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Tropical forest restoration presents a potential lifeline to mitigate climate change and biodiversity crises in the Anthropocene. Yet, the extent to which human interventions, such as tree planting, accelerate the recovery of mature functioning ecosystems or redirect successional trajectories toward novel states remains uncertain due to a lack of long-term experiments. In 2004-2006, we established three 0.25-ha plots at 10 sites in southern Costa Rica to test three forest restoration approaches: natural regeneration (no planting), applied nucleation (planting in patches), and plantation (full planting). In a comprehensive survey after 16-18 years of recovery, we censused >80,000 seedlings, saplings, and trees from at least 255 species across 26 restoration plots (nine natural regeneration, nine applied nucleation, eight plantation) and six adjacent reference forests to evaluate treatment effects on recruitment patterns and community composition. Both applied nucleation and plantation treatments resulted in significantly elevated seedling and sapling establishment and more predictable community composition compared with natural regeneration. Similarity of vegetation composition to reference forest tended to scale positively with treatment planting intensity. Later-successional species with seeds ≥5 mm had significantly greater seedling and sapling abundance in the two planted treatments, and plantation showed similar recruitment densities of large-seeded (≥10 mm) species to reference forest. Plantation tended toward a lower abundance of early-successional recruits than applied nucleation. Trees (≥5 cm dbh) in all restoration treatments continued to be dominated by a few early-successional species and originally transplanted individuals. Seedling recruits of planted taxa were more abundant in applied nucleation than the other treatments though few transitioned into the sapling layer. Overall, our findings show that active tree planting accelerates the establishment of later-successional trees compared with natural regeneration after nearly two decades. While the apparent advantages of higher density tree planting on dispersal and understory establishment of larger seeded, later-successional species recruitment is notable, more time is needed to assess whether these differences will persist and transition to the more rapid development of a mature later-successional canopy. Our results underscore the need for ecological restoration planning and monitoring that targets biodiversity recovery over multiple decades.

Abstract: The effects of vertebrate seed predation on the regeneration of restored forests are not well understood because most past studies have focused on seed predation within the first few years after restoration and have measured seed removal without quantifying subsequent seedling establishment of seeds that avoid predation. Quantifying the establishment of seeds that escape predation in restored forests at later stages of regrowth is crucial for anticipating longer‐term recovery trajectories. Here, we evaluated the potential role of vertebrate seed predators in limiting recruitment of later‐successional tree species in nine forests actively restored ≥15 years prior and in four paired remnant forest fragments embedded in an agricultural landscape in southern Costa Rica. We conducted seed addition experiments with four tree species inside and outside vertebrate exclosures and used camera trapping to detect seed predators. To determine the fate of seeds that avoided predation, we also measured seedling establishment after 1 year, given that other mortality factors may compensate in the absence of vertebrate seed predation. We detected two species of birds and five species of granivorous mammals removing seeds. Seed tagging indicated that most removal resulted in predation. For three of the four tree species tested, vertebrate seed predation reduced seedling establishment. The magnitude of this effect depended on species' susceptibility to other causes of mortality during the seed‐to‐seedling transition. Our study demonstrates that vertebrate seed predators can substantially reduce later‐successional seedling recruitment in restored forests and should be considered alongside dispersal limitation and microsite conditions as factors slowing forest recovery. Abstract in Spanish is available with online material.

With increased interest in forest restoration comes an urgent need to provide accurate, scalable, and cost‐effective monitoring tools. The ubiquity of smartphones has led to a surge in monitoring apps. We reviewed and assessed monitoring apps found through web searches and conversations with practitioners. We identified 42 apps that (1) automatically monitor indicators or (2) facilitate data entry. We selected the five most promising from the first category, based on their relevance, availability, stability, and user support. We compared them to traditional field techniques in a well‐studied restoration project in Costa Rica. We received further feedback from 15 collaborator organizations that evaluated these in their corresponding field restoration sites. Diameter measurements correlated well with traditional tape‐based measurements (R2 = 0.86–0.89). Canopy openness and ground cover showed weaker correlations to densiometer and quadrat cover measurements (R2 = 0.42–0.51). Apps did not improve labor efficiency but do preclude the purchase of specialized field equipment. The apps reviewed here need further development and validation to support monitoring adequately, especially in the tropics. Estimates of development and maintenance costs, as well as statistics on user uptake, are required for cost‐effective development. We recommend a coordinated effort to develop dedicated restoration monitoring apps that can speed up and standardize the collection of indicators and provide evidence on restoration outcomes alongside a centralized repository of this information.

