Early Successional Vegetation Research Articles

Succession in salt marshes – large‐scale and long‐term patterns after abandonment of grazing and drainage

AbstractQuestionsIn the early 1990s, grazing and drainage have been abandoned in many artificially created mainland salt marshes of the Wadden Sea to increase their natural character and heterogeneity of vegetation composition. We asked: how did vegetation succession in the low and high marsh respond to this change in management from a large‐scale and long‐term perspective, and what were the major drivers of successional change?LocationWadden Sea coast, Schleswig‐Holstein, Germany.MethodsWe used vegetation data from the Trilateral Monitoring and Assessment Program (TMAP) for around half of the Wadden Sea mainland salt marshes to identify main successional pathways of the TMAP vegetation types Puccinellia maritima and Festuca rubra, dominating low and high marsh areas, respectively, prior to the change in management. Drivers of succession were analysed using classification and regression tree models, a non‐parametric vegetation modelling technique.ResultsSince the abandonment of grazing and drainage, progressive succession towards the TMAP vegetation types Atriplex portulacoides and Elymus athericus strongly increased and mostly occurred in abandoned areas at medium to high elevation. Retarded and retrogressive succession decreased and mostly occurred in grazed and low‐lying areas. Persistance of the early successional vegetation type Puccinellia maritima in the salt marshes of the northern Wadden Sea suggests that large‐scale gradients of salinity, inundation frequency and sedimentation lead to geographical variation in the pace of succession.ConlusionsConsidered from a large‐scale and long‐term perspective, abandonmnent of grazing and drainage caused spread of grazing‐sensitive plant species from mid‐ and late‐successional stages. This change in vegetation composition affects species diversity and ecosystem functions of the Wadden Sea mainland salt marshes. Grazing regime and elevation were found to be the most important drivers of succession. To achieve and maintain large‐scale heterogeneity in vegetation composition, we recommend management to maintain a mosaic of grazed and ungrazed areas, and to consider the role of large‐scale gradients of environmental factors driving succession.

Shifts in functional traits among tree communities across succession in eastern deciduous forests

Throughout the eastern deciduous forest (EDF) region, disturbances, including fire, wind storms, and landslides, interweave with complex topography and vegetation history to produce a mosaic of forest types and ages. Forest composition and dynamics following disturbance can depend on the interaction of plant traits related to resource capture, regeneration, and growth with changes in the post-disturbance environment. Appropriate traits should vary predictably with the stand age of a forest community as this acts as a proxy for time since last disturbance. We used Forest Inventory and Analysis data to investigate the hypothesis that community level means of seed mass and wood density increase, and leaf nitrogen decreases, with age of eastern deciduous forests, reflecting a shift from light-seeded, fast-growing early successional vegetation to heavier-seeded, slower-growing vegetation. As hypothesized, seed mass and wood density were positively correlated with stand age; however, the relationship differed among ecoregions of the EDF. Northern forests in the Warm Continental Division showed lower seed mass and wood density values in young stands, with a stronger increase in these values as succession advanced relative to more southerly ecoregions. This could reflect slower succession, preponderance of light-seeded and low wood density early post-disturbance deciduous trees such as Populus tremuloides and Betula papyrifera, or presence of conifers in early successional stands. Leaf nitrogen showed no consistent relationship with stand age, suggesting no consistent relationship of photosynthetic rate or soil nitrogen content with tree composition over succession throughout the EDF. Instead, leaf nitrogen differed among the ecoregion divisions and showed a unimodal distribution with latitude, peaking near the middle latitudes of the Hot Continental and Prairie Divisions. Collectively, the results indicate functional trait shifts over succession throughout the EDF, in agreement with a shift from ruderal to more competitive or stress-tolerant strategies, but also point to differences in the strength and shape of that shift among ecoregions. Early post-disturbance forest harbors a unique combination of functional traits. Further, disturbance that creates a mosaic of forest stand ages is important for maximizing not just species diversity, but functional diversity as well.

Skipper Richness (Hesperiidae) Along Elevational Gradients in Brazilian Atlantic Forest.

