A Historical Perspective and Future Outlook on Landscape Scale Restoration in the Northwest Wisconsin Pine Barrens

The concurrent discussions of landscape scale restoration among restoration ecologists, and of historic disturbance pattern as a guideline for forest management among forest scientists, offer a unique opportunity for collaboration between these traditionally separated fields. The objective of this study was to review the environmental history, early restoration projects, and current plans to restore landscape patterns at broader scales in the 450,000 ha northwest Wisconsin Pine Barrens. The Pine Barrens offer an example of a landscape shaped by fire in the past. In northwestern Wisconsin historically the barrens were a mosaic of open prairie, savanna, and pine forests on very poor, sandy soils. The surrounding region of better soils was otherwise heavily forested. Six restoration sites have been managed since the middle of this century using prescribed burns to maintain the open, barrens habitat. However, these sites are not extensive enough to mimic the shifting mosaic of large open patches previously created by fire. Extensive clear‐cuts may be used as a substitute for these large fire patches so that presettlement landscape patterns are more closely approximated in the current landscape. We suggest that such silvicultural treatments can be suitable to restore certain aspects of presettlement landscapes, such as landscape pattern and open habitat for species such as grassland birds. We are aware that the effects of fire and clear‐cuts differ in many aspects and additional management tools, such as prescribed burning after harvesting, may assist in further approximating the effect of natural disturbance. However, the restoration of landscape pattern using clear‐cuts may provide an important context for smaller isolated restoration sites even without the subsequent application of fire, in this formerly more open landscape.     

Restoration of Midwestern U.S. Savannas: One Size Does Not Fit All

Lowland savannas are a rare variant of Midwestern United States savanna occurring on alluvial soils, for which reference information is sparse. To evaluate the appropriateness of using upland savanna as a surrogate source of reference information for lowland savanna, we studied a pre‐Euro‐American lowland savanna using original U.S. Public Land Survey data and other historical records. Historical vegetation was reconstructed and compared among upland savannas, lowland savannas, and lowland forests; we also evaluated potential disturbance dynamics maintaining these systems. We found that all three communities were dominated by members of the genus Quercus but also had extensive representation by many other tree species, especially notable for savannas in this region. There were no clear size–density relationships for species in the genus Quercus, indicating that these historical savannas were not characterized exclusively by large, scattered oak trees but rather by trees of many oak species and nonoak species in a wide range of size classes. Both upland and lowland savannas also contained a substantial shrub component. We found no evidence that lowland savannas were maintained by flooding, although the uneven‐aged canopy structure suggested that periodic disturbance occurred. Restoration of lowland savanna in this region should include provisions for maintaining nonoak species and shrubs, with disturbance timed to maintain an uneven‐aged canopy structure. Although the appropriateness of historical data in the face of climate change may be questionable, in this region, a warmer climate may actually help promote the “oak parkland” that was present from 8,000 BP up to Euro‐American settlement.     

Biodiversity responses to land‐use and restoration in a global biodiversity hotspot: Ant communities in Brazilian Cerrado

Given that land‐use change is the main cause of global biodiversity decline, there is widespread interest in adopting land‐use practices that maintain high levels of biodiversity, and in restoring degraded land that previously had high biodiversity value. In this study, we use ant taxonomic and functional diversity to examine the effects of different land uses (agriculture, pastoralism, silviculture and conservation) and restoration practices on Cerrado (Brazilian savanna) biodiversity. We also examine the extent to which ant diversity and composition can be explained by vegetation attributes that apply across the full land management spectrum. We surveyed vegetation attributes and ant communities in five replicate plots of each of 13 land‐use and restoration treatments, including two types of native vegetation as reference sites: cerrado sensu stricto and cerradão. Several land‐use and restoration treatments had comparable plot richness to that of the native reference habitats. Ant species and functional composition varied systematically among land‐use treatments following a gradient from open habitats such as agricultural fields to forested sites. Tree basal area and grass cover were the strongest predictors of ant species richness. Losses in ant diversity were higher in land‐use systems that transform vegetation structure. Among productive systems, therefore, uncleared pastures and old pine plantations had similar species composition to that occurring in cerrado sensu stricto. Restoration techniques currently applied to sites that were previously Cerrado have focused on returning tree cover, and have failed to restore ant communities typical of savanna. To improve restoration outcomes for Cerrado biodiversity, greater attention needs to be paid to the re‐establishment and maintenance of the grass layer, which requires frequent fire. At the broader scale, conservation planning in agricultural landscapes, should recognize the value of land‐use mosaics and the risks of homogenization.     

