The 2018 newsletter provides a critical overview of the recent changes to tree care and the urban forest with special attention to the biomass industry. An overview of the failure of the municipality to implement a sustainable urban forest policy is also highlighted. A Dutch version will be published soon.
The Netherlands is not known for its natural landscapes, diverse wildlife or old stature trees but rather its impressive dykes and complex water ways; its human crafted landmasses and its highly efficient agriculture. This incredible ability to make and remake the landscape is a wonder to behold. But such technical acuity has not led to the long-term sustainability of less human-oriented landscapes such as forests and wetlands. Nor is this a land renowned for its urban trees. In fact, most locals have never heard of the field of urban forestry, a term which doesn’t translate easily into Dutch (stedelijk bos). In this country, the idea that urban trees might offer some kind of interconnected ecosystem/biotope for humans, animals, plants, and insects is only recognized by but a small group of tree advocates and scientists. And many residents view trees as individual property, as mere yard decorations to be removed at will.
New tree maintenance policy post 2013
Groningen’s urban forest changed in 2013 as our trees were managed in dramatically altered ways. The increasing rates of tree removals in the city and surrounding province was alarming. Since then, we have been losing trees and green spaces from the landscape at a rapid tempo. Once healthy, well-maintained trees were increasingly impacted by aggressive pruning techniques. This seemed to be a national trend as well. Moreover, practices as ‘lions tailing’ and tree topping by local tree workers were still practiced. This was also visible in private residences (my own neighbors topped ALL of their trees). As chair of the newly formed Bomenridders Groningen Stichting, we wrote long letters to the municipal green department, which included copious citations about the importance of maintaining the urban forest. Unfortunately, our entreaties were met with denials that such practices existed here (letters and responses on the Bomenridders Groningen website).
Typically, when the city tree workers were asked why such trees were removed or aggressively pruned – the now familiar refrain was uttered – SAFETY! One day, a tree worker, diligently hollowing out every single inner branch (a practice called ‘lions tailing’ in English), admitted to me that he was even responsible for training others in this standard technique, which he claimed reduced the weight of the branches (the opposite is true). Such techniques had long been discredited in the international arboricultural society (Figart), but still old habits were hard to break. And why would you want to stop topping or hollowing out old, large-stature trees, when these procedures produce volumes of sellable wood (as biomass) and also guarantee a day’s work for a local tree cutter. Eventually such severely damaged trees also require more repair as fast growing compensatory shoots need to be trimmed as well. Just look at the large piles of living wood under a recently ‘trimmed’ tree (picture here).
Was I recognizing a kind of cultural disposition (against trees) as local residents too were engaging in such practices. As I questioned neighbors why they topped their own trees (which didn’t win me lots of friends), I repeatedly heard the same excuses: “That tree was growing too tall”; “that tree might fall during a storm”; “that tree was causing too much shadow”; “that tree let too many leaves and branches fall on my yard” “a tree nearby fell during a storm” (so if one falls the others still living must be removed) or even “I wanted to get the birds out of my yard”. It appeared there was a general fear/dislike of tall trees and low hanging branches. This was disconcerting, the very things that I enjoyed about trees were considered a nuisance to others. Now I understand why international consciousness raising and tree activist movements such as De Bomenridders, TREES ARE GOOD and FRIENDS OF TREES or even LESS ASSHOLES MORE TREES have cropped up all over the world.
VISIBILITY and SAFETY or state sponsored vandalism of urban trees
Other lifespan reducing practices are still executed including knotting or candalabering. The first is a quintessentially Dutch practice. The famous knotted willows, a characteristic part of the Dutch countryside, used to provide accessible edible leaves for grazing cattle as well as pliable twines for basket weaving, yet cattle no longer graze in this way and few baskets are still created from such trees.
