(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

Shigo suggests that above 40 degrees Celsius, air temperature causes a sudden and massive loss in photosynthetic capacity. The graph you have copied here is a more gradual slope up to the 28-35 range, and then a very swift drop by 40.

[Kveldssanger]

Nice fact, Alec!

[Kveldssanger]

24/08/15. Fact #14.

 

Given UKTC's discussions over big urban trees and their benefits, I thought I'd share a fact from a recent study into the perceptions residents have with regards to urban trees.

 

It seems to be that the amenity benefits of trees are markedly more recognisable than other benefits by residents of urban / sub-urban areas. When homeowners of a new development (all of which had trees in their front garden) were surveyed, the 38 respondents identified 55 benefits of trees, of which 36 where aesthetic, 10 environmental, 2 economical, 2 social, 3 none (!!!), and 2 'other'.

 

49 disadvantages were also recognised among the respondents. 16 residents stated the visual or physical obstruction caused by trees was detrimental, 13 stated leaf shedding was an issue, 7 outlined concerns over risk of damage to property or person, 2 were wary over future maintenance needs, and 11 respondents identified no disadvantages.

 

Now here's where it gets more interesting. When residents were informed that the trees in their gardens would reach height x in maturity, 30 of the 38 respondents (79%) stated they would look to restrict the height of their tree. A further three said they would remove their tree. Only five were happy to allow their tree to grow unrestricted. There was a strong association between the disadvantages individuals listed and their probability of restricting tree height (or removing the tree entirely), with the most significant association being that of the tree causing obstruction (light, view, literal obstruction) and pruning work.

 

Small trees under 6m were the stated preference of 23 residents, medium trees of 6-9m were preferred by 13 residents, and only one resident admitted to preferring trees of a large size (9m+). One respondent did not mind.

 

I could go on ad nauseum, though that wouldn't be right! Instead, I'll round up by saying the authors did an i-Tree analysis of two potential scenarios on pollutant removal 10 years into the future: (1) leaving all trees to grow unrestrained for the 10 years and (2) seeing the 79% of trees continually pruned and a further three removed (totaling to 87%), as desired by the respondents, and ascertaining their value after 10 years. The analysis concluded that 149% and 88% of pollutants would be filtered out respectively, after the 10 years had passed, when compared to the value the trees provided at the time the survey was undertaken.

 

Source: Andrew, C. & Slater, D. (2014) Why some UK homeowners reduce the size of their front garden trees and the consequences for urban forest benefits as assessed by i-Tree ECO. Arboricultural Journal. 36 (4). p197-215.

Edited August 24, 2015 by Kveldssanger

[Gary Prentice]

I remember reading that. It's always interesting meeting people (clients) and attempting to illicit their views and perceptions on trees. Very few have any knowledge of the benefits all all, apart from they look nice and generally opinion is that disadvantages outweigh the benefits.

[Kveldssanger]

I can agree with that. I've had a few residents say the only things trees are good for is "making a mess". The fact they quite literally support ecosystems by providing oxygen doesn't even register.

[Kveldssanger]

26/08/15. Fact #15.

 

This one is so obscure I thought it'd be rather interesting to share. Not sure how many of you bear witness to the glory of a Prunus padus covered in ermine silk and the thousands of caterpillars that come alongside, though I can say it's certainly not nice to stand under.

 

On that note...:

 

There are times when a host plant may directly or indirectly mediate an inter-specific competition between two (or more) species. One example of this is when Prunus padus (bird cherry) facilitates indirect inter-specific competition between Yponomueta evonymella (bird cherry ermine moth) and Rhopalosiphum padi (bird cherry aphid). Both species will commonly feed on the same tree at the same time of year, and the resulting competitive effects are indirectly mediated by the host tree.

 

Individual Prunus padus trees will differ from one another in regards to their suitability as a food source for Rhopalosiphum padi, and these host tree differences are consistent (they do not change year-on-year) - essentially, trees with high Rhopalosiphum padi counts in one year will always have high counts. This was proven through studies in Scotland and Finland, where it was shown that trees with an abundance of Rhopalosiphum padi eggs had a low number of Yponomueta evonymella larval shields. As a precursor to the following, the former lays eggs within the angle of the bud and shoot, whilst the latter oviposits on the shoot itself.

