Do Ural owls (Strix uralensis) suffer from the lack of nest sites in managed forests?

Nest site availability, preferences and quality for Ural owls (Strix uralensis) were studied in managed forests and a large nature reserve in Estonia. The owl's density was relatively higher in the reserve. Ural owls bred in tree cavities and stick nests, but preferred the cavities. Suitable cavities were very rare compared to stick nests, and most cavities were found in the reserve. Pairs having no suitable cavities in their territories started to breed less frequently, but no difference was detected in young produced per breeding attempt between cavity nests and stick nests. Used cavities and stick nests as well as unused stick nests were situated in similar stands and landscapes, but nest tree and nest characteristics of cavity nests were distinct. The study shows that in managed forests the lack of large snags and tree cavities may limit the numbers of Ural owls, which accept these structures for breeding more readily than stick nests. Retention of large cavity-forming trees in forestry operations may be an effective conservation strategy for this species.     

Supply of tree-holes limits nest density of cavity-nesting birds in primary and logged subtropical Atlantic forest

Tree cavities are proposed to limit populations and structure communities of cavity-nesting birds. Although the greatest diversity of cavity-nesting birds is found in tropical and subtropical moist forests, little is known about how tropical logging affects the abundance of cavities or cavity-nesting birds. We compared the abundance of cavities and cavity nests between primary and selectively-logged subtropical moist Atlantic forest in Argentina, and conducted the first before-after controlled nest-box addition experiment to determine whether nest sites limit the breeding density of cavity-nesting birds in tropical or subtropical moist forest. Visual inspection of 86 cavities identified through ground-surveys revealed that only 19% were suitable for nesting birds, suggesting that cavity abundance may be overestimated in the literature on tropical forests. Suitable cavities were found in fewer than 1% of 1156 trees <60 cm dbh but 20% of 20 trees >100 cm dbh. Logged forest had half the basal area of primary forest, one third the density of large trees, nine times fewer cavities suitable for nesting birds, and 17 times fewer active nests. When we added nest boxes, nesting density increased on treatment plots but not on control plots in both logged and primary forest, suggesting that cavity supply can limit nest density even in relatively undisturbed forest. This is the first experiment to show how reduced cavity supply in logged tropical forest can limit breeding density of cavity-nesting birds. International initiatives such as forest certification should promote tropical timber management strategies that conserve large live cavity-bearing trees.     

Structure and functioning of earthworm communities in woodland flooding systems used for drinking water production

Earthworms are known to influence water infiltration in soils, but most of the existing knowledge relates to grasslands and arable systems; little is known on the role of earthworms for water infiltration in forests. We studied earthworm populations and water infiltration rates in woodland flooding sites used for groundwater recharge and the production of drinking water. Intensive flooding may detrimentally affect earthworm populations and simultaneously result in clogging of the topsoil, with the latter being a common problem in groundwater recharge systems. However, clogging does not occur at our study site, the “Lange Erlen” (Basel, Switzerland) and total earthworm numbers and biomass in flooded sites exceeded those of non-flooded sites (+51% and +71%, respectively). Total earthworm numbers (r = 0.85***), numbers of endogeic (r = 0.64*) and epigeic (r = 0.81**) earthworms and numbers of two species (Lumbricus rubellus, r = 0.62* and Allolobophora chlorotica, r = 0.77**) significantly correlated with water infiltration rates. The results suggest that short-term flooding (max. 10 days) interrupted by longer recovery periods favor earthworm populations which likely contribute to the long-term (ca. 100 years) sustainability of the studied forest groundwater recharge system and thereby to effective and cost efficient drinking water production.     

