(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

14/02/16. Fact #150.

 

Most towns and cities will have at least one park, which can be used by visitors as a place to relax (via the disassociation with day-to-day life, for example). These parks may – or may not – be heavily planted with trees, and retain vegetation remnants from past land use. It is understood that the presence of such parks is beneficial for visitors, and research has shown that urban parks are beneficial in terms of improving health and well-being for visitors (or those that overlook a park). Not only this, but parks that are well-vegetated (and retain remnant vegetation) are usually far better at providing habitat for species of bird, bat, and otherwise, when compared to vegetated (or non-vegetated) streets surrounding the park. This increased biodiversity presence actually allows park visitors to experience nature to a greater degree than in other urban landscapes, which may be particularly important for those individuals who desire a closer affinity with nature. Therefore, this study sought to determine whether the total tree and remnant vegetation cover influenced the amount of park visitors, and whether social factors influence upon a person’s decision to visit a park with greater vegetation cover, in Brisbane, Australia.

 

The data obtained through this study was collected via an online survey, of which 1,479 individuals within the city responded. Participants were selected on the basis that they had to have been between the ages of 18-70, with an equal distribution of individuals either side of 40. In addition, male and female participants had to be largely similar, and the annual income of each individual surveyed had to reflect Brisbane’s total population. Furthermore, an equal number of individuals had to complete the survey from four different areas of the city, which were reflective of the city’s range in tree canopy cover (so an equal number from poorly-treed areas, and from areas where canopy cover was high).

 

A well-vegetated park in Kangaroo Point, Brisbane. Source: Bugbog.

 

From those surveyed, many questions were asked. In addition to the personal data received from each respondent, they were all asked whether they visit parks (and if so, which ones). Those who answered that they did not visit parks were excluded from the resultant analyses. All respondents were also asked multiple questions to determine how they interacted with nature, in order to ascertain whether those with a better ‘relationship’ with nature opted to visit parks with greater tree.

 

In terms of tree and remnant vegetation cover, overhead maps were used to analyse individual parks. Only those relics over 0.5ha in size were recorded, as they are usually more likely to be home to a greater level of biodiversity. Lastly, Brisbane’s parks were separated into three categoies: local, district, and metropolitan. Local parks tend to have the smallest amount of associated infrastructure to accomodate for visitors, whilst metropolitan parks have a high level of associated infastructure. Not only this, but local parks have a much lower expected ‘catchment zone’ than metropolitan parks, with the latter perhaps attracting visitors from many suburbs and the former only a few streets. More obviously, local parks (1.3ha) are far smaller than district (5.9ha) and metropolitan (20.8ha) parks.

 

Looking at the results obtained through the survey, it is evident that more people visited parks with at least a moderate level of tree cover (see figure below). However, there was found to be no significant difference across tree cover extents. With regards to remnant vegetation cover, it can be seen that most visits were to parks with under 10% remnant cover, though this may be due to the fact that many parks lack extensive remnant cover.

 

Results of what parks the respondents of the survey visited. The black line shows the proportion of respondents who visited each park category.

 

Interestingly, the authors note that 79% of respondents visit parks further afield than the closest one to their address. Those most likley to travel further distances were the individuals who ranked higher in their relationship with nature, as they sought to visit the parks with greater tree and remnant vegetation cover (see below figure). Conversely, individuals living in affluent areas of the city were less likely to visit parks with a higher tree cover. With regards to gender, females were slightly more likely to travel further distances to a park with more tree cover, though there was no significant difference between the genders. On the flip side, males were more likely to travel greater distances to visit parks with higher remnant vegetation cover. Age and income didn’t generally reflect what type of park a respondent would use.

 

Comparing how ‘related’ a respondent was with nature against the type of park they opted to frequent.

 

The larger parks were also home to more trees, and thus greater canopy cover. This may, in part, explain why people who were more connected with nature travelled greater distances to parks with greater tree cover, as local parks were simply less desirable for them.

 

However, by-and-large, visitors chose to frequent parks with only moderate tree cover. The authors remark at this as a bit of a paradox, because parks with a greater tree and remnant vegetation cover are usually more beneficial for human well-being and health, though they are not necessarily the preferred choice. This may be, the authors allege, because ‘western’ cultures tend to prefer open savannah (pastures), in place of heavily-vegetated ones, and because an individual’s perception of safety decreases as canopy cover increases (ironically, research suggests somewhat of the opposite). Similarly, biodiversity will benefit from a greater tree and vegetation cover. Despite this, if parks are to be managed and designed in a way that reflects the desire of Brisbane’s residents, there may be a need to reduce vegetation cover at the cost of safeguarding biodiversity.

 

The fact that only those who seek a higher affinity with nature will travel longer distances to visit parks is also telling. It suggests that only a particular portion of Brisbane’s population actually gains the full benefits associated with parks with greater tree and remnant vegetation cover. What impact may this be having on those who do not visit such parks?