This practice might be useful in certain rural areas, but it is often visible in residential trees. Here you often see trees knotted once they reach a certain size (about four feet), which then prevents it from growing to its DNA driven designated height. Many residents seem to equate knotting of a tree with some kind of required maintenance, something like a haircut, which is believed to stimulate the tree to grow back stronger and healthier the next growing season. Actually, just the opposite is true, such techniques lead to long term trunk rot, infestation, instability and the structural weakness of tree root systems and trunks, resulting from the radical imbalance between a severely reduced canopy and branch structure (“Topping and Lions Tails Are Forbidden”). Moreover, these techniques (crown raising, lion’s tailing, knotting) all lead to a tree’s severely shortened lifespan. Of course, by the next season, residents see leaves and small water shoots springing out of the trees faster than ever and think, see this tree is healthier than ever, but these small shoots are simply the trees defense mechanism as it attempts to recoup the massive loss of nutrients and carbohydrates from all of its foliage producing branches. Moreover, these small shoots are not structural branches, but loosely attached ones which fall easily during storms; they are therefore UNSAFE.
Extreme Crown Raising post 2014
Since 2014, the mandate set out by the beheer and verkeer division required all street trees on highways be raised to 4.5 meters to allow for traffic visibility. In reality, tree workers are cutting trees up to 7 meters. I wonder how trucks and buses survived before 2014. Street trees lining residential streets needed to be raised to 2.5 meters (see letter by gemeente groendienst), but again tree workers are interpreting this as 4 meters. In response to growing critique of this policy, the almighty “SAFETY” mantra is churned out by every bureaucrat, administrator, and tree manager around. Slowly but surely street trees, and now most non-street trees as well, suffered dramatic losses to their basic architecture, sometimes resulting in crown reductions of up to 40%. Most scientific tree pruning manuals warn against ever removing more than 10% of a year’s growth in one trimming (Gilman). They also suggest that no living branches larger than 10 centimeters in diameter are removed, unless they clearly pose a danger (dead, diseased, dying). Yet our ETT (European Tree Technicians) workers seemed to have forgotten the basic principles of photosynthesis and crown architecture. Or was something else guiding these new destructive policies?
Because of the recent national program to promote ‘safety’ and increase mobility, instigated by various powerful agencies from the Ruimte Beheer, Staats Bos Beheer (SBB), VTH, Verkeer en Beheer to the growing biomass industry and the concrete and construction industry, trees have suffered irreversible consequences. As we began to investigate such links between these agencies and the larger polity, it appeared that safety was not the only concern. Rather economics and the transition to green energy guided many of these new rules for the benefit of each of these symbiotically intertwined industries and divisions. I’ll return to this point soon.
It’s amazing to visit another non-Dutch city such as Stockholm, Berlin, or Canberra, Australia where large city trees line busy streets, with much heavier traffic than in Groningen. Trees even have large crowns and low hanging branches. In some cities, trees are even situated comfortably near buildings, providing a living and vital biotope for humans and animals. Visibility is obviously an issue in all urban areas, but in many larger cities, few accidents are reported resulting from obstructed views because of trees. Of course, trees are also trimmed in these non-Dutch cities, but with the view of maintaining the form and health of the tree and the visibility of traffic and pedestrians. Here, the rally call of SAFETY, VISIBILITY and MOBILITY and now DISEASE have reached hysterical proportions; they have entered the standard lexicon of corruption, misused for the short-term economic benefit of particular interests to rationalize such destruction.
In fact, trees with severely reduced and/or raised crows become structurally weak as they stimulate extra growth at the tops of the remaining high branches, which become ‘top heavy’. These severely raised crowns are then susceptible to the turbine effect during storms (Gilman et al, James et al). So, while an extremely raised crown creates more (and often unnecessary visibility) for large trucks, such trees ultimately become more likely to fall during storms, a much more dangerous threat for humans and moving traffic than a few branches brushing near a truck’s cargo bed. In fact, during in a recent storm in October in 2017, many trees with severely raised crows toppled onto streets and houses, yet no investigation was initiated to determine if such ‘maintenance’ had actually compromised the structural integrity of these fallen trees.
In the city’s own inspection guidelines, trees with reduced crowns and hollowed out canopies (graphic below) are considered less vital, but the city itself is currently causing the widespread diminished vitality of our urban forest. As tax payers, we fund the vandalizing of these most precious and irreplaceable trees. It is a wonder they survive even a few years, but as we know trees are resilient despite all of our misguided exploitations. Trees (can) far out live us and live on a much longer time span than humans.
