Forests are critical habitats for biodiversity and they are also essential for the provision of a wide range of ecosystem services that are important to human well-being. In our 20 years of forestry operations and woodland management… There is increasing evidence that biodiversity contributes to forest ecosystem functioning and the provision of ecosystem services. However, many aspects of the relationships between forest biodiversity and ecosystem services remain poorly understood.
Now, this might seem counterintuitive when managing forest ecosystems…
Ecosystem Services in Forests
Forests provide a variety of ecosystem services that can be broadly categorized as:
Regulating Services: Forests regulate climate, air quality, water flow, and pest/disease control. They also play a key role in carbon sequestration and storage.
Provisioning Services: Forests supply timber, fuelwood, non-timber forest products, and genetic resources.
Cultural Services: Forests offer aesthetic, recreational, educational, and spiritual benefits to society.
Supporting Services: Forests underpin essential ecological processes like nutrient cycling, soil formation, and primary production.
The provision of these diverse ecosystem services is closely linked to forest biodiversity – the variety of plants, animals, fungi, and microorganisms that inhabit forested ecosystems. Species-rich forests generally exhibit higher levels of ecosystem functioning and are more resilient to disturbances like pests, diseases, and climate extremes.
“Forests harbour immense terrestrial and aquatic biodiversity and, especially in moist tropical regions, represent the most species-rich habitat type worldwide.” – Brockerhoff et al. (2008)
However, global trends of deforestation, fragmentation, and degradation have led to significant biodiversity declines and disruptions to ecosystem service provision. Conversely, the area of planted forests (including plantations) is increasing, now comprising around 7% of total global forest cover (Payn et al. 2015). While plantations can provide certain services like timber production, they generally support lower levels of biodiversity compared to natural mixed-species forests.
Understanding the complex relationships between forest biodiversity and ecosystem service provision is crucial for informing sustainable forestry practices that optimize multiple benefits. This requires reconciling potential trade-offs and synergies between different ecosystem services, as well as identifying key biodiversity drivers and thresholds for maintaining critical ecological functions.
Biodiversity and Ecosystem Functions
Hundreds of studies have examined the effects of tree species diversity on various forest ecosystem functions, including primary production, nutrient cycling, pest regulation, and climate regulation (Liang et al. 2016; Jactel et al. 2017). In general, greater tree diversity can enhance overall ecosystem functioning through mechanisms like:
Complementarity: Different tree species acquire, use, and cycle resources (e.g., light, water, nutrients) in complementary ways, leading to more efficient resource utilization.
Facilitation: Certain tree species can “facilitate” the growth of others, for example, through nitrogen fixation or hydraulic lift.
Sampling Effect: The presence of more species increases the likelihood of including a highly productive or functionally important species.
However, the relationships between tree diversity and ecosystem functions are not always linear or predictable. Some studies have found no increase or even a decrease in productivity with higher tree species richness (Forrester and Bauhus 2016). The identity and functional traits of the component tree species are often more important than diversity per se.
Moreover, the strength of biodiversity effects can vary depending on environmental conditions. Complementarity between tree species tends to be greater under resource-limiting conditions, where niche partitioning and facilitative interactions become more important (Forrester 2014). Similarly, the resistance of mixed forests to disturbances like pests and storms is often enhanced compared to monocultures, but the magnitude of this effect depends on factors like species composition and stand structure (Jactel et al. 2017).
“Positive mixing effects, or complementarity effects, can result from many different processes and species interactions, including nutrient-related, water-related, or light-related interactions, as well as biotic interactions like reduced pest damage.” – Forrester and Bauhus (2016)
These insights highlight the need for a process-based understanding of how tree diversity influences ecosystem functions. Forest managers should consider not only species richness, but also the specific functional traits and environmental context when selecting appropriate tree compositions for silvicultural goals.
