Influence of Colophospermum mopane canopy cover on litter decomposition and nutrient dynamics in a semi‐arid African savannah

The objective of this study was to investigate the influence of mopane canopy cover on litter decomposition in a semi‐arid African savannah. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10‐ha pocket of open mopane woodland. Litterbags were placed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area. Decomposition was fastest in the intercanopy area exposed to solar radiation (k = 0.35 year^?1), intermediate beneath small trees (k = 0.28 year^?1) and slowest beneath large trees (k = 0.23 year^?1). Soil temperatures beneath small and large trees were 3–5 and 6–9°C lower than in the intercanopy area, respectively. Bacterial and fungal counts were significantly higher (P < 0.05) beneath large than small trees and in the intercanopy area. The amount of N and P released did not vary significantly among sampling sites. Soil moisture in the dry season was similar among sampling sites but rainy‐season soil moisture was significantly greater (P < 0.05) beneath large than small trees and in the intecanopy area. Mopane canopy cover retarded litter decomposition suggesting that photodegradation could be an important factor controlling carbon turnover in semi‐arid African savannahs.     

Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation of Colophospermum mopane savanna by Imbrasia belina larvae

Invertebrate herbivore outbreaks have important impacts on system biogeochemical cycling, but these effects have been poorly documented in African savanna ecosystems. In semi‐arid African savannas, outbreaks of the lepidopteran Imbrasia belina (mopane worm) affect discrete patches of the dominant Colophospermum mopane trees; larvae may completely defoliate trees for up to six weeks during each of the early and late growing seasons. We studied the impact of mopane worm outbreaks on the availability of nitrogen (N), phosphorus (P), and potassium (K) within mopane savanna by quantifying major nutrient pools in defoliated and non‐defoliated savanna patches, including leaves, leaf litter, worm frass, and the soil beneath trees. Within an outbreak area, approximately 44 percent of trees were infested, supporting ~29,000 worms/ha, leading to ~640 kg/ha dry weight frass deposition at 1.4 g of frass/day‐individual (fourth or fifth instar), compared with an average 1645 kg/ha dry weight of leaf on trees most of which should be deposited by litterfall at the end of the growing season. Frass had twofold higher P, 10 percent higher K, but equivalent N content than litter. Taking frass and litter deposition together, the N, P, and K contents added due to the outbreak event at our study site were 0.88, 5.8, and 2.8 times those measured in non‐outbreak patches, a pattern which was reflected in the nutrient contents of soil surfaces beneath defoliated trees. Invertebrate herbivory appears to be an important driver for mopane savanna but has been largely neglected.     

The influence of mistletoes on the litter-layer arthropod abundance and diversity in a semi-arid savanna,Southwest Zimbabwe

Aims

The below-canopy soil moisture content and litter-layer arthropod abundance and diversity of Acacia karroo trees parasitized by each of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) and uninfected A. karroo trees were investigated in semi-arid savanna, southwest Zimbabwe.

Results

The soils below the canopies of mistletoe-infected trees were significantly low in moisture content compared to those beneath uninfected A. karroo trees. Nevertheless, arthropod species diversity was greater by up to 34 % below the canopies of mistletoe-infected trees than beneath uninfected A. karroo trees, with greater abundances beneath trees infected by E. ngamicum and P. kalachariensis. In addition, the majority of the arthropod species associated with mistletoe-infected trees had litter as their dominant foraging substrate.

Conclusions

Our findings show that mistletoes increase the abundance and diversity of litter-dwelling and –foraging arthropods due to increase in the quality and quantity of litterfall beneath mistletoe-infected trees. By altering the below-canopy arthropod communities and soil moisture content, mistletoes have potential to modify ecosystem processes such as decomposition, soil process rates, and nutrient cycling. Therefore, we suggest that the resulting increase in resource heterogeneity plays an important role in determining the structure and functioning of semi-arid savanna ecosystems.     

