Distinct roles of savanna and forest tree species in regeneration under fire suppression in a Brazilian savanna

Questions: Has fire suppression relaxed barriers to the exchange of species between savanna and forest? Do all species or a subset of species participate in this exchange? Would current vegetation structure persist if fire suppression were to cease? Location: A gallery forest edge in the Cerrado region of central Brazil that burned only once in the past 35 years. Methods: Density of tree seedlings, saplings and adults, leaf area index (LAI), tree basal area and diameter were surveyed in 12, 10 m × 70 m transects centred on and perpendicular to the forest–savanna boundary. Community composition was assessed using non‐metric multi‐dimensional scaling (NMDS). Results: Basal area and LAI declined substantially from forest to savanna, with an associated shift in species composition. Savanna tree species were nearly absent in the forest, but accounted for the majority of stems in the savanna. In contrast, forest species comprised 14% of adults and more than one‐third of juveniles in the savanna. Despite the high diversity of trees (85 species) in the forest, five species play a particularly large role in this initial phase of forest expansion. Reintroduction of fire, however, would result in widespread topkill of juveniles and the majority of adult forest trees, thereby interrupting the succession towards forest. Conclusions: After 35 years during which the site burned only once, the savanna still remains dominated by savanna species. Nevertheless, the dominance of forest juveniles in border and savanna tree communities suggests that with a continued policy of fire suppression, the forest will continue to expand.     

Impact of the invasive alien grass Melinis minutiflora at the savanna-forest ecotone in the Brazilian Cerrado

Exotic grasses are a serious threat to biodiversity in the cerrado savannas of central Brazil. Of particular concern is the possible role they may have in impeding tree regeneration at gallery (riverine) forest edges and increasing fire intensity, thereby driving gallery forest retreat. Here we quantify the effect of roads and distance from gallery forests on the abundance of the African grass Melinis minutiflora Beauv. and test for an effect of this species on woody plant regeneration and leaf area index. Melinis was present at approximately 70% of the sites near gallery forest edges, with its frequency declining sharply at greater distances from the edge. Melinis frequency was 2.8 times greater where roads were present nearby. Leaf area index (LAI) of the ground layer was 38% higher where Melinis was present than where it was absent. LAI was strongly correlated to fine fuel mass (r² = 0.80), indicating higher fuel loads where Melinis was present. The abundance of tree and shrub species in the ground layer was negatively related to LAI and to the presence of Melinis. The greater fuel accumulation and reduced tree regeneration caused by Melinis may cause a net reduction in forest area by increasing fire intensity at the gallery forest edge and slowing the rate of forest expansion.     

Experimental Native Tree Seedling Establishment for the Restoration of a Mexican Cloud Forest

The cloud forests of Mexico have been degraded and severely fragmented, and urgently require restoration. However, progress with restoration has been constrained by a lack of information concerning the seedling ecology of native tree species. An experiment was therefore conducted to assess the influence of different environmental factors on the seedling survival and growth of four native tree species (Fagus grandifolia var. mexicana, Carpinus caroliniana, Symplocos coccinea, and Quercus acutifolia). The seedlings were established on three sites, in two contrasting environments: inside forest fragments and on adjacent agricultural land. Highly significant differences were recorded in seedling survival and growth among sites, environments, species, and interactions between these factors. Highest survival was recorded for Quercus, which uniquely among the four species displayed the same survival percentage inside and outside the forest. Survival of the other species was higher inside the forest. In contrast, growth rates of all four species were higher outside the forest. The most important cause of mortality outside the forest was desiccation, although significant seedling predation was also observed on two sites. Results indicate that all four species can be established successfully both within forest fragments and in neighboring agricultural areas, emphasizing the scope for forest restoration. However, the interactions observed between species, sites, and environments highlight the importance of accurate species–site matching if optimum rates of growth and survival are to be obtained. Quercus spp. have great potential for establishment on agricultural sites.     

