I have a point to point of 5Km, with 1Km of bigs trees (Eucalyptus and anothers)
no line of sight, so in one side put a horizontal polarization sectorial anntena 180° 16db, and another side put 27db horizontal polarization directional anntena, with a power of 400mW (ubiquiti) in 16db point, and 65mW (Realtek generic) on 27db point. I know this link is a problem be cause the fresnel zone is committed, but want to know if increasing power in 65mW point to 200mW, link will be better or no...

you must find a "tunnel" or if u would use directional antennas on both sides, but link will be unstable, 900Mhz may help

Yes, direcctional on both sides help, but need sectorial... here some pics. (There don't exist any tunnel )

From you pictures I take it you have a point to multipoint setup. One of the multipoints is the distant radio you want to reach through trees?
Your AP radio gets signals from both relative close clients and one distant.
Since the signal of the distant radio is already scattered by the trees it will loose competition for AP's radio attention against the closer radio's. And when it has the signal is bad and scattered.
Increasing radio output on the distant won´t help you a lot. The signal will still be scattered. And by increasing power on one end only the receipt on the other end will increase. You need to increase power on both ends. Reciept on the end where the output power is increased stays the same unless the 'other side' also has hihget output (Remember both AP and client radio's switch from transmitting to recieving mode continuesly to ´talk´ to each other. So both are transmitting!
Three possible solutions:
1. Change frequency for better penetration, 900Mhz can be a help.
2. Use higher towers to surpass the trees.
3. Use a extra (repeater) radio in between that can ´see´ both others.

I did it!, set each distant point at 200mW and works fine everything. The signal is -75 vary at -80, but not loss packets.