Temperature “feels like”

[Adamski77]

Have a question as spring is slowly coming. Shanghai is very humid and quite a windy place so some days nominal temperature of let’s say +3 degrees Celsius shows “feels like” being negative 2 or 3 degrees. Is this good indicator what the trees feel like too or it’s just human perception. It’s important from reporting perspective as theoretically in above zero temperatures we don’t need necessarily to protect the root system but it’s an entirely different story when temperature goes below zero.
Appreciate some comments…

 

[rockm]

Wind chill doesn't affect plants or animals that don't sweat the way it affects humans. The danger with plants isn't the "feels like" temperature, but the accompanying wind strength and humidity levels. A dry, cold wind will pull moisture from leaves, if the roots are frozen and the wind is blowing hard, the roots can't transfer enough moisture to replace what's being lost through the leaves. If the soil isn't frozen, this isn't much of an issue. That can dry out foliage and kill leaves. You can avoid this issue by protecting plants from strong winds in the winter.

 

[dbonsaiw]

Never really understood what "feels like" refers to. Is the air temp X and the wind makes it feel like less than X to us sweaty humans with nervous systems, or does the wind actually make the air temp less than X? I have the confusion on the other end as well. Iphone tells me its 85 degrees, for example, but the thermostat sitting on the grow box out in full sun reads over 100. What are the trees actually experiencing?

 

[Wires_Guy_wires]

In addition to what rockm said: in a closed biological system like a dormant plant, what matters is the absolute, actual, temperature.
Because their biological processes are based on temperatures at which enzymes and proteins have activity, enzymes don't care if it "feels" colder than it is. What matters to them is the actual temperature they're in.

However, we have to keep in mind that a branch in the wind can be a couple degrees colder than the ambient temperature. So to measure it correctly it would make sense to measure on the plant itself, with a laser guided thermometer for instance.

 

[Tums]

Never really understood what "feels like" refers to. Is the air temp X and the wind makes it feel like less than X to us sweaty humans with nervous systems, or does the wind actually make the air temp less than X? I have the confusion on the other end as well. Iphone tells me its 85 degrees, for example, but the thermostat sitting on the grow box out in full sun reads over 100. What are the trees actually experiencing?

My understanding is "feels like 10" means that you are losing heat to the environment at the same rate that you would be if the air temperature was 10 degrees and there were no other factors such as wind. This only matters until whatever exposed object reaches the air temperature. If it's 20-feels-like-10, an object will lose heat as if the air were 10 degrees until the object reaches 20 degrees.

Your thermostat in the sun is going to be above the air temperature because it absorbs some of the sun's energy that directly hits it. This is also going to be true for tree leaves but they can try to regulate their temperature. Personally, I would try to keep the thermostat out of direct sun just so I could better compare to the local weather forecasts. Different trees would probably heat up by different amounts from each other and the thermostat so I would have a hard time comparing.

 

[Adamski77]

Thank you... this is quite helpful... I think bottom line is to protect against wind... either hot one or cold one... rest seems to be theoretical. Appreciate.