You curse the creature touched such that it carries an aura detectable by any creature in tune with nature - animals, druids, rangers, elementals, and so on. The victim of the curse has a -6 circumstance penalty to Charisma when interacting with such creatures. Additionally, the victim will encounter hostile creatures twice as often as would be normal when he travels outside civilized areas *cities, towns, farms, keeps, and so on).
Further, the victim faces a +5 DC circumstance penalty to all skill checks while outside civilized areas. The penalty doesn't simply manifest as if skill use is harder - the penalty is imposed due to active resistance from the forces of nature. Attempts to start a campfire are hindered because the firewood refuses to burn. If the subject is tracking, the traces he is following fade away.
Syfa's exile from nature may be removed through remove curse by a caster whose caster level is equal to or higher than the caster level of the druid who bestowed the curse. The curse can also be lifted if the victim atones for the crimes that called such a punishment upon him. This requires a druid to cast atonement upon the subject.