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•Pine stand colonization by PPM increases with pine density.•The proportion of attacked pines decreases with pine density.•Birch provides pure associational resistance by reducing ...pine apparency.•Apparency effects occur within and between stands.•Associational resistance fades with time.
Mixed forests are thought to be less prone to pest insect damage than monocultures. This may result from reduced host availability (i.e., density effect) or from non-host trees reducing the physical or chemical apparency of host trees (i.e., associational resistance, AR). However, associational and density effects are often confounded in mixed forests. We aimed to disentangle their relative contribution to attacks of pine trees by a specialist pest, the pine processionary moth (PPM, Thaumetopoea pityocampa). We assessed pine infestation by PPM by counting the number of winter nests during three consecutive years along an experimental gradient of pine density in presence or absence of a fast growing species, namely birch. The total number of PPM nests per plot increased with pine density (maximum in high density monocultures), while the proportion of attacked pine trees decreased along the same gradient. Birch provided associational resistance via reduced pine apparency due to their greatest higher. This mechanism occurred at two spatial scales, whenever birch was planted within pine plots or in adjacent plots. Associational resistance was stronger in dense stands, probably due to reduced distance between pines and neighboring birches. But AR faded with time, pines becoming taller than birches, making density effects preeminent over apparency effects. Our findings suggest that mixing tree species to trigger resistance to pest insects requires taking into account the relative growth rate of associated species together with the relative proportion of associated species, both within and between stands.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The reduction of insect herbivory is one of the services provided by tree diversity in forest ecosystems. While it is increasingly acknowledged that the compositional characteristics of tree species ...assemblages play a major role in triggering associational resistance to herbivores, underlying mechanisms are less well known. We addressed this question in the ORPHEE experiment by assessing pine processionary moth infestations (Thaumetopoea pityocampa) across a tree diversity gradient from pine monocultures to five species mixtures. We showed that tree species richness per se had no effect on the probability of attack by this pest. By contrast, the infestation rate was strongly dependent on plot composition. Mixtures of pines (Pinus pinaster) and birches (Betula pendula) were less prone to T. pityocampa infestations, whereas mixtures of pines and oaks (Quercus spp.) were more often attacked than pine monocultures. By taking into account the relative height of pines and associated broadleaved species, this effect could be explained by pine apparency. Pines were on average 343±5cm height. Birches, as fast growing trees, were slightly taller than pines (363±6cm), while oak trees were significantly smaller (74±1cm). Host trees of T. pityocampa were then partly hidden in mixtures of pines and birches but more apparent in mixtures with oaks. We suggest that reduced pine apparency disrupted visual cues used by female moths to select host trees prior to oviposition. This study highlights the need to take into account tree traits such as growth rate when selecting the tree species that have to be associated in order to improve forest resistance to pest insects.
Die Reduktion von Pflanzenfraß durch Insekten ist eine der Leistungen, die von der Baumdiversität in Waldökosystemen erbracht wird. Während zunehmend anerkannt wird, dass die Zusammensetzung von Baumgemeinschaften eine wichtige Rolle beim Auslösen von gemeinschaftlicher Abwehr gegen Herbivore spielt, ist über die zugrunde liegenden Mechanismen wenig bekannt. Wir untersuchten diese Frage im ORPHEE-Experiment, indem wir den Befall durch den Pinienprozessionsspinner (Thaumetopoea pityocampa) über einen Gradienten von Monokultur bis zur Fünf-Arten-Mischung registrierten. Wir zeigten, dass der Baum-Artenreichtum per se keinen Einfluss auf die Befallswahrscheinlichkeit hatte. Dagegen hingen die Befallsraten stark von der Zusammensetzung der Bestände ab. Systeme von Pinie (Pinus pinaster) und Birke (Betula pendula) wurden weniger stark befallen, während Mischungen von Pinien und Eichen (Quercus spp) häufiger als Reinbestände von Pinien attackiert wurden. Wenn man die relative Höhe von Pinien und der vergesellschafteten Laubbaumarten in Betracht zieht, könnte dieser Effekt mit der Apparenz der Pinien erklärt werden. Die Pinien waren im Mittel 343 ± 5 cm hoch. Die Birken waren als schnellwachsende Bäume etwas höher 363 ± 6 cm) als die Pinien, während die Eichen bedeutend kleiner waren (74 ± 1 cm). Die Wirtsbäume von T. pityocampa waren damit in den Mischbeständen von Pinie und Birke teilweise verborgen, traten bei Vergesellschaftung mit Eichen aber deutlicher in Erscheinung. Wir meinen deshalb, dass die verminderte Apparenz der Pinien visuelle Signale stört, die von den Weibchen genutzt werden, um vor der Eiablage Wirtsbäume auszuwählen. Diese Untersuchung macht deutlich, dass es notwendig ist, Eigenschaften wie die Wachstumsgeschwindigkeit zu berücksichtigen, wenn die Baumarten für eine Mischkultur ausgewählt werden, um die Abwehr eines Forstbestandes gegen Schadinsekten zu verbessern.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
