Dr. Gianni Boris Pezzatti

In the complex Alpine topography, canyon-like terrain morphology combined with steep slopes may cause sudden changes in fire behavior, for instance, turning fast-spreading surface fires into eruptive fires. This phenomenon was observed during the vegetation dormancy in mountain beech (Fagus sylvatica L.) stands, a forest type usually spared from wildfires. The aim of this study is to understand the impact of eruptive fire behavior on the post-fire trajectories of beech trees. To this end, over the course of 3 years, we monitored the post-fire dynamics of 100 beech trees subjected to different fire intensities in February 2020, including a small-scale eruptive fire behavior associated with a steep slope (~41.4° on average) and canyon-like terrain features. Dendrometric and sylvicultural parameters and fire-related damages such as the presence of bark blackening, scars, foliage loss, crashes of branches or whole trees, and parasitic attacks were assessed. The observed medium to high fire severity was highly dependent on the position of the tree within the eruptive fire sector, whereas the relationship with dendrometric and sylvicultural tree characteristics, such as the crown position or the stem diameter, was less clear. Due to the lethal temperatures generated by the heat convection within the eruptive fire sector, the exposed bud and cambium tissues of the beech trees partially or totally failed to develop in the first post-fire season. Beech crown and stem tissue killed by exposure to convective heat fluxes rapidly dries out, loses its elasticity, and becomes brittle. Starting from the second post-fire season, this greatly increases the risk of the crashing of these crown parts and/or entire trees. A detailed understanding of the factors leading to an eruptive fire behavior would highly benefit the fire risk assessment and the detailed planning of the firefighting tactics in mountain areas, eventually increasing the safety of firefighters and preventing post-fire natural hazards, such as rockfall, erosion, surface runoff, and debris flow.

Forests are exposed to human-induced and natural disturbances generating opportunities for new species to establish, including non-native woody species. Understanding how disturbance characteristics interact with the site context and invasive species traits to drive invasion processes is crucial for designing sustainable forest management. Here, we use the case study of the deciduous broadleaved forest belt of Canton Ticino (Switzerland) to identify the main factors determining the presence of non-native invasive woody species in recently disturbed forests. We identified and selected 851 forest gaps caused by natural, silvicultural or other anthropogenic disturbances between 2008 and 2015. For each gap, the presence of non-native invasive woody species as well as the characteristics of the corresponding landscape, site, and the gap itself were determined. For the six most frequent non-native invasive woody species, we identified the parameters that influenced their presence by means of modelling approach. The resulting variable coefficients were then used to create maps of colonisation risk. Among the six target species (i.e., Ailanthus altissima, Buddleja davidii, Robinia pseudoacacia, Paulownia tomentosa, Prunus laurocerasus, and Trachycarpus fortunei), the factors influencing their presence were either shared (e.g., distance to the next colonisation hotspot), partially shared (e.g., distance to buildings, altitude, aspect), or completely species-dependent (e.g., topography, slope, distance to powerlines). Like in other mountainous areas, non-native invasive woody species concentrate at low altitudes and near densely populated areas where hotspots of seed-bearing individuals can be found. Moreover, different life-history groups (i.e., wind-dispersed pioneer species vs. animals-dispersed evergreens) shared specific invasion patterns characteristics. In addition to general management strategies, we argue that more species-specific strategies should be adopted to prevent the colonisation by non-native invasive woody species. In this context, the consideration of seed-bearing individual hotspots should be given highest priority, followed by the type and the characteristics of the disturbance.

Uno studio del WSL ha sviluppato un algoritmo per simulare la propagazione del fuoco in diverse
condizioni, evidenziando l'importanza della gestione del territorio e della preservazione degli spazi aperti per mitigare il pericolo.

In the long run, ongoing climate change is expected to alter fuel production as well as the frequency and severity of fire weather, which may result in an unprecedented frequency of extreme fire events. In this paper we propose a simplified and spatially explicit method to assess the probability of experiencing large fires, based on topography (slope length) as well as extent and aggregation of the forested area (fuel connectivity). We considered 21 homogeneous pyroregions covering entire Switzerland as a study case and computed the length of the upslope paths within the forested areas, simulating ignition points on a systematic 100 × 100 m square grid. We then compared the obtained path lengths for each pyroregion with selected historical large forest fire statistics (e.g., mean area of the largest 5% of fires, maximum burnt area per fire) collected over the course of the last 30 years. This resulted in rather high R² values, ranging from 0.558 to 0.651. The proposed approach was shown to allow for an easy identification and geo-localization of potential hotspots in terms of the likelihood for large fires to occur in mountainous regions, which is a prerequisite for a targeted planning of fire management measures aimed at preventing large fires and related post-fire gravitative natural hazards.