 

And now it gets interesting.

 

Yponomueta evonymella lay their larval shields on the shoots, and such shields are 13mm long. Therefore, a space of at least 13mm is needed, though realistically 20mm is required on the shoot for oviposition to be "comfortable". Therefore, trees with narrow bud spacings are not suitable for Yponomueta evonymella oviposition. Conversely, as Rhopalosiphum padi lay their eggs within the shoot-bud angle, narrowly-spaced buds (which entails buds being more abundant on the whole; therefore meaning more egg-laying sites on the tree) are preferential.

 

Further, trees defoliated by Yponomueta evonymella always re-foliate (assuming the tree doesn't die) during summer. The leaves subsequently senesce at a later date than those from non-defoliated trees, meaning Rhopalosiphum padi egg-laying is not particularly practical given the lack of 'mineralised' nitrogen (which aphids require as a food source) provided by the later senescing leaves of trees where Yponomueta evonymella has defoliated and caused re-foliation. Basically, where leaves senesce at the 'expected' time nitrogen availability is high, though where the leaves senesce later (following Yponomueta evonymella defoliation) the nitrogen is still 'locked' within the leaf when it comes to Rhopalosiphum padi egg-laying time.

 

And we're not finished yet, as trees heavily attacked by Rhopalosiphum padi respond to such attack by... growing buds more densely along the shoots!

 

Therefore, either heavy feeding by Rhopalosiphum padi makes the tree less desirable for Yponomueta evonymella, or defoliation (and subsequent refoliation and later leaf senescence) by Yponomueta evonymella makes the tree less desirable for Rhopalosiphum padi. Therefore, we see higher populations of one or the other on specific Prunus padus.

 

In older Prunus padus, the suitability of which species they are more able to support has long been decided (I would imagine very early on in the life of the tree would such species suitability be determined - perhaps even pre-natally). As research indicates the type of defoliation drives different colonisation habits of both species, perhaps identifying where the fate of the tree is decided is the next step for researchers. I would suggest that genetic traits drive early colonisation abundances, and from there the tree is 'shaped' into a host for (predominantly, though most exclusively) one of the two insects.

 

Source: Leather, S. & Bland, K. (1999) Naturalists' Handbook 27: Insects on cherry trees. UK: The Richmond Publishing Co. Ltd.

[armybloke]

Further to the 'benefits of trees', I am fortunate to be in a position to educate both children and adults alike on the benefits of trees. I teach children predominantly at a Wildlife Watch Group (Wildlife Trust) twice a month and the (almost) favourite subject is now trees. Camp-fires and marshmallows is hard to nudge off the perch! Needless to say that I can talk for ever on the subject of trees and factoids like this just add fuel to my fire (and the camp-fires at the end of the day). The adults have now become the Q&A experts and quiz me for more and more information. This is good and I have digressed again!

 

My point that I was attempting to make was I am being asked by the general public, clients and the like about the benefits of trees over say, an extension to their property etc. I have now added a section in my reports called 'Environmental Benefits' whereby I add a few interesting yet important facts similar to water transpiration to control local water tables etc. It has become very evident that 'some' people want to know more to be able to do more. Refreshing anecdote to my ramble. Keep this thread alive people, it's very useful!

If climate change has now reached an emergency threshold akin to terrorism then we must all take note!

[daltontrees]

Great addition to the discussion there, Julian. Generational turnover is indeed a driver of species and sub-species development. I do wonder that as forest patches become more fragmented whether associated genetic drift will reduce the likelihood of new species developing. It can work the other way too however, with fragmented pockets of a species slowly evolving into a new sub-species (ultimately it would depend on the starting genetic pool of a species, and wouldn't work for vegetative propagation - perhaps genuses and species that reproduce primarily vegetatively don't therefore have as many species and sub-species respectively?). I wonder if there is any research on such a topic...

 

As for today's fact, it's going back to the basics and is again from Shigo's Modern Arboriculture (still reading it!).

 

23/08/15. Fact #13.

 

Photosynthesis, which is an autotrophic means of energy synthesis, involves the conversion of solar radiation (that comes in waves or particles: photons) to sugars (glucose). In the rawest sense, the photon strikes an electron within the chlorophyll molecule, the electron gets excited as a result, and in the process of it returning to an unexcited state the energy it gives off is captured and utilised to split a water molecule and to then bond the split molecule to a carbon dioxide molecule, producing glucose.

