Alternative stable states in Australia’s Wet Tropics: a theoretical framework for the field data and a field-case for the theory

The vegetation of the Wet Tropics bioregion of Far North Queensland is a complex system whose components (mainly tropical rainforests and fire-prone forests and woodlands) have mostly been studied independently from each other. We suggest that many characteristics of the vegetation are consistent with those of a complex, dynamic, spatially heterogeneous system which exhibits alternative stable states. We propose these states are driven and maintained by the interaction of vegetation-specific positive feedback loops with the regions’ environmental parameters (such as topography, steep humidity gradients and seasonality) and result in the rainforest/fire-prone vegetation mosaic that characterises the area. Given the regions’ magnitude, biodiversity and complexity, we propose the Wet Tropics as an important new example and a good testing ground for alternative stable state and resilience theories in large heterogeneous natural systems. At the same time, thinking in terms of alternative stable states and resilience creates a new context for understanding the regions’ biological dynamics.     

Drivers and trends in landscape patterns of stand-replacing fire in forests of the US Northern Rocky Mountains (1984–2010)

Context

Resilience in fire-prone forests is strongly affected by landscape burn-severity patterns, in part by governing propagule availability around stand-replacing patches in which all or most vegetation is killed. However, little is known about drivers of landscape patterns of stand-replacing fire, or whether such patterns are changing during an era of increased wildfire activity.

Objectives

(a) Identify key direct/indirect drivers of landscape patterns of stand-replacing fire (e.g., size, shape of patches), (b) test for temporal trends in these patterns, and (c) anticipate thresholds beyond which landscape patterns of burn severity may change fundamentally.

Methods

We applied structural equation modeling to satellite burn-severity maps of fires in the US Northern Rocky Mountains (1984–2010) to test for direct and indirect (via influence on fire size and proportion stand-replacing) effects of climate/weather, vegetation, and topography on landscape patterns of stand-replacing fire. We also tested for temporal trends in landscape patterns.

Results

Landscape patterns of stand-replacing fire were strongly controlled by fire size and proportion stand-replacing, which were, in turn, controlled by climate/weather and vegetation/topography, respectively. From 1984 to 2010, the proportion of stand-replacing fire within burn perimeters increased from 0.22 to 0.27. Trends for other landscape metrics were not significant, but may respond to further increases proportion stand-replacing fire.

Conclusions

Fires from 1984 to 2010 exhibited tremendous heterogeneity in landscape patterns of stand-replacing fire, likely promoting resilience in burned areas. If trends continue on the current trajectory, however, fires may produce larger and simpler shaped patches of stand-replacing fire with more burned area far from seed sources.

     

Boundaries and scales in shrublands of the Doñana Biological Reserve,southwest Spain

To verify that the stabilized sand dunes of Doñana, southwest Spain, are hierarchically nested, vegetation was sampled along topographic gradients at three spatial scales and Split Moving Window Boundary Analysis was applied to identify vegetation boundaries and ecotones. At small scale, only one window width was used, while for boundaries detection at upper scales the information from five windows was pooled. Environmental factors controlling plant composition were studied along topographic gradients, and diversity was estimated within the boundaries. According to several theoretical frameworks, I discuss the types of boundaries produced at different scales. Lower level boundaries are characterized by transitory gradients linked to local exchanges; intermediate boundaries are symmetric and very stable over the time; the large scale boundary is asymmetric with strong inherent abiotic constraints reinforced by strong biotic feedbacks. In spite of a similar plant composition, a plant community, the mixed shrub, works as an ecocline or an ecotone depending on the spatial scale considered. A certain parallelism exists between shrub composition along dune slopes and dune generations; however, processes at upper scale constraint plant composition at lower scale resulting in different mature formations.     

Cumulative patterns of logging and fire (1940–2009): consequences on the structure of the eastern Canadian boreal forest

Context

Although logging has affected circumboreal forest dynamics for nearly a century, very few studies have reconstructed its influence on landscape structure at the subcontinental scale.

Objectives

This study aims to document spatiotemporal patterns of logging and fire since the introduction of logging in the early twentieth-century, and to evaluate the effects of these disturbances on landscape structure.

Methods

We used historical (1940–2009) logging and fire maps to document disturbance patterns across a 195,000-km² boreal forest landscape of eastern Canada. We produced multitemporal (1970s–2010s) mosaics providing land cover status using Landsat imagery.

Results

Logging significantly increased the rate of disturbance (+74 %) in the study area. The area affected by logging increased linearly with time resulting in a significant rejuvenation of the landscape along the harvesting pattern (south–north progression). From 1940 to 2009, fire was the dominant disturbance and showed a more random spatial distribution than logging. The recent increase of fire influence and the expansion of the proportion of area classified as unproductive terrestrial land suggest that regeneration failures occurred.

