Forests attenuate temperature and air pollution discomfort in montane tourist areas

Forests deliver many ecosystem services, from provisioning to regulating and cultural services. We aimed at demonstrating microclimatic regulation and pollutant removal as especially relevant ecosystem services when considering the tourism vocation of the Alpine regions. A study was realized along an altitudinal gradient (900–1600 m a.s.l.) in Trentino, northern Italy, an area with high touristic presence (ca. 9.3 million overnight stays in summer 2021). Nitrogen dioxide (NO2 , µg m−3 ), ozone (O3 , µg m−3 ) concentrations, air temperature (T, ◦C), and relative humidity (RH, %) were simultaneously measured in three open-field sites (OF) and below-canopy Norway spruce forest stands (FO) during the period 23 May–7 August 2013. The temperature–humidity index (THI) was calculated. We found a distinct mitigating effect of forest on T, with lower maximum (−30.6%) and higher minimum values (+6.3%) in FO than in OF. THI supported a higher comfort sensation in FO than in OF, especially in the central part of the day. NO2 concentrations did not differ between OF and FO; ozone concentrations were lower in FO than OF. This study confirms the role of forests in providing several ecosystem services beneficial for forest users, especially relevant for promoting nature-based tourism in the Alpine regio

Increase in airborne allergenic pollen in Trentino (North Italy): knowledge to adapt to climate change

Pollen allergy affects approximately 25% of adult and 40% of children globally (Nur Husna et al. 2022). Climate change is impacting allergenicity and pollen production, as well as the spread of neophytes that produce allergenic pollen, due to the combined effects of milder weather, air pollution, and elevated CO2 levels (Luschkova et al. 2022). As a result, there is an upward trend in allergic diseases (D’Amato et al. 2015). The study of pollen and its spatio-temporal changes is highly important due to the allergenicity of many airborne pollen taxa. Earlier-onset of pollen, the lengthening of the pollen season, and/or the increase in pollen quantities, can diminish the quality of life of allergic patients. In the "one health" perspective, we examine how climate change impact the ecosystem, affecting human well-being and health. Phenology, the science of natural recurring events, is one of the preferred indicators for observing the impacts of climate change on ecosystems and biological processes (Parmesan 2006). The shift in phenology is a high-temporal resolution signal of this impact and pollen dispersal is often used as a reliable proxy of flowering. This study describes the significant changes that have occurred to the airborne pollen component recorded in San Michele all’Adige, Northern Italy, from 1989 to 2018, analyzing a total of 24 arboreal (AP; trees and shrubs) and non-arboreal pollen taxa (NAP; herbaceous). Airborne pollen was collected using a volumetric Hirst-type aerobiological sampler (Lanzoni VPPS 2000), and the daily concentration of airborne pollen (P*m-3) was calculated for each taxon over a 30-year period from 1989 to 2018. The sampling and analysis of airborne pollen have been performed in accordance with the UNI EN 16868:2019 European standard procedure. The following pollen season descriptors were calculated for each taxon: (i) annual pollen integral (APIn; pollen*day*m-3); (ii) the start and end dates of the main pollen season (MPS), as the day of the year (DOY) when 2.5% and 97.5% of the APIn was reached, respectively; (iii) the length of the MPS, as the difference between the end and start DOY (+1); (iv) peak concentration; and (v) peak date, as the DOY when the maximum concentration was registered. The presence of a monotonic upward or downward temporal trend in pollen season descriptors was verified and changes were analyzed in relation to temperature, precipitation, and land use; in addition, pollen data were analyzed clustered into blocks of one decade each to minimize interannual fluctuations and maximize relevant change signals. The major result is an increase in pollen load (Fig. 1). All arboreal and shrub species (AP) and the majority of herbaceous (NAP) species had an impressive increase in pollen quantities. The extent of the increase in pollen load is evident when analyzing decadic blocks, with a relevant increase in the APIn for the total pollen spectrum, mostly due to AP taxa, with hop hornbeam and cypress family accounting for 49% of the increase (average on the 30-year period). Accordingly, AP shows a significant increase (+31 days) in the number of days with high pollen concentrations (i.e., > 100 pollen grains/m3). Such an increase in pollen quantity is unlikely to be related to changes in land use, given that the increase in forests and semi-natural areas is limited. The finding of an increase in APIn, especially marked for AP taxa, is consistent with previous studies and on a broader scale, from Europe (Ziello et al. 2012) to the entire Northern Hemisphere (Ziska et al. 2019). Moreover, some evidence of early start date for some taxa has been observed (e.g. Poaceae), at the same time as a longer pollen seasons for other taxa (e.g. Cupressaceae). A larger amount of pollen, an increase in the number of days with high pollen concentration, and an early start to the pollen season, which have been occurring since 1990 in the study area, all constitute a worsening situation and a major threat to people with pollen allergies. Thanks to these achievements it is possible to develop proposals for adaptation strategies that include as early stages: (i) development and implementation of risk communication strategies, (ii) implementation of good practices for green management. These proposals will be included in the Climate Change Adaptation Strategy of the Autonomous Province of Trento, which is currently being defined. Figures Fig 1: Increase of total arboreal pollen integral in the 30 years; detail for Ostrya (hop hornbeam) pollen taxonom

