Mac A. Callaham

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.

Policy and management responses to earthworm invasions in North America

The introduction, establishment and spread of non-native earthworm species in North America have been ongoing for centuries. These introductions have occurred across the continent and in some ecosystems have resulted in considerable modifications to ecosystem processes and functions associated with above- and belowground foodwebs. However, many areas of North America have either never been colonized by introduced earthworms, or have soils that are still inhabited exclusively by native earthworm fauna. Although several modes of transport and subsequent proliferation of non-native earthworms have been identified, little effort has been made to interrupt the flow of new species into new areas. Examples of major avenues for introduction of earthworms are the fish-bait, horticulture, and vermicomposting industries. In this paper we examine land management practices that influence the establishment of introduced species in several ecosystem types, and identify situations where land management may be useful in limiting the spread of introduced earthworm species. Finally, we discuss methods to regulate the importation of earthworms and earthworm-containing media so that introduction of new exotic species can be minimized or avoided. Although our focus in this paper is necessarily North American, many of the management and policy options presented here could be applicable to the problem of earthworm invasions in other parts of the world.

Deep Ion Torrent sequencing identifies soil fungal community shifts after frequent prescribed fires in a southeastern US forest ecosystem

Prescribed burning is a common management tool to control fuel loads, ground vegetation, and facilitate desirable game species. We evaluated soil fungal community responses to long-term prescribed fire treatments in a loblolly pine forest on the Piedmont of Georgia and utilized deep Internal Transcribed Spacer Region 1 (ITS1) amplicon sequencing afforded by the recent Ion Torrent Personal Genome Machine (PGM). These deep sequence data (19,000 + reads per sample after subsampling) indicate that frequent fires (3-year fire interval) shift soil fungus communities, whereas infrequent fires (6-year fire interval) permit system resetting to a state similar to that without prescribed fire. Furthermore, in nonmetric multidimensional scaling analyses, primarily ectomycorrhizal taxa were correlated with axes associated with long fire intervals, whereas soil saprobes tended to be correlated with the frequent fire recurrence. We conclude that (1) multiplexed Ion Torrent PGM analyses allow deep cost effective sequencing of fungal communities but may suffer from short read lengths and inconsistent sequence quality adjacent to the sequencing adaptor; (2) frequent prescribed fires elicit a shift in soil fungal communities; and (3) such shifts do not occur when fire intervals are longer. Our results emphasize the general responsiveness of these forests to management, and the importance of fire return intervals in meeting management objectives.

Occurrence of an exotic earthworm ( Amynthas agrestis ) in undisturbed soils of the southern Appalachian Mountains, USA

This study documents the occurrence of an aggressive invasive earthworm species in undisturbed forest soils of the southern Appalachian Mountains of northern Georgia, USA. Earthworms were sorted from samples collected in pitfall traps that had been set in mature, mesic oak-hickory forests in remote, high elevation, locations across northern Georgia. Specimens were continuously collected in these traps over the course of the summer and autumn of 1993, and more than 600 earthworms were collected from 35 different trapping sites. There were at least 9 different earthworm taxa collected during the study including three species not native to North American soils (Amynthas agrestis, Octolasion tyrtaeum, and O. cyaneum). The majority of earthworms collected in the study were A. agrestis. Because large numbers of A. agrestis were trapped at a single site, we made measurements of individuals in an attempt to examine the reproductive status of A. agrestis at that site over time. Small numbers of A. agrestis were trapped in July and August, peak abundance occurred in September, and there was a decline in abundance through November to zero trapped in December. Sexually mature adults were first trapped in small numbers in late August, but made up 80 % of the total population by mid September, and 100 % of the population in October and November.

