How many buffalo does it take to change a savanna? A response to Bowman et al. (2008)

Bowman et al. (Journal of Biogeography, 2008, 35 , 1976–1988) aimed to explain observed increases in woody cover on floodplains and savannas of Kakadu National Park using estimates of buffalo (Bubalus bubalis) density as a causal variable. They found that buffalo were a minor model variable and concluded that buffalo are ‘not a major driver of floodplain and eucalypt dynamics’. However, the authors mislabelled the historical density of buffalo on their site, citing a period as high density instead of low density. Further, their results were not contextualized within the substantial body of scientific and historical evidence of the buffalo’s strong influence on vegetation in Kakadu. The authors instead postulated three unanalysed drivers of observed patterns of change: fire regime, rainfall and atmospheric CO₂. We suggest that further analyses of change in woody vegetation should make use of accurate historical records of grazers as well as available data sets on fire history.     

Do feral buffalo (Bubalus bubalis) explain the increase of woody cover in savannas of Kakadu National Park,Australia?

Aim To study changes in woody vegetation in both floodplains and eucalypt savanna over a 40‐year period using multi‐temporal spatial analysis of variation in density of a large introduced herbivore, the Asian water buffalo (Bubalus bubalis). Feral buffalo built up to high densities in the study area until c. 1985, after which a control programme almost eliminated the animals. From 1990, low densities of managed buffalo were maintained inside an enclosure. We compared trends in woody vegetation when buffalo were high‐density feral, low‐density managed or absent. Location The study area was located in and around a 116‐km² buffalo enclosure inside Kakadu National Park, in monsoonal northern Australia. Methods We analysed sequences of digitized and geo‐rectified aerial photographs, acquired in 1964, 1975, 1984, 1991 and 2004, to chart changes in woody cover on the floodplain and in the savanna. On the floodplain we assessed whether trees were present at these times at 14,568 points, and buffalo density was estimated from the density of animal tracks. In the savanna we estimated woody cover at pre‐selected sites. Generalized linear modelling was used to analyse changes in woody vegetation, using elevation and presence of woody vegetation in neighbouring points on the floodplain, and buffalo regime and initial woody cover in the savanna. Results Changes in animal track density reflected park‐wide historical estimates of buffalo numbers. Tree cover increased in both floodplain and savanna, but this was only weakly related to buffalo density. The best predictor of whether a floodplain cell converted from treeless to woody, or the converse, was the woodiness of neighbouring vegetation. There was slightly less thickening with high buffalo densities. In savanna, low densities of managed buffalo were weakly associated with increases in tree cover relative to either high densities of feral buffalo or no buffalo. Main conclusions Our study indicates that buffalo are not a major driver of floodplain and eucalypt savanna dynamics. Rather, the observed increase in woody cover in both savanna and flood plains concords with regional trends and may be related to increased atmospheric CO₂, increasing rainfall and changing fire regimes during the study period.     

Retreating Melaleuca swamp forests in Kakadu National Park: Evidence of synergistic effects of climate change and past feral buffalo impacts

Melaleuca swamp forests form a fringe around seasonally inundated freshwater flood plains of Kakadu National Park (KNP). Previous studies based on the analysis of aerial photography reported an increase in woody plant cover on these flood plains, apparently associated with changed fire regimes, increased rainfall and possibly increased atmospheric CO₂. In opposition to this woody vegetation encroachment past high densities of feral buffalo in the 1960 to mid 1980s changed the hydrology of the KNP flood plains, allowing increased penetration of saltwater causing extensive death of Melaleuca forests. Climate change has increased sea levels and there is concern that this will threaten the freshwater ecosystems of KNP. We hypothesized that Melaleuca forests that were previously impacted by high densities of feral buffalo have continued to decline because of salinization driven by sea level rise. We examined this hypothesis by overlaying georeferenced aerial photography taken in 1964, 1984 and 2004 in a geographic information environment, and then constructing generalized linear fixed effects and mixed effects models to rank the statistical strength of different drivers of Melaleuca forest contraction. We found that there has been a 5% overall contraction of Melaleuca forests over the last 50 years on our study sites, although the amount of contraction varied both geographically and temporally. The amount of Melaleuca forest contraction was greatest during the 1984–2004 interval, when buffalo densities were low. Contraction was greatest on the Melaleuca forest edges, at low‐lying sites, and where high densities of buffalo were apparent in 1964. These results suggest the enduring legacy effect of past buffalo damage will amplify the effects of sea level rise on the flood plains of KNP.     