 

One of Brisbane’s botanic gardens. Source: Wikimedia Commons.

 

Perhaps there is a need to educate people about the benefits of such ‘natural’ parks. However, if these parks then have a higher number of visitors, will the added disturbance impact upon the biodiversity within? Because such ‘natural’ parks are better for biodiversity, encouraging more visitors may have a negative effect, and not only on biodiversity but maybe also those who go to such parks to feel ‘at one’ with nature. Maybe we can view parks with reduced tree cover as sufficient; if not to satiate the need of many people to visit parks, then to allow the more ‘natural’ parks to continue to provide for those who like them and the biodiversity within.

 

Source: Shanahan, D., Lin, B., Gaston, K., Bush, R, & Fuller, R. (2015) What is the role of trees and remnant vegetation in attracting people to urban parks?. Landscape Ecology. 30 (1). p153-165.

[Kveldssanger]

15/02/16. Fact #151.

 

Mature and veteran trees (often pollarded) are very much important, in terms of the ecological value they provide. An array of organisms utilise such trees, ranging from bats to birds, and from beetles to moths. However, when these trees are found within amenity parklands, the presence of visitors means they will be managed both for their safety and for their amenity value. Therefore, deadwood may be removed, and entire specimens may be felled because of the risk associated with their retention. These actions have adverse impacts upon constituent species, with saproxylic beetles potentially suffering quite notably. In spite of this, little research has been completed on old parkland trees and the saproxylic beetle species they support.

 

In addition, because ‘open’ old trees are declining in abundance, both because of their removal and due to the reversion of some old pastures and parklands to higher woodland (mainly due to a reduction in grazing, though woodlands may also be created), the viable habitat for many beetles is being lost. Old and open trees may thus be found commonly only in large parks that are popular attractions, or within private estates where maintenance costs are less of a concern (and there is a very low risk of a failing tree causing harm to a person). Of course, active wood pastures also contain many old trees, and some of these are (or were) deer parks.

 

In this study, undertaken within a 150km radius of Stockholm, Sweden (see map below), the author looks solely at limes (Tilia spp.), which are commonly found scattered within parks (dominated by oaks) as mature or veteran specimens – often, but not always, as pollards (up until around 1900-1950, when such pollarding lapsed completely). In the natural stands, Tilia cordata is most common, though in parks the prevalent species of lime is Tilia x europaea. Across the sites surveyed, of which eight were designated ‘open’, eleven ‘regrown’, and eight ‘park’, four limes (at each location) that had the potential (through the presence of hollows) to act as a host to beetles were surveyed. Accompanied by the sampling of beetle species (through the use of window traps, active from May through to August / September in the survey year), data relating to the size (circumference) of the limes, the total number of hollow limes on the site, and also the location of the trees was captured.

 

The author thus poses two questions that are to be answered, and these are: (1) will park trees have as much beetle diversity as natural stands?, and; (2) is there variation in natural stands, in relation to whether the site is grazed (open) or regenerating (regrown)?

 

For more detailed descriptions of each site, please see Table 6 in the report (linked at the bottom).

 

At a slight tangent before moving on to the results, typically we may associate saproxylic beetles with species such as oak (Quercus spp.), though it is remarked that beetles won’t always have a host preference in terms of the tree species, but in terms of the qualities of the tree itself (hollows, cavities, snags, dead branches, and so on). Granted, we can observe broadleaved obligates, coniferous obligates, and generalists.

 

Results

 

Following on from the trapping period, 14,460 individuals of 323 different beetle species were found. Around 10% of the total number of individuals found were red-listed species, though their presence accounted for 15% of the total species observed. Most of the species found were associated with the wood and bark of their host, and very few were associated with sap runs. The below table outlines such results.

 

Here we can see the breakdown of surveyed individuals and species, across all sites combined.

 

In terms of which sites had the greatest diversity of species, it was found that ‘open’ sites always ranked the highest (see the graphs below). However, the differences were not always significant. Furthermore, the more lime trees found on a site, the lower the diversity of beetle species found in wood and bark. The circumference of a lime tree was also not considered to be important in determining how abundant populations would be within the host, asides from for red-listed species found only in hollows.

 

A number of graphs that compare the different locations against the number of species present, according to specific data sets.

 

Quite importantly, there was generally no significant difference in species abundance and diversity between natural and park sites, and when park sites are compared to sites regenerating they are shown to support a greater diversity of beetle species in certain instances (such as for red-listed species found in hollows). The fact that park limes were found to support a lesser array of beetle species for wood and bark species (for those not red-listed), the author remarks, is because many of the trees in the parks are managed (and thus, any deadwood may be removed).

