Low-productivity forests are often the last remaining pristine forests in managed forest landscapes and typically overrepresented among protected forests. However, the provisioning of individual and multiple ecosystem services (ES-multifunctionality) by these forests remains poorly assessed, making it difficult to evaluate their importance in forest conservation and management. Using nationwide data on ecosystem services (ES) from forest plots, we test whether levels of ES-multifunctionality and individual ES differ between low-productivity forested mires and rocky outcrops in relation to the levels of productive forests, and as a function of forest age, tree species richness and climate. We defined ES-multifunctionality using different threshold values of the maximum levels (low, medium and high) and weighted these according to land-use objectives (equal weight of all services, greater weight to cultural and supporting ES, or greater weight to production). We show that the ES-multifunctionality of forested mires is consistently lower than those of productive forests. However, the ES-multifunctionality increased with forest age in forested mires but not in productive forests. The ES-multifunctionality of forested rocky outcrops, on the other hand, was higher or equivalent to that of productive forests under equal weight and supporting land-use objectives, respectively. Our findings highlight that forested rocky outcrops can supply multiple ES, especially older forested stands with mixtures of coniferous and deciduous trees. Generally, we found no evidence for strong trade-offs between the ES studied and our results highlight the importance of forest age for increasing the ES-multifunctionality of low-productivity forests.

Synthesis and applications. Low-productivity forests should not be exempt of forestry or protected purely based on low productivity or low land-use conflict if the goal is to conserve multiple ecosystem services (ES). Inclusion grounds for protecting low-productivity forests should instead carefully consider the site type (dry versus wet), forest age, and tree species richness. In order to maintain higher ES-multifunctionality in low-productivity forests, older or deciduous trees should also not be harvested. This will require changes in current conservation or management policies of low-productivity forests of some countries.

Ecosystem service multifunctionality values from forested mires

Ecosystem service multifunctionality (ES-multifunctionality) values calculated from nationwide Swedish data on nine ecosystem services in circular plots (314 m²) located in forested mires and productive forests of similar age, tree species dominance by Scots pine Pinus sylvestris, and geographic location. The ES-multifunctionality values use different threshold values of the maximum levels (low =25%, medium=50% and high=75%) of ecosystem service values and are weighted according to three land-use objectives (equal weight of all services, greater weight to cultural and supporting services, or greater weight to tree biomass production). Abbreviations: ID (individual plot identifier), T25_EQUAL_WT (scaled and summed ES-multifunctionality values surpassing 25% of maximum levels and all services weighted equal), T25_SUPPORTING (ES-multifunctionality values surpassing 25% of maximum levels and and greater weight to cultural and supporting services), T25_PRODUCTION (ES-multifunctionality values surpassing 25% and greater weight to tree biomass production services), T50_EQUAL_WT (scaled and summed ES-multifunctionality values surpassing 50% of maximum levels and all services weighted equal), T50_SUPPORTING (ES-multifunctionality values surpassing 50% of maximum levels and and greater weight to cultural and supporting services), T50_PRODUCTION (ES-multifunctionality values surpassing 50% and greater weight to tree biomass production services), T75_EQUAL_WT (scaled and summed ES-multifunctionality values surpassing 75% of maximum levels and all services weighted equal), T75_SUPPORTING (ES-multifunctionality values surpassing 75% of maximum levels and and greater weight to cultural and supporting services), T75_PRODUCTION (ES-multifunctionality values surpassing 75% and greater weight to tree biomass production services), Site_type (forested mire or productive forest), Forest_stand_age (years), Tree_species_richness (number of tree species with diameter at breast height >= 10 cm), Temp_Ann_99to10 (mean annual temperature averaged over 1999-2010), and Sum_Prec_Season_99to10 (summed precipitation May-November (mm) averaged over 1999-2010). 

Ecosystem service multifunctionality values from forested rocky outcrops

Ecosystem service multifunctionality (ES-multifunctionality) values calculated from nationwide Swedish data on nine ecosystem services in circular plots (314 m²) located in forested rocky outcrops and productive forests of similar age, tree species dominance by Scots pine Pinus sylvestris, and geographic location. The ES-multifunctionality values use different threshold values of the maximum levels (low =25%, medium=50% and high=75%) of ecosystem service values and are weighted according to three land-use objectives (equal weight of all services, greater weight to cultural and supporting services, or greater weight to tree biomass production). Abbreviations: ID (individual plot identifier), T25_EQUAL_WT (scaled and summed ES-multifunctionality values surpassing 25% of maximum levels and all services weighted equal), T25_SUPPORTING (ES-multifunctionality values surpassing 25% of maximum levels and and greater weight to cultural and supporting services), T25_PRODUCTION (ES-multifunctionality values surpassing 25% and greater weight to tree biomass production services), T50_EQUAL_WT (scaled and summed ES-multifunctionality values surpassing 50% of maximum levels and all services weighted equal), T50_SUPPORTING (ES-multifunctionality values surpassing 50% of maximum levels and and greater weight to cultural and supporting services), T50_PRODUCTION (ES-multifunctionality values surpassing 50% and greater weight to tree biomass production services), T75_EQUAL_WT (scaled and summed ES-multifunctionality values surpassing 75% of maximum levels and all services weighted equal), T75_SUPPORTING (ES-multifunctionality values surpassing 75% of maximum levels and and greater weight to cultural and supporting services), T75_PRODUCTION (ES-multifunctionality values surpassing 75% and greater weight to tree biomass production services), Site_type (forested rocky outcrop or productive forest), Forest_stand_age (years), Tree_species_richness (number of tree species with diameter at breast height >= 10 cm), Temp_Ann_99to10 (mean annual temperature averaged over 1999-2010), and Sum_Prec_Season_99to10 (summed precipitation May-November (mm) averaged over 1999-2010).