Nesting habitat of the glossy black-cockatoo in central New South Wales

The reliance of cockatoos upon large hollows for nesting makes them vulnerable to any reduction in this resource. Species inhabiting forests managed for timber production are at risk because logging has the capacity to reduce hollow abundance significantly. In this study I identified the factors significantly associated with the selection of nest trees and nest sites by glossy black-cockatoos. Glossy black-cockatoos nested in vertical spouts in large trees. Nests were more likely to be located relatively high in senescent trees or standing dead trees (snags), factors most likely related to hollow suitability. As the density of potential nest hollows increased within a site, so to did the relative probability of it being used for nesting. The number of potential hollows serves as an index for the availability of suitable hollows. The persistence of glossy black-cockatoos within the study area will require careful management of nesting resources. Maximising the available hollow resource within known nesting areas is desirable. This is most efficiently achieved by facilitating the recruitment of large trees. This will require the exclusion of logging from nesting areas. Snags are a critical nesting resource. Information on snag dynamics is required and active intervention, such as the erection of nest boxes, may be necessary if unsustainable snag loss is occurring.     

The role of nest sites in limiting the numbers of hole-nesting birds: A review

The breeding densities of many bird-species which nest in tree cavities are in some areas limited by shortage of sites. This is evident from circumstantial evidence in which the numbers of breeding pairs in different areas correlate with the numbers of local nest sites, or where changes in the numbers of nest sites resulting from natural processes or human action are followed by changes in the numbers of pairs. It is also shown experimentally, where nest site provision or removal has been followed by a corresponding change in breeding density.

When nest boxes were provided, they were often occupied in the same year, leading to an immediate rise in breeding density. This implied that surplus birds were available in the vicinity and able to take them up. In future years, pair numbers often increased further but eventually they levelled off. This implied that, at this higher level, other limiting factors came into play. Experiments on nest site provision thus provide examples of different factors acting successively to limit breeding density at different levels.

By constraining breeding density, shortage of nest sites not only prevents some birds from breeding, but must also limit the total numbers of breeders and non-breeders, because no population can increase beyond a certain point, when the production of young is limited. Once all available nest sites are occupied, reproduction is inevitably density-dependent with respect to the total population of breeders and non-breeders.

Because several bird species can use the same type of site, competition is frequent, and the numbers of dominant species can affect the numbers and distribution of others. In extreme situations, a species may be totally absent from areas where all suitable nest sites are occupied by dominant competitors. In less extreme situations, the numbers of a subordinate species may vary from year to year or from place to place in inverse relation to the numbers of a dominant species. Both these situations can be changed by the provision of extra sites.

In managed woods and modern tree plantations, most hole-nesting bird species are excluded or kept at extremely low levels by shortage of nest sites. This is a direct result of forestry practice, which usually entails removal of the old and dying trees that normally provide the sites. The problem can be rectified by allowing a number of old and dead trees to remain in managed forests, or (on a more local scale) by the provision of nest boxes. By appropriate design and positioning of the boxes, the most desired species can be favoured.     

Vulnerability of ground-nesting waterbirds to predation by invasive American mink in the Cape Horn Biosphere Reserve, Chile

Biological invasions constitute one of the most important threats to biodiversity. This is especially true for “naïve” birds that have evolved in the absence of terrestrial predators in island ecosystems. The American mink (Mustela vison) has recently established a feral population on Navarino Island (55°S), southern Chile, where it represents a new guild of terrestrial mammal predators. We investigated the impact of mink on ground-nesting coastal waterbirds with the aim of deriving a vulnerability profile for birds as a function of different breeding strategies, habitat, and nest characteristics. We compared rates of nest survival and mink predation on 102 nests of solitary nesting species (Chloephaga picta, Tachyeres pteneres), on 361 nests of colonial birds (Larus dominicanus, Larus scoresbii, Sterna hirundinacea), and on 558 artificial nests. We calculated relative mink and bird densities at all nest sites. Nests of colonial species showed the highest nest survival probabilities (67-84%) and no predation by mink. Nest survival rates for solitary nesting species were lower (5-20%) and mink predation rates higher (10-44%). Discriminant analyses revealed that mink preyed upon artificial nests mainly at shores with rocky outcroppings where mink were abundant. High nest concealment increased the probability for predation by mink. Conservation planning should consider that invasive mink might severely affect the reproduction success of bird species with the following characteristics: solitary nesting, nesting habitat at rocky outcrop shores, and concealed nests. We recommend that work starts immediately to control the mink population with a priority in the nesting habitats of vulnerable endemic waterbirds.     

