Semi-arid Woodland Research Articles

A model analysis of climate and CO2 controls on tree growth and carbon allocation in a semi-arid woodland

Many studies have failed to show an increase in the radial growth of trees in response to increasing atmospheric CO2 concentration [CO2] despite the expected enhancement of photosynthetic rates and water-use efficiency at high [CO2]. A global light use efficiency model of photosynthesis, coupled with a generic carbon allocation and tree-growth model based on mass balance and tree geometry principles, was used to simulate annual ring-width variations for the gymnosperm Callitris columellaris in the semi-arid Great Western Woodlands, Western Australia, over the past 100 years. Parameter values for the tree-growth model were derived from independent observations except for sapwood specific respiration rate, fine-root turnover time, fine-root specific respiration rate and the ratio of fine-root mass to foliage area (ζ), which were calibrated to the ring-width measurements by approximate Bayesian optimization. This procedure imposed a strong constraint on ζ. Modelled and observed ring-widths showed quantitatively similar, positive responses to total annual photosynthetically active radiation and soil moisture, and similar negative responses to vapour pressure deficit. The model also produced enhanced radial growth in response to increasing [CO2] during recent decades, but the data do not show this. Recalibration in moving 30-year time windows produced temporal shifts in the estimated values of ζ, including an increase by ca 12% since the 1960s, and eliminated the [CO2]-induced increase in radial growth. The potential effect of CO2 on ring-width was thus shown to be small compared to effects of climate variability even in this semi-arid climate. It could be counteracted in the model by a modest allocation shift, as has been observed in field experiments with raised [CO2].

A wildfire event influences ecosystem carbon fluxes but not soil respiration in a semi-arid woodland

The importance of arid and semi-arid ecosystems for global net carbon uptake has recently been highlighted. More information about the drivers of carbon fluxes in these ecosystems is required to advance our understanding of the contribution of dry ecosystems to the global carbon budget. In this study, eddy covariance flux data was used to calculate net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Reco) in a semi-arid woodland on sandy soil. In January 2014 a wildfire severely damaged the area around the flux tower, burning trees and spinifex and consuming aboveground bark and leaf litter. The flux tower recorded data for one year before the fire (January–December 2013) and more than one year after the fire (May 2014–July 2015). Soil respiration was measured in-situ monthly after the fire (July 2014–June 2015), in burnt and unburnt areas under Eucalyptus tree canopy and inter-canopy representing 25 and 75% of the area, respectively. Before the fire the ecosystem was a net carbon sink, sequestering 81gCm−2 yr−1 in 2013, but became a carbon source after the fire. Reco and GPP declined by about 35% and 65%, respectively, after the fire. Net carbon uptake resumed 12–15 months after the fire with NEP approaching values similar to those before the fire. Soil respiration was significantly higher under tree canopies (1.5μmol CO2 m−2s−1) than in inter-canopy areas (0.9μmol CO2 m−2s−1). Soil respiration was mainly driven by soil water content and thus magnitude and distribution of precipitation, but was not influenced by the wildfire. Accounting for differences in area, soil respiration from inter-canopy and under canopy contributed 51 and 32% to total ecosystem respiration. It can be concluded that carbon flux in this semi-arid woodland was strongly influenced by precipitation and wildfire, with net carbon uptake of the ecosystem beginning approximately one year after the fire.

