To those unfamiliar with the intensity and focus and freewheeling approach of "jam bands," consider this fact: At the precise moment COVID shut down live entertainment in the spring of 2020, one of the world's most popular and successful jam acts — the Dave Matthews Band — had just started a concert in Sioux City, Iowa.

That concert JUST ENDED LAST WEEK!

Oh, how they jammed! Through the entire waves of plague! Through the 2020 election! Including an eight-month version of "Crush"!

Fortunately for DMB zealots, the group has already revitalized and is primed to play shows Monday and Tuesday in the Mohegan Sun Arena. And help celebrate the band's activism. In 2020, DMB succeeded in their pledge to plant one million trees — and have reupped with the same goal for 2021. To help the cause, go to www.plantabillion.org/DMB.

Also note: All ticket holders must provide printed proof of full vaccination, either the original vaccination card or a printed copy of the card at least two weeks after final dose, or a negative COVID-19 test taken within 48 hours prior to entry at Mohegan Sun Arena. Ticket holders using a negative test for entry will not need to get subsequent tests if they are attending both shows. The Sun also encourages all fans to wear a mask, especially when social distancing is not possible.

Dave Matthews Band, 7:30 p.m. Monday and Tuesday, Mohegan Sun Arena; $87, $117; mohegansun.com.