Genetic diversity of Eucalyptus camaldulensis Dehnh. following population decline in response to drought and altered hydrological regime

The river red gum (Eucalyptus camaldulensis Dehnh.) inhabits riparian zones and associated floodplains throughout Australia. Following changes to hydrological regime due to river regulation and prolonged drought in south‐eastern Australia, river red gum populations within the Murray–Darling Basin have suffered substantial decline. To better understand the effect of drought on river red gum genetic diversity, we examined single nucleotide polymorphism (SNP) variation in 12 candidate genes among six red gum floodplain forest sites in Yanga National Park, which had experienced contrasting levels of drought and associated decline over an eight‐year period. We also examined genetic diversity using these markers in five additional river red gum populations from the Murray–Darling Basin to place genetic diversity results from Yanga in a regional context. Tree condition was significantly lower and mortality higher in the most drought affected sites; however, differences in overall genetic diversity and divergence were not detected among sites. No evidence of genetic adaptation in response to drought in this set of candidate genes was detected when differentiation at individual SNP loci was examined. While the overall condition of E. camaldulensis was strongly influenced by hydrological regime, our results suggest the evolutionary potential of floodplain forests in Yanga were not immediately impacted by population decline linked with drought and changes in hydrological regime. We propose that due to low genetic structure among populations in the region, genetic diversity of river red gums within the Murray–Darling Basin might be effectively conserved during periods of extended drought by protecting representative populations.     

Floodplain ants show a stronger response to an extensive flood than to variations in fallen‐timber load

Understanding how species respond to differences in resource availability is critical to managing biodiversity under the increasing pressures associated with climate change and growing human populations. Over the last century, the floodplain forests of Australia's largest river system, the Murray‐Darling Basin, have been much affected by intensive harvesting of timber and firewood, and increasingly stressed by river regulation and, recently, an extended drought. Fallen timber – logs and shed branches – is known to play a key role in the ecology of several important species on these floodplains. Here, we monitored the response of the ant assemblages of a floodplain forest along the Murray River to a large‐scale (34 ha) experimental manipulation of fallen‐timber load (0 to 80 t ha^?1) over 4 years. The forest was subjected to an incidental, extensive flood that enabled us to examine how two important stressors (timber removal and river regulation) affect ant assemblages. Ants showed little response to the proximity of fallen timber within plots, prior to the flood, or to different loads among plots, unlike other floodplain biota. After the flood, both ant abundance and species richness increased and species composition changed. However, this increase in species richness after flooding was less pronounced in plots with higher amounts of fallen timber. Managing river red gum forest using a mosaic of flood regimes, more representative of historical conditions, is likely to be the most effective way to maintain and enhance the diversity of ants and other biota on these important floodplains.     

Effects of flooding on recruitment and dispersal of the Southern Pygmy Perch (Nannoperca australis) at a Murray River floodplain wetland

Summary With limited evidence linking Australia's Murray‐Darling Basin fish species and flooding, this study assessed annual variation in abundance and recruitment levels of a small‐bodied, threatened floodplain species, the Southern Pygmy Perch (Nannoperca australis), in floodplain habitats (creeks, lakes and wetlands) in the Barmah‐Millewa Forest, Murray River, Australia. Spring and summer sampling over a 5‐year period encompassed large hydrological variation, including 1 year of extended floodplain inundation which was largely driven by an environmental water release, and 2 years of severe regional drought. Recruitment and dispersal of Southern Pygmy Perch significantly increased during the floodplain inundation event compared with the other examined years. This study provides valuable support for an environmental water allocation benefiting a native species, and explores the link between flooding and its advantages to native fish. This suggests that the reduced flooding frequency and magnitude as a result of river regulation may well be a major contributing factor in the species’ decline in the Murray‐Darling Basin.     

