Aliens in the Arctic

In a recent study co-authored by The3DLab-member Ronja Wedegärtner, a team of researchers have mapped invasive plants on Svalbard, and the results leave no doubt; alien plants grow where humans have been.

Two of the researchers on fieldwork in Svalbard. Photo: Lawrence Hislop / Norwegian Polar Institute 

The research team found 36 alien plant species, which grew exclusively in areas with human activity. Both around tourist attractions in settlements, and where there has previously been farming.

All of this might sound minor – finding 36 alien plant species should not be that much work, right? – yet the remoteness and challenging working conditions on Svalbard make organized alien species inventories far from straightforward. With this new study, the researchers finally provided a benchmark for continuous monitoring, that will greatly facilitate keeping track of changing biodiversity in the Arctic in the future.

More details on the study can be found in this nice blogpost.

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And we are live!

Distribution of sensor locations across Flanders. Yellow dots represent private gardens, purple are schools, red is for participating municipalities. The green ones in Antwerp represent a separate project in nature reserves.

There we go, today marks the official launch of CurieuzeNeuzen in de Tuin, the day on which 4500 microclimate sensors pop up across Flanders!

1906 sensors connected at noon on ‘D-day’. These will only start sending data on Sunday night, so only 300 are currently actively transmitting data (bottom)

You can take a look at their distribution on this map here.

These are scary and exciting moments, where we can follow in real-time if the connection of the sensors to the Orange Internet of Things-network are successful. As you can see on the right here, things are starting to look good, with already almost half of the sensors successfully installed.

Don’t underestimate that achievement: this is by far the largest IoT-sensor network that the country has ever seen, and we are thus truly technological pioneers.

But all is working relatively smoothly, while microclimate sensors are popping up in gardens across the whole region. Here at home, there was a little scientist helping out in any case (one that especially loves the little blinking lights that comes when sensors fail to connect to the network and, believe me, we have seen plenty of those during development!)

Location selection was done using our recently published selection algorithm that maximizes environmental heterogeneity. Hence the higher density of points in the more complex southern half of the region, and in urban centers.

Finally, below a sneak peek of the dashboard where participants will be able to follow the patterns in their own data, and how those compare with the rest of the region (available for participants from April 6th).

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Weather station networks, reinvented

We need a different kind of weather station networks to answer most ecological questions. We argue that what we need is countrywide ‘microclimate networks’, that measure weather conditions there where they matter for ecology and nature around us.

Where weather stations are insufficient

To measure global weather and climate, the world is increasingly covered by a network of weather or meteorological stations. On land, these stations are designed in such a way that it ensures all stations, whether in Belgium or Brazil, are recording climate in the same standardized manner: in open landscapes, above short grass, and well away from trees, buildings or mountains. While macro-meteorologists, those who design these networks, did their best to remove these local sources of “noise” in the data, these sources of “noise” are meaningful to many organisms. For example, although trees may cause chaos for meteorologists, because forest cover interrupts and changes local temperatures, these differences in forest cover between for example a beech forest in Flanders and a dense tropical forest in the Amazon rainforest of South America have huge meaning and importance for the animals and plants that live there. As a result, our current weather station network is ill-equipped to provide meaningful data to scientists wanting to know how climate impacts biodiversity. 

To do: build countrywide microclimate networks

A call to action has been made in a recently published study, which calls for a globally coordinated effort to create a new kind of weather station network – one that can tell us what a small lizard is ‘feeling’ in the remotest of habitats. We strongly believe that the world needs microclimate networks in parallel to the existing countrywide weather station network as established by national meteorological institutes, such as the RMI in Belgium. We also believe that we need to be quick about it. In their recent publication, the ecologists stress their case. Actually, we need two things: mini weather stations that measure conditions close to and in the soil, and a network of these sensors that measures in the most relevant environments. From cities to the countryside, from forests to mountain slopes, all those locations traditionally avoided by weather stations should be preferentially sampled by these new microclimate networks. By implementing this kind of network, we will be better equipped to understand climate change impacts on species, ecosystems and our agricultural systems.

A ‘mini weather station’ in action, measuring temperature and soil moisture in a Flemish broadleaf forest.

Selection algorithm

To achieve these countrywide microclimate networks, we provide a handy algorithm to decide where exactly these new networks should come. It selects measurement locations based on the expected microclimate variability of a region, by selecting locations in as broad a range of landscape types as possible. For this, we use a multivariate analysis of the environmental space, based on characteristics from which we know that they matter for microclimate: topography, vegetation cover, urbanity, macroclimate. The algorithm quantifies the distribution of these habitats across the country or region and proposes a set of locations that maximally covers this variability with as few measurement locations as possible.