 

Additionally, whilst the composition of species between park and natural sites was found to be significantly different, many species were found using both parks and natural sites (only sixteen species displayed exclusive preference to parks or natural stands). This means that a park has the potential to host a diversity of saproxylic beetle species similar to that of a natural site. Many species were also found to prefer more sun-exposed conditions, and the author notes that where a park tree may be lacking in deadwood a sun-exposed setting may compensate for the loss of direct habitat associated with deadwood presence. This may perhaps explain why more red-listed species were found in parks, when compared to regrown sites – they require more ‘ideal’ hosts, compared to generalist species. Furthermore, southern sites were found to possess more beetle species, and this is considered to be due to the more favourable climatic conditions (generally, they are warmer).

 

As touched upon earlier, trunk circumference was not found to be a significant factor in determining species diversity. This conflicts with many previous studies, though the fact that most of the limes surveyed were classed as ‘ancient’ may explain this lack in significance – they were already very large in circumference. If limes of a ‘younger’ age (perhaps ‘only’ veterans) were surveyed, trunk circumference may have been significant (or at least more influential).

 

In light of all of the above, we can observe that parks may very well be important for saproxylic beetles – at times, more so than natural stands where a woodland is regenerating around old individuals. This means that the suppression of regrowth may be beneficial for saproxylic beetles, though at the same time there must be an awareness of needing to recruit new veteran and ancient trees. All trees have a point at which they die, and by simply retaining existing old trees and not identifying and safeguarding future ones, beetle species will decline and disappear when the current population of old trees drops or ceases to be.

 

Grazing may be a good means of reducing seedling recruitment surrounding old pollards. Source: Central and East Lakes Rangers.

 

It may also be wise to retain deadwood removed from park trees, either at the base of the tree or in a large pile somewhere else on the site. This may be crucial if beetles exist within the wood structure itself, as its retention allows for the larvae to complete their life cycle by emerging as adults from the wood and (hopefully) reproducing. Not only this, but active management of existing trees may also be beneficial. Many old pollards may be considered highly hazardous and at risk of collapsing, and as pollarding will slow down the rate of growth, viable habitats (such as hollows) can be retained for longer periods in more suitable conditions if the trees do undergo new cycles of pollarding (or crown reduction). If done properly, this may also enable for new trees to more effectively succeed (and eventually replace) the existing old tree population.

 

Most importantly, old park trees should not be felled unless absolutely necessary. Old trees are crucial in terms of the saproxylic species they support (of which some are red-listed), and park managers should therefore incorporate such ecological conservation measures into the management plan for the site as a whole.

 

Source: Jonsell, M. (2012) Old park trees as habitat for saproxylic beetle species. Biodiversity and Conservation. 21 (3). p619-642.

Edited February 15, 2016 by Kveldssanger

[diervek]

I've been meaning to read this thread in its entirety.

When I have a break from my course over Easter , I'm setting aside a day or two to have a proper looksee.

 

Great stuff dude.

[Kveldssanger]

Sweet. Let me know what you think.

 

Doing the lvl 4 / 6?

[diervek]

Neither, lvl 2... 😳

Planning on 4 / 6 in 2017 I think

[Kveldssanger]

Good luck and enjoy.

[Kveldssanger]

16/02/16. Fact #152.

 

Whilst deaths associated with tree failures do happen, they are generally very rare. In the UK, for example, the HSE reported that the chance of dying because of a falling tree (or tree part) was 1 in 10,000,000 when excluding high wind events (you can access the report here – see page 23). In the US, because of more extreme weather events, mortality rates may be slightly different, and the author of this study seeks to invesitgate exactly how many deaths occurred between 1995-2007, and the event that caused the tree to fail.

 

Before delving into the data however, the author notes that tree species vary in their tolerance to wind gusts. Wood properties and structural morphologies will impact upon durability, and by-and-large (for uprooting and stem snapping, though not branch failure) hardwoods will fare ever so slightly better in wind gusts than softwoods (though all tree species can fail if they are subjected to ten minute gusts of over 67mph). However, the condition of the tree (health), its age, size, and setting (how exposed it is) will also impact upon how likely it is to fail under wind loading.

 

Back on track, data was trawled from multiple sources (from the USA) to identify all wind events (extratropical cyclones, thunderstorms, tornadoes, tropical cyclones, though also ice and snow accumulations) where there was at least one death. All of the events were then inspected for deaths caused by a tree falling, and all such deaths were recorded. In the information obtained, multiple aspects relating to the deaths were collected. For example, victim age and gender were noted, as was the type of event that caused the death. In addition, the location of the death was noted, including what the victim was in at the time (house, vehicle, outside).

 

In total, there were 407 tree-related deaths between 1995-2007 (an average of 31 per year) across 41 states. New York had the highest death rate at 30, then Washington at 29 (see the table near the end for a greater breakdown). 62% of victims were male, and the average age was 44. In terms of where the victim was at the time of the tree indicdent, 18% were within their home (mobile or ‘static’), 38% outdoors, and 44% in a vehicle. Below, we look at deaths associated with fallen trees only during different weather events, though the below table and map outline all fallen tree-related deaths and their locations very well.

