Contrasting demographics of tropical savanna and temperate forest eucalypts provide insight into how savannas and forests function. A case study using Corymbia clarksoniana from north‐eastern Australia

Eucalypts (Eucalyptus spp. and Corymbia spp.) dominate many communities across Australia, including frequently burnt tropical savannas and temperate forests, which receive less frequent but more intense fires. Understanding the demographic characteristics that allow related trees to persist in tropical savannas and temperate forest ecosystems can provide insight into how savannas and forests function, including grass–tree coexistence. This study reviews differences in critical stages in the life cycle of savanna and temperate forest eucalypts, especially in relation to fire. It adds to the limited data on tropical eucalypts, by evaluating the effect of fire regimes on the population biology of Corymbia clarksoniana, a tree that dominates some tropical savannas of north‐eastern Australia. Corymbia clarksoniana displays similar demographic characteristics to other tropical savanna species, except that seedling emergence is enhanced when seed falls onto recently burnt ground during a high rainfall period. In contrast to many temperate forest eucalypts, tropical savanna eucalypts lack canopy‐stored seed banks; time annual seed fall to coincide with the onset of predictable wet season rain; have very rare seedling emergence events, including a lack of mass germination after each fire; possess an abundant sapling bank; and every tropical eucalypt species has the ability to maintain canopy structure by epicormically resprouting after all but the most intense fires. The combination of poor seedling recruitment strategies, coupled with characteristics allowing long‐term persistence of established plants, indicate tropical savanna eucalypts function through the persistence niche rather than the regeneration niche. The high rainfall‐promoted seedling emergence of C. clarksoniana and the reduction of seedling survival and sapling growth by fire, support the predictions that grass–tree coexistence in savannas is governed by rainfall limiting tree seedling recruitment and regular fires limiting the growth of juvenile trees to the canopy.     

Fire alters diversity,composition, and structure of dry tropical forests in the Eastern Ghats

Fire is known to have dramatic consequences on forest ecosystems around the world and on the livelihoods of forest‐dependent people. While the Eastern Ghats of India have high abundances of fire‐prone dry tropical forests, little is known about how fire influences the diversity, composition, and structure of these communities. Our study aimed to fill this knowledge gap by examining the effects of the presence and the absence of recent fire on tropical dry forest communities within the Kadiri watershed, Eastern Ghats. We sampled plots with and without evidence of recent fire in the Eswaramala Reserve Forest in 2008 and 2018. Our results indicate that even though stem density increases in the recently burned areas, species richness is lower because communities become dominated by a few species with fire resistance and tolerance traits, such as thick bark and clonal sprouting. Further, in the presence of fire, the size structure of these fire‐tolerant species shifts toward smaller‐sized, resprouting individuals. Our results demonstrate that conservation actions are needed to prevent further degradation of forests in this region and the ecosystem services they provide.     

Mechanisms of rainforest persistence and recruitment in frequently burnt wet tropical eucalypt forests

The role of fire in governing rainforest–eucalypt forest ecotone dynamics is of theoretical interest and has conservation management implications. Several eucalypt forests in the Wet Tropics of Australia have an endangered status due to extensive conversion to rainforest. Rainforest plants are known to survive occasional low intensity fires in the eucalypt forest ecotone. However, the ability of rainforest plants to survive frequent fires remains untested. The timing of rainforest expansion is also a subject of interest, and is generally considered to be delayed until fire has been absent for several years. We used 14 years of data collected across 13 plots in the Wet Tropics of north‐eastern Australia to test predictions regarding rainforest seedling recruitment and post‐fire regenerative capacity. The 13 plots received different numbers of fires, between zero and five, over the 14‐year study. The recruitment of new rainforest plants in the ecotone was most abundant in the initial year after fire. If this post‐fire pulse of recruitment is left undisturbed, it can facilitate the subsequent germination of additional rainforest species. The removal of grass cover, whether temporarily in the immediate post‐fire environment or once a developing rainforest mid strata shades out grasses, appears crucial to abundant rainforest recruitment. A variety of tropical rainforest species can persist under a frequent fire regime through resprouting. The difference in the mode of resprouting, between ground‐level coppicing rainforest plants and canopy resprouting eucalypt forest trees, is the critical mechanism that causes regular fire to maintain an open structure in eucalypt forests. The inability of rainforest species to maintain their height when fires fully scorch their crowns, temporarily resets the forest's open structure and delays the rainforest's ability to dominate through shading out grasses to transform the ecosystem into a closed forest.     

