Seasonal fine fuel and coarse woody debris dynamics in north Australian savannas

2020 ◽  
Vol 29 (12) ◽  
pp. 1109
Author(s):  
Cameron Yates ◽  
Harry MacDermott ◽  
Jay Evans ◽  
Brett P. Murphy ◽  
Jeremy Russell-Smith
Keyword(s):  
Coarse Woody Debris ◽  
Woody Debris ◽  
Dynamic Modelling ◽  
Dry Season ◽  
Annual Rainfall ◽  
Wet Season ◽  
Rainfall Gradient ◽  
Litter Accumulation ◽  
Significant Seasonal Variation ◽  
Savanna Burning

Several studies have separately explored accumulation of the dominant fuels (grass, fine litter (<6mm diameter) and coarse woody debris (CWD, 6–50mm diameter)) in north Australian savannas. We report an analysis of two longitudinal datasets describing how these three fuel components covary in abundance throughout the year in eucalypt-dominated savanna over a rainfall gradient of 700–1700mm mean annual rainfall (MAR). Our observations concur generally with previous observations that litter accumulation results in a late dry season (LDS) peak in biomass, whereas cured grassy fuels typically are seasonally invariant, and CWD inputs are associated with stochastic severe wet season storms and dry season fires. The distinct LDS litter peak contributes significantly to the potential for LDS fires to be of higher intensity, burn more fuel per unit area and produce greater emissions relative to early dry season (EDS) fires. However, Australia’s current (2018) formal savanna burning emissions avoidance methodology erroneously deems greater EDS fine fuel (grass and fine litter) biomass in four of nine designated vegetation fuel types. The study highlights the need to develop seasonally dynamic modelling approaches that better account for significant seasonal variation in fine fuel inputs and decomposition.

Fire patterns in north Australian savannas: extending the reach of incentives for savanna fire emissions abatement

2014 ◽  
Vol 36 (4) ◽  
pp. 371 ◽  
Author(s):  
Peter J. Whitehead ◽  
Jeremy Russell-Smith ◽  
Cameron Yates
Keyword(s):  
Ghg Emissions ◽  
Fire Regimes ◽  
Fire Frequency ◽  
Fire Season ◽  
Annual Rainfall ◽  
Rainfall Gradient ◽  
Fire Emissions ◽  
Savanna Burning ◽  
Anthropogenic Fires ◽  
Large Random Sample

Anthropogenic fires in Australia’s fire-prone savannas produce up to 3% of the nation’s accountable greenhouse gas (GHG) emissions. Incentives to improve fire management have been created by a nationally accredited savanna burning emissions abatement methodology applying to 483 000 km2 of relatively high-rainfall (>1000 mm p.a.) regions. Drawing on 15 years of fire mapping, this paper assesses appropriate biophysical boundaries for a savanna burning methodology extended to cover lower-rainfall regions. We examine a large random sample of points with at least 300 mm of annual rainfall, to show that: (a) relative fire frequencies (percentage of years with fire) decline from 33.3% in higher-rainfall regions (>1000 mm) to straddling ~10% in the range 300–700 mm; (b) there are no marked discontinuities in fire frequency or fire seasonality down the rainfall gradient; (c) at all annual rainfalls, fire frequency is higher when rainfall is more strongly seasonal (very low rainfall in the driest quarter); (d) below 500 mm fire regimes are particularly variable and a large proportion of sampled sites had no fire over the study period; (e) fire is more likely to occur later in the fire season (generating relatively higher emissions) in the 600–700-mm annual rainfall band than in other parts of the rainfall gradient; (f) woodland savannas are most common above and predominantly grassland systems are more common below ~600-mm annual rainfall. We propose that development of a complementary lower-rainfall savanna burning methodology apply to regions between 600 and 1000-mm annual rainfall and ≤15 mm of rainfall in the driest quarter, adding an area more than 1.5 times the existing methodology’s coverage. Given greater variability in biophysical influences on fire regimes and observed levels of fire frequency within this lower-rainfall domain, we suggest that criteria for determining baseline (pre-project) periods require estimates of mean annual emissions equivalent in precision to the project on which the higher-rainfall methodology was based.

