Wisconsin Forest Research Articles

Seasonal dynamics of small mammal populations: resource availability and cold exposure interact to govern abundance

Organisms in seasonal environments respond to both resources in the summer and environmental conditions in winter. Small mammals, in particular, respond quickly to changes in their environment, with many species reliant on the thermal refuge of the subnivium in the winter. However, there has been little research exploring how resources and cold exposure drive the seasonal dynamics of small mammal populations. We studied the populations of three subnivium-specialist small mammal species in seasonally snow-covered forests in Wisconsin, USA across 5 years during summer and winter. In summer, mast availability and canopy cover governed white-footed mouse ( Peromyscus leucopus Rafinesque, 1818) populations, coarse woody debris drove short-tailed shrew ( Blarina brevicauda Say, 1823) populations, and rainfall influenced red-backed vole ( Myodes gapperi (Vigors, 1830)) abundance. Dietary analysis via stable isotopes revealed that shrews primarily consumed arthropods, and mice predominately consumed hard mast despite interannual changes in availability. In winter, white-footed mice and red-backed vole abundances were negatively related to cold exposure. Short-tailed shrew winter population was positively related to their abundances the previous summer. These small mammals responded to species-specific drivers during the growing and snow seasons. Consequently, shorter snow seasons from climate change appear to be restructuring communities by creating a less hospitable environment for winter-adapted species, likely contributing to their regional declines.

Evaluation of the Root Rupture Method for Controlling Belowground Spread of the Oak Wilt Pathogen (Bretziella fagacearum) in Northeast Wisconsin, USA

Abstract Oak wilt, caused by the pathogen Bretziella fagacearum, is a destructive disease on oak (Quercus) species in the United States. Established methods to control the belowground spread of oak wilt are not appropriate in all circumstances; thus, forest health managers have a strong need for alternative methods for disease control. We evaluated the effectiveness of operational stump excavation treatments (i.e., “root rupture” method) applied between 2004 and 2014 to control belowground spread of oak wilt on two forests in northeast Wisconsin, USA. The root rupture method achieved a high level of disease control (≥85% of evaluated disease infection centers) for 5 years by harvesting red oak trees within infection centers and uprooting the stumps and associated root mass. The likelihood of disease control success depended on the initial size of the infection center that was treated, with larger infection centers being less likely to be contained with a single treatment than small infection centers. This study highlights the importance of early detection and prompt management in oak wilt suppression programs. Study Implications: Forest management agencies and organizations in the North Central United States continue to face oak wilt epidemics. No single tool or treatment method ensures complete containment of oak wilt; thus, most managers carefully consider all the tools and techniques available to them and determine what best suits their budget and land use priorities. Stump excavation (i.e., “root rupture” method) is a cost-effective treatment for halting belowground spread of the oak wilt fungus, Bretziella fagacearum, that can achieve a high level of disease control. In northern red oak (Quercus rubra) stands with high economic value, this treatment can be applied as a group selection, with the value of the timber potentially offsetting the cost of treatment. The opportunity for complete disease control decreases as oak wilt infection centers increase in size; thus, monitoring and early control actions are critical.

Temporal Variation in Boxelder Seed Predation by Small Mammals

Acer negundo (Boxelder) is a common tree in eastern North America. Fruits are paired samaras that mature in late summer but persist on trees for months. We examined temporal variation in predation rates by small mammals by attaching samaras to sewing bobbins in a forest in northeastern Wisconsin. We placed samaras in groups of 5 along transects and checked them regularly across 2 fall and 2 spring seasons to determine seed fates. Of the 6702 seeds, 15.26% were consumed, 81.41% were left intact, and 3.33% were aborted. Predation rates were higher in fall than in spring. Granivorous mammals did not secondarily disperse seeds but instead acted solely as seed predators. Releasing seeds over a longer period of time than other species of maples allows trees to increase seed survival by experiencing varying soil conditions and predation rates. Retained sterile fruits may act as decoys that decrease predation rates.