Savannas after afforestation: Assessment of herbaceous community responses to wildfire versus native tree planting

Afforestation and fire exclusion are pervasive threats to tropical savannas. In Brazil, laws limiting prescribed burning hinder the study of fire in the restoration of Cerrado plant communities. We took advantage of a 2017 wildfire to evaluate the potential for tree cutting and fire to promote the passive restoration of savanna herbaceous plant communities after destruction by exotic tree plantations. We sampled a burned pine plantation (Burned Plantation); a former plantation that was harvested and burned (Harvested & Burned); an unburned former plantation that was harvested, planted with native trees, and treated with herbicide to control invasive grasses (Native Tree Planting); and two old-growth savannas which served as reference communities. Our results confirm that herbaceous plant communities on post-afforestation sites are very different from old-growth savannas. Among post-afforestation sites, Harvested & Burned herbaceous communities were modestly more similar in composition to old-growth savannas, had slightly higher richness of savanna plants (3.8 species per 50-m²), and supported the greatest cover of native herbaceous plants (56%). These positive trends in herbaceous community recovery would be missed in assessments of tree cover: whereas canopy cover in the Harvested & Burned site was 6% (less than typical of savannas of the Cerrado), the Burned Plantation and Native Tree Planting supported 34% and 19% cover, respectively. By focusing on savanna herbaceous plants, these results highlight that tree cutting and fire, not simply tree planting and fire exclusion, should receive greater attention in efforts to restore savannas of the Cerrado.     

Quandaries of a decade‐long restoration experiment trying to reduce invasive species: beat them,join them,give up,or start over?

We evaluate the outcomes and consequences of a decade‐long restoration project in a Hawaiian lowland wet forest as they relate to long‐term management actions. Our initial study was designed both to promote native biodiversity and to develop knowledge that would enable land management agencies to restore invaded forests. Our premise of success followed the prevalent perception that short‐term management, such as removal of invasive species, ideally translates into long‐term and sustainable restoration. We were therefore disappointed and perhaps discouraged in our results—little recovery of native biodiversity despite ongoing and labor‐intensive management. Not only did we fail to return the invaded forest to a native‐dominated system but also our efforts lead to recruitment of new non‐native species assemblages. The sobering truth of many restoration projects in Hawaii and elsewhere is that we can never completely walk away and “consider the job finished,” or we have to accept that some ecosystems cannot be returned to an all‐native state. Essentially, costs of restoration may outweigh the accomplishment. This setback gave us an opportunity to reconsider and modify our initial approach. By starting over with a new direction using both native and non‐invasive but non‐native species, we have adopted a new philosophy of “join them.” In our revision, we changed the players in the game by following invasive species removal with outplantings of native and non‐invasive non‐native species that will functionally fill missing roles in the ecosystem. We link social interest in the new experiment to changing attitudes about naturalness.     

Net woody vegetation increase confined to seasonally inundated lowlands in an Australian tropical savanna,Victoria River District,Northern Territory

