Effects of macrophytes on lake‐water quality across latitudes: a meta‐analysis

Macrophytes are widely recognized for improving water quality and stabilizing the desirable clear‐water state in lakes. The positive effects of macrophytes on water quality have been noted to be weaker in the (sub)tropics compared to those of temperate regions. We conducted a global meta‐analysis using 47 studies that met our set criteria to assess the overall effects of macrophytes on water quality (measured by phytoplankton chlorophyll a concentration, total nitrogen concentration, total phosphorus concentration, Secchi depth and the trophic state index) and to investigate how these effects correlate with latitude using meta‐regressions. We also examined if the effects of macrophytes on lake‐water quality differ with growth form and study design in (sub)tropical and temperate areas by grouping the data and then comparing the effect sizes. We found that macrophytes significantly reduced phytoplankton chlorophyll a concentration, total nitrogen concentration, total phosphorus concentration, as well as the trophic state index, but they did not have a significant overall effect on Secchi depth. The effects of macrophytes on reducing phytoplankton chlorophyll a concentration, total nitrogen concentration and the trophic state index did not differ with latitude. However, the reduction of total phosphorus concentration was greater at lower latitudes. We showed that at lower latitudes, the positive effects of macrophytes on water quality are similar to or greater than those at higher latitudes, thus challenging the prevailing paradigm of macrophytes being less effective at enhancing lake‐water quality in the (sub)tropics. Furthermore, our data showed that the macrophyte effects vary by growth forms, and the growth forms that positively affect water quality differ between the (sub)tropical and temperate areas. We showed a lack of significant macrophyte effects in surveys within and outside macrophyte stands, suggesting difference in the sensitivities of study designs or possibly weaker effects of macrophytes in lakes compared to experimental settings.     

Nutrient Addition Differentially Affects Soil Carbon Sequestration in Secondary Tropical Dry Forests: Early‐ versus Late‐Succession Stages

There is considerable interest in the potential use of soils to sequester carbon for climate change mitigation. As such, there is a need to evaluate the potential for carbon accumulation in tropical regions. We compared the effects of three annual additions of nitrogen and/or phosphorus on soil carbon and nitrogen contents and pools (bulk soil, macro‐, meso‐, and microaggregates) of two regenerating secondary tropical dry forest differing in nutrient status and succession stage (10‐year‐old early‐succession stage and approximately 60‐year‐old late‐succession stage). The selected forest sites were located on a shallow calcareous soil in the Yucatán Peninsula (Mexico). The primary production is limited by nitrogen and phosphorus in early‐succession stage and by phosphorus in late‐succession stage. In each forest site, four independent plots (12 × 12 m²) were established, the treatments being: controls and plots fertilized during three consecutive years with nitrogen, phosphorus, or nitrogen plus phosphorus. In both forests, soil carbon and nitrogen contents were consistently high, with soil carbon:nitrogen ratios generally greater than 10. Results indicate that usually there are no significant increases of soil carbon stock associated to late succession but can be increased to 3.7 Mg·ha^?1·yr^?1 with adoption of fertilizer practices. The potential soil carbon sequestration in early‐succession forest was estimated to be 2.7 Mg·ha^?1·yr^?1, and there is no indication that fertilization improves carbon sequestration. In short, results suggest that the soil potential for carbon sequestration in these ecosystems is high and depends on the specific nutrient status of the site.     

Fuzzy rule‐based decision support system for evaluation of long‐established forest restoration projects

Although the importance of monitoring and evaluation of restoration actions is increasingly acknowledged, availability of accurate, quantitative monitoring data is very rare for most restoration areas, particularly for long‐established restoration projects. We propose using fuzzy rule‐based expert systems to evaluate the degree of success of restoration actions when available information on project results and impacts largely relies on expert‐based qualitative assessments and rough estimates of quantitative values. These systems use fuzzy logic to manage the uncertainty present in the data and to integrate qualitative and quantitative information. To illustrate and demonstrate the potential of fuzzy rule‐based systems for restoration evaluation, we applied this approach to seven forest restoration projects implemented in Spain between 1897 and 1952, using information compiled in the REACTION database on Mediterranean forest restoration projects. The information available includes both quantitative and expert‐based qualitative data, and covers a wide variety of indicators grouped into technical, structural, functional, and socioeconomic criteria. The fuzzy rule‐based system translates expert knowledge of restoration specialists and forest managers into a set of simple logic rules that integrate information on individual indicators into more general evaluation criteria. The rule‐based approach proposed here can be readily applicable to any kind of restoration project, provided that some information, even if vague and uncertain, is available for a variety of assessment indicators. The evaluation of long‐established forest restoration projects implemented in Spain revealed important asymmetries in the degree of restoration success between technical, structural, functional, and socioeconomic criteria.     

