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Despite increasing attention for relationships between species richness and ecosystem services, for tropical forests such relationships are still under discussion. Contradicting relationships have been reported concerning carbon stock, while little is known about relationships concerning timber stock and the abundance of non-timber forest product producing plant species (NTFP abundance). Using 151 1-ha plots, we related tree and arborescent palm species richness to carbon stock, timber stock and NTFP abundance across the Guiana Shield, and using 283 1-ha plots, to carbon stock across all of Amazonia. We analysed how environmental heterogeneity influenced these relationships, assessing differences across and within multiple forest types, biogeographic regions and subregions. Species richness showed significant relationships with all three ecosystem services, but relationships differed between forest types and among biogeographical strata. We found that species richness was positively associated to carbon stock in all biogeographical strata. This association became obscured by variation across biogeographical regions at the scale of Amazonia, resembling a Simpson’s paradox. By contrast, species richness was weakly or not significantly related to timber stock and NTFP abundance, suggesting that species richness is not a good predictor for these ecosystem services. Our findings illustrate the importance of environmental stratification in analysing biodiversity-ecosystem services relationships.

Tropical forests are rich in plant diversity while also delivering essential 'ecosystem services': goods and services that benefit our well-being. However, tropical forests are under increasing pressure of deforestation and degradation, threatening our well-being and life on Earth in general. New conservation measures are increasingly focussing on protecting ecosystem services under the assumption that biodiversity and ecosystem services are positively linked. If this assumption is true, then protecting ecosystem services would help to protect biodiversity as well. Yet, for tropical forests, relationships between plant diversity and ecosystem services are unclear. This thesis identified three important knowledge gaps. First, it is unclear how plant diversity in a broad sense (including taxonomic, functional and structural diversity) is related to the 'stock' (which represents potential use) and the 'flow' (representing actual use) components of ecosystem services. Second, questions have been raised on how using a different 'plot size' (the geographical area of the vegetation measurement) or 'geographical extent' (the geographical area from which plots were sampled) can affect the outcome of tested relationships. Third and last, it is unknown how the combination of ecological factors, such as the distribution and production of plant species, and socio-economic factors, such as the cost of harvest and the price on the market, related to the delivery of ecosystem services can influence relationships. CONTENTS Lay Summary ContentsChapter 1 General Introduction Chapter 2 Shedding light on relationships between plant diversity and tropical forest ecosystem services across spatial scales and plot sizes Supplementary Material Chapter 2 Chapter 3 Relationships between species richness and ecosystem services in Amazonian forests strongly influenced by biogeographical strata and forest types Supplementary Material Chapter 3 Chapter 4 Exploring relationships between abundance of non-timber forest product species and tropical forest plant diversity Supplementary Material Chapter 4 Chapter 5 From forest stock to market: assessing the economic value of plant-based non-timber forest products and their conservation relevance in Suriname Supplementary