Herbaceous plant height is an early indicator of groundlayer response to an experimental manipulation of forest structure and deer pressure

There is growing interest in adapting forest management to increase diversity, in both composition and structure, to restore old-growth characteristics and to build resiliency against anthropogenic disturbances. In order to determine appropriate interventions, managers need to evaluate the quality of natural areas but efficient and effective measurements are elusive. Using a suite of herbaceous species and measuring their responses to experimental treatments, we aim to assess (1) the sensitivity of different metrics and (2) the current and likely future effects of gap-generating disturbances and abundant deer on the understory of a northern hardwood forest in Wisconsin, USA. More specifically, we investigated plant cover, density, height, aggregate height and the proportion of individuals producing flowers/fruits under unmanipulated canopies v. three gap sizes, with and without downed woody material (DWM) additions, and inside v. outside of white-tailed deer (Odocoileus virginianus) exclusion fences, approximately seven years after treatment. The effects were taxon-specific with Anemone quinquefolia, Arisaema triphyllum, Laportea canadensis and Trillium grandiflorum being most responsive to canopy structure, Impatiens spp. and T. grandiflorum to deer pressure, and A. triphyllum, Impatiens spp., L. canadensis and Sanguinaria canadensis to canopy structure in combination with DWM. Cover was least responsive to treatments, density and proportion of sexually reproducing individuals sometimes differed, but height was overall the best metric. Mean height and maximum height showed similar results so we suggest that managers focus on measuring maximum height to limit sampling time. We also draw attention to the importance of retaining and/or creating DWM which has long been recognized as an important structural feature promoting diversity in natural forests. In the present study, DWM additions appeared to play a role in mitigating microclimates and/or deer pressure for multiple herbaceous species.

Population and Community Responses of Small Mammals to Single-tree Selection Harvest in Laurentian Hardwood Forests

Small mammals are ubiquitous members of vertebrate communities that are sensitive to habitat change. In the Great Lakes region of North America, small mammal communities have changed rapidly, but experimental tests of potential mechanisms are lacking. Using a before-after, control-treatment design, we quantified the response of small mammals to single-tree selection harvest in Laurentian hardwood forests of Wisconsin, United States. We documented changes in forest structure and small mammal abundance, species diversity, and community similarity from silvicultural treatment. Treatment reduced tree density and canopy cover and increased mean tree diameter, woody stem density, variation in woody stem density, and volume of coarse woody debris. Peromyscus and northern short-tailed shrews (Blarina brevicauda) were dominant community members across treatments and years. White-footed mice (P. leucopus) outnumbered woodland deer mice (P. maniculatus gracilis) before treatment, but declined by almost fifty percent after treatment; deer mice and total rodent (i.e., Rodentia) abundances were unchanged. Small mammal species diversity increased twofold following treatment. Our experiment identified species-specific responses within Peromyscus to timber harvest: white-footed mice, the numerically dominant and generalist species, were most sensitive to habitat change, and their response produced cascading effects to small mammal community structure. Future experiments should assess these small mammal responses in a multi-year framework and quantify their effects on the broader vertebrate community.

How Forest Structure Drives Productivity

Data from northern Wisconsin forest sites uncovered that vertical heterogeneity metrics are the most influential factors underlying rates of photosynthesis.

Modeling the presence and abundance of buckthorn across the forests of Wisconsin, USA using different regression techniques

Common buckthorn (Rhamnus cathartica) and glossy buckthorn (Frangula alnus) are two species of invasive shrubs causing extensive environmental harm across multiple states of the US and Canadian provinces. One important consideration when managing invasive plants is understanding their habitat preferences. Knowing where the species is most likely to occur can allow monitoring and management activities to focus in those areas. In Wisconsin, factors affecting the presence and abundance of buckthorn have been described for small regions but never at the State level. Therefore, the objective of this study was to develop a predictive model for occurrence and abundancy of buckthorn. Data were collected by establishing 616 sample plots across Wisconsin school forests. We constructed five types of models; logistic regression, regular Poisson and negative binomial regression, and zero-inflated Poisson (ZIP) and negative binomial regression (ZINB) using several plot and stand level model explanatory variables. The ZINB, as the best model among them, indicated that stem density, species diversity, and mean diameter at breast height of woody species (not including buckthorn) as well as distance to nearest house, housing density within 1 km, solar irradiation, percent silt, and latitude were important for estimating buckthorn presence and abundance. The models developed in this study can guide land managers on where to target mitigation actions by identifying areas invaded by buckthorn.