High and dry: post‐fire tree seedling establishment in subalpine forests decreases with post‐fire drought and large stand‐replacing burn patches

Aim Climate warming and increased wildfire activity are hypothesized to catalyse biogeographical shifts, reducing the resilience of fire‐prone forests world‐wide. Two key mechanisms underpinning hypotheses are: (1) reduced seed availability in large stand‐replacing burn patches, and (2) reduced seedling establishment/survival after post‐fire drought. We tested for regional evidence consistent with these mechanisms in an extensive fire‐prone forest biome by assessing post‐fire tree seedling establishment, a key indicator of forest resilience. Location Subalpine forests, US Rocky Mountains. Methods We analysed post‐fire tree seedling establishment from 184 field plots where stand‐replacing forest fires were followed by varying post‐fire climate conditions. Generalized linear mixed models tested how establishment rates varied with post‐fire drought severity and distance to seed source (among other relevant factors) for tree species with contrasting post‐fire regeneration adaptations. Results Total post‐fire tree seedling establishment (all species combined) declined sharply with greater post‐fire drought severity and with greater distance to seed sources (i.e. the interior of burn patches). Effects varied among key species groups. For conifers that dominate present‐day subalpine forests (Picea engelmannii, Abies lasiocarpa), post‐fire seedling establishment declined sharply with both factors. One exception was serotinous Pinus contorta, which did not vary with either factor. For montane species expected to move upslope under future climate change (Larix occidentalis, Pseudotsuga menziesii, Populus tremuloides) and upper treeline species (Pinus albicaulis), establishment was unrelated to either factor. Greater post‐fire tree seedling establishment on cooler/wetter aspects suggested local topographic refugia during post‐fire droughts. Main conclusions If future drought and wildfire patterns manifest as expected, post‐fire tree seedling establishment of species that currently characterize subalpine forests could be substantially reduced. Compensatory increases from lower montane and upper treeline species may partially offset these reductions, but our data suggest important near‐ to mid‐term shifts in the composition and structure of high‐elevation forests under continued climate warming and increased wildfire activity.     

Prevalence of Tree Regeneration by Sprouting and Seeding Along a Rainfall Gradient in Hawai'i

Drought stress in tropical dry forests is thought to result in greater asexual regeneration via vegetative sprouting ( e.g ., basal, root, and branch layering) than occurs in moister tropical forests. We tested this hypothesis by examining the prevalence of tree sprouting and seeding in tropical forests located along a rainfall gradient on the island of Hawai'i. Additionally, we examined the potential for novel disturbance, feral pig Sus scrofa rooting and trampling, to alter patterns in tree regeneration mode. We found greater sprouting (in terms of relative density and basal area) in dry forests than in mesic and wet forests, supporting the hypothesis. We also found that feral pig disturbance is negatively correlated with the relative density and basal area of seedlings in wet forests, but is positively correlated with the relative importance of sprouting, and the richness and diversity of sprouting species. Our results suggest rainfall regimes may be an important factor controlling broad-scale patterns in tree regeneration mode, and that exotic ungulates can significantly modify such patterns with potential consequences for the structure and dynamics of tree populations and communities.     

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.     

