Glider pilot reported they lost control of the aircraft during landing resulting in a ground loop and runway excursion.

Narrative

On returning to my home field from a recreational glider flight; I was established on a stable final for Runway XX at 50 knots; wings level with partial dive brakes and comfortable clearance of trees assured but without excessive altitude. For practice I decided to do a short field approach; with a forward slip to land; something I practice often. After clearing the last set of trees between me and the runway and just south of tall trees along the upwind side of the approach; I entered a forward slip to the right. Right rudder; nose into the cross wind; and left stick; wings level maintaining the pre slip pitch attitude. I was immediately surprised and shocked by the a very rapid rate of descent; beyond anything I had ever experienced in any plane; so kicked left rudder to get out of the slip while maintaining the same pitch attitude. I don't recall if I closed spoilers. At that point my entire focus was on arresting the very uncomfortably fast descent by getting the plane out of the slip and back to a normal straight flying attitude. Details are blurry but I recall a touchdown then shortly after that being spun around to the left ground looping in tall grass. The plane came to rest after having having turned 225 degrees to the left ending on a heading of approximately 035 degres. Runway is XX/YY. The nearest Metar from ZZZ1 was reporting 310 at 7G14.I suspect the unusually rapid descent; bottom falling out; on final was due to a combination of the forward slip; partial dive brakes; and turbulence and downdraft caused by the wind from over trees on the northside upwind side of the 26 threshold. I've experienced a surprising descent at that location before but never as abruptly or severely. I will never forget that image of the ground racing up to meet me and am very glad to have been able to walk away from that landing and with only minor damage to the glider. I believe the one significant mistake I made was underestimating the effect of winds from 310 coming over the tall trees 80-100 ft. next to Runway XX. I've since recommended that when winds are from the NW and significant; we brief all pilots to the hazard and plan to come in higher on final until past the parallel trees.