Functional trait data for vascular plant species from northeastern North America.

Wisconsin's plant communities are responding to shifting disturbance regimes, habitat fragmentation, aerial nitrogen deposition, exotic species invasions, ungulate herbivory, and successional processes. To better understand how plant functional traits mediate species' responses to changing environmental conditions, we collected a large set of functional trait data for vascular plant species occupying Wisconsin forests and grasslands. We used standard protocols to make 76,213 measurements of 34 quantitative traits. These data provide rich information on genome size, physical leaf traits (length, width, circularity, thickness, dry matter content, specific leaf area, etc.), chemical leaf traits (carbon, nitrogen, phosphorus, potassium, calcium, magnesium, ash), life history traits (vegetative and flower heights, seed mass), and traits affecting plant palatability (leaf fiber, fat, and lignin). These trait values derive from replicate measurements on 12+ individuals of each species from multiple sites and 45+ individuals for a selected subset of species. Measurements typically reflect values for individuals although some chemical traits involved composite samples from several individuals at the same site. We also qualitatively characterized each species by plant family, woodiness, functional group, and Raunkiaer lifeform. These data allow us to characterize trait dimensionality, differentiation, and covariation among temperate plant species (e.g., leaf and stem economic syndromes). We can also characterize species' responses to environmental gradients and drivers of ecological change. With survey and resurvey data available from >400 sites in Wisconsin, we can analyze variation in community trait distributions and diversity over time and space. These data therefore allow us to assess how trait divergence vs. convergence affects community assembly and how traits may be related to half-century shifts in the distribution and abundance of these species. The data set can be used for non-commercial purposes. The data set is licensed as follows: CC-By Attribution 4.0 International. We request users cite both the OSF data set and this Ecology data paper publication.

Snow depth and woody debris drive variation in small‐mammal winter seed removal

AbstractAimsIn temperate forests, small increases in winter temperature can lead to substantial decreases in snow accumulation, which may alter plant–consumer interactions such as seed predation. However, seed predation by small mammals may also be affected by local habitat structure (e.g., downed woody debris). We tested whether the effect of snow depth on seed predation by small mammals depends on habitat structure (woody debris) that may influence small‐mammal foraging behavior.LocationNorthern temperate forests in Wisconsin, USA.MethodsWe performed a factorial manipulation of snow depth and woody debris presence at 10 sites that differed in site‐level ambient woody debris. At these sites, we monitored seed removal of four temperate tree species (Abies balsamea, Acer rubrum, Acer saccharum, Pinus resinosa).ResultsMean rates of winter seed removal varied among species, as did the effects of snow depth and woody debris. The presence of woody debris decreased Abies balsamea seed removal in plots with snow removed. Regardless of woody debris, snow removal increased Acer saccharum seed removal. Acer rubrum seed removal was lowest at sites with high site‐level woody debris volume, especially in plots with snow removed.ConclusionsWarming winter temperatures may amplify seed removal for some tree species, but local‐scale heterogeneity in woody debris may modify these effects. Because the effects of woody debris and snow removal were much stronger for some tree species than others, changes in seed removal associated with reduced future snow cover or changes in forest management may accelerate regional changes in forest composition.

Effects of forest canopy gaps on the ground‐layer plant community depend on deer: Evidence from a controlled experiment