Applied nucleation and other spatially patterned restoration methods are promising approaches for scaling up projects to meet ambitious international restoration commitments in an ecologically and economically sound manner. Much of the corresponding literature to date, however, has centered around theoretical discussions and small‐scale studies that are largely divorced from constraints faced by restoration practitioners. We briefly review recent academic literature about applied nucleation and other spatially patterned restoration methods and discuss practical challenges to their implementation. We offer several recommendations to move spatially patterned restoration from an academic conversation to scalable application, including: (1) comparing different planting designs and natural regeneration within the same system at an appropriate scale; (2) monitoring ecological outcomes throughout the restored area over sufficient time to evaluate recovery; (3) quantifying costs and documenting other logistical constraints to implementation; and (4) exploring methods for using unplanted areas to provide benefits to landholders until planted vegetation establishes.

Forest restoration is increasingly heralded as a global strategy to conserve biodiversity and mitigate climate change, yet long-term studies that compare the effects of different restoration strategies on tree recruit demographics are lacking. We measured tree recruit survival and growth annually in three restoration treatments-natural regeneration, applied nucleation and tree plantations-replicated at 13 sites in southern Costa Rica-and evaluated the changes over a decade. Early-successional seedlings had 14% higher survival probability in the applied nucleation than natural regeneration treatments. Early-successional sapling growth rates were initially 227% faster in natural regeneration and 127% faster in applied nucleation than plantation plots but converged across restoration treatments over time. Later-successional seedling and sapling survival were similar across treatments but later-successional sapling growth rates were 39% faster in applied nucleation than in plantation treatments. Results indicate that applied nucleation was equally or more effective in enhancing survival and growth of naturally recruited trees than the more resource-intensive plantation treatment, highlighting its promise as a restoration strategy. Finally, tree recruit dynamics changed quickly over the 10-year period, underscoring the importance of multi-year studies to compare restoration interventions and guide ambitious forest restoration efforts planned for the coming decades. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Choosing appropriate forest restoration interventions is challenging. Natural regeneration can rapidly facilitate forest recovery in many situations. However, barriers such as dispersal limitation and competition with non-native species can require assisted restoration approaches to facilitate plant community recovery. We used a study that has directly compared the outcomes of tropical wet forest restoration interventions across 11 replicate sites in southern Costa Rica. Within this framework, we examined the functional recovery trajectories of recruiting tree sapling communities across a gradient of restoration interventions including low (natural regeneration), intermediate (applied nucleation), and high (plantation) initial resource-investment, which we compared to remnant reference forest. We collated leaf and stem functional traits for tree species that comprised the bulk of recruiting saplings, then determined how community-weighted trait means and functional diversity metrics changed over a decade across treatments. Results show that assisted restoration approaches (applied nucleation, plantation) sped the development of more functionally diverse tree communities, more than tripling the functional richness (FRic) of recruiting communities when compared to natural regeneration. However, functional dispersion (i.e., the trait range of dominant species) was equivalent across interventions, and between 28 and 44% lower than remnant forest, indicating that increases in FRic under assisted restoration were driven by species recruiting in low abundances (