Forest Development, Wood Jams, and Restoration of Floodplain Rivers in the Puget Lowland, Washington

Historically in Puget Lowland rivers, wood jams were integral to maintaining an anastomosing channel pattern and a dynamic channel–floodplain connection; they also created deep pools. In the late 1800s, wood was removed from most rivers, rivers were isolated from their floodplains, and riparian forests were cut down, limiting wood recruitment. An exception to this history is an 11-km-long reach of the Nisqually River, which has natural banks and channel pattern and a mature floodplain forest. We use field and archival data from the Nisqually River to explore questions relevant to restoring large rivers in the Pacific Northwest and other forested temperate regions. In particular, we focus on the relation between recovery of in-channel wood accumulations and valley bottom forest conditions and explore implications for river restoration strategies. We find that restoring large rivers depends on establishing riparian forests that can provide wood large enough to function as key pieces in jams. Although the frequency of large trees in the Nisqually valley bottom in 2000 is comparable with that of 1873 land surveys, many formerly more abundant Thuja plicata (western red cedar) were cut down in the late 1800s, and now hardwoods, including Populus trichocarpa (black cottonwood) and Acer macrophyllum (bigleaf maple), are also abundant. Pseudotsuga menziesii (Douglas fir) and fast-growing P. trichocarpa commonly form key pieces that stabilize jams, suggesting that reforested floodplains can develop naturally recruited wood jams within 50 to 100 years, faster than generally assumed. Based on the dynamic between riparian forests, wood recruitment, and wood jams in the Nisqually River, we propose a planning framework for restoring self-sustaining dynamic river morphology and habitat to forested floodplain rivers.     

Ecological impacts of dams,water diversions and river management on floodplain wetlands in Australia

Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Dams, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah‐Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water‐birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 10⁷ ML (10⁶ L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray‐Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983–84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential.     

Low stocks of coarse woody debris in a southwest Amazonian forest

The stocks and dynamics of coarse woody debris (CWD) are significant components of the carbon cycle within tropical forests. However, to date, there have been no reports of CWD stocks and fluxes from the approximately 1.3 million km² of lowland western Amazonian forests. Here, we present estimates of CWD stocks and annual CWD inputs from forests in southern Peru. Total stocks were low compared to other tropical forest sites, whether estimated by line-intercept sampling (24.4 ± 5.3 Mg ha⁻¹) or by complete inventories within 11 permanent plots (17.7 ± 2.4 Mg ha⁻¹). However, annual inputs, estimated from long-term data on tree mortality rates in the same plots, were similar to other studies (3.8 ± 0.2 or 2.9 ± 0.2 Mg ha⁻¹ year⁻¹, depending on the equation used to estimate biomass). Assuming the CWD pool is at steady state, the turnover time of coarse woody debris is low (4.7 ± 2.6 or 6.1 ± 2.6 years). These results indicate that these sites have not experienced a recent, large-scale disturbance event and emphasise the distinctive, rapid nature of carbon cycling in these western Amazonian forests.     

Spangled perch (Leiopotherapon unicolor) in the southern Murray‐Darling Basin: Flood dispersal and short‐term persistence outside its core range

The spangled perch Leiopotherapon unicolor is considered a rare vagrant in the southern Murray‐Darling Basin, Australia, due to its intolerance of the relatively cool water temperatures that prevail during winter months. This study details 1342 records of the species from 68 locations between 2010 and 2014 outside its accepted ‘core adult range’ following widespread flooding during 2010 and 2011. Although records of the species declined over 2013, L. unicolor remained resident in the southern Murray‐Darling Basin as of April 2014. The species persisted in several locations for three consecutive winters with recruitment documented at two sites. This study represents the first identification of the dispersal of large numbers of L. unicolor into the southern Murray‐Darling Basin, persistence beyond a single winter, and recruitment by the species in habitats south of its recognized ‘core adult range’. Targeted research would determine the potential for predicted environmental changes (artificially warmer drainage wetlands, climate change and greater floodplain connectivity) to facilitate longer term persistence and range expansion by the species in the southern Murray‐Darling Basin.     