 

A breakdown of the total number of deaths between 1995-2007.

 

A localtion showing all of the locations where trees caused a death during wind events. The numbers down the side appear to relate to total deaths at each location.

 

Thunderstorms

 

53% (165) of all deaths were during thunderstorms, and 96% of these deaths in the eastern half of the USA were due to fallen trees (because the eastern half of the USA suffers more thunderstorms, and has a higher population density and number of trees). 78% of deaths occurred between May and August (when most storms occur). Most deaths (87%) occurred when the victim was not within their home.

Nonconvective winds (extratropical cyclones, gap winds, downslope winds)

 

A total of 143 (46%) deaths were caused by fallen trees during such winds. 88% of all deaths occurred outside of the home, with 50% being when the victim was in a vehicle. October to April was when 88% of deaths occurred, as this is the time when such extratropical cyclones are most potent.

 

Tropical cyclones

 

15 tropical cyclones caused 57 deaths, though not including deaths from Hurricana Katrina in Louisiana and Mississippi. Deaths were observed at similar rates across all victim locations, be it in the home, outside, or in a vehicle, and all deaths occurred within 200 miles of the coastline. September was when 58% of all deaths were recorded, and the range was from July through to October. The table below breaks down the deaths by each cyclone.

 

Deaths associated with tropical cyclones between 1995-2007.

 

Tornadoes

 

Fallen trees as a result of a tornado caused 28 deaths, accounting for only 4% of all fallen tree-related deaths. 42% of all victims were killed in their own home, which was higher than 32% in a vehicle and 25% outdoors (though not being in a home still leaves an individual with a higher chance of dying, during a tornado event). Deaths as a result of tornadoes occurred all year round, though 32% were in either April or November. Wind speeds of of 70-90mph (or above) are most likely to cause death, during a tornado event.

 

An uprooted tree that, during a tornado event, fell onto a house. Source: NBC News.

 

Snow and ice

 

Ice accumulations were the cause of 10 of the 14 deaths within this category, and most deaths happened whilst victims were outdoors. Snow accumulations did however cause death, too. Most deaths were concentrated in the north east and Washington, which correlates with expected weather patterns for the USA.

 

Final remarks

 

In light of all of the above data, it is evident that thunderstorms and nonconvective winds will cause most deaths, of which most will be outside of the home. The higher likelihood of being killed within a vehicle is interesting, as it suggests that it may very well be street trees that cause deaths. In a way, this is hardly surprising, as trees within a woodland are likely to not have a target zone, though it does highlight the fact that consistently passing within the target zone of trees during loading events increases an individual’s chance of death at the hands of a falling tree. Staying within the home may very well be the safest thing to do. Or, as the author suggests, get in the car and drive into the middle of an open field, and wait there (unless it’s a tornado event, where one must either seek refuge in a large building or drive to beyond the reach of the tornado).

 

Despite this, the chance of dying is still only 1.45 in 1,000,000 (on average – some states have higher death rates, as shown in the below table). Of course, in states where there is a higher population density, the risk of death may likely be higher than the national average.

 

How the total number of deaths were split amongst the ‘top’ (meant in the worst way possible!) 15 states, of the 41 where deaths occurred.

 

We should also remember that this data doesn’t take into account injuries associated with fallen trees, or even indirect deaths caused by trees blocking roads (stopping emergency vehicles), falling on power lines (cutting out electrical power), and so on. Furthermore, the window of investigation spanned only 13 years, which isn’t much in the grand scheme of things. Trees with structural defects may also be more likely to fail during loading conditions, and therefore street trees, or those where there is a target zone beneath, should be inspected more regularly than those where there is not. Granted, a touch of realism is needed, and it must be recognised (again) that the death rate as a result of a fallen tree is incredibly low to negligible.

 

Source: Schmidlin, T. (2009) Human fatalities from wind-related tree failures in the United States, 1995–2007. Natural Hazards. 50 (1). p13-25.

[Kveldssanger]

18/02/16. Fact #153.

 

In spite of Ted Green remarking that he is “stating the obvious” in this chapter of his, it’s nonetheless good to be reminded of the benefits of open-grown trees and how they compare to closed-canopy trees of a similar age. Despite certain similarities, there really are many differences in today’s age, and we’ll explore some of them here. Before that however, it is interesting to note that the utilisation of open-grown trees during ‘ancient’ times was not uncommon. Orchard trees, for example, demonstrate man’s understanding of open-grown trees producing a much greater abundance of fruit than closed canopy trees.

