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  1. Abstract

    Large terrestrial herbivorous mammals (LTH‐mammals) influence plant community structure by affecting seedling establishment in mature tropical forests. Many of these LTH‐mammals frequent secondary forests, but their effects on seedling establishment in them are understudied, hindering our understanding of how LTH‐mammals influence forest regeneration in human‐modified landscapes.

    We tested the hypothesis that the strength of LTH‐mammals' effects on seedling establishment depends on landscape protection, forest successional stage and plant species' traits using a manipulative field experiment in six 1‐ha sites with varying successional age and landscape protection. In each site, we established 40 seedling plot‐pairs, with one plot excluding LTH‐mammals and one not, and monitored seedlings of 116 woody species for 26 months.

    We found significant effects of LTH‐mammal exclusion on seedling survival contingent upon the protection of forests at the landscape level and forest stage. After 26 months, survival differences between LTH‐mammal exclusion and non‐exclusion treatments were greater in protected than unprotected landscapes. Additionally, plant species' traits were related to the LTH‐mammals' differential effects, as LTH‐mammals reduced the survival of seedlings of larger‐seeded species the most. Overall, LTH‐mammals' effects translated into significant shifts in community composition as seedling communities inside and outside the exclosures diverged. Moreover, lower density and higher species diversity were found as early as 12 and 18 months outside than inside exclosures.

    Synthesis and applications.Insight into the interactions between LTH‐mammals and seedling communities in forest regeneration can be instrumental in planning effective restoration efforts. We highlight the importance of landscape protection in seedling survival and the role of LTH‐mammals in promoting seedling diversity in mature forests but also in secondary successional forests. The findings suggest that conservation efforts and possibly trophic rewilding can be important approaches for preserving diversity and influencing the trajectory of secondary tropical forest succession. However, we also caution that an overabundance of LTH‐mammals may adversely impact the pace of forest succession due to their preference for large‐seeded species. Therefore, a comprehensive wildlife management plan is indispensable. Additionally, longer term studies on LTH‐mammals are necessary to understand the effects of temporal fluctuations that are undetected in short‐term studies.

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  2. null (Ed.)
  3. Abstract

    Forest restoration targets are often planned, implemented, measured and reported based on few short‐term lagging indicators (i.e. indicators of realised outcomes), such as the number of seedlings and area planted.

    We propose the use of leading indicators, which denote likelihood of a certain outcome (e.g. odds that seedlings are of quality and properly planted) to complement lagging indicators and describe how this construct differs from the current practice and how they can be used in conjunction with available frameworks for forest restoration.

    Leading indicators have great promise to complement lagging indicators because they address the near‐term factors more likely to influence the progress and performance of restoration efforts. For example, secure land tenure (leading indicator) can increase the likelihood of long‐term maintenance and protection (lagging indicator), and the use of best practices in quality seedling production (leading indicator) can increase survival rate (lagging indicator).

    By observing near‐term leading indicators, management can be adapted towards a goal. Long‐term impacts cannot be verified in the early stages of forest restoration, hence claiming success within the length of project cycles is often unrealistic. Reporting on leading indicators can inform the likelihood that forest restoration goals will be achieved in the longer term.

    Synthesis and applications. Leading indicators complement lagging indicators and can be used in forest restoration beyond monitoring and evaluation. Indicators can also be used in the design, adaptive management and reporting of restoration interventions. Leading indicators can be used to identify issues that might prevent success in a timely manner so they can be addressed.

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  4. null (Ed.)
    Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of five decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both old-growth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modified tropical landscapes. 
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