Here are a couple of short things I've collected from some newsgroup or mailing list.

HAMMER: Originally employed as a weapon of war, the hammer nowadays is used as a kind of divining rod to locate expensive parts not far from the object we are trying to hit.

MECHANIC'S KNIFE: Used to open and slice through the contents of cardboard cartons delivered to your front door; works particularly well on boxes containing seats and motorcycle jackets.

ELECTRIC HAND DRILL: Normally used for spinning steel Pop rivets in their holes until you die of old age, but it also works great for drilling mounting holes in fenders just above the brake line that goes to the rear wheel.

PLIERS: Used to round off bolt heads.

HACKSAW: One of a family of cutting tools built on the Ouija board principle. It transforms human energy into a crooked, unpredictable motion, and the more you attempt to influence its course, the more dismal your future becomes.

VISE-GRIPS: Used to round off bolt heads. If nothing else is available, they can also be used to transfer intense welding heat to the palm of your hand.

OXYACETELENE TORCH: Used almost entirely for lighting various flammable objects in your garage on fire. Also handy for igniting the grease inside a brake drum you're trying to get the bearing race out of.

WHITWORTH SOCKETS: Once used for working on older British cars and motorcycles, they are now used mainly for impersonating that 9/16 or 1/2 socket you've been searching for the last 15 minutes.

DRILL PRESS: A tall upright machine useful for suddenly snatching flat metal bar stock out of your hands so that it smacks you in the chest and flings your beer across the room, splattering it against that freshly painted part you were drying.

WIRE WHEEL: Cleans rust off old bolts and then throws them somewhere under the workbench with the speed of light. Also removes fingerprint whorls and hard-earned guitar callouses in about the time it takes you to say, "Ouc...."

HYDRAULIC FLOOR JACK: Used for lowering a motorcycle to the ground after you have installed your new front disk brake setup, trapping the jack handle firmly under the front fender.

EIGHT-FOOT LONG DOUGLAS FIR 2X4: Used for levering a motorcycle upward off a hydraulic jack.

TWEEZERS: A tool for removing wood splinters.

PHONE: Tool for calling your neighbor to see if he has another hydraulic floor jack.

SNAP-ON GASKET SCRAPER: Theoretically useful as a sandwich tool for spreading mayonnaise; used mainly for getting dog-doo off your boot.

E-Z OUT BOLT AND STUD EXTRACTOR: A tool that snaps off in bolt holes and is ten times harder than any known drill bit.

TIMING LIGHT: A stroboscopic instrument for illuminating grease buildup.

TWO-TON HYDRAULIC ENGINE HOIST: A handy tool for testing the tensile strength of ground straps and brake lines you may have forgotten to disconnect.

CRAFTSMAN 1/2 x 16-INCH SCREWDRIVER: A large motor mount prying tool that inexplicably has an accurately machined screwdriver tip on the end without the handle.

BATTERY ELECTROLYTE TESTER: A handy tool for transferring sulfuric acid from a car battery to the inside of your toolbox after determining that your battery is dead as a doornail, just as you thought.

AVIATION METAL SNIPS: See hacksaw.

TROUBLE LIGHT: The mechanic's own tanning booth. Sometimes called a drop light, it is a good source of vitamin D, "the sunshine vitamin," which is not otherwise found under motorcycles at night. Health benefits aside, its main purpose is to consume 40-watt light bulbs at about the same rate that 105-mm howitzer shells might be used during, say, the first few hours of the Battle of the Bulge. More often dark than light, its name is somewhat misleading.

PHILLIPS SCREWDRIVER: Normally used to stab the lids of old-style paper-and-tin oil cans and splash oil on your shirt; can also be used, as the name implies, to round off Phillips screw heads.

AIR COMPRESSOR: A machine that takes energy produced in a coal-burning power plant 200 miles away and transforms it into compressed air that travels by hose to a Chicago Pneumatic impact wrench that grips rusty bolts last tightened 60 years ago by someone in Springfield, and rounds them off.

PRY BAR: A tool used to crumple the metal surrounding that clip or bracket you needed to remove in order to replace a 50 cent part.

HOSE CUTTER: A tool used to cut hoses 1/2 inch too short.

I think it has to do with the existence or lack thereof, of protruding appendages. If a given tree can disperse it's magnetic field through protuberant extremities (branches) then the need for a concentrated captivating force (the trunk) is lessened. The need for this concentration of magnetism is also diminished by the proximity of sufficiently sized mineralized deposits (rock) which may act as an auxiliary steering device helping to focus the incoming projectile (your bike) towards the center of attraction. The current trend towards increased use of non-ferruginous metallic alloys and thermoplastic resins tends to augment the attractive properties of cellulose based organisms rather than to diminish them.

As for documentation of this force: it HAS been documented (it's called "a ride in the woods") that a tree (or sufficient mass of rock) has the ability to remain stationary while exerting enough external force to make the world around it move. Einstein's theory of relativity comes in to play here, as it doesn't really matter which object moves, the fact remains that convergence in eminent!