Structure and biomass along an Acacia zanzibarica woodland–savanna gradient in a former ranching area in coastal Tanzania

Questions: What factors influence the density, size and growth form of trees in secondary Acacia zanzibarica woodlands on a former humid savanna rangeland? How does tree density relate to variation in tree foliage and spines, and woody and grass biomass? Location: Tropical coastal Tanzania (former Mkwaja Ranch, now in Saadani National Park). Methods: We surveyed 97 circular plots (4‐m radius) representing a gradient from open savanna to dense woodland. Within each plot, we measured all trees and estimated the biomass of spines. Foliage biomass of tree and grass layers was estimated on three occasions, twice during the wet season and once in the dry season. Soil samples were taken from each plot and analysed for texture and nutrient content. Interrelationships among various variables were investigated using linear multiple regression and mixed effects models. Results: Tree densities were highest on more nutrient‐rich, heavy soils. Spinescence was highest on trees in open savanna. Biomass of tree foliage in the wet season was best explained by numbers of ant nests and tree live‐wood ratio. Foliage biomass in the dry season was less than half that in the wet season and best predicted by grass biomass. Variables related to biomass of the grass layer were strongly influenced by fire; living grass biomass also decreased with increasing tree density. Conclusions: A. zanzibarica is a tree with a high water demand, and the association with heavy soils is probably due to greater availability of water on these sites. Establishment of A. zanzibarica woodlands significantly reduced grazing resources at Mkwaja Ranch. Under post‐ranching conditions, however, fires and soil conditions predominate. The woodlands may, therefore, represent a transient state of woody density in a still resilient humid savanna.     

Seasonal leaf dynamics across a tree density gradient in a Brazilian savanna

Interactions between trees and grasses that influence leaf area index (LAI) have important consequences for savanna ecosystem processes through their controls on water, carbon, and energy fluxes as well as fire regimes. We measured LAI, of the groundlayer (herbaceous and woody plants <1-m tall) and shrub and tree layer (woody plants >1-m tall), in the Brazilian cerrado over a range of tree densities from open shrub savanna to closed woodland through the annual cycle. During the dry season, soil water potential was strongly and positively correlated with grass LAI, and less strongly with tree and shrub LAI. By the end of the dry season, LAI of grasses, groundlayer dicots and trees declined to 28, 60, and 68% of mean wet-season values, respectively. We compared the data to remotely sensed vegetation indices, finding that field measurements were more strongly correlated to the enhanced vegetation index (EVI, r ²=0.71) than to the normalized difference vegetation index (NDVI, r ²=0.49). Although the latter has been more widely used in quantifying leaf dynamics of tropical savannas, EVI appears better suited for this purpose. Our ground-based measurements demonstrate that groundlayer LAI declines with increasing tree density across sites, with savanna grasses being excluded at a tree LAI of approximately 3.3. LAI averaged 4.2 in nearby gallery (riparian) forest, so savanna grasses were absent, thereby greatly reducing fire risk and permitting survival of fire-sensitive forest tree species. Although edaphic conditions may partly explain the larger tree LAI of forests, relative to savanna, biological differences between savanna and forest tree species play an important role. Overall, forest tree species had 48% greater LAI than congeneric savanna trees under similar growing conditions. Savanna and forest species play distinct roles in the structure and dynamics of savanna–forest boundaries, contributing to the differences in fire regimes, microclimate, and nutrient cycling between savanna and forest ecosystems.     

Feeding ecology of Lilian’s Lovebird Agapornis lilianae in Liwonde National Park,Malawi

Lilian's Lovebird Agapornis lilianae is a small, near-threatened parrot resident in mopane Colophospermum mopane woodlands. We investigated its diet and foraging behaviour in Liwonde National Park, Malawi. We expected that Lilian's Lovebirds would show little specialisation for a particular food source but generally feed on available seeds, fruits, flowers and other items as observed in other lovebirds. Lilian's Lovebirds fed on 30 different plant species. Lilian's Lovebirds were observed feeding in six habitat types in Liwonde National Park and adjacent areas during the wet season, and four in the dry season. In the wet season lovebirds (23% of observations) foraged in grassy wetland (dambo) areas the most, whilst in the dry season they foraged in grasslands with tree cover (18%) the most. In mopane woodland, foraging flock sizes differed significantly between the wet (mean = 19.8 ± 1.0 lovebirds) and dry season (mean = 33.6 ± 2.3 lovebirds). Grass seeds were lovebirds’ main food source from December to June. The nutritional analysis of preferred foods showed that grass seeds have a relatively high protein and energy content. Grass seed availability is reduced with savanna burning and so early season burning (before May–June) in areas in and outside the park is not recommended.     