AbstractQuestions: How do deer mediate the response of forest ground‐layer plant communities to canopy gap size?Location: Flambeau River State Forest in north central Wisconsin, USA (47°37.4ʹ N, 90°47.8ʹ W).Method: We examined responses of resources, growth forms and temporal guilds to factorial combinations of canopy gap treatments consisting of a range of gap sizes (80, 200 and 380 m2), and deer (Odocoileus virginianus) exclusion (0.64 ha fenced exclosures) 4 years following gap creation (3 years following deer exclusion). We contrasted responses in central and transition zones.Results: In the absence of deer, forb productivity increased from pre‐treatment levels, particularly where light transmittance and soil moisture were high. In contrast, forb productivity decreased in the presence of deer. These effects were stronger among forbs with early‐ and late‐summer leafing phenology than spring ephemeral, and evergreen species. In contrast, deer amplified increases in graminoid productivity, which were related primarily to light transmittance. Deer did not alter responses of ferns, shrubs, trees seedlings or vines. Canopy gaps increased community heterogeneity among gap sizes and zones, but only in the absence of deer. This was related to the effects of deer on the composition and diversity of gap specialists.Conclusions: The maintenance of biodiversity in northern temperate forest ground‐layer plant communities by canopy gap dynamics appears to hinge on deer herbivory, even at relatively modest populations of deer and a productive site. Conversely, increases in resource availability within gaps may function to mitigate some negative effects of deer on forb productivity. Effects may be transient, as species turnover to shrub‐ and sapling‐dominated communities and canopy closure may cause communities to converge in the future. However, populations of undefended gap specialists remain particularly sensitive.

Density dependence and habitat heterogeneity regulate seedling survival in a North American temperate forest

Survival and growth of forest tree seedlings are influenced by many abiotic and biotic forces that may vary across space and time. The simultaneous influences of habitat heterogeneity, temporal environmental variability (including disturbance regimes), and biotic interactions are difficult to disentangle, yet understanding the relative importance of these factors for tree seedling dynamics is critical for conservation of forest biodiversity. Most long term, spatially explicit studies of tree seedling ecology have been set in the tropics; much less attention has been given to tree seedlings in temperate forests. We monitored the survival of over 3000 individual seedlings over an eight-year period in a temperate forest in northeast Wisconsin, USA. Results from four seedling censuses demonstrated that both conspecific density and environmental variables significantly affected seedling survival. Higher densities of conspecific trees consistently reduced the probability of seedling survival over time. At the community level, relatively common species were negatively influenced by neighboring conspecific trees and exhibited higher per capita and per basal area mortality. The negative impacts of high conspecific tree density were most pronounced in areas of higher light and moisture, but these interactions varied over time, as did the importance of other abiotic variables. Patterns of less common species were more clearly explained by abiotic variables, with shifting relevance of specific variables according to species abundance. Conspecific negative density dependence, which interacts with resource gradients, and habitat conditions that shift over time are influencing community composition in this northern temperate forest.

The relationship between biodiversity and wetland cover varies across regions of the conterminous United States.

Identifying the factors that determine the spatial distribution of biodiversity is a major focus of ecological research. These factors vary with scale from interspecific interactions to global climatic cycles. Wetlands are important biodiversity hotspots and contributors of ecosystem services, but the association between proportional wetland cover and species richness has shown mixed results. It is not well known as to what extent there is a relationship between proportional wetland cover and species richness, especially at the sub-continental scale. We used the National Wetlands Inventory (NWI) to model wetland cover for the conterminous United States and the National Land Cover Database to estimate wetland change between 2001 and 2011. We used a Bayesian spatial Poisson model to estimate a spatially varying coefficient surface describing the effect of proportional wetland cover on the distribution of amphibians, birds, mammals, and reptiles and the cumulative distribution of terrestrial endemic species. Species richness and wetland cover were significantly correlated, and this relationship varied both spatially and by taxonomic group. Rather than a continental-scale association, however, we found that this relationship changed more closely among ecoregions. The species richness of each of the five groups was positively associated with wetland cover in some or all of the Great Plains; additionally, a positive association was found for mammals in the Southeastern Plains and Piedmont of the eastern U.S. Model results indicated negative association especially in the Cold Deserts and Northern Lakes & Forests of Minnesota and Wisconsin, though these varied greatly between groups. Our results highlight the need for wetland conservation initiatives that focus efforts at the level II and III ecoregional scale rather than along political boundaries.