Estimating biophysical parameters of Persian oak coppice trees using UltraCam-D airborne imagery in Zagros semi-arid woodlands

This study provides insight into the quantitative assessment of biophysical parameters of Persian oak coppice trees using UltraCam-D (UC-D) very high spatial resolution airborne orthoimagery in Zagros semi-arid woodlands, West Iran. We estimated the parameters across two methods: 1) direct quantification of tree density using line intercept sampling (LIS) method, tree height (TH) by shadow length, crown diameter (CD) by manual measurement, and crown area (CA) using support vector machine classifier, and 2) indirect quantification of diameter at root collar (DRC) and basal area (BA) by the allometric equations employing CD. The validation method consisted of taking field measurements of the parameters of a total of 162 coppice trees in a 30 ha study plot. The results of the validation assessment revealed the effective estimation of TH (R2 = 0.85 and RMSE of 1.00 m), CD (R2 = 0.92 and RMSE of 1.19 m), CA (R2 = 0.85 and RMSE of 16.39 m2), DRC (R2 = 0.87 and RMSE of 0.05 m), and BA (R2 = 0.82 and RMSE of 0.04 m2), when compared against the validation data. Hence, we show that UC-D data are a practical alternative to filed measurements for characterization of coppice tree biophysical parameters in semi-arid woodlands which can be applied for woodland planning and management.

Vessel diameter and related hydraulic traits of 31 Eucalyptus species arrayed along a gradient of water availability.

We present two comprehensive data sets that describe xylem vessel diameters and related sapwood traits for species of Eucalyptus from arid and semi-arid woodlands and forests in Australia. Between 2009 and 2014, sapwood of mature trees was sampled in south-western, south-eastern and eastern Australia. One additional species was sampled from tropical north-western Australia. The first data set describes samples collected from the basal stem section (130cm above ground) of three individuals of 31 species of which eight species were replicated at sites that differed in climatic conditions. The second data set describes vessel characteristics of three trees from each of 10 species that were sampled at 8m below the tree apex. The sampled trees of these 10 species are also part of the first data set. In total, we report diameters (D) for over 25100 vessels, from 494 digital images taken from 117 trees. We also report vessel frequencies, void-to-wood ratios, sapwood densities and hydraulically weighted vessel diameters (Dh). Supporting data of the first data set include tree diameter at breast height (130cm above ground), tree height, sample locations, and summary climate data. In this data set, diameter of individual vessels ranges from 10 to over 300μm, and vessel frequency from 360 to 9070 vessels cm-2 . Wood density ranges from 0.47 to 0.96g cm-3 . Void-to-wood ratio ranges from 6% to 27% and Dh ranges from 46 to 236μm. Mean annual rainfall (P) at sample sites ranges from 246 to 2274mm and FAO56 reference evaporation (E) from 777 to 2110mm. The aridity index (E/P) ranges from 0.15 to 2.93 (dimensionless). Tree diameters range from 9 to 90cm and tree heights range from 6 to 70m. D and Dh in the second data set range from 11 to 271 and 68 to 205μm, respectively. These datasets will make a valuable contribution to future continental-scale and global-scale studies of the relationship between xylem hydraulic architecture and climate. The data sets are unique in the sense that they are phylogenetically constrained, allowing in-depth assessment of plasticity of hydraulic attributes within a single tree genus.

Inter-annual variability in Prosopis caldenia pod production in the Argentinean semiarid pampas: A modelling approach

The driest part of the Argentinean pampas is occupied by semiarid woodlands dominates by Prosopis caldenia Burkart (Calden). Calden pods are a highly valuable fodder supplement for livestock but its production is highly variable. Our objective was to analyze and model the temporal pattern in inter-annual variability of Calden pod production. Our key hypothesis is that weather conditions are the main determinant of the pod masting behaviour. Tree size and climatic variables were evaluated as explanatory covariates using a zero-inflated log-normal modelling approach. The proposed final model structure incorporated 25 parameters, including four variance components, two intercepts for both the logistic and the log-normal parts of the model, and nineteen parameters associated with fixed effects. Climate had a strong influence on the flowering-fruiting Calden process and on the inter-annual variability of the final pod production at the tree level. Temperatures during bud breaking, flowering and fruit shedding, together with the precipitation from the final month of fruit shedding and the total amount of the prior vegetative cycle, were the main weather covariates that affect the processes.

