How effective are broad-scale nutrient mass balances for determining the sustainability of lot-feed manure application?

Nutrient mass balances have been used to assess a variety of land resource scenarios, at various scales. They are widely used as a simple basis for policy, planning, and regulatory decisions but it is not clear how accurately they reflect reality. This study provides a critique of broad-scale nutrient mass balances, with particular application to the fertiliser use of beef lot-feeding manure in Queensland.Mass balances completed at the district and farm scale were found to misrepresent actual manure management behaviour and potentially the risk of nutrient contamination of water resources. The difficulties of handling stockpile manure and concerns about soil compaction mean that manure is spread thickly over a few paddocks at a time and not evenly across a whole farm. Consequently, higher nutrient loads were applied to a single paddock less frequently than annually. This resulted in years with excess nitrogen, phosphorus, and potassium remaining in the soil profile. This conclusion was supported by evidence of significant nutrient movement in several of the soil profiles studied.Spreading manure is profitable, but maximum returns can be associated with increased risk of nutrient leaching relative to conventional inorganic fertiliser practices. Bio-economic simulations found this increased risk where manure was applied to supply crop nitrogen requirements (the practice of the case study farms, 200–5000 head lot-feeders).Thus, the use of broad-scale mass balances can be misleading because paddock management is spatially heterogeneous and this leads to increased local potential for nutrient loss. In response to the effect of spatial heterogeneity policy makers who intend to use mass balance techniques to estimate potential for nutrient contamination should apply these techniques conservatively.     

Optimizing carbon sequestration in commercial forests by integrating carbon management objectives in wood supply modeling

This paper provides a methodology for generating forest management plans, which explicitly maximize carbon (C) sequestration at the forest-landscape level. This paper takes advantage of concepts first presented in a paper by Meng et al. (2003; Mitigation Adaptation Strategies Global Change 8:371–403) by integrating C-sequestration objective functions in existing wood supply models. Carbon-stock calculations performed in Woodstock^TM (RemSoft Inc.) are based on C yields generated from volume table data obtained from local Forest Development Survey plots and a series of wood volume-to-C content conversion factors specified in von Mirbach (2000). The approach is used to investigate the impact of three demonstration forest-management scenarios on the C budget in a 110,000 ha forest in south-central New Brunswick, Canada. Explicit demonstration scenarios addressed include (1) maximizing timber extraction either by clearcut or selection harvesting for greatest revenue generation, (2) maximizing total C storage in the forest landscape and in wood products generated from harvesting, and (3) maximizing C storage together with revenue generation. The level of clearcut harvesting was greatest for scenario 1 (≥15 × 10⁴ m³ of wood and ≥943 ha of land per harvesting period), and least for scenario 2 (=0 m³ per harvesting period) where selection harvesting dominated. Because softwood saw logs were worth more than pulpwood ($60 m⁻³ vs. $40 m⁻³) and were strategic to the long-term storage of C, the production of softwood saw logs exceeded the production of pulpwood in all scenarios. Selection harvesting was generally the preferred harvesting method across scenarios. Only in scenario 1 did levels of clearcut harvesting occasionally exceed those of selection harvesting, mainly in the removal of old, dilapidated stands early in the simulation (i.e., during periods 1 through 3). Scenario 2 provided the greatest total C-storage increase over 80 years (i.e., 14 × 10⁶ Mg C, or roughly 264 Mg ha⁻¹) at a cost of $111 per Mg C due to lost revenues. Scenarios 3 and 1 produced reduced storage rates of roughly 9 × 10⁶ Mg C and 3 × 10⁶ Mg C, respectively; about 64% and 22% of the total, 80-year C storage calculated in scenario 2. The bulk of the C in scenario 2 was stored in the forest, amounting to about 76% of the total C sequestered.     

Heterogeneity shapes invasion: host size and environment influence susceptibility to a nonnative pathogen.

Theoretical study of invasion dynamics has suggested that spatial heterogeneity should strongly influence the rate and extent of spreading organisms. However, empirical support for this prediction is scant, and the importance of understanding heterogeneity for real-world systems has remained ambiguous. This study quantified the influence of host and environmental heterogeneity on the dynamics of a 19-year disease invasion by the exotic and fatal pathogen, Phytophthora lateralis, within a stream population of its host tree, Port Orford cedar (Chamaecyparis lawsoniana). Using dendrochronology, we reconstructed the invasion history along a 1350-m length of infected stream, which serves as the only route of pathogen dispersal. Contrary to theoretical predictions, the temporal progression of the disease invasion was not related to a host's downstream spatial position, but instead was determined by two sources of heterogeneity: host size and proximity to the stream channel. These sources of heterogeneity influenced both the epidemic and endemic dynamics of this pathogen invasion. This analysis provides empirical support for the influence of heterogeneity on the invasion dynamics of a commercially important forest pathogen and highlights the need to incorporate such natural variability into both invasion theory and methods aimed at controlling future spread.     

N fertilization effects on denitrification and N cycling in an aggrading forest.

