Question
QUESTION: I have two nice Lindens - probably 20 years old or more  - and would like to string a hammock between them. Will the strong hook & eye plus the weight cause damage to the trees. The smaller of the two has a trunk with a circumference of about 25 inches.
Thank you.

ANSWER: The weight will not be the problem but drilling into a thin barked tree like the Linden will cause fungi to enter the trunk and decay will over time set in. I would suggest that you use a strap type system for hanging the hammock here is a web link to some of these types.
http://www.hammockstock.com/hammock-hanging-kits/category/421.htm

---------- FOLLOW-UP ----------

QUESTION: Thanks, Jim - that's what I was thinking as I was measuring the tree today (and brings up another question below). But I never thought about a strap system; never seen one before - thank you so much!
my next question: I did notice that the larger of the two Lindens has some round  spots that look like openings (though no holes have ever been drilled) and there is a moist dark orange color there. Any ideas on what to do?

Answer
Sounds like it could be an insect called a borer. These beetles will bore into the trunk and the tree will bleed and a wet area is produced around the wound. I would spray the area with an insecticide called Merit this will kill the insect in the trunk and prevent others from attacking. Borers infest tree under stress so I would fertilize the trees with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered round the tree and watered in good. I would fertilize now and again in the spring. This will increase the health of the trees roots system and the overall health.