 

 

Open-grown individuals

 

Morphologically, a tree that has grown without any marked competition will be vastly different to a tree that has grown amongst its competitive peers. Due to a reduced competition for light, and also because of the greater effect of wind upon its structure, an open-grown tree will be shorter, have a fatter trunk, a wider crown (perhaps with vastly-spreading and near-horizontal limbs), and a more significant anchorage root system. This ensures it is well adjuested to its setting (principally in allowing for optimal photosynthesis whilst retaining structural stability). Amazingly, investigations into the rooting systems of open-grown veteran trees by the Ancient Tree Forum revealed roots with a 2.5cm diameter at a distance of 50m from the base of the tree.

 

A mature open-grown oak pollard, complete with an absurdly broad crown with many near-horizontal limbs. Certainly an effective means of balancing photosynthetic needs with stability!

 

On a biodiversity level, we must also recognise that roots are host to a massive array of mycorrhizal associations. If an open-grown tree has a huge rooting system, associations with the tree (directly) will be potentially vast, though perhaps isolated somewhat (assuming no other trees are about). Shed roots may also support organisms of the decmposition subsystem (fungi, in particular).

 

Looking at the above-ground structure of an open-grown tree, we can also observe associations with a great number of species. For instance, the large limbs and vast canopy area of an open-grown tree will provide habitat for many insect species, and entire trophic systems surrounding their presence (from parasitic wasps to mites, and from birds to fungi and bacteria). Similarly, the very large and broad main stem will have a vast quantity of substrate (wood, cavities, hollows, and so on) available for saproxylic species and nesting birds, which will typically revel in the warmer conditions. The herbaceous plant species surrounding the tree will also provide support for insects, including saproxylic beetles.

 

Closed-canopy individuals

 

Because trees growing within a woodland or forest have to compete for all types of resource (light, water, nutrients, rooting space, branching space), their form will be vastly divorced from the open-grown tree. Investing most of its resources into growing towards the light, stems will be thin, lack taper, and rooting systems will be largely insufficient to support the tree structurally (which is evident when woodland edge trees fall following localised tree felling). However, root grafts (between a single species) and mycorrhizal relationships between individuals (across different species) may ensure that edge trees, which have larger canopies, support trees (via grafted roots and mycorrhizae) in more sheltered but still very local settings. By that same token, older trees may support younger individuals (particularly of the same species).

 

In time, deadwood within woodland stands may build up to significant quantities. As a stand ages, there is a progressive ‘self-thinning’ of the stand, eventually leading to only some (usually mature and quite large) trees remaining. This accumulation of deadwood ensures that the decomposition subsystem can mineralise nutrients, allowing these remaining trees to utilise these resources once again. The same can also be said for leaf litter, which is of far greater quantity within a closed stand (and retained, courtesy of a more sheltered micro-climate). For these reasons, and compiled both with the fact trees will ‘trade’ resources in a sort of peer-to-peer economy and their sheltered setting, rooting systems may be less expansive (compared to open-grown trees). Buttressing may also be lacking, unlike in open-grown individuals.

 

A stand of beech (Fagus sylvatica) last pollarded before 1830. We can see how the crowns of each individual are much more upright and narrow, and the stems have less taper than they would in an open setting. There is however a great abundance of leaf litter on the floor, though an unfortunate lack of coarse woody debris (excluding standing deadwood).

 

The decomposition associated with woodland stands will also be far quicker, given the cooler and moister conditions. As fungi tend to operate most effectively in such settings, the mineralisation of locked-away nutrients will be a much swifter process, when compared to the decomposition of deadwood on and around an open-grown tree. For instance, a large stem of a fallen tree within a woodland may decay in a few deacdes, whilst a fallen and significantly-sized limb of an open grown tree may take up to a century to fully decay.

 

Clearly it’s not possible to compare and contrast trees in different setting in any short space of time, though I felt that this brief entry by Ted Green in the below book was a rewarding read, if not to simply cement existing knowledge.

 

Source: Green, T. (2007) Stating the obvious: the biodiversity of an open-grown tree – from acorn to ancient. In Rotherham, I. (ed.) The History, Ecology, and Archaeology of Medieval Parks and Parklands. UK: Wildtrack Publishing.

[Kveldssanger]

19/02/16. Fact #154.

 

We hear a lot about how residents perceive trees in the research ‘community’, though less frequently do we read reports that assess the views held by industry professionals. This is strange because arborists, planners, landscape architects, and other professionals have a potentally massive impact upon the manner in which individual trees and landscapes containing trees are managed. Recognising the views held by such individuals is therefore very important, and could even facilitate introspection by those within the industry. Furthermore, are views even uniform across the industry, or do they vary across professions and spatial areas? Thankfully, such questions can begin to be answered as a result of this study, by assessing Australian industry professionals (principally arborists) and their perceptions of trees and the conflicts associated with their presence.

 

For the study, the authors interviewed a total of 52 professionals through advertising within the industry (and then via word of mouth across organisations), in the cities of Adelaide, Brisbane, Hobart, Melbourne, Sydney, and Townsville. These cities were selected as they cover a wide geographical area, and are home to large yet varied tree populations in differing climatic regions of the country. The vast majority who responded and were subsequently interviewed identified themselves as arborists (arboriculturalists), though a few did respond by labelling themselves as landscape architects, horticulturalists, or environmental planners.

