One person missing after Swiss village burried beneath landslide.

One person has been reported missing following a landslide in the Swiss canton of Valais which has covered about 90% of the village of Blatten in the Lötschental Valley with rubble and debris on Wednesday 28 May 2025. The landslide occurred after a part of the Birch Glacier broke off, allowing rock held behind it to tumble onto the village. The village had been evacuated since 19 May, when geologists identified that part of the mountain behind the glacier had started to move, following a detected increase in movement from the glacier itself. The missing person has been identified as a man aged 64, but no further details have been given.

Debris covering the village of Blatten in the Lötschental Valley in the canton of Valais, Switzerland, following a landslide on 28 May 2025. Jean-Christophe Bott/Keystone.

The village was evacuated on 19 May after geologists identified the potential for a major landslide hitting the village as a 'worst case scenario' following their assessment of movements on the Birch Glacier. However, despite this 'worst case scenario' having come true, there is now thought to be a significant risk of further problems, with the landslid having covered part of the Lonza River, causing the potential for water to build up behind the debris, which might in turn catastrophically fail, causing flood events further down the valley.

 All glaciers in Switzerland, and the wider Alps, are currently considered to be at risk due to rising global temperatures, with many recording increased flow rates similar to that seen on Birch Glacier. While it is not generally considered possible to say to what extent global warming has contributed to individual incidents, it is highly likely that Alpine regions will be subjected to more incidents of this kind in the future.

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Samaroblattella valmarensis: A Subioblattid 'roachoid' from the Middle Triassic of Monte San Giorgio fauna of Switzerland.

The Eoblattodea, or 'roachoids' form a stem group to the living Dictyoptera, which comprises the Cockroaches, Mantises, and Termites (a stem group contains fossil species more closely related to the living group they are on the 'stem' of than to any other living group, but not descended from the last common ancestor of all living members of that group). This stem group first appeared in the Carboniferous, with the common ancestor of all living Dictyopterans probably living in the Jurassic. The Subioblattids are a small group of 'roachoids' known from the Triassic of South Africa, France, and Central Asia. This group is fairly well-known from its forewing anatomy (the forewings are considered to be reliable on their own for the diagnosis of Insect relationships), but to date no body fossils found to date.

In a paper published in the Swiss Journal of Palaeontology on 10 March 2025, Matteo Montagna of the Department of Agricultural Sciences at the University of Naples Federico II, Fabio Magnani of the Museo Cantonale di Storia Naturale, Giulia Magoga, also of the Department of Agricultural Sciences at the University of Naples Federico II, and André Nel of the Institut de Systématique, Évolution, Biodiversité at the National d’Histoire Naturelle, describe a new species of Subioblattid 'roachoid' from the Middle Triassic of Monte San Giorgio fauna of Switzerland.

The Monte San Giorgio fauna derives its name from Monte San Giorgio, a mountain on the border between Italy and Switzerland in the Lugano Prealps. The exposed geological sequence on this mountain begins in the Lower Permian, where a succession of volcanic rocks mark the onset of the Variscan Orogeny, as the continents of Euramerica and Gondwana collided during the formation of the supercontinent of Pangea. These are overlain by a sequence of Triassic sediments recording a tropical terrestrial environment, a shallow near-shore environment, a deeper marine basin with extensive limestone deposits, a second terrestrial exposure caused by a major marine regression (drop in sealevel) in the Late Triassic, and finally an Early Jurassic marine Basin.

The fossils of the Monte San Giorgio fauna come from shales of the Besano Formation and the overlying Meride Limestone, which were laid down in the Early-Middle Triassic marine basin. These fossils include Bivalves, Marine Reptiles, Fish, Crustaceans, and Cephalopods, as well as terrestrial-derived fossils such as Plants, terrestrial Vertebrates, and Insects. To date, 273 species of Insect have been recorded from Monte San Giorgio, including Thrips, True Bugs, and Flies, as well as representatives of groups such as the Monura and Permithonidae, which were thought to hve died out in the End Permian Extinction until they were discovered here.

Location of the Monte San Giorgio UNESCO World Heritage Site and stratigraphic section of the Middle Triassic sediments. (A0 Map showing the location of Monte San Giorgio and the carbonate Anisian-Ladinian sequence and the location of Val Mara (indicated by a star) where VM 12 site occurs. (B) Stratigraphic section of Middle Triassic sediments in Monte San Giorgio; black arrow indincates the position of VM 12 strata where the Insect fossil was collected. Montagna et al. (2025).

The new species is described from a single specimen from Meride Limestone of Monte San Giorgio. This is placed in the genus Samaroblattella on the basis of its forewing veination, but assigned to a new species, valmarensis, meaning 'from Val Mara' in reference to the location where the fossil was found.

The genus Samaroblattella was first described in 1976 to describe a fossil from South Africa, with a second species described from Kazakhstan, Central Asia, in 2001. Unlike these previously described species, and indeed all other previously described members of the roachoid family Subioblattidae, to which the genus is assigned, Samaroblattella valmarensis has a preserved body as well as wings.

The hind legs of Samaroblattella valmarensisi closely resemble those of the extant Jumping Cockroach, Saltoblattella montistabularis, with both species also having an elongate shape, and a narrow pronotum (plate on the forepart of the prothorax, before the wings) suggesting that this ancient roachoid may have had a similar jumping habit. 

However, a close relationship is not proposed, as Samaroblattella valmarensisi also has an elongated, sword-like, external ovipositor, something absent from crown group Dictyopterans (ctown group comprises all species deecended from the last common ancestor of all living species), which have an internal ovipositor. External ovipositors were found in the earliest Insects, with internal ovipositors having appeared separately several times in different groups.

