Juliann E. Aukema

Economic Impacts of Non-Native Forest Insects in the Continental United States

Reliable estimates of the impacts and costs of biological invasions are critical to developing credible management, trade and regulatory policies. Worldwide, forests and urban trees provide important ecosystem services as well as economic and social benefits, but are threatened by non-native insects. More than 450 non-native forest insects are established in the United States but estimates of broad-scale economic impacts associated with these species are largely unavailable. We developed a novel modeling approach that maximizes the use of available data, accounts for multiple sources of uncertainty, and provides cost estimates for three major feeding guilds of non-native forest insects. For each guild, we calculated the economic damages for five cost categories and we estimated the probability of future introductions of damaging pests. We found that costs are largely borne by homeowners and municipal governments. Wood- and phloem-boring insects are anticipated to cause the largest economic impacts by annually inducing nearly

Historical Accumulation of Nonindigenous Forest Pests in the Continental United States

1.7 billion in local government expenditures and approximately

A comparison of tools for modeling freshwater ecosystem services

830 million in lost residential property values. Given observations of new species, there is a 32% chance that another highly destructive borer species will invade the U.S. in the next 10 years. Our damage estimates provide a crucial but previously missing component of cost-benefit analyses to evaluate policies and management options intended to reduce species introductions. The modeling approach we developed is highly flexible and could be similarly employed to estimate damages in other countries or natural resource sectors.

Economic Impacts of Invasive Species in Forests Past, Present, and Future

Nonindigenous forest insects and pathogens affect a range of ecosystems, industries, and property owners in the United States. Evaluating temporal patterns in the accumulation of these nonindigenous forest pests can inform regulatory and policy decisions. We compiled a comprehensive species list to assess the accumulation rates of nonindigenous forest insects and pathogens established in the United States. More than 450 nonindigenous insects and at least 16 pathogens have colonized forest and urban trees since European settlement. Approximately 2.5 established nonindigenous forest insects per year were detected in the United States between 1860 and 2006. At least 14% of these insects and all 16 pathogens have caused notable damage to trees. Although sap feeders and foliage feeders dominated the comprehensive list, phloem- and wood-boring insects and foliage feeders were often more damaging than expected. Detections of insects that feed on phloem or wood have increased markedly in recent years.

Conservation science: a 20‐year report card

Interest in ecosystem services has grown tremendously among a wide range of sectors, including government agencies, NGOs and the business community. Ecosystem services entailing freshwater (e.g. flood control, the provision of hydropower, and water supply), as well as carbon storage and sequestration, have received the greatest attention in both scientific and on-the-ground applications. Given the newness of the field and the variety of tools for predicting water-based services, it is difficult to know which tools to use for different questions. There are two types of freshwater-related tools--traditional hydrologic tools and newer ecosystem services tools. Here we review two of the most prominent tools of each type and their possible applications. In particular, we compare the data requirements, ease of use, questions addressed, and interpretability of results among the models. We discuss the strengths, challenges and most appropriate applications of the different models. Traditional hydrological tools provide more detail whereas ecosystem services tools tend to be more accessible to non-experts and can provide a good general picture of these ecosystem services. We also suggest gaps in the modeling toolbox that would provide the greatest advances by improving existing tools.

WHERE DOES A FRUIT‐EATING BIRD DEPOSIT MISTLETOE SEEDS? SEED DEPOSITION PATTERNS AND AN EXPERIMENT

Biological invasions by nonnative species are a by‐product of economic activities, with the vast majority of nonnative species introduced by trade and transport of products and people. Although most introduced species are relatively innocuous, a few species ultimately cause irreversible economic and ecological impacts, such as the chestnut blight that functionally eradicated the American chestnut across eastern North America. Assessments of the economic costs and losses induced by nonnative forest pests are required for policy development and need to adequately account for all of the economic impacts induced by rare, highly damaging pests. To date, countrywide economic evaluations of forest‐invasive species have proceeded by multiplying a unit value (price) by a physical quantity (volume of forest products damaged) to arrive at aggregate estimates of economic impacts. This approach is inadequate for policy development because (1) it ignores the dynamic impacts of biological invasions on the evolution of prices, quantities, and market behavior, and (2) it fails to account for the loss in the economic value of nonmarket ecosystem services, such as landscape aesthetics, outdoor recreation, and the knowledge that healthy forest ecosystems exist. A review of the literature leads one to anticipate that the greatest economic impacts of invasive species in forests are due to the loss of nonmarket values. We proposed that new methods for evaluating aggregate economic damages from forest‐invasive species need to be developed that quantify market and nonmarket impacts at microscales that are then extended using spatially explicit models to provide aggregate estimates of impacts. Finally, policies that shift the burden of economic impacts from taxpayers and forest landowners onto parties responsible for introducing or spreading invasives, whether through the imposition of tariffs on products suspected of imposing unacceptable risks on native forest ecosystems or by requiring standards on the processing of trade products before they cross international boundaries, may be most effective at reducing their impacts.