Conclusions

This study reveals how logging has modified the disturbances dynamics, following the progression of the logging frontier. Future management practices should aim for a dispersed spatial distribution of harvests to generate landscape structures that are closer to natural conditions, in line with ecosystem-based management. The challenges of defining sustainable practices will remain complex with the predicted increase in fire frequency, since this factor, in combination with logging, can alter both the structure and potentially the resilience of boreal forest.

     

Suburban habitats and their role for birds in the urban–rural habitat network: points of local invasion and extinction?

Suburban habitats in naturally forested areas present a conundrum in the urban–rural habitat network. Typically, these habitats contain less than half of the native woodland bird species that would exist at these sites if they were not developed. They also contain more total bird species than if these sites were left in a natural state. This apparent contradiction raises the question of “How do suburban habitats function in the urban–rural habitat network?” In this study, we analyze bird distributions on three rural-to-urban gradients in different ecoregions of the United States: Oxford, Ohio; Saint Paul, Minnesota; and Palo Alto, California. All three gradients exhibit similar patterns of extinction of native species followed by invasion of common species and subsequent biotic homogenization with urbanization. This patterning suggests that suburban land uses, those represented by the intermediate levels of development on the gradients, are a point of extirpation for woodland birds as well as an entry point for invasive species into urban systems. Furthermore, there are consistent patterns in the functional characteristics of the bird communities that also shift with intensifying urbanization, providing insight on the possible mechanisms of homogenization and community structure in urban ecosystems including an increase in the number of broods per year, a shift in nesting strategies, a decrease in insectivorous individuals, an increase in granivorous individuals, and a decrease in territoriality. Consequently, it appears that there are specific traits that drive the shift in community composition in response to urban and suburban land use. These results have significant implications for improving understanding of the mechanisms of suburban community ecology and conserving birds in urban habitat networks.     

Analysis of differentially expressed proteins in the pollen of Malus spectabilis (crabapples) and Malus domestica (‘Gala’ apples) and their role in pollination

Our objective was to study the differentially expressed proteins (DEP) in various Malus spectabilis (crabapple) varieties (M. ‘Snowdrift’, M. ‘Hongling’ and M. ‘Hongjin’) in relation to Malus domestica (‘Gala’) and their role in pollination. Our method used a two-dimensional electrophoresis (2-DE) to analyse the differential proteins in the pollen of several crabapples. The 2-DE apples combined with the tandem mass spectrometry (MS-MS) and protein database retrieval helped us to identify the nature and function of DEPs in ‘Gala’ apples and crabapples. We identified 1195 proteins through 2-DE. Among these, six DEPs, namely chloroplast ferritin, Actin, Beta-fructofuranosidase, vacuolarH+-ATPase catalytic subunit, Full = Phosphoglucomutase, and Cytochrome b were identified by MS-MS. This study identified six DEPs among the pollen from the ‘Snowdrift’ crabapple, ‘Hongling’ crabapple, ‘Hongjin’ crabapple, and ‘Gala’ apples. The DEPs included metabolism related proteins, stress/regulatory proteins, and proteins involved in signal transduction.     

Effects of the application of ‘cash’ on the growth,fruit yield,and nutrient status of tomato (Solanum lycopersicum L.) grown in reclaimed saline soil

Summary

The effects of ‘cash’ [a novel 2:5:1 (w/w/w) mixture of calcium sulphate, ground sunflower heads, and humic acid] as a soil amendment on the growth, fruit yield, and leaf nutrient status of tomato (Solanum lycopersicum L.) grown on reclaimed saline soil (EC = 9.4 dS m^–1) were investigated. A glasshouse experiment was performed in a completely randomised design with six treatments (0, 10, 20, 30, 40, or 50 g ‘cash’ kg^–1 soil) each with four replicates. The results indicated that ‘cash’ increased both the shoot dry weight (DW) plant^–1 and the root DW plant^–1, the free proline contents of leaves, and leaf chlorophyll contents. The use of ‘cash’ also increased the number of fruit plant^–1, fruit yield pot^–1, and fruit vitamin C contents, although total soluble solids (TSS) contents were not affected. The contents of nitrogen (N), potassium (K), and calcium (Ca), and the Ca:Na ratios of leaf tissues increased with all application rates of ‘cash’. Leaf phosphorus (P) contents showed no response to any applied level of ‘cash’. Leaf sodium (Na) contents declined gradually with an increase in the level of ‘cash’ applied to the soil. We concluded that ‘cash’ has a pronounced positive effect on the growth and fruit yield of tomato plants grown in reclaimed saline soil. ‘Cash’ therefore has the potential to be used as a soil amendment for vegetable crops such as tomato to overcome the adverse effects of salinity in newly-reclaimed soils.     