Myth‐busting tropical grassy biome restoration

The historical focus in research and policy on forest restoration and temperate ecosystems has created misunderstandings for the restoration of tropical and subtropical old‐growth grassy biomes (TGB). Such misconceptions have detrimental consequences for biodiversity, ecosystem services, and human livelihoods in woodlands, savannas, and grasslands worldwide. Here, we demystify TGB restoration myths to promote a positive agenda to increase the likelihood of success of ambitious landscape‐scale restoration goals of nonforest ecosystems. The 10 TGB restoration myths are: (1) grasslands originate from degraded forests, (2) tree cover is a reliable indicator of habitat quality, (3) planting trees is always good for biodiversity and ecosystem services, (4) grasslands are biodiversity‐poor and provide few ecosystem services, (5) enhancing plant nutrition is needed in restoration, (6) disturbance is detrimental, (7) techniques used to restore temperate grasslands also work for TGB, (8) grasslands represent early stages of forest succession, (9) grassland restoration is only about grasses, and (10) grassland restoration is fast. By demystifying TGB restoration, we hope that policymakers, scientists, and restorationists come to understand and embrace the value of these ecosystems and are motivated to establish policies, standards, indicators, and techniques that enhance the success of TGB restoration. We must abandon misperceptions and misunderstandings of TGB ecology that result in ill‐conceived policies and build an informed and compelling global ecosystem restoration agenda that maintains and improves the well‐being of all inhabitants of grassy biomes.     

A pre‐adaptive approach for tropical forest restoration during climate change using naturally occurring genetic variation in response to water limitation

Effective reforestation of degraded tropical forests depends on selecting planting material suited to the stressful environments typical at restoration sites that can be exacerbated by increased duration and intensity of dry spells expected with climate change. While reforestation efforts in nontropical systems are incorporating drought‐adapted genotypes into restoration programs to cope with drier conditions, such approaches have not been tested or implemented in tropical forests. As the first effort to examine genetic variation in plant response to drought in a tropical wet forest, we established a watering experiment using five replicated maternal lines (i.e. seedlings from different maternal trees) of five dipterocarp species native to Borneo. Apart from the expected species level variation in growth and herbivory (3‐fold variation in both cases), we also found intraspecific variation so that growth in some cases varied 2‐fold, and herbivory 3‐fold, among genetically different maternal lines. In two species we found that among‐maternal line variation in growth rate was negatively correlated with tolerance to water limitation, that is, the maternal lines that performed the best in the high water treatment lost proportionally more of their growth during water limitation. We argue that selection for tolerance to future drier conditions is not only likely to impact population genetics of entire forests, but likely extends from forest trees to the communities of canopy arthropods associated with these trees. In tropical reforestation efforts where increased drought is predicted from climate change, including plant material resilient to drier conditions may improve restoration effectiveness.     

Multiple successional pathways in human‐modified tropical landscapes: new insights from forest succession,forest fragmentation and landscape ecology research

