Cork Oak Repot Experiment

[0soyoung]

I have just potted 8 cork oak (quercus suber) seedlings, officially starting my experiment (similar to what I described in the “Let’s All Get Some Answers and Not Wait for the Book” thread). My experiment design is given by the following table and notes.

tree	repot	rhizo	cuts	shoot pru	defol
1	-	-	-	+	+
2	+	-	-	-	-
3	-	+	-	-	+
4	+	+	-	+	-
5	-	-	+	+	-
6	+	-	+	-	+
7	-	+	+	-	-
8	+	+	+	+	+

o repot ‘+‘ = Aug/Sep
o repot ‘-‘ = spring
o rhizo ‘+‘ = nested clear orchid pot & proLeague
o rhizo ‘-‘ = MVP in black pot
o cuts ‘+’ = cuts at stem base done at repotting
o cuts ‘-‘ = do nothing
o shoot pru ‘+’ = nip shoot tip to just remove terminal leaves
o shoot pru ‘-‘ = do nothing
o defoliate ‘+’ = remove fraction of leaves by cutting through petiole
o defoliate ‘-‘ = do nothing

Again, all this table says is that tree 1, for example, will be repotted this coming Aug/Sep. I just potted it in a gallon sized pot of Turface MVP. When it starts sprouting new leaves, I will remove the terminal shoot and a bit later in the season I will (partially) defoliate it.

I decided that I will try to measure root growth, in addition to monitoring the ‘above ground’ growth. I am using 6 inch clear orchid pots as mini rhizotrons to do this. Because it is difficult to discern roots from damp MVP, I have filled these pots with dark colored Turface proLeague Heritage Red. Hence I have a new experiment factor, ‘rhizo’ that is a different soil/pot. These ‘rhizotrons’ are nested within a gallon size black plastic pot. Soon I will start looking at them weeky to measure the root length.

I am using Turface for two reasons. First is that MVP is my chosen planting medium. Second, is that it can be removed without disturbing the root mass by just gently agitating the tree roots in a bucket of water. This likely is also the case with non-compacting mixes (e.g., pumice, scoria).
Earlier I stated that I intended to make 8 lengthwise cuts (the cuts factor) around the base of the trees. I have only made 4 this time because of the small size of the seedlings.

I've tabulated the data that I collected just prior to planting my 8 cork oaks for the first time. I used a caliper to measure the stem diameter and a 1gram resolution scale to weigh each. Again, I selected the trees randomly with a simple intuitive procedure:
• Write the id numbers on a potting stick
• Put the sticks, numbered ends down, in a cup
• Pick a seedling/tree
• Pick a stick
• Perform the actions required for that id.

tree id	base dia (mm)	cuts	wt (gm)	clr pot
1	5.79	no	23	no
2	5.6	no	20	no
3	4.12	no	11	yes
4	3.8	no	9	yes
5	5.18	yes	24	no
6	3.79	no	11	no
7	5.09	yes	18	yes
8	4.32	no	23	yes

 

[JudyB]

That looks like a lot of work to me. I appreciate the time you have put into this. I think it's great that you're willing to get to the bottom of the question.
For me, it would take the fun out of it... Like having to do homework on vacation....

 

[davetree]

I think it would be a better experiment if you used clones instead of seedlings, and increase the number of plants from 8 to a hundred or so.

 

[Poink88]

I think it would be a better experiment if you used clones instead of seedlings, and increase the number of plants from 8 to a hundred or so.

True, but at least he is doing 8 while most of us are doing nothing.

 

[davetree]

Well I don't think it will prove anything. A bad experiment is no better than none at all. Eight different seedlings is a lot if variability.

 

[daygan]

I think the point about clones is interesting, and perhaps valid to some extent, (certainly valid in certain contexts) but I think also that 1. use of clones is not mandatory when experimenting, and 2. not using clones is helpful to establish patterns / tendencies that exist across the gamut of an entire species despite slight genetic variation. An experiment done with clones can easily establish the effect of a certain stimulus on a particular individual plant, because while results may vary, genetic variation can be ruled out as an influencing factor, and data analysis can be used to establish the percent of correlation between the stimulus and the observed results. However, if the intent is to confirm or deny correlation between stimulus and results across the entire species, use of one genetic sample is not enough, and eventually, data must be gathered from a larger sampling of the entire population. Therefore, genetic variation, in this case, is in fact necessary.

