(Arboricultural-styled) 'Fact of the Day'

[JaySmith]

I think the standard of driving is getting worse, that coupled with the increase in road traffic only gives one outcome = more crashes.

 

I'm currently wading through one of the biomechanics assignments at the mo. Who are you doing your lvl4 with?

[Kveldssanger]

Absolutely. I am doing mine with TreeLife. Yourself?

[JaySmith]

Doing mine with The Training Tree at Painshill, all good so far. You must be at Harlow then?

[Kveldssanger]

I am indeed at Harlow. A lovely setting for the course.

 

Sticking with NTSG...

 

01/12/15. Fact #90.

 

When a tree within a park area is identified to be in a poor state, and the area beneath it is considered a target zone of at least some significance, then the first question asked is not "what works must be done to the tree?" but "can the target be moved?".

 

Assuming the target can be moved, NTSG provide an array of options that can be drawn from. These are:

 

- deter informal cark parking beneath the tree (also reduces root damage via compaction, in particular)

- re-locate facilities such as play equipment, benches, commemorative plaques, etc, out of the reach of the tree if it ever fell or shed limbs

- re-direct paths, if legally practicable

- design paths that can be mowed so that they run through long meadow grass, drawing foot traffic away from the target area

- have assembly points and other structures built for 'congregations' out of the target zone

 

Altneratively, access can be full-out deterred by:

 

- planting thorny scrub

- creating log piles around the tree

- allow grass to grow long

- leave brash around the base of the tree

- create exclusion zones (temporary or permanent - weather-dependent)

- alter the area's overall land use designation (from pasture to hay meadow, for example)

 

Source: NTSG. (2011) Common sense risk management of trees. UK: Forestry Commission.

[Kveldssanger]

03/12/15. Fact #91.

 

Spurred on by the i-Tree report for London, I thought I'd start looking at both the report and the wider understood benefits trees provide in urban areas. In this case, we'll be looking at stormwater management.

 

Both the crown and root system of the tree aid with the reduction in storm water accumulation, via interception of water from the foliage and crown structure above ground, and the rooting system below ground increasing soil-water infiltration rates (by up to 60 times in as little as two years after planting) by allowing water to flow down alongside channels created by root elongation and presence.

 

By reducing the risk of storm water accumulation, not only is the risk of flooding lower, but surface pollutants are washed away at a more staggered pace, thereby reducing the likelihood of pollutant-rich storm water causing environmental problems downstream.

 

The i-Tree Report for London in fact concluded that the 8.421m trees in London alleviate 3.4m cubic metres of stormwater every year, which amounts to a financial value of £2.8m.

 

Sources:

 

Bartens, J., Day, S., Harris, J., Dove, J., & Wynn, T. (2008) Can urban tree roots improve infiltration through compacted subsoils for stormwater management?. Journal of Environmental Quality. 37 (6). p2048-2057.

 

Dover, J. (2015) Green Infrastructure: Incorporating plants and enhancing biodiversity in buildings and urban environments. UK: Routledge.

 

NTSG. (2011) Common sense risk management of trees. UK: Forestry Commission.

 

Rogers, K., Sacre, K., Goodenough, J., & Doick, K. (2015) Valuing London's Urban Forest. UK: Treeconomics London.

 

Xiao, Q. & McPherson, E. (2002) Rainfall interception by Santa Monica's municipal urban forest. Urban Ecosystems. 6 (4). p291-302.

[Kveldssanger]

04/12/15. Fact #92.

 

Of the estimated 8,421,000 trees within London (constitutes Inner and Outer London), approximately 57% are privately-owned whilst 43% are publically-owned. Inner London has a total estimated tree population of 1,600,000, compared to Outer London's 6,800,000. Tree density stands at 53 per hectare (squared), which is lower than the national average, generated by similar surveys, of 58 per hectare. Tree cover within London is considered to be around 14%. Space to theoretically increase the tree population does exist, though as nearly 40% of London is currently of an impermeable surface (cement, tarmac, building, etc), and because of the large abundance of underground services, careful planning is required. At present, London has from between 3-6% of land classified as 'bare soil', so trees could be planted here without removing anything else, assuming there is space above- and below-ground.

 

Source: Rogers, K., Sacre, K., Goodenough, J., & Doick, K. (2015) Valuing London's Urban Forest. UK: Treeconomics London.

Edited December 4, 2015 by Kveldssanger

[Kveldssanger]

Some interesting charts from the above source:

 

 

 

[Kveldssanger]

05/12/15. Fact #93.