Fragmentation reduces the importance of niche‐based factors relative to dispersal traits in structuring temperate forest understories

AbstractAimThe relative importance of stochastic and deterministic niche processes can affect the assembly of communities in response to land use context and change. In this study, we quantified the relative importance of dispersal‐ vs niche‐based processes in structuring forest plant metacommunities and sought to understand how these processes have changed in these forests over the past 50 years.LocationWisconsin, USA.MethodsWe used plant understorey community survey data in both the 1950s and 2000s from 142 upland forest stands in southern and northern Wisconsin forests to relate compositional similarity to geographic and environmental distances among sites (reflecting dispersal and niche‐based processes, respectively). We then partitioned the variance to determine their relative importance over time. Finally, we classified species into three dispersal groups based on seed mass, dispersal mode, and plant height to assess how these affect community structure.ResultsBoth niche and dispersal processes influence the structure of Wisconsin's forest plant understories. Niche‐based processes related to environmental differences among sites dominate the mostly continuous northern upland forests. In contrast, dispersal processes dominate community assembly in the more fragmented southern upland forests. Dispersal processes increased in importance in both regions and especially in more fragmented southern upland forests over the past 50 years. We detected no differences among dispersal groups in how similarity decays with geographic distance.ConclusionsIn regions retaining heavy forest cover, niche‐based assembly still predominates while in areas with smaller scattered patches of forest, stochastic dispersal plays a greater role. Dispersal‐based processes increasingly dominate forest metacommunity dynamics in both regions.

Re-evaluating pattern and process to understand resilience in transitional mixed conifer forests.

A key challenge to maintaining resilient landscapes is adapting to and maintaining dynamic ecological processes. In fire-dependent ecosystems, this includes identifying and defining mechanisms through which fire influences forest structure and functionality. Interpretations of tree patterns via land survey records in the Lake States have often highlighted the importance of infrequent moderate to extreme disturbance events. However, historical survey methods are limited to observing higher severity disturbances and over large landscapes, thus it is not clear if the origin, structure, and forcing factors for either patterns or processes are adequately quantified by these methods. We used dendrochronological methods to determine how fire history and stand structure, including cohort structure, tree density, and spatial patterning, are linked within Lake States mixed conifer forests in Wisconsin. We found relatively short mean fire return intervals (MFRIs) ranging from 6 to 13yr with little variation in fire frequency among sites. Current densities of red-pine-dominated forests are 4-37 times historical (ca. 1860) densities (mean12×) and almost entirely spatially random, whereas historically forests were spatially aggregated at stand scales. Stands also contained multiple and/or loosely defined cohort structures suggesting very different controls operating historically than currently. Heterogeneity that helped maintain ecosystem resilience in these ecosystems historically came from frequent fire disturbance processes that affected stand-scale forest resistance. This was likely the historical dynamic across fire-adapted transitional pine forests of the Lake States.

Land-use and climatic causes of environmental novelty in Wisconsin since 1890.

Multiple global change drivers are increasing the present and future novelty of environments and ecological communities. However, most assessments of environmental novelty have focused only on future climate and were conducted at scales too broad to be useful for land management or conservation. Here, using historical county-level data sets of agricultural land use, forest composition, and climate, we conduct a regional-scale assessment of environmental novelty for Wisconsin landscapes from ca. 1890 to 2012. Agricultural land-use data include six cropland types, livestock densities for four livestock species, and human populations. Forestry data comprise biomass-weighted relative abundances for 15 tree genera. Climate data comprise seasonal means for temperature and precipitation. We found that forestry and land use are the strongest cause of environmental novelty (NoveltyForest =3.66, NoveltyAg =2.83, NoveltyClimate =1.60, with Wisconsin's forests transformed by early 20th-century logging and its legacies and multiple waves of agricultural innovation and obsolescence. Climate change is the smallest contributor to contemporary novelty, with precipitation signals stronger than temperature. Magnitudes and causes of environmental novelty are strongly spatially patterned, with novelty in southern Wisconsin roughly twice that in northern Wisconsin. Forestry is the most important cause of novelty in the north, land use and climate change are jointly important in the southwestern Wisconsin, and land use and forest composition are most important in central and eastern Wisconsin. Areas of high regional novelty tend also to be areas of high local change, but local change has not pushed all counties beyond regional baselines. Seven counties serve as the best historical analogues for over one-half of contemporary Wisconsin counties (40/72), and so can offer useful historical counterparts for contemporary systems and help managers coordinate to tackle similar environmental challenges. Multi-dimensional environmental novelty analyses, like those presented here, can help identify the best historical analogues for contemporary ecosystems, places where new management rules and practices may be needed because novelty is already high, and the main causes of novelty. Separating regional novelty clearly from local change and measuring both across many dimensions and at multiple scales thus helps advance ecology and sustainability science alike.

