Timothy R. Seastedt

University of Colorado Boulder | CUB · Department of Ecology and Evolutionary Biology (EBIO)

Patterns of soil bacterial richness using operational taxonomic units (OTUs) and abundance of bacterial groups (phylum or class) were studied in relation to plant richness and soil characteristics in the alpine at Niwot Ridge, Colorado, U.S.A. The study used a landscape gradient and snow fence in addition to plots amended with nitrogen (N). Bacteri...

Aims Global change agents are creating novel climatic and edaphic conditions that may favor introduced species. We attempted to identify mechanisms and impacts of Bromus tectorum invasion in the Colorado Front Range mixed-grass prairie under changing conditions. Methods We conducted an in-situ experiment with three removal treatments (removal of B...

Global change drivers are altering climatic and edaphic conditions of ecosystems across the globe, and we expect novel plant communities to become more common as a result. In the Colorado Front Range, compositional changes have occurred in the mixed-grass prairie plant community in conjunction with shifts in winter precipitation and atmospheric nit...

Bacterial community composition and diversity was studied in alpine tundra soils across a plant species and moisture gradient in 20 yr-old experimental plots with four nutrient addition regimes (control, nitrogen (N), phosphorus (P) or both nutrients). Different bacterial communities inhabited different alpine meadows, reflecting differences in moi...

The exotic grass Bromus tectorum (cheatgrass) is a ubiquitous invader in the western USA. Cheatgrass is a proficient competitor, frequently displacing native plants, forming monotypic stands and reducing biodiversity in ecosystems it invades. Our experiment tested whether short-term soil modification by cheatgrass and a predominant native grass, Pa...

Background: Gradients in the amounts and duration of snowpack and resulting soil moisture gradients have been associated with different plant communities across alpine landscapes.Aims: The extent to which snow additions could alter plant community structure, both alone and in combination with nitrogen (N) and phosphorus (P) additions, provided an e...

Background: The extent to which nutrient availability influences plant community composition and dynamics has been a focus of ecological enquiry for decades.Aims: Results from a long-term nitrogen (N) and phosphorus (P) addition experiment in alpine tundra were used to evaluate the importance of the two nutrients in structuring plant communities in...

Background: Current understanding of treeline or forest-alpine ecotone (FAE) dynamics does not fully explain past and present FAE patterns and their underlying processes, nor allow prediction of their response to climate change.Aims: We address the overarching hypothesis that the FAE is a mosaic of distinct landscape units of vegetation and landfor...

Background: There is a paucity of information for mountain catchments, and in particular a lack of long-term data collection in alpine areas.Aims: The focus of this special issue is to synthesize alpine research undertaken in the last 20 years at high altitude research sites that comprise the Niwot Ridge Long Term Ecological Research (NWT LTER) pro...

Although much research has been conducted to measure vegetation response to directional shifts in climate change drivers, we know less about how plant communities will respond to extreme events. Here, we evaluate the response of a grassland community to an unprecedented 43 cm rainfall event that occurred in the Front Range of Colorado in September,...

In a complex urban-impacted landscape, native black-tailed prairie dogs (Cynomys ludovicianus) amplify the trajectory at which grassland plant communities deviate from historical configurations. Prairie dog removal has been proposed as an intervention method based upon the premise that removing a major directional driver of change will initiate the...

Shifting precipitation patterns resulting from global climate change will influence the success of invasive plant species. In the Front Range of Colorado, Bromus tectorum (cheatgrass) and other non-native winter annuals have invaded grassland communities and are becoming more abundant. As the global climate warms, more precipitation may fall as rai...

Ustilago bullata is a fungal pathogen that infects grasses in western North America. It infects the grass Bromus tectorum, sometimes at epidemic levels, and has been considered as a biocontrol agent in regions where B. tectorum is invasive. During a study of the effects of variation in precipitation on B. tectorum demography in Colorado, USA, we ob...

The reality confronting ecosystem managers today is one of heterogeneous, rapidly transforming landscapes, particularly in the areas more affected by urban and agricultural development. A landscape management framework that incorporates all systems, across the spectrum of degrees of alteration, provides a fuller set of options for how and when to i...

Contents 'Summary'I.'Introduction'II.'The science of biological control'III.'Trajectories of biological control efforts'IV.'Current research'V.'Social dimensions of biological control'VI.'The future for the application of biological control of plant invasions' 'Acknowledgements' ReferencesSummaryThe science of finding, testing and releasing herbivo...