Cultural legacies,fire ecology,and environmental change in the Stone Country of Arnhem Land and Kakadu National Park,Australia

We use the fire ecology and biogeographical patterns of Callitris intratropica, a fire‐sensitive conifer, and the Asian water buffalo (Bubalus bubalis), an introduced mega‐herbivore, to examine the hypothesis that the continuation of Aboriginal burning and cultural integration of buffalo contribute to greater savanna heterogeneity and diversity in central Arnhem Land (CAL) than Kakadu National Park (KNP). The ‘Stone Country’ of the Arnhem Plateau, extending from KNP to CAL, is a globally renowned social–ecological system, managed for millennia by Bininj‐Kunwok Aboriginal clans. Regional species declines have been attributed to the cessation of patchy burning by Aborigines. Whereas the KNP Stone Country is a modern wilderness, managed through prescribed burning and buffalo eradication, CAL remains a stronghold for Aboriginal management where buffalo have been culturally integrated. We surveyed the plant community and the presence of buffalo tracks among intact and fire‐damaged C. intratropica groves and the savanna matrix in KNP and CAL. Aerial surveys of C. intratropica grove condition were used to examine the composition of savanna vegetation across the Stone Country. The plant community in intact C. intratropica groves had higher stem counts of shrubs and small trees and higher proportions of fire‐sensitive plant species than degraded groves and the savanna matrix. A higher proportion of intact C. intratropica groves in CAL therefore indicated greater gamma diversity and habitat heterogeneity than the KNP Stone Country. Interactions among buffalo, fire, and C. intratropica suggested that buffalo also contributed to these patterns. Our results suggest linkages between ecological and cultural integrity at broad spatial scales across a complex landscape. Buffalo may provide a tool for mitigating destructive fires; however, their interactions require further study. Sustainability in the Stone Country depends upon adaptive management that rehabilitates the coupling of indigenous culture, disturbance, and natural resources.     

Prevalence of bovine tuberculosis in African buffalo at Kruger National Park

Bovine tuberculosis (BTB) was first detected in Kruger National Park (KNP) in a single African buffalo (Syncerus caffer) in 1990. In 1991/1992, 2,071 African buffalo were examined for BTB as part of a culling program that removed animals from all known herds in KNP. The prevalence of BTB in 1991/1992 was estimated to be 0%, 4.4% (+/-0.6%), and 27.1% (+/-1.4%), in the north, central, and south zones of KNP, respectively. In 1998, a stratified, two-stage cluster sampling method was used to estimate that the prevalence of BTB was 1.5% (+/-2.5%), 16% (+/-5.3%), and 38.2% (+/-6.3%), in the north, central, and south zones, respectively. This represented a significant increase in prevalence (P < or = 0.05) in the south and central zones, but not in the north zone. Continued monitoring of BTB in KNP is important for understanding disease transmission risks, potential population effects, and the efficacy of disease management strategies. The methodology and sample sizes used in 1998 are appropriate for future BTB monitoring in KNP.     