Rainfall seasonality and drought performance shape the distribution of tropical tree species in Ghana

Tree species distribution in lowland tropical forests is strongly associated with rainfall amount and distribution. Not only plant water availability, but also irradiance, soil fertility, and pest pressure covary along rainfall gradients. To assess the role of water availability in shaping species distribution, we carried out a reciprocal transplanting experiment in gaps in a dry and a wet forest site in Ghana, using 2,670 seedlings of 23 tree species belonging to three contrasting rainfall distributions groups (dry species, ubiquitous species, and wet species). We evaluated seasonal patterns in climatic conditions, seedling physiology and performance (survival and growth) over a 2‐year period and related seedling performance to species distribution along Ghana's rainfall gradient. The dry forest site had, compared to the wet forest, higher irradiance, and soil nutrient availability and experienced stronger atmospheric drought (2.0 vs. 0.6 kPa vapor pressure deficit) and reduced soil water potential (?5.0 vs. ?0.6 MPa soil water potential) during the dry season. In both forests, dry species showed significantly higher stomatal conductance and lower leaf water potential, than wet species, and in the dry forest, dry species also realized higher drought survival and growth rate than wet species. Dry species are therefore more drought tolerant, and unlike the wet forest species, they achieve a home advantage. Species drought performance in the dry forest relative to the wet forest significantly predicted species position on the rainfall gradient in Ghana, indicating that the ability to grow and survive better in dry forests and during dry seasons may allow species to occur in low rainfall areas. Drought is therefore an important environmental filter that influences forest composition and dynamics. Currently, many tropical forests experience increase in frequency and intensity of droughts, and our results suggest that this may lead to reduction in tree productivity and shifts in species distribution.     

Recovery from clearing,cyclone and fire in rain forests of Tonga,South Pacific: Vegetation dynamics 1995–2005

Abstract In late 2001 a category 3 cyclone impacted forest plots that were established in Tonga in 1995, and additionally, one plot was accidentally burned by an escaped land‐clearing fire. Subsequent surveys provide observations of 10 years of forest dynamics in this poorly studied region, and the first reported observations of large interannual variation in juvenile (seedling and sapling) abundance in the western tropical Pacific. The severely disturbed (burned) plot was initially colonized by a non‐native early pioneer, Carica papaya L., but 3.5 years later a native pioneer, Macaranga harveyana (Muell. Arg.) Muell. Arg., was the most abundant tree species. The seedling layer included some long‐lived pioneers and shade‐tolerant species. Two mature forest plots affected only by the cyclone changed very little over a decade. Late‐successional shade‐tolerant species that dominated the overstory were also abundant as seedlings and saplings. This is in contrast with a 30‐ to 40‐year‐old, formerly cultivated, secondary forest plot that still shows no recruitment of late‐successional dominants, in spite of the proximity of remnant forest patches. This study suggests differing pathways of succession following shifting cultivation versus cyclone and fire disturbances in Tonga. Land use legacies appear to have a long‐lasting effect on community composition.     

When is a ‘forest’ a savanna,and why does it matter?

Savannas are defined based on vegetation structure, the central concept being a discontinuous tree cover in a continuous grass understorey. However, at the high‐rainfall end of the tropical savanna biome, where heavily wooded mesic savannas begin to structurally resemble forests, or where tropical forests are degraded such that they open out to structurally resemble savannas, vegetation structure alone may be inadequate to distinguish mesic savanna from forest. Additional knowledge of the functional differences between these ecosystems which contrast sharply in their evolutionary and ecological history is required. Specifically, we suggest that tropical mesic savannas are predominantly mixed tree–C₄ grass systems defined by fire tolerance and shade intolerance of their species, while forests, from which C₄ grasses are largely absent, have species that are mostly fire intolerant and shade tolerant. Using this framework, we identify a suite of morphological, physiological and life‐history traits that are likely to differ between tropical mesic savanna and forest species. We suggest that these traits can be used to distinguish between these ecosystems and thereby aid their appropriate management and conservation. We also suggest that many areas in South Asia classified as tropical dry forests, but characterized by fire‐resistant tree species in a C₄ grass‐dominated understorey, would be better classified as mesic savannas requiring fire and light to maintain the unique mix of species that characterize them.     

Is the spatial pattern of a tree population in a seasonally dry tropical climate explained by density‐dependent mortality?