Experimental manipulation of termites (Isoptera,Macrotermitinae) foraging patterns in a Sahelo-Sudanese savanna: effect of litter quality

Summary The foraging pattern of four sympatric fungus-growing termite species was followed for five months of the dry season in a semi-arid savanna (Senegal). Experimental plots were established with and without termites (exclusion with insecticide) and amended with different litter quality: Acacia leaves, millet canes, ground millet (<500 µm), Combretum wood and cattle manure. Results showed different foraging patterns between the fungus-growing species. Odontotermes nilensis, for example, rapidly developed its foraging activity on the litter. In contrast, Macrotermes subhyalinus delayed its foraging activity but, extensively collected the food after its discovery. Differences in food preference were evident between the termite species: Odonto-termes nilensis foraged preferentially on millet, canes and Acacia leaves, Macrotermes subhyalinus preferred cane and ground millet. Ancistrotermes guineensis selected the millet, and Microtermes sp. was mostly recorded foraging on pieces of dead wood. Relationships between different foraging parameters were established to assess the relative intensity of this activity over the dry season. The comparison between untreated plots and plots treated with Fipronil® (Aventis) clearly demonstrated that the exclusion of termites from part of the savanna is possible and that this possibility can be used to study their role on the soil and organic matter cycle in situ.     

Effects of fire regimen on two species of epiphytic orchids in tropical savannas of the Northern Territory

The effect of four fire regimens (early dry season annual, late dry season annual, early dry season biennial, unburnt) on the numbers of epiphytic orchids in a savanna community in Kakadu National Park was investigated. These fire regimens had been maintained on I ha plots for 16 years. Two species of epiphytic orchid were present — Cymbidium canaliculatum and Dendrobium affine. The numbers of Cymbidium plants were insufficient to enable statistical analysis, but plants were present in the unburnt, early annual and early biennial fire treatments. Dendrobium occurred in substantial numbers irrespective of fire treatment, but the extent of colonization of all available host trees was greater in the unburnt than the burnt treatments. The lower numbers of Dendrobium plants in burnt treatments was due to a lower proportion of potential host trees being colonized and a lower number of orchids on each colonized tree. The proportion of small trees colonized was markedly lower in burnt treatments. Frequent fires late in the dry season may prevent recruitment of the main host species. Eucalyptus tectifica. The survival of orchids despite frequent fires depended on the availability of relatively protected sites for colonization and the ability of the orchids to withstand some fire damage.     

Nutrition ofPinus caribaea in its native savanna habitat

Summary Fertility levels in soils beneathPinus caribaea trees were examined in the Mountain Pine Ridge savannas, Belize, where fire control has precipitated the development of pine woodland. Slight surface soil enrichment was recorded beneath pine canopies, but to levels well below those found beneath associated hardwoods. Estimates of total nutrient pools beneath trees showed modest cation accumulation beneath a 73 year old tree but some defecits in Ca and Mg beneath a 24 year old tree. A tap root cutting experiment on trees of the same species revealed no significant declines in foliar nutrient levels after 19 months. It is concluded that no pronounced long-term deterioration in soil fertility levels is developing beneath stands ofP. caribaea in the savanna, although some temporary nutrient declines may exist beneath young pine stands. Atmospheric inputs are the most likely source of nutrient accretion and it is suggested that the establishment of hardwood associates with pine may enhance the rates of nutrient capture from this source.     