Thresholds of potential concern as benchmarks in the management of African savannahs

In the Kruger National Park (KNP), South Africa, ecosystem managers use a series of monitoring endpoints, known as thresholds of potential concern (TPCs), to define the upper and the lower levels of accepted variation in ecosystems. For woody vegetation, the current TPC suggests that woody cover should not drop by more than 80% of its 'highest ever' value. In this paper, we explore the utility of palaeoecological data in informing TPCs. We use calibrated fossil pollen data to explore variability in vegetation at two sites over the past 5000 years, to provide a long-term record of changes in woody vegetation cover and a context for interpreting more recent vegetation change. The fossil pollen data are calibrated using studies of modern pollen and vegetation from KNP; arboreal pollen percentage was simulated using pollen-landscape modelling software for savannah landscapes of varying woody vegetation cover, and the relationship between vegetation and pollen data was quantified using nonlinear regression. This quadratic equation was then applied to fossil pollen data in order to estimate woody vegetation cover from arboreal pollen percentages. Our results suggest that the TPCs have not been exceeded during the period represented in the pollen record, because estimated woody vegetation cover has remained above 20% of its highest ever value. By comparing the fossil pollen data with TPCs, our study demonstrates how palaeoecological data can be presented in a form that is directly relevant to management objectives.     

Current Loads of Coarse Woody Debris on Southeastern Australian Floodplains: Evaluation of Change and Implications for Restoration

We evaluated the status of coarse woody debris (CWD, fallen wood) on floodplains of the southern Murray‐Darling basin of southeastern Australia. The floodplains are dominated floristically by the river red gum Eucalyptus camaldulensis. Aerial survey techniques were used to estimate the amounts of woody debris within 200 m of the channels along 2,442 km of 11 rivers of the system, including the Murray and Darling Rivers and the Darling Anabranch. Aerially based indices were converted into wood volumes by using ground‐truthing at a selection of sites; there was a strong correlation between index values and measured wood volume densities. For thickly forested sites such as Barmah, Gunbower Island, and the Ovens floodplains, the aerial method was not useful, so ground measurements at randomly positioned sites within the forests were used. Volumes were translated into mass by using conversion factors drawn from the literature. We estimated that total tonnage on approximately 221,000 ha of floodplain forests was 4.175 ± 0.579 × 10⁶ tonne. In the larger forested blocks (>7,000 ha), mean wood densities ranged between approximately 12 tonne/ha on the lower Goulburn up to approximately 24 tonne/ha at Barmah State Forest. The area‐weighted mean for the entire area was approximately 19 tonne/ha. A main purpose of the research was to place these figures into an historical perspective to evaluate implications for restoration. A thorough search of historical documentation revealed that there are no extant data upon which to estimate pre‐European settlement levels. We used information from an apparently undisturbed “unmanaged” site in the Millewa forests of southern New South Wales as a basis. Wood density there corresponded to a mean figure of 125 tonne/ha wood‐mass density. By using this figure we estimate that CWD levels on the southern Murray‐Darling basin may be of the order of 15% of pre‐European settlement levels. Full restoration of the 221,000 ha surveyed would require 23.5 ± 0.579 × 10⁶ tonne, which is equivalent to about 600,000 mature (1 m diameter at breast height) river red gum trees or the amount of timber derived from clear felling about 115,000 ha of river red gum forest at current stocking levels. We discuss the implications of this massive deficit and possible short‐ and long‐term solutions.     

Genetic diversity and isolation in African Buffalo (Syncerus caffer)

We studied genetic diversity in 58 buffalo from the Kruger National Park (KNP) and Willem Pretorius Nature Reserve (WPNR). Thirty-three protein-encoding loci were resolved; three were polymorphic. Average heterozygosity (H) values did not differ substantially between adult and sub-adult animals from the KNP (2.65 and 2.89%, respectively), but were lower in animals from the isolated WPNR herd (H = 1.48% and only 3% polymorphic loci compared to 9.1%). Representative levels of genetic diversity exist in the large but disease-carrying herd, whereas the smaller disease-free herds available for translocations appear less polymorphic.     