Next up? Implementation! We hope that governments, scientists  or anybody else pay heat to our plea for microclimate networks and use our proposed selection tool to implement them in their own region. As such, we reach out to anybody else to start thinking on this parallel network of microclimate sensors to complement the global weather station network.

Our selection algorithm exemplified for France, with 453 suggested measurement locations on the left, and distribution of these locations (red dots) in the environmental space of France on the right, exemplified for elevation, the Topographic Roughness Index (the complexity of the terrain), and FAPAR (the amount of light absorbed by plants, a proxy of how green the area is).

SoilTemp

With the global SoilTemp-network, we made a great start in that regard, bringing together microclimate data from over 13.000 sensors from over 60 countries. The algorithm proposed here can however help us to switch gears even more, and design these networks specifically with microclimate measuring and global and regional coverage of microhabitats in mind.

We also already have a first example to showcase their approach: the new citizen science project ‘Nosy parkers in the garden’ ( www.curieuzeneuzen.be/home-en) has used it to select gardens for their project on heat and drought impacts on lawns. In this large citizen science project, 4400 citizens were asked to install a mini weather station (‘the garden dagger’) in their garden to measure the impact of heat and drought on urban environments.

A microclimate sensor (little white dot in the grass) taking the heat of a forest clearing

Link to the publication in Global Ecology & Biogeography: https://doi.org/10.1111/geb.13290

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Taking the temperature of forest microclimate research

Imagine: it’s a hot summer day. You’re sweating away in an urban apartment. Perhaps ice-cream would come to mind, or a dive in a swimming pool. Or a nice stroll through a lush and cool summer forest. Yes, that last one could be a great solution as well: forest microclimates contrast strongly with the climate outside forests, and on a bright summer day that difference could be up to several degrees Celsius. However, the climate inside forests is significantly more complicated than simply this air-conditioning on a hot summer day. Nevertheless, it is crucial for the understanding of the biodiversity and functioning of our forests to get to this true forest microclimate and integrate it into our ecological research.

The beautiful diversity of forest canopies (pictures by Eva Gril and Hugo Mahier)

Despite the potentially broad impact of this microclimate on the response of forest ecosystems to global change, we have long lacked a good idea of how microclimates within and below tree canopies drive nature’s response to global change. Recently, however, the importance of microclimate has moved firmly into the spotlights (see e.g. Zellweger et al. 2020, Lembrechts and Nijs 2020), and our understanding of what climate means below our forest canopies has been rapidly increasing.

With a team of (forest) microclimate experts, we decided we’d have to sit together and ‘take the temperature’ of what we know and what we don’t about forest microclimates. We met in a beautiful mansion in the middle of Sweden during a winter snowstorm in late February 2020 (for many of us the last time we got another view than our own home office as soon after the world got into lockdown). In that inspiring atmosphere, we discussed our current knowledge on forest microclimate and set a first step towards a paper summarizing that knowledge. That paper is now out for all to read!

A Swedish winter wonderland

In this review paper, we explain how variation in forest microclimates over space and time results from an interplay of forest features, topography and landscape composition. We stress and exemplify the importance of considering forest microclimates to understand variation in biodiversity and ecosystem functions across forest landscapes. Next, we explain how macroclimate warming (of the free atmosphere) can affect microclimates, and vice versa, via interactions with land-use changes across different biomes. We summarize all drivers of forest microclimate to provide a good idea of the many factors at play and how they are influencing the outcome (as shown in the figure below).

Overview of drivers of microclimate from the paper. Multiple vegetation drivers of microclimate might be of different importance in forest at boreal (top), temperate (middle), and tropical (bottom) latitudes, even if most processes are general. Increasing tree density from open non-forest habitats (A), to plantations with a simple canopy structure (B), to (semi-)natural forest with complex structure (C) reduces below-canopy wind speeds above ground. Forest canopies can reduce ground snow cover and thus decrease the insulating effect of snow cover on cool soil temperatures during the cold season (D). Vertical vegetation distribution (E-F) influences the amount and quality of incoming shortwave radiation, outgoing longwave radiation and moisture exchange. Disturbances can create canopy gaps (G), providing a local shift in microclimate. Seasonal reductions in canopy cover (tree phenology, H) during the cool and/or dry season increases the exposure of the internal forest to ambient conditions. Forests also buffer the temporal (i.e. daily, seasonal and interannual) variability in temperature conditions compared to adjacent non-forest systems (bottom panel). This buffering effect varies with vegetation height and structure, with reduced buffering in secondary, post-agricultural forests (I) relative to primary or ancient, (semi-)natural forests (J). Microhabitats within a forest, such as those created by epiphytic plants (K) can offer an even more buffered microclimate, critical for the ecology and physiology of many forest species. Finally, the temperature offset in forests can change throughout the day, with cooler forest interiors vs. open areas during the day (L) and warmer at night (M). For the sake of simplicity, we chose to depict wind, shortwave radiation, and temperature in the boreal, temperate, and tropical panel, respectively. However, of course all of these microclimate variables can be relevant to systems across latitudes.