We report the first evidence of establishment of the palm borer moth Paysandisia archon (Burmeister, 1879; Lepidoptera: Castniidae) in southern Switzerland. Originally from South America, P. archon has been increasingly spotted in southern Europe in recent years, where it poses a substantial threat to palms as its larvae bore into their meristem, feeding on the inner tissues, weakening the plants, and, in most cases, leading to their demise. We conducted non-systematic surveys and compiled reports of sightings of P. archon and its attributed damages, which were then all stored in an online database. Sightings and damage caused by P. archon have been confirmed across multiple locations in southern Switzerland, with major infestations reported on the northern shore of the Lago Maggiore and affecting various palm species. While P. archon poses a major threat to cultivated palm specimens that are iconic for the (sub)urban landscape of southern Switzerland, it may also help control the undesired spread of the invasive Chinese windmill palm Trachycarpus fortunei in the periurban forests.

The emergence of novel ecosystems, characterized by shifts in species composition and interactions, abiotic conditions and altered ecosystem functioning, is a major and inevitable challenge to contemporary ecosystem management. This study examines the ecological implications of Trachycarpus fortunei, a non-native evergreen palm, currently involved in a biome shift from deciduous temperate forest to evergreen laurophyllous forest in the Southern European Alps. Specifically, we investigated the effects of T. fortunei encroachment in peri-urban forests on flying and ground-dwelling arthropod communities as well as on leaf-litter decomposition. We found that the presence of T. fortunei altered arthropod community composition, mostly by reducing the number of herbivore species. This effect was likely driven by the lower quality of palm leaves as a food source compared to deciduous, dicotyledonous tree leaves and by a lower plant richness in the herb and shrub layer. Furthermore, we observed higher rates of leaf-litter decomposition associated with increasing abundance of young palm trees, which was not explained by predictors commonly associated with litter decomposition (i.e., detritivore abundance, litter depth and air temperature). Hence, the slow decay of palm leaves appears to be counterbalanced by the favourable conditions for litter decomposition within dense palm stands. Overall, our findings indicate that high densities of the non-native palm species (T. fortunei) impacts herbivore arthropod communities in the Southern European Alps, providing first evidence of possible effects on ecosystem functioning of this ongoing biome shift. These outcomes are integral components of the broader process of laurophyllisation in the study region, a phenomenon linked to climate warming and land use change, encompassing both native and non-native species.

Questions: Does the non-native evergreen Chinese windmill palm (Trachycarpus fortunei) affect native plant community and forest regeneration in deciduous forests? Are effects modulated by soil moisture? What are the implications for forest management and nature conservation?
Location: Broadleaved deciduous low-elevation forests on the southern slope of the Alps across the Swiss–Italian border region.
Methods: We compared the native herbaceous and woody plant composition, species richness, Shannon diversity and abundance at ten deciduous forest sites on two moisture conditions (six mesic–moist sites and four mesic–dry sites). Each site consisted of three plots measuring 400 m² along a gradient of T. fortunei presence, ranging from "dominant", to "present but not dominant" to "absent".
Results: In mesic–moist forests with high densities of T. fortunei, species richness and Shannon diversity of native plants and recruiting woody species in the herb and shrub layers were significantly reduced compared to similar sites where T. fortunei is absent or not dominant. However, in mesic–dry forests these variables did not differ between palm-invaded and uninvaded plots. The abundance of recruiting woody individuals did not differ between plots invaded by palms and uninvaded control plots in either forest type.
Conclusions: We expect detrimental consequences for plant diversity in mesic–moist alluvial forests with high T. fortunei densities and few detrimental consequences in the more widespread non-alluvial forests. We recommend multifaceted management, including targeted eradication in alluvial forests identified as hotspots of native plant diversity, accompanied by hands-off management of T. fortunei in non-alluvial forests, recognizing the ongoing and inevitable "laurophyllisation"; a biome shift toward mixed-evergreen forest that may increase ecosystem climate resilience under ongoing climatic warming.

The hybrid Bohemian knotweed [Polygonum ×bohemicum (J. Chrtek & Chrtková) Zika & Jacobson [cuspidatum × sachalinense]; syn.: Reynoutria ×bohemica Chrtek & Chrtková] is part of the worldwide problematic rhizomatous invasive plants that impact (semi-)natural and agricultural systems. In this context, precise knowledge about the morpho-anatomy and resprouting capacity of the underground organs is key information for developing efficient eradication measures. In the present study, we aimed at (1) clarifying existing differences in the morpho-anatomical characteristics of rhizomes and roots, (2) developing an easy-to-apply field identification method for the underground organs, and (3) identifying the main morpho-anatomical features enhancing the rhizomes’ resprouting ability. For this purpose, we collected the underground organs of two wild populations of P. ×bohemicum in Canton Ticino (southern Switzerland) and analyzed the morpho-anatomical differences between rhizomes and roots, using high-resolution microscope images and microtome sections. Collected material was then used for a resprouting capacity test after assessing rhizome characteristics such as weight, total diameter, pith diameter, pith brightness, and pith color. In contrast to roots, rhizomes are characterized by pith tissue in the center and display nodes with peripheral dormant buds that enable them to resprout. Resprouting ability of rhizomes was high (87.1% on average) and depended on the ontogenetic developmental stage of the organs (peak values of 97% for young and clearer-colored organs, 50% for old and dark ones). In conclusion, the smooth pith tissue of rhizomes represents a key discriminating feature between rhizomes and roots, whereas relating existing nodes to the corresponding rhizome pith color allows assessment of the resprouting potential of a knotweed population.