Coarse woody debris in Australian forest ecosystems: A review

Abstract Coarse woody debris (CWD) is the standing and fallen dead wood in a forest and serves an important role in ecosystem functioning. There have been several studies that include estimates of CWD in Australian forests but little synthesis of these results. This paper presents findings from a literature review of CWD and fine litter quantities. Estimates of forest‐floor CWD, snags and litter from the literature are presented for woodland, rainforest, open forest and tall open forest, pine plantation and native hardwood plantation. Mean mass of forest floor CWD in Australian native forests ranged from 19 t ha^?1 in woodland to 134 t ha^?1 in tall open forest. These values were generally within the range of those observed for similar ecosystems in other parts of the world. Quantities in tall open forests were found to be considerably higher than those observed for hardwood forests in North America, and more similar to the amounts reported for coniferous forests with large sized trees on the west coast of the USA and Canada. Mean proportion of total above‐ground biomass as forest floor CWD was approximately 18% in open forests, 16% in tall open forests, 13% in rainforests, and 4% in eucalypt plantations. CWD can be high in exotic pine plantations when there are considerable quantities of residue from previous native forest stands. Mean snag biomass in Australian forests was generally lower than the US mean for snags in conifer forests and higher than hardwood forest. These results are of value for studies of carbon and nutrient stocks and dynamics, habitat values and fire hazards.     

Home Range Size and Micro‐habitat Density Requirements of Egernia napoleonis: Implications for Restored Jarrah Forest of South Western Australia

Compared to natural forests, coarse woody debris (CWD) is typically scarce in restored forests due to the long time it takes to develop naturally. In post‐mining restored forests in the Jarrah forest of south western Australia, CWD is returned at densities of one log pile per hectare. We tested the adequacy of these densities for meeting the micro‐habitat requirements of Napoleon's skink (Egernia napoleonis), a species rarely found within restored sites. Home range size and overlap, and micro‐habitat densities used by skinks, were measured by radio‐tracking 12 individuals in natural, unmined forest. Napoleon's skinks had small home ranges (0.08 ± 0.02 ha), based on 8 individuals with sufficient fixes. All skinks overlapped in home ranges, with average overlaps of 43.5 ± 8.6%. Ten of the 12 skinks shared micro‐habitats and 4 shared them simultaneously, which indicates some social tolerance. This will influence as to how many micro‐habitats are required. Micro‐habitats were used at high densities: logs at 49.2 ± 8.8 ha^?1 and woody debris piles at 12.4 ± 4.8 ha^?1. Based on these densities, it is recommended that CWD is returned to restored forests at densities of 60 ha^?1, which should provide sufficient micro‐habitats for multiple skinks. Due to the infeasibility of returning such CWD densities across large areas of restored forest, CWD could be preferentially returned as patches, large enough for numerous home ranges, adjacent to unmined forest, or as corridors between unmined forest. These recommendations for returning micro‐habitats should be tested for effectiveness in encouraging recolonization of restored forest by Napoleon's skink and other species.     

Sequential patterns of colonization of coarse woody debris by Ips pini (Say) (Coleoptera: Scolytidae) following a major ice storm in Ontario

