Summary In tropical countries where little natural forest remains, such as the Philippines, small‐holder monocultures and mixed‐species plantations potentially provide conservation values by providing habitat for local fauna and recruiting diverse understorey species. However, little information exists as to whether monocultures offer a framework to kick‐start understorey species recruitment and how this compares to mixtures. In this study, species and trait diversity were measured within the understories of three different forest types on the Island of Leyte, Philippines: mixed‐species forests (known as ‘Rainforestation Farming’), Swietenia macrophylla monocultures and regenerating selectively logged forests. All plants less than 2 m in height were identified, and dispersal type, fruit type, seed and fruit size were extracted from literature and online data bases. We found that overall seedling richness and diversity were lower within the monoculture forests compared with the regenerating selectively logged forests, with the Rainforestation forests showing intermediate seedling diversity, including trait diversity. Monoculture understories had a higher proportion of large fruited domesticated species that are likely dispersed by people and significantly lower wind‐dispersed native seedlings than the other forest types. Higher understorey diversity was generally negatively correlated with soil nutrients and positively correlated with increased leaf area index, that is more canopy cover. Our results confirm that mixed‐species plantations and regenerating selectively logged forests recruit higher species diversity, but we also found evidence that monocultures can recruit diverse species in the understorey. However, monoculture understories were depauperate of native wind‐dispersed traits that are often important emergent species in tropical rain forests. Synthesis and applications. Overall, our results show that just having trees in a cleared landscape provides conservation value, but if monocultures are used as less costly and technically simpler solutions for initiating recruitment, then wind‐dispersed native species (e.g. species from the Dipterocarpaceae family) in addition to other limited functional traits (e.g. large‐seeded species) should be planted to enhance long‐term survival of ecologically significant native tree populations.

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Alternative methods for restoring tropical forests influence the ecological processes that shape recruitment of understory species. In turn, the traits of species recruited will influence the ecological processes the forests provide now and over the long term. We assess the phylogenetic and functional structure of seedlings beneath monoculture plantations, mixed-species plantations (both active restoration) and regenerating selectively logged native forests (passive restoration), considering traits of specific leaf area (SLA, including within-species variation), leaf nitrogen and phosphorus content, life-form, potential plant height, and dispersal type. Monoculture plantations comprised seedlings that were more closely related then would be expected by chance (i.e., phylogenetically clustered), and regenerating forest contained species more distantly related then would be expected by chance (i.e., phylogenetically overdispersed). This suggests that seedlings beneath monocultures assemble through environmental filtering and through the dispersal limitation of predictable functional guilds. However, dispersal limitation is frequently overcome by human-assisted dispersal, increasing trait diversity. Comparing SLA values revealed that regenerating forests recruit seedlings with both high and low mean and variation of SLA, leading to higher overall diversity. Regenerating forest seedlings showed signs of environmental filtering, only based on within-species variation of SLA. Regenerating forest understories appear to favor species that show a high intraspecific variation in SLA values (e.g., Pterocarpus indicus Willd.) and at the same time provided habitat for later successional seedlings that show a lower intraspecific variation in SLA (e.g., Canarium luzonicum (Blume) A.Gray). This trait diversity suggests limiting similarity or competitive exclusion may be reduced because of niche differences, allowing species with different traits to coexist. Phylogenetic and functionally distinct species are restricted in their regeneration capacity, many of which are of conservation significance (under the IUCN Red List). Reforestation projects should maximize desired ecological services (including conservation value) by actively managing for the recruitment of species that are phylogenetically and functionally (including intraspecifically) distinct. This management aim will increase the probability of fulfilling a wider array of niche spaces and potentially increase the diversity of ecosystem services provided.

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