A national scale inventory of resource provision for biodiversity within domestic gardens

The human population is increasingly disconnected from nature due to urbanisation. To counteract this phenomenon, the UK government has been actively promoting wildlife gardening. However, the extent to which such activities are conducted and the level of resource provision for biodiversity (e.g., food and nesting sites) within domestic gardens remains poorly documented. Here we generate estimates for a selection of key resources provided within gardens at a national scale, using 12 survey datasets gathered across the UK. We estimate that 22.7 million households (87% of homes) have access to a garden. Average garden size is 190 m², extrapolating to a total area of 432,924 ha. Although substantial, this coverage is still an order of magnitude less than that of statutory protected areas. Approximately 12.6 million (48%) households provide supplementary food for birds, 7.4 million of which specifically use bird feeders. Similarly, there are a minimum of 4.7 million nest boxes within gardens. These figures equate to one bird feeder for every nine potentially feeder-using birds in the UK, and at least one nest box for every six breeding pairs of cavity nesting birds. Gardens also contain 2.5-3.5 million ponds and 28.7 million trees, which is just under a quarter of all trees occurring outside woodlands. Ongoing urbanisation, characterised by increased housing densities, is inevitable throughout the UK and elsewhere. The important contribution domestic gardens make to the green space infrastructure in residential areas must be acknowledged, as their reduction will impact biodiversity conservation, ecosystem services, and the well-being of the human population.     

Organic matter addition, N, and residue burning effects on infiltration, biological, and physical properties of an intensively tilled silt-loam soil

Seventy years of different management treatments have produced significant differences in runoff, erosion, and ponded infiltration rate in a winter wheat (Triticum aestivum L.)–summer fallow experiment in OR, USA. We tested the hypothesis that differences in infiltration are due to changes in soil structure related to treatment-induced biological changes. All plots received the same tillage (plow and summer rod-weeding). Manure (containing 111 kg N ha⁻¹), pea (Pisum sativum L.), vine (containing 34 kg N ha⁻¹), or N additions of 0, 45 and 90 kg ha⁻¹ were treatment variables with burning of residue as an additional factor within N-treatments. We measured soil organic C and N, water stability of whole soil, water stable aggregates, percolation through soil columns, glomalin, soil-aggregating basidiomycetes, earthworm populations, and dry sieve aggregate fractions. Infiltration was correlated (r = 0.67–0.95) to C, N, stability of whole soil, percolation, and glomalin. Basidiomycete extracellular carbohydrate assay values and earthworm populations did not follow soil C concentration, but appeared to be more sensitive to residue burning and to the addition of pea vine residue and manure. Dry sieve fractions were not well correlated to the other variables. Burning reduced (p < 0.05) water stability of whole soil, total glomalin, basidiomycetes, and earthworm counts. It also reduced dry aggregates of 0.5–2.0 mm size, but neither burning nor N fertilizer affected total C or total N or ponded infiltration rate. Water stability of whole soil and of 1–2-mm aggregates was greater at 45 kg N ha⁻¹ than in the 0 and 90 kg N ha⁻¹ treatments. Zero N fertilizer produced significantly greater 0.5–2.0 mm dry aggregate fractions. We conclude that differences in infiltration measured in the field are related to relatively small differences in aggregate stability, but not closely related to N or residue burning treatments. The lack of an effect of N fertilizer or residue burning on total C and N, along with the excellent correlation between glomalin and total C (r = 0.99) and total N (r = 0.98), indicates that the major pool of soil carbon may be dependent on arbuscular mycorrhizal fungi.     