Abstract

• 1 It is widely known that many bark and wood‐boring beetle species use nonresistant coarse woody debris (CWD) created by disturbances; however, the ability of these secondary species to cause mortality in healthy trees following a build‐up of their populations remains unclear. We characterized the pattern of colonization by Ips pini (Say) following a major ice storm that created large amounts of CWD varying in resistance to colonization (i.e. ranging from snapped tops with no resistance to heavily damaged trees with intact root systems). A major question was how the beetles responded to the different types of storm‐damaged material and whether healthy undamaged trees were colonized and killed following increases in beetle populations.
• 2 Six red pine, Pinus resinosa Ait., plantations in eastern Ontario were monitored from 1998 to 2001 inclusive: three with high storm damage (approximately 120 m³/ha CWD) and three with minimal damage (approximately 20 m³/ha CWD). Transects (200 × 2 m) were sampled yearly in each plantation to assess the type and amount of damaged pine brood material colonized by the pine engraver beetle, I. pini.
• 3 Beetles preferentially infested the most nonresistant material available each year (i.e. all snapped tops in year 1, all standing snags, up‐rooted trees and many bent trees by year 2, but still less than 50% of trees blown over but with intact root systems by year 3). By years 3 and 4, the majority (approximately 75%) of severely damaged trees (with > 50% crown loss) died prior to beetle colonization.
• 4 The size of the beetle population tracked the abundance of available woody material from year‐to‐year within a plantation; populations were very large in the first 2 years, and declined significantly in the last 2 years.
• 5 Healthy standing red pines were apparently resistant to colonization by the beetles, despite the significant build‐up in their populations. Hence, the results of the present study suggest that native bark beetle populations will not cause further tree mortality following such a disturbance in this region.

     

Hypoxic blackwater event severely impacts Murray crayfish (Euastacus armatus) populations in the Murray River,Australia

Prolonged flooding in 2010/11 ended a decade of drought and produced a large‐scale hypoxic blackwater event across the southern Murray‐Darling Basin, Australia. The hypoxic conditions caused fish kills and Murray crayfish Euastacus armatus to emerge from the water onto the river banks to avoid the poor water quality. This study examined the medium‐term impact of this blackwater event on Murray crayfish populations in the Murray River, where approximately 1800 km of the main channel were affected by hypoxia. Murray crayfish populations were surveyed in July 2012, along a 1100‐km section of the Murray River at 10 sites affected by hypoxic blackwater and six sites that were not affected, and data were compared with surveys of the same sites undertaken in July 2010, four months before the hypoxic blackwater event (before‐after‐control‐impact experimental design). Murray crayfish abundance in 2012 (post‐blackwater) was significantly lower at blackwater affected sites (81% reduction from 2010), but not at non‐affected sites. The hypoxic blackwater impacted Murray crayfish of both sexes and all size‐classes in a similar manner. The results demonstrate that prolonged periods of hypoxia can markedly impact populations of the long‐lived and slow‐growing Murray crayfish despite the species ability to emerge from hypoxic water. The findings highlight important challenges for the management of both the recreational fishery for this species and riverine flows in relation to hypoxic blackwater events.     

Tree Species Composition, Structure, and Aboveground Wood Biomass of a Riparian Forest of the Lower Miranda River, Southern Pantanal, Brazil

The aboveground wood biomass (AWB) of tropical forests plays an important role in the global carbon cycle, and local AWB estimates provide essential data that enable the extrapolation of biomass stocks to ecosystem or biome-wide carbon cycle modelling. Few AWB estimates exist in Neotropical freshwater floodplains, where tree species distribution and forest structure depend on the height and duration of periodic inundations. We investigated tree species composition, forest structure, wood specific gravity, and AWB of trees ≥10 cm dbh in 16 plots totalling an area of 1 ha in a seasonally inundated riparian forest of the lower Miranda River, southern Pantanal, Brazil. The 443 tree individuals belonged to 46 species. Four species (Inga vera, Ocotea suaveolens, Tabebuia heptaphylla and Cecropia pachystachya) comprised more than 50% of the Total Importance Values (TIV), and floristic similarities between the plots averaged 38%. Although we detected an overall increase in species diversity correlated with decreasing flood levels, the most important tree species had almost identical distribution patterns along the flooding gradient. The stand basal area per plot (±?s.d.) amounted to 3.0?±?1.1 m² (47.8?±?18.1 m²/ha), and the tree heights averaged 10.9?±?1.4 m. Multiplying the individual basal areas by individual tree heights and a form factor of 0.6, we estimated the aboveground wood volume (AWV) for each individual, and for each plot (24.4?±?11.7 m³, 391.1?±?188 m³/ha). Wood specific gravity (SG) varied between 0.39 g/cm³ (Cecropia pachystachya) and 0.87 g/cm³ (Tabebuia heptaphylla), with a stand level average of 0.63?±?0.12 g/cm³. Multiplying the individual AWV with species SG, we estimated the plot AWB to be 16.2?±?6.4 Mg (259.4?±?102 Mg/ha). This value is comparable to that reported for late-successional forest stands of Amazonian floodplain forests, and it is close to the worldwide tropical average AWB. Because tree heights in the present forest were comparatively low when compared to other Neotropical forests, we found that resprouting of stems accounted for comparatively high basal areas. We argue that stem resprouting is an adaptation of tree species originating in non-flooded Cerrado to the seasonal inundations of riparian forests.     