Background/Question/Methods Over the last several decades, the Front Range of Colorado has been experiencing increased invasion of exotic cool season plants. Among the most problematic of these species is Bromus tectorum, an annual grass with severe impacts on arid and semi-arid ecosystems of the Intermountain West but not historically abundant i...

Background/Question/Methods Plague, caused by Yersinia pestis, is a significant disturbance that results in periodic epizootics on black-tailed prairie dog (Cynomys ludovicianus) colonies. Changes in vegetation on prairie dog colonies before and after plague in urban and suburban areas may exhibit unusual patterns because urban areas experience a...

While modelling efforts suggest that invasive species will track climate changes, empirical studies are few. A relevant and largely unaddressed research question is ‘How will the presence of exotic species interact with precipitation change to alter ecosystem structure and function?’ We studied the effects of changes in seasonal timing of precipita...

Cheatgrass (Bromus tectorum) and other exotic winter-active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre-empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4-year stu...

We examined the presence of the exotic weevil Rhinocyllus conicus Fröelich on native thistles at high elevations in the Rocky Mountains of Colorado. We tested whether the distribution of R. conicus was related to elevation by performing 2 separate studies. First, transects along an elevation gradient were sampled in Rocky Mountain National Park and...

Historically, prairie dogs (Cynomys spp.) have been considered essential keystone species of western United States grassland ecosystems because they provide unique services and increase vegetation community richness, evenness, and diversity. However, the effects of black-tailed prairie dogs (Cynomys ludovicianus) on lands adjacent to or surrounded...

Biological control is an essential component of sustainable crop management that attempts to maximize one ecosystem service—production of food and fiber—while concurrently contributing in a positive manor to other ecosystem services required for human health and wellbeing. Biological control techniques are both plant species and site specific, so e...

Predicting site vulnerability to nonnative plant establishment remains a difficult goal. Seedling survival is an important component of population dynamics and can affect the success of control strategies. Field manipulations allow potential causal mechanisms of site vulnerability to be evaluated under realistic environmental conditions. We conduct...

One significant unanswered question about biotic responses to climate change is how plant communities within topographically complex landscapes will respond to climate change. Alpine plant communities are strongly influenced by topographic microclimates which can either buffer or compound the effects of more regional climatic changes. Here, we anal...

Background/Question/Methods Over the last several decades, the Front Range of Colorado has been experiencing increased invasion of exotic cool-season grasses and forbs. Over the same time period, winter precipitation and nitrogen (N) availability have increased due to climate change and anthropogenic nitrogen deposition. To determine whether thes...

Background/Question/Methods Both moisture and nutrient limitation are known to influence plant community composition and both variables are components of global environmental change. Alpine communities are thought to be particularly sensitive to changes in the timing of snowmelt. Previous studies have demonstrated changes in productivity and dive...

Background/Question/Methods Shifts in precipitation patterns resulting from global climate change have the potential to influence success of invasive plant species. In the Front Range of Colorado, Bromus tectorum (cheatgrass) and other non-native winter annuals are invading grassland communities. As the climate warms, yearly precipitation may shi...

The literature is inconsistent regarding the ability of herbivory to control or reduce densities of a major invasive plant species of North America, spotted knapweed (Centaurea stoebe). Here, findings from experimental manipulations of spotted knapweed and long-term monitoring of seed production and insect abundance were used to parameterize a popu...

Background and aims Vegetation can have direct and indirect effects on soil nutrients. To test the effects of trees on soils, we examined the patterns of soil nutrients and nutrient ratios at two spatial scales: at sites spanning the alpine tundra/subalpine forest ecotone (ecotone scale), and beneath and beyond individual tree canopies within the t...

Throughout the history of invasion biology, there has been long-standing and sometimes fierce debate on the perception and management of non-native species. Some argue that non-native species are universally undesirable for their unpredictability and their ability to at times dramatically disrupt native species and systems. Others argue for an appr...

39.1 INTRODUCTION Scientists and conservation advocates have acknowledged the need for actions that contribute to local, regional and global sustainability (Clark and Dickson 2003 ; Rockström et al. 2009). The sustainability mission involves using the environment to meet the needs of society without jeopardizing resources needed by future generatio...

This chapter provides a framework that helps managers, whether scientists or stewards, navigate the decisions that lead to new management approaches in hybrid and novel ecosystems. It first presents a decision-making flowchart that can be used as roadmap to navigate possible management actions. The chapter then explores the role of ecological and s...