For forest sustainability and vulnerability assessment, the landscape scale is considered to be more and more relevant as the stand level approaches its known limitations. This review, which ...describes the main forest landscape simulation tools used in the 20 European case studies of the European project “Future-oriented integrated management of European forest landscapes” (INTEGRAL), gives an update on existing decision support tools to run landscape simulation from Mediterranean to boreal ecosystems. The main growth models and software available in Europe are described, and the strengths and weaknesses of different approaches are discussed. Trades-offs between input efforts and output are illustrated. Recommendations for the selection of a forest landscape simulator are given. The paper concludes by describing the need to have tools that are able to cope with climate change and the need to build more robust indicators for assessment of forest landscape sustainability and vulnerability.
•The percentage of PPM infested trees is higher in stands with fewer trees.•PPM concentrates on more apparent trees, i.e., taller or at stand edge.•Stand edges with westerly aspect are more at risk ...of PPM infestation.•Attack patterns within and between stands may be due to female moth preference.
The pine processionary moth (PPM, Thaumetopoea pityocampa) is the main defoliator of pines in the Mediterranean area, necessitating constant surveillance and regular pest management. A sound understanding of the spatial distribution of infested trees, both within and between stands, is required to increase management efficiency. We hypothesized that both host tree density at stand scale and tree apparency at individual tree scale were responsible for between- and within-stand patterns of PPM infestation. We tested these hypotheses on a sample of 171 maritime pine stands in the Landes de Gascogne, the largest plantation forest in Europe. We showed that PPM infestation (percentage of infested trees) decreased significantly with stand density, and was therefore greater in older than in younger stands. The probability of a pine tree being attacked increased significantly with tree height and proximity to the edge of the stand. Mortality rates of exposed sentinel egg batches did not differ with distance from the stand edge. We discuss three likely explanations for higher infestation of taller trees at stand edges: better survival of larvae on sun-exposed trees, and random interception vs. active host selection by gravid females. Our findings suggest that stand management could be adapted in order to decrease the risk of damage by the pine processionary moth, and that predictive tools for infestation dynamics can be based on forest growth models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aim of study: Adaptation of silviculture in planted forest may help to mitigate damage due to biotic and abiotic hazards. However, compromises have to be found because it is not possible to minimize ...the risk from all hazards through application of a single forest management approach. The objective of this study was to improve a multi-criteria risk analysis (MCRA) method that makes it possible to rank forest management alternatives (FMAs) according to multiple risks.
Material and Methods: We defined eight FMAs for maritime pine forests in France, Spain and Portugal. We used as the definition of risk the combination of hazard, susceptibility and exposure. Hazard level was estimated using archive data on occurrence and severity of damaging agents over the last few decades. Forest susceptibility to hazards was evaluated by experts who scored the effect on stand resistance of eleven silvicultural operations characterizing each FMA. Exposure was estimated as value at stake, which combined forest standing volume, simulated with forest growth models, and wood prices.
Main Results: Using the PROMETHEE algorithm, we found that the overall ranking of FMAs was consistent across all countries, with short rotation plantations to produce pulpwood or energy wood were the least at risk. The ranking was mainly driven by forest values at stake. We found that by improving the accuracy of forest values exposed to damage, based on growth models and representative wood prices, the MCRA outcomes were more useful and realistic.
Research highlights: Our methodology provides a relevant framework to design FMAs that would minimize risks while maintaining income.