Vectors, viscin, and Viscaceae: mistletoes as parasites, mutualists, and resources

We conducted an intensive review of conservation science to find out whether the field has tracked priorities over the past 20 years. A total of 628 papers from the literature, for the years 1984, 1994, and 2004, were surveyed. For each paper, we recorded where conservation research was done and what was studied. We found geographic gaps in conservation research, with marine, tundra, and desert biomes being studied less than other systems. We also found taxonomic gaps, with amphibians being understudied as compared to other, less threatened, taxonomic groups. Finally, we discovered that studies of invasive species are still lacking, despite the magnitude of the threat they pose to global biodiversity. Although there was a weak trend towards filling these gaps between 1984 and 2004, progress has been slow. To be more effective, the research community must quickly redirect research to better match conservation priorities.

FEMALE‐DIRECTED DISPERSAL AND FACILITATION BETWEEN A TROPICAL MISTLETOE AND A DIOECIOUS HOST

The distribution of desert mistletoes (Phoradendron californicum) among mesquite (Prosopis velutina) hosts is significantly aggregated. We hypothesized that the aggregation of mistletoes among hosts is produced by the pattern of seed rain generated by seed dispersers. We tested whether frugivorous Phainopeplas (Phainopepla nitens) foraged preferentially, and hence deposited mistletoe seeds disproportionately, in already parasitized mesquites. We found that Phainopeplas favored parasitized tall trees as perching and feeding sites and deposited mistletoe seeds disproportionately on trees with these characteristics. To assess experimentally the effect of the presence of mistletoes on seed deposition, we removed mistletoes from host trees. Before mistletoe removal, seed deposition was equivalent and temporally correlated in pairs of control and removal trees. After removal, deposition was lower into removal trees than into unmanipulated trees. Although mistletoe removal resulted in lower seed deposition, it did not eliminate it. We inferred that seed deposition into parasitized hosts can result from deposition of seeds originating from within a host and from other infected hosts. We conclude that the response of seed-dispersing birds to mistletoes leads to disproportionate seed deposition into already parasitized trees and that the heterogeneous distribution of seeds among hosts created by birds contributes to the clumped distribution of mistletoes among hosts.

Plant-frugivore interactions as spatially explicit networks: integrating frugivore foraging with fruiting plant spatial patterns.

Mistletoes are aerial, hemiparasitic plants found on trees throughout the world. They have unique ecological arrangements with the host plants they parasitize and the birds that disperse their seeds. Similar in many respects to vector-borne macroparasites, mistletoes are often detrimental to their hosts, and can even kill them. Coevolution has led to resistance mechanisms in hosts and specialization by mistletoes. Birds act as “disease vectors” for the mistletoe host in a mutualistic relationship. To disperse their seeds, mistletoes attract and manipulate their avian vectors in ways that are typical of both plants (offering a fruit reward) and parasites (changing vector behavior once they have been ingested). Mistletoes are important elements of the landscape that influence the spatial distribution of ecosystem resources. Their patchy distribution and complex interactions make their biology intriguing and their management and conservation challenging.

Mistletoes as parasites and seed-dispersing birds as disease vectors: current understanding, challenges and opportunities.

Phoradendron hexastichum is a bird-dispersed mistletoe that infects the dioecious tree Cecropia schreberiana. Because both species share frugivore seed dispersers, we hypothesized that female Cecropia would have a greater probability and intensity of mistletoe infection than males due to more frequent visitation by shared frugivores. Over 50% of female Cecropia were infected, in contrast with 25% of males. On average, female trees had twice as many mistletoes as male trees. Infection probability and intensity increased with basal area in females but not in males, suggesting that lifetime reinfection was also female biased. We found mistletoe frugivores visiting uninfected fruiting females twice as often as males. Although mistletoes were mostly consumed by the mistletoe specialist Euphonia musica, we did not record Euphonia visiting uninfected Cecropia trees. Uninfected Cecropia trees were frequently visited by generalist frugivores (such as Spindalis portoricensis) that used both mistletoes and Cecropia fruits. The Cecropia–frugivores– Phoradendron network of interactions seems to have led to the spatial linkage of the two plant species through directional dispersal, to plant–plant facilitation through shared frugivores, and to bird–bird facilitation in which generalist frugivores start new foci of infection that specialist frugivores can use.