Building an Urban Forestry Foundation – Tree inventories and compensation
In addition to such reckless tree maintenance procedures, we have witnessed a dramatic increase in trees disappearing from our streets, parks, forests, and neighborhoods. Since 2015, I have seen more than a hundred trees removed from my daily bike commute from Haren to Groningen. This has been a sad phenomenon to observe. And only a few dozen trees have since been replanted. With the Bomenridders Groningen, one of our first priorities was to inquire about yearly inventories of trees felled and planted, a standard and fundamental practice for all urban forestry departments. To our surprise, we were told that no, the Municipality of Groningen (or Haren or many other villages in the province) no longer compiles yearly inventories. In Groningen, the last inventory was made in 2013 (“Evaluatie Boombeheer 2013”). In this evaluation, a figure of 180,000 trees in the city of Groningen was estimated, but this figure was last stated in 2008 and therefore is now 10 years out of date. If the municipality allows some 1,200-2,000 tree removals per year (not to mention all the trees felled by SBB in areas not requiring permits), then we can surely conservatively estimate thatthe city now has less than 170,000 trees, but this is only an estimate based upon the three evaluation reports from 2008 which I’ve updated by compiling with yearly averages of tree permits published online (see permits published on website Overheid bekendmaken).
This is a shocking discovery. So, in this time of environmental and ecological crisis, when urban forestry lobbies for increased recognition of how urban trees mitigate against climate change and improve the environment from improved air quality, increased water filtration, and as a defense against pollution and heat islands, apparently, their destruction (or restoration) is simply not monitored. Further, we were dismayed to discover that no measure of the total tree cover in Groningen had been made. This, despite the wide-spread and internal availability of aerial photo programs such the one used by the entire province. I even volunteered to make such an inventory based upon established data collection methods such as iTree Tools in the village of Haren, but the green department became increasingly adamant that there were no resources for yearly inventories, nor was there immediate interest in developing one. In Groningen, we’ve since heard that a pilot project with iTreeTools may be adapted, which appears as a small light at the end of this dark, expanding, concrete tunnel. From all the current literature within urban forestry, the first step is always explicitly named: one must first know the size of the urban tree cover before a long-term urban forest plan can be enacted.
With the current city planning moto of Groningen Berijkbaar (Reachable Groningen), it is perhaps not coincidental that the last years have seen a massive increase in development and infrastructure within the province including the billion-euro highway project Aanpak Ring Zuik, the turbo bike highway program (FietsRoutePlus), several building projects (commercial and residential such as Kempkensberg in Groningen), and the replacement of the city’s sewage pipes and cables. It is rather convenient that all of these projects are funded and executed without a proper image of how much green spaces are destroyed, nor how they will be compensated. Finally, in March of 2017, there was a motion to update the compensation requirements for tree fellings, but this has yet to materialize nor has there been provisions ensured for the monitoring of green compensation regulations (see Groen Compsenation 2017). For this, the Bomenridders and later Boomwachters Groningen provided a model for appropriate compensation based upon actual statistics such as tree mass, cover and species, and with measurable calculations of greenhouse gas mitigation, oxygen, biodiversity, mass, pollutant filtration etc. But this was not accepted, and rather a 1-to-1 tree compensation + financial model was initiated (not yet implemented). Yet this again gravely underestimates the various values of mature trees versus young trees. How does one compare a 70-year-old tree with a 5-year-old tree? In such cases a 1-to-1 compensation fails completely. In architectural terms – how can we compare a castle with a shed?
The second goal of the Bomenridders Groningen was to influence how trees removed were compensated, so that the overall percentages of tree cover could be protected and maintained as infrastructure changed and as pollutions expanded because of increased traffic and concretization. This too was met with nothing but a few cursory mentions of tree permits and BEAs in which promises were made that some trees would be compensated. No mention of when, where, and how these new trees would be protected was specified. Together through persistence WOB (Freedom of information) inquiries, we came to realize that in most cases, only a small number and sometimes no trees were compensated for large-scale development projects such as the DUO building in Groningen, which displaced much of the local green corridor in a prized ecological spot near the Sterrebos on the south-east side of the center. A decade earlier, this green corridor had been explicitly allocated as an ecological zone for local flora and fauna including the few remaining bats in the city, which remain protected under The Nature Law (Natuur Wet 2017). Part of this corridor is now the current site of a massive highway expansion project (Aanpak Ring Zuid) where already hundreds of the slated 600 to 800 trees, plus several hundred hectares of green spaces, have been removed. Many of these are larger stature trees (Oaks, Maples, Ash, Beech), the most valuable trees for bats and other animals and for mitigating greenhouse gas emissions, not to mention that these large stature trees are the most majestic and beautiful in this area.