Temporal and spatial variation of fine roots in a northern Australian Eucalyptus tetrodonta savanna

2008 ◽  
Vol 24 (2) ◽  
pp. 177-188 ◽  
Author(s):  
David P. Janos ◽  
John Scott ◽  
David M. J. S. Bowman
Keyword(s):  
Fine Roots ◽  
Soil Surface ◽  
Dry Season ◽  
Annual Rainfall ◽  
Tropical Savannas ◽  
Wet Season ◽  
Temporal And Spatial Variation ◽  
Deep Roots ◽  
Temporal And Spatial ◽  
Peak Abundance

Abstract:Six rhizotrons in an Eucalyptus tetrodonta savanna revealed seasonal changes in the abundance of fine roots (≤ 5 mm diameter). Fine roots were almost completely absent from the upper 1 m of soil during the dry season, but proliferated after the onset of wet-season rains. At peak abundance of 3.9 kg m−2 soil surface, fine roots were distributed relatively uniformly throughout 1 m depth, in contrast with many tropical savannas and tropical dry forests in which fine roots are most abundant near the soil surface. After 98% of cumulative annual rainfall had been received, fine roots began to disappear rapidly, such that 76 d later, less than 5.8% of peak abundance remained. The scarcity of fine roots in the upper 1 m of soil early in the dry season suggests that evergreen trees may be able to extract water from below 1 m throughout the dry season. Persistent deep roots together with abundant fine roots in the upper 1 m of soil during the wet season constitute a ‘dual’ root system. Deep roots might buffer atmospheric CO2 against increase by sequestering carbon at depth in the soil.

Abundance, Zonation and Foraging Ecology of Birds in Mangroves of Darwin Harbour, Northern Territory.

1996 ◽  
Vol 23 (4) ◽  
pp. 443 ◽  
Author(s):  
RA Noske
Keyword(s):  
Foraging Ecology ◽  
Avicennia Marina ◽  
Abundant Species ◽  
Dry Season ◽  
Mangrove Forests ◽  
Resident Species ◽  
Wet Season ◽  
Mangrove Species ◽  
Significant Seasonal Variation ◽  
Melaleuca Cajuputi

The density, seasonality, habitat utilization and foraging ecology of birds in mangals (mangrove forests) at a site on the upper reaches of Darwin Harbour were investigated by transect censusing and colour-banding over three years. Despite having only 10 species of plants, the site supported 17 confirmed and five probable breeding resident species of birds, and was visited by 30 more. From variable-width transect censuses, the mean density of birds on a 4-ha plot was estimated to be 25 ha-1, fairly consistent with densities obtained from territory mapping of colour-banded birds. Nearly 70% of the individuals belonged to just 4 species: two mangal-dependent species, the red-headed honeyeater (Myzomela erythrocephala) and the yellow white-eye (Zosterops lutea) and two more generalised species, the large-billed gerygone (Gerygone magnirostris) and the brown honeyeater (Lichmera indistincta). Only the red-headed honeyeater showed significant seasonal variation in abundance, with highest numbers during the late dry season after breeding. This coincided with the period of greatest food (nectar) availability in the mangal, due to flowering Bruguiera exaristata. Lowest numbers of the red-headed honeyeater (and the brown honeyeater) occurred in the late wet season when nectar was scarce in the mangal but abundant in Melaleuca cajuputi fringing the mangal. Several resident species held permanent territories, while others apparently shifted landward during the wet season, possibly due to the wetter conditions created by freshwater runoff and high spring tides Many species showed strong associations with particular mangal zones. Large-billed gerygones, grey whistlers (Pachycephala simplex), shining flycatchers (Myiagra alecto) and mangrove fantails (Rhipidura phasiana) were associated with the Rhizophora zone at the wetter (more frequently inundated) end of the plot; mangrove robins (Eopsaltria pulverulenta) and mangrove gerygones (Gerygone laevigaster), were encountered most in the Ceriops zone; and green-backed gerygones (Gerygone chloronata) strongly favoured the dry landward edge. Four foraging guilds were evident among 13 of the most abundant species, the largest of which was the insectivorous foliage-foraging guild. Species in this group partitioned resources by differential selection of mangrove species, heights and foraging techniques. The tiny (6.4 g) mangrove gerygone was the most specialized species, spending 80% of its time on Avicennia marina. Contrary to the literature, breeding of mangal-dwelling birds peaked during the dry season. The ecology, evolution and biogeography of mangrove-endemic birds is reviewed in the light of this study and recent information from Western Australia.

