RESUMEN

Native grasslands have been vastly transformed with the expansion of human activities. Applied fire regimes offer conservation-based management an opportunity to enhance remaining grassland biodiversity and secure its persistence into the future. Fire regimes have complex interactions with abiotic and biotic ecosystem components that influence environmental heterogeneity and biodiversity. We examined the pyrodiversity-biodiversity hypothesis, which suggests that more species are supported where pyrodiversity, that is, the level of environmental heterogeneity associated with different fire regimes, is greater. A mesocosm-type field experiment, maintained for 38 yr, was used to determine the response of plant diversity to 1-, 2-, 5- and 12-yr fire-return interval treatments, with early-dormant, middormant and early-growing season burns. Our sampling regime was designed to assess the influence of fire treatments and combinations thereof, over spatial scale, on plant diversity. Pyrodiversity was maximized where fire regime diversity, simulated by varying the size of patches with different fire treatments, was greatest. Species richness was predicted to be reduced at short and long extremes of fire-return interval, as suggested by the intermediate-disturbance hypothesis. The influence of fire treatments on alpha and beta diversity, and plant functional groups, were tested using multivariate and Bayesian models. Multilevel models of plant height and growth form, with fire-return interval, reflected the strong indirect influence of fire-return interval on sward structure and the plant environment. The pyrodiversity-biodiversity and intermediate-disturbance hypotheses were only partially supported and depended on the plant group and spatial scale of assessment. Although both frequent and infrequent burns made important contributions to overall species richness, richness peaked where 20-40% of the area was protected from frequent fires. The larger contribution of frequent burning to diversity was due to an interaction with scale and forb turnover over the trial area. Extremes in fire-return intervals reduced forb richness, supporting the predictions of the intermediate-disturbance hypothesis. Spring burns had a weak negative influence on forb alpha diversity, but only at small scales. For a meaningful contribution of management to plant diversity, traditional fixed biennial burns need to be supplemented with smaller patches burned with longer fire-return intervals, and extremes in fire-return intervals avoided.

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RESUMEN

Loss of biodiversity caused by impact of elephants (Loxodonta africana) on African woodlands may require a management response, but any action should be based on an understanding of why elephants choose to utilise trees destructively. Comprehension of elephant feeding behaviour requires consideration of the relative value of the plant groups they may potentially consume. Profitability of available food is partly determined by the time to locate a food patch and, therefore, as a foundation for understanding the influence of food availability on diet selection, key controls on the density of grass, forb, and browse patches were investigated across space and time in a semi-arid African savanna. Density of food patches changed seasonally because plant life-forms required different volumes of soil water to produce green forage; and woody plants and forbs responded to long-term changes in soil moisture, while grasses responded to short-term moisture pulses. Soil texture, structure of woody vegetation and fire added further complexity by altering the soil water thresholds required for production of green forage. Interpolating between regularly-timed, ground-based measurements of food density by using modelled soil water as the predictor in regression equations may be a feasible method of quantifying food available to elephants in complex savanna environments.

RESUMEN

Habitat loss and climate change are primary drivers of global biodiversity loss. Species will need to track changing environmental conditions through fragmented and transformed landscapes such as KwaZulu-Natal, South Africa. Landscape connectivity is an important tool for maintaining resilience to global change. We develop a coarse-grained connectivity map between protected areas to aid decision-making for implementing corridors to maintain floristic diversity in the face of global change. The spatial location of corridors was prioritised using a biological underpinning of floristic composition that incorporated high beta diversity regions, important plant areas, climate refugia, and aligned to major climatic gradients driving floristic pattern. We used Linkage Mapper to develop the connectivity network. The resistance layer was based on land-cover categories with natural areas discounted according to their contribution towards meeting the biological objectives. Three corridor maps were developed; a conservative option for meeting minimum corridor requirements, an optimal option for meeting a target amount of 50% of the landscape and an option including linkages in highly transformed areas. The importance of various protected areas and critical linkages in maintaining landscape connectivity are discussed, disconnected protected areas and pinch points identified where the loss of small areas could compromise landscape connectivity. This framework is suggested as a way to conserve floristic diversity into the future and is recommended as an approach for other global connectivity initiatives. A lack of implementation of corridors will lead to further habitat loss and fragmentation, resulting in further risk to plant diversity.

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RESUMEN

As a foundation for understanding the diet of African savanna elephants (Loxodonta africana), adult bulls and cows were observed over an annual cycle to determine whether harvesting (Pt ), chewing (Ct ) and handling times (Ht ) differed across food types and harvesting methods (handling time is defined as the time to harvest, chew and swallow a trunkload of food). Bulls and cows were observed 105 and 26 times, respectively (94 and 26 individuals), with a total of 64 h of feeding recorded across 32 vegetation types. Some food types took longer to harvest and chew than others, which may influence intake rate and affect choice of diet. The method used to gather a trunkload of food had a significant effect on harvesting time, with simple foraging actions being comparatively rapid and more difficult tasks taking longer. Handling time was constrained by chewing for bulls, except for the processing of roots from woody plants, which was limited by harvesting. Time to gather a trunkload had a greater influence on handling time for cows compared to bulls. Harvesting and handling times were longer for bulls than cows, with the sexes adopting foraging behaviors that best suited their energy requirements.