不同光强下几种南亚热带森林乔木的种子萌发和幼苗生长观察

对泡桐,春椿,木蝴蝶,枳Ｊｕ扁斗青冈和罗浮柿等亚热带森林乔木树种在不同强条件下的种子萌发及其幼苗生长进行观察,泡桐和枳Ｊｕ种子在光（１００％）条件下的萌发率最高,香椿和罗浮肺种子在轻阴（６２．２％）条件下的萌发率最高,木蝴蝶和扁斗青冈种子在中阴（３４．４％）条件下萌发率最高,阳性树种泡桐,香椿,木蝴蝶和枳Ｊｕ幼苗生长速度较快,属速生型树种,其幼苗在自然光条件下的总生物量最大;扁斗青冈和罗浮柿幼苗生     

Seed Size,Seed Germination,and Seedling Survival of Brazilian Tropical Tree Species Differing in Successional Status1

Seed germination and seedling establishment patterns have been used to classify species as shade tolerant or intolerant. The main objective of this research was to investigate, under controlled conditions, seed germination of species from different successional positions as well as to follow seed germination and seedling survival under natural shade in the field. The species studied were Solarium granuloso‐leprosum, Trema micrantha, Cecropia pachystachya, Croton piptocalyx, Bauhinia forficata subsp. pruinosa. Senna macranthera, Schizolobium parahyba, Piptadenia gonoacantha, Chorisia speciosa, Pseudobombax grandiflorum, Ficus guaranitica, Esenbeckia leiocarpa, Pachystroma longifolium, Myroxylon peruiferum, and Hymenaea courbaril. Field trials were carried out at Santa Genebra Municipal Reserve, Campinas, SP, Brazil, at the forest edge and in the understory. No significant correlations were detected between successional status and seed size or seed water content. Light‐regulated germination was present only in small‐seeded species. In field experiments, most species, including the light‐sensitive ones, were able to germinate under the canopy, where a low red/far‐red ratio predominates. Most species, mainly those of early‐ and intermediate successional positions, presented low seedling survival rates under shade. Myroxylon peruiferum was the most shade tolerant species, while 5. granuloso‐leprosum, C. speciosa, P. gonoacantha, F. guaranitica, T. micrantha, and 5. parahyba were the most shade intolerant. These latter species showed little or no survival under the shade conditions.     

Ant Species Identity has a Greater Effect than Fire on the Outcome of an Ant Protection System in Brazilian Cerrado

Although fire‐ and ant–plant interactions influence the community structure and dynamics of Neotropical savannas, no previous studies have considered their simultaneous effects on target host plants. We monitored the effect of ant exclusion for 3 years on leaf area loss to leaf chewing insects, thrips abundance, and reproductive output of the extrafloral nectary‐bearing shrub, Peixotoa tomentosa (Malpighiaceae). We predicted that the impact of ants on herbivores and plants would depend on the ant species, and that fire would reduce the effect of ants. We deliberately chose control plants that differed in their occupant ant species. Fire occurred in the second year of the study, allowing us to determine its effect on the benefit afforded by ants. Ants reduced leaf area loss and thrips abundance, and increased fruit and seed production in all 3 years. Some ant species were more effective than others, while plants with multiple ant species suffered higher leaf area loss than plants with a single ant species. In the year following the fire, leaf damage was greater than in the other years, regardless of the ant species, and the proportional effect of ants in reducing damage was less. Interactions affecting thrips abundance did not change following fire, nor was the benefit to the plant proportionally reduced. Overall, the identity of the ant species had a greater effect than did the occurrence of fire on the ant–herbivore–plant interaction: the identity of the ant species influenced leaf area loss, thrips numbers, and bud and seed production, while fire only modified the impact of ants on the amount of leaf area consumed by insect herbivores.     

Forest Succession and Distance from Forest Edge in an Afro‐Tropical Grassland1

Forest succession on degraded tropical lands often is slowed by impoverished seed banks and low rates of seed dispersal. Within degraded landscapes, remnant forests are potential seed sources that could enhance nearby forest succession. The spatial extent that forest can influence succession, however, remains largely unstudied. In abandoned agricultural lands in Kibale National Park, Uganda, recurrent fires have helped perpetuate the dominance of tall (2–3 m) grasses. We examined the effects of distance from forest and grassland vegetation structure on succession in a grassland having several years of fire exclusion. At 10 and 25 m from forest edge, we quantified vegetation patterns, seed predation, and survival of planted tree seedlings. Natural vegetation was similar at both distances, as was seed (eight species) and seedling (six species) survival; however, distance may be important at spatial or temporal scales not examined in this study. Our results offer insight into forest succession on degraded tropical grasslands following fire exclusion. Naturally recruited trees and tree seedlings were scarce, and seed survival was low (20% after 7 mo). While seedling survival was high (95% after 6 to 8 mo), seedling shoot growth was very slow (x?= 0.5 cm/100 d), suggesting that survivorship eventually may decline. Recurrent fires often impede forest succession in degraded tropical grasslands; however, even with fire exclusion, our study suggests that forest succession can be very slow, even in close proximity to forest.     