We investigated N cycling and denitrification rates following five years of N and dolomite amendments to whole-tree harvested forest plots at the long-term soil productivity experiment in the Fernow Experimental Forest in West Virginia, USA. We hypothesized that changes in soil chemistry and nutrient cycling induced by N fertilization would increase denitrification rates and the N2O:N2 ratio. Soils from the fertilized plots had a lower pH (2.96) than control plots (3.22) and plots that received fertilizer and dolomite (3.41). There were no significant differences in soil %C or %N between treatments. Chloroform-labile microbial biomass carbon was lower in fertilized plots compared to control plots, though this trend was not significant. Extractable soil NO3- was elevated in fertilized plots on each sample date. Soil-extractable NH4+, NO3-, pH, microbial biomass carbon, and %C varied significantly by sample date suggesting important seasonal patterns in soil chemistry and N cycling. In particular, the steep decline in extractable NH4+ during the growing season is consistent with the high N demands of a regenerating forest. Net N mineralization and nitrification also varied by date but were not affected by the fertilization and dolomite treatments. In a laboratory experiment, denitrification was stimulated by NO3- additions in soils collected from all field plots, but this effect was stronger in soils from the unfertilized control plots, suggesting that chronic N fertilization has partially alleviated a NO3- limitation on denitrification rates. Dextrose stimulated denitrification only in the whole-tree-harvest soils. Denitrification enzyme activity varied by sample date and was elevated in fertilized plots for soil collected in July 2000 and June 2001. There were no detectable treatment effects on N2O or N2 flux from soils under anaerobic conditions, though there was strong temporal variation. These results suggest that whole-tree harvesting has altered the N status of these soils so they are less prone to N saturation than more mature forests. It is likely that N losses associated with the initial harvest and high N demand by aggrading vegetation is minimizing, at least temporarily, the amount of inorganic N available for nitrification and denitrification, even in the fertilized plots in this experiment.     

Parasitic flies (Diptera: Phoridae) influence foraging rhythms and caste division of labor in the leaf-cutter ant,Atta cephalotes (Hymenoptera: Formicidae)

Summary Three lines of evidence, including interspecific comparisons, temporal division of foraging between size castes, and experimental manipulations, suggest that the diurnal parasitoid Neodohrniphora curvinervis (Diptera: Phoridae) influences both the caste sizes and numbers of leaf-cutter ants (Atta cephalotes) that leave their underground nests to collect leaves. At Parque Nacional Corcovado in Costa Rica, A. cephalotes was attacked by Neodohrniphora during the daytime, and foraged less during the day than at night; a closely related ant at the same site, A. colombica, had no phorid parasites and foraged exclusively during the day. Most daytime foragers of A. cephalotes were smaller than the lower size threshold for attack by Neodohrniphora, while nocturnal foragers, active when parasitoids were absent, were both larger than this threshold and within the energetically optimal size range for foraging. When I supplied artificial lighting to allow phorids to hunt at A. cephalotes colonies past dusk, ants foraged less than when light was provided but flies were removed. The influence of Neodohrniphora on the foraging activity of A. cephalotes may explain why investigations focusing on abiotic factors have largely failed to discover what drives this ant's daily foraging cycles, and suggests that forager sizes are influenced not only by energetic efficiency, but also by the threat of parasitism.     

Conservation Implications of the Natural Loss of Lineages in Wild Mammals and Birds

Because populations in zoological parks and nature reserves often are derived from only a few individuals, conservationists have attempted to minimize founder effects by equalizing family group sizes and increasing the reproductive contributions of all individuals. Although such programs reduce potential losses of genetic diversity, information is rarely available about the actual persistence of family groups or genetic lineages in natural populations. In the absence of such data, it can be difficult to weigh the importance of human intervention in the conservation of small populations. Separate long-term studies of two mammals, the North American bison (Bison bison) and the white-nosed coati (Nasua narica), and a bird, the Acorn Woodpecker (Melanerpes formicivorus), demonstrate differential extinction of genetic lineages. Irrespective of the mechanisms affecting population structure, which may range from stochastic environmental events to such behavioral phenomena as poor intrasexual competitive abilities, our results show that lineages can be lost at rapid rates from natural populations. A survey of comparable studies from the literature indicates that the loss of matrilines over the course of the study varies from 3% to 87% in wild mammals and from 30% to 80% in birds, with several small mammals losing approximately 20% of matrilines per year of study. These lineage extinctions were not an artifact of the length of the study or the generation time of the species. Such rapid losses of lineages in less than 20-year periods in natural populations suggest that efforts to maintain maximal genetic diversity within populations may not always reflect processes that occur in the wild. Conservation biologists need to give further thought to the extent to which parity among genetic lines should be a primary goal of management of captive and small wild populations.     

