Herbivore diversity effects on Arctic tundra ecosystems: a systematic review.

BACKGROUND: Northern ecosystems are strongly influenced by herbivores that differ in their impacts on the ecosystem. Yet the role of herbivore diversity in shaping the structure and functioning of tundra ecosystems has been overlooked. With climate and land-use changes causing rapid shifts in Arctic species assemblages, a better understanding of the consequences of herbivore diversity changes for tundra ecosystem functioning is urgently needed. This systematic review synthesizes available evidence on the effects of herbivore diversity on different processes, functions, and properties of tundra ecosystems. METHODS: Following a published protocol, our systematic review combined primary field studies retrieved from bibliographic databases, search engines and specialist websites that compared tundra ecosystem responses to different levels of vertebrate and invertebrate herbivore diversity. We used the number of functional groups of herbivores (i.e., functional group richness) as a measure of the diversity of the herbivore assemblage. We screened titles, abstracts, and full texts of studies using pre-defined eligibility criteria. We critically appraised the validity of the studies, tested the influence of different moderators, and conducted sensitivity analyses. Quantitative synthesis (i.e., calculation of effect sizes) was performed for ecosystem responses reported by at least five articles and meta-regressions including the effects of potential modifiers for those reported by at least 10 articles. REVIEW FINDINGS: The literature searches retrieved 5944 articles. After screening titles, abstracts, and full texts, 201 articles including 3713 studies (i.e., individual comparisons) were deemed relevant for the systematic review, with 2844 of these studies included in quantitative syntheses. The available evidence base on the effects of herbivore diversity on tundra ecosystems is concentrated around well-established research locations and focuses mainly on the impacts of vertebrate herbivores on vegetation. Overall, greater herbivore diversity led to increased abundance of feeding marks by herbivores and soil temperature, and to reduced total abundance of plants, graminoids, forbs, and litter, plant leaf size, plant height, and moss depth, but the effects of herbivore diversity were difficult to tease apart from those of excluding vertebrate herbivores. The effects of different functional groups of herbivores on graminoid and lichen abundance compensated each other, leading to no net effects when herbivore effects were combined. In turn, smaller herbivores and large-bodied herbivores only reduced plant height when occurring together but not when occurring separately. Greater herbivore diversity increased plant diversity in graminoid tundra but not in other habitat types. CONCLUSIONS: This systematic review underscores the importance of herbivore diversity in shaping the structure and function of Arctic ecosystems, with different functional groups of herbivores exerting additive or compensatory effects that can be modulated by environmental conditions. Still, many challenges remain to fully understand the complex impacts of herbivore diversity on tundra ecosystems. Future studies should explicitly address the role of herbivore diversity beyond presence-absence, targeting a broader range of ecosystem responses and explicitly including invertebrate herbivores. A better understanding of the role of herbivore diversity will enhance our ability to predict whether and where shifts in herbivore assemblages might mitigate or further amplify the impacts of environmental change on Arctic ecosystems.

Is enhanced biodiversity protection conflicting with ambitious bioenergy targets in eastern Finland?

The study describes how qualitative stakeholder feedback can be used in quantitative scenarios to simulate forest resource use under alternative management objectives. In earlier studies in the region of eastern Finland, stakeholders did not see a possible conflict between increased bioenergy use and nature conservation; this finding is contrary to the results of other studies. The aim of this study was to test with a quantitative modelling approach whether the stakeholder expectation holds and whether forest management in eastern Finland can simultaneously increase biomass utilization and biodiversity protection. Prior to this study, three alternative scenarios on forest resource use were created in a participatory stakeholder process, involving a broad range of stakeholders, with half of them being from research and education. In the current study, a large-scale forest resource planning model (MELA) and a sustainability impact assessment tool (ToSIA) were used to simulate the different alternative scenarios and present the results back to the stakeholders in order to evaluate them. The scenarios were evaluated by stakeholders using multi-criteria analysis. In a survey, the stakeholders indicated that biodiversity, employment, recreational value and greenhouse gas emissions were the most important indicators to them, whereas growing stock, amount of harvested roundwood, energy wood and protected forest area were considered less important. Of the created scenarios, the scenario combining bioenergy and biodiversity targets was the most preferred by the stakeholders as it performed well on those indicators that were identified by stakeholders as the most important. In this scenario, the area of protected forest and bioenergy production were increased simultaneously. With this study we offer a framework for evaluating different alternatives for future land use. The framework helps to identify key issues that are important to the stakeholders so that they can be taken into consideration in future land-use planning. In addition, the results confirm the stakeholder expectation that by protecting more forests while simultaneously increasing the mobilization of potentially available wood resources, both targets can be met without compromising too much other forest functions such as timber production and recreation.

Stakeholder engagement in scenario development process - bioenergy production and biodiversity conservation in eastern Finland.

In this study participatory approaches were used to develop alternative forest resource management scenarios with particular respect to the effects on increased use of forest bioenergy and its effect on biodiversity in Eastern Finland. As technical planning tools, we utilized a forest management planning system (MELA) and the Tool for Sustainability Impact Assessment (ToSIA) to visualize the impacts of the scenarios. We organized a stakeholder workshop where group discussions were used as a participatory method to get the stakeholder preferences and insights concerning forest resource use in the year 2030. Feedback from the workshop was then complemented with a questionnaire. Based on the results of the workshop and a questionnaire we developed three alternative forest resource scenarios: (1) bioenergy 2030 - in which energy production is more centralized and efficient; (2) biodiversity 2030 - in which harvesting methods are more nature friendly and protected forests make up 10% of the total forest area; and (3) mixed bioenergy + biodiversity 2030 scenario - in which wood production, recreation and nature protection are assigned to the most suitable areas. The study showed that stakeholder engagement combined with the MELA and ToSIA tools can be a useful approach in scenario development.