Early Secondary Forest Research Articles

Demographic and net primary productivity dynamics of primary and secondary tropical forests in Southwest China under a changing climate

AbstractTropical forests are major carbon sinks on the Earth's land surface. However, our understanding of how the demographic rate and carbon sink capacities of tropical forests respond to climate change remains limited. In this study, we investigated the impacts of environmental drivers on forest growth, mortality, recruitment, and stem net primary productivity (NPPstem) over 16 years at five tropical forest plots in Xishuangbanna, Southwest China. These plots are along a successional gradient spanning three tropical secondary forests (tropical secondary forest‐1 [TSF‐1], tropical secondary forest‐2 [TSF‐2], and tropical secondary forest‐3 [TSF‐3]) and two primary forests (tropical rainforest [TRF] and tropical karst forest [TKF]). Our results showed that early successional secondary forests (TSF‐2 and TSF‐3) had higher diameter growth rates and relative mortality rates. An extreme drought event during 2009–2010 reduced the growth rate, relative recruitment rate, and NPPstem for most plots while increasing mortality in early successional forest plots. We observed significant negative effects of maximum temperature (Tmax) on NPPstem and diameter growth rate across all plots. Additionally, we found that precipitation had significant positive effects on diameter growth rate across all plots. Furthermore, tree mortality increased with rising Tmax, whereas precipitation significantly enhanced tree recruitment. Our findings highlight the vulnerability of tree growth, mortality, recruitment, and productivity in tropical forests to extreme drought events in Southwest China. Continued climate warming and more frequent droughts will induce higher mortality rates and impede growth, thus reducing the carbon sink capacity of tropical forests, especially in early successional stage tropical secondary forests.

Strong floristic distinctiveness across Neotropical successional forests.

Forests that regrow naturally on abandoned fields are important for restoring biodiversity and ecosystem services, but can they also preserve the distinct regional tree floras? Using the floristic composition of 1215 early successional forests (≤20 years) in 75 human-modified landscapes across the Neotropic realm, we identified 14 distinct floristic groups, with a between-group dissimilarity of 0.97. Floristic groups were associated with location, bioregions, soil pH, temperature seasonality, and water availability. Hence, there is large continental-scale variation in the species composition of early successional forests, which is mainly associated with biogeographic and environmental factors but not with human disturbance indicators. This floristic distinctiveness is partially driven by regionally restricted species belonging to widespread genera. Early secondary forests contribute therefore to restoring and conserving the distinctiveness of bioregions across the Neotropical realm, and forest restoration initiatives should use local species to assure that these distinct floras are maintained.

From canopy complementarity to asymmetric competition: The negative relationship between structural diversity and productivity during succession

Abstract Positive relationships between structural diversity and forest productivity have been documented in controlled experiments and early secondary forests, however, negative relationships have also been observed in late successional forests. The mechanisms causing observed relationships between structural diversity and productivity are not well‐established, but complementarity among crowns and asymmetric competition have been suggested. We used LiDAR and repeated census data to examine the relationship between canopy structural diversity and productivity in nine 1‐ha subtropical forest plots along a disturbance gradient in southeastern China. We quantified the relative importance of community composition, species diversity, canopy structural diversity, leaf area index (LAI) and disturbance regime on productivity using piecewise structural equation modelling. We also tested how vertical leaf area distribution affected productivity. Contrary to many prior observations, we found a negative relationship between canopy structural diversity and forest productivity. The negative effect may stem from asymmetric competition between overstorey and understorey leaves, leading to a lower leaf area efficiency (i.e. wood production per leaf area). Asymmetric competition was suggested by a negative relationship between understorey leaf area and total productivity. Changes in community composition over the disturbance gradient, but not species diversity, had a significant effect on productivity. Synthesis. Our study suggests that leaf area and canopy structural diversity have contrasting effects on productivity in this subtropical forest, and this needs to be considered when estimating rates of carbon sequestration in secondary forests. The negative effect of asymmetric competition on productivity is comparable to that of the shift in species composition over succession, highlighting the role of canopy structural diversity in shaping forest productivity.