 

Most roots will grow within the first 50-75cm of soil as, below such levels, soil aeration progressively falls. As roots need to uptake oxygen in order for respiration to occur, such depths beyond 1m are typically less desirable; unless soils are very fine and sandy, or cracks within rock faces allow for a greater penetration depth of oxygen. For most species, when the oxygen levels falls below 10–15 % in the soil, root growth is inhibited – growth stops completely at 3–5%. Such conditions occur when air-spaces in the soil are replaced by more soil (compaction), water (flooding – particularly detrimental during the growing season and where flood waters are static and warm), or gases such as carbon dioxide, hydrogen sulphide, and methane (gas leaks are perhaps the principal driver, here).

 

Sources:

 

Crow, P. (2005) The influence of soils and species on tree root depth. Edinburgh: Forestry Commission.

 

Davis, M. (2015) A Dendrologist's Handbook. UK: The Dendrologist.

 

Shigo, A. (1986) A New Tree Biology. USA: Shigo and Trees Associates.

[Kveldssanger]

06/12/15. Fact #94.

 

Root crown excavation is a relatively contemporary method of treating landscape trees that are either in decline or are visibly dying, as a result of being distinctly below grade (either because they were planted too deeply, or because the soil profile has subsequently been raised). The process involves removing excess soil from the root plate region, be it by hand (trowel, spade, etc) or through mechanical means (air spades), and also undertaking remedial works to the root crown itself (if necessary) - this may involve removing potentially girdling roots, for example.

 

In this study, eight tests at different sites (where trees were planted below grade) were conducted over a period of four years, to determine the impacts of root crown excavation on the health of the subject trees. Each study site had, on average, 40 trees, and the age of all trees across all sites was between 0.5-9 years - very much were all the trees still juveniles. Each site contained many specimens of an indivudal species, which differed between sites - oak, elm, maple (x2 sites), spruce, ash, and gleditsia species (x2 sites) featured within the study.

 

At this point, all sites were separated into two equal groups - one control group (where no root crown excavation was undertaken), and one group where root crown excavation did occur (the 'study' group). In this study group, potential girdling roots were removed.

 

For the excavation of the root crown area, compressed air was used, and saw soil removed to a radius of 18in from the base of the tree. Where soil was removed from the root plate to lower the grade of the soil profile, it was done to the point that the main lateral roots within the radius were exposed (slightly, upon their upper surface) to ambient conditions.

 

Measurements were then subsequently made after 18 months following root crown excavation (and then again at intervals untl the four year period ended), and involved ascertaining foliar chlorophyll content, the rate of secondary thickening at 1.4m up the stem, the rate of primary elongation, the increase in specimen height, and the activity (and abundance) of pests associated with the tree species.

 

Results suggested that there was no significant difference in the foliar chlorophyll content between the control and study group, nor was there any significant difference in growth rate, at four of the eight sites (oak, 2x gleditsia, spruce).

 

On the other four sites, it was shown that the 'treated' trees did respond significantly as a result of the excavation works. On the sites where maple was the species studied, the trees exhibited reduced foliar chlorophyll content and reduced growth rates. It is thought that the removal of roots that may have developed into girdlers did not help, as such root severance may have induced moisture stress. On another site (where elm was studied), chlorophyll content of leaves improved and there was a huge surge in height growth on the individuals that were treated with root crown excavation. At the final site, where ash were studied, it was shown that the treated ash responded favourably and exhibited increased foliar chlorophyll content.

 

It was thus suggested that the response to root crown excavation work was species-specific, though more work is needed, over a much longer period of time, and to a more diverse age range of trees, to ascertain exactly how different species respond to such treatments. In the period between this study and any long-term, comprehensive ones, trees planted (or existing) below grade should, at the very least, have the excess soil removed so to expose the main laterals to ambient conditions upon their upper surface. Caution should be exercised if the severing of future girdling roots on maples is being considered.

 

Source: Rathjens, R. & Sydnor, D. (2009) Evaluating root crown excavation as a treatment for landscape trees. In Watson, G., Costello, L., Scharenbroch, B., & Gilman, E. (eds.) The Landscape Below Ground III. USA: International Society of Arboriculture.

Edited December 6, 2015 by Kveldssanger

[Kveldssanger]

No fact today, but a load of videos courtesy of the Ancient Tree Forum. I don't recall seeing them on the site a few months ago, though it seems they were provided by Vetree, which ended in 2014 (so the videos may be one or two years old). Very informative, I must say.

 

Veteran tree management | Ancient Tree Forum

Edited December 7, 2015 by Kveldssanger