Holotype of Samaroblattella valmarensis. Arrows highlight specifc body parts: f, fore legs (femora)[ ml, mid legs (femora and tibiae); hl, hind legs (femora and tibiae); ce, cerci; ov, ovipositor. Scale bar is 5 mm. Montagna et al. (2025).

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A meteoric iron arrowhead from the late Bronze Age of Switzerland.

The Iron Age is considered to have begun when people started smelting iron from iron oxide ores. However, some iron artefacts predate this, having been produced from a source which did not require smelting: meteoric iron. In the Old World, Bronze Age meteoric iron artefacts are known from Turkey, Greece, Syria, Iraq, Lebanon, Egypt, Iran, Russia, China, and Poland. To date, the entire complement of Bronze Age meteoric iron artefacts from Europe comprises two rings and an amulet from Greece, a pair of bracelets from Czestochowa-Rakowa in Poland, and an iron axe from Wietrzno, also in Poland. Attempts have recently been made to locate other meteoric iron objects in archaeological collections, using X-ray fluorescence analysis, concentrating on areas where meteoric iron is thought likely to have been available. One such potential source is the Twannberg iron meteorite strewn field in the Jura Mountains of Switzerland, which has led archaeologists to re-examine many Bronze Age artefacrs in Swiss museum collections.

In a paper published in the Journal of Archaeological Science on 25 July 2023, Beda Hofmann of the Naturhistorisches Museum Bern and the Institute of Geological Sciences at the University of Bern, Sabine Bolliger Schreyer of the Bernisches Historisches Museum, Sayani Biswas and Lars Gerchow of the Paul Scherrer Institute, Daniel Wiebe, Marc Schumann, Sebastian Lindemann, and Diego Ramírez Garíca of the Physics Insitute at the University of Freiburg, Pierre Lanari, also of the Naturhistorisches Museum Bern, Frank Gfeller, also of the Naturhistorisches Museum Bern and the Institute of Geological Sciences at the University of Bern, Carlos Vigo, Darbachan Das, and Fabian Hotz, also of the Paul Scherrer Institute, Katharina von Schoeler of the Institute for Particle Physics and Astrophysics at ETH Zürich, Kuzihiko Ninomiya of the Institute of Radiation Sciences at Osaka University, Megumi Niikura of the RIKEN Nishina Center for Accelerator Based Science, Narongrit Ritjoho of the School of Physics at Suranaree University of Technology, and Alex Amato, again of the Paul Scherrer Institute, describe the discovery of a Bronze Age meteoric iron arrowhead in the collection of the Bernisches Historisches Museum.

The arrowhead (specimen number A/7396), was recovered from the Mörigen Pile Dwelling, a Bronze Age stilt house settlement attributed to the Urnfield Culture, on Lake Biel in Bern Canton, which is about 4-8 km south of the Twannberg iron meteorite strewn field. The Mörigen site was discovered by local fishermen in 1843, and was the subject of various amateur excavations until 1873, when the Bern government banned such activities, and arranged for a formal exploration of the site under the leadership of archaeologist Eduard von Jenner and geologist Edmund von Fellenburg. Exactly when arrowhead A/7396 was found is unclear, but it is thought to have been recovered during Jenner and Fellenburg's excavations in 1873 and 1874. It was first observed that the arrowhead was iron rather than bronze by Monika Bernatzky-Goetze in 1987, during a wider examination of arrowheads from Mörigen, though she made no further investigation of it at that time. It has a mass of 2.904 g, and measures 39.3 mm long, 25 mm wide, and 2.6 mm wide, and has a triangular blade with a 13 mm tang. 

(a) Overview of the Mörigen arrowhead (A/7396). Note adhering bright sediment material. Remnants of an older label on the left of the sample number. Total length is 39.3 mm. ( b) Side view of the Mörigen arrowhead. Layered texture is well visible. Point is to the right. Thomas Schüpbach in Hofmann et al. (2023).

Hofmann et al. carried out a metallurgical comparison of arrowhead A/7396, comparing it to two fragments of the Twannberg Meteorite, TW1 (NMBE 36467) and TW934 (NMBE 43747), but found that it was metallurgically quite distinct from these, and therefore derived from a different meteorite. The arrowhead was also examined by light microscopy, X-ray micro-computer tomography, muon induced X-ray emission spectography, scanning electron microscopy, gamma spectroscopy, and Ramen spectroscopy.

The arrowhead is comprised of rust covered iron with a very laminated texture, in places patches of sediment can still be seen attached to the surface, and very small amounts of unrusted iron are visible within a crack on the surface. The surface of the arrowhead has grinding or scratch marks in several places, which are beneath the attached organic material and sediment particles where these are found on the same part of the arrowhead.

X-ray tomography revealed that the rust layer, although covering most of the sirface, is very thin (less than 0.1 mm). The crack observed visually can be seen to extend across almost the whole width of the arrowhead in X-ray tomography, and is largely filled with fine-grained silt sediment. -ray tomography also showed the arrowhead to be of uneven thickness, being 1.2 mm thick on one side, while the other is only 0.6 mm thick. The metal has a pronounced layering parallel to the frontal plane of the arrowhead, something which would not be expected in an iron meteorite, and which is therefore presumed to be an artefact of the way in which the arrowhead was made.

X-ray tomographic sections of the Mörigen arrowhead. (a) Shows four sagittal sections, (b) shows 10 transversal sections. Brightest (densest) areas correspond to metallic iron, brightness of iron metal is variable due to flatness of the object. The layered structure and fractures filled with iron (hydr)oxides/sediment material resulting from oxidative volume expansion are well visible. Hofmann et al. (2023).