Cladistic and phylogenetic biogeography: the art and the science of discovery

All methods used in historical biogeographical analysis aim to obtain resolved area cladograms that represent historical relationships among areas in which monophyletic groups of taxa are distributed. When neither widespread nor sympatric taxa are present in the distribution of a monophyletic group, all methods obtain the same resolved area cladogram that conforms to a simple vicariance scenario. In most cases, however, the distribution of monophyletic groups of taxa is not that simple. A priori and a posteriori methods of historical biogeography differ in the way in which they deal with widespread and sympatric taxa. A posteriori methods are empirically superior to a priori methods, as they provide a more parsimonious accounting of the input data, do not eliminate or modify input data, and do not suffer from internal inconsistencies in implementation. When factual errors are corrected, the exemplar presented by M.C. Ebach & C.J. Humphries (Journal of Biogeography, 2002, 29 , 427) purporting to show inconsistencies in implementation by a posteriori methods actually corroborates the opposite. The rationale for preferring a priori methods thus corresponds to ontological rather than to epistemological considerations. We herein identify two different research programmes, cladistic biogeography (associated with a priori methods) and phylogenetic biogeography (associated with a posteriori methods). The aim of cladistic biogeography is to fit all elements of all taxon–area cladograms to a single set of area relationships, maintaining historical singularity of areas. The aim of phylogenetic biogeography is to document, most parsimoniously, the geographical context of speciation events. The recent contribution by M.C. Ebach & C.J. Humphries (Journal of Biogeography, 2002, 29 , 427) makes it clear that cladistic biogeography using a priori methods is an inductivist/verificationist research programme, whereas phylogenetic biogeography is hypothetico‐deductivist/falsificationist. Cladistic biogeography can become hypothetic‐deductive by using a posteriori methods of analysis.     

The biogeography of avian extinctions on oceanic islands revisited

A recent paper by Karels et al ., 'The biogeography of avian extinctions on oceanic islands' ( Journal of Biogeography , 2008, 35 , 1106–1111), uses structural equation modelling to assess the causes of the number of island bird species driven extinct in the historical period. Here, we critically assess the conclusions of the paper and argue that it does not provide the new insights into the causes of extinction in island birds that its authors claim.     

The relevance of fire frequency for the floodplain vegetation of the Okavango Delta, Botswana

The study investigates the relevance of fire frequency for the floodplain vegetation of the Okavango Delta in Botswana, considering species composition, species richness, vegetation structure and tree density. Based on flood and fire frequency data derived from a series of satellite images, active and drying floodplains were separated and study plots were selected with fire frequencies up to ten burns between 1989 and 2003. Both for drying and active floodplains, no typical species assemblage could be associated with fire frequency. On drying floodplains, fire frequency showed no effect on species composition, but rather on vegetation structure. While small woody species showed higher cover values on high fire frequency, large trees showed significantly lower cover values on high fire frequency. For active floodplains, a significant response to fire frequency, both positively and negatively could be determined for specific species. But as almost none of these species appear at low or high frequency only, no differences in species composition could be associated with fire frequency. Rather flood frequency and specific annual flood cycles could be described as the determining factors for the vegetation on active floodplains.     

The Long‐term Impact of Timber Harvesting on the Resource Base of Chimpanzees in Kibale National Park,Uganda

Commercial timber harvesting results in the loss of critical habitat for tropical forest fauna, and large‐bodied frugivores (including chimpanzees and most other apes) may experience particularly detrimental effects. Few quantitative data, however, are available to evaluate the long‐term impact of harvesting on chimpanzees and other apes. In particular, few data are available to compare population demographics and/or forest composition before and after timber harvesting at the same site. Utilizing detailed forestry department records of logging operations conducted in the late 1960s, present‐day botanical surveys, and long‐term data on the feeding ecology of chimpanzees in Kibale National Park (KNP), Uganda, I examined the impact that logging has had on KNP chimpanzee communities of known size and demography. Although some important chimpanzee food resources were harvested in high abundance during commercial logging operations, the overall impact on the most predominant dietary items (those making up roughly 75% of the chimpanzees' diet) and on presumably critical subsistence resources was limited. Furthermore, the low density of chimpanzees inhabiting the logged region of KNP is apparently not attributable to the impact of logging at the site: comparisons of resource densities at this ‘low‐chimpanzee‐density’ site with that of an unlogged and ‘high‐chimpanzee‐density’ KNP site did not differ when logging concessions at the low‐chimpanzee‐density site were excluded from the analysis. This study suggests that low‐intensity logging can be compatible with the conservation of large‐bodied frugivores, provided that dietary data are taken into account in forest management planning.     