Spatial variability of an invasive earthworm (Amynthas agrestis) population and potential impacts on soil characteristics and millipedes in the Great Smoky Mountains National Park, USA

European and Asian earthworm invasions are widespread in North America. European earthworms especially are well-known to cause dramatic changes in ecosystems in northern, formerly glaciated portions of the continent, but less is known about the impacts of earthworm invasions in unglaciated areas inhabited by indigenous earthworms. We monitored fluctuations in the spatial extent of an Amynthas agrestis (Megascolecidae) population in the Great Smoky Mountains National Park in eastern Tennessee, USA. Two years of monthly growing-season observations revealed that the distribution of the earthworm population was dynamic, but overall distribution was closely linked to temperature and moisture with dramatic reductions of earthworm numbers associated with very dry conditions. In plots where A. agrestis were more often detected, we measured increased A-horizon soil aggregation and decreased thickness of the Oe/Oa-horizon. However, A. agrestis was not related to A-horizon microbial biomass, A-horizon C:N, Oi-horizon (litter) thickness, or mass of forest floor (O-horizon). Reductions in millipede species richness and density were associated with frequency of A. agrestis presence, possibly due to direct competition for food resources (Oe/Oa material). This evidence for potentially negative interactions between millipedes and A. agrestis suggests that expansion of the non-native earthworm into new habitats in the Park may alter soil physical properties and could pose a threat to native millipede diversity.

Stable isotopic studies of earthworm feeding ecology in tropical ecosystems of Puerto Rico.

Feeding strategies of earthworms and their influence on soil processes are often inferred from morphological, behavioral and physiological traits. We used (13)C and (15)N natural abundance in earthworms, soils and plants to explore patterns of resource utilization by different species of earthworms in three tropical ecosystems in Puerto Rico. In a high altitude dwarf forest, native earthworms Trigaster longissimus and Estherella sp. showed less (15)N enrichment ((15)N = 3-6 per thousand) than exotic Pontoscolex corethrurus ((15)N =7-9 per thousand) indicating different food sources or stronger isotopic discrimination by the latter. Conversely, in a lower altitude tabonuco forest, Estherella sp. and P. corethrurus overlapped completely in (15)N enrichment ((15)N = 6-9 per thousand), suggesting the potential for interspecific competition for N resources. A tabonuco forest converted to pasture contained only P. corethrurus which were less enriched in (15)N than those in the forest sites, but more highly enriched in (13)C suggesting assimilation of C from the predominant C(4) grass. These results support the utility of stable isotopes to delineate resource partitioning and potential competitive interactions among earthworm species. Copyright 1999 John Wiley & Sons, Ltd.

Feeding ecology and emergence production of annual cicadas (Homoptera: Cicadidae) in tallgrass prairie

Abstract The emergence phenology and feeding ecology of annual cicadas in tallgrass prairie are poorly documented. However, these large insects are abundant, and their annual emergence represents a potentially important flux of energy and nutrients from belowground to aboveground. We conducted a study at Konza Prairie Research Natural Area in eastern Kansas to characterize and quantify cicada emergence and associated energy and nutrient fluxes. We established emergence trap transects in three habitat types (upland prairie, lowland prairie, and riparian forest), and collected cicadas every 3 days from May to September. A subset of trapped cicadas was used for species- and sex-specific mass, nutrient, and stable isotope analyses. Five species were trapped during the study, of which three were dominant. Cicadetta calliope and Tibicen aurifera exhibited significantly higher emergence production in upland prairie than in lowland prairie, and were not captured in forested sites at all. T. dorsata emerged from all three habitat types, and though not significant, showed a trend of greater abundance in lowland grasslands. Two less abundant species, T. pruinosa and T. lyricen, emerged exclusively from forested habitats. Nitrogen fluxes associated with total cicada emergence were estimated to be ∼4 kg N ha–1 year–1 in both grassland habitats, and 1.01 kg N ha–1 year–1 in forested sites. Results of stable isotope analyses showed clear patterns of resource partitioning among dominant cicada species emerging from grassland sites. T. aurifera and C. calliope had δ13C and δ15N signatures indicative of feeding on shallowly rooted C4 plants such as the warm-season grasses dominant in tallgrass prairie ecosystems, whereas T. dorsata signatures suggested preferential feeding on more deeply rooted C3 plants.

