I'm sorry you are having to deal with this situation. I know it is frustrating and since squirrels are so common in our environment, it is hard to control them. You lost a very new tree and that is unfortunate. From a squirrel's perspective the softer bark and limbs within their jumping range make it much more attractive when there are limited food sources available in the winter. I don't believe your larger tree is in danger of dying from the limited damage that I see. I have several silver maples in our yard that get this type of damage annually. Unless it girdles the trunk (removes the bark all the way around the tree in one spot that won't allow nutrients to get to the crown), the tree should survive these minor squirrel injuries. There are some things that can be done to newer trees like wrapping the trunk and lower branches during months were there are fewer food sources available to them. The link below has some general information about squirrels, including some management techniques. While it is from U of Missouri Extension, and the hunting/trapping options are not relevant to CO, it does provide some good information.
https://extension.missouri.edu/publications/g9455
Things will change from year to year with the squirrel population and there are things to protect younger trees.

Good luck!

CSU Master Gardeners

CSU Master Gardener.

Hello,
There isn't great data on the effects of metal banding of trees. See this article https://extension.colostate.edu/docs/pubs/garden/treereclist.pdf. If you do it, I would be sure to leave plenty of room between the trunk and the metal so disease and pests don't collect there. I would also attach the metal in a way that does not require you to screw anything into the tree as any open wounds in the tree will provide additional opportunities for disease and insect damage.
You can trap and relocate squirrels but if you live in an area with lots of squirrel, moving one squirrel out just provides a space for a new squirrel to move in. It's not very effective where squirrels are abundant.
In terms of leaving food out, I agree it isn't a good idea with bears and the squirrels will just eat that food and continue to climb the trees. They'll just be even more well fed that they already are! 
Admittedly, there are not any fantastic solutions but if you use the metal band, be sure to check your tree every month to make sure moisture, debris or any damage to the metal is not hurting the tree. Good luck!

CSU,

I am going to forward your Ask Extension email to our wildlife agent Leslie Gonzales as we do not deal with any wildlife specific inquiries. She will be in touch through this email. Thanks.

Hi Betsy,

The Colorado Parks and Wildlife laws state traps must be checked daily. You must notify Colorado Parks and Wildlife in advance of the relocation and the release site must be an appropriate habitat for the squirrels. The site must be within 10 miles of the capture site.  You must get permission from the landowner or managing agency where they will be released.  Please follow the link below to see the nuisance wildlife laws in Colorado. 

Nuisance Wildlife Laws in Colorado (state.co.us)

We have a volunteer group called the Wildlife Masters in Boulder County. They are extremely knowledgeable on these topics. One of them will contact you by email to discuss your squirrel problem in more depth.  

Best regards,

Lyndsay Gonzalez, Boulder County Small Acreage Management Coordinator 

Lyndsay,