Tree Fruit Growing—Research and Production in Germany: A Statistical and Bibliometric Analysis of the Period 1950–2010

Germany is one of the leading European countries in tree fruit growing and the fruit produced has an actual production value of 794?million?€. Six decades, from 1950 to 2010, of fruit production and internationally relevant scientific output for fruit crops—apple, pear, cherry, plum, apricot, and peach—were analysed in this study. Bibliographic and bibliometric analyses were based on the Science Citation Index^?. Data were compared and discussed in the European and global context. The German annual per capita consumption of fruit amounts to 125.5?kg/a originating from commercial intensive fruit growing, including 71.8?kg/a of fresh fruit, 48.3?kg/a of citrus and tropical fruit, 3.8?kg/a nut fruit, and 1.6?kg/a dry fruit. Approximately 25?kg per annum and inhabitant has to be added to the total fruit consumption, since a conspicuous amount of fruit originates from meadow orchards and house gardens. Nevertheless, Germany’s self-supply with fruit is a low 22.4%. Within the EU (2009/2010), Germany ranks fourth in apple production, tenth in pear production, fifth in cherry production, sixth in plum production, and 15th in the production of apricots and peaches. Based on the number of international scientific articles published in Germany, fruit crops can be ranked in descending order: apples, cherries, pears, plums, peaches and apricots. Relating the scientific output over the last six decades to the production data of the same country nowadays achieved, we obtain an indicator for the scientific impact on the crop production. On a worldwide comparison Germany ranks tenth for apple, sixth for pears, 21st for cherries, 17th for plums and first for apricots and peaches. With regard to the absolute output of scientific original articles Germany ranks fourth worldwide for apples, eighth for pears, second for cherries, fifth for plums, ninth for apricots and 14th for peaches, indicating that research on tree fruit growing in Germany supports the economic competitiveness of its production regions with highly specialized knowledge.     

Influence of soil hydrothermal environment,irrigation regime,and different mulches on the growth and fruit quality of strawberry (Fragaria × ananassa L.) plants in a sub-temperate climate

Summary

The present study was undertaken over two consecutive years under sub-temperate climatic conditions in the mid-hill region of Himachal Pradesh (30°52'N, 77°11'E; 1,175 m asl) on loamy sand Inceptisols. The aim was to investigate the effects of irrigation and mulch material on the growth, flowering, fruiting behaviour, relative leaf water content (RLWC), yield, and quality of strawberry (Fragaria × ananassa L. ‘Chandler’). The drip irrigation treatments included irrigation with 100, 80, or 60% (coded 1.0, 0.8, and 0.6 V) of the total water requirement. Both mulches increased the minimum soil temperature to a depth of 5 cm. The drip and surface irrigation treatments raised the minimum soil temperature by 3.0º – 5.4ºC, and lowered the maximum temperature by 2.2º – 5.8ºC compared to the rainfed control. Hay mulch was more effective in raising the minimum temperature and lowering the maximum soil temperature than black polyethylene mulch. Moisture conservation increased by 2.8 – 12.8% under the black polyethylene mulch compared to the no-mulch treatment. Drip and surface irrigation methods, as well as mulching, were found to be effective for enhancing the growth, irrigation water use efficiency (IWUE), fruit yield, and quality of strawberry plants. However, the number of crowns per plant, the percentage berry set, the RLWC, root length density (RLD), and fruit yield were highest under treatment M3I3 [i.e., black polyethylene mulch plus drip irrigation (1.0 V)] by 565.5%, 94.5%, 32.8%, 394.5%, and 549.6%,respectively, compared to the no mulch plus rainfed control. The maximum IWUE values for plant biomass [1.39 metric tonnes (MT) ha^–1 m^–1] and fruit yield (2.79 MT ha^–1 m^–1) were recorded under treatment M3I5 [i.e., black polyethylene mulch plus drip irrigation (0.6 V)]; whereas, the lowest values (0.39 and 0.68 MT ha^–1 m^–1, respectively) were observed using treatment M1I2 (i.e., without mulch, plus surface irrigation). Fruit size, weight, sugar content, and anthocyanin content increased significantly under treatment M2I3 [i.e., hay mulch, plus drip irrigation (1.0 V)] compared with all other treatments. Total soluble solids (TSS) contents and total acidity (TA) were highest under treatment M1I1 (i.e., no mulch, plus rainfed). A linear regression model could describe the variations in quality parameters of strawberry plants grown under sub-temperate climatic conditions. Root density was found to be the best indicator with which estimate fruit quality.     