Abstract Georeferenced digital aerial photographs were used to assess changes in overstorey vegetation cover since 1948 in the Victoria River District, Northern Territory, Australia, across a range of lowland tropical savanna habitats and with explicit consideration of known and variable site‐specific grazing and fire management histories. Vegetation surveys at corresponding locations on the ground identified five distinct woody vegetation communities defined primarily by water drainage and secondarily by soil characteristics. Air‐photo analyses revealed that, contrary to popular perceptions and in contrast to results from other habitats, there has been no generalized net increase in overstorey woody vegetation cover across the full range of lowland savanna habitats. Rather, different habitats exhibited distinctly different vegetation change mechanisms: low‐lying seasonally inundated ‘wet’ habitats have experienced woody vegetation increase since 1948, whereas well‐drained ‘dry’ habitats have experienced overstorey vegetation stability or loss. In almost every instance woody vegetation increase could be attributed to the invasion or proliferation of a single species, Melaleuca minutifolia F.Muell. The extent of M. minutifolia increase was unrelated to historical grazing/fire regime. Demographic analyses for this species revealed that recruitment was often episodic and that synchronized recruitment events occurred uniformly across the full range of historical management treatments, most likely as a consequence of favourable climatic conditions in years with an extended wet season. Heavy grazing facilitated juvenile survival and/or recruitment, most likely by reducing grassy fuel loads and eliminating landscape fire. We conclude that while there has been no generalized net increase in overstorey woody vegetation cover in lowland environments, savanna dynamics are complex, and multiple change mechanisms have occurred simultaneously in different habitats, some of which have been significantly transformed since 1948. Where net woody vegetation increase has occurred it is primarily a natural consequence of episodic M. minutifolia establishment in climatically favourable years, but the extent and magnitude of this effect is likely mediated by fire/grazing regime.     

A Landscape-Scale,Applied Fire Management Experiment Promotes Recovery of a Population of the Threatened Gouldian Finch,Erythrura gouldiae,in Australia’s Tropical Savannas

Fire is an integral part of savanna ecology and changes in fire patterns are linked to biodiversity loss in savannas worldwide. In Australia, changed fire regimes are implicated in the contemporary declines of small mammals, riparian species, obligate-seeding plants and grass seed-eating birds. Translating this knowledge into management to recover threatened species has proved elusive. We report here on a landscape-scale experiment carried out by the Australian Wildlife Conservancy (AWC) on Mornington Wildlife Sanctuary in northwest Australia. The experiment was designed to understand the response of a key savanna bird guild to fire, and to use that information to manage fire with the aim of recovering a threatened species population. We compared condition indices among three seed-eating bird species–one endangered (Gouldian finch) and two non-threatened (long-tailed finch and double-barred finch)—from two large areas (> 2,830 km²) with initial contrasting fire regimes (‘extreme’: frequent, extensive, intense fire; versus ‘benign’: less frequent, smaller, lower intensity fires). Populations of all three species living with the extreme fire regime had condition indices that differed from their counterparts living with the benign fire regime, including higher haematocrit levels in some seasons (suggesting higher levels of activity required to find food), different seasonal haematocrit profiles, higher fat scores in the early wet season (suggesting greater food uncertainty), and then lower muscle scores later in the wet season (suggesting prolonged food deprivation). Gouldian finches also showed seasonally increasing stress hormone concentrations with the extreme fire regime. Cumulatively, these patterns indicated greater nutritional stress over many months for seed-eating birds exposed to extreme fire regimes. We tested these relationships by monitoring finch condition over the following years, as AWC implemented fire management to produce the ‘benign’ fire regime throughout the property. The condition indices of finch populations originally living with the extreme fire regime shifted to resemble those of their counterparts living with the benign fire regime. This research supports the hypothesis that fire regimes affect food resources for savanna seed-eating birds, with this impact mediated through a range of grass species utilised by the birds over different seasons, and that fire management can effectively moderate that impact. This work provides a rare example of applied research supporting the recovery of a population of a threatened species.     