Spatial pattern of tropical plants is initially generated by limited seed dispersal, but the role of density‐dependent and independent mechanisms as modifiers of these patterns across ontogeny is poorly understood. We investigated whether density‐dependent mortality (DDM) and environmental heterogeneity can drive spatial pattern across the ontogeny of a tree in a seasonally dry tropical climate. We used Moran's I correlograms and spatial analysis by distance indices (SADIE) to assess the spatial patterns of the pre‐ and post‐germinative stages of Cordia oncocalyx (Boraginaceae), an abundant tree endemic in the deciduous thorny woodland in the northeastern Brazilian semiarid region. We also used RDA to analyse the effect of DDM and environmental heterogeneity (measured by microtopography and canopy openness) in the mortality and recruitment. Seeds, seedlings, juveniles and adults showed aggregated spatial patterns; infants and immatures were randomly distributed; adults, seeds and seedlings attracted each other while adult, juveniles and immatures repulsed each other. Infant and seedling mortality rates were related to DDM and the recruitment from infant to juvenile was more influenced by spatial heterogeneity. Attraction was determined by local dispersal; repulsion was related to DDM and environment heterogeneity, which allowed the return to aggregation in adult stage. Together, these results indicated that spatial pattern can change across ontogeny, in which the initial stages are responsive to DDM and the final stages are influenced by spatial heterogeneity.     

Wood Decomposition of Cyrilla racemiflora (Cyrillaceae) in Puerto Rican Dry and Wet Forests: A 13‐year Case Study1

We studied the decomposition of Cyrilla racemiflora logs over a 13‐yr period in tropical dry and wet forests in Puerto Rico. The mean mass loss, ratio of soft to hard wood, nutrient concentrations, and the diversity of wood‐inhabiting organisms were greater in logs decomposing in the dry forest than in the wet forest. Termites were also more abundant in the logs collected from the tropical dry forest than the tropical wet forest. High moisture content and a low animal diversity on the logs in the wet forest seem to retard wood decay in this habitat. Wood decay rates in the tropical dry forest can be related to the high diversity of species and functional groups of wood‐inhabiting organisms.     

Regeneration of Juvenile Woody Plants after Fire in a Seasonally Dry Tropical Forest of Southern India

Woody tree species in seasonally dry tropical forests are known to have traits that help them to recover from recurring disturbances such as fire. Two such traits are resprouting and rapid post‐fire growth. We compared survival and growth rates of regenerating small‐sized individuals (juveniles) of woody tree species after dry season fire (February–March) at eight adjacent pairs of burnt and unburnt transects in a seasonally dry tropical forest in southern India. Juveniles were monitored at 3‐mo intervals between August 2009 and August 2010. High juvenile survivorship (>95%) was observed in both burnt and unburnt areas. Growth rates of juveniles, analyzed at the community level as well as for a few species individually (especially fast‐growing ones), were distinctly higher in burnt areas compared to unburnt areas after a fire event, particularly during the pre‐monsoon season immediately after a fire. Rapid growth by juveniles soon after a fire may be due to lowered competition from other vegetative forms such as grasses, possibly aided by the availability of resources stored belowground. Such an adaptation would allow a juvenile bank to be retained in the understory of a dry forest, from where individuals can grow to a possible fire‐tolerant size during favorable conditions.     

Convergence in growth responses of tropical trees to climate driven by water stress

