THE INSTRUCTOR (CFI) WAS PROVIDING TAKEOFF & LANDING INSTRUCTIONS TO HIS SON, A STUDENT PLT. AFTER MAKING A TAKEOFF & LANDING, THEY TOOK OFF AGAIN ON RWY 22. AT LIFT-OFF, THE CFI NOTICED A CESSNA 180 BEING TAXIED FOR TAKEOFF. AT APRX 300 FT AGL, THEY MADE A RIGHT TURN-AROUND, SO AS TO PASS OVER THE ARPT AT MIDFIELD TO KEEP THE CESSNA 180 IN SITE. THE CESSNA 180 REMAINED IN THE RUN-UP AREA, SO THE STUDENT TURNED TO PARALLEL A RIDGE LINE THAT ANGLED TOWARD THE RWY CENTERLINE & EXTENDED BEYOND THE APPROACH END OF RWY 22. WHILE THE CFI WAS LOOKING OVER HIS LEFT SHOULDER TO MONITOR THE POSITION OF THE CESSNA, HE ASKED THE STUDENT TO TURN TO THE RIGHT, BACK TO THE RWY. THIS TURN WAS BACK TOWARD THE RIDGE LINE WHICH ROSE 150 TO 200 FT ABOVE THEIR ALTITUDE. WHEN THE CFI REALIZED THE PROXIMITY OF THE HILL, HE TOOK CONTROL TO PREVENT THE STUDENT FROM STALLING THE ACFT, BUT WAS UNABLE TO CLEAR OVER TREES. THE ACFT STRUCK BRANCHES & BLACKBERRY BUSHES, THEN AFTER TOUCHDOWN, COLLIDED WITH A TREE.