It’s not going to be often that I share things outside of what we’d probably consider ‘true’ arboriculture or forestry (and environmental conservation, for that matter, as the two go somewhat hand-in-hand), though I’m sitting here reading Trees in Towns and Cities by Mark Johnston and listening to the music of a folk band from Finland called Nest (they use the kantele, a Finnish instrument, to very good effect, as well as a Didgeridoo). There’s one particular song of theirs that is very poignant and may likely have reference to man’s urbanisation and industrial pursuits, which I thought I’d share below (lyrics included).
You can listen to the track here, if you so desire.
Once we played in this forest in the shade of the tall trees at the dawn of this particular time. But many an aeon has passed since and many a fate has changed.
…and our great woods died. No new seeds have been planted for ages And those that were have been torn out from the soil.
I took the below photo a few weeks ago, whilst visiting a large parkland nearby to where I live. I initially just saw it as a good photo (in part, because of the sky and the slight haze), though having looked at it again just today I have noticed how it’s full of diversity.
Not only can we see that there is a large area clear of trees in the foreground, indicative perhaps of old grazing land or an agricultural field, but an array of trees in different settings and of different morphologies behind. In the centre of the image, a large monolith can be seen, and to its right both a tree that appears to have suffered storm damage to its right limb, and a young tree of more recent birth (all the way to the right, amongst the haze). To the monolith’s left, we have a cluster of mature trees (some with epicormic / basal sprouting) that may perhaps have been an old field boundary. Behind the mature trees, woodlands can also be seen (to both sides, though more noticeably to the right).
Such rich landscape diversity means that the site’s ecology may be rather diverse, as we have exposed mature trees with large swathes of heartwood that will incubate any boring insects (as the sun will heat the wood), and likely have cavities home to birds and bats (most notably the monolith). Additionally, fungal species will be present and decaying the heartwood (which would provide habitat for the wood-boring insects). The woodland may also bring with it woodland bird species, otherwise not found in a more pasture-like landscape, and support mammals including bats and dormice.
I was walking around some of the nearby fields yesterday afternoon, and came across a long-dead oak. I had almost passed it, when I caught the glimpse of a fungal bracket right at the base. As I didn’t have my camera on me, I went home to grab it and returned to get the below photos.
What I like about this Ganoderma applanatum is that it’s fruiting out from behind some of the only remaining bark left on the tree. I have seen it fruit on exposed heartwood, as have I seen it (more often) fruit through bark, though this was an intriguing example of a middle-ground of sorts.
We could discuss this topic to the ends of the earth, outlining both positives and negatives of tree presence within urban environments, though there is a mounting pile of evidence to suggest that trees really do have a (largely) beneficial impact upon humans in terms of health and well-being. However, most studies have looked at trees on a macro-environmental scale (such as exposure to general green spaces), and not looked at the linkages between individual trees and the impacts such trees have upon residents in the close locale. Therefore, the authors of this study sought to change this, by investigating the health benefits of trees to a “low granularity”, and instead of assessing such ‘greenery’ from the ground, they related their study to tree canopy sizes only – it was considered (by the authors) that tree canopy is the most important of all the ‘green’ available within urban areas. Thus, the study was planned, and the city of Toronto, Canada, was chosen as the location for the project.
The authors particularly sought to assess the relationship between street tree canopy density and its impacts upon: (1) overall health ‘perception’ (this was chosen as subjective perceptions of personal health has been found to influence mortality rates, and is considered a strong indicator of actual health of an individual); (2) cardio-metabolic conditions (including high blood pressure, obesity, high blood glucose, high cholesterol, and diabetes), and; (3) mental health problems (depression, anxiety, and addiction). Similarly, the benefits of trees in parks was also assessed, enabling for comparisons to be drawn between trees in differing locations.
In terms of the results found, I have segmented the three aforementioned categories into different sections. The manner in which the results section was written was rather disjointed by tables and seemingly tangential (but still contextually beneficial) points, though I pulled out the most important parts and included them below.