Emerging opportunities for developing a diversified land sector economy in Australia’s northern savannas

2018 ◽  
Vol 40 (4) ◽  
pp. 315 ◽  
Author(s):  
Jeremy Russell-Smith ◽  
Kamaljit K. Sangha
Keyword(s):  
Beef Cattle ◽  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
National Parks ◽  
Dry Season ◽  
Annual Rainfall ◽  
Focal Region ◽  
Wet Season ◽  
Gas Emissions ◽  
Northern Regions

We explore sustainable land sector opportunities for Australia’s 1.2 million km2 northern savanna rangelands where extensive beef cattle pastoralism is the predominant contemporary land use. Our focal region is characterised by mean annual rainfall exceeding 600 mm, ecologically bountiful wet season water availability followed by 6–8 months of surface water deficit, mostly nutrient-poor soils, internationally significant biodiversity and carbon stock values, very extensive dry season fires in pastorally unproductive settings, a sparse rural population (0.14 persons km–2) comprising a high proportion of Indigenous people, and associated limited infrastructure. Despite relatively high beef cattle prices in recent seasons and property values escalating at a spectacular ~6% p.a. over the past two decades, long-term economics data show that, for most northern regions, typical pastoral enterprises are unprofitable and carry significant debt. Pastoral activities can also incur very significant environmental impacts on soil and scarce dry season water resources, and greenhouse gas emissions, which currently are not accounted for in economic sustainability assessments. Over the same period, the conservation sector (including National Parks, Indigenous Protected Areas) has been expanding rapidly and now occupies 25% of the region. Since 2012, market-based savanna burning projects aimed at reducing greenhouse gas emissions occur over a further 25%. Returns from nature-based tourism focussed particularly on maintaining intact freshwater systems and associated recreational fishing opportunities dwarf returns from pastoralism. The growth of these latter industries illustrates the potential for further development of profitable ‘ecosystem services’ markets as part of a more environmentally and socially sustainable diversified regional land sector economy. We outline some of the imminent challenges involved with, and opportunities for developing, this new industry sector.

Fire, growth and survivorship in a Neotropical savanna grass Andropogon semiberbis in Venezuela

1989 ◽  
Vol 5 (4) ◽  
pp. 387-400 ◽  
Author(s):  
Juan F. Silva ◽  
Fernando Castro
Keyword(s):  
Seedling Growth ◽  
Canopy Structure ◽  
Structural Complexity ◽  
Dry Season ◽  
Root Competition ◽  
Annual Rainfall ◽  
Grass Species ◽  
Mortality Factors ◽  
Wet Season ◽  
Adult Plants

ABSTRACTThis study was conducted in a woodland savanna in western Venezuela exclosed from grazing and burnt once a year towards the end of the dry season. Mean annual rainfall is 1500 mm, with a strong seasonality.Two cohorts of seedlings of Andropogon semiberbis were tagged and monitored for up to three years. Several variables such as survivorship, plant size, seedling density, fire damage and distance to the nearest adult were measured or estimated. Two burning experiments to measure survivorship before and after fire, and two seedling-growth experiments to assess competitive interference from adult plants of three grass species were performed.The highest mortality takes place during the dry season and is due to fire. This decreases as the plants get bigger due to increasing structural complexity of the clump by growth which gives added protection to the meristems. Other mortality factors such as desiccation, uprooting and shading seem to be important during the wet season, when mortality rate is relatively constant. Survivorship during the first year and after three years is strongly correlated to the size attained by the end of the first growing season.Seedling densities are rather low and do not seem to play any role in survivorship in this population. Adult interference with seedling growth decreases with distance and seems to be due to root competition, although there is a tendency toward increased foliage interference related to the canopy structure of adult plants.