Effects of Timber Harvesting on Southern Appalachian Salamanders

We compared the species richness and abundance of salamanders on six recent clearcuts (< 10 years old) with that of salamanders on 34 mature forest stands (>50 years old) in southern Appalachian forests in western North Carolina, U.S.A. Catches of salamanders from plots in mature forest stands were about five times higher than those on recent clearcuts. Almost all species and major taxonomic groups of salamanders were adversely affected by timber removal. Mean number of species collected per plot was about twice as great in mature forest stands as in clearcuts. Analyses of stand age versus salamander catch for 47 plots indicate that 50–70 years are required for populations to return to predisturbance levels following cutting. We conservatively estimate that clearcutting in U.S. national forests in western North Carolina results in a loss of nearly 14 millton salamanders annually. It also is chronically reducing regional populations by more than a quarter of a billion salamanders (9%) below that which could be sustained if mature forests were not cut.     

Blue-winged warblers (Vermivora pinus) “recognize” dialects in type II but not type I songs

Summary Male blue-winged warblers (Vermivora pinus) sing two distinctly different song types (I and II). Type II songs from eastern New York and western Massachusetts, USA, are different (Fig. 1), and during playback experiments males respond stronger to local than to foreign songs (Fig. 2). Type I songs are more stereotyped geographically (Fig. 1), and males do not differentiate between local and foreign Type I songs (Fig. 3). Differing degrees of intra- and inter-sexual selection on these two forms may have promoted variability in Type II songs and stereotypy in Type I songs among locations.     

Influence of environment, disturbance, and ownership on forest vegetation of coastal Oregon.

Information about how vegetation composition and structure vary quantitatively and spatially with physical environment, disturbance history, and land ownership is fundamental to regional conservation planning. However, current knowledge about patterns of vegetation variability across large regions that is spatially explicit (i.e., mapped) tends to be general and qualitative. We used spatial predictions from gradient models to examine the influence of environment, disturbance, and ownership on patterns of forest vegetation biodiversity across a large forested region, the 3-million-ha Oregon Coast Range (USA). Gradients in tree species composition were strongly associated with environment, especially climate, and insensitive to disturbance, probably because many dominant tree species are long-lived and persist throughout forest succession. In contrast, forest structure was strongly correlated with disturbance and only weakly with environmental gradients. Although forest structure differed among ownerships, differences were blurred by the presence of legacy trees that originated prior to current forest management regimes. Our multi-ownership perspective revealed biodiversity concerns and benefits not readily visible in single-ownership analyses, and all ownerships contributed to regional biodiversity values. Federal lands provided most of the late-successional and old-growth forest. State lands contained a range of forest ages and structures, including diverse young forest, abundant legacy dead wood, and much of the high-elevation true fir forest. Nonindustrial private lands provided diverse young forest and the greatest abundance of hardwood trees, including almost all of the foothill oak woodlands. Forest industry lands encompassed much early-successional forest, most of the mixed hardwood-conifer forest, and large amounts of legacy down wood. The detailed tree- and species-level data in the maps revealed regional trends that would be masked in traditional coarse-filter assessment. Although abundant, most early-successional forests originated after timber harvest and lacked legacy live and dead trees important as habitat and for other ecological functions. Many large-conifer forests that might be classified as old growth using a generalized forest cover map lacked structural features of old growth such as multilayered canopies or dead wood. Our findings suggest that regional conservation planning include all ownerships and land allocations, as well as fine-scale elements of vegetation composition and structure.     

Antipredator responses of California ground squirrels to rattlesnakes and rattling sounds: the roles of sex,reproductive parity,and offspring age in assessment and decision-making rules

California ground squirrels (Spermophilus beecheyi) and northern Pacific rattlesnakes (Crotalus viridus oreganus) have an adversarial relationship. Adults are partially protected by venom resistance and harass rattlesnakes in part to defend their more vulnerable offspring. Larger, warmer snakes are more dangerous than smaller colder snakes, and in escalated conflict squirrels could benefit from risk assessment strategies. Rattlesnakes often rattle at harassing squirrels and rattling sounds produce cues related to body size and temperature. In study 1 we played back rattling sounds from snakes that varied in dangerousness and evaluated the roles of sex and parity in squirrel risk assessment strategies. In general, squirrels tail flagged and stood bipedally more, and were slower to reapproach the playback speaker following playbacks of rattling sounds from more dangerous snakes. In comparison with males and nonmothers, mothers were most responsive to rattling sounds and more sensitive to variation in snake dangerousness. Mothers tail flagged more than males and nonmothers, and this behavior tracked variation in snake dangerousness most closely, perhaps reflecting the effects of snake size and temperature on pup vulnerability. These findings suggest that many aspects of squirrel antisnake behavior are governed by their effects on descendant kin. In study 2 we tested the effects of offspring age on mothers responses to live rattlesnakes and rattling sounds. According to the offspring value hypothesis, mothers should take more risks in defense of older offspring because they are more likely to survive to reproductive age. By contrast, under the offspring vulnerability hypothesis, older offspring are less vulnerable to predators and thus mothers should take fewer risks. Risk-taking, as measured by behaviors that bring the squirrel close to the snakes strike range, was either unaffected by or negatively correlated with offspring age. Thus, our findings suggest that whereas offspring value is unimportant in squirrel antisnake behavior, offspring vulnerability may affect maternal defense. We suggest that offspring vulnerability in mammals, in comparison with birds, may play a larger role in parental defense against predators.Communicated by P.A. BednekoffAn erratum to this article can be found at