Arbor Day was founded in April 1872 as a time to "plant, nurture and celebrate trees."

But long before that, another tree-centric holiday had already been promoting arboreal appreciation for centuries. Tu Bishvat — also spelled Tu B'Shvat, Tu B'Shevat or Tu BeShvat — is an ancient Jewish holiday known as the "new year for trees." Its original role was to calculate the age of fruit trees, but today it has a broader ecological tone, earning it nicknames like "Jewish Arbor Day" and even "Jewish Earth Day."

This year, Tu Bishvat begins at sunset on Feb. 9 and ends in the evening of Feb. 10. It marks one of four new years on the Jewish calendar. While many religious and secular observers honor the holiday by planting trees, it has also inspired lots of other eco-friendly traditions over the years, from sustainable seders to tree-sitting.

So whether you're pining for environmental awareness, or simply want to branch out and try new foods, consider turning over a new leaf this year by celebrating the original Arbor Day. To help you get started, here's a quick look at the holiday's roots:

When and what is it?

Many people celebrate Tu Bishvat with a seder that includes dates, like the ones on these palm trees in Israel. (Photo: Alexandra Lande/Shutterstock)

Tu Bishvat always occurs on the 15th of Shvat, a 30-day Jewish month that generally lasts from mid-January to mid-February. (In fact, "Tu Bishvat" means "15th of Shvat" in Hebrew.) But since Jewish and secular calendars don't quite match, Tu Bishvat jumps around a bit on the latter.

The original purpose of Tu Bishvat was to calculate the age of fruit trees, which helped Jews in ancient Israel comply with this biblical edict from Leviticus 19:23-25:

"And when ye shall come into the land, and shall have planted all manner of trees for food, then ye shall count the fruit thereof as forbidden; three years shall it be as forbidden unto you; it shall not be eaten. And in the fourth year all the fruit thereof shall be holy, for giving praise unto the Lord. But in the fifth year may ye eat of the fruit thereof, that it may yield unto you more richly the increase thereof: I am the Lord your God."

With fruit deemed off-limits during a tree's first four years, Tu Bishvat helped people keep track by standardizing tree-planting times. According to jewfaq.org: "Each tree is considered to have aged one year as of Tu B'Shevat, so if you planted a tree on Shevat 14, it begins its second year the next day. ... [B]ut if you plant a tree two days later, on Shevat 16, it does not reach its second year until the next Tu B'Shevat."

And since growers at the time often donated a tenth of their fruit to religious leaders — a practice known as tithing — the holiday was also a sort of tax day for trees.

How is it celebrated?

Tu Bishvat seders focus on the 'seven species' of Israeli crops — wheat, barley, grapes (pictured), figs, pomegranates, olives and dates. (Photo: PhotoStock-Israel/Shutterstock)

While Tu Bishvat's early days may have been less about partying than pragmatism, the holiday has become more celebratory over time. In the 1500s, for example, Kabbalists began holding a seder on Tu Bishvat modeled after the Passover meal. This seder typically involved tree fruits native to Israel, according to Yitzhak Buxbaum's "A Person Is Like a Tree: A Sourcebook for Tu BeShvat," as well as discussions on "philosophical and Kabbalistic concepts associated with the day."

Tu Bishvat seders are now common, often focusing on the "seven species" of Israeli crops listed in Deuteronomy 8:8 — wheat, barley, grapes, figs, pomegranates, olives and dates (honey). This tradition has helped some Jewish environmental groups use Tu Bishvat to promote sustainable, locally grown food. U.S.-based Hazon, for one, offers tips on sustainable seders and on finding local seven-species options. (If fresh seven-species fruit isn't available, Hazon suggests raisins, dried figs and dates, honey, jelly, and even wine — ideally all local and organic.)

And since trees are what Tu Bishvat is all about, perhaps the most salient way to celebrate is simply to plant more of them. A variety of groups in Israel and elsewhere sponsor local tree-planting or broad afforestation projects on Tu Bishvat, and many families plant a new tree on their property or join volunteer efforts on public land. Others mark the holiday with just a walk in the woods.

"Tu Bishvat is a good reminder of our connection to the Earth," says David Krantz, president and chairman of the Green Zionist Alliance, a Jewish environmental group. "We have a symbiotic relationship with trees, but we tend to forget that. Humans and trees are dependent on each other. When we harm trees, we harm ourselves."

In that spirit, some people see Tu Bishvat as a time not just to plant new trees, but to protect existing ones. That's why two New York summer-camp directors prepared for Tu Bishvat in 2012 by living in the canopy of 200-year-old California redwoods, part of a long-term "tree-sitting" campaign to save them from being cut down. Yoni and Vivian Stadlin, founders of Eden Village Camp in Putnam Valley, New York, said in a press release that spending a week in redwoods was "like living in the lungs of the Earth."

Many people follow this example on a smaller scale, using Tu Bishvat to launch other environmental efforts like composting or home gardening. But however you spend this ancient holiday, Krantz says it should be more than a one-day diversion.

"Tu Bishvat serves in part as a holiday telling us to stop and think about how we breathe, stop and think about our connections to trees and our connection to the environment as a whole," he says. "While Tu Bishvat is a great holiday and a fun holiday, it's important that we don't let our environmental thoughts end when Tu Bishvat ends. We should let them carry our commitment throughout the year."