Habitat management of little terns in Japan’s highly developed landscape

The little tern (Sterna albifrons) is a species of shorebird that nests in colonies on sandy beaches and riverbanks with little vegetation cover. In Japan, the natural breeding habitats of the terns have decreased drastically, and the species is listed under the category “vulnerable” in the Red List of the Government of Japan. To reduce the effects of habitat loss on the terns, conservationists are attempting to create and manage artificial colony sites in highly developed landscapes, such as reclaimed lands located in Tokyo Bay, central Japan. We present the factors that contribute to breeding success for this species and the habitat characteristics related to nest-site selection in the artificial colony sites along Tokyo Bay. Our data show that around 3 ha of a building rooftop without vegetation cover could sustain more than 2000 little tern nests. We found a strong positive relationship between colony size and hatching success, observing that a colony size of more than 100 lowered predation rates of eggs. On sites built upon white crushed-concrete, nest densities were high and predation rates of eggs were low. We also found that feeding rates were affected by foraging habitats, of which the best types were the shoreline of sandy beaches and mud flats. The 40 km dispersal range of the breeding terns, inferred from distribution data, should be considered when establishing a network of the multiple colony sites.     

Temporal patterns of nutrient availability around nests of leaf-cutting ants (Atta colombica) in secondary moist tropical forest

Leaf-cutting ants consume up to 10% of canopy leaves in the foraging area of their colony and therefore represent a key perturbation in the nutrient cycle of tropical forests. We used a chronosequence of nest sites on Barro Colorado Island, Panama, to assess the influence of leaf-cutting ants (Atta colombica) on nutrient availability in a neotropical rainforest. Twelve nest sites were sampled, including active nests, recently abandoned nests (<1 year) and long-abandoned nests (>1 year). Waste material discarded by the ants down-slope from the nests contained large concentrations of nitrogen and phosphorus in both total and soluble forms, but decomposed within one year after the nests were abandoned. Despite this, soil under the waste material contained high concentrations of nitrate and ammonium that persisted after the disappearance of the waste, although soluble phosphate returned to background concentrations within one year of nest abandonment. Fine roots were more abundant in soil under waste than control soils up to one year after nest abandonment, but were not significantly different for older sites. In contrast to the waste dumps, soil above the underground nest chambers consistently contained lower nutrient concentrations than control soils, although this was not statistically significant. We conclude that the ‘islands of fertility’ created by leaf-cutting ants provide a nutritional benefit to nearby plants for less than one year after nest abandonment in the moist tropical environment of Barro Colorado Island.     

Using a global VNIR soil-spectral library for local soil characterization and landscape modeling in a 2nd-order Uganda watershed

Combining global soil-spectral libraries with local calibration samples has the potential to provide improved visible and near-infrared (VNIR, 400–2500 nm) diffuse reflectance spectroscopy (DRS) soil characterization predictions than with either global or local calibrations alone. In this study, a geographically diverse “global” soil-spectral library with 4184 samples was augmented with up to 418 “local” calibration soil samples distributed across a 2nd-order Ugandan watershed to predict the amount of clay-size material (CLAY), soil organic carbon (SOC) and proportion of expansible 2:1 clays (termed “montmorillonite” or MT in the global library). Stochastic gradient boosted regression trees (BRT) were employed for model construction, with a variety of calibration and validation schemes tested. Using the global library combined with 13- and 14-fold cross-validation by local profile for CLAY and SOC, respectively, yielded dambo/upland RMSD values of 89/68 g kg^− 1 for CLAY (N = 429/410) and 4.2/2.6 g kg^− 1 for SOC (N = 272/105). These results were obtained despite the challenge of combining spectral libraries constructed using different spectroradiometers and laboratory reference measurements (total combustion vs. Walkley–Black, hydrometer vs. pipette). Using only the global library, a VNIR-derived index of MT content was significantly correlated with the square root of X-ray diffraction (XRD) MT peak intensity for local dambo soils (r² = 0.52, N = 59, p < 0.0001), an acceptable result given the semi-quantitative nature of the reference XRD method. Though VNIR predictions did not approach laboratory precision, for soil-landscape modeling VNIR characterization worked remarkably well for clay mineralogy, was adequate for mapping dambo “depth to 35% clay”, and was insufficiently accurate for SOC mapping.     