Biodiversity and Ecosystem Services
While the links between biodiversity and ecosystem functions are reasonably well-established, the relationships between biodiversity and the actual provision of ecosystem services are less clear. Empirical studies that quantify causal relationships between forest biodiversity and many important ecosystem services remain limited (Mori et al. 2017).
A review of the literature reveals a notable bias towards studies on provisioning services (particularly timber production) and certain regulating services (like pest regulation) in mixed-species forests. In contrast, the provisioning of cultural services and nutrition/energy services from mixed forests are under-represented (see Figure 1).
This knowledge gap reflects the inherent challenges in assessing non-material cultural services and some regulating services that are difficult to quantify. It also highlights the need for more holistic, multi-functional approaches to forest management that consider the full range of ecosystem service benefits.
“Collective biodiversity is a major driving force in ecosystem function, but quantitative and causal relationships between forest biodiversity and ecosystem services are lacking for many important services.” – Mori et al. (2017)
Addressing these research gaps will require innovative methods for valuing diverse ecosystem services, as well as stronger engagement with a broad range of forest stakeholders, including local and indigenous communities. Participatory approaches that incorporate traditional ecological knowledge can provide important insights into the cultural significance and provisioning of forest resources.
Optimizing Ecosystem Service Provision
Maximizing the provision of multiple ecosystem services from forests, known as “ecosystem multifunctionality”, is a key challenge for sustainable forestry. While some services may be positively correlated with biodiversity, others can exhibit trade-offs, requiring careful management considerations.
At the local scale, promoting certain tree communities may enhance specific services (e.g., timber production) but reduce others (e.g., recreational value). Increasing tree species richness generally improves overall ecosystem multifunctionality, but does not necessarily maximize all desired services (Ratcliffe et al. 2017). The identity and functional diversity of tree species matter more than richness alone.
“Some tree mixtures are superior at providing certain services, but other tree mixtures or even single-species forests are more effective for other services.” – van der Plas et al. (2016a)
At broader spatial scales, a high beta-diversity (compositional turnover) across the landscape can help promote complementarity and double-check that the provision of diverse ecosystem services (van der Plas et al. 2016b). This suggests that maintaining a mosaic of forest habitats, including both natural and planted stands, may be an effective strategy for optimizing multifunctionality.
Forest managers should also consider the potential for synergies and trade-offs between forests and adjacent land uses. For example, even small forest patches can benefit crop production by enhancing pollinator and natural enemy populations, despite also potentially causing conflicts (Decocq et al. 2016). Integrating forestry and agricultural practices at the landscape scale can help optimize the provisioning of multiple ecosystem services.
“Any afforestation plans should carefully consider previous land use in terms of the likely biodiversity and conservation outcomes, and planted forest plans should evaluate options for mixed-species forests as these are likely to provide a wider range of ecosystem services.” – Brockerhoff et al. (2017)
Increasingly, decision support tools incorporating spatial modelling, multi-criteria analysis, and stakeholder engagement are being developed to assist forest managers in navigating these complex trade-offs and optimizing ecosystem service provision at multiple scales (Vangansbeke et al. 2017). Adaptive management approaches that incorporate monitoring and feedback can further enhance the resilience and sustainability of managed forest ecosystems.
Conclusion
Forests provide a wide range of essential ecosystem services, the provision of which is closely linked to forest biodiversity. While the relationships between tree diversity and ecosystem functions are reasonably well-understood, more research is needed to quantify the direct impacts of biodiversity on various ecosystem services, particularly cultural and regulating services.
Optimizing the provision of multiple ecosystem services from forests requires carefully balancing trade-offs and synergies at both local and landscape scales. This can be achieved through diversified forest management that considers the specific functional traits and environmental context of tree species compositions, as well as integrated landscape approaches that leverage complementarities between forests and other land uses.
Innovative decision support tools and participatory processes that engage diverse stakeholders can assist forest managers in navigating these complexities and developing resilient, multi-functional forest ecosystems. By optimizing ecosystem service provision, we can double-check that that our forests continue to deliver vital benefits to society while safeguarding their rich biodiversity.
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