Efficiency of sample-based indices for spatial pattern recognition of wild pistachio (Pistacia atlantica) trees in semi-arid woodlands

The efficiency of sample-based indices proposed to quantify the spatial distribution of trees is influenced by the structure of tree stands, environmental heterogeneity and degree of aggregation. We evaluated 10 commonly used distance-based and 10 density-based indices using two structurally different stands of wild pistachio trees in the Zagros woodlands, Iran, to assess the reliability of each in revealing stand structure in woodlands. All trees were completely stem-mapped in a nearly pure (40 ha) and a mixed (45 ha) stand. First, the inhomogeneous pair correlation function [g(r)] and the Clark–Evans index (CEI) were used as references to reveal the true spatial arrangement of all trees in these stands. The sampled data were then evaluated using the 20 indices. Sampling was undertaken in a grid based on a square lattice using square plots (30 m × 30 m) and nearest neighbor distances at the sample points. The g(r) and CEI statistics showed that the wild pistachio trees were aggregated in both stands, although the degree of aggregation was markedly higher in the pure stand. Three distance- and six density-based indices statistically verified that the wild pistachio trees were aggregated in both stands. The distance-based Hines and Hines statistic (h t ) and the density-based standardised Morisita (I p ), patchiness (IP) and Cassie (C A ) indices revealed aggregation of the trees in the two structurally different stands in the Zagros woodlands and the higher clumping in the pure stand, whereas the other indices were not sensitive enough.

Rainfall intensity switches ecohydrological runoff/runon redistribution patterns in dryland vegetation patches.

Effectively managing net primary productivity in drylands for grazing and other uses depends on understanding how limited rainfall input is redistributed by runoff and runon among vegetation patches, particularly for patches that contrast between lesser and greater amounts of vegetation cover. Due in part to data limitations, ecohydrologists generally have focused on rainfall event size to characterize water redistribution processes. Here we use soil moisture data from a semiarid woodland to highlight how, when event size is controlled and runoff and interception are negligible at the stand scale, rainfall intensity drives the relationship between water redistribution and canopy and soil patch attributes. Horizontal water redistribution variability increased with rainfall intensity and differed between patches with contrasting vegetation cover. Sparsely vegetated patches gained relatively more water during lower intensity events, whereas densely vegetated ones gained relatively more water during higher intensity events. Consequently, range managers need to account for the distribution of rainfall event intensity, as well as event size, to assess the consequences of climate variability and change on net primary productivity. More generally, our results suggest that rainfall intensity needs to be considered in addition to event size to understand vegetation patch dynamics in drylands.

Response of respiration and nutrient availability to drying and rewetting in soil from a semi-arid woodland depends on vegetation patch and a recent wildfire

Abstract. Semi-arid woodlands, which are characterised by patchy vegetation interspersed with bare, open areas, are frequently exposed to wildfire. During summer, long dry periods are occasionally interrupted by rainfall events. It is well known that rewetting of dry soil induces a flush of respiration. However, the magnitude of the flush may differ between vegetation patches and open areas because of different organic matter content, which could be further modulated by wildfire. Soils were collected from under trees, under shrubs or in open areas in unburnt and burnt sandy mallee woodland, where part of the woodland experienced a wildfire which destroyed or damaged most of the aboveground plant parts 4 months before sampling. In an incubation experiment, the soils were exposed to two moisture treatments: constantly moist (CM) and drying and rewetting (DRW). In CM, soils were incubated at 80 % of maximum water holding capacity (WHC) for 19 days; in DRW, soils were dried for 4 days, kept dry for another 5 days, then rewetted to 80 % WHC and maintained at this water content until day 19. Soil respiration decreased during drying and was very low in the dry period; rewetting induced a respiration flush. Compared to soil under shrubs and in open areas, cumulative respiration per gram of soil in CM and DRW was greater under trees, but lower when expressed per gram of total organic carbon (TOC). Organic matter content, available P, and microbial biomass C, but not available N, were greater under trees than in open areas. Wild fire decreased the flush of respiration per gram of TOC in the open areas and under shrubs, and reduced TOC and microbial biomass C (MBC) concentrations only under trees, but had little effect on available N and P concentrations. We conclude that the impact of wildfire and DRW events on nutrient cycling differs among vegetation patches of a native semi-arid woodland which is related to organic matter amount and availability.