The Mörigen arrowhead is very flat, and has probably had its thickness increased somewhat by oxidation. This is not a natural shape for meteors or meteor fragments, suggesting that the metal has been flattened as well as being sharpened. Such working of the metal is a plausible origin for the laminations visible in the X-ray tomograph images of the arrowhead, which is probably a deformed Widmanstätten pattern (Widmanstätten patterns are interleaving of kamacite and taenite bands found in nickel-iron meteorites, where they are believed to be formed by very slow cooling of the metal, probably over millions of years). Similar patterns have been observed in artefacts from Greenland, which are known to have been made by cold working of material from the Cape York meteorite. These Greenland artefacts also have a very flat form, and a layered microstructure made from flattening of large kamacite and taenite grains. Hot working is also a possibility, though heating to above about 700° would probably result in the loss of the banding due to recrystallization. The grinding marks seen on the surface of the arrowhead in places may be a result of this working process. Thus, although the arrowhead is of a similar shape to the bronze arrowheads also found at Mörigen, it appears to have reached this shape via quite a different working process. 

An undeformed Widmanstätten pattern in a section of a meteorite from the Gibeon Cluster in Namibia. Kevin Walsh/Wikimedia Commons.

The oxidised surface of the arrowhead is a less than ideal target for X-ray fluorescence spectroscopy, and is likely to be responsible for the variation in nickel concentrations across the surface of the object; up to 22%, which is improbable on an unoxidized surface, and probably results from element partition during the corrosion process. Muon induced X-ray emission spectography, which can penetrate the surface of objects, found that the nickel content increased and stabilised with depth in both the arrowhead and meteorite fragment TW934 (which also has an oxidised surface) but not meteorite fragment TW1, which does not. Iron, nickel, cobalt, gallium, and germanium, all typical components of iron-nickel meteorites, were all detected by X-ray fluorescence spectroscopy, as were arsenic and copper, which are much more unusual. High levels of lead were found on the parts of the arrowhead with white numbering, implying that a lead-oxide based paint was used.

Scanning electron microscopy revealed the presence of bith taenite and kamacite, which are nickel-rich and nickel-poor phases found in iron-nickel meteorites. Some organic material was present on the surface, and were sediment particles, showing calcium, carbon, oxygen, and silicon, which would fit with a mixture of calcium carbonate and quartz. The pigment of the label was found to contain bith leand and tin.

Scanning electron microscopy images of typical surface areas of the arrowhead. (A) Thin lamina of taenite (Ta) surrounded by oxidation products (Feox) and nearby kamacite (Ka), Backscattered electron image; (B) Iron oxidation products (Feox) covered by organic material, probably Birch tar (Org, dark) and a latest layer of adhering sediment (Sed), Backscattered electron image image. (C), (D) Scratched surface (Scr) below organic material (wood tar; Org) and sediment (Sed). Scanning electron images. Hofmann et al. (2023).

Gamma spectrometry of the arrowhead was able to detect the presence of the isotopes aluminium²⁶, potassium⁴⁰, uranium²³⁸, thorium²²⁸, cobalt⁶⁰, and cesium¹³⁷. Ramen spectroscopy of the organic material produced a signal typical of a tar-like material, which was probably birchwood tar used to attach the arrowhead to the arrow. 

The presence of aluminium²⁶ strongly supports the meteoric origin of the metal suggested by the presence of nickel, cobalt, gallium, and germanium, and the ratios of iron to nickel and nickel to cobalt. The presence of the Widmanstätten patterns and taenite rule out an origin from the Twannberg Meteorite, fragments of which have only ever been found to contain kamacite. The concentrations of nickel and germanium in the metal are consistent with the parent meteor having mostly likely been an IAB type iron meteorite, such as the Cañon Diablo Meteorite from Arizona or the Campo de Cielo meteorites from Argentina. The composition of the metal could also correspond to an IC group meteorite, although these are much rarer, with only 13 known examples, none of them from Europe. 

Aluminium²⁶ is a cosmogenic isotope, found close to the surface of iron-nickel Solar System bodies, where it is formed by cosmic rays bombarding magnesium²⁶, the element to which it also decays, with a half-life of 717 000 years. This short half-life means that aluminium²⁶ and magnesium²⁶ reach an equilibrium point, witht the proportion of aluminium²⁶ decreasing deeper within the body. The proportion in the metal of the Mörigen arrowhead implies that it was at a depth of about 40 cm when it was in the parent body, implying a meteorite with an original diameter of about 80 cm. Such a meteorite would have had a minimum mass of about two tonnes.

The metal of the arrowhead is likely to have undergone some modification since it arrived on Earth. The most obvious modification is the layer of rust (iron oxide) which has formed on its surface, but the presence of copper and arsenic, elements not usually found in nickel-iron meteorites, is probably a result of Human actions, possibly originating when the metal was worked with tools used to work on bronze, but also quite possibly a result of being stored with bronze items.

The chemical and isotopic composition of the Mörigen arrowhead suggests that it derived from an IAB type meteorite with a minimum mass of about two tonnes. Three large IAB meteorites with compositions compatible with the Mörigen arrowhead are known from Europe; the Bohumilitz Metoerite from the Czech Republic, the Retuerte de Bullaque Meteorite from Spain and the Kaalijarv Meteorite from Estonia. Of these, the Kaalijarv is known to have been particularly large, producing a series of craters, the largest of which, the Kaalijärv Crater on the island of Saarema in Estonia, is 110 m in diameter. This object is thought to have had an original mass of several hundred tonnes, most of which was destroyed during the impact, leaving only small fragments of shrapnel. A piece of shrapnel from the Kaalijarv Meteorite would be a plausible source for the metal of the Mörigen arrowhead, although it is possible that the metal was broken off a larger mass, with other iron artefacts (now lost to us) being made from the remaining material. About 10 kg of material has been recovered from the Kaalijarv Meteorite to date, with dating based upon the stratigraphic location of these fragments suggesting the meteorite fell between 1870 and 1440 BC. This Bronze Age date, combined with the parent body having been sufficiently large to produce a fragment with the aluminium²⁶ signature seen in the Mörigen arrowhead, and the fact that it fell in an area known to have been inhabited during the Bronze Age, and therefore would have been observed, makes the Kaalijarv Meteorite the most likely source for the material used to make the arrowhead. 