Hesperiidae are claimed to be a group of elusive butterflies that need major effort for sampling, thus being frequently omitted from tropical butterfly surveys. As no studies have associated species richness patterns of butterflies with environmental gradients of high altitudes in Brazil, we surveyed Hesperiidae ensembles in Serra do Mar along elevational transects (900-1,800m above sea level) on three mountains. Transects were sampled 11-12 times on each mountain to evaluate how local species richness is influenced by mountain region, vegetation type, and elevational zones. Patterns were also analyzed for the subfamilies, and after disregarding species that exhibit hilltopping behavior. Species richness was evaluated by the observed richness, Jacknife2 estimator and Chao 1 estimator standardized by sample coverage. Overall, 155 species were collected, but extrapolation algorithms suggest a regional richness of about 220 species. Species richness was far higher in forest than in early successional vegetation or grassland. Richness decreased with elevation, and was higher on Anhangava mountain compared with the two others. Patterns were similar between observed and extrapolated Jacknife2 richness, but vegetation type and mountain richness became altered using sample coverage standardization. Hilltopping species were more easily detected than species that do not show this behavior; however, their inclusion did neither affect estimated richness nor modify the shape of the species accumulation curve. This is the first contribution to systematically study highland butterflies in southern Brazil where all records above 1,200m are altitudinal extensions of the known geographical ranges of skipper species in the region.

Early successional vegetation assembly in a spatially variable hydrologic regime

Mitigation wetlands are intended to replace the ecological conditions of wetlands lost to development or drainage, resulting in a theoretical expectation that the replacement wetland will support a species composition and diversity comparable to a reference standard. I analyze a freshwater mitigation wetland in central Ohio, USA to evaluate factors that influence spatial patterns of plant community assembly in terms of floristic quality and diversity. Soil seed bank, bulk density, organic content, and pH are evaluated, along with average depth, exposure time, depth variance, and spatial location within the wetland basins, for their relationship with plant community characteristics in the first three years after wetland creation. The plant community was highly variable during the study period, with general trends toward greater diversity and more hydrophilic vegetation. The spatial distribution of nonnative cover, planted cover, mean coefficient of conservatism, and diversity in the third-year plant community were unrelated to soil and seed bank metrics; however, all were strongly related to hydrologic metrics. Shallow depth (<0.2 m) and moderate depth variance were found to facilitate plant community diversity, while floristic quality is more likely in deep (>0.2 m) and relatively stable water levels (<60% exposure time). Nonnative vegetation cover was particularly high at shallow locations with high depth variance and long exposure times. Geographic analysis of floristic quality and diversity indicates a weak spatial correlation between the two, suggesting that these two measures of the plant community are unlikely to coincide in early succession. The implications are that site design and hydrologic manipulation can drive the early successional vegetation characteristics, and that site design, compliance criteria, and monitoring regimes should seek to concertedly facilitate species composition, community diversity, or both.

Responses of white‐tailed deer and northern bobwhite food plants to a gradient of stand‐establishment intensities in pocosin pine plantations

AbstractLoblolly pine (Pinus taeda) plantations are established using various treatments to manage competing vegetation and increase pine production. Although young pine plantations historically supported early successional vegetation communities that contained abundant wildlife forage, increasing intensity of stand‐establishment treatments, particularly herbicides, has caused concern regarding potential effects on composition, availability, and quality of wildlife forage within young pine plantations. Few long‐term studies have described relationships between intensity of site preparation and effects on important forage plants for 2 economically and ecologically important game species: white‐tailed deer (Odocoileus virginianus) and northern bobwhite (Colinus virginianus). Therefore, we examined effects of 6 treatments of increasing stand‐establishment intensity via combinations of mechanical and chemical site preparation with herbaceous weed‐control on deer and bobwhite food plants from 1 year to 8 years after site preparation in loblolly pine plantations (n = 6) within pocosins in the Lower Coastal Plain of North Carolina, USA, during summers of 2002–2005, 2007–2009. Although woody and vine forage plants for deer and quail were common on all treatments, chemical site preparation resulted in long‐term decreases (approx. 50% for 8 yr) in coverage of these plants. Type of mechanical site preparation–spacing and herbaceous weed‐control had few effects on woody and herbaceous deer and quail food plants. Dissimilar from research in other regions, reduction in woody cover did not provide a concurrent increase in herbaceous food plants. Because of relatively poor forage quality in pocosin habitats, vegetation management practices may reduce deer and quail food quantity without increasing quality. However, because abundance of low‐quality forage is high in pocosin habitats, localized forage reductions due to site‐preparation techniques may not affect overall carrying capacity in these areas. © 2012 The Wildlife Society.