Availability of coarse woody debris in a boreal old‐growth Picea abies forest

Abstract. This study reports temporal (based on cross‐dated dead trees) and spatial patterns of availability of coarse woody debris (CWD) from Picea abies in a Swedish boreal landscape with discrete old‐growth forest patches in a wetland matrix. Data were collected from 29 patches ranging in size from 0.3 to 28 ha. A total of 897 dead trees with a minimum diameter of > 15 cm occurred on the 7.2 ha area analysed. The year of death was established for 50% of these trees. CWD volume ranged from 17 to 65 m³/ha for downed logs and from 0.5 to 13 m³/ha for standing snags. CWD of all decay stages and diameter classes occurred abundantly and the probability of finding logs of all decay stages and sizes was very high at the scale of single hectares. Tree mortality differed among 5 yr periods. However, during the last 50 yr no 5 yr period produced less than 3 logs/ha. Decay rates were highly variable among different logs. Logs with soft wood and some wood pieces lost (decay stage 5) died ca. 34 years ago. This suggests a fairly rapid decay in this northern forest. The data indicate a high and continuous availability of CWD of all types. It is likely, therefore, that selection pressures for efficient dispersal among CWD dependent species may not be very high. Consequently, species with narrow habitat demands and/or low dispersal ability may have evolved and this may contribute to the decrease of certain species in the managed landscape.     

Dynamic patch mosaics and channel movement in an unconfined river valley of the Olympic Mountains

1. River valleys resemble dynamic mosaics, composed of patches which are natural, transient features of the land surface produced by the joint action of a river and successional processes over years to centuries. They simultaneously regulate and reflect the distribution of stream energy and exchanges of sediment, wood and particulate organic matter between riparian and aquatic environments. 2. We determined the structure, composition, dynamics and origin of seven patch types at the reach scale in the Queets River valley in the temperate coastal forests of the Olympic Mountains, Washington (U.S.A.). Patch types included: (1) primary and (2) secondary channels; (3) pioneer bars; (4) developing and (5) established floodplains; and (6) transitional and (7) mature fluvial terraces. 3. Lateral channel movements strongly shape patch distribution, structure and dynamics. The primary channel moved laterally 13 m year^?1, on average from 1939 to 2002, but was highly variable among locations and over time. Mean lateral movement rates ranged from 1 to 59 m year^?1 and moving averages (2 km) ranged from 3 to 28 m year^?1 throughout the valley. 4. Each patch type exhibited characteristic vegetation, soil and accumulations of large wood. Pioneer bars contained peak stem density (69 778 stems ha^?1) and volume of large wood (289 m³ ha^?1). Mature fluvial terraces contained the highest mean stem (1739 m³ ha^?1) and canopy volume (158 587 m³ ha^?1). These patches also contained the most soil nitrogen (537 kg ha^?1) and carbon (5972 kg ha^?1). 5. Patch half‐life (the time required for half of the existing patches to be eroded) ranged from 21 to 401 years among forested patch types. Erosion rates were highest in pioneer bars (2.3% year^?1) and developing floodplains (3.3% year^?1), compared with only 0.17% year^?1 in mature fluvial terraces. New forests formed continually, as pioneering vegetation colonised 50% of the channel system within 18 years, often unsuccessfully. 6. In the Queets River, the structure, composition, and dynamics of the patchy riparian forest depends on the interplay between channel movements and biophysical feedbacks between large wood, living vegetation and geomorphic processes. The cycle of patch development perpetuates a shifting‐mosaic of habitats within the river valley capable of supporting diverse biotic assemblages.     