Spatial Distribution of Aboveground Carbon Stock of the Arboreal Vegetation in Brazilian Biomes of Savanna, Atlantic Forest and Semi-Arid Woodland.

The objective of this study was to map the spatial distribution of aboveground carbon stock (using Regression-kriging) of arboreal plants in the Atlantic Forest, Semi-arid woodland, and Savanna Biomes in Minas Gerais State, southeastern Brazil. The database used in this study was obtained from 163 forest fragments, totaling 4,146 plots of 1,000 m2 distributed in these Biomes. A geographical model for carbon stock estimation was parameterized as a function of Biome, latitude and altitude. This model was applied over the samples and the residuals generated were mapped based on geostatistical procedures, selecting the exponential semivariogram theoretical model for conducting ordinary Kriging. The aboveground carbon stock was found to have a greater concentration in the north of the State, where the largest contingent of native vegetation is located, mainly the Savanna Biome, with Wooded Savanna and Shrub Savanna phytophysiognomes. The largest weighted averages of carbon stock per hectare were found in the south-center region (48.6 Mg/ha) and in the southern part of the eastern region (48.4 Mg/ha) of Minas Gerais State, due to the greatest predominance of Atlantic Forest Biome forest fragments. The smallest weighted averages per hectare were found in the central (21.2 Mg/ha), northern (20.4 Mg/ha), and northwestern (20.7 Mg/ha) regions of Minas Gerais State, where Savanna Biome fragments are predominant, in the phytophysiognomes Wooded Savanna and Shrub Savanna.

Configuration and geometry of sap-holes drilled by the White-fronted Woodpecker (Melanerpes cactorum): effects of tree-structure, sap-traits and plant health

Several species of woodpecker drill holes in living trees to feed on flows of sap. We describe sap-holes drilled by the White-fronted Woodpecker (Melanerpes cactorum) on plant species in semi-arid woodlands of northern Argentina, and examine, for the first time, attributes of the plants that may help to explain the configuration and geometry of sap-holes made by a species of woodpecker. Sap-holes vary among plant species, mostly in size and shape, and in their arrangement and location on tree branches. Moreover, patterning of sap-hole are closely similar in structurally similar species, showing foraging decisions of White-fronted Woodpeckers associated with plant structure-types at a supra-specific level. In large trees, sap-holes were small, round and arranged in rows on branches or trunks of large diameter, whereas in smaller Prosopis trees, sap-holes were rectangular and located on branches of small diameter. In other species of tree and shrub sap-holes were large and irregular, and on branches of intermediate diameter. The size of holes was positively correlated with substrate diameter for small and intermediate branches of a given group of species, but was independent of diameter in tree species with holes on the trunk. The switch between sap-consumption strategies related to attributes of trees opens the possibility that White-fronted Woodpeckers drill sap-holes trying to maximise sap-harvesting.

Spatial and environmental patterns of off-road vehicle recreation in a semi-arid woodland