Airborne pollen in Alpine sites

Airborne pollen is usually monitored at urban centers, where most people live, to provide information on types and amount of allergenic pollen. Thus, very few aerobiological data are available for remote, mountainous sites. This study aims to characterize the biological quality of the air in an alpine valley in Trentino (North Italy), a region highly interested by the presence of tourists (e.g., 9.3 million overnight stays registered during June - September 2021). Materials and Methods An aerobiological study was carried out during late spring and summer in 2020 and 2021 in Val di Rabbi, an alpine valley located in the Trentino sector of Stelvio National Park. Gravitational Sigma2 samplers were selected for the survey, for their reliability and efficiency (VDI_2119 2013) and easy handling at remote sites (Gottardini et al. 2021), and installed at 2 m above ground level in 5 sites located at altitudes ranging from 700 to 2000 m a.s.l. Sampling surfaces, treated with an adhesive medium, were analyzed by optical microscopy (OM; 400×; Leitz Diaplan) for pollen identification and count (weekly samples); the average daily sedimentation rate (P cm–2 d–1 ) was calculated for the June-August period. In 2021, an active Hirst-type sampler was concurrently installed in one of the five sites (daily samples). Samples were processed and analyzed following conventional techniques and standardized protocols (UNI EN 16868:2019). Results and Discussion In the two study periods, the number of identified pollen taxa ranged from 25 at the highest elevation site (2000 m a.s.l.) to 39 at the lowest elevation (700 m a.s.l.). The proportion of arboreal pollen slightly decreased with the altitude, from 51% to 42%. The three most abundant pollen taxa were pine (Pinus), grasses (Poaceae) and neetle (Urticaceae), even if in different proportion at each site. The only grass and nettle allergenic pollen represented on average the 52% of the total pollen. The pollen season peak for grasses showed a delay of about 4 days every 100 m of elevation (Figure 1). 47 pollen taxa were identified, by active sampling, 10 more than by the passive one. The most abundant pollen taxa detected by active sampling were pine, grasses, and nettle, as for passive sampling, with the last two representing even the 71% of the total. The pollen season peak for grasses was on 22nd June, coherently with the passive sampling results at the same site. Conclusions Our mountain aerobiological study reveals the presence of allergenic pollen even at high altitude, with noteworthy shifts in the pollen season. The surveyed data can be further exploited for studying the plant biodiversity in remote areas, as well as to provide useful information for allergic tourist and hikers. Moreover, passive sampling proved to be a feasible solution for aerobiological studies in remote or orographically complex areas, typically excluded in routine air quality monitoring. References Gottardini et al. (2021). AAQR, Vol. 21, https://doi.org/10.4209/aaqr.210010 VDI_2119 (2013). Ambient air measurements. Sampling of atmospheric particles > 2.5 μm on an acceptor surface using the Sigma-2 passive sampler. Characterization by optical microscopy and calculation of number settling rate and mass concentration. ICS: 13.040.01. Beuth Verlag, Berlin. Germany. Acknowledgements The study was partially financed by Provincia Autonoma di Trento (IT). We are grateful to Mattia Precazzini and Gabriele Canella for the support in field work, and to Maria Cristina Viola for the microscope pollen analysis

The late flowering of invasive species contributes to the increase of Artemisia allergenic pollen in autumn: an analysis of 25 years of aerobiological data (1995–2019) in Trentino-Alto Adige (Northern Italy)

Artemisia pollen is an important aeroallergen in late summer, especially in central and eastern Europe where distinct anemophilous Artemisia spp. produce high amounts of pollen grains. The study aims at: (i) analyzing the temporal pattern of and changes in the Artemisia spp. pollen season; (ii) identifying the Artemisia species responsible for the local airborne pollen load. Daily pollen concentration of Artemisia spp. was analyzed at two sites (BZ and SM) in Trentino-Alto Adige, North Italy, from 1995 to 2019. The analysis of airborne Artemisia pollen concentrations evidences the presence of a bimodal curve, with two peaks, in August and September, respectively. The magnitude of peak concentrations varies across the studied time span for both sites: the maximum concentration at the September peak increases significantly for both the BZ (p < 0.05) and SM (p < 0.001) site. The first peak in the pollen calendar is attributable to native Artemisia species, with A. vulgaris as the most abundant; the second peak is mostly represented by the invasive species A. annua and A. verlotiorum (in constant proportion along the years), which are causing a considerable increase in pollen concentration in the late pollen season in recent years.. The spread of these species can affect human health, increasing the length and severity of allergenic pollen exposure in autumn, as well as plant biodiversity in both natural and cultivated areas, with negative impacts on, e.g., Natura 2000 protected sites and crops