Specialised woodpeckers and naturalness in hemiboreal forests – Deriving quantitative targets for conservation planning

In many parts of the world’s forests, intensive management has resulted in habitat loss for several species. Among these, specialised woodpeckers (Aves: Picidae) have been affected negatively due to their high requirements for resources that are scarce in managed forests. We used the gradient of anthropogenic impact on forests in northern Europe’s Baltic Sea region to (1) assess the relationship between the presence of four focal woodpecker species and forest naturalness and (2) quantify their requirements regarding specific resources in four different areas (south-central Sweden, southern Sweden, Lithuania and northeastern Poland). This study focused on specialised woodpecker species of the Dendropicini tribe: the three-toed (Picoides tridactylus), middle spotted (Dendrocopos medius), white-backed (Dendrocopos leucotos) and lesser spotted (Dendrocopos minor) woodpeckers. The occurrence of these species in landscape units of 100 ha was generally related positively to the degree of forest naturalness and to the amounts of resources considered critical for the suitability of their respective habitats. For the middle spotted woodpecker, basal areas 1.0 m²/ha of large-diameter deciduous trees (DBH  40 cm) were associated with a high probability of occurrence (0.9). For the white-backed woodpecker, the same probability of occurrence was found for basal areas 1.4 m²/ha of deciduous snags (DBH  10 cm). Relationships between the occurrence of the three-toed and lesser spotted woodpeckers and snag abundance were more variable among study areas. The results suggest that specialised woodpeckers would benefit from an increase in the area of forest with natural properties. Moreover, they allow defining tentative quantitative targets for sustainable forest management.     

Carbon management index based on physical fractionation of soil organic matter in an Acrisol under long-term no-till cropping systems

The carbon management index (CMI) is derived from the total soil organic C pool and C lability and is useful to evaluate the capacity of management systems to promote soil quality. However, the CMI has not been commonly used for this purpose, possible due to some limitations of the 333 mM KMnO₄-chemical oxidation method conventionally employed to determine the labile C fraction. We hypothesized, however, that physical fractionation of organic matter is an alternative approach to determine the labile C. The objectives of this study were (i) to assess the physical fractionation with density (NaI 1.8 Mg m⁻³) and particle-size separation (53 μm mesh) as alternative methods to the KMnO₄-chemical oxidation (60 and 333 mM) in determining the labile C and thus the CMI, and (ii) to evaluate the capacity of long-term (19 years) no-till cropping systems (oat/maize: O/M, oat + vetch/maize: O + V/M, oat + vetch/maize + cowpea: O + V/M + C, and pigeon pea + maize: P + M) and N fertilization (0 and 180 kg N ha⁻¹) to promote the soil quality of a Southern Brazilian Acrisol, using the CMI as the main assessment parameter. Soil samples were collected from 0 to 12.5 cm layer, and the soil of an adjacent native grassland was taken as reference. The mean annual C input of the cropping systems varied from 3.4 to 6.0 Mg ha⁻¹ and the highest amounts occurred in legume-based cropping systems and N fertilized treatments. The C pool index was positively related to the annual C input (r² = 0.93, P < 0.002). The labile C determined by density (4.4–10.4% of C pool) and particle-size separation (9.5–17.7% of C pool) had a close relationship (r = 0.60 and 0.85, respectively) with the labile C determined using 60 mM KMnO₄ (7.3–10.5% of C pool). The labile C resulting from the three methods was related to the annual C input imparted by the cropping systems (r² = 0.67–0.88), reinforcing the possibility of using physical fractionation as an alternative approach to determine labile C. In contrast, the chemical method using 333 mM KMnO₄ was not sensitive to different cropping systems and resulted in too high percentage of labile C, varying from 16.8 to 35.2% of the C pool. The CMI based on physical fractionation was a sensitive tool for assessing the capacity of management systems to promote soil quality, as evidenced by its close correlation (r = 0.88, at average) with soil physical, chemical, and biological attributes. The introduction of winter (vetch) and, especially, summer legume cover crops (cowpea and pigeon pea), or application of fertilizer-N, improved the capacity of the management system into promote soil quality in this subtropical Acrisol.     