Reversing large-scale habitat degradation and deforestation goes beyond what can be achieved by site-level ecological restoration and a landscape ecology perspective is fundamental. Here we assess the relative importance of tree cover and its configuration on forest-dependent birds and late-successional tree seedlings in restoration sites in southern Costa Rica. The abundance and species richness of birds increased in landscapes with more corridors, higher tree cover, and lower levels of fragmentation, highlighting the importance of riparian corridors for connectivity, and continuous tree cover as suitable habitat. Landscape variables affected abundance and species richness of seedlings similarly, but effects were weaker, possibly because seedlings face establishment limitation in addition to dispersal limitation. Moreover, the scale of landscape effects on seedlings was small, likely because proximal individual trees can significantly influence recruitment in restoration plots. Results underscore the importance of incorporating landscape-level metrics to restoration projects, as knowing the extent, and how the landscape may affect restoration outcomes can help to infer what kind of species will arrive to restoration plots.

Abstract: In degraded tropical landscapes, lack of seed dispersal can strongly limit recovery, and restoration interventions can overcome this barrier by attracting dispersers. However, seed dispersal patterns are typically studied over short time periods, thus the influences of temporal and spatial variability on seed arrival cannot be teased apart. The choice of management approach can have important implications for restoration‐mediated community reassembly. Accordingly, we used a 3.5‐year record of seed deposition in pre‐montane tropical wet forest in southern Costa Rica to examine how seed arrival differed between passive (natural regeneration) and active (applied nucleation, plantation) restoration after a decade of recovery, compared to remnant forest. We investigated: (a) how restoration treatments affected seed deposition rates and community composition; (b) how within‐plot heterogeneity of animal‐dispersed seed deposition varied by intervention; and (c) how interannual variation influenced animal‐dispersed seed arrival across treatments. Overall seed rain composition and diversity in restoration treatments was converging towards, but still differed substantially from, remnant forest (89.7%, 86.6% and 76.3% Shannon diversity recovered in applied nucleation, plantation and natural regeneration respectively). Within‐plot animal‐dispersed seed heterogeneity was similar in applied nucleation and remnant forest, 27.0% more heterogeneous in applied nucleation than plantation, and equivalent when comparing natural regeneration to either applied nucleation or plantation. In contrast to active interventions, animal‐dispersed tree and shrub communities did not differ year to year in natural regeneration, which may promote the assembly of relatively homogeneous plant communities at this successional stage. Synthesis and applications. Compared to natural regeneration, active restoration interventions: (a) catalysed the recovery of seed diversity (overall Shannon diversity 17.5% and 13.4% higher in applied nucleation and plantation respectively), (b) shifted seed community composition towards remnant forest more rapidly (overall Shannon diversity 13.4% and 10.2% closer), (c) almost doubled the proportion of later‐successional tree species arriving, and (d) had seed communities that differed year to year—a pattern not observed in natural regeneration. Finally, applied nucleation was the only intervention where seed arrival was as spatially heterogeneous as remnant forest, highlighting that this approach may facilitate the recovery of specific natural dispersal processes.

Both dispersal- and niche-based factors can impose major barriers on tree establishment. Our understanding of how these factors interact to determine recruitment rates is based primarily on findings from mature tropical forests, despite the fact that a majority of tropical forests are now secondary. Consequently, factors influencing seed limitation and the seed-to-seedling transition (STS) in disturbed landscapes, and how those factors shift during succession, are not well understood. We used a 3.5-yr record of seed rain and seedling establishment to investigate factors influencing tree recruitment after a decade of recovery in a tropical wet forest restoration experiment in southern Costa Rica. We asked (1) how do a range of restoration treatments (natural regeneration, applied nucleation, plantation), canopy cover, and life-history traits influence the STS and (2) how do seed and establishment limitation (lack of seed arrival or lack of seedling recruitment, respectively) influence vegetation recovery within restoration treatments as compared to remnant forest? We did not observe any differences in STS rates across restoration treatments. However, STS rates were lowest in adjacent later successional remnant forests, where seed source availability did not highly limit seed arrival, underscoring that niche-based processes may increasingly limit recruitment as succession unfolds. Additionally, larger-seeded species had consistently higher STS rates across treatments and remnant forests, though establishment limitation for these species was lowest in the remnant forests. Species were generally seed limited and almost all were establishment limited; these patterns were consistent across treatments. However, our results suggest that differences in recruitment rates could be driven by differential dispersal to treatments with higher canopy cover. We found evidence that barriers to recruitment shift during succession, with the influence of seed limitation, mediated by species-level seed deposition rates, giving way to niche-based processes. However, establishment limitation was lowest in the remnant forests for large-seeded and late successional species, highlighting the importance of habitat specialization and life-history traits in dictating recruitment dynamics. Overall, results demonstrate that active restoration approaches such as tree planting catalyze forest recovery, not only by decreasing components of seed limitation, but also by developing canopy cover that increases establishment rates of larger-seeded species.

