Sunlight and Temperatures: Finland versus Europe, part II

In the previous post the amount of sunlight in Finland was compared against some cities in Europe.

The sunlight itself is not enough for the plant to thrive. Combination of temperatures which stimulate photosynthetic ability and activity is what the tree makes grow. Also has to be kept in mind that the amount of sunlight shown in the previous post represents exactly that: amount of sunlight but not the light which is absorbed by the plant! The continuation tries to address that issue.


From the same site as earlier the average high temperatures are extracted being shown in the graph below:


The light blue thick line is Helsinki data. The high average temperatures are used because they represent the day temperatures, not the night ones when the trees metabolism slows down.

That together with previously documented graph of sunshine…

Sunny hours

… served as the basis for the next step.

The rate of photosynthesis

In order to asses the ability of the tree to grow it is necessary to estimate the trees photosynthesis rate which depends on the temperature.

The photosynthetic rate is extracted from the documented table. The simplified curve (triangular shape) was created for temperate coniferous trees with initial/boundary points as below:

Temperature Photosynthesis rate
-3 0
25 1
35 0

Multiplying photosynthetic rate (as a function of temperature) with the available sunlight amount makes the next graph:


The bell curve of Helsinki is very strong in summer, especially July with sudden drop in August and very low values for September.

It is also visible that too high temperatures are not favorable for the tree to grow. I consider the drops (very strong for Athens, less for other cities) as a clear sign of the summer dormancy. Does that itself defines it is another story but this is nearer the reality than the sunlight or temperature alone can show.

Annual growth

Comparing the curves form the latest graph is not simple. The simplest way is to create an integral on them to estimate the surface area which would represent the annual “growth ability” (the latest is purely my term :D).

Those values normalized around the Helsinki value (which now equals to 1) makes the data for the next graph showing the relative growth ability (there must be a better name but right now my brain is stuck with this!). Now the comparison is much simpler and it gives also more value than just “better” or “worse”.


Growth period extension

On all graphs above I included the line/bar with title “Helsinki (extended), Finland“. On line graphs it is the dashed light blue line which is mostly overlapping with the basic Helsinki curve.

The “extended” values are the same as basic Helsinki set of data except that the average high temperatures for March and April are increased by 5 degrees C. The idea was to compare the difference in other curves/comparisons if the spring would be more favorable and what I kept in mind was the greenhouse ability to keep the temperatures even just by 5 degrees above the normal ones (in average) over those 2 months.

The latest graph shows that Helsinki jumps to be in par with Berlin and right after the rest all way more south European cities. The rest of north and west was left behind.

Update: Growth period extension 2

After Janis comment I added the next step. “Extending” growth season even more for September and October by also 5 degrees C. The values are marked by “Helsinki (extended2), Finland”.

The results show that Helsinki jumped over Berlin, though not really coming much closer to Istanbul which is very much understandable.

Conclusion of mine

This is plain theory! Yes, yes and absolutely yes.

Do you need this calculation to know that warmer spring helps in growth?! No, of course not but in order to play with concrete values, to be able to compare them one to another some data manipulation is needed. Before this “research” I would not consider stating that growing a bonsai in Finland might be easier than in UK/Central Europe after figuring out how to avoid the winter dangers of course.

But now I can. It is just my statement but as such it suffices to me 🙂

Understanding the potential could lead to other implications on the way how to grow bonsai here in the north. Some are already mentioned in Janis blog and for sure will come more when practical actions/procedures prove them.

Also to be kept in mind is the following:

  • the used values are average per month over longer period of years
  • the “temperate trees” is very generic and should be considered as such

The data and all calculation is available here.

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  1. Jani

    Very very interesting! My Japanese maples started to grow again in autumn, when I put them to cold frame with translucent cover. How about extending the growth period even more, from August to October? In the spring it is a question of getting trees to leaf out more quickly, in the autumn they have full leaves and the drop in sunshine could be a problem.

    Starting spring earlier is a fact with cold frame.

    • tato

      Thanks for comment Jani!
      I tried to simulate September/October +5C increment. See the graphs above. Data given by label “Helsinki (extended2), Finland”.

  2. Jani

    Not much difference! That is no doubt because of low light in the autumn. Still, that could make some difference, because there is some activity even after leaves have fallen. But plain protection from rain is probably a bigger factor.

    • Anonymous

      Yes, not as much as hoped for 🙂
      But honestly, it is better the calculation doesn’t promote/promise too good results because it would be difficult to believe it.
      I think having a possibility to be right after the south of Europe is already quite much comparing where we are positioned.

  3. Jani

    Exactly. And we need to be extra careful not to waste any precious summertime for recovering from repotting and other things like that, or to cut trees too often.

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