Restoring Savanna Using Fire: Impact on the Breeding Bird Community

Restoration of many terrestrial plant communities involves the reintroduction of fire. However, there have been few studies of the effects of fire on the avifauna during the restoration process. To study the effects of oak savanna restoration on avian communities, breeding birds were censused and the vegetation structure documented in seven experimental burn units (8–18 ha) that had experienced different frequencies of controlled burns during the past 31 years (0–26 burns). Data were analyzed with both direct and indirect gradient analyses using multivariate techniques. The results showed that, as savanna restoration proceeded, there was a general decline in predominantly insectivorous species, particularly those that feed in the upper canopy region (leaves and air space), and a general increase in omnivorous species, particularly those that feed on the ground and in the lower canopy. Insectivorous bark gleaners (woodpeckers) also increased during restoration and were correlated with the increase in standing dead trees resulting from the fires. Overall, savanna restoration resulted in increases in the abundance of many open country bird species, including many species that have been declining in central and eastern North America, including red‐headed woodpecker, Baltimore oriole, eastern kingbird, vesper sparrow, field sparrow, lark sparrow, brown thrasher, American goldfinch, and brown‐headed cowbird. The shifts in species and guilds were correlated with changes in burn frequency and the macro vegetation structure—tree and shrub density, leaf area index, and relative proportion of standing dead trees. The findings show that savanna restoration can increase bird diversity and provide important habitat for uncommon or declining bird species. These birds are most likely attracted to one or more of the distinctive habitat features of the restored savanna environments, including scattered mature trees, standing dead trees and snags, and presence of both shrubby and grassland vegetation. The findings also suggest that restoration ecologists and wildlife biologists will need to work together to achieve desired goals, since different types of savanna restoration efforts may produce different effects on the breeding bird community.     

Ecological restoration, carbon sequestration and biodiversity conservation: The experience of the Society for Wildlife Research and Environmental Education (SPVS) in the Atlantic Rain Forest of Southern Brazil

Since 1999, SPVS has been involved in three projects that combine two fundamental goals over the course of 40 years: the conservation of one of Brazil's most important remnants of Atlantic Forest and the implementation of projects for carbon sequestration. In addition, there is an interest in replicating these projects in order to restore other degraded areas, protect the Brazilian biomes, and help to diminish deforestation and forest fire, therefore reducing carbon emissions. The acquisition of 19,000 ha of degraded areas of high biological importance in southern Brazil was the first step towards the implementation of the projects. These areas are owned by SPVS, a Brazilian NGO, and are being restored, conserved and transformed into Private Natural Reserves, in partnership with the NGO – The Nature Conservancy, and financed by the companies – American Electric Power, General Motors and Chevron Texaco. The process of forest restoration involves several stages: soil studies, surveying the region's native plants, planning for restoration by means of a Geographical Information System, production of seedlings, application of different techniques for planting (such as manual or mechanised planting with seedlings and stakes), and biomass and biodiversity monitoring. To guarantee the survival of the seedlings on the planted areas, during the first three years, there is a continuous and systematic maintenance programme including weeding of undergrowth, crowing and organic fertilisation. The three projects already planted around 500,000 seedlings of native species until September 2004, and aim to plant a further 300,000 until 2008.     

A NOTE ON THE CROP CONTENTS OF TWO CRESTED GUINEA-FOWL GUTTERA EDOU ARDI(HARTLAUB)

Dean, W. R. J. 1987. Birds associating with fire at Nylsvley Nature Reserve, Transvaal. Ostrich 58:103-106. Observations of 76 species of birds associating with 54 fires on Nylsvley Nature Reserve, Transvaal, South Africa, in an area of savanna woodland during 1979-82 are described. The fire front was attended mainly by insectivores which took their prey in the air and on the ground. Burnt areas were utilized by both seed and insect eaters after fires.     

Strategies for Savanna Restoration in the Southern Great Plains: Effects of Fire and Herbicides

Woody plant encroachment has degraded grassland and savanna ecosystems worldwide by decreasing herbaceous production and diversity, and altering these physiognomies toward woodlands. This study evaluated the long-term efficacy of fire and herbicide restoration strategies used in the southern Great Plains to reduce Honey mesquite ( Prosopis glandulosa ) dominance, restore a grassland/savanna physiognomy, and increase herbaceous production and diversity. Three treatments were evaluated: high-intensity winter fire, aerial spray of clopyralid + triclopyr (C + T), and aerial spray of clopyralid and were compared to untreated mesquite woodland (control). Post-treatment mesquite stand physiognomy was different between fire (low mortality, high basal sprouting), C + T (high mortality, high basal sprouting of surviving plants), and clopyralid (moderate mortality, low basal sprouting of surviving plants) treatments. From 6 to 8 years post-treatment, herbaceous production was increased in C + T and clopyralid treatments but not in the fire treatment. Mesquite regrowth in the fire treatment exerted a competitive influence that limited herbaceous production. Herbaceous functional group diversity was increased in fire and C + T treatments due to a decrease in C₃ perennial grass dominance and an increase in C₄ perennial grasses and/or C₃ forbs. Treatments that maintained mesquite overstory (control and clopyralid) had lower herbaceous diversity due to C₃ perennial grass dominance and lower C₄ perennial grass cover. The clopyralid treatment demonstrated greatest potential for long-term restoration of southern Great Plains savanna by reducing mesquite canopy cover to historic levels, limiting mesquite basal regrowth and increasing grass production.     