Earthworm community structure on five English golf courses

A clear understanding of the size and structure of earthworm communities is important to sports turf facilities managers if they are to control the activity of earthworms within the soil. Earthworms are directly linked to a wide range of biogeochemical nutrient cycles, and are frequently described as ecosystem engineers. In this role they assist land managers in maintaining a healthy turf sward. Despite this, earthworm populations in sports turf were frequently suppressed using organochloride based vermicides prior to such compounds being banned in the UK. A survey of earthworm species diversity was carried out over 1 year, using mustard extraction at five golf courses in Bedfordshire and Buckinghamshire, UK, to investigate how species diversity varied temporally and was influenced by the physical environment within different course surfaces. Rank–abundance analysis indicated that four species of earthworm (Aporrectodea rosea, Lumbricus rubellus, Aporrectodea longa and Lumbricus terrestris) were more dominant in the community than any other. The endemic earthworm population number of the five study sites was found to differ significantly (p < 0.01) related to their geographical location, and the most diverse communities were found where the population was greatest. A very strong linear correlation was found between the number of earthworms recovered and the sand content of the soil (r² = 0.97). Significant differences in the size of the earthworm populations were recorded at different times of the year (p < 0.01). A distinct and non-linear relationship between species diversity and microbial biomass C was shown (p < 0.01).     

Spatial variation in anthropic and natural factors regulating the breeding success of the cinereous vulture (Aegypius monachus) in the SW Iberian Peninsula

The management of the cinereous vulture (Aegypius monachus) populations, the largest bird of the Western Palæarctic and considered an umbrella species, requires the understanding of the factors limiting the breeding success. As part of a management program, we studied such factors in seven breeding colonies in Extremadura (SW Iberian Peninsula). Using a Geographic Information System and multivariate models, we analyzed the relationship of breeding success with anthropic and natural factors at the nest site and in the foraging area of the adults. We incorporated into the models density-dependent effects between pairs and the spatial autocorrelation of the environmental variables. The differences in breeding success resulted from spatial variations in natural and anthropic conditions, with present human disturbance to nests and future alteration of climate having an expected negative effect at all the sites. Management measures must set calendar restrictions for the immediate environment of the nests, mainly with respect to forestry and hunting activities. A second key element is the protection of the habitats at the nest sites and in their surrounding area, with the aim of there being both wooded areas available for the location of the nest and open environments for the availability of food. The Special Protection Areas showed a partial effectiveness of conservation measures for the species, and the need for future improvement. Lastly, in a scenario of global warming, management policies with respect to nesting habitats will have to be extended to higher altitude zones, actions that should be guided by the study of the selection of potential nesting habitat.     

Modelling human impacts on the Tasmanian wedge-tailed eagle (Aquila audax fleayi)

