For a sport that has its roots in the community of Yosemite climbers, and was spread to Europe by other climbers that had visited that same valley, it is easy to understand why this sport was, and continues to be, dominated by men. This is because slacklining was since the beginning connected to climbing, and basically the only way for it to reach other people was by the "passing the word" method, and since climbing has always been dominated by men, specially in fanatic zones like the Yosemite Valley, one understands that the tendency was that the same would happen to slackline.
Eventually, the sport became commercial, specially with tricklining. And with that came publicity, allowing a wider and not so male centered spread of this sport. More and more we see athletes coming from all kinds of other sports, like gymnastics, outdoor sports like, skating, bmx, inline skates, etc. One of the most known figures in this sport is the athlete Cihan Calis , famous for having created his own tricklining style called "Gambit", in wich one can see the traces of breakdancing.
The result of this spread of the sport is noticeable, today there are female slackliners at a very high level, just look at the Brazilian Giovanna Petrucci, a phenomenal trickliner that is at the same level as some of the best male trickliners in the world, as well as other very good trickliners, like Ellie Schulte, Melissa Bowe, and more.
But the scales are still unbalanced, specially in highlining. And it is there that we start talking about a well know person in highlining, Faith Dickey, holder of 5 feminine world records, with an immense repertoire of walked and estabilished highlines, and one of the few pro athletes in this sport actually. Faith is also the organizer of the annual event called "Girls only Slackline Festival", wich is already in its 4th edition, whoose objective is to provide to all female slackliners around the world the opportunity to highline in the company of other women without any man around. This project, that came to life when Faith felt the need to create a special atmosphere for women, and after she heard some women expressing feeling intimidated by the ammount of men in the sport, their high level energy at the lines and the loud atmosphere the often encountered, has been a success, and an excellent mean to bring more women into this branch of the sport.
With this said, I am sure that we will start to see more and more women slacklining in the park, discovering the pleasures of this wonderful sport, and understanding that slackline can be done by anyone, no matter what sex, age, weight, and even previous history in sports that person has, it is a sport compatible to anyone.