Kaalijärv Crater on the island of Saarema in Estonia. Kaspars Priede/Wikimedia Commons.

However, this does not rule out other meteorites, such as Bohumilitz or Retuerta de Bullaque, or even an unknown impactor, as sources of the material. The Morasko IAB strewn field in Poland, which has been dated to about 3000 BC and which produced craters up to 90 m in diameter, can be ruled out, as all recovered fragments of this meteorite have much higher levels of germanium (about 500 parts per million) than seen in the Mörigen arrowhead. The Wietrzno Axe and Czestochowa-Rakowa Bracelets are close in time to the Mörigen arrowhead, but have much higher nickel contents, suggesting that they were made with material from a different meteorite.

A search for meteoric iron artefacts near to the Twannberg strewn field produced only a single item, and this was clearly derived from a different meteorite. This suggests that Bronze Age peoples were not aware of the Twannberg Impact, and had no means of detecting and utilizing metal from buried fragments of this object. The artefact uncovered, an iron arrowhead from the Mörigen Pile Dwelling in Bern Canton appears to have been derived from the Kaalijarv Meteorite, which fell in Estonia in about 1500 BC, implying that meteoric iron was a commodity traded across Europe before 800 BC (the approximate age of the Mörigen settlement), with the arrowhead, or the metal from which it was made, apparently having been transported about 1600 km. 

Since it is highly unlikely that only a single artefact would have been made from a source such as the Kaalijarv Meteorite once people were aware of it, there is a distinct possibility that other objects made from iron derived from this source are present in archaeological collections elsewhere in Europe, and possibly beyond. While it is possible that larger objects were made from this source, the highly fragmented nature of the material makes it more likely that most artefacts were small, and out current understanding of the ability of Bronze Age people to work iron, also suggests any objects will be very flat, giving a clear set of parameters for searching archaeological collections for more objects.

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One person dead after tornado hits town in Switzerland.

 One person has died and another fifteen people have been injured on the morning of Monday 24 July 2023, after a tornado hit the city of La Chaux-de-Fonds in Neuchâtel Canton, Switzerland, close to the border with France. The person killed is described as having been in their fifties, and to have died when they were hit by a falling crane from a construction site. Damage has been reported to a village hall, a church, a school and about fifteen houses in Switzerland, and about thirty houses on the French side of the border, although no injuries have been reported in France. The storm is reported to have been associated with a thunderstorm which swept along the north side of the Jura Mountains, bringing with it winds gusting at up to 217 km per hour.

A house damaged by a tornado in La Chaux-de-Fonds, Switzerland, on 24 July 2023. Fabrice Coffrini/AFP.

Thunderstorms occur when warm, moist bodies of air encounter cooler, drier air packages. The warm air rises over the cooler air until it rises above its dew point (the point where it cools to far to retain its water content as vapour), and the water precipitates out, falling as rain, sleet or hail. Warm moist air passing over the surface of the Earth acts as an electrical generator, creating a negative charge in the cloud tops and a positive charge at the ground (or occasionally in a second cloud layer). The atmosphere acts as an electrical insulator, allowing this potential to build up, until water begins to precipitate out. This allows a channel of ionised air to form, carrying a current between the clouds and the ground, which we perceive as lightning.

Tornadoes are formed by winds within large thunderstorms called super cells. Supercells are large masses of warm water-laden air formed by hot weather over the sea, when they encounter winds at high altitudes the air within them begins to rotate. The air pressure will drop within these zones of rotation, causing the air within them so rise, sucking the air beneath them up into the storm, this creates a zone of rotating rising air that appears to extend downwards as it grows; when it hits the ground it is called a tornado. 

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Estimating the benefits of agroforestry to European wildlife.

The term agroforestry is used to denote practices in which the cultivation of trees is integrated either with the rearing of livestock (in which case it is called silvopasturalism) or other plant crops (silvoarablism). This is a traditional practice across much of Europe, where methods such as grazing livestock in orchards are very widespread, with newer methods being developed more recently, such as short-rotation coppicing being carried out alongside rows of other crops. Systems in which productive trees are grown around the edges of fields are also sometimes considered to be agroforestry, although in these cases the trees are managed separately to the other produce, and may be under separate ownership.

 

Pigs grazing in an open Oak forest system in Spain, a system known as a 'dehesa'. Álvarez (2016).

Europe has suffered particularly severe losses of biodiversity compared to other parts of the world, and this is particularly severe in areas where intensive agriculture is prevalent. Agroforestry promotes a more diverse landscape than arable monoculture, potentially resulting in higher biodiversity. Quantifying the benefits of this could potentially lead to the system being more heavily prioritised under the European Common Agricultural Policy or any successor system.

Agroforestry systems have been well studied in tropical environments, where the evidence suggests that the system offers significant advantages in biodiversity preservation over intensive monocultural systems, but nevertheless tends to lead to reduced biodiversity compared to both primary and secondary forests. The system is less well studied in temperate regions, with most studies tending to concentrate on single groups of Animals, such as Birds or Insects. This leaves the benefits of such systems in Europe somewhat unclear, particularly as the definitions of agroforestry can vary, leading to differences in what systems are included in studies, making comparisons between studies difficult. 

 

Hazel short rotation coppice system alongside crops in Suffolk, UK. Smith et al. (2014).

