UV-B) exposure, to living leaves of cottonwood plants resulted in a decrease in decomposition rate of litter derived from damaged leaves. De- composition rates were -50% slower for litter from damaged plants, and there was a twofold increase in the refractory fraction. Contrary to expectation, there was a negative relationship between rate of decomposition and litter nitrogen content. Our finding of slow decompo- sition of high-nitrogen litter is explained by a general mechanism whereby cellular damage causes increases in complex phenolic material. Such materials can lead to reductions in decomposition and binding of available nitrogen. We suggest that this mechanism can translate a common occurrence, damage by a diversity of processes, into long-term and possibly large-scale alterations in detritus processing.