Selective logging in a chronosequence of Atlantic Forest: drivers and impacts on biodiversity and ecosystem services

Selective logging impacts biodiversity and ecosystem services in forest ecosystems, but we know little about its main drivers in the Atlantic Forest. We investigated selective logging along a chronosequence (mature, late secondary and early secondary forests) in a State Park in Pernambuco, Brazil, and hypothesised that it is driven by variables of supply (forest age, density, richness and biomass of living trees) and access (nearest edge and declivity). Selective logging was described by richness, density and biomass of logged trees. We predicted the relationship of logging to be positive with supply and negative with the distance of access. Logged trees comprised 267 stumps, 55 species and 5.11 Mg.ha-1 in one year, corresponding to 2.8%, 20.8% and 0.37% of living trees density, richness and biomass. Selective logging was the highest in richness in mature forest, influenced by access and forest age. Access influenced higher species removal in the early-secondary forest, despite its lower richness, while the lowest logging values were recorded in the late-secondary forest, regardless of its higher supply than early-secondary forest. Logging occurs in more accessible areas, where tree species exploitation will depend on the available supply. In this scenario, integrated actions for biodiversity and ecosystem services conservation should account for socioeconomic demands, vigilance and control.

Effects of forest succession on the richness and composition of Zingiberales in a forest fragment in the southwestern Amazon

Tropical forests have been increasingly modified by human activities and the forest recovery through succession has caused an increase in the amount of secondary forests in the landscape. Little is known about changes in the richness and composition of non-woody species throughout the succession in tropical forests; therefore, the objective of this work was to evaluate the effects of forest succession on a community of herbs in the order Zingiberales. Zingiberales and soil were sampled and data on vegetation structure, including bamboo abundance, canopy opening, and basal area were collected from nine 80 × 90 m plots installed on the Catuaba Experimental Farm, Acre, representing three successional stages: early secondary forest, late secondary forest, and mature forest. Early secondary forest areas were experimentally deforested, burned, and sprayed with herbicide in the dry season of 2001 and the late secondary forest areas suffered deforestation followed by burning for agricultural cultivation between 1985 and 1986. A total of 3,831 individuals and 26 species distributed in nine genera and five families was registered. Both soil characteristics and vegetation structure variables showed significant differences among the successional stages. The richness of Zingiberales was lower in the early secondary forest areas and did not differ among the other successional stages. Canopy opening was the variable that best explained the variation in the richness of Zingiberales among the areas. The composition of Zingiberales differed among the successional stages, with the late secondary forest and mature forest stages being most similar. The soil characteristics, canopy opening, bamboo abundance and basal area were the variables that best explained a variation in the composition of Zingiberales. In the areas of initial secondary forest the group of dominant species was composed of Renealmia breviscapa, Calathea altissima and Heliconia rostrata, in the areas of late secondary forest by Chamaecostus lanceolatus Calathea polytricha, Calathea sp.1 and in the areas of mature forest by Heliconia acuminata, Calathea mansonis and Phenakospermum guyannense. These results show that the disturbance caused by cutting, burning, and herbicide application alters the community of Zingiberales. These data also highlight the importance of late secondary and mature forests in maintaining and recovering biodiversity.

Spatial pattern dynamics among co-dominant populations in early secondary forests in Southwest China