In a paper published in the journal BMC Ecology and Evolution on 23 October 2021, Anne‑Christine Mupepele of Nature Conservation and Landscape Ecology and Biometry and Environmental System Analysis at the University of Freiburg, and Matteo Keller and Carsten Dormann, also of Environmental System Analysis at the University of Freiburg, present the results of a meta-analysis which combined results from a number of studies of agroforestry systems across Europe.

Mupepele et al. sought to answer three questions, 'What is the effect of agroforestry on biodiversity relative to forests, pastures, cropland or abandoned, shrub-encroached agroforestry?', 'Is the effect of agroforestry on biodiversity influenced by environmental variables, specifically the kind of agroforestry system (silvopasture or silvoarable), sampling method, the specific measure of biodiversity, sampling year, country, climate and the reference used?' and 'How strong and robust is the underlying evidence of these results?'

To which end they located 1411 previous studies of agroforestry systems in Europe, 50 of which were eventually included in the study, representing 69 individual agroforestry sites. Each of these had a direct comparison of a type of agroforestry (silvoarable or silvopastoral) to forests, cropland, pasture, and/or abandoned agroforestry systems.

 

Map of Europe with the number of effect sites per country. Mupepele et al. (2021).

The studies included in the analysis covered sites across Europe where agroforestry systems have been studied between 1984 and 2019. The majority of these sites were caried out in Iberia and the Mediterranean region, with twelve studies from Spain, eight from Portugal, five from Italy, one from France and one from Turkey. Temperate central Europe was represented by six studies from the UK, four from Romania, two each from France, Germany, and Switzerland, and one each from Belgium and northern Italy. The northern boreal region was represented by four studies from Sweden and two from Finland.

Thirty six of the included studies looked at silvopastoral systems, with thirty six studies looking at 52 sites, while silvoarable systems were the subject of thirteen studies looking at seventeen sites. The biodiversity of agroforestry was most commonly compared to that of pasture (23 sites), or forests (21 sites), then abandoned agroforestry systems (thirteen sites) and cropland (12 sites).

 

Sheep grazing in a plantation of Pine and Eucalyptus in Spain. Monica Pelliccia/Mongabay.

The different studies measured biodiversity in different ways, and concentrated on different groups. In order to make a comparison between these diverse studies, Mupepele et al. divided the measured wildlife into five groups, Arthropods, Birds, Bats, Plants, and 'Fungi plus Lichens and Bryophytes', Most of the included studies measured biodiversity at the 'species richness level', although other measures were used.

Mupepelele et al.'s results showed no overall benefit for biodiversity compared to the average derived from all systems. However, silvoarable systems were found to host considerably more biodiversity than other croplands, although they generally hosted less biodiversity than forests. Silvopastoral systems produced less clear results, with measures often producing conflicting results in different studies (i.e. one study might show higher Avian biodiversity in a silvopastoral system than a forest, while another showed the reverse.

Birds and Artropods were typically found at higher levels of diversity in agroforestry envoronments than other systems, Where the original group sorted Arthropods into different groups (e.g. Bees, Beetles and Spiders', then this biodiversity increassed, although this was across all environments, with no change in the beneficial effect of agroforestry.

 

Cereal crops grown alongside trees in Bedfordshire, UK. Agroforestry Research Trust.

Mupepele et al. note that the quality of the studies they were referencing varied somewhat, with some using replicated experimentation with clear controls, whilst others were more observational in nature. To compensate for this, they tried applying a statistical weighting method that gave more value to the more statistically strong studies, but found this made no difference to the overall result. They also carried out funnel plot and Egger’s regression tests for undetected biases in their data, but did not find bias was a problem.

A previous  meta-analysis led by Mario Torralba of the Department of Geosciences and Natural Resource Management at the University of Copenhagen found that agroforestry had a much stronger impact on biodiversity, which caused Mupepele et al. to consider the differences between their findings and that of the earlier study. They note that Torralba et al.'s study was published in 2016, and contained the results from two studies published in 2015 on the benefits of agroforestry in Mediterranean ecosystems, both of which produced very strong positive results, and that if these were excluded from Torrialba et al.'s data then the result was closer to that of Mupepele et al. who included several post 2015 studies with less clear results.

Properly done, meta-analyses can provide a powerful tool for understanding ecological systems in ways not possible from individual studies or unsystematic literature searches. However, the robustness of these results is dependent on the methods used to analyse the data, and in particular the use of weighting to take into account the quality of the studies being referenced. This needs to be done carefully, as failure to apply the right weighting can often lead to very different results. This said, applying weighting to Mupepele et al.'s results resulted in no significant change in the outcome of the study, which strongly supports the robustness of their findings. 

The application of repeated meta-analyses to the same data set can reveal changes over time, as new studies add to the overall picture, dampening the results from atypical studies that might have a profound impact on a smaller data-set. By building a cumulative model in which data were added in chronological order, Mupepele et al. were able to demonstrate that the impact of agroforestry upon biodiversity remained essentially unchanged over time, despite the presence of some anomalous data. They do, however, note that silvoarable systems make up a relatively small proportion of the whole, and that the addition of a higher proportion of studies of these systems in future might change the results of the meta-analysis.

 

Merino Sheep under a Cork Oak in a montado silvopastoral system in Portugal. European Agroforestry Foundation.

The ability to reproduce results is an important principle in science, but can be difficult in fields like ecology, which look at complex natural systems, no two of which are ever completely the same. Mupepele et al.'s results differed strongly from the earlier results of Torralba et al., resulting in their drawing different conclusions; Torralba et al. concluded that agroforestry has a general positive impact upon biodiversity, while Mupepele et al. concluded that this benefit was only clear when agroforestry was compared to croplands, despite both studies having used much of the same data. Mupepele et al. note that Torralba et al. included hedgerows and woody riparian buffers to agricultural land as agroforestry, while Mupepele et al. excluded them on the basis that they are not emplaced for silvicultural purposes (i.e. the trees used in these settings are grown for their value as boundaries, not as a crop in themselves). Neither did Torralba et al. include data from studies which suggested agroforestry had a negative impact on biodiversity. Mupepele et al. believe that scientists should be very clear about what data they are including in meta-analyses, the criteria for choosing this data, and the reasons to do so, in order to help policy-makers judge the significance of different studies. 