Old‐growth tropical forests are being extensively deforested and fragmented worldwide. Yet forest recovery through succession has led to an expansion of secondary forests in human‐modified tropical landscapes (HMTLs). Secondary forests thus emerge as a potential repository for tropical biodiversity, and also as a source of essential ecosystem functions and services in HMTLs. Such critical roles are controversial, however, as they depend on successional, landscape and socio‐economic dynamics, which can vary widely within and across landscapes and regions. Understanding the main drivers of successional pathways of disturbed tropical forests is critically needed for improving management, conservation, and restoration strategies. Here, we combine emerging knowledge from tropical forest succession, forest fragmentation and landscape ecology research to identify the main driving forces shaping successional pathways at different spatial scales. We also explore causal connections between land‐use dynamics and the level of predictability of successional pathways, and examine potential implications of such connections to determine the importance of secondary forests for biodiversity conservation in HMTLs. We show that secondary succession (SS) in tropical landscapes is a multifactorial phenomenon affected by a myriad of forces operating at multiple spatio‐temporal scales. SS is relatively fast and more predictable in recently modified landscapes and where well‐preserved biodiversity‐rich native forests are still present in the landscape. Yet the increasing variation in landscape spatial configuration and matrix heterogeneity in landscapes with intermediate levels of disturbance increases the uncertainty of successional pathways. In landscapes that have suffered extensive and intensive human disturbances, however, succession can be slow or arrested, with impoverished assemblages and reduced potential to deliver ecosystem functions and services. We conclude that: (i) succession must be examined using more comprehensive explanatory models, providing information about the forces affecting not only the presence but also the persistence of species and ecological groups, particularly of those taxa expected to be extirpated from HMTLs; (ii) SS research should integrate new aspects from forest fragmentation and landscape ecology research to address accurately the potential of secondary forests to serve as biodiversity repositories; and (iii) secondary forest stands, as a dynamic component of HMTLs, must be incorporated as key elements of conservation planning; i.e. secondary forest stands must be actively managed (e.g. using assisted forest restoration) according to conservation goals at broad spatial scales.     

The transparency,reliability and utility of tropical rainforest land‐use and land‐cover change models

Land‐use and land‐cover (LULC) change is one of the largest drivers of biodiversity loss and carbon emissions globally. We use the tropical rainforests of the Amazon, the Congo basin and South‐East Asia as a case study to investigate spatial predictive models of LULC change. Current predictions differ in their modelling approaches, are highly variable and often poorly validated. We carried out a quantitative review of 48 modelling methodologies, considering model spatio‐temporal scales, inputs, calibration and validation methods. In addition, we requested model outputs from each of the models reviewed and carried out a quantitative assessment of model performance for tropical LULC predictions in the Brazilian Amazon. We highlight existing shortfalls in the discipline and uncover three key points that need addressing to improve the transparency, reliability and utility of tropical LULC change models: (1) a lack of openness with regard to describing and making available the model inputs and model code; (2) the difficulties of conducting appropriate model validations; and (3) the difficulty that users of tropical LULC models face in obtaining the model predictions to help inform their own analyses and policy decisions. We further draw comparisons between tropical LULC change models in the tropics and the modelling approaches and paradigms in other disciplines, and suggest that recent changes in the climate change and species distribution modelling communities may provide a pathway that tropical LULC change modellers may emulate to further improve the discipline. Climate change models have exerted considerable influence over public perceptions of climate change and now impact policy decisions at all political levels. We suggest that tropical LULC change models have an equally high potential to influence public opinion and impact the development of land‐use policies based on plausible future scenarios, but, to do that reliably may require further improvements in the discipline.     

Inter‐annual monitoring improves diversity estimation of tropical butterfly assemblages

Monitoring programs for diverse tropical butterfly assemblages are scarce, and temporal diversity patterns in these assemblages are poorly understood. We adopted an additive partitioning approach to determine how temporal butterfly species richness was structured at the levels of days, months, and years in five tropical/subtropical sites across three continents covering up to 9 years of monitoring. We found that observed butterfly richness was not uniformly distributed across temporal extents. Butterfly species composition differed across months and years, potentially accounting for the fact that temporal butterfly species richness contributed a high proportion to total species richness. We further examined how species richness of common and uncommon species (> and <0.5% of total abundance, respectively) were structured across temporal extents. The results showed that the common species relative contribution to total species richness was higher at lower‐temporal levels, whereas uncommon species contributed more at higher‐temporal resolutions. This suggests that long‐term sampling will be more effective in capturing patterns of rare species and the total species pool while lower‐temporal level sampling (e.g., daily or weekly) may be more useful in examining common species demographic patterns. We therefore encourage careful consideration of temporal replication at different extents in developing butterfly monitoring schemes. Long‐term monitoring is essential for improvement in the resolution of species estimation and diversity patterns for tropical ecosystems. Abstract in Chinese is available with online material.     