The canopy of subtropical natural forests usually consists of several co-dominant populations (CDPs), which play a crucial role in forest structure, formation of the forest environment, and ecological function. However, little attention has been given to changes in spatial patterns in CDPs during natural succession. Cyclobalanopsis glauca (Thunb.) Oerst., Quercus variabilis Blume, and Pinus yunnanensis var. tenuifolia W.C. Cheng & Y.W. Law are canopy species that form CDPs in zonal forests along the Nanpan River in southwest China. We used the g(r) function and its bivariate distribution model, g12(r), which is based on distances between pairs of points, to explore the dynamics of the three CDP species with respect to distribution patterns and spatial correlations in two secondary forests (one 30-year-old forest [30-YF] and one 57-year-old forest [57-YF]). The following key results were obtained: (1) there was a clumped pattern in the 30-YF, but the intensity of aggregation varied among populations and life stages. The distribution pattern gradually shifted to become random with longer succession time (i.e., 30-YF vs. 57-YF), expansion of the observation scale (r = 0–20 m), and at later life stages. (2) Aside from the mid-sized C. glauca trees and large P. yunnanensis trees, the trees repulsed each other at certain scales (r = 0–2, 5–6, 11–12, 14–16 m) in the 30-YF. Almost all of the life stages in the CDPs were independently correlated. This independent correlation was exacerbated by a longer succession time. (3) An increase in life stages and longer succession also promoted independent changes in intraspecific correlations. (4) Intraspecific correlations were stronger than interspecific correlations. Our results showed that reducing exclusive competition is essential to coexistence in CDPs. Inter- and intra-specific repulsion may occur at the same time, but intraspecific repulsion was the main driving force behind the random distributions and independent correlations.

Appraising forest diversity in the seasonally dry tropical region of the Gulf of Mexico

Seasonally dry tropical regions in the Neotropics are remarkably biodiverse and provide valuable ecosystem services. Thus, it is crucial to increase and update our information on the biodiversity still preserved within them, particularly in poorly studied areas such as the central coastal plain of the Gulf of Mexico, our study area. A total of 5,583 individuals belonging to 157 species, 113 genera, and 43 families were recorded in 29 forest patches (total sampling area = 8.7 ha). From the floristic composition of these patches, 6 vegetation types were identified: Tropical Dry Oak Forest, Tropical Deciduous Forest, Semi-deciduous Forest, Late Secondary Forest, Intermediate Secondary Forest and Early Secondary Forest. Spatial variation in composition was strongly related to edaphic variables (pH, organic matter, carbon content). Some patches had high local (α) diversity, but even more noteworthy was the distinctively high regional (β) diversity of all the patches together. In spite of the high degree of forest fragmentation in central Veracruz, our results show that it is essential to acknowledge the value of this region to biodiversity and the urgency of developing and implementing protection and management policies that ensure the ecological functions of the landscape and the sustainable development of human activities.

Bee diversity in secondary forests and coffee plantations in a transition between foothills and highlands in the Guatemalan Pacific Coast.

BackgroundAlthough conservation of pristine habitats is recognized in many countries as crucial for maintaining pollinator diversity, the contribution of secondary forest conservation is poorly recognized in the Latin American context, such as in Guatemala. San Lucas Tolimán (SLT) is a high-quality coffee production region from the Atitlan Province, which has the second highest deciduous forest cover in Guatemala and pristine forest is prioritized for conservation. In contrast, secondary forest protection is undetermined, since these forests are normally removed or strongly affected by coffee farming practices. This situation may affect the diversity of native pollinators, mainly bees, which usually rely on the secondary forest for food resources.MethodsWe conducted a study to investigate the importance of secondary forests around the SLT coffee plantations (Coffea arabica L.) for pollinators. We compared bee diversity (richness, abundance and composition) in secondary forests of different age and coffee plantations with diverse farming techniques. Being the first study of pollinators in Guatemalan coffee plantations, we also recorded data for an entire year (2013–2014) in order to describe bee seasonality.ResultsWe found significant differences in bee diversity between the coffee plantations and secondary forests, particularly early secondary forests showed higher bee abundances but diversity indices were similar between different vegetation type plots. In the early dry season, secondary forests showed the greatest native bee diversity. During the late dry season, when the coffee was flowering, honey bees were dominant in the same plots. This study provides important management insights to support the conservation of pollinators, since our results offer guidelines to improve coffee production by increasing native pollinator diversity.