Harvesting wood as Green Energy – Biomass
In 2013, after the signing of the Paris Climate Accord, the current Dutch administration agreed to reduce its greenhouse gas emissions by 20% by 2020 (“Europe 2020 Indicators”). It also made a commitment to move towards sustainable, green energy sources. Sounds good? Yes, on paper, but for both the urban and the local provincial forests, this drive and the resulting policies nationwide have already had dramatic and devastating consequences for our urban and national forest.
In Haren, such changes were clearly visible in the liberalization of the tree felling permit policy of 2016, during which trees with a trunk circumference of less than 100 centimeters (so trees often as old as 50 to 60 years) could be cut without permits. And all backyard trees could now be cut without permits. Further, before this new liberalization policy was enacted (approved in the Haren Board by everyone but Groen Links representative) there already existed a general laisez faire attitude towards private trees. Even though the municipality required that private trees (before 2016) with a circumference over 60 centimeters require a permit for felling, over 98% of all permit requests were granted. And in fact, between 2010 and 2015, on average, over 600 trees were cut per year. This, in a village which prided itself as the Green Pearl of the Netherlands. Clearly a new conception of the tree management was underway, where trees were no longer cherished nor allowed to grow old and big, but rather expensive objects to be managed, limited, and standardized. Trees are allowed to exist only until they became a nuisance for residents or obstacles in the way of new building projects and infrastructure. Further, increasingly, trees are also commodities to be sold as biomass in order to meet our new ‘green’ energy mandate.
It was at this point that Bomenridders Groningen as well as many tree activists’ groups (of which there are now dozens) sought to discover exactly how changes dreamed up high in the national energy policy campaign were impacting the management of our local urban and provincial forest. Through three years of obsessive and voracious study of government documents, interviews of local green managers, and finally discussions with disgruntled tree ecologists, we came to some surprising conclusions. These conclusions were reached via the perusal of difficult to find but by no means invisible documentation of the local tree policy (“Sterke Stammen”, “Benutting Biomassa”). For one, the push for more green energy, combined with the privatization of tree maintenance in the late 1990s, led to an industry which now repurposes trees as commodities to be extracted for their value in weight as biomass (of course trees have always had secondary value in other industries but not as energy). In fact, this policy was publically articulated in a letter by the board in 2013 in which the municipality stressed its upcoming goal of acquiring all of green refuse collected by city green workers (“Benutting biomass”). These temporarily employed green workers, largely outsourced by second parties, were encouraged to sell green ‘refuse’ back to the city as biomass for experimental wood burning ovens in the five large-scale sporting centers in Groningen. Biomass was also to be collected for RWE for the giant plants such as the one in Eemshaven.
When we began asking both provincial officials as well as the city green division if the collected tree refuse as well as felled trees were sold in weight as biomass, we were met with a variety of statements. Some acknowledged that wood was sold, others claimed that this was not directed towards the new biomass industry. Other documents followed in 2016, which explicitly named the goal of increasing wood as biomass from 15% to 30% for burning as fuels by 2020 (“Benutting biomassa”). Finally, after much persistence, we were invited to visit one of the experimental green energy wood ovens in the sport center Kardinge in North Groningen, one of five sports centers transiting to the use of wood chips as fuel for heating its facilities. Our WOB request led to figures of some 600 tonnes per year burned in this one single oven. In the entire city of Groningen, some 400 tonnes of wood are collected per year. This meant that ALL of the so-called wood refuse of the city of Groningen was used in this one single wood stove (also confirmed by our contact there), and this wood stove still required significant extra energy from natural gas to fully heat this center. The idea that we could therefore provide 30% of our total energy needs in biomass is utterly ridiculous when you realize just how much wood is required for one single oven heating one sport facility.