Historical range of variability for restoration and management in Wisconsin

In Wisconsin, as in other states, management goals sometimes include restoration of historical forest conditions, which may prepare forests to be more compatible with future climates, disturbances such as drought and fire, and forest health threats. We quantified historical (1830–1866) composition and structure to develop historical reference conditions for restoration and documented changes based on current (2005–2009) forest surveys in Wisconsin. We provided structural metrics, functional group composition, and forest types for 186 ecological land types, and we also summarized trends in composition and structure. Wisconsin forests historically were comprised of 46% oak or pine savanna or woodland, 6% pine forest, and 48% forests primarily consisting of late-successional eastern broadleaf forest species and early-successional northern mixed forest species; densities of these forest types ranged from 60 to 460 trees/ha. In the Eastern Broadleaf Forest ecological division, increased composition of the early-successional and mid-successional eastern broadleaf forest groups (from 10 to 40%) and (planted) pine group (8–23%) occurred along with decreased fire-tolerant oak composition (from 65 to 23%). Density increased in current forests compared to historical forests by a factor of 2.2; despite increased density, basal area increased only slightly due to the presence of larger diameter trees in historical tree surveys. In the Northern Mixed Forest ecological division, increased composition of the mid-successional eastern broadleaf forest group (from 12 to 24%) and late-successional northern mixed forest group (from 10 to 17%) occurred due to decreased composition of the fire-tolerant pine group (from 17 to 9%) and late-successional eastern broadleaf forest group (from 30 to 20%). Density remained similar in current forests compared to historical forests but current basal area was 50% of historical basal area. The transition from open fire-tolerant oak and pine forests, with rarity of early-successional tree species, to closed forests composed of a variety of early- and mid-successional tree species parallels results from other research. Replacement of open oak or pine forest ecosystems by dense forests has moved Wisconsin outside of the historical range of variability, likely reducing plant and wildlife species associated with open oak and pine ecosystems.

Mounds facilitate regeneration of light-seeded and browse-sensitive tree species after moderate-severity wind disturbance

Using natural disturbance as a guide to management is an approach to develop resilience, maintain or restore natural processes, and sustain ecosystem goods and service. Here, we compare features of mounds resulting from tree uprooting, tree structure and composition, and browsing in recent 10–12-year-old moderate-severity wind disturbance events and reference stands in old hemlock– (Tsuga canadensis–) hardwood forests in Wisconsin, USA. Compared to reference stands, recent, partial blowdown stands had reduced overstory tree density and canopy heights, and more large gaps, coarse woody debris, exposed mineral soil, and newly-created mounds. Regeneration of light-seeded species was greater in blowdown stands relative to reference stands. We found an association between old mounds and overstory eastern hemlock and yellow birch, indicating mounds provide a long-term competitive advantage for these light-seeded species relative to pits and undisturbed areas. Notably, we found that the distance to the canopy was shortened by 30% for trees regenerating on young mounds in blowdown stands. In addition, light-seeded species, such as yellow birch, grew above browse height (2 m) in 10+ years on young mounds. In contrast, on flat and pit microsites, saplings were short (<2 m) and more likely browsed. Maintaining and/or protecting naturally created mounds may facilitate regeneration of light-seeded, browse-sensitive species in mixedwood forests that evolved under infrequent, moderate-severity wind storms. Therefore, reserving a subset of uprooted trees from salvage operations could provide suitable substrate for germination and long-term development advantages, especially for light-seeded and browse-sensitive species and stands managed for high conservation values.