Discolouring the Amazon Rainforest: how deforestation is affecting butterfly coloration

Butterflies are among the most colourful organisms in the world and colour plays a central role in many of their life-history strategies. However, the efficacy of coloration strategies in these and other animals could be affected by sudden environmental changes, including anthropogenic disturbances such as habitat loss and fragmentation. Here we investigate the effect of forest disturbance gradients on the colours of fruit-feeding butterflies in the Amazon Rainforest. The disturbance gradients tested represented habitat-size (continuous primary forests versus forest fragments of 1, 10 and 100 ha) and succession gradients (continuous primary forests, 30 year old secondary forests, and three year old early successional forests). Using digital image analysis, we obtained intrinsic measures of butterfly colour patches corresponding to hue, saturation, brightness, in addition to measures of the contrast among patches and of the overall wing-colour diversity corresponding to 220 individuals, belonging to 60 species. Our results showed that butterflies in the secondary forest and continuous primary forest are more colourful than those found in early succession and fragments of forests. Individuals occurring in forests of early succession showed higher average values of hue and saturation, but lower brightness. Accompanying changes in colour composition, wing-colour diversity among species was lower in human-disturbed habitats, such as those of early forest succession and secondary forest. Forest fragments have smaller effects on butterfly colour composition, indicating that well-structured forest habitats can house butterfly assemblages with more diverse phenotypic features and colours. We show how high deforestation rates in recent years is linked with negative changes in functional coloration strategies (e.g. camouflage, warning colours), something that has to date been poorly explored or demonstrated for butterflies. Specifically, human interference has apparently placed butterflies under strong selection for lower diversity in their colours and range of defensive strategies. Those species that are most colourful are the first to be locally extinguished, likely due to removal of native vegetation and increased exposure to predators, and more broadly owing to inhospitable environmental conditions. This illustrates an accelerated loss of local fauna and a “discolouration” of the Amazonian butterflies due to anthropogenic impacts.

Species richness, forest types and regeneration of Schima in the subtropical forest ecosystem of Yunnan, southwestern China

BackgroundSchima genus of Theaceae is confined to subtropics and tropics of South, East and Southeast Asia. Thirteen species of Schima are distributed in subtropical China. Many of them appear as dominant canopy species in the subtropical forests. To date, Schima species richness distribution patterns of China have remained unknown. Meanwhile, there has been a longtime debate as to whether forests dominated by Schima species are early or late successional forests. We aim to clarify Schima species richness patterns and these species’ roles in the forest succession and regeneration dynamics of the subtropical ecosystem in Yunnan Province, China.MethodWe mapped Schima species richness distribution patterns in China. Based on 71 vegetation plots, we analyzed forest characteristics, population structure, and regeneration dynamics of Schima species in Yunnan.ResultsYunnan was found to harbor the greatest richness and the highest rarity-weighted richness of Schima species in the subtropical regions of China. We classified five primary and six secondary forest types containing Schima species as one of dominants. Yunnan had the high floristic diversity and varying stand structure of forests containing Schima species. The Schima species studied generally had a sporadic regeneration type and a long life-span. Four species (Schima argentea, Schima villosa, Schima sinensis, Schima sericans) were shade-intolerant. But three species (Schima noronhae, Schima khasiana and Schima wallichii) were considered as bi-modal type species having shade-intolerant and shade-tolerant traits. Schima noronhae was seen to be a top dominant in late successional forests, while S. wallichii was found as a top-dominant in early or middle or late successional forests. S. khasiana, Schima villosa, Schima sinensis usually appeared as a top dominant in early or middle successional secondary forests, though they also presented as a second dominant in late-successional forests. Schima argentea and Schima sericans dominated only in the early or middle/seral successional forests. Schima species’ regeneration establishment depended mainly on forest canopy gap formation through moderate human and natural disturbances.ConclusionsYunnan has high species richness and rarity-weighted richness of Schima. Both moderate human and natural disturbances have provided regeneration niches for Schima species. Some of the Schima species studied as a second dominant (rare as the top-dominant) present in the late-successional forests. Some of them are more often as the top-dominant in early or middle successional forests, where as time goes by the dominance of Schima species would be replaced by their associated dominant taxa such as Castanopsis species.

Seasonally dry tropical forests of the Gulf of Mexico: A degraded landscape undergoing homogenization or a promising, resilient reservoir?