 

The interviews with the professionals had some sort of structure, though were ‘open’ enough to permit conversation away from a typical question and answer scenario. This, the authors recognised, allowed the interviewees to discuss matters they felt were important to them, and this had the benefit of ensuring interviews were fruitful in terms of the data collected. However, a general trend was present within the interviews, in the sense that details regarding how the professionals thought about and interacted with trees were obtained, as were thoughts on other ‘tree professions’, ‘non-tree professions’, legal frameworks, and residents. Alongside the interviews, a survey was sent out to residents across the same cities, of which 736 survey responses were obtained. This survey investigated how residents chose what trees to plant, and offered them to add any other comments they desired to their response (about anything tree-related, including industry professionals).

 

Once all interviews had been completed and surveys returned, they were analysed by the authors for trends. Before going on, it’s necessary to point out that the authors found five distinct ‘groups’ amongst the interview data, with public and private sector workers being very distinct from each other, though the city the individual was based within and their actual profession also were found to cause distinct difference in opinion in particular instances. Gender was not a driver behind varying opinions, nor was location (on the whole). Further results are detailed below.

 

 

How arborists view residents

 

Probably not surprisingly, a common trend amongst all interviewed professionals was their perception of residents hating trees (or some types of tree). However, the rationale behind such thoughts differed across the 52 individuals. Another general theme was that residents put too much weighting on the risks trees pose, thereby over-playing the ‘risk factor’.

 

Further themes amongst the data, though generally variable across the groups and held in particular abundance by arborists from Adelaide, Brisbane, and Hobart, was that older people viewed trees with less fondness, and that residents would readily scapegoat trees without evidence of the trees causing a problem. However, it was Melbourne arborists that felt trees were most actively removed because of the perception residents held about them causing fires (scapegoating). This may be as a result of the ‘Black Saturday’ fire some ten months prior, which scourged parts of Melbourne.

 

In this image, wildfire encroaches upon a residential property in Melbourne. Source: Wikimedia Commons.

 

Other opinions aired by over 20% of the 52 individuals (indicating a sort of ‘theme’) included things such as residents needed to be educated about trees, immigrants don’t like ornamental trees, people dislike trees because of the mess they make, people on low incomes don’t like trees, but that most people actually still love trees. However, opinions that were very much varied between professionals interviewed (and were, at times, contradictory) included whether the affluent demand tree care, whether conflicts arise between neighbouring land owners with regards to trees, and whether ‘tree Nazis‘ are annoying. Therefore, whilst trends amongst the responses are evident, there is still a wide pool of thought held by individuals within the industry.

 

 

How residents perceive professionals

 

Curiously, residents surveyed made very little mention of arborists, but instead saw the management of trees as something simply done by the council (as a whole) or by the planners (part of the council). Only one respondent, who was an arborist himself, referred to arborists being part of the management of publicly-owned trees.

 

It was also found that residents saw local councils as an enemy to trees, and particularly by the so-called ‘tree Nazis’. One individual, for example, lamented over the council’s removal of healthy trees along a street. Other individuals commented that councils plant the wrong trees in the wrong places and then refuse to remove ones in a supposedly ‘wrong’ place, failing to educate the public about trees, not planting a young tree near to one set to be removed and instead doing the re-planting afterwards, and making grotesque forms from trees following aggressive pruning management (all whilst refusing to allow protected trees on private land to suffer a similar fate).

 

Residents were also critical of urban planners, saying that they failed to ensure tree plantings were incorporated into new developments, and should see trees more as ornaments that complement the landscape in place of something much the opposite.

 

 

How professionals perceive trees

 

Planners and other professionals who held a more strategic position (in place of actually being an arborist) were found to hold more ‘abstract’ views of trees. For intance, they saw trees as helping to reduce energy costs (associated with cooling in the summer). Their stance was also much less emotional than other professionals, in the sense that they formed their views on trees from more analytical (niche?) thought processes. However, planners were found to not consider street trees as important for biodiversity as much as other industry professionals did, though did see trees in other urban settings as important. Perhaps their isolation from working ‘with’ trees has led to such a perspective, because it cannot be argued that there is an abundance of data highlighting how critical street trees are for biodiversity.

 

As more of a collective however (totalling to 40% of all interviewees), professionals considered a mix of native and exotic tree species to be important, citing that pragmatism is key in the selection and management of the urban forest. Interestingly, this also translates over into residential (privately-owned) trees (albeit likely for different reasons), where residents were found to not discriminate for or against either native or exotic tree species. A mix of natives and exotics is therefore present across the six cities, outside of the publicly-owned realm.