Widely documented for temperate and cold forests in both hemispheres, variations in tree growth responses to climate along environmental gradients have rarely been investigated in the tropics. Seven tree‐ring chronologies of Centrolobium microchaete (Fabaceae) in the Cerrado tropical forests of Bolivia are used to determine the growth responses to climate along a precipitation gradient. Chronologies are distributed from the humid Guarayos forests (annual precipitation > 1600 mm) in the transition to the Amazonia to the dry‐mesic Chiquitos forests (annual precipitation < 1200 mm) in the proximity to the dry Chaco. On a large spatial scale, radial growth is positively influenced by rainfall and negatively by temperature at the end of the dry season. However, this regional pattern in climate‐tree growth relationship shows differences along the precipitation gradient. Relationships with climate are highly significant and extend over longer periods of the year in sites with low rainfall and extremely severe dry seasons. At wet sites, larger water soil capacity and endogenous forest dynamics partially mask the direct influence of climate on tree growth. Stronger similarities in tree‐growth responses to climate occur between sites in the dry Central Chiquitos and in the transition to the Guarayos forests. In contrast, the relationships show fewer similarities between sites in the humid Guarayos. We conclude that growth responses to climate in the tropics are more similar between sites with limited rainfall and severe and prolonged dry seasons. Our study points to a convergence in the patterns of growth responses of tropical trees to climate, modulated by scarce rainfall and marked seasonality. The negative impact of water deficits on tree physiological processes induces not only the documented reduction in forest species richness, but also a convergence in tree‐growth responses to climate in dry tropical forests.     

Seedling Traits Determine Drought Tolerance of Tropical Tree Species

Water availability is the most important factor determining tree species distribution in the tropics, but the underlying mechanisms are still not clear. In this study, we compared functional traits of 38 tropical tree species from dry and moist forest, and quantified their ability to survive drought in a dry‐down experiment in which wilting and survival were monitored. We evaluated how seedling traits affect drought survival, and how drought survival determines species distribution along the rainfall gradient. Dry forest species tended to have compound leaves, high stem dry matter content (stem dry mass/fresh mass), and low leaf area ratio, suggesting that reduction of transpiration and avoidance of xylem cavitation are important for their success. Three functional groups were identified based on the seedling traits: (1) drought avoiders with a deciduous leaf habitat and taproots; (2) drought resisters with tough tissues (i.e., a high dry matter content); and (3) light‐demanding moist forest species with a large belowground foraging capacity. Dry forest species had a longer drought survival time (62 d) than moist forest species (25 d). Deciduousness explained 69 percent of interspecific variation in drought survival. Among evergreen species, stem density explained 20 percent of the drought survival. Drought survival was not related to species distribution along the rainfall gradient, because it was mainly determined by deciduousness, and species with deciduous seedlings are found in both dry and moist forests. Among evergreen species, drought survival explained 28 percent of the variation in species position along the rainfall gradient. This suggests that, apart from drought tolerance, other factors such as history, dispersal limitation, shade tolerance, and fire shape species distribution patterns along the rainfall gradient.     

Termite diversity in Neotropical dry forests of Colombia and the potential role of rainfall in structuring termite diversity

Termites are ecosystem engineers that play an important role in the biotransformation and re‐distribution of nutrients in soil. The dry forests are endemic repositories, but at same time, they are most threatened by extensive livestock and crop farming, fires, and climate change. In Colombia, the best‐protected dry forests are located in the north. The termite fauna of dry forests are poorly known. The aim was to identify the termite species occurring in tropical dry forests of the Colombian Caribbean coast in relation to diet and precipitation, temperature, elevation, and soil properties. A total of 32 species in 1,103 occurrences were found. Termitidae accounted for 78% of the species richness with the Anoplotermes‐group, Microcerotermes, and Nasutitermes being the dominant genera. Differences in species composition and abundance were found across sites. These differences may be linked to anthropogenic disturbance and polygyny and polydomy. Strikingly, our highest elevation site (334 m) had the highest species richness much higher than the two lower elevation sites. This implies an inversion of the common elevation‐diversity gradient, also found for termites which can be explained by increasing precipitation with elevation in the dry forest. An analysis of termite species richness at the global scale confirms that termite species richness correlates positively with rainfall. Hence, rainfall seems to positively affect termite diversity. In line, the studied Colombian tropical dry forests had low diversity compared to rain forests. A decline of species‐rich soil‐feeding termites with increasing aridity may explain why the highest termite diversity occurs in humid tropical rain forests. Abstract in Spanish is available with online material.     