Soil temperature and depth of legume germination during early and late dry season fires in a tropical eucalypt savanna of north‐eastern Australia

Abstract Temperatures that significantly increase seed germination of some tropical legumes (i.e. 80–100°C) were documented in the topsoil during the passage of early (May) and late (October) dry season fires in a tropical eucalypt savanna of north‐eastern Australia. Elevated temperatures penetrated at least 30 mm into the soil during the higher‐intensity, late dry season fires, but were only detected at 10 mm during the early dry season fires. The depth from which germination of two native legume forbs Galactia tenuiflora and Indigofera hirsuta occurred was positively related to the temperature elevation in the topsoil and was greater after late compared with early dry season fires. A broader range in germination depth, resulting in higher seedling densities, was recorded for I hirsuta after late dry season fires. These results suggest that seedling emergence of native leguminous forbs is likely to occur at a greater density after late rather than early dry season fires in tropical eucalypt savannas of north‐eastern Australia. Therefore, the season of burning, as a result of its relationship to fire intensity, can influence species composition through its effect on seed germination.     

Attributes of trees used by nesting and foraging woodpeckers (Aves: Picidae) in an area with old pollarded Oaks (Quercus spp.) in the Taurus Mountains,Turkey

We used three woodpecker species as umbrella species for old deciduous forests, and analysed their preferences in an area with old pollarded oaks in the Taurus Mountains, Turkey. Using plot inventories, we physically characterised trees utilised for nesting and foraging amongst woodpeckers in general and the Middle Spotted Woodpecker (Leiopicus medius) in particular. Trees more frequently visited by foraging woodpeckers differed from randomly chosen trees by being taller, having a larger circumference, greater bark furrow depth and shorter distance to neighbouring trees. Nesting trees were taller, had a higher proportion of dead wood but a lower surface area of natural cavities. Our results suggest that the woodpeckers in the study area rely upon woodlands containing mature trees, thus have the potential to function as suitable umbrella species’ to highlight the conservation value of oak forest habitats in southern Turkey.     

Termite mounds differ in their importance for herbivores across savanna types,seasons and spatial scales

Herbivores do not forage uniformly across landscapes, but select for patches of higher nutrition and lower predation risk. Macrotermes mounds contain higher concentrations of soil nutrients and support grasses of higher nutritional value than the surrounding savanna matrix, attracting mammalian grazers that preferentially forage on termite mound vegetation. However, little is known about the spatial extent of such termite influence on grazing patterns and how it might differ in time and space. We measured grazing intensity in three African savanna types differing in rainfall and foliar nutrients and predicted that the functional importance of mounds for grazing herbivores would increase as the difference in foliar nutrient levels between mound and savanna matrix grasses increases and the mounds become more attractive. We expected this to occur in nutrient‐poor areas and during the dry season when savanna matrix grass nutrient levels are lower. Tuft use and grass N and P content were measured along transects away from termite mounds, enabling calculation of the spatial extent of termite influence on mammalian grazing. Using termite mound densities estimated from airborne light detection and ranging (LiDAR), we further upscaled field‐based results to determine the percentage of the landscape influenced by termite activity. Grasses in close proximity to termite mounds were preferentially grazed at all sites and in both seasons, but the strength of mound influence varied between savanna types and seasons. In the wet season, mounds had a relatively larger effect on grazers at the landscape scale in the nutrient‐poor, wetter savanna, whereas in the dry season the pattern was reversed with more of the landscape influenced at the nutrient‐rich, driest site. Our results reveal that termite mounds enhance the value of savanna landscapes for herbivores, but that their functional importance varies across savanna types and seasons.     