The influence of environmental factors on the morphology of red‐backed voles Myodes gapperi (Rodentia,Arvicolinae) in Québec and western Labrador

Geographical patterns of morphological variation in small mammals are often associated with environmental factors. The southern red‐backed vole Myodes gapperi is a widespread and abundant small mammal in Canada, occurring in environments as diverse as mixed‐wood forests and taiga. First upper molars and skulls from nine populations of southern red‐backed voles distributed across three ecozones and approximately 10° of latitude were analysed by means of geometric morphometric techniques, and their relationships with environmental variables were examined. A weak, non‐linear trend of size increase towards higher latitudes was observed in voles' skulls. Environmental variables appeared to be important drivers of shape differentiation among populations from the three distinct ecozones analysed. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 204–218.     

Coarse woody debris in undisturbed and logged forests in the eastern Brazilian Amazon

Coarse woody debris (CWD) is an important component of the carbon cycle in tropical forests. We measured the volume and density of fallen CWD at two sites, Cauaxi and Tapajós in the Eastern Amazon. At both sites we studied undisturbed forests (UFs) and logged forests 1 year after harvest. Conventional logging (CL) and reduced impact logging (RIL) were used for management on areas where the geometric volumes of logs harvested was about 25–30 m³ ha^?1. Density for five classes of fallen CWD for large material (>10 cm diameter) ranged from 0.71 to 0.28 Mg m^?3 depending upon the degree of decomposition. Density of wood within large fallen logs varied with position relative to the ground and with distance from the center of the log. Densities for materials with diameters from 2 to 5 and 5 to 10 cm were 0.36 and 0.45 Mg m^?3, respectively. The average mass (±SE) of fallen CWD at Cauaxi was 55.2 (4.7), 74.7 (0.6), and 107.8 (10.5) Mg ha^?1 for duplicate UF, RIL, and CL sites, respectively. At Tapajós, the average mass of fallen CWD was 50.7 (1.1) Mg ha^?1 for UF and 76.2 (10.2) Mg ha^?1 for RIL for duplicate sites compared with 282 Mg ha^?1 for live aboveground biomass. Small‐ and medium‐sized material (<10 cm dia.) accounted for 8–18% of the total fallen CWD mass. The large amount of fallen CWD at these UF sites relative to standing aboveground biomass suggests either that the forests have recently been subjected to a pulse of high mortality or that they normally suffer a high mortality rate in the range of 0.03 per year. Accounting for background CWD in UF, CL management produced 2.7 times as much CWD as RIL management. Excess CWD at logging sites would generate a substantial CO₂ emission given the high rates of decay in moist tropical forests.     

Groundwater change forecasts widespread forest dieback across an extensive floodplain system

1. Regulation of rivers for human demands has led to extensive forest dieback on many floodplains. If these important ecosystems are to be maintained under future drier climates, we need accurate tools for predicting forest dieback. In the absence of spatially explicit flooding histories for many floodplains, changes in groundwater conditions may be a good indicator of water availability and, therefore, an important environmental indicator. 2. Eucalyptus camaldulensis forests of Australia are an acute example of forest dieback, with 70% of the Victorian Murray River floodplain dying back. We quantified the relationship between forest dieback and ground water across this extensive floodplain (c. 100 000 ha of forest over 1500 km of river length). 3. A combination of extensive ground surveys, remotely sensed data and modelling methods was used to predict forest dieback at the time of the survey and in the past. This approach provides a valuable tool for accurately monitoring forest condition over large spatial scales. Forest dieback was estimated to have increased from 45 to 70% of the floodplain between 1990 and 2006. 4. Accurate groundwater data (depth and salinity) over a 20‐year period were obtained for 289 bores and summarised using nonlinear regression. Groundwater depth and salinity were strong predictors of stand condition. This suggests that changes in groundwater conditions could be used to signal areas vulnerable to forest dieback and prioritise the limited water available for managed flooding. 5. In the upper Murray, where ground water is predominantly fresh (<15 mS cm^?2), dieback increased with increasing groundwater depth. In contrast, the condition of stands in the lower Murray improved with increases in groundwater depth due its high salinity (>30 mS cm^?2). These regional differences in response of the same tree species to groundwater conditions show that our understanding of the drivers of forest dieback is best achieved at spatial and temporal scales representative of the problem.     