Airborne pollen: a potential warning alert for tickborne encephalitis risk

The circulation of tick-borne encephalitis virus (TBEv) depends on population dynamics of host tick and rodents, which in turn depend on nutrient resources. Tree seeds are the main food for rodents, and their fluctuating production is strongly correlated to pollen abundance. Our study aims to fill the gap and investigate whether airborne pollen is directly associated to recorded TBEv human cases in the Alpine biogeographical region. Materials and Methods We focused our study within the province of Trento (northern Italy, 6,000km2, 500,000 inhabitants). The territory is included in the Alpine biogeographical region (EEA Report No 1/2002) and the main forest tree species growing within a 5-km radius from the pollen sampler are represented by hop-hornbeam (Ostrya carpinifolia Scop.), beech (Fagus sylvatica L.), spruce (Picea abies L.), pine (Pinus sylvestris L. and P. nigra J. F. Arnold), downy oak (Quercus pubescens Willd.), manna ash (Fraxinus ornus L.), and hazel (Corylus avellana L.). Airborne pollen concentration has been monitored since 1989 at Fondazione Edmund Mach, in San Michele all’Adige (Latitude 46.19 N, Longitude 11.13 E, 220 m a.s.l.), while TBEv human cases have been recorded since 1992 by the local Public Health Agency. Airborne pollen was sampled by a Hirst-type trap, processed, and analyzed following conventional techniques and standardized protocols (UNI EN 16868:2019). First, we statistically investigated the association between the annual total pollen concentration of the dominant arboreal plant taxa and the annual number of TBEv human cases (1989-2020) with different time lags by univariate linear models. Consequently, we built a full model by considering all significant covariates, we computed all possible sub-models and finally we selected the best (the one with the lowest Akaike’s Information Criterion score). Results and Discussion We found a significant positive association between pollen abundances for beech (p=0.04), oak p=0.012), hop hornbeam (p=0.013) and TBEv human cases with a two-year lag (Figure 1). All other lags and taxa resulted in non-significant relationships. Subsequently, we identified the best model, which considered only hop-hornbeam and oak pollen quantities, both with positive coefficients, consistently with the univariate analysis. Conclusions To the best of our knowledge, this is the first attempt at quantifying the potential relationship between airborne pollen abundances of tree species and TBEv infections, based on a three-decade time series of data. If validated at a larger spatial scale, pollen data might therefore be used to realize an early warning system for the risk of TBEv transmission, two years in advance. Moreover, as pollen monitoring is routinely performed worldwide at multiple sites and provides quantitative measures, the association between pollen abundances and TBEv infections could be replicated in different biogeographical regions

Impact of pollen on throughfall biochemistry in European temperate and boreal forests

Pollen is known to affect forest throughfall biochemistry, but underlying mechanisms are not fully understood. We used generalized additive mixed modelling to study the relationship between long-term series of measured throughfall fluxes in spring (April–June) at forest plots and corresponding airborne pollen concentrations (Seasonal Pollen Integral, SPIn) from nearby aerobiological monitoring stations. The forest plots were part of the intensive long term monitoring (Level II) network of the UNECE International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with dominant tree genera Fagus, Quercus, Pinus and Picea, and were distributed all across Europe. We also conducted a 7-day laboratory dissolution experiment with bud scales and flower stalks of European beech (Fagus sylvatica L.), pollen of beech, common oak (Quercus robur L.), silver birch (Betula pendula L.), Scots pine (Pinus sylvestris L.), Corsican pine (Pinus nigra Arnold ssp. laricio (Poiret) Maire), Norway spruce (Picea abies (L.) Karst.) and sterilized pollen of silver birch in a nitrate (NO3--N) solution (11.3 mg N L-1). Throughfall fluxes of potassium (K+), ammonium (NH4+-N), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) showed a positive relationship with SPIn whereas NO3--N fluxes showed a negative relationship with SPIn. In years with massive seed production of beech and oak SPIn and throughfall fluxes of K+ and DOC were higher, but fluxes of NO3--N were lower. The experiment broadly confirmed the findings based on field data. Within two hours, pollen released large quantities of K+, phosphate, DOC and DON, and lesser amounts of sulphate, sodium and calcium. After 24-48 hours, NO3--N started to disappear, predominantly in the treatments with broadleaved pollen, while concentrations of nitrite and NH4+-N increased. At the end of the experiment, the inorganic nitrogen (DIN) was reduced, presumably because it was lost as gaseous nitric oxide (NO). There was no difference for sterilized pollen, indicating that the involvement of microbial activity was limited in above N transformations. Our results show that pollen dispersal might be an overlooked factor in forest nutrient cycling and might induce complex canopy N transformations, although the net-impact on N throughfall fluxes is rather lo