Seasonally dry tropical forests are amongst the most threatened ecosystems in the world due to severe and long-lasting anthropic disturbances. In this study, the spatial variation in plant diversity for the seasonally dry tropical region in central Veracruz was assessed at three different scales: among forested vegetation types, within each vegetation type and within forested patches. This region is characterized by extensive deforestation and today only 12% of its original forest cover remains. Of this, more than a third is early secondary forest. Woody vegetation was sampled in 29 forested patches (three 20 × 50 m transects per patch: 8.7 ha in total) belonging to six vegetation types. A total of 157 species were recorded (sample coverage >97%). Richness per patch was 3–33 spp., and 9 to 88 spp. per vegetation type. Species composition varied greatly across the region as indicated by the low values of compositional similarity (<35%) detected among all six vegetation types, particularly for the most abundant species. Also, relatively low similarity was detected between patches, including small patches of secondary vegetation that are contributing different species to regional diversity. The latter, when allowed to grow over 20 years contributed greatly to β-diversity. Thus, the spatial turnover of species at different scales is remarkably high, favoring the maintenance of a rich species pool at both the local and the regional scales and at the same time indicates that crucial ecological processes such as natural regeneration are still occurring within the region. This could indicate that despite the pervasive landscape modification and long history of forest fragmentation, the region is not currently experiencing the homogenization of its still remarkably rich woody flora.

Dung beetle responses to successional stages in the Amazon rainforest

Amazon rainforest is facing several threats due to anthropogenic activities causing loss of habitat, species, and ecosystem functions. However, several areas are being abandoned after anthropic use allowing secondary succession to occur, which can lead to the passive restoration of community parameters that have been lost. We aimed to investigate the effects of vegetation structure on dung beetle assemblages along a successional gradient in the western Amazon rainforest. Dung beetles were sampled and forest structure variables were measured using standardized protocols along primary, late secondary, and early secondary forests. We used a combination of generalized linear models and multivariate analyses to test for differences in assemblage composition and structure among successional stages and their relationships with vegetation variables. We found that primary forests have different species compositions from both late and early successional forests, with several species strongly associated with primary forests. Dung beetle abundance was higher in primary forests and influenced by variables describing the successional stages (i.e., tree density). Species turnover was the most important β-diversity component among and within each successional stage, with lower values in early secondary forests. Different pathways followed by secondary forests during forest succession may lead to increased species turnover similar to that found in primary forests. Biodiversity conservation will only work if secondary forests are allowed to recover to a late successional stage close to a primary forest stage. The loss of primary forests can cause an irreversible loss of species in need of conservation and with great functional importance in the Amazon rainforest.

Forest restoration in southern Amazonia: Soil preparation triggers natural regeneration

Forest regeneration in abandoned pastures in Amazonia has been well studied, but active restoration of non-resilient pastures has not. In this work, we evaluated large-scale active restoration of intensively used pastures in southern Amazonia, where the highest deforestation rates are observed. With the construction of the Jirau Dam in the Madeira river (state of Rondônia, Brazil), a 3000-ha forest buffer zone has been established. This area was previously covered by African pasture grasses for cattle ranching. Eight mixed-species planting sites with variable grass management and ranging from 6 to 60 months post-planting were measured three times over 2.5 years. We also tested a gradient of restoration intensity in an experimental planting: (i) no intervention (control), (ii) harrowing and herbicides to control grasses, and (iii) harrowing and herbicides plus tree planting. Our goals were to understand the initial trajectory of actively restored sites, the role of harrowing and herbicide application in triggering natural regeneration, and the role of seedling planting on the initial vegetation structure. All tree species ≥30 cm in height were sampled in five circular 10-m-radius plots per site. Plant cover was also monitored using the step-point method. At 18 months, stem density ranged from 2500 to 14,490 ind·ha−1, demonstrating that density increased suddenly in most sites through colonization, although this was highly variable. Tree cover reached 81% in five years, virtually eliminating grass cover after 36 months. Recruits contributed more to basal area than planted seedlings. Although 17 species, on average, were planted in restoration sites, the number of species at the sites steadily increased over time, at a rate of 7 species·yr−1 per 1570 m2. Cecropia spp. and Trema micrantha recruits had the highest stem densities and basal areas. Harrowing and grass control were enough to trigger succession in sites where natural regeneration was not taking place, shifting these sites to the highly resilient route of early secondary forest succession in the Amazon. Future restoration efforts should use a combination of methods, first evaluating the potential for natural regeneration and then gradually eliminating barriers.