 

A line of large and mature eucalypts in Canberra, Australia. Note the womnderful shading beneath. The linked source has some more great photos. Source: Treelogic.

 

However, a diversity of thought was evident with regards to the risk management of trees. Around 33% of professionals considered risk to be appropriately measured and managed, whilst 40% saw both local governments and residents as exaggerating the risk a tree poses (that could be classed as ‘risk averse’). 10% of the interviewed professionals also considered that such risk management lead to the loss of large trees, in spite of the fact larger trees are usually held in higher regard by residents, whilst 40% (mostly professionals working for local government) saw managing old trees as highly important but nonetheless challenging.

 

As touched upon earlier, there was also a trend held by professionals (particularly if they were based near to where natural wildfire and storm events occurred) that trees are unfairly scapegoated. 75% of professionals in Melbourne saw the removal of trees following on from wildfire as abhorrent and as a “gross over-reaction” to the situation. Similarly, Queensland professionals thought residents unfairly blamed trees following on from storms, and the public must be educated more about the ‘true’ risk of trees.

 

A large beech tree that fell following high winds. Source: Cazort.

 

Quite intiguingly, many professionals also saw engineers as people who hated trees, and developers as people who try to “corrupt” arborists. Not only this, but professionals saw electricity organisations as doing a bad job of maintaining trees beneath lines (and focussing too intently on just keeping their service operating without hindrance). Such thoughts probably exist the world over, within the industry! However, private arborists (not employed by councils) were found to be in a difficult situation, because their income depended upon work by developers (in part), and even though they felt they were placed in positions they did not necessarily like, turning down work for moral reasons was not always feasible. One canny individual did however suggest that developers will tend to employ arborists who are lenient to the developers, thus making their operations easier by getting trees removed more readily. Whether such arborists have so much of a dilemma about removing otherwise probably healthy trees is open to debate.

 

 

…so what?

 

On the whole, it is evident that there is a vast opinion pool amongst professionals within the industry, though common themes are pervasive across individuals found in all six cities. The fact that many professionals consider the risks associated with trees to be over-played is important, as it highlights a need for residents and other laymen to be informed of the real risk trees pose (and even local councils). Whether this would actually impact upon their fears is open to question, though there is no doubt that they should at least be presented with such information. Such an action may in fact help to reduce the evident gap between professionals and residents with regards to their view of trees. Professionals, throughout the survey, were identified to view trees more positively. Such a stance can only be because of the greater level of knowledge possessed, as there is absolutely no argument relating to the great benefits (and importance) of trees, particularly in the ecological and environmental senses.

 

Furthermore, there is a need for planners to recognise that residents do not hold them in high regard. Communication between such professionals and the residents would therefore be a good idea, in an attempt to at least construct the beginnings of a more harmonious relationship between the two groups. However, perhaps there is also need for developers and electricity companies to quell their pursuits, and foster a healthier partnership with professionals (particularly arborists) who consider them to be abusing their (perhaps inherently advantageous, thanks to the law and the flow of money) position.

 

Of course, many more conclusions can be drawn, though I’d be here all night discussing this one if I didn’t stop somwhere!

 

Source: Kirkpatrick, J., Davison, A., & Harwood, A. (2013) How tree professionals perceive trees and conflicts about trees in Australia’s urban forest. Landscape and Urban Planning. 119 (1). p124-130.

[Kveldssanger]

21/01.16. Fact #155.

 

I have written a lot about trees in the urban environment, and I can certainly continue to write about them forever more, though when I stumbled upon the study I am to write about below I thought it would be interesting to touch upon vegetation beyond the realm of trees. Of course, the benefits trees provide, and the issues they create, are well understood, and there will always be a torrent of new research articles dealing with their presence in the urban setting. However, I am not aware of such an abundance of research for shrubs and other types of vegetation that may exist within urban environments. This is probably not all too surprising given trees are simply bigger and more noticable than other types of vegetation, though when we work with trees we also will generally work with shrubs, grasses, and so on. Combined, or even exclusively, such vegetation (and the form adopted – formal or ‘wilded’) will impact upon the lives of residents, and understanding exactly how is always going to be vital to their successful incorporation into an urban landscape. In this instance, the residents of two German cities (Berlin and Cologne) are the focus.

 

In Cologne, the authors asked passers-by (a total of 108 were questioned) on a main arterial road (see the below image) just outside of the inner portion of the city how they perceived roadside vegetation (with regards to what they valued in terms of the functions the vegetation provides), what types of roadside vegetation they knew about and preferred, amongst other related topics (including how they thought vegetation established within the urban environment). The passers-by were stopped and questioned over the course of three weekdays from the morning through to the evening, during summer. All answers were written down either by them, or by the authors. 56% of passers-by who answered the questions were below 30 years of age, and 58% were male.

 

This was the site used by the authors for their Cologne study. We can see vegetation occupying different ‘tiers’, with some higher canopy trees with smaller shrubs beneath (some appear to be coniferous, in the foreground).