Population genetics of pike,genus <Emphasis Type="Italic">Esox</Emphasis> (Actinopterygii,Esocidae), in Northern Italy: evidence for mosaic distribution of native,exotic and introgressed populations

Biomanipulation, or management actions aimed to structure biological communities to achieve certain goals, has often been used in the restoration of aquatic ecosystems. In 2000, The Nature Conservancy acquired the Emiquon Preserve, which included two former Illinois River floodplain lakes, to restore these ecosystems. Restoration included stocking to establish a native fish community commensurate with historical records. Largemouth bass (Micropterus salmoides, bass) were also introduced to control poor water clarity and invasive common carp (Cyprinus carpio, carp). We summarized fish community characteristics and tested whether bass contributed to water clarity maintenance and limited carp during 2007–2014. The fish community was dominated by species stocked in greatest abundance, 13 of 32 species initially stocked have not been collected, and species diversity increased. No carp were observed in bass diets, water clarity declined significantly, and carp relative abundance increased. Increasing water levels during 2008–2009 diffused bass predation potential upon zooplanktivorous fishes and carp and weakened potential trophic cascading interactions. Our findings suggest that water level management, greater stocking of piscivores to maintain predator densities, prevention of gizzard shad (Dorosoma cepedianum) introduction, and/or a more diverse fish community including other native piscivores may be required to achieve long-term restoration goals.     

Fire‐sensitive species dominate seed rain after fire suppression: Implications for plant community diversity and woody encroachment in the Cerrado

Woody encroachment is becoming common in tropical savannas. We studied natural seed rain and performed seed addition experiments in a Brazilian savanna that had not been burned for several decades. We found greater abundance of fire‐sensitive species in the seed rain, likely contributing to woody encroachment. Flexible fire management policies that allow for natural and prescribed fires may be required to maintain savanna diversity.     

The Lack of Favorable Responses of an Endangered Pitcher Plant to Habitat Restoration

Restoring habitat structure that existed before active and inadvertent fire suppression is thought to be critical to maintaining populations of some rare plants in fire‐suppressed habitats. Nevertheless, the impacts of habitat restoration on most endangered plants are poorly understood. Current theory predicts and empirical studies have shown that the reduction of shade or competition (frequently a goal of many habitat restoration projects in degraded fire‐dependent ecosystems) benefits plants adapted to nutrient‐poor soils by increasing the benefit‐to‐cost ratio of adaptations for enhanced nutrient capture. Here, I examined how experimental reduction of neighboring plants in a wet longleaf pine community dominated in the ground cover by shrubs and stump sprouts influenced the growth, the reproduction, the carnivorous effort, and the benefits of carnivory in a U.S. federally endangered species, Sarracenia rubra ssp. alabamensis. Two years of data showed no significant effects of neighbor reduction or prey exclusion on any of several indicators of plant performance, nor was there any evidence of a hypothesized morphological trade‐off between shade avoidance and prey capture. These results were unexpected. Inadequate replication and atypical precipitation patterns were ruled out as possible explanations. The population studied here (unlike that of a different, but morphologically similar, species growing in a fire‐maintained pine grass–sedge savanna) did not exhibit the ability to respond to variation in competition from neighboring plants.     