We then asked our contacts at the sports center Kardinge about how this wood was collected and paid for. We were told that the Staats Bos Beheer was the party responsible for delivering this wood. In fact, some six contractors throughout Groningen are responsible for collecting wood refuse from these outsourced tree cutters (and sometimes whole parts of trees are turned into chips in a local tree chipping facility). This summary confirmed what we had suspected, a new economic model of tree maintenance was actually fully underway, which adversely motivates tree ‘workers’ to remove a greater percentage of a tree’s crown in so-called maintenance schedules. Further, we deduced that the increased tree removals were also stimulated by economic reward for tree workers whose livelihoods had now become precarious. In short, the province no longer employed long-term tree workers with established knowledge about how to sustain trees for long-term health, but rather managers with backgrounds in an economic sector responsible for hiring temporary workers to cut and trim trees to meet new expanded yearly quotas for the increasing demand for biomass (in order to continue acquiring subsidies from the EU for green energy). This model now supports the excessive extraction of healthy wood from local trees and shrubs to increase the amount of wood available for biomass to meet our greenhouse gas mandates by 2020.
Since 2013, when this new program was initiated, three important programs aired, which highlighted the disastrous consequences of this biomass industry, the Zembla program Bos als Brandstof (March 2017), the VPRO Tegenlicht program De Waarde de Natuur in Nov. 2017 and the Green Gold documentary on NPO in January of 2018. Each made the very basic point that burning wood as biomass based upon the false promise of a zero-greenhouse gas emissions balance was in reality a panacea, a wild and impossible dream. Obviously, the released CO2 of all felled trees (which even if the entire forested area of the Netherlands were to be harvested, we would not have enough biomass for a single year) requires some 30 to 80 years to re-absorb the released greenhouse gases from felled trees, this is time we simply don’t have to improve our carbon output percentages. There is currently uproar everywhere about this ill-advised and irreversible policy.
Deforestation in NL
Despite the good intentions of harvesting our urban and provincial forests for so-called green energy, the immediate consequences are already visible. In fact, a recent study by Wageningen University researchers concluded that between 2013 and 2017, the Netherlands has lost over 5,400 hectares of forested land (“Ook in Nederland vindt ontbossing plaats”). And in the province of Groningen, we have lost forest at an even greater rate than the Amazon rain forest, with over 1000 hectares lost since 2013, with an average of 330 hectares per year (“Ook in Nederland vind ontbossing plaats”). This sounds like an outrageous claim, but it was later substantiated in the Volkskrant (van Dijk). Such studies reveal the speed and irreversible damage of such ‘get rich fast’ policies. If anything, we should be doing everything to PRESERVE our existing forests and individual trees, not add them to yet one more commodity to be commodified for the machinery of capitalism. This is certainly a race to the bottom.
It is time we began to recognize trees for what they are – the very things that sustain us; living entities which provide the oxygen that we breathe. They announce the seasons in glory and splendor, they provide shade and coolness, and protect us from wind during the winter. They relieve us from the fatigue of the concrete jungle, and as biotopies for birds, small mamals and insects, they provide an interconnected ecosystem for wildlife of which we are a part. They titillate us with mysterious and reassuring soundscapes (the rustling of leaves). They provide play places where our children learn how to climb and fall. They are repositories of memory and cultural heritage. They deserve our respect and humility. Yet again and again, they are treated as mere objects to be mutilated, denuded, dwarfed, moved aside, cut down, sold, and burned.
The Relentlessness of Capitalism
This is the rationalized, masculinist manner of interacting with nature. This masculinist approach towards tree management works its way into all facets of tree activities from the attitude of on the ground tree workers (coincidentally the majority of which are men) who rightly see trees as objects of hard physical labor, and those annoying complaining women (and a few men) – the tree activists who view trees as both aesthetic wonders and physical environmental and ecological assets to their communities. Then there are men and women who simply view trees as nuisances – they shade their terraces or drop leaves and twigs on their cars and grass. For them trees are a burden messing up their tidy gardens. Finally, are the middle layer of green division communications officers who are also mostly women. These are the people who have the terrible jobs of fielding all of the questions and complaints from both tree activists and from those who seek to remove trees from their premises.