Effects of Canopy Gaps,Topography, and Soils on the Distribution of Woody Species in a Central Brazilian Deciduous Dry Forest1

The interrelationships between the distribution of woody species and environmental variables were investigated in an area of deciduous dry forest in Santa Vitöria, central Brazil. This is the first study of a vanishing type of dry forest which grows on base-rich soils originating from the basalt bedrocks of southern Goiás and western Minas Gerais. A survey of topography, soil properties, canopy gaps and woody plants (≥5 cm diameter at the base of the stem) was conducted in 50–15 × 15 m quadrats. The soils were classified into the following soil series: Hapludolls → Haplustolls → Haplustolls → Ustropepts → Rhodustalfs. This series corresponded to a gradient of increasing elevation and effective soil depth and decreasing slope gradient, soil organic matter and total exchangeable bases. A canonical correspondence analysis and a detrended correspondence analysis indicated that plant species’abundance distribution was significantly correlated with both the relative area of canopy gaps in the quadrats and the soil-topography gradient. Presumably, the critical factors involved in these two gradients are, respectively, light and ground water regimes. The influence of canopy gaps (i.e., light) was surprising and has not been documented previously for tropical deciduous dry forests.     

Amblyomma sculptum: genetic diversity and rickettsias in the Brazilian Cerrado biome

Amblyomma sculptum (Ixodida: Ixodidae) Berlese, 1888 is the most important tick vector in Brazil, transmitting the bioagent of the most severe form of spotted fever (SF) in part of the Cerrado (in the states of Minas Gerais and São Paulo). In another part of the Cerrado (Central‐West region of Brazil), a milder form of SF has been recorded. However, neither the rickettsia nor the vector involved have been characterized. The aim of the current study was to analyse genetic variation and the presence of rickettsia in A. sculptum in Cerrado, from silent areas and with the milder form of SF. Samples were subjected to DNA extraction, amplification and sequencing of 12S rDNA, cytochrome oxidase subunit II and D‐loop mitochondrial genes (for tick population analyses), and gltA, htrA, ompA and gene D (sca4) genes for rickettsia researches. Exclusive haplotypes with low frequencies, high haplotype diversity and low nucleotide diversity, star‐shaped networks and significant results in neutrality tests indicate A. sculptum population expansions in some areas. Rickettsia amblyommatis, Candidatus Rickettsia andeanae and Rickettsia felis were detected. The A. sculptum diversity is not geographically, or biome delimited, pointing to a different potential in vector capacity, possibly associated with differing tick genetic profiles.     

Variation in Seedling Density and Seed Predation Indicators for the Emergent Tree Dipteryx panamensis in Continuous and Fragmented Rain Forest1

Seedling density and the condition of stony endocarps of the tree Dipteryx panamensis were assessed in protected continuous forest and two forest fragments exposed to hunting and selective logging. Seedling density was higher in forest fragments than in continuous forest, while more whole endocarps and fewer chewed and half endocarps were found in fragments, indicating lower seed predation at fragment sites. These findings appear to contradict two earlier D. panamensis studies and we discuss methodological differences that could account for our disparate results. Hunting and fragmentation effects on mammal populations are suggested as a cause for the altered recruitment pattern in fragments.     

Edge Effects and Seedling Bank Depletion: The Role Played by the Early Successional Palm Attalea oleifera (Arecaceae) in the Atlantic Forest

In this study, we examined the impacts of Attalea oleifera on the structure of seedling bank and discuss potential mechanisms of palm influence. Seed rain, seedling bank, and palm leaf fall were assessed beneath the canopy and in the vicinity of 16 adult palms across the edges of a large fragment (3500 ha) of the Atlantic forest. Moreover, we examined A. oleifera impacts on seed germination and seedling mortality by experimentally submitting seeds and seedlings to prolonged palm-leaf covering. As expected, seedling bank beneath the adults exhibited reduced abundance and species richness at local and habitat scale. Small to large seeds (3.1–30 mm) were underrepresented in the seed rain below adults palms, while experimental leaf covering drastically reduced both seed germination and seedling survivorship. A. oleifera leaf fall occurred over the whole year (3.6±2.7 leaves/individual/yr), which resulted in deep leaf litter mounds (10.7±9.2 cm). Finally, adult palm density (21.6±11.9 individuals/ha) correlated negatively with seedling density across Attalea clusters. Our results suggest that A. oleifera exerts negative effects on the seedling bank by reducing seedling abundance and richness as a consequence of two complementary mechanisms: impoverished and size-biased seed rain plus reduced seed germination and increased seedling mortality due to prolonged covering by fallen leaves.     