Effects of farmyard manure on soil organic carbon stock,the pattern of fertility build-up,and plant growth in ‘Mallika’ mango (Mangifera indica L.)

Summary

A field experiment was conducted on mango (Mangifera indica L.) to study the effects of farmyard manure (FYM) on soil organic carbon (SOC) content and on the build-up of fertility over three growing seasons (2006–2007, 2007–2008, and 2008–2009) at Bhubaneswar, Orissa, India. Five treatments, including the application of FYM at 5.0 kg plant^–1, 7.5 kg plant^–1, or 10.0 kg plant^–1, the recommended dose of a chemical fertiliser (RDF; N:P:K=75:20:60), and a non-fertilised control, were evaluated in a randomised block design. The results indicated that SOC contents increased significantly in the FYM-treated plots. The highest SOC density (554 g m^–2) and stock (5.55 Mg ha^–1) were recorded in the treatment with FYM at 10 kg plant^–1. The rate of increase in SOC density was highest (193 g m^–2 year^–1) with FYM at 10 kg plant^–1, and lowest in the untreated control (15 g m^–2 year^–1). Regular addition of FYM had a positive effect on the build-up of soil fertility. However, the greatest increases in soil N, P, K contents were in the 7.5 kg plant^–1 FYM treatment (means = 319.9, 19.1, and 270.8 kg ha^–1 for N, P, K, respectively). Farmyard manure significantly influenced the growth parameters of mango trees over the three seasons. There was a positive and linear relationship between increasing rates of application of FYM and trunk cross-sectional area.     

Using an individual-based model to examine the roles of habitat fragmentation and behavior on predator–prey relationships in seagrass landscapes

Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure.     

Residential runoff – The role of spatial density and surface cover,with a case study in the Höjeå river catchment,southern Sweden

Depending on the spatial density of built cover and location within a catchment, residential areas make varying contributions to surface runoff throughout different rainfall events. This study examined these contributions and the associated effect of different surface covers and sustainable drainage systems on runoff generation. The Soil Conservation Service curve number (SCS-CN) method was applied to analyse urban development in the Höjeå river catchment in southern Sweden.The results indicated that identical amounts of surface runoff are generated by low-density residential areas on heavy clay soils and high-density residential areas on sandy soils. However, increasing the density of built-up areas on sandy soils is likely to be more disruptive to the hydrological balance and to generate a greatly increasing difference in runoff as building density and impermeable surface area increase. A similar pattern is likely to occur if rainfall intensity increases. It may therefore be appropriate to apply different planning considerations to residential developments depending on the existing soil group, e.g. conserving existing vegetated surfaces on sandy soil and incorporating permeable paving materials and sub-surface infiltration beds in development on clayey soils. Increased area of impermeable surface cover will increase surface runoff in all residential areas, irrespective of building density, soil group and rainfall intensity. However, adapting a systems approach in combining vegetative structures and permeable paving materials with subsurface infiltration beds can help mitigate the impact of surface runoff, particularly in urban developments on clay-rich soils.     

Cyto-nuclear discordance in the genetic relationships among Tunisian fig cultivars (Ficus carica L.): Evidence from non coding trnL–trnF and ITS regions of chloroplast and ribosomal DNAs

Genetic diversity studies were conducted to evaluate intra-specific relationships in Tunisian fig (Ficus: Moraceae) using sequences of the ITS regions of nuclear ribosomal DNA and the chloroplast non-coding region trnL–trnF (trnL intron, and trnL [UAA]–exon–trnF [GAA] intergenic spacer). All data sets suggest that the sequences obtained showed variations either on their lengths or on their nucleotide compositions. The mean size of these nuclear and cytoplasmic non-coding regions is 697.5 and 1035 base pairs for ITS and trnL–trnF chloroplast DNA, respectively. Our results suggest that the substitution rate estimated for the ITS sequences of nuclear DNA is greater than the one unregistered for the non-coding regions of chloroplast DNA. Therefore, chloroplast DNA shows more homoplasy than the nuclear ribosomal DNA. In fact, the consistency (CI) and retention (RI) indexes calculated for nuclear and cytoplasmic DNAs show values of 0.420 and 0.490 for chloroplast DNA and 0.573 and 0.387 for ribosomal DNA, respectively. The nuclear DNA has more resolution of genetic relationships between cultivars. In addition, the result suggests that the cultivars studied are clustered independently from their geographical origin and the male trees did not thoroughly diverge from the common figs. The discordance between chloroplast and the nuclear topology is revealed. The lack of congruence between the two data sets may be a result of hybridization or introgression. Our result showed that the nuclear and cytoplasmic sequences are useful for germplasm discrimination as well as for investigation of patterns of variation in fig.