Predicted range expansion of Chinese tallow tree (Triadica sebifera) in forestlands of the southern United States

Aim We present an integrated approach for predicting future range expansion of an invasive species (Chinese tallow tree) that incorporates statistical forecasting and analytical techniques within a spatially explicit, agent‐based, simulation framework. Location East Texas and Louisiana, USA. Methods We drew upon extensive field data from the US Forest Service and the US Geological Survey to calculate spread rate from 2003 to 2008 and to parameterize logistic regression models estimating habitat quality for Chinese tallow within individual habitat cells. We applied the regression analyses to represent population spread rate as a function of habitat quality, integrated this function into a logistic model representing local spread, and coupled this model with a dispersal model based on a lognormal kernel within the simulation framework. We simulated invasions beginning in 2003 based on several different dispersal velocities and compared the resulting spatial patterns to those observed in 2008 using cross Mantel’s tests. We then used the best dispersal velocity to predict range expansion to the year 2023. Results Chinese tallow invasion is more likely in low and flat areas adjacent to water bodies and roads, and less likely in mature forest stands and in pine plantations where artificial regeneration by planting seedlings is used. Forecasted invasions resulted in a distribution that extended from the Gulf Coast of Texas and Louisiana northward and westward as much as 300 km, representing approximately 1.58 million ha. Main conclusions Our new approach of calculating time series projections of annual range expansion should assist land managers and restoration practitioners plan proactive management strategies and treatments. Also, as field sampling continues on the national array of FIA plots, these new data can be incorporated easily into the present model, as well as being used to develop and/or improve models of other invasive plant species.     

Of Asian forests and European fields: Eastern U.S. plant invasions in a global floristic context

Background

Biogeographic patterns of species invasions hold important clues to solving the recalcitrant ‘who’, ‘where’, and ‘why’ questions of invasion biology, but the few existing studies make no attempt to distinguish alien floras (all non-native occurrences) from invasive floras (rapidly spreading species of significant management concern), nor have invasion biologists asked whether particular habitats are consistently invaded by species from particular regions.

Methodology/Principal Findings

Here I describe the native floristic provenances of the 2629 alien plant taxa of the Eastern Deciduous Forest of the Eastern U.S. (EUS), and contrast these to the subset of 449 taxa that EUS management agencies have labeled ‘invasive’. Although EUS alien plants come from all global floristic regions, nearly half (45%) have native ranges that include central and northern Europe or the Mediterranean (39%). In contrast, EUS invasive species are most likely to come from East Asia (29%), a pattern that is magnified when the invasive pool is restricted to species that are native to a single floristic region (25% from East Asia, compared to only 11% from northern/central Europe and 2% from the Mediterranean). Moreover, East Asian invaders are mostly woody (56%, compared to just 23% of the total alien flora) and are significantly more likely to invade intact forests and riparian areas than European species, which dominate managed or disturbed ecosystems.

Conclusions/Significance

These patterns suggest that the often-invoked ‘imperialist dogma’ view of global invasions equating invasion events with the spread of European colonialism is at best a restricted framework for invasion in disturbed ecosystems. This view must be superseded by a biogeographic invasion theory that is explicitly habitat-specific and can explain why particular world biotas tend to dominate particular environments.     

Population dynamics of autotrophic picoplankton in a southeastern U.S. Reservoir

Reservoirs typically exhibit a gradient along their longitudinal axis in turbidity, nutrient flux, and algal biomass. We utilized these characteristics to examine factors influencing temporal and spatial patterns in abundance, biomass, composition, and production of epilimnetic autotrophic picoplankton (APP) in Sardis Reservoir, Mississippi, USA. Over a 18-month period, APP abundance varied between about 15,000 and 700,000 cells ml⁻¹. Both APP abundance and APP biomass were closely linked to APP production and temperature. On an annual basis, the contribution of APP to total algal biomass and light-standardized production ranged between 15–47%, and 5–40%, respectively. Prokaryotes comprised more than 95% of all APP in summer, but eukaryotes dominated the APP community in winter. During the nutrient-depleted summer period, APP decreased in number but tended to increase in the percentage of total algal biomass and production, from the uplake riverine zone to the downlake lacustrine zone. Only in the second year of the study, when reservoir water residence time was more than four times greater than in the first year, were there significant differences in biomass and productivity of APP between the uplake and downlake regions. We suggest that, particularly in years or at times of the year when water-flow through the reservoir is slow, the importance of APP in Sardis Reservoir reflects a spatial and temporal gradient in nutrient availability.     