Booming the Cutover: The Campaign for Explosives in the Wisconsin Forest, 1916–1928

By 1910 lumber companies had stripped the Great Lakes states of their white pines, leaving behind a forty-million-acre expanse that came to be known as the "cutover." Business interests, university scientists, and state governments worked aggressively to redevelop this land for crop agriculture. A key challenge was ridding the land of stumps. Especially after the First World War, explosives were touted as a ready means of converting cutover scrub land to crop acreage, thus building instant equity for the farmer. This study focuses on Wisconsin, whose drive for land clearing was the most far-reaching. From 1919 to 1928 the University of Wisconsin College of Agriculture distributed nearly nineteen million pounds of war-surplus explosives to farmers. Michigan, Minnesota, and states in the American South and West did likewise, for a nationwide total exceeding sixty-three million pounds. A massive public relations campaign urged plowmen to clear as many acres as possible, and journalists at all levels signed on to promote cutover farming. However, explosives often proved dangerous in untrained hands, and the hoped-for agricultural bonanza never materialized. As crop prices slumped in the 1920s, submarginal acres were taken out of production, and the ethos of "land clearing" was replaced with one of multifaceted "land use."

Homogenization of species composition and species association networks are decoupled

AbstractAimEcological communities are composed of both species and the biotic relationships (interactions or spatial associations) among them. Biotic homogenization in species composition (i.e., increased site‐to‐site similarity) is recognized as a common consequence of global change, but less is known about how the similarity of species relationships changes over space and time. Does homogenization of species composition lead to homogenization of species relationships or are the dynamics of species relationships decoupled from changes in species composition?LocationWisconsin, USA.Time period1950–2012.Major taxa studiedVascular plants.MethodsWe used long‐term resurvey data to analyse changes in plant species association patterns between the 1950s and 2000s at 266 sites distributed among three community types in Wisconsin, USA. We used species associations (quantified via local co‐occurrence patterns) to represent one type of relationship among species. Species pairs that co‐occur more or less than expected by chance have positive or negative associations, respectively. We then measured beta diversity in both species composition and species association networks over time and space.ResultsShifts in species associations consistently exceeded the shifts observed in species composition. Less disturbed forests of northern Wisconsin have converged somewhat in species composition but little in species associations. In contrast, forests in central Wisconsin succeeding from pine barrens to closed‐canopy forests have strongly homogenized in both species composition and species associations. More fragmented forests in southern Wisconsin also tended to converge in species composition and in the species’ negative associations, but their positive associations diverged over the last half century. Species composition and associations are generally affected by a similar set of environmental variables. Their relative importance, however, has changed over time.Main conclusionsLong‐term shifts in species relationships appear to be decoupled from shifts in species composition despite being affected by similar environmental variables.

Phantom species: adjusting estimates of colonization and extinction for pseudo‐turnover

Ecologists rely on field surveys to monitor long‐term ecological change but finite sampling and the prevalence of rare species mean that surveys inevitably miss some species present at a given location. These ‘phantom species’ produce pseudo‐turnover by inflating observed rates of local colonization and extinction in resurvey studies, especially among rare species. In this paper, we quantify the probability that pseudo‐turnover occurs due to imprecise plot relocation and/or shifts in where individuals are located. Using sampling models derived from the binomial distribution, we estimate probabilities of missing species as a function of local abundance and sampling intensity. Spatially explicit simulations confirm that our binomial model is robust to non‐random sampling schemes and clumped species distributions. False absences decline predictably as species abundance and sampling intensity increase allowing us to statistically adjust naïve estimates of colonization and extinction for expected rates of pseudo‐turnover. To illustrate the model's real‐world utility, we analyze apparent colonizations and extinctions for 331 species distributed over 83 sites in southern Wisconsin forests surveyed in both the 1950s and 2000s. Limited sampling in the 1950s means expected rates of pseudo‐colonization are appreciable. Accounting for pseudo‐turnover thus reduces estimated community‐wide colonization rates by 51% compared to naïve (observed) rates. More complete sampling in the 2000s limited overestimates of local extinction to 14%. We distinguish three zones of inference based on sampling intensity and species abundance where: 1) naïve estimates approximate true values of turnover, 2) adjustments are important, and 3) species are too rare relative to sampling to reliably infer turnover. Accounting for phantom species substantially improves our ability to accurately estimate local colonization and extinction rates, enhancing our ability to infer community dynamics and monitor long‐term ecological change.