Sandpits provide critical refuge for bees and wasps (Hymenoptera: Apocrita)

Evidence-based conservation allows the evaluation of both the collateral benefits and the drawbacks of a wide range of human activities, like quarrying. In this study, the community structure of bees and wasps (Hymenoptera:Apocrita) in Central European sandpits was investigated, focusing on the changes caused by quarrying cessation and technical reclamation, as well as on the changes caused by spontaneous succession leading to the increased availability of food resources but also to the loss of the number and size of available bare sand patches. The bees and wasps demonstrated an exceptional ability to colonize the newly emerging sand quarrying areas, and to survive in them unless these were quarried as intensively as to not allow the development of any early successional vegetation. Both active and closed sandpits were found to serve as important regional refuges for the persistence of many rare species. In total, 221 species were detected, 53 of those were red-listed, with two species thought to be regionally extinct. Typically, active quarrying was associated with the presence of Bembecinus tridens, Halictus subauratus, H. maculatus, and Andrena nigroaenea. The list of the species of conservation interest is provided, and so is the detailed analysis of the life-history traits of the species in relation to the presence of bare sand patches, vegetation cover, quarrying intensity, and time elapsed since the formation of each artificial habitat patch. Sandpits as refuges for xerothermophilous and psammophilous hymenopterans are usually completely and irreversibly lost if the current legislature enforcing the technical reclamation over spontaneous or assisted succession is applied in all or most of the post-mining areas.

Maladaptive Habitat Selection of a Migratory Passerine Bird in a Human-Modified Landscape

In human-altered environments, organisms may preferentially settle in poor-quality habitats where fitness returns are lower relative to available higher-quality habitats. Such ecological trapping is due to a mismatch between the cues used during habitat selection and the habitat quality. Maladaptive settlement decisions may occur when organisms are time-constrained and have to rapidly evaluate habitat quality based on incomplete knowledge of the resources and conditions that will be available later in the season. During a three-year study, we examined settlement decision-making in the long-distance migratory, open-habitat bird, the Red-backed shrike (Lanius collurio), as a response to recent land-use changes. In Northwest Europe, the shrikes typically breed in open areas under a management regime of extensive farming. In recent decades, Spruce forests have been increasingly managed with large-size cutblocks in even-aged plantations, thereby producing early-successional vegetation areas that are also colonised by the species. Farmland and open areas in forests create mosaics of two different types of habitats that are now occupied by the shrikes. We examined redundant measures of habitat preference (order of settlement after migration and distribution of dominant individuals) and several reproductive performance parameters in both habitat types to investigate whether habitat preference is in line with habitat quality. Territorial males exhibited a clear preference for the recently created open areas in forests with higher-quality males settling in this habitat type earlier. Reproductive performance was, however, higher in farmland, with higher nest success, offspring quantity, and quality compared to open areas in forests. The results showed strong among-year consistency and we can therefore exclude a transient situation. This study demonstrates a case of maladaptive habitat selection in a farmland bird expanding its breeding range to human-created open habitats in plantations. We discuss the reasons that could explain this decision-making and the possible consequences for the population dynamics and persistence.

Conservation where people work: A role for business districts and industrial areas in enhancing endangered butterfly populations?

Urbanization is often identified as a primary cause of species decline. Yet little is known about biodiversity conservation in human settlements, the ‘places where people live and work’. In this study, conducted in the densely populated Netherlands, our main objective was to explore new conservation planning strategies to strengthen metapopulations in urbanized landscapes. We focused on a rarely studied part of the city: business sites, the places where people work. We selected eight endangered butterfly species, all habitat specialists of low-productive, early-successional vegetation. Potentially, vacant lots, lawns and green roofs at business sites could offer habitat patches for these butterflies. Our analysis combined national distribution data on both butterflies and business sites. We explored the extent to which the creation of additional habitat at business sites within dispersal distance of adjoining populations could enhance the sustainability of the entire population network. We found that for four endangered butterfly species ( Aricia agestis, Hipparchia semele, Issoria lathonia and Ochlodes sylvanus), additional habitat developed at nearby business sites could support a substantial proportion (19–33%) of the currently vulnerable populations in the Netherlands. Moreover, in numerous occasions the business sites could offer sufficient habitat to upgrade vulnerable butterfly populations into viable metapopulations. The present study illustrates that – even for habitat specialists such as the selected butterfly species – urbanized areas may provide yet unexplored conservation opportunities.