Nitrogen and phosphorus dynamics in hot desert streams of Southwestern U.S.A.

Nitrogen to phosphorus ratios and concentrations of nitrate and soluble reactive phosphate are presented for an array of Southwestern streams as evidence that nitrogen is the limiting nutrient where such limitation occurs. Nitrate uptake in sections of intermittent streams was attributable to autotrophic activity. Uptake of soluble reactive phosphate was unrelated to any indicator of autotrophic activity, thus concentrations of this nutrient in desert and semi-desert stream waters may be controlled by other factors.     

Morphological and physiological responses of nine southern U.S. rice cultivars differing in their tolerance to enhanced ultraviolet-B radiation

The impact of climatic change on crop production is a major global concern. One of the climatic factors, ultraviolet-B radiation (UV-B; 280–320 nm), which is increasing as a result of depletion of the global stratospheric ozone layer, can alter crop productivity. As the initial step in development of UV-B tolerant rice cultivars for the southern U.S., in this study we screened popular southern U.S. rice cultivars for variation in tolerance to elevated UV-B radiation with respect to morphological, phenological and physiological parameters. Plants grown in the greenhouse at the Texas AgriLife Research and Extension Center in Beaumont, Texas, U.S. were exposed to 0, 8 or 16 kJ m⁻² day⁻¹ UV-B radiation for 90 days. Our results showed differences among southern US rice cultivars in response to UV-B treatments with respect to leaf photosynthetic rate (P_n), leaf phenolic concentration, pollen germination (PG), spikelet fertility (SF), leaf number, leaf area, and yield. For most of the cultivars, plants exposed to enhanced UV-B radiation showed decreased P_n, PG, SF and yield and increased spikelet abortion and leaf phenolic concentration compared to the plants grown in a UV-B-free environment. In this study, cultivar ‘Clearfield XL729’ performed better than the other cultivars under enhanced UV-B radiation.     

Benthic macroinvertebrate community structure, function and production with respect to habitat type, reach and drainage basin in the southern Appalachians (U.S.A.)

1. Benthic macroinvertebrates were sampled for 1 year to assess functional and taxonomic differences in invertebrate biomass and production with respect to habitat types, reaches and catchments in Wine Spring Basin, western North Carolina. Quantitative samples were collected from depositional, cobble-riffle and bedrock outcrop habitats at four stream reaches (two headwater sites, one second order, and one third order). Other measures included physical parameters, periphyton and organic matter standing crops. Invertebrate data from the Wine Spring catchment were also compared with data from another catchment (Ball Creek) within the same region. 2. The three habitat types had different current velocities and mean substratum particle sizes; both measures were greatest in bedrock outcrop habitats and lowest in depositional habitats. Organic matter standing crops, invertebrate functional group productivity and biomass also differed significantly with respect to habitat type. Cobble-riffle areas had the lowest standing crops of organic matter, invertebrate productivity and biomass. 3. Both invertebrate communities and organic matter standing crops differed significantly between the two headwater reaches. First- to third-order reaches differed in taxonomic composition at the genus level, yet had similar relative functional group productivity and biomass. 4. Annual mean invertebrate biomass and secondary production were greater in the Wine Spring Basin than in Ball Creek. Sites in both the Wine Spring and Ball Creek catchments, however, exhibited similar functional group distributions per habitat type. 5. Local geomorphology and related physical parameters influenced the structure of invertebrate functional group composition, and the distribution of organic matter standing crops. Furthermore, comparison of community structure in Wine Spring with that in Ball Creek suggested that taxonomic composition was more related to catchment-specific parameters (e.g. thermal regime, evolutionary history) than stream size.     

The spatial spread of invasions: new developments in theory and evidence

We review and synthesize recent developments in the study of the spread of invasive species, emphasizing both empirical and theoretical approaches. Recent theoretical work has shown that invasive species spread is a much more complex process than the classical models suggested, as long range dispersal events can have a large influence on the rate of range expansion through time. Empirical work goes even further, emphasizing the role of spatial heterogeneity, temporal variability, other species, and evolution. As in some of the classic work on spread, the study of range expansion of invasive species provides unique opportunities to use differences between theory and data to determine the important underlying processes that control spread rates.     

Impact of selected pesticides on field population dynamics of parasitic Hymenoptera (Pteromalidae) in caged-layer poultry manure in southern California, U.S.A.