This chapter describes a case study where a transformation is occurring as a result of events operating on an ecosystem already undergoing responses to a suite of global environmental change (GEC) factors. In the Front Range of Colorado, intensive grazing by black-tailed prairie dogs (Cynomys ludovicianus) in urban and suburban landscapes is intera...

This chapter considers the case of prairie dogs along the Colorado Front Range to illustrate the challenges of managing possible novel ecosystem as highlighted by the decision framework. It presents a case where stakeholders asked managers to preserve historically present flora and fauna under altered environmental constraints. In particular, publi...

We discuss the adoption of a bottom-up, resource-based vulnerability approach in evaluating the effect of climate and other environmental and societal threats to societally critical resources. This vulnerability concept requires the determination of the major threats to local and regional water, food, energy, human health, and ecosystem function re...

Alpine ecosystems are thought to be particularly sensitive to small environmental changes in climate and other parameters due to the plants and soil organisms being on the edge of environmental tolerances. Snow distribution is critical to microclimate in the alpine, affecting soil temperature, growing season duration, and nutrient cycling. Moreover...

Unlabelled: • Premise of the study: Human nitrogen (N) inputs to terrestrial ecosystems have greatly increased in recent years and may have important consequences for plant growth, reproduction, and defense. Although numerous studies have investigated the effects of nitrogen addition on plants, few have examined both above- and belowground respo...

Background/Question/Methods Prairie dogs (Cynomes spp.) were historically essential to the health of prairie ecosystems by acting as both a keystone species and transforming the landscape as ecosystem engineers. However, with increasing anthropogenic activities in the west, the positive role that prairie dogs once played may have changed. Prair...

Background/Question/Methods Shifts in precipitation patterns resulting from global climate change are expected to affect composition and ecosystem function of plant communities. A very relevant, and largely unaddressed, research question is: how will the presence of non-native species interact with climate change to alter ecosystem structure, fun...

Background/Question/Methods Disturbance is a key factor for providing invasive species a foothold into a new environment. However, not all sites are equally vulnerable to invasion. Seedling germination and establishment studies have been used to examine the success of a wide variety of species in native and non-native environments. Manipulative f...

Background/Question/Methods Recognizing that degradation of mountain ecosystems affects nearly half the world’s population, the United Nations declared 2002 the International Year of Mountains. We published Rocky Mountain Futures, An Ecological Perspective that same year in an attempt to look objectively at the cumulative ecological effects of hu...

Background/Question/Methods A status report and prognosis for grasslands of the Rocky Mountain region was presented over a decade ago. The term ‘novel ecosystem’ had yet to appear, but the grasslands were identified using terminology now identifying these communities that contain both native and non-native species and exhibit biogeochemical chara...

Plant performance is influenced by both top-down (e.g., herbivores) and bottom-up (e.g., soil nutrients) controls. Research investigating the collective effects of such factors may provide important insight into the success and management of invasive plants. Through a combination of observational and experimental field studies, we examined top-down...

The US National Science Foundation–funded Long Term Ecological Research (LTER) Network supports a large (around 240) and diverse portfolio of long-term ecological experiments. Collectively, these long-term experiments have (a) provided unique insights into ecological patterns and processes, although such insight often became apparent only after man...

North American and European grasslands consist of relatively young communities that have evolved under human influences. These communities are uniformly sensitive to top-down controls and exhibit rapid changes in plant composition when the intensity and frequency of these controls are altered. These changes are intensifying due to the suite of glob...

Background/Question/Methods Nitrogen (N) deposition can affect soil microbial community structure and function via a variety of mechanisms. Direct effects can be caused through increases in the substrate pool for nitrifiers, denitrifiers and for general microbial growth and assimilation. Indirect effects can be mediated through changes in the qua...

Background/Question/Methods Cheatgrass (Bromus tectorum) and other non-native winter-annual plants are becoming abundant in the grasslands along the Front Range of Colorado. These species can be aggressive invaders in native grasslands, growing earlier in the spring than native plants and preempting soil resources. Currently, removal of other inv...

Background/Question/Methods Long term deposition of nitrogen is increasing in the Colorado Front Range concurrently with changes in the forms and amounts of precipitation. Both of these factors impact the diversity and composition of plant communities. Alpine systems are considered particularly sensitive to these inputs due to historically low le...

Background/Question/Methods Soil nitrogen availability plays a key role in plant resource allocation to growth, reproduction, and defense. Human nitrogen inputs in terrestrial ecosystems have dramatically increased in recent years and these inputs may alter plant allocation patterns, plant defense, and plant-herbivore interactions. Although a num...