土壤种子库对漫溢区受损植被更新的贡献

在塔里木河下游选择两个典型漫溢区,在野外进行了土壤种子库萌发试验,并与河水漫溢区的幼苗库进行比较,以确定土壤种子库对受损植被更新的贡献度.结果表明：两个漫溢区土壤种子库物种数均为12种,生活型组成以多年生草本和灌木为主;种子库密度分别为282.5和173.2粒·m^-2,表层土壤(0～2 cm)种子密度分别占总密度的76.9%和71.0%.土壤种子库对实生幼苗的物种组成和密度具有显著影响,两个漫溢区实生幼苗数量分别有84.7%和99.4%来源于土壤种子库.两个漫溢区土壤种子库与实生幼苗库物种相似性系数分别为0.72和0.63;实生幼苗密度与种子库密度具有很好的正相关性,说明土壤种子库对植被更新具有重要贡献.     

On the International Code of Area Nomenclature (ICAN): a reply to Zaragüeta-Bagils et al.

In 2007 the Systematic and Evolutionary Biogeographical Association (SEBA) wrote and ratified the first draft of the International Code of Area Nomenclature (ICAN), which was posted subsequently on the SEBA website. The ICAN was published, along with an explanatory discussion, by Ebach et al. ( Journal of Biogeography , 35 , 2008, 1153–1157), an article that is the subject of criticism by Zaragüeta-Bagils et al. ( Journal of Biogeography , 36 , 2009, 1617–1618). We welcome discussion of the issues raised by these authors and respond to them briefly here. For many reasons, we reject the proposition that implementation of the ICAN be postponed until it is flawless. The ICAN has already been implemented. Further, it is the nature of nomenclatural codes to be proposed and then revised periodically to suit our applications. Most importantly, standardization of area names in biogeography is long overdue.     

Contingent effects of water balance variation on tree cover density in semiarid woodlands

Aim The local distribution of woody vegetation affects most functional aspects of semiarid landscapes, from soil erosion to nutrient cycling. With growing concern about anthropogenic climate change, it has become critical to understand the ecological determinants of woody plant distribution in semiarid landscapes. However, relatively little work has examined the determinants of local variation in woody cover. Here we examine water balance controls associated with patterns of tree cover density in a topographically complex semiarid woodland. Location Los Pinos Mountains, Sevilleta National Wildlife Refuge LTER, New Mexico, USA. Methods To explore the relationship between local water balance variation and tree cover density, we used a combination of high‐resolution (1 × 1 m), remotely sensed imagery and quantitative estimates of water balance variation in space and time. Regression tree analysis (RTA) was used to identify the environmental parameters that best predict variation in tree cover density. Results Using six predictor variables, the RTA explains 39% of the deviance in tree cover density over the landscape. The relationship between water balance conditions and tree cover density is highly contingent; that is, similar tree cover densities occur under very different combinations of water balance parameters. Thus, the effect of one environmental parameter on tree cover density depends on the values of other parameters. After tree cover density is adjusted for water balance conditions, residual variation is related to tree cover density in the neighbourhood of a particular location. Conclusion In semiarid landscapes, vegetation structure is largely controlled by water supply and demand. Results presented here indicate that localized feedbacks and site‐specific historical processes are critical for understanding the responses of semiarid vegetation to climate change.     

Spatial and temporal variations in densities of small fishes across different temporary floodplain types of the lower Okavango Delta,Botswana