Field studies were conducted at caged-layer poultry facilities in southern California, U.S.A., to determine the effect of selected pesticides on beneficial Pteromalidae. Weekly parasite sampling was conducted using sentinel Musca domestica L. pupae to assess changes in parasitization in relation to pesticide treatment. Sites were sampled weekly for 5 weeks before treatment and for 8-10 weeks post-treatment. Treatments were applied twice to six hen houses (four treated plus two controls) at each of two sites. Treatments were: (1) dimethoate (0.5%), spot-treatment to wet areas only (approximately 5-10% of manure surface); (2) dimethoate (0.5%), entire manure surface; (3) cyromazine (0.1%), entire manure surface; and (4) permethrin (0.05%) applied to all hens in the house for northern fowl mite [Ornithonyssus sylviarum (Canestrini and Fanzago)]. The two discrete pesticide applications during an 8-day period had no significant effect on activity of Muscidifurax spp. and Spalangia spp. at either site.     

Stream channel geomorphology influences mussel abundance in southern Appalachian streams, U.S.A.

1. Studies of North American streams have shown that hydraulic parameters and stream geomorphology can explain unionid mussel abundance at both the reach and catchment scale. However, few studies have examined applicability of hydrogeomorphic variables across broader spatial scales, such as across whole catchments, or have elucidated conditions under which spates can affect mussel populations in streams. 2. We quantified freshwater mussel abundance and species richness and their physical habitat at 24 sites in eight streams in southern Appalachian catchments in 2000 and 2001. In addition, we modelled site‐specific hydraulic parameters during summer baseflow and bankfull stages to estimate high‐ and low‐discharge conditions, respectively. 3. Mussel abundance was related to stream geomorphology, whereas richness was related to stream size. Baseflow habitat parameters explained only minor variation in abundance or richness, and both measures were highly correlated with mean current velocity or stream size. Bankfull shear stress composed a relatively low proportion of overall mussel habitat variability, but it accounted for significant variation in abundance and richness. 4. Mussel abundance was highly variable at sites subject to low‐shear stress during spates, whereas abundance always was low at sites subject to high‐shear stress. These data suggest that habitat conditions during floods, rather than those at summer baseflow, limit the abundance of mussels in Appalachian streams. These data also suggest that mussel abundance and assemblage structure may be sensitive to any changes in channel geomorphology and hydraulic conditions that might result from land use in the catchment.     

Life cycles, microdistribution and production dynamics of six species of net-spinning caddisflies in a large southeastern (U.S.A.) river

Hydropsyche incommoda. H. rossi, Cheumalopsyche pasella, Mocronema Carolina. Chimarra moslyi , and Neureclipsis crepuscularis were studied on woody substrates (snags) in the lower Savannah River. Distribution of most species biomass was positively correlated with attached macrophytes on snags at medium (25–50 cm s^-1) current velocities. All species were bivoltine at the study site with the exception of M. Carolina which was univoltine. Annual and cohort production estimates (Hynes and removal-summation methods) were obtained for each species at three velocity ranges. Total annual caddisfly production calculated by the Hynes method was 12.6, 41.4, and 22.7 g (ash free dry wt m^-2 of snag surface area at low, medium and high velocities, respectively; 9.6, 34.4, and 19.9 g with removal-summation; and, 11.5, 36.1 and 21.1 g when the Hynes method was applied to discrete cohorts. Higher cohort production was attained by the overwintering generation because of higher terminal instar body weights. Dissolved organic carbon comprised most of the total organic load transported by the river; however, abundant paniculate organic food was also apparently available for filler feeders. Organic and inorganic seston concentrations were highest in winter months and lowest in autumn. Over 90 percent of the seston (by weight) was <105 μm. It is suggested that the variation in catchnet mesh size, coupled with spatial heterogeneity of the snag habitat, allows the caddisflies to partition space, which is apparently the limited resource.     

A comparison of modern and presettlement pollen from southern Michigan (U.S.A.)

Use of samples of modern pollen to interpret assemblages of fossil pollen requires that the effects of man's impact be identified in the modern pollen. A comparison of the modern and presettlement pollen in 23 short cores taken within the lower peninsula of Michigan reveals a varied effect of man's activities on the vegetation. When obvious indicators of human activity (such as ragweed pollen) are removed from the pollen sum, many differences in the composition of the arboreal pollen are still evident between presettlement and modern records. When compared to presettlement data, birch, elm, and willow pollen in the modern data appear in proportionately higher quantities throughout the state, whereas beech, maple, and hemlock are in lower quantities. Within the region of primeaval pine forests, white pine values are much lower and oak values show an increase. Despite these differences in the pollen record, the modern pollen reflect the same basic patterns in the vegetation as the presettlement pollen. Principal component analysis shows the same patterns to exist in the modern data as are in the presettlement pollen.