Originally Posted by
DrTimPerkins
Sounds like it was not seeds that got damaged, but flowers. These don't typically require a lot of energy to form, and if killed at the early stages the loss would be minimal in terms of affecting the overall carbohydrate status of affected trees. Most of the energy going into forming seeds happens during the actual growing season when there is (assuming good growing conditions) adequate carb supply available. If there isn't for some reason (drought being a big one), then the seeds can abort to cut the losses to the tree.
Not really...the carb balance in the tree is accumulated, used, and dispersed over many years. The average sap sugar coming from a tree comes out to about 3 yrs old, but spans anyone from just a few months old to several decades old (but the average is 3 yrs). The sugar that makes up the sap we collect and syrup we make is derived from several years of growth and tree rings. Sugar tends to go down as we go deeper into the trunk (into older tree rings), partly because some of the sugar in older rings gets used up. There is also the issue of reduced hydraulic conductivity...vessels become less functional as we get deeper. So overall, more sugar and more sap from the outer rings to the inner rings.
Trees don't "anticipate" things the way people do. If the conditions are right, they'll respond. However, one of the conditions for something like producing seeds is to have adequate carbohydrate reserves to accomplish that. Trees that have decent sun exposure tend to have reasonable reserves. Some amount of that is lost when sapwood turns to heartwood in the tree. Any carbs left in those rings is cut off from the trees vascular system and thus no longer available.
They are making some carbs early on, but it takes a little while (a few weeks depending on the weather) for photosynthetic function to ramp up to maximum productivity. Similarly, when they turn color in the fall there is some continued export of carbs for a while.
Great question. The first thing to keep in mind is that air temperature isn't the critical thing...it is sap temperature in the branches and stem, and wood doesn't change temperature nearly as quickly during freezing and thawing as air does and not all the wood is at the same temperature. The branches freeze first, and start to generate a vacuum immediately upon freezing. The transition from liquid to solid (liquid to ice) is critical. It causes a huge vapor pressure deficit (humidity is very low over ice compared to humidity when liquid is present), which helps to generate the negative pressure (vacuum) to result in water uptake. This vacuum is propagated through the rest of the tree as the tree branches/wood freezes, and eventually is transmitted down into the roots where water is drawn in. That is why a nice slow freeze is good for water uptake. What is kind of weird is that this occurs in different parts of the tree at different times since them temperature is not the same throughout. So for example, the core (or north side) of the tree may still be frozen, so not participate in flow or uptake at all. The branches might be freezing up, generating a suction, but the stem might still have some stem pressure in it for a time. Over time though there is this wave of suction that builds up and moves through the stem to cause uptake.
On the flip side, when the tree thaws, there is essentially no pressure at all, then all of a sudden the pressure spikes upward to a peak value, then stem pressure decays downward over the next few days as sap flows out.