Seasonal variation in leaf traits between congeneric savanna and forest trees in Central Brazil: implications for forest expansion into savanna

The ecology of forest and savanna trees species will largely determine the structure and dynamics of the forest–savanna boundaries, but little is known about the constraints to leaf trait variation imposed by selective forces and evolutionary history during the process of savanna invasion by forest species. We compared seasonal patterns in leaf traits related to leaf structure, carbon assimilation, water, and nutrient relations in 10 congeneric species pairs, each containing one savanna species and one forest species. All individuals were growing in dystrophic oxisols in a fire-protected savanna of Central Brazil. We tested the hypothesis that forest species would be more constrained by seasonal drought and nutrient-poor soils than their savanna congeners. We also hypothesized that habitat, rather than phylogeny, would explain more of the interspecific variance in leaf traits of the studied species. We found that throughout the year forest trees had higher specific leaf area (SLA) but lower integrated water use efficiency than savanna trees. Forest and savanna species maintained similar values of predawn and midday leaf water potential along the year. Lower values were measured in the dry season. However, this was achieved by a stronger regulation of stomatal conductance and of CO₂ assimilation on an area basis (A _area) in forest trees, particularly toward the end of the dry season. Relative to savanna trees, forest trees maintained similar (P, K, Ca, and Mg) or slightly higher (N) leaf nutrient concentrations. For the majority of traits, more variance was explained by phylogeny, than by habitat of origin, with the exception of SLA, leaf N concentration, and A _area, which were apparently subjected to different selective pressures in the savanna and forest environments. In conclusion, water shortage during extended droughts would be more limiting for forest trees than nutrient-poor soils.     

Late glacial and Holocene vegetation,climate and fire history inferred from Lagoa Nova in the southeastern Brazilian lowland

The pollen and charcoal record of a 1,500-cm-long lake sediment core from Lagoa Nova allows a reconstruction of vegetation, climate and fire history in the Atlantic lowland of southeastern Brazil. Today the potential vegetation of the study region would be dense and tall semi-deciduous forest, related to a dry season of 4 months and 1,250 mm precipitation per year. The lowermost core section of Lagoa Nova is probably of late Glacial age and contains only few, poorly preserved pollen grains, indicating dry environmental conditions. Pollen preservation was good above 1,005-cm core depth. Extrapolating from four radiocarbon dates, this interval represents about the last 10,000 years. During the early Holocene (until about 8,500 b.p.), the landscape was dominated by savanna of the campo cerrado type (open shrub woodland), with frequent trees of Curatella americana and small areas of gallery forests along the drainage system. Savanna fires, probably natural, were frequent at that time. The palaeovegetation pattern is consistent with a long dry season of about 6 months and annual precipitation lower than today. Then, up to about 7,560 b.p., gallery forests expanded in the valleys, reflecting a shorter dry season of about 5 months and somewhat higher annual rainfall. Fire was less frequent during this wetter period. Between about 7,560 and 6,060 b.p., savanna expanded and gallery forests retreated, indicating a return to drier climatic conditions of probably between 5 and 6 months dry season and lower precipitation. Fire was again frequent, but not as frequent as during the early Holocene. During the mid to late Holocene period between about 6,060 and 2,180 b.p., the valleys were covered by semi-deciduous forest, but on the hills cerrado vegetation continued to grow. The dry season was probably around 5 months and rainfall was higher than in the preceding period. During the following period between about 2,810 and 600 b.p., the open cerrado on the hills changed to closed cerrado, reflecting wetter conditions with a shorter dry season than in the previous period. It was only after about 600 b.p. that dense semi-deciduous forests expanded throughout the study region, indicating the start of modern, wet climatic conditions with an annual dry season of about 4 months. Fire was nearly absent during this period. The reconstructed palaeoenvironment from the Lagoa Nova record is similar to that of Lago do Pires, indicating that changes in past vegetation, climate and fire frequency are regionally consistent in southeastern Brazil.     