Nitrogen Fixation Inputs in Pasture and Early Successional Forest in the Brazilian Amazon Region: Evidence From a Claybox Mesocosm Study

AbstractThe role of biological nitrogen fixation (BNF) during secondary forest succession and in tropical pastures has been investigated and debated for several decades. Here we present results of a replicated experimental study in a degraded cattle pasture of eastern Amazonia using mass balance and a 15N tracer in lined soil pit mesocosms with three treatments: (1) plant‐free control plots, (2) pasture grass Brachiaria brizantha, and (3) regrowth of early successional secondary forest species. Accumulation of N in grass biomass slightly exceeded estimates of net N mineralization from the plant‐free control plots but was within the margin of error, so inputs of BNF may not have been needed. In contrast, the secondary forest vegetation accumulated about 3 times as much biomass N annually as the net N mineralization estimate, suggesting at least some role for BNF. Based on isotopic and mass measurements of N‐fixing species, BNF was estimated to contribute at least 27 ± 3% of mean annual plant uptake in the secondary forest regrowth vegetation plots. Although BNF is probably important for recuperation of tropical secondary forests following land use change, the majority of the N taken up by both grasses and secondary forest regrowth arose from mineralization of the stocks of soil N.

Warming increases the sensitivity of seedling growth capacity to rainfall in six temperate deciduous tree species.

Predicting the effects of climate change on tree species and communities is critical for understanding the future state of our forested ecosystems. We used a fully factorial precipitation (three levels; ambient, -50 % ambient, +50 % ambient) by warming (four levels; up to +4 °C) experiment in an old-field ecosystem in the northeastern USA to study the climatic sensitivity of seedlings of six native tree species. We measured whole plant-level responses: survival, total leaf area (TLA), seedling insect herbivory damage, as well as leaf-level responses: specific leaf area (SLA), leaf-level water content (LWC), foliar nitrogen (N) concentration, foliar carbon (C) concentration and C:N ratio of each of these deciduous species in each treatment across a single growing season. We found that canopy warming dramatically increased the sensitivity of plant growth (measured as TLA) to rainfall across all species. Warm, dry conditions consistently reduced TLA and also reduced leaf C:N in four species (Acer rubrum, Betula lenta, Prunus serotina, Ulmus americana), primarily as a result of reduced foliar C, not increased foliar N. Interestingly, these conditions also harmed the other two species in different ways, increasing either mortality (Populus grandidentata) or herbivory (Quercus rubra). Specific leaf area and LWC varied across species, but did not show strong treatment responses. Our results indicate that, in the northeastern USA, dry years in a future warmer environment could have damaging effects on the growth capacity of these early secondary successional forests, through species-specific effects on leaf production (total leaves and leaf C), herbivory and mortality.