Keywords: Pinus pinaster; vulnerability; hazards; growth modelling; expert assessment; wood price; southwestern Europe.
To ensure that forest ecosystem services will be maintained in future climate conditions, the challenge of developing and implementing forest adaptation strategies has become a priority shared across ...Europe (European Commission 2010) and around the world (FAO 2012). A critical aspect of any adaptation (and mitigation) strategy is to ensure that management choices have sufficient flexibility and are consistent with sustainable forest management (SFM) principles that balance the forest’s social, ecological and economic outputs. Most current studies, however, still tend to consider forest adaptation independently of exogenous developments (Seppälä et al. 2009), or are based on forecasting and thus only extrapolate from current trends. Yet the futures of forest systems are also uncertain because change may come mainly from socio-economic, and not ecological, drivers (Schoene and Bernier 2012). Climate change will, moreover, have a highly uncertain effect on socio-ecological systems such as forests. A number of authors and international publications on the environment have posited that scenarios studies offer a framework for dealing with strong uncertainties and the complexity of socio-ecological systems: “Comparisons among a set of contrasting scenarios are used to understand the systemic interrelation and dynamics of complex socio-ecological systems and to define a range of possibilities and uncertainties in quantitative and qualitative terms” (Thompson et al. 2012). Likewise, SFM practices are beginning to underscore the importance of taking into account landscape-level views of the forest, and of the many exogenous drivers of regional change, when thinking about integrated land use (Schoene and Bernier 2012). Adaptation strategies must therefore move away from single technical solutions and must not rely on one-size-fits-all mechanisms. New modes of governance that enable rapidly accelerating social, economic and institutional changes are required (Seppälä et al. 2009). Recent emphasis has also been placed on the importance of implementing regionally based forest adaptation strategies that are accepted by local stakeholders (Spathelf et al. 2013). A scenario planning approach that engages stakeholders in scenario development could be a way to overcome such challenges by combining anticipatory learning of climate change impacts (Tschakert and Dietrich 2010) with land use planning. Thus, forest adaptation could be seen from a perspective of forest planning rather than of forest management. It could involve a more indirect form of management that is broader in scale in terms of time, space and organisational level (Mermet and Farcy 2011).The objective of this paper is to discuss how a foresight approach and scenario planning can offer an appropriate framework for dealing with climate change uncertainties at local level, and for elaborating a plurality of forest adaptation strategies derived from plausible sectoral, socio-ecological and regional changes. To test this assumption, the Landes de Gascogne Forest (LGF) 2050 case study (Mora et al. 2012) appears particularly interesting, due both to recent storm damage in 1999 and 2009 and because of the increasing, diverse demands in changing economic and social conditions for various forest ecosystem goods and services. The Landes region of south-western France is located at the intersection of Northern Europe and the Iberian Peninsula. It covers a surface area of about 15,000 km2. The major biophysical features of the area include temperate, oceanic climate conditions, podzolic sandy soils and shallow groundwater levels. The LGF, which was expanded in the nineteenth century to become the largest cultivated and privately owned (92 %) forest in Europe, is primarily composed of maritime pine (Pinus pinaster). The LGF covers two thirds of the Landes de Gascogne region, with agricultural and built-up land representing 18 and 7 %, respectively (Mora et al. 2012). The forest also has a significant economic impact through its forestry and forest-based industries. A unique aspect of the Landes forest-wood chain is the location of both timber processing stages within the region and its largely exclusive use of local maritime pine wood resources. However, the forestry and forest-based sector have faced difficulties since the Martin and Klaus storms in 1999 and 2009 that created approximately 70 million cubic metres of windthrow damage. The forestry sector is also experiencing structural challenges as synergies among industry subsectors weaken and biorefinery activities gain prominence. Bordered by the Atlantic Ocean to the west and the large urban centres of Bordeaux to the north and Bayonne to the south (Fig. 1), the Landes area has become an increasingly popular place to live and to work. Almost all of the 390 municipalities in the region are now experiencing population growth, urbanisation, the emergence of a broader base of economic activity and, more generally, a diversification of their forest-derived goods and services. The contribution of forest-related activities to the rural economy and to social well-being may change as a result of these trends (Slee et al. 2004).
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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