Seasonal selection of soil types and grass swards by roan antelope in a South African savanna

Roan antelope are distributed mainly in regions characterized by infertile soils, offering food of low quality. We hypothesized that roan may select localities with higher soil nutrient levels and/or grass swards with more favourable properties in terms of food abundance or quality than generally available in those regions. Roan antelope were observed in a savanna region in South Africa where soils of widely varying nutrient status occurred. Roan favoured open grassland over wooded savanna areas. During the wet season, roan preferred sites with felsite‐derived soil of intermediate soil nutrient status. Grasslands growing on nutrient enriched alluvial soils were preferred outside of the early wet season, although most of the favourable sward characteristics were present in other landscape units. Food quantity, rather than quality appeared to attract roan to foraging sites in the late wet and early dry seasons. Food quality appeared more important in the early wet and late dry seasons. The higher degree of clustering of leafy material within foraging swards seemed to be an additional discriminating factor. The factors governing the selection of foraging sites by roan did not seem notably different from those influencing other species of grazing ruminant, but roan nevertheless seemed tolerant of stemmy grasslands growing on nutrient richer substrates.     

Litterfall and nutrient return in a semi-arid southern African savanna woodland dominated by <Emphasis Type="Italic">Colophospermum mopane</Emphasis>

The objective of this study was to investigate litter production, litter standing crop and nutrient return to soil in a semi-arid southern African savanna in Bulawayo, Zimbabwe. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10-ha pocket of Colophospermum mopane-dominated open woodland protected from grazing and fire. Litter traps were installed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area, representing 27, 3 and 62% of the woodland area, respectively. Mean annual total litterfall over 2 years of observations was 197, 83 and 35 g m⁻² yr⁻¹ beneath large and small trees as well as in the intercanopy area, respectively. Leaf proportions of total litterfall beneath large and small trees and in the intercanopy area were 68.6, 73.0 and 75.3%, respectively. Litterfall followed a uni-modal distribution pattern and was much higher during the period of May–September (dry period) compared to other months. The total potential annual element inputs via litterfall beneath large trees were 2 and 5 times greater than beneath small trees and in the intercanopy area, respectively. Total litter standing crop was 405, 177 and 67 g m⁻² beneath large and small trees and in the intercanopy area, respectively. Concentrations of N, P and K in litterfall and surface soil were closely correlated with each other. At all sampling sites, element accession to soil through litterfall followed the decreasing sequence C > Ca > N > Mg > K > P. These results suggest that litterfall is a major process responsible for soil organic matter and nutrient enrichment beneath isolated trees in semi-arid savannas.     

Removal of palm fruits and ecosystem engineering in palm stands by white-lipped peccaries (Tayassu pecari) and other frugivores in an isolated Atlantic Forest fragment

Long-term studies in a 2,178 ha fragment of semideciduous Atlantic Forest demonstrated important interactions between white-lipped peccaries (Tayassu pecari) and the common palms, Syagrus romanzoffiana and Euterpe edulis. We conducted fruit removal and medium-to-large-sized mammalian exclusion experiments to: (1) quantify seasonal fruit consumption from high-density patches beneath parent trees by T. pecari and other consumers, and (2) measure impacts of T. pecari rooting and foraging activities on seedling dynamics in E. edulis stands. A diverse array of fauna consumed S. romanzoffiana fruits. During the dry season, when S. romanzoffiana palms provided 68% of fruit dry weight in the fragment, T. pecari consumed significantly greater amounts than other consumers, and along with Pecari tajacu and Tapirus terrestris, were potential seed dispersers. The rodents, Sciurus ingrami and Agouti paca, consumed most S. romanzoffiana fruits in the wet season, acting as both seed dispersers and predators. More than 95% of E. edulis fruit removal was due to seed predation by T. pecari. Intense removal during the dry season was closely linked with previously documented range shifts and habitat preferences by T. pecari. Exclusion plot experiments in E. edulis (palmito) stands showed that the number and proportion of nonpalmito (not E. edulis) seedlings increased dramatically in the absence of T. pecari rooting and foraging activities that disturbed soil and thinned seedlings. We discuss the importance of these ecosystem engineering activities and palm-peccary trophic interactions for long-term maintenance of E. edulis stands and T. pecari populations, as well as water balance, in the forest fragment.     

