tresspasssss
O.k. In history, the king gave you "right" to the land out into the sky--you were keeping it for the king (You did NOT own anything, just on loan from God and God's man, the king...). U.S. did the same until aircraft then they limited it to 7,500 feet or so.
So formerly the person who stood on one side of your land and threw something (a rock???) across so it landed outside your land, STILL TRESPASSED.
First order of business is proof. With the widespread availability of cameras, even in phones, you should have no problem documenting your problem. The more the better. MAKE COPIES. Save in secure place(s). Don't have it all in one place so if your house or shed burns down it is gone! Ohyes, if you wish to go "old fashioned" and set up a camera with a flash so the biker trips the flash and is blinded for a time... poor baby... your land... you were trying to photograph wildlife as in animals... where the biker lands is not your concern. Just call the EMTs and then follow the boob to the hospital (EMT's will get his/her info) so you can bill them for messing up your wildlife set...
b). what do you care to do? You are permitted any lawful use of your land, by law, with proper permits. Now if you "booby trap" the trail... "shame on you." At the same time, if you have the proper permit/permission to store "junk" on your land, or "recyclables"... , say a stack of metal fence posts, or used boards with nails in them... in weeds where they are not easily seen... car bodies... or just frames... loads of gravel (you might even charge the owner rent). grain? ... and "no trespass signs" in the area... The trail on your land is yours and you can do with it as you please, subject to permit... Bikers hit them... tough... In fact you can follow the SOB to the hospital to get their name so you can sue them for damaging or scattering your "recyclables!!!" Bleeding on your used lumber... And as a good citizen, you insist on calling the EMTs/ambulance... The boob might be hurt! EMT's have badges and can compell the person to provide information. You cannot.[This could raise the cost of the insurance on the bike A TON!]
Then there are the sticker plants that put thorns thru the sidewall of modern tires like it isn't there... Ask extension. Say you don't want them messing up your tires when you drive around working on your land. Then find yourself some REAL SIX ply side wall tires. And cactus juice.
THEN, as suggested, you file WRITTEN COMPLAINTS with every legal authority you can think of. States Attorney General down to c ounty attorney and city attorney. (At the same time, you complain loudly to elected officials... don't forget to mention that you will see that this is discussed in the next campaign, unless you are happy with the outcome and forget... "when they feel the heat, they see the light...")
At the same time, this lady who profits "owes" you a share of the money (and if she ends up in the "red" guess what she will do? QUIT!) for the use of your land. Have an attorney send her a bill. Unreasonably large, but then her conduct is unreasonable. (Don't talk about this or your neighbors will too and there will be less for you.)
After a couple bills, threaten to sue. (You didn't think she would pay willingly?) Then sue. You could keep it low enough, each bill, that you can use "small claims court" by yourself. That can be fun. You show the judge pictures and copies of the bill for the use of your land. Cite some state statue law and a couple similar cases. (Finding cases involves visiting a legal library. One in every county seat. For the courts, but if you are patient and ask nicely, often they, WHEN NOT BUSY, will help you. You do pay for it with taxes...) She may well not show up in small claims court. Then put a lein on her land. And in 5 years? 10 years? unpaid, you own the land... (Ask a lawyer.)
Enlist the greenies to whine about all the pollution that she is permitting with all those bikes (2 bangers??? with oil/gas mix???) in the newspapers... She could look like a real WITCH... (any spelling)...
Basically, you make her life more unhappy than yours and she will quit. You don't and she will continue. luck