Mupepele et al. conclude that silvoarable systems produce an increase in biodiversity compared to conventional croplands, particularly with regard to Birds and Arthropods, but that this increase is not large, and there was no overall positive benefit of agroforestry to all other settings. Notably, silvopasturalism showed no clear benefit over either forestry or conventional pasturelands. Where previous studies have produced enthusiastic support for agroforestry, and strongly suggested these systems are linked to a significant increase in biodiversity, Mupepele take a more cautious approach, noting that relatively few studies find an unqualified link between agroforestry and increased biodiversity, and that literature reviews and meta-analyses need to be careful to include both the positive and negative impacts of systems when drawing on data from multiple studies. Nevertheless, they do conclude that agroforestry can have a positive impact on biodiversity under some circumstances, as well as providing carbon sequestration and other ecosystem services, and that a better understanding of how these systems work could lead to more informed future decisions by policy makers.

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Araneus diadematus: Observations of a dramatic population density decline in the once very abundant Garden Spider.

When the Krefeld Entomological Society published their famous longterm study (the 'Krefeld study') in 2017, it became known that the biomass of flying Insects had declined by approx. 75% over the past three decades in over 60 nature protection areas of Germany. Another long-term study (the 'Munich study') confirmed the Krefeld results, providing evidence that strong abundance declines of Insect populations had occurred in farmland and forests across vast areas of Germany and Switzerland. Similar abundance declines of insect populations have been documented in other long-term studies of other European and North American regions. It is generally accepted that we now live in an era of global Insect meltdown. This has dramatic ecological implications: the fact that Insects comprise the basis of many food chains and food webs means that in a world without insects, countless insectivorous species will ultimately become extinct due to starvation. In this context, aerial web-spinning Spiders are a group of utmost interest. These Spiders (including the Orbweaving species in the families Araneidae) trap flying Insects with the aid of aerial webs. In the temperate climatic zone, aerial web-spinning Spiders feed for the most part on small Dipterans, Aphids, and Hymenopterans, which are exactly the types of Insects known to have most dramatically decreased in abundance and biomass in recent decades. Aerial webspinning Spiders, because of their reliance upon flying prey, are therefore a highly vulnerable predator group in regions characterized by a high loss of flying Insects, such as Germany and Switzerland. While a larger number of studies on population declines of various groups of Insects has been conducted in recent years, potential cascading effects have only been documented so far for insectivorous Birds.

In a paper published in the journal Insects on 15 April 2020, Martin Nyffeler of the Department of Environmental Sciences at the University of Basel, and Dries Bonte at the Terrestrial Ecology Unit at Ghent University, present the results of a study which used the European Garden Spider, Araneus diadematus, as a model system to address whether evidence for population declines in aerial web-spinning Spiders in the Swiss midland can be found.

The female European Garden Spider, 10–18 mm in length, reaches adulthood in late summer, at which time it spins roughly 30 cm diameter orbs. The webs are built 0.5–2 m off the ground. This Animal, with its conspicuous white, cross-shaped mark on the upper side of the abdomen, is one of the best known Spider species in western Europe.

By comparing historical abundance data (20th century) with present-day data (2019), Nyffeler and Bonte examined whether the abundance of Araneus diadematus has changed over the past few decades. This work is based on extensive experience gathered during graduate research in the Swiss midland in the 20th century and supplemented by a present-day population density survey in the same geographical area. To make the comparison more robust, the data base was expanded by including published population density values extracted from the scientific literature.

Population density assessments were conducted at 20 locations in the Swiss midland, and a visual censusing technique was applied at 18 locations. This technique was modified insofar as curved line transects were used in addition to straight line transects in some cases, depending on the paths used. Martin Nyffeler slowly walked along the edge of a path and intensively searched by eye the vegetation within 1 m to one side of the path and from ground level to a height of 2 m (based on the fact that Araneus diadematus habitually constructs its webs at heights of 0.5–2 m off the ground). Each adult Araneus diadematus web encountered within the transect was recorded. Transects 1 to 5 were 1000 m long, Transects 6 to 10 were 500 m long, and Transects 11 to 18 were 200 m long (transect lengths depended on the nature of the landscape). The search focused on webs of adult females in habitats typical for this species (i.e. gardens, parks, graveyards, hedgerows, forest edges, and forest trails). Only webs occupied by a Spider were counted (regardless whether the Spider was present in the web or hiding in a nearby retreat), since only those webs could be counted beyond any doubt as belonging to Araneus diadematus. All counts were conducted on rain-free afternoons in August and September 2019. It has been suggested in the literature that Spider counts obtained using this method may result in underestimating the true population densities because of the Spiders’ cryptic lifestyles. This might well be the case if densities of well-camouflaged, nocturnal, and/or small, immature Spiders are included in the assessment. However, in the case of Araneus diadematus, a bias of this type is highly unlikely because this is a species of which the adult females construct large, conspicuous webs which are unlikely to be overlooked by a keen observer. The immature stages of Araneus diadematus are more likely to be overlooked with this method because their smaller-sized webs are less conspicuous; however, in the current study this objection was not relevant because immature spiders were not counted.

Additionally, web counts in two organic gardens, covering 330 m² and 800 m² ground area, respectively, were conducted. In these gardens, the vegetation and the exterior of the buildings were thoroughly searched for webs of adult female Araneus diadematus on several consecutive days in August and September 2019.