scholarly journals Effects of climate change on future extreme rainfall indices over Thailand

2014 ◽  
Vol 16 (2) ◽  
pp. 306-315
Keyword(s):  
Extreme Rainfall ◽  
Dry Season ◽  
Southern Region ◽  
Andaman Sea ◽  
Annual Rainfall ◽  
Reference Period ◽  
Wet Season ◽  
Dry Spell ◽  
The Future ◽  
Projected Changes

<div> <p>Extreme rainfall indices were calculated based on daily rainfall data derived from the outputs of MM5-RCM simulations. Projected changes of these indices in the future (2020s) under the IPCC Special Report on Emissions Scenarios (SRES) A1B compared to the reference period (1990s) were analyzed. Before calculating the indices, the raw outputs from the MM5-RCM were adjusted in order to reduce biases as part of the bias-correction process. The validation demonstrates that the average and cycle of annual rainfall in the reference period are reproduced reasonably in the bias-corrected MM5-RCM results. The projected changes of the rainfall indices suggest that in the future most areas of northern, western, and northeastern Thailand will become wetter in the wet season and drier in the dry season. Central and eastern Thailand will become drier in the wet season while in the dry season rainfall will become more intense, and rainy days will become more scattered with a higher number of heavy rainfall days. In the south, the length of the wet spell will be decreased in the Southern Andaman Sea area and increased in East-Southern Region. The dry spell will likely be shorter throughout the southern region for all seasons. &nbsp;</p> </div> <p>&nbsp;</p>

Improvement of native pasture with Townsville stylo in the dry tropics of sub-coastal northern Queensland

1979 ◽  
Vol 19 (98) ◽  
pp. 325 ◽  
Author(s):  
P Gillard
Keyword(s):  
Dry Season ◽  
Early Years ◽  
Annual Rainfall ◽  
Wet Season ◽  
Heteropogon Contortus ◽  
Pasture Quality ◽  
Native Pasture ◽  
Annual Grasses ◽  
Townsville Stylo ◽  
Pasture Yield

The results of a grazing experiment in which Townsville stylo was oversown into native pasture in sub-coastal northern Queensland are reported. The region receives 650 mm average annual rainfall compared with >850 mm at other experimental sites where Townsville stylo has been tested under grazing. The experiment included three treatments in a factorial combination: timber clearing or not, application of 125 kg ha-1 superphosphate or not and stocking rates of 0.4 and 0.2 beasts ha-1. The yield of Townsville stylo depended on treatments and annual rainfall but was generally low in this environment. Over the ten year period of the experiment the pastures remained dominated by Heteropogon contortus and Bothriochloa bladhii, and there was no invasion of annual grasses. Clearing of the timber increased the pasture yield by 77%. There was no regrowth of trees after clearing. Within each year cattle gained weight in the wet season, when pasture quality was high, and lost weight in the dry season, when pasture quality declined. Mean liveweight gain over all treatments was correlated (r = 0.97) with the length of the growing season. A significant response in liveweight gain to fertilizer occurred only in years of average or above rainfall when there was also a response in Townsville stylo yield. The effect was due to increased gains during the wet season; there were no differences in liveweight gain during the dry season, when Townsville stylo became decomposed. Significantly greater liveweight losses occurred on the heavily stocked treatments during the dry season of drought years. The yield of Townsville stylo in the early years of the experiment was significantly higher on the cleared treatments and there was a corresponding response in liveweight gains in the wet season during this period. Liveweight losses in the dry season were also significantly higher on the timbered treatments in years of drought. The powerful influence of climatic variation on the treatments places reservations on their practical application. The increased pasture yield from tree clearing is likely to be a benefit to cattle only in years of drought. The responses to superphosphate fertilizer only in years of high rainfall suggests that its use is unlikely to be profitable on Townsville stylo based pastures in this environment.