QUESTIONS: Natural regeneration is increasingly recognized as a potentially cost‐effective strategy to reach ambitious forest landscape restoration targets, but rates of recovery are notoriously variable. We asked how well initial habitat conditions after cessation of agriculture predict forest recovery after nearly a decade. We aimed to provide land managers with general rules of thumb to assess when it is necessary to invest resources in active restoration, such as tree planting, to accelerate forest recovery. LOCATION: Coto Brus County, Puntarenas, Costa Rica. METHODS: We compiled data on initial vegetation structure, soil nutrients, prior land‐use history and surrounding forest cover at 13 sites. After 8.5 years, we measured vegetation indicators commonly used to assess forest recovery, namely amount of canopy closure and number and diversity of woody recruits. RESULTS: Two variables, grass cover and canopy closure, measured 1.5 years after site abandonment, explained 47–87% of five of the six response variables after 8.5 years; recovery was faster in sites with lower grass cover and higher canopy closure initially. Waiting an additional year to measure initial vegetation variables did not improve model fit. Time since the original forest was cleared explained 62% of change in canopy cover, whereas percentage of surrounding forest cover, length of pasture use and soil variables explained minimal additional variation. CONCLUSIONS: Our results suggest that two easily measurable vegetation variables can provide guidance to land managers and policy makers about where to invest scarce restoration resources to facilitate forest recovery.

Applied nucleation and other spatially patterned restoration methods are promising approaches for scaling up projects to meet ambitious international restoration commitments in an ecologically and economically sound manner. Much of the corresponding literature to date, however, has centered around theoretical discussions and small‐scale studies that are largely divorced from constraints faced by restoration practitioners. We briefly review recent academic literature about applied nucleation and other spatially patterned restoration methods and discuss practical challenges to their implementation. We offer several recommendations to move spatially patterned restoration from an academic conversation to scalable application, including: (1) comparing different planting designs and natural regeneration within the same system at an appropriate scale; (2) monitoring ecological outcomes throughout the restored area over sufficient time to evaluate recovery; (3) quantifying costs and documenting other logistical constraints to implementation; and (4) exploring methods for using unplanted areas to provide benefits to landholders until planted vegetation establishes. [ABSTRACT FROM AUTHOR]

Establishing diverse mycorrhizal fungal communities is considered important for forest recovery, yet mycorrhizae may have complex effects on tree growth depending on the composition of fungal species present. In an effort to understand the role of mycorrhizal fungi community in forest restoration in southern Costa Rica, we sampled the arbuscular mycorrhizal fungal (AMF) community across eight sites that were planted with the same species (Inga edulis, Erythrina poeppigiana, Terminalia amazonia, and Vochysia guatemalensis) but varied twofold to fourfold in overall tree growth rates. The AMF community was measured in multiple ways: as percent colonization of host tree roots, by DNA isolation of the fungal species associated with the roots, and through spore density, volume, and identity in both the wet and dry seasons. Consistent with prior tropical restoration research, the majority of fungal species belonged to the genus Glomus and genus Acaulospora, accounting for more than half of the species and relative abundance found on trees roots and over 95% of spore density across all sites. Greater AMF diversity correlated with lower soil organic matter, carbon, and nitrogen concentrations and longer durations of prior pasture use across sites. Contrary to previous literature findings, AMF species diversity and spore densities were inversely related to tree growth, which may have arisen from trees facultatively increasing their associations with AMF in lower soil fertility sites. Changes to AMF community composition also may have led to variation in disturbance susceptibility, host tree nutrient acquisition, and tree growth. These results highlight the potential importance of fungal-tree-soil interactions in forest recovery and suggest that fungal community dynamics could have important implications for tree growth in disturbed soils.