Araneus diadematus population density values assessed in the 1970s in the Zurich area were taken from two graduate research theses. These were supplemented by data taken from the literature. Overall, a total of 12 reports (including 18 population density values) were gathered. In these studies, plots ranging from 17.5 to 3300 m² in ground area were used for the assessment of Araneus diadematus densities.

It is noticeable that the present habitat distribution was different from the habitats studied in the past, e.g. no fallow grassland was studied in 2019. The fallow grassland areas used in the Swiss studies 40 years ago have fallen victim to urbanization and could not be surveyed. However, Araneus diadematus is a habitat generalist, widely distributed over a large number of different habitat types. All the study areas used in the present density assessment represent habitat types in which this species is typically found, such as forested areas. The past century’s Spider density values for grasslands were not above that century’s overall mean value. and tree- and shrub-dominated habitats appear to provide the most suitable sites for construction of the webs of this species. This implies that omission of grassland habitats in the 2019 density assessment should not have compromised Nyffeler and Bonte's investigation.

Population densities of Araneus diadematus assessed in the Swiss midland in August/September 2019 are compared with 20th century population density data for this species from a variety of European locations. This revealed that present-day population densities of adult female Araneus diadematus in the Swiss midland were generally extremly low. In ⅔ of the 20 investigated transects, no webs of adult female Araneus diadematus could be found.

By contrast, historical population densities of Araneus diadematus in its typical habitats were considerably higher. The difference between the 20th century European densities and the present-day Swiss densities was statistically highly significant. The present-day Swiss overall mean density of Araneus diadematus was roughly 140 times lower than the 20th century European overall mean. If the seven Swiss 20th century values were exclusively compared with the twenty Swiss 21st century values, the difference between the two groups was still statistically significant.

Adult female Araneus diadematus in web in a garden in Flawil, northeastern Switzerland. Rätus Fischer in Nyffeler & Bonte (2020).

Furthermore, the webs contained significantly fewer prey compared to previous studies (These figures refer to mean numbers of prey per web counted in mid-afternoon as a proxy for the daily prey capture rate of large Orbweaving Spiders).

This study revealed that the large orb-weaving spider Araneus diadematus occurred in extraordinarily low population densities in the Swiss midland in 2019. Araneus diadematus Spiders take down their webs during the night and rebuild them early in the morning. However, as laboratory experiments and field observations have revealed, not all individuals rebuild their webs the following day. Some Spiders, after consuming exceptionally large amounts of food at particularly favorable hunting sites, may cease feeding and rebuilding their webs for one or more days. Thus, the percentage of Spiders found with webs within an Araneus diadematus population is, in general, lower than 100% and usually in the range of 66% to 88%, depending on the availability of food at a particular time and location. The question arises of whether the method of web counting applied in this study might have resulted in underestimation of the true population densities by overlooking a certain percentage of satiated Spiders which had not rebuilt their webs at the time of the surveys. On this issue, it may be noted that densities assessed in the past century were for the most part also based on web counts, so the same methodological bias was involved at both time periods. Furthermore, since unsatiated Spiders tend to rebuild their webs more frequently than fully satiated Spiders, and since present-day Spiders living in the era of insect loss are more likely to be unsatiated compared with half a century ago, the frequency of web building nowadays might be expected to be rather higher. Thus, the possibility that the extraordinarily low present-day population densities were underestimations due to this particular type of methodological bias is highly unlikely.

In 2019, the webs appeared to be rather fragile compared with the stronger webs from previous decades, as is the case when malnourished Spiders make webs with thinner threads. This is in good agreement with laboratory experiments, in which the amount of thread produced is reduced if Araneus diadematus Spiders are kept deprived of food and it agrees with Nyffeler and Bonte's observation that the webs contained significantly fewer prey compared to previous studies. The overall impression gained during the survey was that there has been a paucity of prey throughout the entire study area in recent decades, which has been confirmed by the observations of other researchers.

The abundance decline we show here of this once common Spider in the Swiss midland is evidently revealing a bottom-up trophic cascade in response to prey scarcity recently documented in the same area, and more widely across western Europe. The hypothesis that the availability of flying Insect prey in the study area had drastically declined over the past decades is confirmed by the 'windshield phenomenon' noticed throughout the Swiss midland (i.e. compared with previous decades, many times fewer flying Insects are nowadays killed on the front windshields of cars). This is in sharp contrast to the situation a few decades ago, when fairly frequent 'wasteful killing' (and, coupled with it, 'partial consumption') of Insects in Araneus diadematus webs at favorable sites could be observed (with capture rates of sometimes up to 1000 prey per web per day). The reduced food intake of Araneus diadematus in recent years is likely to have negatively impacted the fecundity and survival of this Spider, which in turn may have led to the abundance decline documented in this study. Sublethal effects of chemical pollution may have additional negative impacts on this Spider’s survival.

Aside from food scarcity due to insect population declines and chemical pollution, other negative environmental developments have additionally contributed to the decreasing population densities of large Orbweaving Spider species in the western European landscape. These include adverse effects of modern forestry practices (e.g. removal of forest understory and of shrubs at forest margins, large-scale aerial spraying for the purpose of Caterpillar or Bark Beetle control), the transformation of traditional farmland into large-scale depauperate monocultures (accompanied by the loss of weedy field margins and hedges), the transformation of fallow grassland patches into construction sites, and the removal of shrubs and trees in urban and suburban gardens. That habitat conversion and degradation can have a strong detrimental effect on large Orbweaving Spider abundance is well demonstrated by the example of the fate of a plot of land located near Zurich-Oberengstringen (in between Highway A3 and the Limmat riverbank). In the 1970s, tall grassland interspersed with shrubs covered this plot, and at that time, large Orbweaving Spiders occurred there in high numbers (up to 6 m² in small, local patches). During a visit to this site, 40 years later, it became apparent that the land had been converted to a highway rest area with short-cut lawns and, as a result, the density of large Orbweaving Spiders had declined to a very low value of 0.002 m². Similar habitat conversions resulting in the destruction of suitable habitats for large Orbweaving Spiders have been noted elsewhere.