It was found that people who live on streets where there are more trees, and / or trees with larger canopies, report better health perceptions (after accounting for demographic factors: age, income, etc) – for every 400 square centimetre increase in ‘treed area’ per one metre squared of neighbourhood area, it was shown that health perceptions would rise by around 1% (around an extra 10 trees per block, of which there are 25 blocks per district area). In fact, this incremental increase in health perception as a result of there being more trees, or larger trees, was on par with an income increase of $10,200 per year per household, or an individual being 7 years younger. However, the authors note that trees alone do not majorly influence health perception (they only do so by a few percent) – there are many others factors that will impact upon an individual’s view of themselves.
Where trees are present within streets, the authors found that fewer cardio-metabolic issues were present in individuals. For every 11 trees within a city block, the occurrence of such health issues fell by around 0.5%, and is as impactful as an average increase of $20,200 in household income per year, or being 1.4 years younger. Again, tree presence isn’t the sole driver behind better cardio-metabolic health, though certainly plays a role (albeit, perhaps a rather small one – a few percent).
The authors found no statistical significance of tree presence upon the mental health of individuals, so will be undertaking further investigations to further analyse the relationship.
In light of the survey data, the authors conclude that an increase in tree presence along urban streets will have a beneficial impact upon an individual’s health perception, and to their cardio-metabolic health. With regards to their comparisons to annual income increases, the authors make an interesting point in that a household earning $10,200 more than another household, whilst on paper would be ‘better off’ in terms of health perception, may not actually be so – if the other family has over 10 additional trees in their block compared to the block where the higher income household is, the lower-income household may perceive themselves as healthier than the higher income household.
Therefore, as Toronto’s street tree density is on average between 0.2%-20.5% (including parks, it is around 28%), if tree planting rates increase (by as little as 10 more per block) – and canopy cover subsequently increases – then the health of residents will improve. However, the authors do note that Canada has a nationalised healthcare system, and therefore other countries where no such healthcare programme exists then the average income of a household may hold more weighting. This means that an increase in 10 trees per block in another country may equate to less of an increase in comparison to household income increase – 10 more trees may only equate to a $4,000 increase in household income, for example.
Curiously, the improved health of residents did not rank so significantly for trees within green spaces. This means, so the authors hypothesise, that it is the trees that are situated directly within the locality of a household (and within view) that will have the most beneficial impact on health, though the authors recognise that the other benefits of the street trees (such as reducing air pollution) will play a role. However, parks are still beneficial – that is not being disputed. The results simply underline the necessity for street trees – we cannot rely on parks exclusively to bolster the health of a populace.
It is also suggested that once tree density becomes significant (perhaps once over 20%) that the health benefits of trees becomes less significant (though are still evident). Additionally, an area with many evergreen trees does not mean residents who may view them have a better perception of their health – a great variety of trees, both deciduous and coniferous, are required to improve health perceptions of individuals impacted by their presence. However, residents living within areas occupied by many evergreen trees do report a better cardio-metabolic status.
Having recently shared a study that looked at the urban forest and bird species diversity, I thought we could use the momentum from that article and build upon it by looking at bats and the urban forest. The bird species diversity article highlighted the criticality of good landscape connectivity within urban environments (the opposite of habitat fragmentation), and the authors of this study suggest much the same from the very beginning – alongside fragmentation (usually coupled with urban sprawl / urbanisation) comes a decline in species diversity within urban areas, and it can be anticipated that bats are no exception to this.
The authors undertook this study in Vitoria, a city in the southeastern part of Brazil, with an intent of assessing whether wooded streets were used by bats (this would allow the authors to conclude whether urban street trees are beneficial in terms of connectivity for bats). Vitoria, home to 1.8 million people, expanded significantly during the 1940s and onwards, following industrial advancements. Such expansion lead to the destruction of the surrounding environment (including the Atlantic Forest) and its ecosystems, and the increased pollution levels have further taxed remaining vestiges. However, the city is still marked as a site important for biodiversity conservation, likely because of its eight municipal parks acting as habitat for a great variety of wildlife to the now (locally) fragmented Atlantic Forest.