Outdoor recreation is a widely recognized cultural ecosystem service. Ensuring that appropriate, high quality recreation opportunities are available requires, among other factors, knowledge of the environmental preferences of recreation users and spatial indicators of where those environmental features exist on the landscape and offer the potential to meet recreation goals. Diverse types of outdoor recreation exist, and different forms of recreation may be associated with different environmental features. The focus of this study is off-road vehicle (ORV) recreation. We demonstrate how readily available spatial environmental datasets, including high resolution image data provided within GoogleEarth, can be used to develop a cost-effective, objective indicator of ORV recreation across a landscape, which can inform management to provide desired recreation opportunities while protecting ecologically sensitive areas.ORV recreational tracks were delineated from GoogleEarth imagery throughout our study area in the Great Western Woodlands of Western Australia. In this region, ORV use is a popular recreation activity and a growing concern of conservation organizations, but is not yet actively managed. Most recreational ORV tracks in the study area are informal and user-created. Mapped ORV recreation tracks were used to model and map the environmental associations of ORV recreation. The pattern of existing tracks indicated associations between recreation and noteworthy environmental amenities in the study area such as the shores of salt lakes and rock outcrops with high ecological and cultural value. However, one of the most important determinants of ORV track presence was accessibility, especially proximity to a road. Access infrastructure, such as proximity to roads, is often used to proxy demand and use in expert-based spatial assessments of ecosystem services. The results of our empirical model underscore the importance of incorporating patterns of both supply (i.e., desired natural amenities) and demand (i.e., access) into ecosystem service assessments. In addition, when integrated with maps of environmental sensitivity and more detailed information about human use, the predictive map of areas providing potential recreation experiences can be used for comprehensive spatial planning of sustainable ORV recreation. One possibility suggested by our results is that careful planning and management of access routes may be an effective means to achieve sustainable ORV recreation.

Evidence for the Spatial Self-organisation of Litter Patches in a Semi-arid Woodland

Spatial self-organisation of plants and soils is a typical feature of many systems. Different mechanisms have been proposed to explain self-organised patterns, including scale-dependent feedbacks and disturbance recovery mechanisms. In semi-arid systems, there is limited evidence for the spatial self-organisation of leaf litter despite its obvious presence within self-organised vegetation patches. Here we provide field-based evidence for the spatial self-organisation of surface litter. We measured the cover, size distribution and spatial arrangement of perennial vegetation patches and surface litter patches in four vegetation communities in a semiarid woodland, one of which had been cleared of trees 50 years previously. The effects of tree removal were still evident 50 years after clearing, with greater perennial patch cover and greater variability in surface litter arrangement in the cleared community than the uncleared analogue. Across all communities, we detected a high correlation between perennial patch cover and litter cover. We found no evidence to support scale-dependent feedbacks occurring between litter and perennial patches, with little relationship between perennial patch size and the strength of its association with litter. The distribution of litter patch sizes was consistent with a truncated power law relationship, suggesting that disturbance‐recovery mechanisms may play an important role in the spatial self-organisation of litter, particularly through large-scale processes such as wind disturbance.

Synergetic effects of fire, climate, and management history on Prosopis caldenia recruitment in the Argentinean pampas

Semiarid woodlands dominated by caldén (Prosopis caldenia Burkart) thrive at the dry edge of the Argentinean Pampas. While the area of original woodlands shrinks due to deforestation, adjacent areas experience the advance of caldén. The aim of this study was to determine the factors that favoured recruitment of caldén along its natural range and in adjacent grasslands and ecotone woodlands. Eight sampling sites were selected in the original calden's woodlands, in the grassland and in the ecotone. Standard dendrochronological techniques were applied to estimate establishment dates, date fire events and growth releases. Recruitment of caldén was massive and episodic. Two recruitment events were noticed in the woodland area in the 1790s and 1870s, which coincided, respectively, with the first settlement of aborigines and the generalised use of fire. Two periods with contrasted patterns of caldén establishment were distinguished in the 20th century: 1920–1969 with an abundant recruitment that started with land abandonment by foreigner colonizers, and 1970–2010 with almost no regeneration. Tree establishment was linked to fire. Sheep numbers had a positive effect on growth release of caldén. Caldén recruitment should be considered a multi-causal process that integrates the effects of several factors mostly driven by anthropogenic land-use changes.

Natural abundance (δ¹⁵N) indicates shifts in nitrogen relations of woody taxa along a savanna-woodland continental rainfall gradient.