Variation in Aboveground Cover Influences Soil Nitrogen Availability at Fine Spatial Scales Following Severe Fire in Subalpine Conifer Forests

Following fire, fine-scale variation in early successional vegetation and soil nutrients may influence development of ecosystem structure and function. We studied conifer forests burned by stand-replacing wildfire in Greater Yellowstone (Wyoming, USA) to address two questions: (1) How do the variability and spatial structure of aboveground cover and soil nitrogen availability change during the first 4 years following stand-replacing fire? (2) At fine scales (2–20 m), are postfire soil inorganic N pools and fluxes related to aboveground cover? Aboveground cover, soil N pools, and annual net N transformations were measured from 2001 to 2004 using a spatially explicit sampling design in four 0.25-ha plots that burned during summer 2000. Within-stand variability (coefficient of variation) in postfire live vegetative cover declined with time since fire, whereas variability in bare mineral soil, charred litter and fresh litter was greatest 2-3 years postfire. The soil nitrate pool was more variable than the soil ammonium pool, but annual net nitrification was less variable than annual net N mineralization. Spatial structure (quantified by semivariograms) was observed in some aboveground cover variables (for example, graminoids and fresh litter), but there was little spatial structure in soil N variables and no obvious congruence in spatial scales of autocorrelation for soil N and aboveground cover. Significant Spearman correlations (at the sample point) indicated that aboveground cover and soil N were coupled following severe fire, and the dominant influence was from aboveground cover to soil N, rather than from soil N to vegetation. Initial patterns of fire severity and re-vegetation contributed to fine-scale heterogeneity in soil N availability for at least 4 years after severe fire.

Contrasting needs of grassland dwellers: habitat preferences of endangered steppe beetles (Coleoptera)

Temperate grasslands are local biodiversity hotspots. In Europe, their extent was mostly reduced to isolated habitat patches, whose biota is subject to extinction debt. Knowledge on requirements of dry-grassland inhabitants is thus vital to slow down decline of grassland biodiversity. We studied habitat requirements of eight flightless steppe beetles, including some of the most endangered dry-grassland specialists of the continent. The beetles were sampled using 167 pitfall traps at a pannonian dry-grassland fragment, the Pouzdrany steppe, SE Czech Republic, from March to November 2006. The number of each species captures in each trap was related to vegetation and abiotic habitat characteristics; captures of all beetles were related to each other. Two of the studied species required relatively humid microhabitats, including tall-grass steppe with litter (Carabus hungaricus, Carabidae) and grassland of high herb cover (Meloe proscarabaeus, Meloidae). Others were associated with xeric habitats (e.g. Meloe scabriusculus) and their early-successional stages, including short-turf vegetation (Dorcadion fulvum, D. pedestre, Cerambycidae) and/or bare-ground patches (Blaps lethifera, Tenebrionidae; Meloe decorus, M. uralensis). Our findings point to key importance of early-successional vegetation for grassland biodiversity, and to the fact that locally co-occurring and closely related grassland specialists may exhibit contrasting habitat needs. Spatially and temporarily highly diversified patch management creating a fine scale mosaic of various seral stages from bare soil to tall-grass steppe is therefore the most appropriate approach for managing isolated grasslands. Prescribed burning and support of burrowing herbivores are recommended and discussed together with other measures for restoration of habitat diversity in dry-grassland fragments.