Benchmarks and predictors of coarse woody debris in native forests of eastern Australia

Fallen coarse woody debris (CWD) is critical to forest biodiversity and function. Few studies model factors that influence CWD availability, although such investigations are critically needed to inform sustainable forest management. We assess benchmark levels of CWD in unharvested native forests and those harvested for timber, across a range of forests in north‐east New South Wales, Australia. We found timber‐harvesting was the dominant driver of CWD, with almost double the count (pieces ha^?1) and volume (m³ ha^?1) of total CWD in selectively harvested than unharvested sites. This pattern was consistent across wet and dry forest types. Harvested sites had greater counts of hollow‐bearing logs, and greater volumes of small and medium‐sized CWD (15–50 cm diameter) than unharvested sites. There was no effect of harvesting on the volume of large CWD (>51 cm diameter). Total volumes of CWD (>15 cm diameter) varied from 114 to 166 m³ ha^?1. We found few differences in CWD counts and volumes between forest types, with grassy woodlands and forests containing less CWD than other dry and shrubby forest types, reflecting lower potential input rates. The CWD levels recorded here are similar to those recorded in dry and wet sclerophyll forests elsewhere in Australia and are typical of global estimates for ‘old growth’ forests. Using general linear models we captured up to 57% of the variation in CWD across sites, and found that timber harvesting, topography and the numbers of standing hollow‐bearing and dead trees were significant predictors of CWD. Values for unharvested forest provide a benchmark that could be used to inform retention guidelines for CWD in managed forests in this region. Further assessment of the effect of repeat timber harvesting is needed to fully understand its impact on CWD dynamics, especially if forest residues resulting from timber harvesting are removed from native forests for bioenergy production.     

Zonal distribution of coarse woody debris and its contribution to net primary production in a secondary mangrove forest

Coarse woody debris (CWD) plays an important role in long-term carbon storage in forest ecosystems. However, few studies have examined CWD in mangrove forests. A secondary mangrove forest on an estuary of the Trat River showed different structures along vegetation zones ranging from the river’s edge to inland parts of the forest (the Sonneratia–Avicennia, Avicennia, Rhizophora, and Xylocarpus zones, respectively). The mass distribution of CWD stock in downed wood and standing dead trees along these vegetation zones was evaluated. Most of the CWD stock in the Sonneratia–Avicennia and Avicennia zones was found in downed wood, while it mainly accumulated in standing dead trees in the Rhizophora and Xylocarpus zones. The total mass of CWD stock that accumulated in each zone ranged from 1.56–8.39 t ha^?1, depending on the forest structure and inundation regimes. The annual woody debris flux in each zone was calculated by summing the necromass (excluding foliage) of dead trees and coarse litter from 2010 to 2013. The average woody debris flux was 5.4 t ha^?1 year^?1, and its zonal variation principally depended on the necromass production that resulted from forest succession, high tree-density, and lightning. Over all the zones, the above- and below-ground net primary production (ANPP and BNPP, respectively) was estimated at 18.0 and 3.6 t ha^?1 year^?1, respectively. The magnitude of BNPP and its contribution to the NPP was markedly increased when fine root production was taken into consideration. The contribution of the woody debris flux without root necromass to the ANPP ranged from 12 to 28%.     

The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.