Natural regeneration and biodiversity: a global meta‐analysis and implications for spatial planning

Natural regeneration offers a cheaper alternative to active reforestation and has the potential to become the predominant way of restoring degraded tropical landscapes at large‐scale. We conducted a meta‐analysis for tropical regions and quantified the relationships between both ecological and socioeconomic factors and biodiversity responses in naturally regenerating areas. Biogeographic realms, past disturbance, and the human development index (HDI) were used as explanatory variables for biodiversity responses. In addition, we present a case study of large‐scale natural regeneration in the Brazilian Atlantic Forest and identify areas where different forms of restoration would be most suitable. Using our dataset for tropical regions, we showed that natural regeneration was predominantly reported within: the Neotropical realm; areas that were intensively disturbed; and countries with medium HDI. We also found that biodiversity in regenerating forests was more similar to the values found in old growth forests in: countries with either low, high, or very high HDI; less biodiverse realms; and areas of less intensive past disturbance. Our case study from Brazil showed that the level of forest gain resulting from environmental legislation, in particular the Brazilian Forest Code, has been reduced, but remains substantial. Complementary market incentives and financial mechanisms to promote large‐scale natural regeneration in human‐modified agricultural landscapes are also needed. Our analysis provides insights into the factors that promote or limit the recovery of biodiversity in naturally regenerating areas, and aids to identify areas with higher potential for natural regeneration.     

Using structured decision‐making to set restoration objectives when multiple values and preferences exist

Achieving global targets for restoring native vegetation cover requires restoration projects to identify and work toward common management objectives. This is made challenging by the different values held by concerned stakeholders, which are not often accounted for. Additionally, restoration is time‐dependent and yet there is often little explicit acknowledgment of the time frames required to achieve outcomes. Here, we argue that explicitly incorporating value and time considerations into stated objectives would help to achieve restoration goals. We reviewed the peer‐reviewed literature on restoration of terrestrial vegetation and found that while there is guidance on how to identify and account for stakeholder values and time considerations, there is little evidence these are being incorporated into decision‐making processes. In this article, we explore how a combination of stakeholder surveys and workshops can be used within a structured decision‐making framework to facilitate the integration of diverse stakeholder values and time frame considerations to set restoration objectives. We demonstrate this approach with a case of restoration decision‐making at a regional scale (southeast Queensland, Australia) with a view to this experience supporting similar restoration projects elsewhere.     

Applying an animal‐centric approach to improve ecological restoration

Traditionally, ecological restoration is based on re‐establishing patterns of vegetation communities with the expectation that wildlife will recolonize, restoring the ecological function. However, in many restoration projects, wildlife fails to recolonize, even when vegetation is restored, in many cases because revegetated habitats lack the critical features required by wildlife. We present a new approach to restoration, based on a detailed understanding of ecological process, the mechanisms by which wildlife respond to landscape patterns. Our animal‐centric approach involves measuring the risk‐sensitive decision‐making of individual animals as they balance searching for food, mates, and breeding sites with avoiding being eaten by predators and relates this to fine‐scale habitat and landscape structure. The outcome of these decisions can be measured in occupancy of habitat, the information on which conventional restoration is based. Incorporating landscape genetics allows retrospective assessment of the outcome of dispersal decisions by individual animals on a deeper time frame and at regional scales. Fine‐scale connectivity models can be parameterized with these multiscale spatial and temporal data to direct restoration efforts. We are translating this novel approach to practice in the large Midlands restoration project (4 years, AUD $6 million) in Tasmania, Australia, in partnership with Greening Australia. More than 200 years of intensive agricultural practice in this National Biodiversity Hotspot has resulted in extensive landscape modification, high densities of feral cats, and decline of many native mammals. Our research–practice partnership will alter the way that restoration is done, leading hopefully to successful restoration of wildlife, gene flow, and ecological function.     