Water and nitrogen (N) interact to influence soil N cycling and plant N acquisition. We studied indices of soil N availability and acquisition by woody plant taxa with distinct nutritional specialisations along a north Australian rainfall gradient from monsoonal savanna (1,600-1,300 mm annual rainfall) to semi-arid woodland (600-250 mm). Aridity resulted in increased 'openness' of N cycling, indicated by increasing δ(15)N(soil) and nitrate:ammonium ratios, as plant communities transitioned from N to water limitation. In this context, we tested the hypothesis that δ(15)N(root) xylem sap provides a more direct measure of plant N acquisition than δ(15)N(foliage). We found highly variable offsets between δ(15)N(foliage) and δ(15)N(root) xylem sap, both between taxa at a single site (1.3-3.4 ‰) and within taxa across sites (0.8-3.4 ‰). As a result, δ(15)N(foliage) overlapped between N-fixing Acacia and non-fixing Eucalyptus/Corymbia and could not be used to reliably identify biological N fixation (BNF). However, Acacia δ(15)N(root) xylem sap indicated a decline in BNF with aridity corroborated by absence of root nodules and increasing xylem sap nitrate concentrations and consistent with shifting resource limitation. Acacia dominance at arid sites may be attributed to flexibility in N acquisition rather than BNF capacity. δ(15)N(root) xylem sap showed no evidence of shifting N acquisition in non-mycorrhizal Hakea/Grevillea and indicated only minor shifts in Eucalyptus/Corymbia consistent with enrichment of δ(15)N(soil) and/or decreasing mycorrhizal colonisation with aridity. We propose that δ(15)N(root) xylem sap is a more direct indicator of N source than δ(15)N(foliage), with calibration required before it could be applied to quantify BNF.

Continental-scale impacts of intra-seasonal rainfall variability on simulated ecosystem responses in Africa

Abstract. Climate change is expected to modify intra-seasonal rainfall variability, arising from shifts in rainfall frequency, intensity and seasonality. These intra-seasonal changes are likely to have important ecological impacts on terrestrial ecosystems. Yet, quantifying these impacts across biomes and large climate gradients is largely missing. This gap hinders our ability to better predict ecosystem services and their responses to climate change, especially for arid and semi-arid ecosystems. Here we use a synthetic weather generator and an independently validated vegetation dynamic model (SEIB-Dynamic Global Vegetation Model, DGVM) to virtually conduct a series of "rainfall manipulation experiments" to study how changes in the intra-seasonal rainfall variability affect continent-scale ecosystem responses across Africa. We generate different rainfall scenarios with fixed total annual rainfall but shifts in (i) frequency vs. intensity, (ii) rainy season length vs. frequency, (iii) intensity vs. rainy season length. These scenarios are fed into SEIB-DGVM to investigate changes in biome distributions and ecosystem productivity. We find a loss of ecosystem productivity with increased rainfall frequency and decreased intensity at very low rainfall regimes (<400 mm year−1) and low frequency (<0.3 event day−1); beyond these very dry regimes, most ecosystems benefit from increased frequency and decreased intensity, except in the wet tropics (>1800 mm year−1) where radiation limitation prevents further productivity gains. This result reconciles seemingly contradictory findings in previous field studies on the impact of rainfall frequency/intensity on ecosystem productivity. We also find that changes in rainy season length can yield more dramatic ecosystem responses compared with similar percentage changes in rainfall frequency or intensity, with the largest impacts in semi-arid woodlands. This study demonstrates that intra-seasonal rainfall characteristics play a significant role in influencing ecosystem function and structure through controls on ecohydrological processes. Our results suggest that shifts in rainfall seasonality have potentially large impacts on terrestrial ecosystems, and these understudied impacts should be explicitly examined in future studies of climate impacts.