Consider this idea in a couple slightly different (but relevant) contexts:

In medicine, when testing the effects of products on multiple test subjects, results are not thrown out because the subjects tested are not clones. In fact, it's important that they are not clones, because researchers are looking for tendencies in reactions to their product that may or may not exist across the general population.

Likewise, when a survey is conducted to gather information about social trends, results are not thrown out because respondents are not homogeneous. Despite the fact that diversity within the population exists, trends can still be identified.

Take a look at the following two articles: Designing Experiments on plantingscience.org and Plant Growth Experiments in the "Cornell Composting" section of Cornell University's web site. Both of these articles discuss plant experimentation using multiple subjects, and both involve the use of multiple subjects which are not genetic clones. In fact, no mention is made of clone use at all. I'm sure anyone could find quite a number of similar articles from reliable sources with enough searching. While clones can be helpful for certain purposes, I personally don't see that they are a necessity to make a good experiment in this particular case.

 

[gergwebber]

in any case if there is someone out there who has got cork oak cuttings to take I would like to know. There is talk of air-layers working, but I have not yet seen it documented

 

[catfish chapstick]

I think the point about clones is interesting, and perhaps valid to some extent, (certainly valid in certain contexts) but I think also that 1. use of clones is not mandatory when experimenting, and 2. not using clones is helpful to establish patterns / tendencies that exist across the gamut of an entire species despite slight genetic variation. An experiment done with clones can easily establish the effect of a certain stimulus on a particular individual plant, because while results may vary, genetic variation can be ruled out as an influencing factor, and data analysis can be used to establish the percent of correlation between the stimulus and the observed results. However, if the intent is to confirm or deny correlation between stimulus and results across the entire species, use of one genetic sample is not enough, and eventually, data must be gathered from a larger sampling of the entire population. Therefore, genetic variation, in this case, is in fact necessary.

Consider this idea in a couple slightly different (but relevant) contexts:

In medicine, when testing the effects of products on multiple test subjects, results are not thrown out because the subjects tested are not clones. In fact, it's important that they are not clones, because researchers are looking for tendencies in reactions to their product that may or may not exist across the general population.

Likewise, when a survey is conducted to gather information about social trends, results are not thrown out because respondents are not homogeneous. Despite the fact that diversity within the population exists, trends can still be identified.

Take a look at the following two articles: Designing Experiments on plantingscience.org and Plant Growth Experiments in the "Cornell Composting" section of Cornell University's web site. Both of these articles discuss plant experimentation using multiple subjects, and both involve the use of multiple subjects which are not genetic clones. In fact, no mention is made of clone use at all. I'm sure anyone could find quite a number of similar articles from reliable sources with enough searching. While clones can be helpful for certain purposes, I personally don't see that they are a necessity to make a good experiment in this particular case.

Good point. I think he mentioned clones so that the genetic factor was a control and not a variable considering all the other controls/variables. Just like all the seedlings will be in the same zone. It's still worth experimenting still.

 

[0soyoung]

Just like all the seedlings will be in the same zone.

True, but the basic concept of this is a 'group grope' for mutual benefit.

Maybe someone else, say Daygan in China as an example, would also secure a number of cork oaks and repot some in the spring and some in 'Aug/Sep'. Then if we share our data, we would have results for two different climes with the same/similar specie.

You might have noticed that I've also started similar experiments with lodgepole pines and Douglas firs, both of which are widely distributed species. While I have my own reasons for this experimentation, my ancillary aim is that others in different climes might want to also repot some trees in Aug/Sep versus spring and report their data for BNuts' benefit.

 

[0soyoung]

Progress - initial potting effects

All 8 of the cork oak seedlings that I purchased from Forest Farm and potted this spring are doing well. I was concerned for a while because several defoliated themselves – their leaves turned brown and fell off. Only two trees still have their old leaves. On one they are completely brown and hanging onto what is probably a dead shoot (it has other new growth). On the other, the old leaves are still green and there are also new leaves as I expect to be normal for cork oaks (i.e., my understanding is that new leaves come in spring and old leaves hang on to the end of their second summer, though I must wait until next year to ‘discover’/verify this from this experiment).

