Ecological and Socioeconomic Impacts of Climate-Induced Tree Diebacks in Highland Forests

Background

[caption id="attachment_2340" align="alignleft" width="300"] Figure 1. Entomologists sampling stands of Norway spruce dieback in the Bavarian Forest National Park, Germany. Photo: Heiner M.-Elsner.


Mountain forests play a major role in the preservation of biodiversity and provide important ecosystem services such as climate regulation. However, some of these forests show extensive tree mortality (“forest diebacks”) caused by a combination of factors, such as severe and recurrent summer drought, pollution, and insect and pathogen outbreaks. Some of the most spectacular cases of forest diebacks are caused by bark beetle outbreaks, which have killed millions of hectares of conifer forests worldwide (Fig. 1).

Forest diebacks are expected to become more widespread, frequent and severe. Indeed, warm and dry climate conditions increase the number of bark beetle generations per year and decrease tree vigor. Diebacks are accompanied by changes in tree species composition, which can happen either by natural regeneration or by artificial replacement with better-adapted species (i.e., those less sensitive to drought). The question of how to manage forest diebacks is a significant concern for forest stakeholders. Which tree species should be replanted? What should be done with the large volumes of deadwood? The ecological impact of harvesting and removing dead, dying trees (salvage logging, sanitation salvage) is the subject of heated debate.

[caption id="attachment_2339" align="alignright" width="297"] Figure 2. A Malayse sample containing thousands of ying insects kept in ethanol.


How forest diebacks and associated tree replacements affect changes in biodiversity and ecosystem functions and services remains poorly known. Similarly, how global changes in mountain forests affect local economic activities is poorly understood. The lack of data on the ecological impact of mountain forest diebacks is partly due to insufficient biomonitoring. Traditional biomonitoring schemes are expensive and very labor-intensive, as they require managing large amounts of samples and taxa (Fig. 2).

Fortunately, the recent development of affordable high- throughput sequencing is revolutionizing the eld of biomonitoring. High-throughput sequencing allows the user to simultaneously amplify and sequence specimens of all species in mixed samples, a technique known as meta-barcoding.

Main Objectives

• To measure the ecological impact of mountain forest die-offs and the salvage harvest of four ecologically and economically important conifers: Norway spruce (Picea abies) in the German Bohemian forest; silverfir (Abies alba) in the French Pyrenees; Scots pine (Pinus sylvestris) in the Italian Alps, and Yunnan pine (Pinus yunnanensis) in China by inventorying terrestrial and freshwater invertebrates and fungi in experimental forest plots.
• To develop a new biomonitoring pipeline that will be simple to use and provide an affordable, reliable, and verifiable way of monitoring forest biodiversity at a large geographical scale.
• To measure the socioeconomic impact of forest mountain die-offs and salvage logging from surveys in Europe and China.
• To identify the ecological and economic factors that influence stakeholder decisions and recommend more specific policy actions based on the findings of the socio-economic study.

ClimTree Consortium

[caption id="attachment_2338" align="alignleft" width="300"] Figure 3. Laurent Larrieu, Philippe Deuffic and Marius Mayer assessing the level of silver fir dieback in the Pyrenees


Our team comprises researchers from 13 institutions and four countries (China, Italy, Germany and France) with strong expertise in community ecology, social science, economy, geography, entomology, DNA (meta)barcoding, biostatistics, freshwater ecology and forest management. Three PhD students and seven Master students will be trained during the three-year project.

Current Work

Experimental plots with various degrees of forest decline have been identified in the French Pyrenees (France), Bavarian Forest National Park (Germany), and Yunnan mountains (China). Environmental characterization of experimental plots using both dendrometric measurements and dieback assessment is underway (Fig. 3). Malayse traps have been set up in the Bavarian Forest National Park and Yunnan mountains (Fig. 4). Samples will be metabarcoded in the forthcoming months. Flying saproxylic beetles are sampled with two cross-vane flight interception traps (PolytrapTM) per plot. Terrestrial micro-invertebrates living in leaf litter (meiofauna) are extracted in the lab from soil samples collected in the field.

[caption id="attachment_2336" align="alignright" width="300"] Figure 5. Participants of the 1st ClimTree meeting at Espezel (Pays de Sault, France)


ClimTree held its first meeting 10-11 October 2016 at INRA Toulouse in southern France (Fig. 5). We visited some experimental plots that show various degrees of forest diebacks of silver r in the Pays de Sault in the eastern Pyrenees. Silver fir is a drought sensitive tree species with low nutrient demands but high moisture requirements. Since 2003, silver r shows severe growth decline in the Pyrenees and Southern Alps, particularly below 1000 m of altitude and on south facing slopes, rocky crests, and limestone areas.

A field campaign is currently planned for 2017, including qualitative and quantitative socio-economic surveys.

This article was published in the Mountain Views / Mountain Meridian by Carlos Lopez Vaamonde, URZF INRA, Orléans, France

Pictures by the authors unless noted otherwise.