Soil and litter arthropods represent a large proportion of tropical biodiversity and perform important ecosystem functions, but little is known about the efficacy of different tropical forest restoration strategies in facilitating their recovery in degraded habitats. We sampled arthropods in four 7- to 8-year-old restoration treatments and in nearby reference forests. Sampling was conducted during the wet and dry seasons using extractions from litter and pitfall samples. Restoration treatments were replicated in 50 × 50-m plots in four former pasture sites in southern Costa Rica: plantation - trees planted throughout the plot; applied nucleation/islands - trees planted in patches of different sizes; and natural regeneration - no tree planting. Arthropod abundance, measures of richness and diversity, and a number of functional groups were greater in the island treatment than in natural regeneration or plantation treatments and, in many cases, were similar to reference forest. Litter and pitfall morphospecies and functional group composition in all three restoration treatments were significantly different than reference sites, but island and plantation treatments showed more recovery than natural regeneration. Abundance and functional group diversity showed a much greater degree of recovery than community composition. Synthesis and applications: The less resource-intensive restoration strategy of planting tree islands was more effective than tree plantations in restoring arthropod abundance, richness, and functional diversity. None of the restoration strategies, however, resulted in similar community composition as reference forest after 8 years of recovery, highlighting the slow rate of recovery of arthropod communities after disturbance, and underscoring the importance of conservation of remnant forests in fragmented landscapes.

© 2015 Society for Ecological Restoration. Neotropical fruit bats (family Phyllostomidae) facilitate forest regeneration on degraded lands by dispersing shrub and tree seeds. Accordingly, if fruit bats can be attracted to restoration sites, seed dispersal could be enhanced. We surveyed bat communities at 10 sites in southern Costa Rica to evaluate whether restoration treatments attracted more fruit bats if trees were planted on degraded farmlands in plantations or island configurations versus natural regeneration. We also compared the relative influence of tree cover at local and landscape spatial scales on bat abundances. We captured 68% more fruit bat individuals in tree plantations as in controls, whereas tree island plots were intermediate. Bat activity also responded to landscape tree cover within a 200-m radius of restoration plots, with greater abundance but lower species richness in deforested landscapes. Fruit bat captures in controls and tree island plots declined with increasing landscape tree cover, but captures in plantations were relatively constant. Individual species responded differentially to tree cover measured at different spatial scales. We attribute restoration effects primarily to habitat structure rather than food resources because no planted trees produced fruits regularly eaten by bats. The magnitude of tree planting effects on fruit bats was less than previous studies have found for frugivorous birds, suggesting that bats may play a particularly important role in dispersing seeds in heavily deforested and naturally regenerating areas. Nonetheless, our results show that larger tree plantations in more intact landscapes are more likely to attract diverse fruit bats, potentially enhancing seed dispersal.

We agree with Prach and del Moral that passive recovery is often a desirable and effective restoration strategy. Passive and various active restoration approaches need to be weighed on a case-by-case basis and depend on the goals, relative rates of recovery desired, and various social and financial costs implicit in each option. That said, we stress that passive restoration has a unique set of challenges and costs, which we highlighted in our original article and briefly reiterate here.