Next year I will apply the defoliation treatment at the same time as the spring repotting (treatment). This year will be just observation and repotting half of them sometime in Aug/Sep.

 

[0soyoung]

Stem/Trunk Thickening

When I potted my cork oak seedlings this spring I painted a mark about 10cm (4 inches) above the soil level and used this site for measuring the trunk thickness of each seedling every week or two with an inexpensive digital caliper. Each time I measured the seedlings, I measured each three times so that I could also gage my measurement accuracy and, therefore, whether the individual trees were indeed thickening while I was making measurements during the season.

I’ve rendered my data on the attached chart by the average thickness measured across all 8 trees and have normalized the data to represent the fraction of the seasonal increment (i.e., the normalized average thickness at the end of the season is 1). I’ve also represented the standard error of my measurements by error bars on the attached chart.

For me, the most interesting thing that comes from this is the red dashed curve of the rate of thickening (the slope of the curve through the data points). The rate of thickening increased during the season until ca. 9 July and has steadily declined since. This is quite interesting for folks that like to understand how trees work, but the only practical value I see to this for bonsai is to explain why wire is best applied in August or later in the season (alternatively, why ‘wire biting’ is so hard to avoid when one wire’s in the spring, before the solstice) – as though we didn’t know this already. For tree geeks, of course, it is significant that the time of maximum thickening occurs just after the summer solstice.

A couple of relevant details that I should add are that my measurement accuracy was about 0.046mm (surprisingly good) and that the average thickness increment for my cork oak seedlings this year was about 0.85mm (which amounts to about a 30% increase in thickness for one growing season).

24Oct: Scholarly papers suggest that the maximum growth rate is controlled by daylight hours and that the dormancy period is controlled by (low) temperature.

 

[Poink88]

For me, the most interesting thing that comes from this is the red dashed curve of the rate of thickening (the slope of the curve through the data points). The rate of thickening increased during the season until ca. 9 July and has steadily declined since. This is quite interesting for folks that like to understand how trees work, but the only practical value I see to this for bonsai is to explain why wire is best applied in August or later in the season (alternatively, why ‘wire biting’ is so hard to avoid when one wire’s in the spring, before the solstice) – as though we didn’t know this already. For tree geeks, of course, it is significant that the time of maximum thickening occurs just after the summer solstice.

Well I am on the opposite (as always LOL). I like to wire before the maximum thickening (lignification) because it will help the branch to set the fastest (isn't that the goal???)

The reason most wire later in the season is because it is easier to wire after fall (no leaves for deciduous trees at least).

Please correct me on both counts if I am mistaken.

 

[0soyoung]

Well I am on the opposite (as always LOL). I like to wire before the maximum thickening (lignification) because it will help the branch to set the fastest (isn't that the goal???)

Check some scholarly papers, such as the discussion around Figure 1 of Thibeault-Martel, Maxime, et al. "Cambial activity and intra-annual xylem formation in roots and stems of Abies balsamea and Picea mariana." Annals of botany 102.5 (2008): 667-674, for example. I think you will see that most of the 'lignification' occurs during the summer, after this peak in the rate of thickening.

Letting the wire 'bite in', as you prefer to do, may work because it induces reaction wood. Those of us who have used a wire tourniquet for air layering have seen the thickening above the tourniquet that is far, far more than any similar thickening induced by girdling and the normal thickening of a stem.

 

[Poink88]

Letting the wire 'bite in', as you prefer to do, may work because it induces reaction wood.

BIG assumption on your part. I never said that and I don't let it happen as much as possible. There are times it did though. I remove the wire once they start to bite in and rewire if need be (usually not).

 

[0soyoung]

the First Season

For this past season, the only treatment that was applied (other than to make 4 length-wise cuts at the bases of two spring potted trees, #5, #7) was potting in Turface MVP (in one gallon black plastic pots) versus finer grained Pro League (in clear orchid pots). In pictures, the two groups look to me to be about the same. Maybe I should instead say that I don’t see anything that would make me choose to use Pro League over MVP (or vice versa) – which is to say there is no effect.
Cork oaks in Orchid pots of Turface Pro League

Cork oaks in 1 gal pots of Turface MVP


Since I’ve learned that I can measure trunk thickening, one might also ask if the trunks thickened more pronouncedly in one group versus the other. With numbers, the principle is the same – are the two groups like we would expect from random chance (no effect) or not? I compared this season’s trunk thickness increment; long story short: there is no effect (yet?).

