The people of the Pine Ridge Indian Reservation are no strangers to hardship or to the risk of lives being cut short. But a string of seven suicides by teenagers in recent months has shaken this impoverished Midwestern U.S. community to its core and sent school and tribal leaders on an urgent mission to stop the deaths.

On Dec. 12, a 14-year-old boy hanged himself at his home on the reservation, a sprawling expanse of badlands on the border between the states of South Dakota and Nebraska. On Christmas Day, a 15-year-old girl was found dead, followed weeks later by a high school cheerleader. Two more teenagers took their lives in February and two more in March, along with several more attempts. The youngest to die was 12.

Somewhere between 16,000 and 40,000 members of the Oglala Sioux Tribe live on the reservation, which at over 2 million acres (nearly 1 million hectares) is among the largest in the U.S. Famous as the site of the Wounded Knee massacre, in which the U.S. Army slaughtered about 300 tribe members in 1890, it includes the county with the highest poverty rate in the U.S., and some of the worst rates of alcoholism and drug abuse, violence and unemployment. Life expectancy for men is below 50 years, the lowest in the Western Hemisphere.

Suicide has been a persistent problem, say tribal officials.

Students at the reservation's high school and middle school grades have been posting Facebook messages wondering who might be next, with some even seeming to encourage new attempts by hanging nooses near homes. Worried parents recently met at a community hall to discuss what's happening. And the U.S. Public Health Service has dispatched teams of mental health counselors to talk to students.

"The situation has turned into an epidemic," said Thomas Poor Bear, vice president of the tribe, whose 24-year-old niece was among two adults who also committed suicide this winter. "There are a lot of reasons behind it. The bullying at schools, the high unemployment rate. Parents need to discipline the children."

Most people on the reservation live in clusters of mobile homes, some so dilapidated that the insulation is visible from outside. At night, trailers are surrounded by seven or eight rusting cars, not because someone is hosting a party, but because 20 or 25 people live inside. Horses wander on the seemingly endless pastures, some with their rib bones showing.

Nearly 1,000 suicide attempts were recorded on the reservation between 2004 and 2013. Few weeks go by without a suicide, said Yvonne "Tiny" DeCory, a suicide-prevention outreach worker at Pine Ridge.

But the teenagers' deaths are especially shattering.

"Why so young?" she said. "Why do these kids think there is no hope? Well, look around," DeCory, who has worked on the reservation for almost 30 years.

Federal experts say that some reservation children experience a form of post-traumatic stress from exposure to family turmoil. The symptoms are comparable to those of military veterans returning from war zones.

Friends of Alanie Martin, a 14-year-old who hanged herself on Jan. 31, are still trying to understand her death. The cheerleader at Pine Ridge High School traveled to basketball games and, by various accounts, had lots of friends and was all smiles.

"She was very active. She knew everybody," Ieisha Lefthand, 17, said choking back tears.

In February, Poor Bear said, a parent came to him with an alarming Facebook post: Nooses hanging in trees near Porcupine, a community of about 1,000 people. Tribal police later took down four nooses, apparently left there as an invitation, but could not determine who was responsible.

"A lot of the older teenagers are encouraging the younger ones on Facebook, leaving messages that say you know, 'You need to end your life and go to a different life,' and that's encouraging them to go commit suicide," Poor Bear said.

At the community meeting, many parents said the causes of the suicides included the decimation of their Oglala Lakota culture. The Sioux were forced onto the reservation in 1868. Tribal members for years were steered into boarding schools where only English was allowed. Religious ceremonies were discouraged.

After the tribe appealed for help in February, volunteer federal mental health professionals began two-week rotations at the reservation to supplement the nine full-time counselors at the Indian Health Service hospital who were overwhelmed. They encourage students to come forward if a friend is considering suicide.

Teachers recently foiled a plan by several high school girls to take their lives simultaneously.