Planned lifecycle of urban trees?

[agg221]

Hi All,

 

I am interested in people's thoughts on the planned lifecycle of urban trees. I am thinking particularly of street settings, as opposed to semi-natural settings such as parks.

 

The growth and development of trees in a natural setting could be considered in three stages - growth, maturity and decay. In a tree grown without intervention, it is the end point of the latter which is usually taken as the lifespan. For trees in settings with more intervention, I would anticipate that they would pretty much never reach the natural end through decay, so the effective lifespan is shortened.

 

I am interested in views as to what the expectations of lifespan would therefore be. I suppose the simple ones are short-lived trees such as flowering cherries, which will probably not ever outgrow a space. However, I can see the potential conflict in, say, removing a row of street limes because their trunk diameter and root structure is now blocking the pavement, even though their crowns are well maintained in the available space. I have seen plane trees of 2m across in parkland, where in a street setting they would block the road, let alone the pavement.

 

Any thoughts on how these expectations are managed?

 

I am particularly interested because of the current position with elms. There are now elm strains and hybrids which have proved highly resistant in controlled testing and are now fairly widely planted in The Netherlands, but of course nobody knows how resistant they will be in the field, or how they will perform over their lifespan. The most controlled approach would be to plant out and monitor in settings which do not matter, but 300yrs of monitoring is a bit much! Hence the interest in thoughts as to what would be satisfactory for a realistic specification?

 

Cheers

 

Alec

[Dean O]

I would say that most towns - mainly their pedestrian areas, are redeveloped every 15 years or so, that along with the changes many of our roads are going to see in the future is going to influence the life expectancy of any tree planted in the urban environment... (along side the other pressures).

 

I suppose a long lived tree could be chosen as long as it is accepted that it may be removed before maturity - for example a fastigiated oak chosen for its architectural shape - removed during a revamp as it no longer suits the redesigned environment

 

rather than selecting a short lived species that may feel the pressures of an urban environment before its ultimate life span and require removal or management.

 

I cant see large trees such as elm, lime, plane being selected for many urban/suburban tree scapes (unless it is accepted that they may be removed prematurely) - such as street avenues unless roads and pavements can be torn up, services sorted out (rather than running all over the place like spilt spaghetti) and a cellular type system installed (such as arbor-raft?)

 

Certainly its common in these parts that when something large such as a lime/plane is removed, it is simply not replaced as its said that they don't have the underground room due to services.

 

 

I think that the shift from large long lived trees to small short lived trees reflects that we now accept that the urban environment is likely to change at a much quicker speed than was expected

[agg221]

I would say that most towns - mainly their pedestrian areas, are redeveloped every 15 years or so, that along with the changes many of our roads are going to see in the future is going to influence the life expectancy of any tree planted in the urban environment... (along side the other pressures).

 

I think that the shift from large long lived trees to small short lived trees reflects that we now accept that the urban environment is likely to change at a much quicker speed than was expected

 

Thanks for that, very useful to know. 15yrs really is quite short - I presume planting heavy standards at a typical age of around 10yrs? If so that is 25yrs total life on the tree.

 

That is very interesting with regard to elms as it indicates what would be a suitable planting trial.

 

Cheers

 

Alec

[Dean O]

:thumbup:should say - just my thoughts really - based on anecdote rather than cold hard reference material

[Jon Heuch]

Alec

 

You pose some interesting questions which are really fundamental to how trees are managed in urban areas. There is firstly the technical/biological aspect of how trees grow and secondly there is the aspect of how this is communicated to the public, councillors and other professions.

 

In terms of technical aspects you might want to consider the difference between life span (looking towards the maximum) and life expectancy (an awkward parameter reflecting the average life span of a population).

 

In terms of managing expectations I am led to believe in the Netherlands it is possible to grow a cedar tree in your front possibly small garden and cut it down when it gets too big - a very practical approach and apparently not controversial; here, we seem to have an obsession with growing things too long and too big, afraid of change so we end up with numerous disputes which may lead to disatisfaction and possibly great expense. It's a great opportunity for education, planning, discussion etc etc if you have the time and inclination but my experience from tree felling in both forestry and arboriculture in landscape situations is that people don't like change; they get used to agricultural fields being ploughed and harvested, hedges being pruned but trees being felled seems a bit much.....although once done you can get joys of glee when vistas open up and dark corners of parks are removed.

[fagus]

Certainly in new designs, including industrial sites, comments have to made at the planning and highway stage to avoid narrow roadside verges; but get those green spaces aggregated into large public open spaces away from the highway.

These large opens spaces can take larger forest type trees which make a decent landscape impact; and leave the Cherries and small ornamentals for the house owners to plant in their gardens.

Roadside verges are also zoned to put service pipes /cables in so tree planting in narrow verges is not possible leading to a poor urban a streetscape.