Relationship between arrival timing and breeding success of intra‐tropical migratory Fork‐tailed Flycatchers (Tyrannus savana)

For migratory birds, early arrival at breeding areas has many benefits, such as acquisition of better territories and mates. This strategy has been found in numerous species breeding at north‐temperate latitudes, but has not been yet reported for intra‐tropical migratory species. We evaluated the relationship between arrival date, initiation of breeding, and breeding success of Fork‐tailed Flycatchers (Tyrannus savana) breeding in southeastern Brazil and overwintering in northern South America. We color‐banded adult flycatchers during three breeding seasons and searched for them during the following breeding seasons. We also monitored nests from construction until either failure or fledging of young. We found that: (1) male Fork‐tailed Flycatchers arrived at the breeding site earlier than females, (2) males that arrived earlier had greater breeding success, and (3) nests where eggs were laid earlier in the breeding season were more likely to be successful than those where eggs were laid later. Male Fork‐tailed Flycatchers appeared to benefit from early arrival at a tropical breeding site, potentially mediated by their ability to acquire a high‐quality territory and mate as early as possible, and by the ability of their mate to begin breeding as early as possible. Breeding success for female Fork‐tailed Flycatchers may be determined primarily by a combination of the arrival date of their mate and how quickly they can begin breeding. Our results suggest that protandry occurs in an intra‐tropical migratory bird and that early arrival of males and early initiation of reproduction by females results in greater reproductive success. A better understanding of the underlying mechanisms that control the timing of migration and reproduction of this and other intra‐tropical migratory species is important for evaluating the challenges they face in light of current and future rapid environmental changes.     

Historical climate‐human‐ecosystem interaction in East Africa: a review

The palaeoecological visibility of historical human impact on natural ecosystems in tropical East Africa is strongly impeded by an overriding dominant signature of climate change at decadal‐to‐millennial time scales. Better knowledge of the relative magnitude and timing of present and past human impact and climate variability is, however, instrumental to properly assess the resilience, and recovery potential, of East Africa's natural ecosystems. Here, we briefly review comprehensive previous attempts to assess past ecosystem responses to climate change and human impact. We further discuss some key issues of climate‐human‐ecosystem relationships in a multidisciplinary framework and address some future challenges and outcomes, which may pave the way to a better understanding of past climate‐human‐ecosystem interaction‐ in tropical Africa.     

Seasonality of peak metabolic rate in non‐migrant tropical birds

Birds that are year‐round residents of temperate and tropical regions have divergent life histories. Tropical birds have a slower ‘pace of life’, one characteristic of which includes lower peak metabolic rate and daily activity levels. Temperate resident birds are faced with seasonal variation in thermogenic demand. This challenge is met with seasonally increased peak metabolic rate during winter. These thermogenic demands are much lower in birds that are year‐round tropical residents. By measuring peak (summit) metabolic rate in tropical and temperate resident bird species during summer and winter, we asked whether tropical birds exhibit seasonality in peak metabolic rate, and if the direction of seasonality differs between tropical and temperate species. We measured summit metabolism in seven tropical and one temperate species during the winter and during the summer breeding season to test the hypothesis that summit metabolism of tropical residents would change seasonally. We consider whether metabolic seasonality is associated with breeding season for tropical species. We found that summit metabolism was significantly greater during the summer for most tropical residents, while the temperate resident matched several previous reports with higher summit metabolism in winter. We conclude that metabolic seasonality occurs in tropical residents and differs from temperate residents, suggesting that breeding during the summer may be driving relatively higher metabolism as compared to winter thermogenesis in temperate birds.     

Male and female rufous‐and‐white wrens do not match song types with same‐sex rivals during simulated territorial intrusions

In birds with song repertoires, song‐type matching occurs when an individual responds to another individual's song by producing the same song type. Song‐type matching has been described in multiple bird species and a growing body of evidence suggests that song‐type matching may serve as a conventional signal of aggression, particularly in male birds in the temperate zone. Few studies have investigated song‐type matching in tropical birds or female birds, in spite of the fact that avian biodiversity is highest in the tropics, that female song is widespread in the tropics, and that female song is the ancestral state among songbirds. In this study of rufous‐and‐white wrens Thryophilus rufalbus, a resident neotropical songbird where both sexes sing, we presented territorial males and females with playback that simulated a territorial rival producing shared and unshared songs. In response, both males and females sang matched song types at levels statistically equal to levels expected by chance. Furthermore, males and females exhibited similar levels of aggression and similar vocal behaviours in response to playback of both shared and unshared songs. These results indicate that rufous‐and‐white wrens do not use song‐type matching in territorial conflicts as a conventional signal of aggression. We discuss alternative hypotheses for the function of song‐type sharing in tropical birds. In particular, we point out that shared songs may play an important role in intra‐pair communication, especially for birds where males and females combine their songs in vocal duets, and this may supersede the function of song‐type matching in some tropical birds.     