Finally, we wanted to know what had to come next. With all those present at the meeting in this beautiful and peaceful Swedish mansion, we did a priority ranking of future research questions at the interface of microclimate ecology and global change biology. We realized progress was needed (and luckily soon to be expected) on three key themes: (1) disentangling the drivers and feedbacks of forest microclimates; (2) global and regional mapping and predictions of forest microclimates; and (3) the impacts of microclimate on forest biodiversity and ecosystem functioning in the face of climate change.

Priority ranking of forest microclimate research ideas

We end with a very positive note: good microclimate data is increasingly becoming available (see e.g. Lembrechts et al. 2020), opening the door to accurate and trustworthy models of climate variability at spatial and temporal scales relevant to our forests. This will revolutionize our understanding of the dynamics, drivers and implications of forest microclimates on biodiversity and ecological functions, and the impacts of global change. Yet this data is coming not a minute too late, as it is urgently needed to support the sustainable use of forests and to secure their biodiversity and ecosystem services for future generations. Together, and with good data at hand, we can make that last point a reality.

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Wet nature as airco?

Cycle from the city to a nearby nature reserve during a hot summer day, and you’ll immediately notice a few degrees difference. The higher temperatures are a result of the urban heat island effect. Smart urban planning with room for greenery and water can help to counteract this urban fever. Natural areas close to the city may also provide natural air conditioning.

Together with nature conservation organization Natuurpunt, CurieuzeNeuzen investigates how natural areas can take up their role as natural climate buffer and air conditioning for our living environment. Stefan Versweyveld, head of the Projects Department of Natuurpunt: “We are looking for answers to questions such as: is the cooling effect of a nature reserve greater close to the city than further away from it? Is the cooling effect of natural areas perceptible in the surrounding gardens?” Therefore, researcher Stijn Van de Vondel (University of Antwerp) will install 200 “garden daggers” in nature reserves across the province of Antwerp. The results will be compared with measured values in nearby gardens.

Wetlands4Cities

It is mainly the wetlands that can play a role in cooling our cities in summer. Stefan: “Wetlands provide very important ecosystem services. They retain water in the event of severe drought, replenish the groundwater level, mitigate flooding during heavy rainfall, and possibly play a crucial role in cooling our warm urban environment during heat waves.” Because Flanders has lost some 75% of its wetlands over the past 60 years, Natuurpunt has started the ‘Wetlands4Cities’ project: restoring and creating existing and new wetlands to give a boost to wetlands in urbanized areas. “CuriousNoses in the Garden now makes it possible to start effectively quantifying the cooling ecosystem services of wetlands.”

The management of these nature reserves is in the hands of Natuurpunt’s voluntary nature managers. They are responsible for the purchase, management and opening up of 25,000 hectares of Flemish nature. And it is these volunteers who will follow up the measurements in the field.

“The volunteer nature managers are very involved in their nature reserves,” says Stefan. “They observe the negative effects of climate change and desiccation on a daily basis. It poses great challenges to them and to us: mowing seasons have to be brought forward, large summer floods send site management into disarray, and the absence of frosts prevents ice mowing.” *

Through the dashboard, the nature managers themselves gain insight into the state of their area. “Because good water management in a nature area is crucial for plants and animals, our managers also already monitor water levels at regular intervals to keep track of their evolution. The soil sensors and the associated Internet of Things technology from the citizen science project ‘CurieuzeNeuzen in de Tuin’ will be of great benefit. After all, the data are immediately available, and in this way we can monitor the situation much more closely. We therefore expect to use more of these new monitoring techniques in the future. Our volunteers are therefore enthusiastic to participate in the project.”

More information (in Dutch) on the CurieuzeNeuzen website.