 

The two principal drivers of photosynthesis (excluding plant vigour and vitality - genetic trait and situational trait respectively) are light and temperature. Efficient photosynthesis can occur, at least on paper, when light availability is akin to 1,500 foot candles and temperature is between 28-35 degrees Celsius. Once temperature reaches 40 degrees or above, regardless of light availability, efficiency is significantly impacted.

 

Interestingly, only 0.1%* of the sun's solar energy is captured by plants (for any given increment of time - a second, a minute, an hour...). Of this 0.1%, 50% is captured by trees.

 

Source: Shigo, A. (1991) Modern Arboriculture. USA: Shigo & Trees, Associates.

 

*I believe the 0.1% would be of 1.08x10(to the power of 14) kW, going by this source. That means 108,000,000,000 kW (one hundred and eight billion) of energy is utilised by plants per second, of which 54,000,000,000 kW (fifty four billion) is used by trees (someone please double-check this!).

 

The calcualtions are correct but be careful. Shigo says 0.1% is 'trapped' by plants. You then use the terms 'captured', 'utilised' and 'used'. Perhaps Shigo meant 'stored' but the otehr words you use could mean that and lesser interceptions such as warmth that is given out again as part of a daily cycle or as kinetic energy of released oxygen dioxide and heat energy of transpired water vapour.

 

Then it gets all very complicated. Photosynthesis (storage of energy) is acelerated by warmth, so plants use solar energy indirectly too.

 

What would be really interesting is to know how much energy is stored in plants as wood.

 

Shigo concludes his bit on energy and mass by saying tha thte trapping of energy by trees is "the major benefit of trees to our living world". Much as I hate to disagree with 'the man', it is worth a mention (and referreing back to the fundamental chemistry of photosynthesis and respiration) that -

 

6 x water + 6 x carbon dioxide = monosaccharide (e.g. glucose) + 6 x Oxygen

6CO2 + 6H20 = C6H12O6 +6O2

 

That oxygen is not just a major benefit, it is essential to all animal life. Looking at trees and being warmed by firewood are benefits to life, but rank a little below breathing.

 

Let's hear it for trees! Plants give, everything else just takes.

[Kveldssanger]

I spoke to some colleagues who work in another department today about my job, letting them know what I do day-to-day. I started going on about how leaves lobe to become more 'aerodynamic' in the wind, and hazards associated with trees, and they actually were very receptive. If you show you care when speaking, that passion will come through and people will respond accordingly. Keep up the good work, armybloke!

 

Jules, you make great points. I think Shigo went on to say that man looks for continuous patterns in nature (linear / bell-shaped curves, for example), but nature never works by our laws and preferences. Therefore, the photosynthesis comment can indeed only be what one would 'expect'.

 

Wouldn't burning wood and measuring joules of energy be a means of determining energy stored within the wood?

 

We're thieving buggers - the trees are being all charitable, and we just make it harder for them to live via fragmentation and pollution and then cut them down.

[Kveldssanger]

27/08/15. Fact #16.

 

Bit of a short one, and again quite odd, but certainly something to bring up in conversations about vegetative propagation (does such a conversation ever occur!?).

 

The ability for trees to be coppiced and subsequently re-sprout derives from the tree's natural response to wounding / significant stress (snapping of main stem, uprooting, fire damage, browsing damage, drought, flooding, pests, disease, etc). Such a trait is initially believed to have originated in early woody angiosperms, where the shady, disturbed, wet habitats made clonal reproduction the most advantageous means of species continuation.

 

Such examples of clonal reproduction can be seen today, albeit likely infrequently. In southern England, clonal Prunus avium accounted for 48% and 65% on managed and unmanaged sites, respectively. Such expanses but pale in comparison to a case of Populus tremuloides extent in Utah (USA) however - the 'pando' colony of trembling aspen comprises of 47,000 stems and covers 43ha of land (!!!!).

 

Source: Buckley, P. & Mills, J. (2015) Coppice Silviculture: From the Mesolithic to the 21st Century. In Kirby, K. & Watkins, C. (eds.) Europe's Changing Woods and Forests: From Wildwood to Managed Landscapes. UK: CABI.