Nyffeler and Bonte of course realize that the recorded declines were not based on systematic long-term monitoring and that they could be attributed to normal population cycling. However, while they are not able to provide a smoking gun, several elements support a systematic decline. First of all, the dramatic decline up to 1% of the reference baseline from 40 years ago has never been observed at shorter temporal time frames, and reaches far beyond the typical natural fluctuations in population sizes, even when they are known to be linked to resource pulses. Second, records from other locations show that this decline is occurring at such large spatial scales that it can only be explained by large-scale, more global environmental drivers like land-use change, climate change, or the global use of pollutants. Indeed, the extraordinarily low population densities of Araneus diadematus in the Swiss midland observed in the 2019 survey are supported by statements of biology students at the University of Basel, according to whom generally very few large orb-weaving spiders have been spotted in recent years during walks through forests and fields in the Basel region. Furthermore, in mid-June 2017, a group of over 40 biology experts conducted an extensive faunistic survey in the grounds of the Merian Gardens, a park-like area covering 180 000 m² located on the outskirts of Basel. In the course of this survey, only three specimens of Araneus diadematus could be found over a time period of 24 hours suggesting that nowadays this once 'abundant Garden Spider' must have become rare in that area. The only large Orbweaver species still found in high densities during the 2019 survey in the Swiss midland was the Bridge Spider, Larinioides sclopetarius. This nocturnal species, which lives near water and frequently builds its webs on street lights and illuminated bridge railings, still gets sufficient amounts of food in the form of flying adults of semiaquatic Insects (Chironomids, Ephemeropterans, Trichopterans, etc.) attracted in large numbers to the artificial light. Because of its capability to exploit these artificially high prey densities, Larinioides sclopetarius is, in contrast to other large Orbweavers, extremely successful in colonising urban habitats in high density even in the 21st century, not only in Switzerland, but also in other parts of western Europe.

Similar extraordinarily low population densities of Araneus diadematus (0.0004 adult females m² at a landscape scale) were also recorded in an extensive survey in nine landscapes of the Ghent region, northern Belgium, in the summer of 2014. In Switzerland, likewise, densities were one order of magnitude or more lower than those recorded one decade earlier (e.g. during a survey in 2004–2006, densities at two locations were 10–20 times higher compared to those ten years later). Interestingly, while other Orbweaver species, especially the larger ones, showed dramatic declines in both abundance and species richness along an urbanisation gradient, Araneus diadematus was found to reach similar low densities across this land-use gradient. In other words, local densities at spatial scales of approx. 100 km were alarmingly low in both the more natural and Human-impacted regions, demonstrating regional declines beyond the scale of local land use. Thus, extraordinarily low present-day population densities of Araneus diadematus have been recorded in two different regions of western Europe, roughly 500 km apart. These declines extend beyond local environmental changes at small scales and suggest common negative impacts of intensive urbanisation, climate change, or any other large-scale stressor across the entire landscape over the past half century. 

Nyffeler and Bonte's study and that from northern Belgium suggest that the notion that Araneus diadematus is an abundant Spider, as pointed out in much of the literature, has these days turned out to be a myth, at least in highly urbanised western European landscapes such as the Swiss midland and northern Belgium. So far, the apparent abundance decline of this species in western Europe has been ignored by the faunists in charge of compiling local Red Lists for Spiders. Red Lists are based on the number of different locations within a landscape in which a species has been recorded, and not on absolute population densities. The fact that Araneus diadematus is still found in many places (although in highly reduced densities) may explain why it is still labeled an 'abundant species'.

In contrast, present-day population densities of Araneus diadematus in some areas outside of continental western Europe still appear to be rather high. For instance, exterminators of the pest control firm Senske Services removed more than 75 Araneus diadematus spiders from the exterior of a '2500 square foot home' (232.5 m²) in Seattle (USA) in August 2016. Evidently, the Spiders at this particular location were still capturing sufficient food in the form of flying Insects to enable them to build up a population density roughly 290 times that of the present-day Swiss overall mean density. Future detailed assessments of the population densities of this spider species in different parts of its geographic range are urgently needed, and may provide important information on the extent of the loss of flying Insects in various regions of western Europe and further afield. Nyffeler and Bonte would in this respect like to promote the use of new citizen-science tools such as SpiderSpotter to achieve these highly needed insights, and especially to guide short-term action to mitigate alarming declines in these sentinel Arthropod top predators.

The drastic decline in the abundance of the Orbweaving Spider Araneus diadematus over the past half-century documented in this study apparently reveals a bottom-up trophic cascade in response to the widespread Insect losses that have occurred across large parts of Europe in recent decades. There is evidence that other groups of aerial web-spinning Spiders, which likewise depend on flying Insects as food, have also become much rarer over the recent past. So, for instance, the mesh-web weaver Dictyna uncinata (together with other Dictynid species), whose small, tangled webs were found in large numbers on the leaves of garden plants a few decades ago has apparently become very rare these days.  The ongoing abundance decline of the Spiders parallels the dramatic abundance declines in other insectivorous animals such as insectivorous Birds, Bats, Frogs, and Lizards documented in recent decades. 

To sum up, the findings of this study support the notion by other researchers that we now live in the midst of an ecological crisis in which trophic webs are being eroded and degraded as a result of adverse, man-made environmental impacts. If this disastrous trend cannot be halted or even reversed in the very near future, 'entire ecosystems will collapse due to starvation'.

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