Early-successional vegetation changes after roadside prairie restoration modify processes related with soil functioning by changing microbial functional diversity

Because of their rapidly changing vegetation dynamics and harsh environmental conditions, roadside prairies in semi-arid regions represent an exceptional study system in which to investigate the effects of plant-soil interactions on ecosystem functioning. We conducted a two-year field experiment on two roadside embankments in semi-arid central Spain differing in construction age to answer the following questions: (i) do commonly used restoration treatments (hydroseeding, fertilization and irrigation) affect soil microbial functional diversity and processes related to soil functioning (basal respiration, total N and P and in situ N availability rate)? (ii) what portion of plant effects on processes related to soil functioning is mediated indirectly by microbial functional diversity? Except for a small and negative irrigation effect on the microbial functional diversity in the three-year old site, the restoration treatments employed did not affect this variable. Fertilization increased plant diversity, an effect likely mediated by the enhanced soil nutrient availability with this treatment at early stages of secondary succession. In contrast, hydroseeding did not affect processes related to soil functioning. The total effect of the plant community on these processes was higher than that of the microbial functional diversity alone, suggesting that the studied slopes are to the greater extent regulated by plants. However, soil microbes are a key proximate influence in the system, as the indirect effects of plant community on soil functioning processes mediated by soil microbes represented 37e41% of the total plant effects observed. Our results indicate that the restoration of recently built slopes can potentially be improved with treatments that promote plant compositional shifts, such as fertilization, or alter soil function, such as the enhancement of soil microbial functional diversity. They also highlight that plant-soil interactions are an important process that can be manipulated for restoration purposes in early-successional stages, especially in nutrient-poor semi-arid ecosystems.

Spontaneous Urban Vegetation: Reflections of Change in a Globalized World

Urban habitats are characterized by high levels of disturbance, impervious paving, and heat retention. These factors, acting in concert, alter soil, water, and air conditions in ways that promote the growth of stress-tolerant, early-successional vegetation on abandoned or unmaintained land. In most urban areas, a cosmopolitan array of spontaneous plants provide important ecological services that, in light of projected climate change impacts, are likely to become more significant in the future. Learning how to manage spontaneous urban vegetation to increase its ecological and social values may be a more sustainable strategy than attempting to restore historical ecosystems that flourished before the city existed.

Biotic and abiotic controls on tree colonization in three early successional communities of Chiloé Island, Chile

Summary 1. Most studies of tree regeneration are limited to particular environments and may not capture variation in the biotic or abiotic factors that regulate recruitment at larger spatial scales. Critical processes such as competition and facilitation can vary spatially, along gradients in resource availability and environmental stress, and temporally, with plant development. 2. We examined patterns of natural tree recruitment and experimentally followed germination and seedling survival of five tree species (pioneer to late seral) in three early successional communities of contrasting bio‐physical environments in a rural landscape on Chiloé Island, Chile. 3. We quantified natural recruitment of juveniles and saplings and assessed relationships between tree density and local environment. We used a removal experiment to test the influence of early successional vegetation on seed germination and early survival of tree species. In each community, seeds and seedlings were placed in paired experimental plots from which vegetation was removed or left intact (control). To identify potential correlates of germination and seedling survival, we measured light transmittance and soil properties in each plot. 4. In all communities, established vegetation had either a positive or neutral effect on germination and/or survival although responses varied among life stages and species. Germination and survival were correlated with the lower levels of light in controls, consistent with negative correlations between natural tree densities and light. Vegetation cover was not dense enough to facilitate survival of late successional species, but not too dense to inhibit survival of shade‐intolerant or mid‐tolerant species. Among communities, natural densities of juveniles were greatest under conditions where experimental germination rates were highest. Seedling height growth was lowest in the community characterized by waterlogged soils, consistent with the naturally low transition rate from juveniles to saplings and a negative correlation between density of shade‐intolerant trees and soil moisture. 5. Synthesis. Our experiments indicate strong, mostly positive controls (facilitation) on tree recruitment in early seral shrublands with differing bio‐physical environments. Benefits of shading are manifested at different stages in the life history. However, community context is critical: variation in seasonal patterns of soil moisture may explain spatial variation in the density and size structure of natural tree recruitment.