The wedge-tailed eagle is Australia’s largest bird of prey and one of the largest eagles in the world. Aquila audax fleayi is an endemic Tasmanian subspecies isolated for 10,000 years from the nominate subspecies on the Australian mainland. The Tasmanian wedge-tailed eagle is classified nationally and at a State level as endangered due to its small number of breeding pairs, low breeding success and high rate of mortality from unnatural causes. The subspecies experiences mortality throughout its range from shooting, poisoning, trapping, road accidents, electrocutions and collisions with wind turbines, aircraft, fences and overhead wires, which we term ‘un-natural mortality’. A portion of the subspecies’ range is managed for timber production, which can lead to disturbance of nest sites and the loss of nest trees. We use a model of the eagle population from the Bass District in northeast Tasmania to explore the relative importance of different sources of mortality and nesting habitat loss, and the potential for mitigating impacts associated with unnatural mortality, disturbance, nesting habitat loss and human access to forests. We create a habitat map including suitable nest sites and link it to a dynamic landscape population model based on life history traits and disturbance responses. Using the program RAMAS-Landscape, we model alternative forest management scenarios, ranging from no timber harvesting and a natural wildfire regime, to scenarios prescribing native forest harvesting and regeneration and different levels of conversion of native forest to plantation under the same natural wildfire regime. The results indicate that the Tasmanian wedge-tailed eagle is sensitive to unnatural mortality, plantation establishment and native forest harvesting. The predicted decline over the next 160 years (65%) will most likely be driven largely by loss of current and potential future nest sites associated with harvesting activities, exacerbated by unnatural mortality in the wider landscape. Interventions that minimise unnatural mortality, reduce nest disturbance, and retain breeding habitat and nest sites may improve the prospects for the subspecies in the Bass District. If nest disturbance and unnatural mortality continue at the rates modelled here, the species appears to face a high risk of declining substantially in the region.     

Careful partial harvesting in conservation stands and retention of large oaks favour oak regeneration

In Europe, many semi-open pasture woodlands with oaks (Quercus robur and Q. petraea) have been invaded by other trees. The management alternatives for such stands are often debated. Protection (i.e. no cutting) versus partial harvest to favour oak regeneration was studied in two matched plots in 25 forests in Sweden. A mast year produced on average 45,000 oak seedlings/ha in 2001. On average 26% of the tree basal area, but no large oaks, was harvested in experimental plots in the winter 2002/03. In 2005, seedling densities were on average 3,900 per ha in control plots (protected) and 11,600 in experimental plots (mainly seedlings from 2002 to 2004). Seedling survival and growth rate from 2003 to 2005 were higher in experimental than cutting plots (66% vs 44%; and +2.8 cm vs −0.8 cm, respectively). Survival and growth were positively related to canopy openness; other vegetation, pH, and oak basal area had no or little effect. Seedling height before cutting was also a positive predictor of survival. The plots contained many more intermediate and large oaks than small oak trees. The number of small oak trees (1.3 m tall to 5 cm in diameter at 1.3 m) was positively related to canopy openness, but unrelated to other measured factors. Thus, minor partial cutting increases seedling densities, and adequate light favours seedlings/small trees. When oak regeneration is important for mixed closed canopy stands with high biodiversity values, such partial cutting is useful (e.g. for CO₂-neutral biofuel) but needs careful evaluation, including effects on biodiversity.     

A short-term investigation of trace gas emissions following tillage and no-tillage of agroforestry residues in western Kenya

Improved-fallow agroforestry systems are increasingly being adopted in the humid tropics for soil fertility management. However, there is little information on trace gas emissions after residue application in these systems, or on the effect of tillage practice on emissions from tropical agricultural systems. Here, we report a short-term experiment in which the effects of tillage practice (no-tillage versus tillage to 15 cm depth) and residue quality on emissions of N₂O, CO₂ and CH₄ were determined in an improved-fallow agroforestry system in western Kenya. Emissions were increased following tillage of Tephrosia candida (2.1 g N₂O-N ha⁻¹ kg N applied⁻¹; 759 kg CO₂-C ha⁻¹ t C applied⁻¹; 30 g CH₄-C ha⁻¹ t C applied⁻¹) and Crotalaria paulina residues (2.8 g N₂O-N ha⁻¹ kg N applied⁻¹; 967 kg CO₂-C ha⁻¹ t C applied⁻¹; 146 g CH₄-C ha⁻¹ t C applied⁻¹) and were higher than from tillage of natural-fallow residues (1.0 g N₂O-N ha⁻¹ kg N applied⁻¹; 432 kg CO₂-C ha⁻¹ t C applied⁻¹; 14.7 g CH₄-C ha⁻¹ t C applied⁻¹) or from continuous maize cropping systems. Emissions from these fallow treatments were positively correlated with residue N content (r = 0.62–0.97; P < 0.05) and negatively correlated with residue lignin content (r = −0.56, N₂O; r = −0.92, CH₄; P < 0.05). No-tillage of surface applied Tephrosia residues lowered the total N₂O and CO₂ emitted over 99 days by 0.33 g N₂O-N ha⁻¹ kg N applied⁻¹ and 124 kg CO₂-C ha⁻¹ t C applied⁻¹, respectively; estimated to provide a reduction in global warming potential of 41 g CO₂ equivalents. However, emissions were increased from this treatment over the first 2 weeks. The responses to tillage practice and residue quality reported here need to be verified in longer term experiments before they can be used to suggest mitigation strategies appropriate for all three greenhouse gases.     