Il Campus di ricerca di Cadenazzo, in collaborazione con diverse istituzioni ticinesi, ha di recente approfondito la conoscenza del Sorgo d'Aleppo, una neofita invasiva. Si tratta di una graminacea esotica in fase di forte espansione a sud delle Alpi.

I poligoni asiatici sono fra le piante rizomatose a carattere invasivo più problematiche della Svizzera. Conoscere meglio le specificità della loro capacità di riproduzione vegetativa significa poterle combattere in modo più efficace.

Les renouées asiatiques font partie des plantes envahissantes rhizomateuses les plus problématiques en Suisse. Bien connaître leur mode de reproduction végétative permet de mieux les combattre.

In sub-Mediterranean ecosystems, shade-tolerant broadleaf evergreens, especially the invasive Trachycarpus fortunei, are spreading uncontrollably in the forest understorey, impeding the regeneration of the native deciduous woody vegetation. Most invasive species benefit from high-light environments, as they often have a resource-acquisitive strategy with high photosynthetic rates. Yet, evergreen neophytes, such as T. fortunei, grow mainly in dark understoreys, which raises the question about the physiological mechanisms allowing it to thrive and, eventually, outcompete the native vegetation. For one year, we compared the photosynthetic light-use efficiency of T. fortunei and seven competitors (one evergreen and six deciduous species) to understand possible physiological drivers of this invasion process. The work was done in invaded sub-Mediterranean forests in Southern Switzerland and Northern Italy. Measurements included the seasonal photosynthetic capacity (A_max), net assimilation (A_net), apparent quantum yield (q_LCP), light compensation point of photosynthesis (LCP), chlorophyll content (CC), chlorophyll fluorescence (F_v /F_m), leaf soluble sugar (SS_L) and starch concentrations (ST_L), nitrogen (LNC), and dry matter (LDMC) contents. During the entire year, T. fortunei had similar assimilation rates to the evergreen and deciduous competitors. However, in October, A_max and A_net of T. fortunei were higher than the other evergreen species, while most deciduous plants started losing their foliage. While no photosynthetic disadvantage was found for T. fortunei, we observed less seasonal variability in A_net, q_LCP, SS_L, ST_L, and LDMC, and a lower or similar q_LCP, F_v/F_m, CC, SS_L, ST_L, and LDMC in this species than in its competitors. We highlight that October was the only month when T. fortunei had a photosynthetic advantage over the native sub-Mediterranean evergreen vegetation, while during the rest of the year, it showed similar assimilation rates as evergreen and deciduous species. Forests with sparse canopies in October might be particularly favourable for T. fortunei, due to the benefits of high light conditions for its assimilation rates compared to native evergreens. Moreover, the low seasonal variability in physiological traits indicates that as winters get milder and growing seasons longer, the invasive palm may take a further competitive advantage over the native vegetation.

Wann, wie oft, warum und wie intensiv es in einem Gebiet brennt, hängt von vielen Faktoren ab. Kurzfristig wirken sich vor allem zwei auf die Waldbrandgefahr aus. Zum einen bestimmt die Wetterlage mit extremer Trockenheit oder Regen, wie leicht sich das brennbare Material entzündet. Hinzu kommt der kontrollierte oder fahrlässige Umgang der Menschen mit Feuer im Freien. Langfristig sind neben der Klimaveränderung die
Landschaftsnutzung und der Bevölkerungsdruck inklusive der allgemeinen Einstellung der Menschen gegenüber der Umwelt entscheidend. Ziel eines modernen Waldbrandmanagements ist es, das Waldbrandgeschehen so zu beeinflussen, dass es zu keinen schwerwiegenden Auswirkungen auf die Umwelt und die Waldfunktionen kommt.

Die Alpensüdseite bekommt klimatische Veränderungen schon heute zu spüren und ist besonders anfällig für Sommerdürren, Verbuschung und damit verbundene grosse Waldbrände. Laubwälder auf der Alpensüdseite werden durch ihre klimatischen und forstgeschichtlichen Besonderheiten zum Freilandlabor und zur Frühwarnregion für die Tieflandwälder der gesamten Schweiz.

Nel corso dell'estate 2023 è stata confermata la presenza in Ticino del castnide della palma (Paysandisia archon), un lepidottero originario del Sud America ma già presente da quatche tempo in più aree del Sud dell'Europa.

Auf der Alpennordseite sind Waldbrande ein seltenes und unregelmassiges Phano­men. Sie sind meist durch den Menschen verursacht und treten vorwiegend im spaten Fruhling und im Hochsommer auf.

Il fulmine è l'unica causa naturale di incendi boschivi in Svizzera. Nel presente articolo, degli specialisti di questo campo presentano le specificità di questi eventi particolari.

La foudre est la seule cause naturelle d'incendie de forêt en Suisse. Dans cet article, des spécialistes du domaine présentent les spécificités de ces événements particuliers.