Forests are frequently exposed to natural disturbances, which are likely to increase with global change, and may jeopardize the delivery of ecosystem services. Mixed-species forests have often been shown to be more productive than monocultures, but it is unclear whether this results from mixed stands being in part more resistant to various biotic and abiotic disturbance factors. This review investigates the relationships between tree diversity and stand resistance to natural disturbances and explores the ecological mechanisms behind the observed relationships. Mixed forests appear to be more resistant than monocultures to small mammalian herbivores, soil-borne fungal diseases and specialized insect herbivores. Admixing broadleaves to conifers also increases the resistance to fire and windstorms when compared to pure conifer stands. However, mixed forests may be more affected by drought depending on the species in the mixture. Overall, our findings suggest that mixed forests are more resistant to natural disturbances that are relatively small-scale and selective in their effect. However, benefits provided by mixtures are less evident for larger-scale disturbances. Higher tree diversity translates into increased resistance to disturbances as a result of ecological trait complementarity among species, reduction of fuel and food resources for herbivores, enhancement of diversion or disruption processes, and multi-trophic interactions such as predation or symbiosis. To promote resistance, the selection of tree species with different functional characteristics appears more important than increasing only the number of species in the stand. Trees with different levels of susceptibility to different hazards should be intermixed in order to reduce the amount of exposed resources and to generate barriers against contagion. However, more research is needed to further improve associational resistance in mixed forests, through a better understanding of the most relevant spatial and temporal scales of species interactions and to optimize the overall provision of ecosystem services.

Tree Diversity Drives Forest Stand Resistance to Natural Disturbances

Mixed-species versus monocultures in plantation forestry: Development, benefits, ecosystem services and perspectives for the future

The planting of forests has been met with both scepticism and support in international forest policy and management fora Discussions regarding the values of plantations for extrinsic purposes such as timber supply, carbon sequestration, water quality and biodiversity conservation, reveal widely varying opinions across and within different settings Recent research highlights the role of planted forests in providing multiple ecosystem services to human society However, there has been little assessment of ecosystems services, partly due to lack of suitable frameworks and evaluation tools Planted forests generally have low ecosystem services values initially and are more vulnerable to erosion and other impacts of mismanagement than natural forests Careful monitoring of change in ecosystem services values over time is therefore vital to investors and all stakeholders in plantations Drawing on lessons derived from ecosystem services assessment for various land use types, here we propose an easy-to-apply framework to assess ecosystem services from planted forests that could be used in various planted forest types around the world A necessary next step for researchers and practitioners is to test the proposed framework under various settings

https://www.cifor.org/publications/pdf_files/articles/ABaral1604.pdf

A proposed framework for assessing ecosystem goods and services from planted forests

How climate change adaptation and mitigation strategies can threaten or enhance the biodiversity of production forests: Insights from Sweden

Knowledge gaps about mixed forests: What do European forest managers want to know and what answers can science provide?

Whereas there is evidence that mixed-species approaches to production forestry in general can provide positive outcomes relative to monocultures, it is less clear to what extent multiple benefits can be derived from specific mixed-species alternatives. To provide such insights requires evaluations of an encompassing suite of ecosystem services, biodiversity, and forest management considerations provided by specific mixtures and monocultures within a region. Here, we conduct such an assessment in Sweden by contrasting even-aged Norway spruce (Picea abies)-dominated stands, with mixed-species stands of spruce and birch (Betula pendula or B. pubescens), or spruce and Scots pine (Pinus sylvestris). By synthesizing the available evidence, we identify positive outcomes from mixtures including increased biodiversity, water quality, esthetic and recreational values, as well as reduced stand vulnerability to pest and pathogen damage. However, some uncertainties and risks were projected to increase, highlighting the importance of conducting comprehensive interdisciplinary evaluations when assessing the pros and cons of mixtures.

/pdf/replacing-monocultures-with-mixed-species-stands-ecosystem-4w7jiy99iz.pdf

Kristina Wallertz

Papers

Replacing monocultures with mixed-species stands: Ecosystem service implications of two production forest alternatives in Sweden