Viability and patch occupancy of a swamp rabbit metapopulation at the northern edge of its distribution

Swamp rabbits (Sylvilagus aquaticus) are state-endangered in Indiana, USA, and population decline has been attributed to habitat loss. We conducted pellet surveys as part of a long-term survey effort that has been conducted at approximate 10-year intervals over the last 40 years. We modeled patch occupancy and conducted a spatially-explicit population viability analysis (PVA). Although occupancy of individual patches varied over time, occupancy rate has been constant for the last 30 years, and Indiana swamp rabbits exist as a metapopulation that appears to be stable. Metapopulation dynamics were best characterized as being stationary, but area was an important factor in extinction rates; occupied patches (142 ± 37 ha) were significantly larger (P = 0.01) than unoccupied patches (79 ± 20 ha). We did not find strong support for models with colonization rates as a function of distance to neighboring patches, nor was distance to contiguous patches of habitat significantly different (P = 0.12) for occupied and unoccupied sites. Population viability analysis corroborated our findings based on occupancy modeling, and evaluation of the PVA model using occupancy data for the period 1985–2006 resulted in predictions that nearly matched our field observations (33% observed patch occupancy vs. 25% predicted patch occupancy). Population viability was most sensitive to reductions in survival and fecundity rates, but was otherwise robust to changes in parameters such as initial abundance and carrying capacity. Our findings provide novel insights into a poorly studied member of Sylvilagus and into species metapopulation dynamics at the edge of the range.     

Tallgrass prairie management and bird nest success along roadsides

The attributes of roadside vegetation, an important bird habitat in grassland ecosystems, have been shown to affect bird abundance, distribution composition, and diversity, yet there are relatively few works on reproductive success of birds nesting along roadsides. Because roadsides are linear habitats, management at the landscape scale can affect nest success in roadsides through bottom-up and top-down effects. In northeastern Oklahoma tallgrass prairie is subjected annually to prescribed spring fires. In the short term fires can alter both arthropod abundance and predator access to nests. We explored effects of burning on bird nest success with a five-year study along roads that traversed tallgrass prairie habitat. Using data from ∼1400 nests of 23 species, we generated nest survival curves for groups of altricial species defined by nest substrate (ground, shrub, tree, or culvert). We then determined if these curves were affected by management practice (spring burning), food abundance (arthropod biomass), and habitat attributes (tree density and height). Nest substrate had a large effect on nest success: despite their shorter nest exposure period, ground nests were least successful and culvert nests were most successful. An increase in arthropod biomass following burning was possibly the cause for the increased nest success in burned plots, regardless of substrate, suggesting bottom-up control. Tree height and nest height were correlated positively with nest success, whereas tree density had no effect. Conversely, nest predation rates were correlated negatively with nest success, with ground nests experiencing the highest predation, culvert nests the lowest. Our results suggest that burning may increase nest success through bottom-up processes, but some species may not benefit from the increase in food abundance as a result of a concomitant increase in predation.