 

The Berlin study was somewhat different, and whilst it also was conducted along a similar main arterial road on a summer day (which had wilded vegettion growing along the pathways, below the trees – see the image below), it asked different questions. Principally, the questionnaire provided to the passers-by was standardised, though some open-ended questions did feature. For example, the main bulk of the questionnaire was asking the individuals what type of vegetation cover they thought would work best on the arterial road they were walking down (no vegetation, maintained vegetation, wilded vegetation, or no preference). However, individuals could give reasons as to why they chose the answer they did, and were also asked what they thought about the current ‘wild’ appearance of the roadside vegetation.

 

This was the exact location of the Berlin survey. All passers-by who stopped to answer the questions thus, in response to the open-ended question asking for their thoughts on the street’s current view, formed their opinion from this vista.

 

For the Berlin study, 40% of respondents were beloe 30 years of age, and gender distribution was almost equal. 74% of the individuals lived either near to the street or in an inner city borough of Berlin, and 78% were familiar with the street to some degree.

 

 

Results

 

In Cologne, just over half (52%) of the respondents considered trees to be the main vegetation type that feature along roads. The remaining 48% therefore detailed shrubs, perennials, and grasses – some individuals were specific to the species, as well. Furthermore, a wide array of landscaping features were also identified by the respondents, with flower beds, tree pits, and planting tubs being but three examples. In terms of how the individuals thought the vegetation had become established, the vast majority (87%) considered artificial planting to be the cause (be it through public or private hands). Only 13% suggested that natural regeneration could have led to the street vistas of Cologne.

 

A great number of the surveyed individuals also valued roadside vegetation as important, and for a variety of reasons (see the below table). Responses ranged from their presence being good for amenity to being beneficial for improving air quality, though most answers related to the vegetaton’s amenity value. So positive were the answers that many had a desire to see a greater amount of roadside vegetation of all types, of which some answers pushed a greater number of ‘wilded’ scenes more akin to a rural and naturalised scene. The reason for this ‘wilded’ desire varied, though answers included for the benefit of insects such as bees, to simpy being more interesting to the eye and making the streets more “lively”.

 

This table compares how respondents valued different ecosystem services, across the two cities.

 

For respondents in Berlin, 48% considered the current ‘wild’ appearance of the street undesirable, and suggested it should be more formal in character (dubbed ‘urban devotees’). Conversely, 43% liked the vegetation as it was (dubbed ‘wilderness enthusiasts’). The remaining 8% did not mind, or were undecided. Therefore, there is certainly a similar mix of individuals who like ‘wilded’ streets and those who don’t. Unspurprisingly, it was the wilderness enthusiasts that most routinely saw the vegetation on the street as greatly improving the landscape’s character, because they considered the street to have a greater association with nature (a total of 40% of all respondents responded in such a manner). On the other hand, the ~30% of individuals who didn’t like the ‘wilded’ vegetation were more frequently from the urban devotee group (and this group cited the poor safety and amenity of the ‘wilded’ area as their reasons for such an opinion). The below table shows the disparity of opinion.

 

A breakdown of how urban devotees and wilderness enthusiasts valued the current ‘wilded’ streetside vegetation.

 

Across both sities, neither age or gender were significant in determining how an individual viewed vegetation cover.

 

 

Concluding remarks

 

From the results detailed, there is no question that there is a wide range of opinion regarding what vegetation types are most valued by individuals, and the form that these vegetation types adopt (formal or ‘wilded’). It is entirely evident that there will always be a significant minority of people who do not appreciate the vegetation cover an urban area possesses, and it is also evident that people will value vegetation presence for different reasons (though mostly, it is for the aesthetic benefit provided – even then, what is considered as aesthetic beauty differs from person to person). Despite this, more vegetation (in general) on streets was in demand.

 

It is nonetheless curious that a good portion of those surveyed valued ‘wild’ vegetation (particularly in Berlin, and likely because individuals were more routinely exposed to such vegetation cover), though perhaps still considered this ‘wilded’ character as originating from man’s intervention. Only a small selection of respondents understood that the vegetation on streets may also regenerate naturally. By a similar token, the fact that many respondents recognised that trees are not the only type of urabn vegetation cover that may grace street scenes is suggestive of a need to incorporate complex landscaping vistas into urban sites – simply having canopy cover is not ‘enough’, perhaps. At the same time however, the desire of many for safe and formal landscapes may mean that constituent vegetation is maintained to some degree. Perhaps there is scope to have both more formal and ‘wilded’ vegetation types, assuming a street can accomodate such diversity (this requires size and desire).

 

Source: Weber, F., Kowarik, I., & Säumel, I. (2014) A walk on the wild side: Perceptions of roadside vegetation beyond trees. Urban Forestry & Urban Greening. 13 (2). p205-212.