Non‐Native Grass Removal and Shade Increase Soil Moisture and Seedling Performance during Hawaiian Dry Forest Restoration

Invasive non‐native species can create especially problematic restoration barriers in subtropical and tropical dry forests. Native dry forests in Hawaii presently cover less than 10% of their original area. Many sites that historically supported dry forest are now completely dominated by non‐native species, particularly grasses. Within a grass‐dominated site in leeward Hawaii, we explored the mechanisms by which non‐native Pennisetum setaceum, African fountain grass, limits seedlings of native species. We planted 1,800 seedlings of five native trees, three native shrubs, and two native vines into a factorial field experiment to examine the effects of grass removal (bulldozed vs. clipped plus herbicide vs. control), shade (60% shade vs. full sun), and water (supplemental vs. ambient) on seedling survival, growth, and physiology. Both grass removal and shade independently increased survival and growth, as well as soil moisture. Seedling survival and relative growth rate were also significantly dependent on soil moisture. These results suggest that altering soil moisture may be one of the primary mechanisms by which grasses limit native seedlings. Grass removal increased foliar nitrogen content of seedlings, which resulted in an increase in leaf‐level photosynthesis and intrinsic water use efficiency. Thus in the absence of grasses, native species showed increased productivity and resource acquisition. We conclude that the combination of grass removal and shading may be an effective approach to the restoration of degraded tropical dry forests in Hawaii and other ecologically similar ecosystems.     

Effects of a short fire‐return interval on resources and assemblage structure of birds in a tropical savanna

Fire frequency is a key land management issue, particularly in tropical savannas where fire is widely used and fire recurrence times are often short. We used an extended Before‐After‐Control‐Impact design to examine the impacts of repeated wet‐season burning for weed control on bird assemblages in a tropical savanna in north Queensland, Australia. Experimentally replicated fire treatments (unburnt, singularly bunt, twice burnt), in two habitats (riparian and adjacent open woodland), were surveyed over 3 years (1 year before the second burn, 1 year post the second burn, 2 years post the second burn) to examine responses of birds to a rapid recurrence of fire. Following the second burn, species richness and overall bird abundance were lower in the twice‐burnt sites than either the unburnt or singularly burnt sites. Feeding group composition varied across year of survey, but within each year, feeding guilds grouped according to fire treatment. In particular, abundance of frugivores and insectivores was lower in twice‐burnt sites, probably because of the decline of a native shrub that produces fleshy fruits, Carissa ovata. Although broader climatic variability may ultimately determine overall bird assemblages, our results show that a short fire‐return interval will substantially influence bird responses at a local scale. Considering that fire is frequently used as a land management tool, our results emphasize the importance of determining appropriate fire‐free intervals.     

Edge Effects Act Differentially on Multiple Early Regeneration Stages of a Shade‐tolerant Tree Tapirira mexicana

Forest fragmentation is pervasive in tropical landscapes, and one pathway by which fragmentation may negatively impact populations is via edge effects. Early life‐stages are particularly important for species regeneration as they act as bottlenecks, but how edge effects may act differentially on different life‐stages is unknown. This study evaluated edge effects on multiple early life‐stages of a currently common animal‐dispersed, shade‐tolerant tree Tapirira mexicana (Anacardiaceae). The study was conducted in tropical premontane wet forest fragments in a highly deforested region of Costa Rica. The stages assessed were pre‐dispersal predation, primary dispersal, post‐dispersal predation, secondary dispersal, ex situ germination, in situ seed longevity, first and second year seedling abundance, second year seedling survivorship, and basal diameter growth. Results showed that impacts of edge effects were not equal across stages, but were limited to specific stages and times. One stage which may act as a bottleneck for species regeneration was pre‐dispersal predation. Over 60 percent of the seeds were predated by larvae, and predation was higher near the edge than interior habitat. Seeds lost viability within 10 d in the forest. Germination to first year seedling stage was also lower near edges, but such effect was eliminated within a year after that. Primary dispersal, seedling survivorship, and growth were not affected by proximity to edges, and both secondary dispersal and post‐dispersal predation were rare. This study demonstrates that current population abundance may not guarantee future species persistence and the importance of considering multiple life‐stages for a comprehensive assessment of forest fragmentation effects on species regeneration.     