Small-sized and juvenile fishes as well as physicochemical water parameters in various primary, secondary and rarely flooded temporary floodplains of the Okavango Delta were assessed during the different hydrological phases of the 2009–2010 flooding season. Small fishes were sampled in the marginal zone of the floodplains using a throw-trap net and a suite of physicochemical properties were measured. Both physicochemical water quality parameters and densities of small fishes showed spatiotemporal variations across the temporary floodplain types. Turbidity, dissolved oxygen, conductivity, woody debris and chlorophyll a were all highest in rarely flooded floodplains compared to both primary and secondary floodplains (ANOVA, p < 0.05). Fish from 38 fish taxa belonging to 11 families were identified and classified during the study. The fish families Cichlidae (dominated by tilapias), Poeciliidae (Aplocheilichthys spp.) and Cyprinidae (Barbus spp.), were the most abundant across the study floodplains. The poeciliids were most abundant in frequently flooded primary and secondary floodplains, whereas juvenile cichlids dominated in rarely flooded floodplains. During high floods the rarely flooded portions of the delta function as important nursery habitats for juvenile cichlids, implying that a significant reduction in flooding may have negative effects on the delta's tilapia stocks due to reduced recruitment success.     

Redundancy or progress? A response to Driscoll et al. (2019)

Driscoll et al. (Journal of Biogeography, 2019, 46, 2850–2859) provide a critique of ‘Countryside Biogeography’, but also include ‘Conservation Biogeography’ and ‘Agriculture Biogeography’ in their criticisms. Their main thesis is that these new sub-disciplines offer a ‘conceptual wrapper’ rather than distinctive frameworks and that the consequent redundancy of terms has the potential to sow confusion among biogeographers and slow progress. Here we argue that, far from sowing confusion Conservation Biogeography, for example, has provided important focal points for emerging scientific discourse, promoting new research, spawning undergraduate and graduate courses, and facilitating the formation of new scientific collaborations. The success or failure of a new sub-discipline depends on its utility. If new framings sow confusion, introduce redundancy and provide no new insights they will not be widely adopted and cited. The development of new sub-disciplines is a strong indicator of a vibrant, socially relevant and intellectually adventurous research area.     

Challenges and opportunities in synthesizing historical geospatial data using statistical models

We classified land cover types from 1940s historical aerial imagery using Object Based Image Analysis (OBIA) and compared these maps with data on recent cover. Few studies have used these kinds of maps to model drivers of cover change, partly due to two statistical challenges: 1) appropriately accounting for spatial autocorrelation and 2) appropriately modeling percent cover which is bounded between 0 and 100 and not normally distributed. We studied the change in woody cover at four sites in California's North Coast using historical (1948) and recent (2009) high spatial resolution imagery. We classified the imagery using eCognition Developer and aggregated the resulting maps to the scale of a Digital Elevation Model (DEM) in order to understand topographic drivers of woody cover change. We used Generalized Additive Models (GAMs) with a quasi-binomial probability distribution to account for spatial autocorrelation and the boundedness of the percent woody cover variable. We explored the relative influences on current percent woody cover of topographic variables (grouped using principal component analysis) reflecting water retention capacity, exposure, and within-site context, as well as historical percent woody cover and geographical coordinates. We estimated these models for pixel sizes of 20, 30, 40, 50, 60, 70, 80, 90, and 100 m, reflecting both tree neighborhood scales and stand scales. We found that historical woody cover had a consistent positive effect on current woody cover, and that the spatial autoregressive term in the model was significant even after controlling for historical cover. Specific topographic variables emerged as important for different sites at different scales, but no overall pattern emerged across sites or scales for any of the topographic variables we tested. This GAM framework for modeling historical data is flexible and could be used with more variables, more flexible relationships with predictor variables, and larger scales. Modeling drivers of woody cover change from historical ecology data sources can be a valuable way to plan restoration and enhance ecological insight into landscape change.     

Fire as a dimension of historical ecology: a response to Bowman et al. (2011)

Bowman et al. (Journal of Biogeography, 2011, 38 , 2223–2236) attempt a synthesis of the current status of study into human use of fire as an ecosystem management tool and provide a framework for guiding research on the human dimensions of global fire. While we applaud this ambitious effort, we believe the proposed ‘pyric phase and transition’ model to be too deterministic and simplistic to account for the complexity and diversity in human–fire relationships. After reviewing theoretical problems with the proposed framework, we question policy implications of their conclusions concerning tropical forest systems. We suggest that a theoretically informed perspective should build on an historical fire ecology framework for investigating social and ecological aspects of human–environment interactions.