Size and connectivity of upslope runoff‐source areas modulate the performance of woody plants in Mediterranean drylands

AbstractFeedbacks between vegetation spatial pattern and resource redistribution from bare areas (sources) to vegetation patches (sinks) are considered critical to the functioning of dryland ecosystems. However, experimental fieldworks testing the underlying assumptions and quantifying the feedbacks involved are very scarce. We hypothesized that the size and surface conditions of the upslope runoff‐source areas control the transfer of resources to the downslope vegetation patch, and thereby vegetation performance. In a restored semiarid woodland in Alicante, SE Spain, we investigated the performance of planted shrubs (Olea europaea and Pistacia lentiscus) in response to the size, upslope length, internal connectivity and soil surface properties of their respective upslope runoff‐source areas (drainage microcatchments). Growth of O. europaea seedlings increased with drainage microcatchments size, whilst their water–stress level decreased with the upslope hillslope length. Lower plant density and higher bare‐soil connectivity within the respective microcatchments improved the performance of O. europaea seedlings. Seedling survival was much lower for P. lentiscus than for O. europaea, and growth and water–stress of alive P. lentiscus seedlings showed no significant relationships with any of the microcatchment properties assessed. Survival of P. lentiscus seedlings increased with hillslope length upslope the seedling location. Overall, results point to the interplay between the size and connectivity of the bare‐soil upslope interpatch and the relative location on the hillslope as the most relevant control factors for seedling performance. Observed linkages between source–sink dynamics and plant performance provide valuable information for improving the design of conservation and restoration actions in semiarid lands. Copyright © 2014 John Wiley & Sons, Ltd.

Parameter optimization of image classification techniques to delineate crowns of coppice trees on UltraCam-D aerial imagery in woodlands

Estimating the optimal parameters of some classification techniques becomes their negative aspect as it affects their performance for a given dataset and reduces classification accuracy. It was aimed to optimize the combination of effective parameters of support vector machine (SVM), artificial neural network (ANN), and object-based image analysis (OBIA) classification techniques by the Taguchi method. The optimized techniques were applied to delineate crowns of Persian oak coppice trees on UltraCam-D very high spatial resolution aerial imagery in Zagros semiarid woodlands, Iran. The imagery was classified and the maps were assessed by receiver operating characteristic curve and other performance metrics. The results showed that Taguchi is a robust approach to optimize the combination of effective parameters in these image classification techniques. The area under curve (AUC) showed that the optimized OBIA could well discriminate tree crowns on the imagery (AUC=0.897), while SVM and ANN yielded slightly less AUC performances of 0.819 and 0.850, respectively. The indices of accuracy (0.999) and precision (0.999) and performance metrics of specificity (0.999) and sensitivity (0.999) in the optimized OBIA were higher than with other techniques. The optimization of effective parameters of image classification techniques by the Taguchi method, thus, provided encouraging results to discriminate the crowns of Persian oak coppice trees on UltraCam-D aerial imagery in Zagros semiarid woodlands.

Growth, recruitment and attrition of Eucalyptus tree species in semi-arid temperate woodland

Conservation planning for many fauna relies on an ability to predict length of time lags to production of habitat requirements in restoration plantings or with natural regeneration. One key consideration is the growth rate of dominant trees, as tree age and size are linked to characteristics that provide fauna habitat, such as canopy cover, tree hollows and coarse woody debris. In this study we examined growth rate and mortality of Eucalyptus species for all individuals with diameter at breast height (DBH)⩾15cm on forty one-ha sites in temperate semi-arid woodland in eastern Australia. Over five years (2008–2013) encompassing drought and flood, mean growth was <2.5cm in DBH. Mixed effects models indicated that growth rate differed among species, and decreased with increasing senescence and greater initial foliage projective cover on the site. There was no link between initial tree DBH and growth rate for most species. Growth in DBH was similarly variable in large and small trees. Consequently increases in cross-sectional area, and hence biomass accumulation, are likely to be faster in larger trees. Growth of E. microcarpa, E. camaldulensis, E. blakelyi and E. conica did not significantly differ but was faster than that of E. populnea and E. melliodora. The random factors site and tree identity (for multi-stemmed trees) explained around 10% and 30% of the overall variability in growth rate respectively. Twelve trees (∼1%) died and 4 live trees were cut down and removed. Five (6.5%) of the 75 standing dead trees present in 2008 collapsed, and a further eight (10.5%) were cut down and removed by people. Forty saplings of four species with DBH<15cm in 2008 grew to DBH⩾15cm by 2013, equating to a recruitment rate of <4%, but this occurred on only nine of the 40 sites. Our study suggests mortality rate is being met by recruitment rate at the regional scale, but recruitment was extremely patchy and may result in site scale extinctions. The growth rates measured indicate that trees planted to create fauna habitat may take centuries to reach sizes that would contain large nesting or roosting hollows for fauna.