This hierarchy wonderfully mirrors the patriarchal control of the industrial versus natural world in that those who exploit trees for money stand at the top, supported by the persistent but precarious hard physical labor of those paid to extract such commodities (the tree cutters), and down to the women paid to act as pleasant mediators (the veneer of civility), creating a barrier between angered residents and the decision makers who are impervious and unreachable, unwilling to justify their actions to those they are paid to represent. This relationship often leads to burnouts and frustrations, yet these very women often have very little power to challenge the top down decisions of contractors working for and alongside the powerful and independent industrialists such as the Staats Bos Beheer.
During the official bezwaar (objection) process and subsequent hoorzittings (sitting) of upcoming tree removals, this dynamic evolves into a time-tested theatrical farce, where women activists (the tree lovers) are meant to argue against another group of (bureaucratic) women, who presumably speak for the men who actually make the decisions and have the power to cut down such trees. This is a futile exercise as neither has autonomy or power to change the existing system and so such civic hearings only serve to condone the existing tree destroying policy of the state, while providing a veneer of democratic process and participation. Even worse, the so-called BEA’s (bomen effect analysis – tree impact analsis), the individual research reports of proposed cut trees, serve a similar purpose. They progress the tree felling process to its ultimate conclusion, even though these inspections were originally designed to force municipalities to enact thorough investigations of a tree’s value for local flora and fauna in order to make informed decisions about whether a tree should be removed. In this machinery, everyone is exploited but the Industrialists, who too eventually shoot themselves in their foot, as they are fundamentally a part of and dependent upon trees in the end.
As the chair of the local Bomenridders Association, I am consistently involved in this legal process. It begins with persistent attempts to talk to the actual managers responsible for deciding which trees will be removed in yearly tree removal (‘bomenkap’) quotas (yes these are written in policy letters!). It then involves investigating how decisions are made about how trees are maintained (such as in Haren where through our WOB inquires, we have not yet been allowed access to this person actually responsible for such decisions). In fact, in general, very few of the procedures for trimming trees or for choosing which trees were to be felled are ever explained or documented beyond a yearly list of trees chosen for cutting which range from dozens to hundreds of trees in a single permit. During our proceedings to protest particular tree removals, highly formal, legalize-ridden letters are filled with fancy words signifying nothing. Next to this futile process exists a powerless commission who can do no more than offer advice, but even here, in reality such commissions almost always support the existing decision of the municipality, so yet again more trees are cut and even more drastic measures are taken to make local environments (yes you got it) SAFE. And so the tree removals, extreme crown raising, and hollowing out and topping of precious trees continues (along with denials of such activities). When one finally discovers who the key managers are and tries to contact them (these are the same contractors who collect the wood for sale to the SBB for the biomass industry), they are unwilling to defend their decisions. And they certainly do not like their authority being challenged. Such arrogance has always guided industrial endeavors, where the profit margins drive the management and extraction of precious resources by managers who don’t actually own them. Urban forests are for all of us (animals and humans alike). These managers have lost sight of why they are here and how they live.
Women’s role in restoring our (urban) forest
Every time I walk in the center of Groningen, I’m happy to see the giant plane tree near the old V & D. This tree remains because of the sheer persistence of one fierce tree advocate, mevrouw Kiki (Picture).
We at Bomenridders refer to this tree as the “Kiki tree”. Women have long been involved in preserving, protecting and restoring green spaces, but until we are given a full and important voice in their design and care of our own communities, in the very near future, our communities will not only become bird and insect free (many neighborhoods in NL are already bird free), with fewer and fewer trees, but we will be susceptible to the urban calamities befalling other over-developed cities throughout the world. If anything is to be learned from the last year in cities like Houston, where rapid urban expansion (concretization) and a push for ‘mobility’ led to the massive removal of green spaces, combined with extreme weather, these actions resulted in the massive flooding of thousands of homes. If we fail to do more to protect our existing urban forest, we too will be left with little more than expensive buildings, expanded concrete highways, and turbo treeless bike paths. It is time to rethink such short-sighted planning and foster ways to preserve our urban forests. Making a basic inventory is the important and essential first step. Keeping the trees that we have is cheaper and more effective than cutting them down and replanting new smaller and less valuable trees (if new ones are ever planted).