On 4 Sep, I washed the Turface out of the roots of #2, #4, #6, and #8 so I could check the weights. These four trees added a roughly 10% weight gain in weight this season – (16+-0.71 grams; the group weighted 15.75+-6.8 grams just before they were potted on 17 Mar). However, I am surprised at how meager the season’s root growth was. I presume this is just the nature of cork oaks since I have no previous experience with them.
#2, #4, #6, #8 on 4 Sep

#2, #4, #6, #8 on 17 Mar


The last thing I note is that the stem on #6 died early in the season. Unfortunately this was the stem I had marked for ‘trunk thickening’ measurements. I left it on thru the season, though, and only removed it after having weighed #6. Two of the trees (#6 and #8) were given four longitudinal cuts equally spaced around the circumference of their stem bases, partially defoliated, and reweighed before being replaced in their original containers and washed ‘soil’as planned.

 

[0soyoung]

Maybe After One More Season

Seedling #6 died over the winter of 2013-2014. Again I had several trees with leafs that turned brown and (the majority of them, anyway) fell off [see Corks_23mar14.jpg]; consequently, it was not possible to execute defoliation as a factor. Also, shoot pruning was only done to clean off dead stems/leafs.

As with my other repotting experiments, I use the bottom of a 1 gal plastic pot as the template for root pruning. In all instances, a negligible amount of cork oak root has ever been removed; so little, in fact, that it would be fair to say that the ‘repotting’ has really been just ‘slip potting’ and, therefore, that the results to date just reflect what we all know to be true – slip potting can be done at any time.

The surviving 7 trees grew well enough in 2014 [see Corks_7sep14.jpg] that I am interested in keeping them and continuing this experiment for at least one more season.

ID	repot	medium	cuts	P0 wt	RP1 wt b4	RP1 wt after	RP2 wt b4	repot wt removed	seasonal wt gain
1	-	-	-	23	38	34		4	15
2	+	-	-	20	35	33	134	2	101
3	-	+	-	11	17	16		1	6
4	+	+	-	9	26	23	68	3	45
5	-	-	+	24	52	41		11	28
6	+	-	+	11	omitted	16	dead
7	-	+	+	18	47	45		2	29
8	+	+	+	23	39	28	32	11	4

• Potting time0 was on 17 Mar 13
• RePot1 was on 4 Sep 13 for fall repotting (+); on 23 March 14 for spring repotting (-)
• RePot2 was on 7 Sep 14 for fall repotting (+)
• Weight removed in repotting is the difference between RP1 after and RP1 before.
• Seasonal weight gain is the response to the factors repot, medium, and cuts

o for spring (-) repotting = (RP1 wt b4) – (P0 wt)
o For fall (+) = (RP2 wt b4) – (RP1 wt after)​

 

[Fonz]

Just stumbled upon this thread while googling if Quercus Suber are common in forest plantings...
How are yours doing btw?

 

[0soyoung]

They are all still alive, but grow slowly in my climate (rarely gets much above 72F/23C). A nice trunk of what was the biggest one died back, (then resprouted from the base) though.

They back bud strongly in spring when buds begin to push off the old leaves. So, I find it convenient to defoliate and repot them in late spring, even though they do fine with repotting later on, when new growth isn't extending.

 

[LittleDingus]

Just stumbled upon this thread while googling if Quercus Suber are common in forest plantings...
How are yours doing btw?

I don't think you'll find many q suber forest plantings. I was searching for the same a few months ago and turning up blank. They are ever green so typically have no winter sillhuette. Not much interest in a forest over what could be done with a single tree. In fact, easier to show off the bark with a single tree.

I did plant a few of mine to start what I hope will be a small savannah style planting in a few years. I bought a bunch of acorns a few years back and all but 2 sprouted so I'm currently flush with 2cyear old suber saplings!!!