Natural regeneration as a tool for large‐scale forest restoration in the tropics: prospects and challenges

A major global effort to enable cost‐effective natural regeneration is needed to achieve ambitious forest and landscape restoration goals. Natural forest regeneration can potentially play a major role in large‐scale landscape restoration in tropical regions. Here, we focus on the conditions that favor natural regeneration within tropical forest landscapes. We illustrate cases where large‐scale natural regeneration followed forest clearing and non‐forest land use, and describe the social and ecological factors that drove these local forest transitions. The self‐organizing processes that create naturally regenerating forests and natural regeneration in planted forests promote local genetic adaptation, foster native species with known traditional uses, create spatial and temporal heterogeneity, and sustain local biodiversity and biotic interactions. These features confer greater ecosystem resilience in the face of future shocks and disturbances. We discuss economic, social, and legal issues that challenge natural regeneration in tropical landscapes. We conclude by suggesting ways to enable natural regeneration to become an effective tool for implementing large‐scale forest and landscape restoration. Major research and policy priorities include: identifying and modeling the ecological and economic conditions where natural regeneration is a viable and favorable land‐use option, developing monitoring protocols for natural regeneration that can be carried out by local communities, and developing enabling incentives, governance structures, and regulatory conditions that promote the stewardship of naturally regenerating forests. Aligning restoration goals and practices with natural regeneration can achieve the best possible outcome for achieving multiple social and environmental benefits at minimal cost.     

Post‐fire vegetation dynamics in nutrient‐enriched and non‐enriched sclerophyll woodland

Abstract Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low‐nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run‐off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: ‘Are there differences in post‐fire resprouting and germination of native and exotic species in nutrient‐enriched communities, compared with communities not disturbed by nutrient enrichment?’ We found that in non‐enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient‐enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient‐enriched. In nutrient‐enriched areas after fire, the diversity of native species was lower than in the non‐enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non‐enriched areas. We suggest that although fire can be a useful tool for short‐term removal of exotic plant biomass from nutrient‐enriched areas, it does not promote establishment of native species that were not already present.     

Improving Planting Stocks for the Brazilian Atlantic Forest Restoration through Community‐Based Seed Harvesting Strategies

High‐diversity reforestation can help jumpstart tropical forest restoration, but obtaining viable seedlings is a major constraint: if nurseries do not offer them, it is hard to plant all the species one would like. From 2007 to 2009, we investigated five different seed acquisition strategies employed by a well‐established tree nursery in southeastern Brazil, namely (1) in‐house seed harvesters; (2) hiring a professional harvester; (3) amateur seed harvesters; or (4) a seed production cooperative, as well as (5) participating in a seed exchange program. In addition, we evaluated two strategies not dependent on seeds: harvesting seedlings from native tree species found regenerating under Eucalyptus plantations, and in a native forest remnant. A total of 344 native tree and shrub species were collected as seeds or seedlings, including 2,465 seed lots. Among these, a subset of 120 species was obtained through seed harvesting in each year. Overall, combining several strategies for obtaining planting stocks was an effective way to increase species richness, representation of some functional groups (dispersal syndromes, planting group, and shade tolerance), and genetic diversity of seedlings produced in forest tree nurseries. Such outcomes are greatly desirable to support high‐diversity reforestation as part of tropical forest restoration. In addition, community‐based seed harvesting strategies fostered greater socioeconomic integration of traditional communities in restoration projects and programs, which is an important bottleneck for the advance of ecological restoration, especially in developing countries. Finally, we discuss some of the limitations of the various strategies for obtaining planting stocks and the way forward for their improvement.