Roost selection by the north Queensland long-eared bat Nyctophilus bifax in littoral rainforest in the Iluka World Heritage Area,New South Wales

Abstract The aim of this study was to describe the roosts of Nyctophilus bifax in littoral rainforest in Iluka Nature Reserve on the north coast of New South Wales. Radio-telemetry was used to track 17 bats in November 1988 (lactation season) and 11 in May 1989 (mating season) to 87 roosts in 49 trees within the littoral rainforest. The bats frequently changed roosts, which were clustered within a small area. During November, lactating females moved twins between diurnal roosts and some carried twins while foraging. Twins represented a load of up to 95% of their mother's bodyweight. Bats roosted communally in foliage and tree hollows, beneath peeling bark, among epiphytes, and between strangler figs and host trees. Hollows were used more frequently when bats were lactating, while the use of foliage roosts was greater during the mating season. Roosts were concentrated in four tree species, although a wide range of other tree species was used. Roost trees used in November were taller (17m) than those used in May (8. 2 m), and reflect selection of Syzygium leuhmannii and Acmena hemilampra, both trees of the forest interior. The converse applied for selection of Cupaniopsis anacardioides, a small tree of the littoral zone, in May. These results identify the need for conserving a diversity of roosts for this species of bat.     

Metabolic rates,food consumption and thermoregulation in seasonal acclimatization of the Cape porcupine Hystrix africaeaustralis

Summary Metabolic rates by means of oxygen consumption (VO₂) at various ambient temperatures (T _a) and food consumption as well as water intake and thermoregulation were compared between individuals of the Cape porcupine Hystrix africaeaustralis acclimated to T _a=32°C with a photoperiod of 16L:8D summer-acclimated and T _a=10°C; 8L:16D winter-acclimated. The lower critical temperature as well as overall minimal thermal conductance were lower for the winter-acclimated porcupines when compared to summer-acclimated ones, while VO₂ at the thermoneutral-zone was significantly (P<0.001) higher in the winter-acclimated porcupines. Dry matter intake, apparent digestible dry matter intake, gross digestible energy intake, as well as water intake, were significantly higher in the winter-acclimated porcupines. Yet, while dry matter intake increased 4 times in the winter-acclimated porcupines, apparent digestible dry matter increased only at a rate of 2.9 times. This difference is better reflected in terms of digestibility efficiency which in the winter-acclimated porcupines is only at a rate of 67.5% while in the summer-acclimated porcupines it is at a rate of 90%. From the results of this study, it is possible to assume that heat production in the winter-acclimated porcupines is partly increased by food intake. Increased heat production on the one hand, and a decrease in overall minimal thermal conductance on the other, seem to be important mechanisms in winter acclimatization of the Cape porcupine.     

Effect of fire regime on plant abundance in a tropical eucalypt savanna of north‐eastern Australia

Abstract Changes in plant abundance within a eucalypt savanna of north‐eastern Australia were studied using a manipulative fire experiment. Three fire regimes were compared between 1997 and 2001: (i) control, savanna burnt in the mid‐dry season (July) 1997 only; (ii) early burnt, savanna burnt in the mid‐dry season 1997 and early dry season (May) 1999; and (iii) late burnt, savanna burnt in the mid‐dry season 1997 and late dry season (October) 1999. Five annual surveys of permanent plots detected stability in the abundance of most species, irrespective of fire regime. However, a significant increase in the abundance of several subshrubs, ephemeral and twining perennial forbs, and grasses occurred in the first year after fire, particularly after late dry season fires. The abundance of these species declined toward prefire levels in the second year after fire. The dominant grass Heteropogon triticeus significantly declined in abundance with fire intervals of 4 years. The density of trees (>2 m tall) significantly increased in the absence of fire for 4 years, because of the growth of saplings; and the basal area of the dominant tree Corymbia clarksoniana significantly increased over the 5‐year study, irrespective of fire regime. Conservation management of these savannas will need to balance the role of regular fires in maintaining the diversity of herbaceous species with the requirement of fire intervals of at least 4‐years for allowing the growth of saplings >2 m in height. Whereas late dry season fires may cause some tree mortality, the use of occasional late fires may help maintain sustainable populations of many grasses and forbs.