Land use as a filter for species composition in Amazonian secondary forests

AbstractQuestionsSecondary succession in the tropics can follow alternative pathways. Land‐use history is known to engender alternative successional communities, but the underlying mechanisms driving and sustaining divergence remain unclear. In this study we aim to answer the following questions: (1) does previous land use act as a filter for species composition in secondary forests; and (2) what are the relative roles of management practices, soil properties and landscape composition in determining species composition?LocationCentral Amazon, Brazil.MethodsWe sampled trees, shrubs and palms (≥1cm diameter) in 38 early secondary forests (5 yr after abandonment) located along gradients of land‐use intensity in five shifting cultivation landscapes. We measured the diameter and height of each sampled plant, identified it to species or morpho‐species level and checked if it was resprouting or not. At each secondary forest we also collected soil samples for chemical and physical analyses and estimated the amount of old‐growth forest surrounding it (landscape composition).ResultsWe found that previous land‐use intensity determined species composition. With increasing land‐use intensity, management practices of cut‐and‐burn and associated reduction in soil quality filtered out seed‐dependent species and favoured strong sprouters and species that can cope with low nutrient availability. Landscape composition had a weak effect on species assemblages. We found specific species assemblages and indicator species associated with different levels of previous land‐use intensity. As a consequence of these local filters, species α‐ and β‐diversity decreased and therefore early successional communities became more similar to each other.ConclusionSpecies composition of successional forests is strongly determined by different land‐use intensities. Dispersal limitation has a limited effect on determining the composition of the dominant species. Filtering effects of management practices and soil quality determine the species dominating the canopy at early stages of succession and narrow down the range of species able to colonize and establish. This study highlights how land use shapes successional communities and suggests that alternative successional pathways are determined at early stages of succession. Therefore, accounting for land‐use history is crucial to improve the understanding of tropical secondary succession. We present a list of indicator species for different levels of previous land‐use intensity that can be used to support conservation and restoration decisions in the Amazon.

Regeneration response of Brazilian Atlantic Forest woody species to four years of Megathyrsus maximus removal

Guinea-grass (Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs – Poaceae) is an invasive C4 grass that known to slow ecological succession in restoration sites. This study aimed to evaluate the responses of the woody species and M. maximus itself to manual removal in a 20-year-old reforestation site. Forty-five 5×5-m plots were established in 2008 and evaluated until 2012. The plots were divided into three treatments: control (CON), manual removal for one year (MR1), and manual removal for two years (MR2). All individuals of woody species >10cm were sampled. Canopy cover, grass cover, and the number of seedlings of M. maximus were also recorded. After the first weeding, M. maximus seedlings were manually uprooted every four months, for a total of three times in MR1 (2008–2009) and six times in MR2 (2008–2010). After the manual removal was stopped, the seedlings of M. maximus were counted and were allowed to grow in order to assess its reestablishment potential. The number of new grass seedlings decreased drastically after the first year with repeated removals and did not differ between removal treatments at any time, even after removals halted, indicating that one year of removal was sufficient to displace the grass. With the exclusion of Guinea-grass, an increase in the abundance and richness of other exotic species was observed until the second year. However, the increase in canopy cover during the four years likely benefited native woody species and impaired M. maximus and other exotics. In addition, after four years, although the woody species richness did not differ between the three treatments, the total abundance and pioneer species richness were higher in both removal treatments. These findings suggest that the grass slows ecological succession. However, both the increase in canopy cover and decrease in grass cover indicate that, in the absence of fire, native vegetation will suppress Guinea-grass. Furthermore, grass removal from the understory of early secondary forests and reforestations can be used to accelerate succession, reducing both fire risk and failures of ecological restoration initiatives.

The home range and multi-scale habitat selection of the threatened maned three-toed sloth (Bradypus torquatus)

Habitat selection is a scale-dependent process of paramount importance to the understanding of how species deal with environmental variation. This process has practical implications for wildlife conservation, aiding in the identification of key resources for animals and in the definition of scales relevant to the proposal of practical conservation actions. In this study, we investigated in different spatial scales the habitat selection of the maned three-toed sloth (Bradypus torquatus), a threatened and endemic arboreal folivore of the Atlantic rainforest (vulnerable, sensu IUCN). We radio-tracked and monitored seven sloths for 18 months in landscapes of Southern Bahia, Brazil, the current core region of the species’ distribution. The average values of the home-range estimates were low, but varied considerably among individuals regardless of the estimator (from 0.95 to 27.8ha, MCP method, and from 0.39 to 21.52ha, fixed kernel method). At the landscape scale, the maned sloths preferred early secondary forest and shade cacao plantations, avoided open areas, and occupied late secondary forest as expected compared to its availability. At the home range scale, however, the sloths did not show preference for any forest category, though, again, avoided open areas. At smaller spatial scales, the sloths were highly selective towards forest patches characterized by complex vegetation structures (i.e., areas with a high density of trees, closed and dense canopies), and selected large trees with lianas and bromeliads and also with connected crowns. The high selectivity observed at finer scales appeared to be the result of limited spatial perception and experience due to the species’ characteristic slow mobility. Our results support the notion that maned sloths can effectively occupy (and even select for) disturbed forested habitats. However, we do not know whether sloth populations are viable in landscapes containing only disturbed habitats or low proportions of undisturbed habitats.