scholarly journals Direct observations of rock moisture, a hidden component of the hydrologic cycle

2018 ◽  
Vol 115 (11) ◽  
pp. 2664-2669 ◽  
Author(s):  
Daniella M. Rempe ◽  
William E. Dietrich
Keyword(s):  
Land Surface ◽  
Unsaturated Zone ◽  
Global Climate ◽  
Dry Season ◽  
Annual Rainfall ◽  
Recent Theory ◽  
Wet Season ◽  
Soil Thickness ◽  
Moisture Storage ◽  
Pass Through

Recent theory and field observations suggest that a systematically varying weathering zone, that can be tens of meters thick, commonly develops in the bedrock underlying hillslopes. Weathering turns otherwise poorly conductive bedrock into a dynamic water storage reservoir. Infiltrating precipitation typically will pass through unsaturated weathered bedrock before reaching groundwater and running off to streams. This invisible and difficult to access unsaturated zone is virtually unexplored compared with the surface soil mantle. We have proposed the term “rock moisture” to describe the exchangeable water stored in the unsaturated zone in weathered bedrock, purposely choosing a term parallel to, but distinct from, soil moisture, because weathered bedrock is a distinctly different material that is distributed across landscapes independently of soil thickness. Here, we report a multiyear intensive campaign of quantifying rock moisture across a hillslope underlain by a thick weathered bedrock zone using repeat neutron probe measurements in a suite of boreholes. Rock moisture storage accumulates in the wet season, reaches a characteristic upper value, and rapidly passes any additional rainfall downward to groundwater. Hence, rock moisture storage mediates the initiation and magnitude of recharge and runoff. In the dry season, rock moisture storage is gradually depleted by trees for transpiration, leading to a common lower value at the end of the dry season. Up to 27% of the annual rainfall is seasonally stored as rock moisture. Significant rock moisture storage is likely common, and yet it is missing from hydrologic and land-surface models used to predict regional and global climate.

scholarly journals Morphological composition and fiber partitioning along regrowth in elephant grass CT115 intended for ethanol production

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
José A. Rueda ◽  
Juan de Dios Guerrero-Rodríguez ◽  
Sergio Ramírez-Ordoñes ◽  
Cecilio U. Aguilar-Martínez ◽  
Wilber Hernández-Montiel ◽  
...  
Keyword(s):  
Ethanol Yield ◽  
Inverse Correlation ◽  
Dry Season ◽  
Age And Growth ◽  
Annual Rainfall ◽  
Elephant Grass ◽  
Wet Season ◽  
Biomass Quality ◽  
Green Leaves ◽  
The Given

Abstract Leaf share, plant age and growth season are often overlooked as modifiers of the biomass quality in energy crops. The current work studied the effect of the given factors on the biomass yield and the biomass quality in Elephant grass CT115, intended for bioethanol production, in Veracruz, Mexico. Two seasons per year, 5 months each, were tracked on a 2-weeks basis. The climate is warm wet with summer rains, 1,142 mm of annual rainfall, and 26 °C monthly temperature. From day 56 of the wet season or from day 84 of the dry season, stems accumulated 12 or 6 Mg ha−1, respectively, while green leaves increased only 1 Mg. Higher biomass quality was recorded for the leaf fraction, or for the wet season regrowth. For instance, lignin contained in stems meant twice that of leaves, whereas stems recorded 20% less lignin in the wet season as compared to the dry season. Despite holocellulose being similar between fractions or seasons, hemicellulose and cellulose showed inverse correlation, while lignin and cellulose contents were directly correlated in stems. Increasing the annual harvest of green leaves will improve biomass quality, which is known to increase biodegradability and might improve the annual ethanol yield.

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