The Entomology of the Isle of Rhum National Nature Reserve

Entomological records for the Island of Rhum have been brought together to form an inventory of 2158 species of insects. It is the result of intense surveys conducted in the 1960s combined with casual collecting by visiting and resident entomologists and includes documented records since 1895.
The diversity of insects recorded is, perhaps, greater than might have been anticipated in a bleak and windswept Hebridean island. Man-made habitats in the form of mixed woodland, farmland and gardens support the greatest range of species present though most of the resident insect rarities occur in coastal or upland habitats.
The island is a National Nature Reserve owned by the Nature Conservancy Council whose management policies include a large scale woodland restoration programme aimed at recreating forest formations composed of native trees and shrubs, as well as studies on the effects of red deer Cervus elaphus and other grazing animals on existing vegetation communities outwith the planting areas. This catalogue serves as a baseline by which changes resulting from these management activities, as well as cyclical population changes, can be measured.     

Managing fire‐dependent vegetation in Byron Shire,Australia: Are we restoring the keystone ecological process of fire?

Fire is a keystone ecological process in many ecosystems. In such ecosystems, the exclusion of fire can lead to fundamental shifts in vegetation structure, composition and distribution and poses a major threat to the biodiversity dependent on these habitats. Programmes to manage and restore native vegetation have increased rapidly over recent decades, and while many such programmes have demonstrable success managing a range of environmental threats, their effectiveness in identifying and addressing the major threat of fire exclusion in fire‐dependent vegetation is questionable. This study sought to identify impediments to the management of fire‐excluded vegetation at the assessment and planning stage of ecological management programmes in Byron Shire in north‐east New South Wales. Sixty ecological management and restoration plans for sites known to be fire‐excluded in the shire were reviewed to determine the rate at which fire exclusion was identified and addressed in planning over the last decade. Document analysis found the majority of plans failed to accurately identify fire exclusion or to recommend the reintroduction of fire in fire‐excluded management sites. Absence of standardised guidelines that require comprehensive consideration of fire exclusion in ecological management and restoration plans is suggested as a key factor in the low response rates observed. Furthermore, it was found that existing implicit prompts to address inappropriate‐fire regimes generally, including government policies, project objectives and site‐assessment prompts had little effect on identification and response rates, further confirming the need for more‐explicit assessment prompts relating to fire‐frequency issues. Without improvements of the current ecological assessment and planning process to increase identification and management of fire exclusion in the study area, fire‐dependent biodiversity values will continue to decline wherever fire exclusion remains unmanaged. It is recommended that explicit assessment and planning templates are developed and implemented to effectively manage fire exclusion and conserve the fire‐dependent biodiversity of Byron Shire and the far north coast of NSW.     

Patterns of abundance of fire ants and native ants in a native ecosystem

Abstract 1. This correlational study examines the relationship between the red imported fire ant (Solenopsis invicta) and native ants in a longleaf pine savanna. Fire ants are frequently associated with a decline in native ants throughout the invaded range, but fire ant invasion is often coupled with habitat disturbance. Invasion of fire ants into the longleaf pine savanna provides an opportunity to examine the structure of the ant community in the absence of habitat disturbance. 2. Pitfall trapping was conducted within the longleaf pine savanna as well as across a naturally occurring soil moisture gradient, in plots that had been artificially watered. 3. Species richness did not vary as a function of fire ant density. There was an inverse relationship between native ant density and fire ant density, but this abundance pattern does not necessarily imply a causal link between fire ant invasion and native ant decline. For individual species, fire ant densities were negatively correlated with the densities of only two native ant species, including Solenopsis carolinensis, a native species that potentially limits the invasion of fire ants. Additionally, fire ants and native ants respond differently to soil moisture, with native ants favouring drier conditions than fire ants. 4. The possible exclusion of fire ants by some native ants, as well as differences in habitat preferences, provide alternative explanations for the frequently observed negative correlation between fire ants and native ants.     