Habitat Affinity of Resident Natural Enemies of the Invasive &lt;I&gt;Aphis glycines&lt;/I&gt; (Hemiptera: Aphididae), on Soybean, With Comments on Biological Control

We integrated a natural enemy survey of the broader landscape into a more traditional survey for Aphis glycines Matsumura (Hemiptera: Aphididae), parasitoids and predatory flies on soybean using A. glycines-infested soybean, Glycine max (L.) Merr., placed in cropped and noncropped plant systems to complement visual field observations. Across three sites and 5 yr, 18 parasitoids and predatory flies in total (Hymenoptera: Aphelinidae [two species] and Bracondae [seven species], Diptera: Cecidomyiidae [one species], Syrphidae [seven species], Chamaemyiidae [one species]) were detected, with significant variability in recoveries detected across plant system treatments and strong contrasts in habitat affinity detected among species. Lysiphlebus testaceipes Cresson was the most frequently detected parasitoid, and no differences in abundance were detected in cropped (soybean, wheat [Triticum aestivum L.], corn [Zea mays L.], and alfalfa [Medicago sativa L.]) and noncropped (poplar [Populus euramericana (Dode) Guinier] and early successional vegetation) areas. In contrast, Binodoxys kelloggensis Pike, Starý & Brewer had strong habitat affinity for poplar and early successional vegetation. The low recoveries seasonally and across habitats of Aphelinus asychis Walker, Aphelinus sp., and Aphidius colemoni Viereck make their suitability to A. glycines on soybean highly suspect. The widespread occurrence of many of the flies reflects their broad habitat affinity and host aphid ranges. The consistent low field observations of parasitism and predation suggest that resident parasitoids and predatory flies are unlikely to contribute substantially to A. glycines suppression, at least during the conventional time period early in the pest invasion when classical biological control activities are considered. For selected species that were relatively well represented across plant systems (i.e., L. testaceipes and Aphidoletes aphidimyza Rondani), conservation biological control efforts may be fruitful. The additional information gained from expanding the natural enemy survey into the broader landscape was essential in making these distinctions relevant to conservation biological control, while adding agroecosystem-specific information valuable to classical biological control.

Vegetation Response to Early Holocene Warming as an Analog for Current and Future Changes

Temperatures in southwestern North America are projected to increase 3.5-4 degrees C over the next 60-90 years. This will precipitate ecological shifts as the ranges of species change in response to new climates. During this shift, rapid-colonizing species should increase, whereas slow-colonizing species will at first decrease, but eventually become reestablished in their new range. This successional process has been estimated to require from 100 to over 300 years in small areas, under a stable climate, with a nearby seed source. How much longer will it require on a continental scale, under a changing climate, without a nearby seed source? I considered this question through an examination of the response of fossil plant assemblages from the Grand Canyon, Arizona, to the most recent rapid warming of similar magnitude that occurred at the start of the Holocene, 11,700 years ago. At that time, temperatures in southwestern North America increased about 4 degrees C over less than a century. Grand Canyon plant species responded at different rates to this warming climate. Early-successional species rapidly increased, whereas late-successional species decreased. This shift persisted throughout the next 2700 years. I found two earlier, less-extreme species shifts following rapid warming events around 14,700 and 16,800 years ago. Late-successional species predominated only after 4000 years or more of relatively stable temperature. These results suggest the potential magnitude, duration, and nature of future ecological changes and have implications for conservation plans, especially those incorporating equilibrium assumptions or reconstituting past conditions. When these concepts are extended to include the most rapid early-successional colonizers, they imply that the recent increases in invasive exotics may be only the most noticeable part of a new resurgence of early-successional vegetation. Additionally, my results challenge the reliability of models of future vegetation and carbon balance that project conditions on the basis of assumptions of equilibrium within only a century.

Predisposition to bark beetle attack by root herbivores and associated pathogens: Roles in forest decline, gap formation, and persistence of endemic bark beetle populations