Influence of Edge Exposure on Tree Seedling Species Recruitment in Tropical Rain Forest Fragments1

Edge creation has a pronounced influence on the understory vegetation, but the effects of edges on seedling species recruitment are still poorly understood. In Central Amazonia, 9–19 years after fragmentation, we recorded species richness and net seedling recruitment rate in 1 ha blocks exposed to none, one, or multiple edges within forest fragments. One‐hectare blocks were located in the center (no edge), the edge (one edge), the corners (two edges) of 10 and 100 ha fragments, and in a 1 ha fragment (four edges). In 1991, we counted all tree seedlings 5–100 cm tall found within permanent 1 m² plots located within the 1 ha blocks. In May 1993, we manually removed all seedlings that were smaller than 1 m tall from the permanent plots. Six years and five months later (October 1999), all new seedlings recruited into the plots were counted and classified into distinct morphospecies. Species richness of recruited seedlings, scaled by total seedling density, declined from the center to the edge, the corner blocks, and then to the 1 ha fragment. Overall, the four‐edged, 1 ha fragment had the poorest species richness and the non‐edged 100 ha central block the highest. The total number of recruited individuals was 40 percent less than that previously present, with the 100 ha corner having the lowest recruitment. Pairwise comparisons showed that species similarity was related to edge number for the 100 and 1 ha fragments. Species rank/abundance curves showed that a subset of species was common in all blocks within the fragments, and that the 100 ha center held more rare species than any other 1 ha block. This study demonstrated that, in a given fragment patch, the number of tree seedling species recruited varied inversely with the number of edges.     

Trade‐offs between savanna woody plant diversity and carbon storage in the Brazilian Cerrado

Incentivizing carbon storage can be a win‐win pathway to conserving biodiversity and mitigating climate change. In savannas, however, the situation is more complex. Promoting carbon storage through woody encroachment may reduce plant diversity of savanna endemics, even as the diversity of encroaching forest species increases. This trade‐off has important implications for the management of biodiversity and carbon in savanna habitats, but has rarely been evaluated empirically. We quantified the nature of carbon‐diversity relationships in the Brazilian Cerrado by analyzing how woody plant species richness changed with carbon storage in 206 sites across the 2.2 million km² region at two spatial scales. We show that total woody plant species diversity increases with carbon storage, as expected, but that the richness of endemic savanna woody plant species declines with carbon storage both at the local scale, as woody biomass accumulates within plots, and at the landscape scale, as forest replaces savanna. The sharpest trade‐offs between carbon storage and savanna diversity occurred at the early stages of carbon accumulation at the local scale but the final stages of forest encroachment at the landscape scale. Furthermore, the loss of savanna species quickens in the final stages of forest encroachment, and beyond a point, savanna species losses outpace forest species gains with increasing carbon accumulation. Our results suggest that although woody encroachment in savanna ecosystems may provide substantial carbon benefits, it comes at the rapidly accruing cost of woody plant species adapted to the open savanna environment. Moreover, the dependence of carbon‐diversity trade‐offs on the amount of savanna area remaining requires land managers to carefully consider local conditions. Widespread woody encroachment in both Australian and African savannas and grasslands may present similar threats to biodiversity.     

Restoration of Araucaria Forest: The Role of Perches, Pioneer Vegetation, and Soil Fertility

The Araucaria forest is Brazil's highly threatened subtropical forest ecosystem that has been disappearing in recent decades. Restoration programs involving this forest type are scarce, and there is a lack of scientific information on how ecological processes such as competition, facilitation, and seed dispersal influence natural forest restoration. This work aims to investigate how use of perches to attract seed dispersers and the influence of pioneer vegetation and soil fertilization could affect the colonization of woody species in a degraded area. An experiment was conducted in an abandoned field where the natural establishment of seeds and seedlings of woody species was monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control); and (3) perches (presence and absence). Seed and seedling abundance, seed and seedling species richness, and seedling mortality were recorded monthly during 12 months. Seed abundance and species richness were significantly greater in places with perches than in control plots. These results were consistent over the year and more pronounced when the surrounding forest produced a higher amount of fruit. Species richness and abundance of seedlings were significantly greater in places with perches than in control plots, and in places with vegetation than without. Soil fertility did not influence seedling establishment. Facilitation and seed dispersal are important factors affecting the colonization of woody species in this subtropical area. Nutrient availability neither regulates the facilitation process nor influences species replacement during the early stages of Araucaria forest succession.