Differential seedling regeneration patterns across forest–grassland ecotones in two tropical treeline species (Polylepis spp.)

Successful forest expansion into grassland can be limited by seed dispersal and adverse conditions for tree seedlings in the grassland environment. In the high‐elevation Andes, human‐induced fragmentation has exacerbated the patchy distribution of Polylepis forests, threatening their unique biological communities and spurring restoration interest. Studies of Polylepis forest extent in Peru suggest that forest borders have remained stable over the past century despite decreasing anthropogenic disturbance, suggesting that tree seedling recruitment is being limited in the open grassland habitat. We studied natural seedling dispersion patterns of Polylepis sericea and Polylepis weberbaueri (Rosaceae) at forest–grassland edges across a range of environmental conditions to examine seedling recruitment and colonization of grasslands in Huascaran National Park (Peru). Using data from 2367 seedlings found in 48 forest–grassland edge plots (15 m × 15 m) at forest patches between 3900–4500 masl, we employed generalized mixed modelling to identify the significant associations of seedling densities with environmental covariates. In addition, we compared these associations to patterns of adult presence on the landscape. Seedling densities were associated with a combination of variables varying within (distance to forest edge) and among (elevation and dry season solar irradiation) plots across the landscape. For both species, seedling densities decreased with increasing distance away from the forest in a manner consistent with short‐distance seed dispersal by wind. Our results suggest that such short‐distance dispersal may slow forest expansion, but that there also appear to be substantial post‐dispersal limitations to seedling establishment in the grassland. Polylepis sericea densities decreased with elevation, while P. weberbaueri increased with elevation and decreased with solar irradiation. Associations of adult presence with elevation and solar irradiation mirrored those of seedling densities. Management of areas with forest patches dominated by these species should consider these differences in their environmental tolerances, particularly during species selection and zonation for reforestation.     

Fire regimes in north-eastern Cambodian monsoonal forests, with a 9300-year sediment charcoal record

Aim To provide insights concerning changes in fire regime in north‐eastern Cambodia over the course of the Holocene, and discuss implications of these long‐term data for fire management in the present day. Location Southern Ratanakiri Province, north‐eastern Cambodia. The lake sites sampled here are embedded in a mosaic of mostly open, strongly deciduous dipterocarp forest, with patches of riparian, semi‐evergreen and evergreen forests. Methods Background information on the environmental and cultural setting comes from informal and semi‐structured interviews of local villagers to determine present‐day burning patterns and customs. Primary data come from analysis of changes in charcoal concentration within sediments from small, closed basin lakes. Charcoal data are compared with changes in pollen and sediment physical characteristics, and to present‐day local customs, to infer or speculate on changes in human use of fire. Results Interviews with local people reveal two general types of human‐induced fires, one type for swidden cultivation in denser forests, the other type for clearance of ground layer vegetation in more open forests. A 9300‐year sediment record of microscopic charcoal deposition shows strongest fire activity ending by 8000 years ago, and the remainder of the early Holocene reflecting a strong summer monsoon and low fire activity. Beginning c. 5500 years ago, forest disturbance and fire activity increased. A subtle change in the record at c. 3500 years ago and more marked change at c. 2500 years ago suggest that fire frequency, and maybe human control over fire, became more important during that period and continuing up to the present. Main conclusions With this type of empirical data from only one site, it is impossible to make accurate conclusions about long‐term human impacts from burning. However, this record does show that present‐day charcoal input from fire activity is among the lowest for the last 9300 years. Considered together with other changes in the record and with present‐day customs, there is a suggestion that anthropogenic fire is an adaptation to the monsoonal environment, and may be conservative of forest cover in open forest formations. This long‐term perspective on the role of indigenous land‐use customs in landscape evolution should be considered in forest management and biological conservation, as it differs significantly from the traditional rationale for policies of fire suppression in tropical forests.