Bark beetles are largely known for their ability to undergo intermittent population eruptions that transform entire landscapes and pose significant economic hardships. However, most species do not undergo outbreaks, and eruptive species usually exert only minor disturbances. Understanding the dynamics of tree-killing noneruptive species can provide insights into how beetles persist at low densities, and how some spatiotemporal patterns of host predisposition may more likely favor breaching eruptive thresholds than others. Elucidating mechanisms behind low-density populations is challenging, however, due to the requirement of long-term monitoring and high degrees of spatial and temporal covariance. We censused more than 2700 trees annually over 7 years, and at the end of 17 years, in a mature red pine plantation. Trees were measured for the presence of bark beetles and wood borers that breed within the primary stem, root weevils that breed in root collars, and bark beetles that breed in basal stems. We quantify the sequence of events that drive this decline syndrome, with the primary emergent pattern being an interaction between below- and above-ground herbivores and their fungal symbionts. This interaction results in an expanding forest gap, with subsequent colonization by early-successional vegetation. Spatial position strongly affects the likelihood of tree mortality. A red pine is initially very likely to avoid attack by tree-killing Ips beetles, but attack becomes increasingly likely as the belowground complex spreads to neighboring trees and eventually make trees susceptible. This system is largely internally driven, as there are strong gap edge, but not stand-edge, effects. Additional stressors, such as drought, can provide an intermittent source of susceptible trees to Ips beetles, and elevated temperature slightly accentuates this effect. New gaps can arise from such trees as they subsequently become epicenters for the full complex of organisms associated with this decline, but this is not common. As Ips populations rise, there is some element of positive feedback, in that the proportion of killed trees that were not first colonized by root organisms increases. This positive feedback is very weak, however, and we propose the slope between beetle population density and reliance on host stress as a quantitative distinction along a gradient from noneruptive through eruptive species. Almost all trees colonized by Ips were subsequently colonized by wood borers, likely a source of negative feedback. We discuss implications to our overall understanding of cross-scale interactions, between-guild interactions, forest declines, and eruptive thresholds.

Take Me to Your Leader: Does Early Successional Nonhost Vegetation Spatially InhibitPissodes strobi(Coleoptera: Curculionidae)?

The spatial influences of host and nonhost trees and shrubs on the colonization patterns of white pine weevil Pissodes strobi (Peck) were studied within a stand of planted interior hybrid spruce [Picea glauca (Moench) Voss x Picea engelmannii (Parry) ex Engelm.]. Planted spruce accounted for one third of all trees within the stand, whereas the remaining two thirds were comprised of early-successional nonhost vegetation, such as alder (Alnus spp.), paper birch (Betula papyrifera Marsh.), black cottonwood [Populus balsamifera ssp. trichocarpa (T. Ng.) Brayshaw], lodgepole pine [Pinus contorta (Dougl.) ex Loud.], trembling aspen (Populus tremuloides Michx), willow (Salix spp.), and Canadian buffaloberry [Shepherdia canadensis (L.) Nutt.]. Unlike the spruce trees, nonhost vegetation in the stand was not uniformly distributed. Spatial point process models showed that Canadian buffaloberry, paper birch, black cottonwoood, and trembling aspen had negative associations with damage caused by the weevil, even though the density of the insects' hosts in these areas did not change. Moreover, knowing the locations of these nonhost trees provided as much, or more, inference about the locations of weevil-attacked trees as knowing the locations of suitable or preferred host trees (i.e., those larger in size). Nonhost volatiles, the alteration of soil composition, and overstory shade are discussed as potential explanatory factors for the patterns observed. New research avenues are suggested to determine whether nonhost vegetation in early successional stands might be an additional tool in the management of these insects in commercially important forests.

Stand structure and the abundance and diversity of plants and small mammals in natural and intensively managed forests