* In the winter, reeds are cut to get dense reed vegetation and to keep the water clear. If the water is frozen, this can be done by mowing or cutting the reeds on the ice.

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Urban invaders loving the heat

Guest post by Charly Géron, PhD student in The 3D Lab and lead author of a new study on how urban microclimates might facilitate plant invasions in cities.

They are submerging the news, movies, papers and talks everywhere. I am of course talking about the challenges the world has to face right now such as urbanization, climate warming and invasive species to only cite three. Anxiety is quite growing for a year now since we are directly affected by Covid 19 which can actually be placed in that last category (let me tell you that us humans can also be considered as belonging to that category 😉 ).

However, we don’t have to be frightened by these concerns, and we should look for ways to tackle them. My PhD has been an excellent way so far to better understand how they can interact with each other. Indeed, invasive species are listed among the biggest threats to the native nature but also to human activities. Historically, alien plant invasions have been mainly studied in natural environments focusing on their impacts on the local biota for example. It is only in the last few decades that alien plant invaders have received growing attention in cities. Urban environments are usually not perceived as containing major native species richness due to the habitat modifications by anthropogenic activities. 

Cities are incredibly connected via a dense transport infrastructure network, and they are hubs of exchanges of goods and people. This leads to a high number and proportion of alien plant species in urban areas, and especially of new comers. Moreover, one has for sure noticed how warm a city center can get in a heatwave compared to the fresh rural outskirts. This is one of the signs of the modified microclimatic conditions of the urbanized environments. They not only display higher temperatures but also drier soils due to the important use of materials such as asphalt or concrete characterizing our often – too – gray cities. It is also important to note that these microclimatic differences present along the urban-to-rural gradients are predicted to be more prominent in the coming years with climate change.

Ailanthus altissima taking over urban landscape

Cities then sound as the perfect laboratories to study emergent alien plant invasions. They not only display warmer and drier growing conditions, but they also concentrate newly arrived alien plant species. We decided to test the long lasting hypothesis that urban alien plant invaders are coming from warmer native climates. Indeed, the successful colonization of new environments by alien plant species highly depends on the match between their requirements and the local environmental conditions. Moreover, several observations and study have proven for other alien species from more favorable climates the clear link between warm cities and their establishment. For example, the persistence of alien aquatic animals locally depends on heated water effluents from cities in Germany. We focused on the European regions with a temperate oceanic climate termed “oceanic Europe”, which represents an area from the north of Spain to the south of Norway, through France, the UK, Belgium, the Netherlands, Germany and Denmark. We selected alien plant species that still have a limited distribution there, and we modelled their native range with a species distribution model framework, to visualize their native range climatic conditions. We analyzed their distribution in oceanic Europe along the urban-to-rural gradients using the percentage of built up area, with high values corresponding to highly urbanized areas.

Paulownia tomentosa at ease on top of brick walls.

We analyzed if the distribution of the selected alien plant species along the urbanization gradient in oceanic Europe was linked to their native climate conditions along 3 variables: the winter temperatures, the summer temperatures and the precipitation quantities, while taking into account the year of first observation in the wild. We found that more urban alien plants in oceanic Europe were coming from warmer or drier native ranges than the one currently found in oceanic Europe. A very good predictor of the distribution along the urbanization gradient of oceanic Europe was the annual mean temperature of the native ranges of the studied species, with the ones developing in more urban areas coming from warmer native ranges than oceanic Europe.

Mean urbanity (in %) of the studied alien plant species as a function of their native range climatic conditions. Mean urbanity of alien plant species as a function of: a) “precipitation” axis with high values indicating more precipitation; b) “summer temperature” axis with high values indicating higher temperatures, and c) the scaled year of first observation in the wild, ranging from 1683 (low values) to 2008 (high values). Each point corresponds to a species, colored following the main Köppen-Geiger climate class in which it was observed the most in its modelled native range. Full lines correspond to significant effects, while dashed lines correspond to non-significant effects.

We argue that despite the fact that alien plant invasions depend on a complex set of components, microclimatic barriers might be one of the reasons why some alien plant species thrive in urban areas, while others prefer rural environments. However, with the global changes listed earlier, the barriers that currently constrain numerous alien plant species to cities may be lifted. As cities are now recognized as hotspots for plant invasions, they could act as new potential “sites” for the seeding of future plant invasions, with the help of structures such as rivers or roads for their spread. We are now trying to disentangle what could be the underlying reasons of the preference of urban areas for some alien plant species, but this is for later.

Roads as paths for urban plant invaders?

The full story got published in Biological Invasions here.

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