This study chose to look at three of those eight parks for the presence of bats: (1) Pedra da Cebola Municipal Park, with 100,005 square metres of land that once acted as a transition between coastal shrubland at the Atlantic Forest; (2) Horto de Maruipe Municipal Park, with 60,000 square metres of land and covered by native Atlantic Forest vegetation (though with many introduced species of wildlife), and; (3) Fazendinha Municipal Park, with 22,653 square metres that – like Pedra da Cebola Municipal Park – was a transition zone between the coast and the Atlantic Forest. Three wooded streets, and three non-wooded streets, were also surveyed for bat presence. By surveying the parks and the streets, comparisons could be drawn between the two, and there would be scope to determine whether bats remain isolated to the parks. Sampling for the bats (with the use of mist nets) took place over the course of a year, with visits taking place for three days each month.
In total, 172 individuals were captured a total of 174 times. Most were found within the municipal parks, followed by the wooded streets, and then the non-wooded streets. However, the vast majority were only found within the urban parks (both in terms of species diversity and species abundance), with wooded and non-wooded streets not displaying a marked difference between one another. The authors do note that limited samplings perhaps lead to this, and suggest that more sampling visits to all areas would potentially show more individuals of more species using all three environments (only 10 species were recorded, whilst the region has 36 bat species – the authors do suggest that Vitoria may not harbour all species, however). The table below breaks down species presence by environment.
In light of their research, the authors in fact suggest that wooded streets are not particularly important for bat species, though they do recognise that increasing sampling visits and having sampling methods utilise ultrasonic devices may have improved the results obtained. For example, Noctilo sp. bats were observed, though not recorded with the netting method.
The fact that Artibeus lituratus was the most frequently observed one across all three environments, the authors allege, is due to its opportunistic behaviour. It has previously been recorded using urban environments, and may have a tolerance to urbanisation as a result (unlike other species). However, other research papers have suggested more species of bat (some found in this study) do use urban areas for feeding, particularly where lights attract insects (insectivorous bat species will benefit most for this).
So what does this study mean? As sampling was admittedly quite limited, perhaps it’s not a foregone conclusion that bats don’t use street trees as vehicles to move between larger park areas (or for other reasons), though it does suggest that maybe the urban forest is not structurally supportive of many bat species. Could more be done in the planning stages of development, or even following development, to attract more bats to the urban streets of Vitoria? The authors suggest that using native trees in place of exotic ones may be a good starting point.
I followed the growth of two Ganoderma resinaceum sporophores at the butt of a mature roadside Quercus robur during the summer just gone, to ascertain rate of growth and the way in which the fungus developed morphologically. The below photos detail its growth from 12th August 2015 to 2nd November 2015.
Piptoporus betulinus (birch polypore) is almost exclusively confined to Betula spp., though it has been observed rarely on Fagus sylvatica. Its spores will gain entry via stem injury, then attack the tree’s sapwood and heartwood once the host is under stressed conditions. There is therefore a period of latency within the colonisation strategy of Piptoporus betulinus. As with most parasitic fungi, it may also act saprophytically.
The fungus induces a brown rot in principal branches and the main stem, as its mycelium secrets enzymes that digest the wood substrate, which soon causes wood to discolour to a reddish brown (in turn followed by the characteristic cubical rot of brown rotting fungi).
Because the wood progressively become more brittle, it will ultimately fracture due to such a weakened condition. By the time fruiting bodies appear it is usually too late for any remedial action however, given decay is rapid and loss of mass is therefore swift across the entire cross-section, in addition to the fact that fungal presence establishes and becomes extensive on an already weakened host. Decline can therefore be readily observed in infected hosts, though whether cause is fungal decay or general poor health remains uncertain.
Given weakened trees act as hosts, in addition to the swift decay caused by Piptoporus betulinus, treatment is likely to be ineffective and impractical. Removal is typically the preferred option, though depending upon the context (no significant target zone), retention for ecological reasons and subsequent routine inspections to determine decay extent are necessary (if even that, as colonised birch within woodlands, where the fungus is most common, may likely just be left standing). Limiting pruning wound size and ensuring potential hosts are not exposed to undesirable and adverse site conditions may aid with prevention, though as colonisation may be followed by a latent period, ascertaining when a potential host becomes infected is difficult. Research has also identified that cadmium application can reduce or entirely halt mycelium growth, though as cadmium disturbs tree processes, application to an already stressed host is likely to only aggravate the situation.