Plant functional traits, in particular specific leaf area (SLA), wood density and seed mass, are often good predictors of individual tree growth rates within communities. Individuals and species with high SLA, low wood density and small seeds tend to have faster growth rates. If community-level relationships between traits and growth have general predictive value, then similar relationships should also be observed in analyses that integrate across taxa, biogeographic regions and environments. Such global consistency would imply that traits could serve as valuable proxies for the complex suite of factors that determine growth rate, and, therefore, could underpin a new generation of robust dynamic vegetation models. Alternatively, growth rates may depend more strongly on the local environment or growth-trait relationships may vary along environmental gradients. We tested these alternative hypotheses using data on 27 352 juvenile trees, representing 278 species from 27 sites on all forested continents, and extensive functional trait data, 38% of which were obtained at the same sites at which growth was assessed. Data on potential evapotranspiration (PET), which summarizes the joint ecological effects of temperature and precipitation, were obtained from a global data base. We estimated size-standardized relative height growth rates (SGR) for all species, then related them to functional traits and PET using mixed-effect models for the fastest growing species and for all species together. Both the mean and 95th percentile SGR were more strongly associated with functional traits than with PET. PET was unrelated to SGR at the global scale. SGR increased with increasing SLA and decreased with increasing wood density and seed mass, but these traits explained only 3.1% of the variation in SGR. SGR-trait relationships were consistently weak across families and biogeographic zones, and over a range of tree statures. Thus, the most widely studied functional traits in plant ecology were poor predictors of tree growth over large scales. Synthesis. We conclude that these functional traits alone may be unsuitable for predicting growth of trees over broad scales. Determining the functional traits that predict vital rates under specific environmental conditions may generate more insight than a monolithic global relationship can offer. The most widely studied functional traits in plant ecology, specific leaf area, wood density and seed mass, were only weakly associated with tree growth rates over broad scales. Assessing trait-growth relationships under specific environmental conditions may generate more insight than a global relationship can offer.

Past studies have shown that tropical forest regeneration on degraded farmlands is initially limited by lack of seed dispersal, but few studies have tracked changes in abundance and composition of seed rain past the first few years after land abandonment. We measured seed rain for 12 months in 10 6-9-year-old restoration sites and five mature, reference forests in southern Costa Rica in order to learn (1) if seed rain limitation persists past the first few years of regeneration; (2) how restoration treatments influence seed community structure and composition; and (3) whether seed rain limitation is contingent on landscape context. Each restoration site contained three 0.25-ha treatment plots: (1) a naturally regenerating control, (2) tree islands, and (3) a mixed-species tree plantation. Sites spanned a deforestation gradient with 9-89% forest area within 500 m around the treatment plots. Contrary to previous studies, we found that tree seeds were abundant and ubiquitous across all treatment plots (585.1 ± 142.0 seeds · m(-2) · yr(-1) [mean ± SE]), indicating that lack of seed rain ceased to limit forest regeneration within the first decade of recovery. Pioneer trees and shrubs comprised the vast majority of seeds, but compositional differences between restoration sites and reference forests were driven by rarer, large-seeded species. Large, animal-dispersed tree seeds were more abundant in tree islands (4.6 ± 2.9 seeds · m(-2) · yr(-1)) and plantations (5.8 ± 3.0 seeds · m(-2) · yr(-1)) than control plots (0.2 ± 0.1 seeds · m(-2) · yr(-1)), contributing to greater tree species richness in actively restored plots. Planted tree species accounted for < 1% of seeds. We found little evidence for landscape forest cover effects on seed rain, consistent with previous studies. We conclude that seed rain limitation shifted from an initial, complete lack of tree seeds to a specific limitation on large-seeded, mature forest species over the first decade. Although total seed abundance was equal among restoration treatments, tree plantations and tree islands continued to diversify seed rain communities compared to naturally regenerating controls. Compositional differences between regenerating plots and mature forests suggest that large-seeded tree species are appropriate candidates for enrichment planting.