Emergence of Periodical Cicadas (Magicicada cassini) From a Kansas Riparian Forest: Densities, Biomass and Nitrogen Flux

Abstract The 1998 emergence of 17-y periodical cicadas (Magicicada cassini) on Konza Prairie Research Natural Area (KPRNA), Kansas, was quantified using emergence trap transects and counts of emergence holes. Emergence density, biomass (emergence production) and associated nitrogen flux were estimated for the entire 100 ha gallery forest of Kings Creek, the major drainage network on KPRNA. Emergence commenced on 22 May 1998 and lasted for 24 d, with 87% of the individuals emerging within the first 9 d. Males dominated early during the emergence, and the sex ratio for the entire population was estimated at 54:46 male:female. Average emergence abundance and biomass estimated from trap transects located in low areas where cicadas were most abundant were 152/m2 and 34.9 g ash-free dry mass (AFDM)/m2, respectively. Based on emergence hole counts, average density and biomass for the 59 ha of gallery forest where cicadas emerged were 27.2 individuals/m2 and 6.3 g AFDM/m2, and emergence hole densities >100/m2 were evident in low areas of the drainage. Emergence density generally decreased with increasing elevation in the catchment. Belowground to aboveground N flux associated with M. cassini emergence in high density areas was ∼3 g N/m2, and the average for the entire emergence area was 0.63 g N/m2. The total number of individuals that emerged from the Kings Creek riparian forest was estimated at 19.6 million, which represents 4.6 metric tons AFDM and ∼0.5 metric tons N. This linear, fragmented, gallery forest of the Flint Hills supports a high density of M. cassini, and an emergence event constitutes a significant belowground to aboveground flux of energy and nutrients. Thus, the periodical cicada may be an exception to the notion that insects generally do not represent important resource pools at the ecosystem level.

Survey to Evaluate Escape of Eucalyptus spp. Seedlings from Plantations in Southeastern USA

Interest in biomass-based energy in the southeastern Unites States has led to increased need for fast-growing tree species. Several Eucalyptus species exhibit characteristics that make them attractive in the bioenergy context. However, some of these also possess traits that suggest they could become invasive. To make a preliminary assessment of the risk of seedling establishment in the vicinity of Eucalyptus plantations, we conducted surveys at 3 sites in South Carolina and 16 sites in Florida. In South Carolina, no seedlings were detected in any sample transect. In Florida, we found seedlings within the boundaries of Eucalyptus plantations at 4 of the 16 sites surveyed. We also detected seedlings outside the boundaries of these same four plantations, but only two seedlings were detected at distances >45 m from plantation boundaries. All seedlings from Florida were either E. amplifolia, E. robusta, or E. grandis. The most predictive variable evaluated was latitude, with 27°N being the highest latitude at which seedlings established with regularity. Results of this survey indicate that, under current conditions, the spread of Eucalyptus spp. from plantations should be possible to manage with appropriate monitoring, but this should be evaluated further before Eucalyptus spp. are adopted for widespread planting.

Annual Fire, Mowing and Fertilization Effects on Two Cicada Species (Homoptera: Cicadidae) in Tallgrass Prairie

Abstract In tallgrass prairie, cicadas emerge annually, are abundant and their emergence can be an important flux of energy and nutrients. However, factors influencing the distribution and abundance of these cicadas are virtually unknown. We examined cicada emergence in plots from a long-term (13 y) experimental manipulation involving common tallgrass prairie management practices. The plots were arranged in a factorial experimental design, incorporating annual burning, mowing and fertilization (10 g N m−2 and 1 g P m−2). One cicada species, Cicadetta calliope, responded positively to fire, but negatively to mowing, and was most abundant in plots that were burned, unmowed and fertilized. Increased density of C. calliope in this treatment combination is related, in part, to increased availability of oviposition sites aboveground. Furthermore, C. calliope females from fertilized plots were significantly larger in body size relative to females from unfertilized prairie. Another cicada species, Tibicen aurifera, emerged only from unburned plots. The mechanism underlying this negative response to fire is unclear, but may be related to the presence of standing dead vegetation or improved quality (i.e., N content) of belowground plant tissue in unburned plots. In contrast to C. calliope, the density of T. aurifera was not affected by mowing or fertilization. However, like C. calliope, the body size of T. aurifera females was significantly greater in fertilized plots. Cicada emergence resulted in N flux ranging from 0.05–0.16 g N m−2 in unburned plots, but N flux (as cicada biomass) from annually burned plots was negligible.