Loss of secondary‐forest resilience by land‐use intensification in the Amazon

Summary Understanding how land‐use intensification affects forest resilience is a key for elucidating the mechanisms underlying regeneration processes and for planning more sustainable land‐use systems. Here, we evaluate how the intensification of a swidden cultivation system affects secondary‐forest resilience in the Amazon. Along a gradient of land‐use intensity, we analysed the relative role of management intensity, soil properties and landscape configuration in determining the resilience of early secondary forests (SFs). We assessed resilience as the recovery level of forest structure and species diversity achieved by SFs 5 years after abandonment. We used as a reference the recovery level achieved by SFs subjected to the lowest intensity of use, given that these SFs are part of a dynamic system and may not develop to old‐growth forests. Therefore, we interpreted a deviation from this reference level as a change in forest resilience. The recovery of forest structure was determined by management intensity, while the recovery of species diversity was driven by landscape configuration. With increasing number of cycles and weeding frequency along with decreasing fallow period and patch area, SF basal area and canopy height decreased, regeneration shifted from a seed‐ to sprout‐dependent strategy, and liana infestation on trees increased. With decreasing area covered by old‐growth forest, species richness and Shannon diversity decreased. Secondary‐forest resilience decreased with land‐use intensification, mainly mediated by the effect of management intensity upon regeneration strategies. Our findings demonstrate the – many times overlooked – importance of previous management intensity in determining the structure of SFs and highlight the importance of regeneration strategy for forest resilience. Synthesis. Swidden cultivation supports people's livelihoods and transforms landscapes in the tropics. The sustainability of this system depends on ecosystem services provided by SFs that develop during the fallow period. Land‐use intensification reduces the resilience of SFs and ultimately may drive the system towards an arrested succession state that holds a lower potential to deliver ecosystem services to the Amazonian people. Under an intensification scenario, the adaptation of management practices is needed to guarantee the resilience of swidden cultivation systems.

Seedling fate across different habitats: The effects of herbivory and soil fertility

The impact of extinction of predators and subsequent herbivore release on ecosystem functioning has been well studied in temperate ecosystems, yet we have very little information on threatened tropical rainforests. Herbivore overbrowsing can have profound effects on ecosystem processes through overconsumption or by altering organic inputs of leaves and roots as well as changing soil physical and chemical properties. We evaluated the fate of transplanted seedlings of four tropical tree species and nutrient availability in open control plots and enclosed plots that permitted free access by insects and excluded vertebrates and collected soil samples in old-fields, early secondary forests and old-growth forests. Seedling damage predominantly occurred in the dry season and produced an overall seedling mortality of 72%, with values of 43% and 86% in the plots that prohibited and permitted vertebrate access, respectively. Except for Myrsine coriacea in the old-fields and Syagrus romanzoffiana in the early secondary forest, seedlings suffered greater rates of damage and mortality in the open plots, showing that the aboveground large herbivores, such as capybaras (Hydrochoerus hydrochaeris), might prevent or at least delay plant recruitment in tropical areas supporting elevated densities. However, delayed deaths from disease by soil fertility-related factors were observed in late summer in the old-field seedlings, suggesting that previous activities in these areas had led to profound changes in the soil properties. Herbivores may have important consequences for tropical forest regeneration, as overconsumption may slow down nutrient cycling, promote cascading bottom-up effects on consumers, and ultimately lead to ecological meltdown. These consequences provide insight into the ecological effects of faunal change on human-altered tropical habitats.