Effects of landscape composition and connectivity on the distribution of an endangered parrot in agricultural landscapes

The extent and connectivity of individual habitat types strongly affects the distribution and abundance of organisms. However, little is known of how the level of connectivity and the interactions between different habitat types influences the distribution of species. Here, we used the geographically restricted and endangered regent parrot Polytelis anthopeplus monarchoides as a case study to examine the importance of composition and connectivity between different elements in 39 complex landscape mosaics (each 10 km radius). We compiled a database of 674 regent parrot nesting records, regional vegetation maps and measures of multipath connectivity between core vegetation types under different scenarios of resistance to movement provided by landscape elements. The occurrence of regent parrot nests was strongly affected by landscape composition, being positively related to the extent Eucalyptus camaldulensis riverine forest, but negatively related to the extent of semi-arid woodlands dominated by Eucalyptus largiflorens. Connectivity between E. camaldulensis forest (principal nesting habitat) and mallee (preferred feeding habitat) was a strong predictor of nest locations. Our study shows that the suitability of fragmented agricultural landscapes for supporting species can be greatly affected by connectivity and interactions between preferred and non-preferred habitats. For species that require complementary habitats such as the regent parrot, conservation management activities may be ineffective if they simply focus on a single core habitat type or the impacts of human land uses without regard to the interrelationships among landscape elements. While increasing the amount of primary preferred habitat should remain a cornerstone goal, increasing the extent and improving connectivity with alternative landscape elements also should be priority management objectives.

Divergent responses of fire to recent warming and drying across south‐eastern Australia

The response of fire to climate change may vary across fuel types characteristic of differing vegetation types (i.e. litter vs. grass). Models of fire under climatic change capture these differing potential responses to varying degrees. Across south-eastern Australia, an elevation in the severity of weather conditions conducive to fire has been measured in recent decades. We examined trends in area burned (1975-2009) to determine if a corresponding increase in fire had occurred across the diverse range of ecosystems found in this part of the continent. We predicted that an increase in fire, due to climatic warming and drying, was more likely to have occurred in moist, temperate forests near the coast than in arid and semiarid woodlands of the interior, due to inherent contrasts in the respective dominant fuel types (woody litter vs. herbaceous fuels). Significant warming (i.e. increased temperature and number of hot days) and drying (i.e. negative precipitation anomaly, number of days with low humidity) occurred across most of the 32 Bioregions examined. The results were mostly consistent with predictions, with an increase in area burned in seven of eight forest Bioregions, whereas area burned either declined (two) or did not change significantly (nine) in drier woodland Bioregions. In 12 woodland Bioregions, data were insufficient for analysis of temporal trends in fire. Increases in fire attributable mostly to warming or drying were confined to three Bioregions. In the remainder, such increases were mostly unrelated to warming or drying trends and therefore may be due to other climate effects not explored (e.g. lightning ignitions) or possible anthropogenic influences. Projections of future fire must therefore not only account for responses of different fuel systems to climatic change but also the wider range of ecological and human effects on interactions between fire and vegetation.