We urge you to join and support us at the Bomenridders. We urge you to contact your local municipal government and demand that a new accounting of urban forests in implemented. We urge our local governments to respect and allow women to gain a significant voice in this process, so that the arrogant, masculinist and capitalist-driven exploitation of trees for profit can be overturned for the long-term health and flourishing of those species who will endeavor to live on this earth long after us. We know that without our trees, none of us stands a chance.
“Advies voor Groencompensaite – Toespraak voor Beheer en Verkeer.” Bomenridders Groningen. 13 April 2017: http://bomenriddersgroningen.nl/wp-content/uploads/2017/12/Groen-Compensatie-Toespraak-voor-Beheer-en-Verkeer-final-JH-e-JPJ.pdf
Arets, Eric. “Ook in Nederland vindt Ontbossing plaats.” Nature Today. Wageningen Environmental Research (Alterra). “Alles bij elkaar komen we tot de conclusie dat tussen 2013 en 2017 de Nederlandse bosoppervlakte netto met zo’n 5400 hectare is afgenomen, dat is gemiddeld 1350 hectare per jaar,” zegt bosbouwkundig onderzoeker Eric Arets van Wageningen Environmental Research (Alterra).
“Beleidsregels APVG vellen van een houtopstand” (groen compensatie regels): http://bomenriddersgroningen.nl/wp-content/uploads/2017/12/Groencompensatieregeling.pdf
“Benutting biomassastromen uit gemeentelijk groenbeheer.” Letter by Groningen College. 24 may 2012: http://bomenriddersgroningen.nl/wp-content/uploads/2017/12/benutting-biomassa-stromen-raad-groningen-2012-februari.pdf
Dijk, Thomas van. 2017. “Ontbost Nederland inderdaad even snel als het Amazongebied?”. Volkskrant (29 sept 2017). https://www.volkskrant.nl/wetenschap/ontbost-nederland-inderdaad-even-snel-als-het-amazonegebied~a4519148/
“Evaluatie boombeheer 2013.” Gemeente Groningen: http://bomenriddersgroningen.nl/wp-content/uploads/2017/12/Boombeheer-evaluatie-2014-copy.pdf
“Europe 2020 Indicators: Climate and Energy.” 2017. Euostat – Statistics Explained: http://ec.europa.eu/eurostat/statistics-explained/index.php/Europe_2020_indicators_-_climate_change_and_energy.
Figart, Larry. “Lions tail pruning won’t protect your trees: Pruning method leaves branches less resilient in high winds.” University of Florida, 2009.
Gilman et al. “Pruning Affects Tree Movement in Hurricanes”, Arboriculture & Urban Forestry 2008: 34(1): 20–28.
James, Kenneth, Nicholas Haritos and Peter K. Ades. “Mechanical stability of trees under dynamic loads”, American Journal of Botany, 2006.
“Mededeling van het voornemen aan het bevoegd gezag in het kader van de m.e.r. procedure voor de verhoging van het aandeel biomassa in de RWE Eemshavencentrale in opdracht van RWE Eemshaven Holding II B.V.” Letter by the Gemeente Groningen. July 2017. http://bomenriddersgroningen.nl/wp-content/uploads/2017/11/170714-Mededeling-voornemen-RWE-verhoging-aandeel-biomassa-brandstoffen-Eemshavencentrale.pdf (Letter about 15% to 30% increase of biomass)
“Ook in Nederland vindt ontbossing plaats”. 2017. Wageningen Universiteit. https://www.wur.nl/nl/nieuws/Ook-in-Nederland-vindt-ontbossing-plaats.htm
Schelhaas, Mart-Jan, Eric Arets en Henk Kramer. “Het Nederlandse Bos als Bron van Co2.” (Wageningen Environmental Research) Vakblad Natuur Bos Landschap. September 2017. https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=23773&utm_source=dlvr.it&utm_medium=twitter&utm_campaign=web-rss-nb http://bomenriddersgroningen.nl/wp-content/uploads/2017/09/edepotlink_t59c2507e_001.pdf
“Topping and lion’s tailing are forbidden“, National Arborist Association, official website.
 which when asked about these with citations from international textbooks on the dangers of such strategies – responses varied from outright denial to claims about the sickness or lack of maintenance in prior years.