Secondary forests comprise an increasing area of the tropics and play an important role in global carbon cycling. We compare above-ground biomass accumulation of both planted and naturally regenerating trees, as well as C in the top soil layer, in three restoration treatments replicated at 14, six to eight year old restoration sites in southern Costa Rica. Restoration strategies include: control (no planting), planting tree islands, and conventional, mixed-species tree plantations. We evaluate the importance of past land-use, soil nutrients, understory cover, and surrounding forest cover in explaining variation in above-ground biomass accumulation (ABA) rate across sites. Total ABA and planted tree ABA rate were highest in plantations, intermediate in islands, and lowest in control treatments, whereas ABA rate of naturally regenerating trees did not differ across treatments. Most ABA in plantations (89%) and islands (70%) was due to growth of planted trees. Soil carbon did not change significantly over the time period of the study in any treatment. The majority of across-site variation in both total and planted tree ABA rate was explained by duration of prior pasture use. Tree growth in the first two years after planting explained approximately two-thirds of the variation in ABA rate after 6-8. years. Soil nutrient concentrations explained relatively little of the variation in planted or naturally recruiting ABA rate. Our results show that planting trees substantially increases biomass accumulation during the first several years of forest recovery in former agricultural lands and that past-land use has a strong effect on the rate of biomass accumulation. Planting tree islands is a cost-effective strategy for increasing ABA and creating more heterogeneous habitat conditions than tree plantations. We recommend small scale planting trials to quickly assess potential biomass accumulation and prioritize sites for ecosystem service payments for carbon sequestration. © 2014 Elsevier B.V.

Birds both promote and prosper from forest restoration. The ecosystem functions birds perform can increase the pace of forest regeneration and, correspondingly, increase the available habitat for birds and other forest-dependent species. The aim of this study was to learn how tropical forest restoration treatments interact with landscape tree cover to affect the structure and composition of a diverse bird assemblage. We sampled bird communities over two years in 13 restoration sites and two old-growth forests in southern Costa Rica. Restoration sites were established on degraded farmlands in a variety of landscape contexts, and each included a 0.25-ha plantation, island treatment (trees planted in patches), and unplanted control. We analyzed four attributes of bird communities including frugivore abundance, nectarivore abundance, migrant insectivore richness, and compositional similarity of bird communities in restoration plots to bird communities in old-growth forests. All four bird community variables were greater in plantations and/or islands than in control treatments. Frugivore and nectarivore abundance decreased with increasing tree cover in the landscape surrounding restoration plots, whereas compositional similarity to old-growth forests was greatest in plantations embedded in landscapes with high tree cover. Migrant insectivore richness was unaffected by landscape tree cover. Our results agree with previous studies showing that increasing levels of investment in active restoration are positively related to bird richness and abundance, but differences in the effects of landscape tree cover on foraging guilds and community composition suggest that trade-offs between biodiversity conservation and bird-mediated ecosystem functioning may be important for prioritizing restoration sites.

Restoring small-scale habitat heterogeneity in highly diverse systems, like tropical forests, is a conservation challenge and offers an excellent opportunity to test factors affecting community assembly. We investigated whether (1) the applied nucleation restoration strategy (planting tree islands) resulted in higher habitat heterogeneity than more homogeneous forest restoration approaches, (2) increased heterogeneity resulted in more diverse tree recruitment, and (3) the mean or coefficient of variation of habitat variables best explained tree recruitment. We measured soil nutrients, overstory and understory vegetation structure, and tree recruitment at six sites with three 5- to 7-year-old restoration treatments: control (no planting), planted tree islands, and conventional, mixed-species tree plantations. Canopy openness and soil base saturation were more variable in island treatments than in controls and plantations, whereas most soil nutrients had similar coefficients of variation across treatments, and bare ground was more variable in control plots. Seedling and sapling species density were equivalent in plantations and islands, and were substantially higher than in controls. Species spatial turnover, diversity, and richness were similar in island and plantation treatments. Mean canopy openness, rather than heterogeneity, explained the largest proportion of variance in species density. Our results show that, whereas canopy openness and soil base saturation are more heterogeneous with the applied nucleation restoration strategy, this pattern does not translate into greater tree diversity. The lack of a heterogeneity-diversity relationship is likely due to the fact that recruits respond more strongly to mean resource gradients than variability at this early stage in succession, and that seed dispersal limitation likely reduces the available species pool. Results show that planting tree islands facilitates tree recruitment to a similar degree as intensive plantation-style restoration strategies.