Return of Fire as a Restoration Tool: Long‐Term Effects of Burn Severity on Habitat Use by Mexican Fox Squirrels

After decades of suppression, fire is returning to forests of the western United States through wildfires and prescribed burns. These fires may aid restoration of vegetation structure and processes, which could improve conditions for wildlife species and reduce severe wildfire risk. Understanding response of wildlife species to fires is essential to forest restoration because contemporary fires may not have the same effects as historical fires. Recent fires in the Chiricahua Mountains of southeastern Arizona provided opportunity to investigate long‐term effects of burn severity on habitat selection of a native wildlife species. We surveyed burned forest for squirrel feeding sign and related vegetation characteristics to frequency of feeding sign occurrence. We used radio‐telemetry within fire‐influenced forest to determine home ranges of Mexican fox squirrels, Sciurus nayaritensis chiricahuae, and compared vegetation characteristics within home ranges to random areas available to squirrels throughout burned conifer forest. Squirrels fed in forest with open understory and closed canopy cover. Vegetation within home ranges was characterized by lower understory density, consistent with the effects of low‐severity fire, and larger trees than random locations. Our results suggest that return of low‐severity fire can help restore habitat for Mexican fox squirrels and other native wildlife species with similar habitat affiliations in forests with a historical regime of frequent, low‐severity fire. Our study contributes to an understanding of the role and impact of fire in forest ecosystems and the implications for forest restoration as fire returns to the region.     

Post‐Establishment Seedling Success in the Brazilian Cerrado: A Comparison of Savanna and Forest Species1

Due to frequent fire, low nutrient availability, and prolonged drought, tropical savanna is a stressful environment for the survival and growth of woody plant seedlings. To understand why forest species do not succeed in this environment while savanna species are able to persist, the effects of fire and woody cover on seedlings of these two functional groups were investigated in the Brazilian Cerrado. Seedlings were established in experimental plots under three densities of woody cover, in sites protected from fire and sites to be subjected to fire. There was a clear difference in the ability of savanna and forest species to survive fire. None of the three forest species were able to survive fire during the first two years of life, whereas eight of the nine savanna species were able to resprout following fire. The small seed size of the ninth savanna species, Miconia albicans, predisposed its seedlings to be sensitive to fire, because there was a strong positive correlation between seed size and survivorship. Savanna species were less dependent on woody cover than were forest species, which exhibited higher growth and survival under tree canopies than in open grassland. The low rates of establishment and survival of forest trees in savanna, combined with high sensitivity to fire, appear sufficient to prevent the expansion of forest into savanna under current fire regimes in the Cerrado.     

Long‐term variability and rainfall control of savanna fire regimes in equatorial East Africa

Fires burning the vast grasslands and savannas of Africa significantly influence the global carbon cycle. Projecting the impacts of future climate change on fire‐mediated biogeochemical processes in these dry tropical ecosystems requires understanding of how various climate factors influence regional fire regimes. To examine climate–vegetation–fire linkages in dry savanna, we conducted macroscopic and microscopic charcoal analysis on the sediments of the past 25 000 years from Lake Challa, a deep crater lake in equatorial East Africa. The charcoal‐inferred shifts in local and regional fire regimes were compared with previously published reconstructions of temperature, rainfall, seasonal drought severity, and vegetation dynamics to evaluate millennial‐scale drivers of fire occurrence. Our charcoal data indicate that fire in the dry lowland savanna of southeastern Kenya was not fuel‐limited during the Last Glacial Maximum (LGM) and Late Glacial, in contrast to many other regions throughout the world. Fire activity remained high at Lake Challa probably because the relatively high mean‐annual temperature (~22 °C) allowed productive C₄ grasses with high water‐use efficiency to dominate the landscape. From the LGM through the middle Holocene, the relative importance of savanna burning in the region varied primarily in response to changes in rainfall and dry‐season length, which were controlled by orbital insolation forcing of tropical monsoon dynamics. The fuel limitation that characterizes the region's fire regime today appears to have begun around 5000–6000 years ago, when warmer interglacial conditions coincided with prolonged seasonal drought. Thus, insolation‐driven variation in the amount and seasonality of rainfall during the past 25 000 years altered the immediate controls on fire occurrence in the grass‐dominated savannas of eastern equatorial Africa. These results show that climatic impacts on dry‐savanna burning are heterogeneous through time, with important implications for efforts to anticipate future shifts in fire‐mediated ecosystem processes.