Background/Question/Methods Spotted knapweed (Centaurea stoebe) occurs in over three million ha in rangeland across North America. We developed graphical models to conceptualize the invasion process and to identify the conditions required to explain the current, contradictory findings on biological control, and then employed a series of manipulati...

Litter-bag studies and simulation modeling were used to examine the relationship between mass loss and nitrogen content of decaying prairie foliage and root litter. In contrast with forest studies, grassland roots were low in lignin and nitrogen, decayed more rapidly than foliage, and demonstrated very low nitrogen immobilization potentials. Our fi...

The physiological responses of plants to variable levels of root and shoot herbivory in the field may yield valuable insights regarding potential compensation or tolerance responses for herbivory. In an infestation of Centaurea stoebe (spotted knapweed) located in the Colorado foothills, we measured physiology, biomass, and flower production of ind...

Root dynamics were studied using root windows at Konza Prairie, a tallgrass prairie in north central Kansas, during dry (1984) and wet (1985) years. Amounts, production, and disappearance of root length decreased during drought but increased when rains resumed; however, standing crop remained low. The 1985 root lengths increased throughout the grow...

The soils across treeline should vary because of direct effects of biological differences of coniferous subalpine forest and the herbaceous alpine tundra in Colorado. In addition, the change in life form may indirectly affect soils because of interactions of the vegetation and wind-driven deposition processes. This is particularly important as nitr...

We measured seed germination and seedling survivorship of spotted knapweed, Centaurea stoebe, in a series of laboratory and field experiments to evaluate the efficacy of seed limitation as a management focus. This work was initiated 6years after introduction of several biological control agents. The soil seed bank of the site used in this study con...

Spotted knapweed (Centaurea stoebe) is found in over 3 million ha of rangeland and forests across North America, and evidence supporting the use of biological control as a regional method to reduce infestations and their associated impacts remains inconclusive. Several species of insects have been reported to reduce plant densities in some areas; h...

Substantial controversy surrounds the efficacy of biological control insects to reduce densities of Centaurea stoebe, a widespread, aggressive invasive plant in North America. We developed a graphical model to conceptualize the conditions required to explain the current contradictory findings, and then employed a series of manipulations to evaluate...

Background/Question/Methods Plant physiological responses to simultaneous above- and belowground herbivory in the field are seldom measured. Linking these responses to plant fitness could improve predictions of the efficacy of biological control agents for use on invasive plants, ultimately improving our understanding of variable success in contro...

Restoring competition, enemies, or both can reduce an invasive species' success over the long term in range-fields. Overgrazing allows introduced annuals to replace the dominant native perennial, kangaroo grass, in Southeast Australia. The introduced annuals continue to dominate the site without intervention. The most common is using herbicides to...

The responses and impacts of five insect species that feed on Centaurea diffusa Lamarck, diffuse knapweed, to soil nitrogen and phosphorus additions were studied in grasslands east of the Colorado Front Range. We predicted that fertilization was unlikely to have a direct effect on herbivory but that if the insects preferentially select vigorous pla...

The forest-alpine tundra ecotone in the Front Range of Colorado typically occurs as a gradual transition from the treeless tundra to the closed canopy coniferous subalpine forest. We evaluated the patterns of snow, deposition inputs, and soil properties at three spatial scales: across the entire ecotone, with distance from tree limit in the transit...

Interactions between climate and ecosystems with complex topographic gradients generate unique source and sink habitats for water and nutrients as a result of precipitation, energy, and chemical redistribution. We examined these phenomena for a high-elevation site in the Colorado Front Range. Current changes in climate and atmospheric deposition of...

Background/Question/Methods The fragmentation of steep, tropical montane landscapes due to anthropogenic activity has increased in recent years, and our ability to predict the significance of these disturbances relies upon an understanding the consequences of these activities on the sustainability of these ecosystems. Effective management and conse...

Many plants introduced to new habitats have fewer microbial pathogens than when in their home range, and have the ability to grow rapidly. Such a combination may make for especially troublesome immigrants.

Mechanical thinning for fire mitigation has become increasingly widespread in recent years throughout the western United States. A common practice in fire-mitigation procedures is the conversion of slash into chipped mulch (referred to as “woodchips”) that is spread on-site. Here, we investigated: (1) the effect of woodchip amendments on soil nitro...

The response of ecosystem processes to current and future climatic events may be affected by historical disturbance regimes. Here, we address the interaction between reduced precipitation and the legacy effects of two contrasting long-term burn regimes in a tallgrass prairie (20 years of annual burning versus fire suppression). We examined rates of...

Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi-arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Ari...

Root harvests and root windows were used to study the influence of fire, mowing and nitrogen additions on root lengths, biomass, and nitrogen content in tall-grass prairie. Four years of nitrogen additions (10 g m2 yr−1) increased below-ground mass by 15 % and nitrogen concentration in that mass by 77 %. In general, live roots and rhizomes exhibite...

Four species of biocontrol insects (knapweed root weevil, lesser knapweed flower weevil, spotted knapweed seedhead moth, and bronze knapweed root borer) were released at a diffuse knapweed site located about 10 km east of the Colorado Front Range. Two other biocontrol agents (banded gall fly and knapweed seed head fly) were already present at this...

The 24 projects of the National Science Foundation's Long Term Ecological Research Network, whose sites range from the poles to the Tropics, from rain forests to tundras and deserts, and from offshore marine to estuarine and freshwater habitats, address fundamental and applied ecological issues that can be understood only through a long-term approa...

Spotted knapweed is native to Eastern Europe, with a locally scarce but widespread distribution from the Mediterranean to the eastern region of Russia. The plant is one of over a dozen Centaurea species that were accidentally introduced into North America and now is found in over 1 million ha of rangeland in the USA and Canada. Land managers spend...

Most ecosystems are now sufficiently altered in structure and function to qualify as novel systems, and this recognition should be the starting point for ecosystem management efforts. Under the emerging biogeochemical configurations, management activities are experiments, blurring the line between basic and applied research. Responses to specific m...

The suitability of the foliar N/P ratio was evaluated as a predictor of nutrient limitation in an alpine ecosystem of the Colorado Front Range. We hypothesized that foliar N/P ratios are directly correlated with the alpine soil nutrient status. We used a long-term fertilization experiment con- ducted in three alpine plant communities, where 48 plot...

A relatively small subset of exotic plant species competitively exclude their neighbors in invaded “recipient” communities but coexist with neighbors in their native habitat. Allelopathy has been argued as one of the mechanisms by which such exotics may become successful invaders. Three approaches have been used to examine allelopathy as a mechanis...

Cover and richness of a 5-year revegetation effort were studied with ,respect to small-scale disturbance and nutrient manipulations. The site, originally a relict tallgrass prairie mined for gravel, was replanted to native grasses using a seed mixture of tall-, mixed-, and short-grass species. Following one wet and three relatively dry years, a com...

For agriculture to meet goals that include profitability, environmental integrity, and the production of ecosystem services beyond food, fuel, and fiber requires a comprehensive, systems-level research approach that is long-term and geographically scalable. This approach is largely lacking from the US agricultural research portfolio. It is time to...

1] The nature of the snowpack has the potential to strongly influence the patterns of alpine plant productivity and composition by governing soil moisture levels, growing season duration and the thermal regime of alpine soils. This study evaluates these relationships by modeling the interrelationships of snow depth, snow water equivalent (SWE), sno...

ABSTRACT Long-term reductions in invasive plant species are few, and studies documenting the response of plant communities to such reductions are equally rare. We quantified plant species richness and cover during a nine-year period at a grassland site in central Colorado where,the introduction of biological control insects reduced,the invasive non...

Abundances and interactions among biological control insects and their effects on target invasive plants were monitored within the flower heads and roots of diffuse knapweed, Centaurea diffusa, and in spotted knapweed, Centaurea stoebe, along the Colorado Front Range. Flower weevils, (Larinus species) and root-feeders (Cyphocleonus achates and Sphe...

Phosphorus (P) has been proposed to directly limit primary productivity in some temperate grassland ecosystems. Our study of a recovering prairie on Colorado's Front Range suggests that P availability, possibly via regulation of nitrogen (N) fixation, may strongly influence N availability in recovering prairie soils. Consequently, increased P avail...

Plant species that colonize new environments tend to favour habitats with ample water and nutrients. But invasive plants can be more efficient in their use of resources than that observation might imply.

Knapweeds (Centaurea spp.) are among the most invasive of non-indigenous plant species that have colonized western North America over the last century. We conducted a 4-year experiment in a reconstructed grassland to test hypotheses related to the ability of grasslands to resist the invasion of diffuse knapweed (C. diffusa). We experimentally invad...

Toadflax invasion into natural areas has prompted interest in weed management via biological control. The most promising biological control agent currently available for the control of Dalmatian toadflax is Mecinus janthinus, a stem-boring weevil that has been shown to significandy reduce toadflax populations. Some land managers, however, are reluc...