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Figure 20 - from "Disturbances of EU forests caused by biotic agents - Final Report"

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arrow_backarrow_forwardDESCRIPTION AND DAMAGE PATHWAY Before the turn between the 19" — 20" Centuries, the American chestnut (Castanea dentata) was arguably the most important broadleaved tree in the forests of the eastern USA, comprising some 25% of the individual trees present in these ecosystems which covered some 81 million hectares. Estimates suggest that over 4 billion chestnut trees were present in the eastern broadleaved forests at the end of the 19” Century. Some of the largest angiosperm trees ever recorded were chestnuts present in these forests. Moreover, the trees were heavily exploited. The fine, hard and durable timber was in great demand for all manner of applications, from carpentry to make furniture, to construction, to railway sleepers (Anon. 1995a). Chestnuts produced reliable seed crops each year and were gathered for sale by many people in the native range of C. dentata. The chestnuts were also an important food source for many wild animals.

DESCRIPTION AND DAMAGE PATHWAY Before the turn between the 19" — 20" Centuries, the American chestnut (Castanea dentata) was arguably the most important broadleaved tree in the forests of the eastern USA, comprising some 25% of the individual trees present in these ecosystems which covered some 81 million hectares. Estimates suggest that over 4 billion chestnut trees were present in the eastern broadleaved forests at the end of the 19” Century. Some of the largest angiosperm trees ever recorded were chestnuts present in these forests. Moreover, the trees were heavily exploited. The fine, hard and durable timber was in great demand for all manner of applications, from carpentry to make furniture, to construction, to railway sleepers (Anon. 1995a). Chestnuts produced reliable seed crops each year and were gathered for sale by many people in the native range of C. dentata. The chestnuts were also an important food source for many wild animals.

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Figure 1
enhancing other goods such as non-wood goods, ecosystem services, and values. between hazard likelihood, susceptibility, and exposure (Kron 2002). Any change in one of these factors will lead to a corresponding change in risk level. In addition, the effects of different forest factors, such as forest types, management traditions, and values, as well as global influences such as climate change and globalised trade need to be considered to cope with biotic disturbances (Figure 1-1). Forest management practices to reach given management goals impact stand composition, structure, and vitality, and consequently affect biotic hazard and the susceptibility of forests to damaging agents. These practices may also include those that aim at enhancing other goods such as non-wood goods, ecosystem services, and values. The different components of biotic risk are difficult to gage. Biotic hazard is much more difficul to characterise than abiotic hazard. Biotic hazard is mainly influenced by the characteristics o the biotic agent. But the sheer diversity of agents of biotic disturbances, comprising pathogens fungi, insect and mammals translates in a diversity of life histories that make generalisation: difficult. Many insects are favoured by warm and dry conditions (Speight and Wainhouse 1989) but fungi favour more moist conditions (Coakley et al. 1999). Low winter temperatures may reduce insect survival rates (Leather et al. 1993), but may on the other hand be favourable for the synchronisation of life cycles with host plant species (Buse and Good 1996). Overall, biotic hazarc depends on the dispersion capacity of the agent, it survival and reproduction conditions, and or biotic interactions (whether negative control by natural enemies, or positive control by mutualism). Clearly thus, biotic hazard will differ between native and alien species, which have not evolved with the native communities and may bring new functions to the forest ecosystem.
Figure 3
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Although many forest services’ do not have clear markets, it seems that overall services providec by forest ecosystems have a greater value than forest products coming from them (EEA 2009). Fo! instance, wood products only represent 35% of the total economic value of Mediterranean forests whereas watershed protection, recreation, and other non-use values add up to half of this value (Merlo and Croitoru 2005; Figure 2-1). When accounting for all those services, the loss of one hectare of Mediterranean forest is estimated to amount to about 133 €/ha/yr. In a mountain fores in Romania, this cost has been estimated at 317€ per year for each hectare of forest, half of whict for water flow regulation, with all timber and non-timber forest goods responsible for 40% 3. These costs are likely to be underestimates; other estimates may reach up to 4100 €/ha/yr (Holmes et al 2006, Mavsar and Riera 2007).
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Table 2-1 Damage caused by the top ten wood-borers in Europe (Grégoire and Evans 2004) Abiotic disturbances, such as storms and droughts, may increase the risks of outbreaks
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Pierre SONIGO
Disturbances of EU forests caused by biotic agents - Final Report

Abstract: We thank all the experts and stakeholders who kindly provided feedback during the course of this study. DISCLAIMER: This report contains the research conducted by the project team and is not to be perceived as the opinion of the European Commission. Please cite this publication as: BIO Intelligence Service (2011), Disturbances of EU forests caused by biotic agents, Final Report prepared for European Commission (DG ENV) Photo credit: cover @ Vik Nanda Disturbances of EU forests caused by biotic agents | 3 Table of Contents LIST OF ACRONYMS CHAPTER 1: INTRODUCTION 1.1 Aim of this report 1.2 Managing forest ecosystems 1.3 State of EU forests 1.4 Disturbances in forest ecosystems 1.5 How to manage biotic risks 1.6 Structure of this report CHAPTER 2: PANORAMA OF THE CURRENT RISKS CAUSED BY BIOTIC AGENTS TO THE DELIVERY OF GOODS AND SERVICES 2.1 Key points 2.2 Trends in damage to EU forests caused by biotic agents 2.2.1 Biotic damages to EU forests 2.2.2 Types of biotic agents 2.2.3 Spatial and temporal scale of damages 2.2.4 Trends in biotic agents over the past fifty years 2.2.5 Influence of forest factors on biotic occurrence and damage 2.2.6 Drivers of changing biotic agents distribution 2.3 Impacts and trends for selected biotic agents 2.3.1 Ips typographus 2.3.2 Anoplophora chinensis 2.3.3 Thaumetopoea pityocampa 2.3.4 Bursaphelenchus xylophilus 2.3.5 Ash dieback 2.3.6 Chestnut Canker 2.3.7 Dutch elm disease 2.3.8 Phytophtora ramorum CHAPTER 3: TOWARDS ECOSYSTEM MANAGEMENT FOR ADAPTATION AND MITIGATION 149 3.1 Key points 3.2 Natural forest dynamics as a benchmark 3.2.1 Successional dynamics-six development stages Disturbances of EU forests caused by biotic agents | 5 5.5.2 Case study of the Swedish forest health monitoring system-a multi-dimensional system with an early warning function 5.5.3 Case study: the EWS for forest health threats in the US 5.6 Conclusions 5.6.1 Key characteristics for an efficient monitoring of forest biotic threats 5.6.2 What can the EU do to improve forest health monitoring?

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