Little attention has been given to investigating biodiversity in managed forests. Pre-commercial thinning (PCT) and fertilization have been used successfully to increase growth of coniferous trees, vegetative succession, and overall stand structure in second-growth stands. This study was designed to test the hypotheses (H) that PCT and repeated fertilization of young (20–25 years) even-aged lodgepole pine ( Pinus contorta) stands would enhance (H1) coniferous stand structure; (H2) abundance and diversity of understory vegetation; and (H3) abundance and diversity of forest-floor small mammals, to levels found in mature and old-growth forests. Replicate study areas were located near Summerland and Kelowna in south-central British Columbia, Canada. Each study area had six stands: young plantation, thinned stand (1000 stems/ha), thinned–fertilized stand (1000 stems/ha), unthinned stand, mature forest, and old-growth forest. Coniferous stand structure, understory vegetation, and forest-floor small mammals were sampled during a 5-year period from 1999 through 2003. The smaller tree sizes (diameter, height, basal area) in the young lodgepole pine stands did not support the tree size part of H1. Similar abundance of overstory and total conifers did support the abundance part of H1. The diversity component was supported by the similarity in species and structural diversity of total conifers among the intensively managed and older unmanaged stands. Response of understory vegetation was dominated by the abundance of herbs in the thinned–fertilized stands. There was no difference in shrub abundance among stands, but mosses and terrestrial lichens were most numerous in the mature and old-growth stands. Our results supported the abundance part of H2, at least for herbs and shrubs. Species richness and diversity of vascular plants were similar in managed and old-growth forests, and richness was lowest in the mature stands. H3 was supported for total abundance, species richness, and diversity of small mammals, and for the generalist species Peromyscus maniculatus and Tamias amoenus, but not for the old forest specialist Myodes gapperi. Two insectivores, Sorex monticolus and Sorex cinereus, were at comparable or higher abundance in the managed stands than in the older unmanaged forests. Three other microtines: Microtus pennsylvanicus, Microtus longicaudus, and Phenacomys intermedius were early successional vegetation specialists, and hence did not fit the prediction of H3. Thus, despite overall quantitative differences in stand structure and species-specific variability between our intensively managed and older natural stands, old-growth attributes seem to be developing in a time-span of decades rather than the centuries depicted by long rotations.

The western jewel butterfly (Hypochrysops halyaetus: Lycaenidae) II: factors affecting oviposition within native Banksia bushland in an urban setting

Oviposition by western jewel butterflies (Hypochrysops halyaetus Hewitson) was studied in the urban Koondoola regional bushland reserve, Western Australia in 1999. Observations were made in a small (70 × 120 m) localised breeding area the ‘microdistribution study area’, and in 14 paired 20 × 20 m quadrats randomly placed along established tracks in the interior of the northern half of the reserve. The principal host plant was Jacksoniasternbergiana with the secondary host being Daviesiadivaricata. More Jacksonia were used for oviposition and attended by ants (40 and 71%, respectively) in the microdistribution study than plants in the ‘quadrat’ study (8 and 25%, respectively). Jacksonia stems with basal diameters below 5 mm were less likely to have eggs. PCA showed Jacksonia to be associated with disturbed conditions with a high proportion of bare ground whereas Daviesia was associated with more mature vegetation. Jacksonia density was principally correlated with the proportion of bare ground and time since the last fire. Host ant (Crematogasterperthensis) presence and proportion of bare ground were the most important factors influencing oviposition. The presence of ants was closely associated with bare ground conditions and the presence of coccids. Conservation management for floristic diversity and maturity of vegetation in reserves is likely to be a widespread phenomenon, and may negatively affect the persistence of species requiring ephemeral patches of early successional vegetation. For H. halyaetus, a species dependent on disturbed/ephemeral habitat conditions, this conflict may threaten its survival, especially in small reserves, and as a result its conservation status may be underestimated. Management options are discussed.

Hydrologic controls on nitrogen availability in a high-latitude, semi-arid floodplain

Past research shows a discrepancy between apparent nitrogen supply and the annual growth requirements for early successional plant communities along the Tanana River floodplain in interior Alaska. Because previous measurements of nitrogen fixation, mineralization, and deposition can only account for approximately 26% of these communities' nitrogen requirements, other mechanisms of nitrogen supply should be operating. This study examined the potential for subsurface hydrology to supply nitrogen to the rooting zones of early successional plant communities. Three transects of ground water wells were established along the floodplain, and hydrologic characteristics and soil/water chemistry were measured for 2 y. Hydrologic measurements were then used to model the potential nitrogen contributions from advective flow and capillary rise. Ion exchange membranes and stable isotope tracers were used to identify the use of hyporheic nitrogen by vegetation. Nitrogen accumulation on ion exchange membranes showed a large input of nitrogen during a period of high water in 2003. Plants showed uptake of hyporheic 15N-labelled nitrogen at 2 of 4 locations. Models of capillary rise and advective flow estimated that nitrogen supply from subsurface water equalled or exceeded total nitrogen supply from nitrogen mineralization and nitrogen fixation combined. These findings underscore the importance of hyporheic processes in controlling nutrient supply to early successional vegetation on the Tanana River floodplain.