In my QTH, in a forest at about 1000 meter up the see level, I can assure that vertical  is not the best  performing antenna. I did two main experiments. I started with Butternut for 40/80 meter and I increased the ground system with 10 radials, 25 meter long.But the inverted Vee dipole at 27 meters was performing better in receiving and , for sure, in transmitting. The other vertical I used was with my aluminium tower.

I made it resonant, shunt feeded.The tower had on top monobander for 10-15-20 and was 30 meter high (top of the mast).As grounding system I put on terrain about 1 km of radials, distributed as 40 radials of 25 meter long.I used a wide grounding cable as resonant hot wire, and the distance length from tower has been achieved with PVC tube used to set-up electric system.The ON4UN low band dxing and the Antenna Book tuning procedure have been used as reference and I can assure that I found the description valid. 

Tuning was long and boring but at the end the result was the same: the inverted Vee dipole at 27 meters was performing better in receiving and , for sure, in transmitting, switch and report form Dxer at end.

The Low band dxing explains clearly my situation in the chapter 8 and 9.  

(Chapter 9, tnx ON4UN)......What about trees closer in? Trees can be reasonably good conductors and can be very lossy elements in the near field of a radiator. A case has been reported in the literature where a λ/4 vertical with an excellent ground system showed a much lower radiation resistance than expected. It was found that trees in the immediate area were coupling heavily with the vertical and were causing the radiation resistance of the vertical to be very low. Under such circumstances of uncontrolled coupling into very lossy elements, far from optimum performance can be expected. Of course, if the trees are short in relation to the quarter wavelength, it is reasonable to assume that the result of such coupling will be minimal. Even though neighboring (lossy) structures such as trees may not be resonant, they will always absorb some RF to an unknown degree. Other objects that are likely to affect the performance of a vertical are nearby antennas and towers. Mutual coupling can be considered the culprit if the radiation resistance of the vertical is lower than expected.  

(Chapter 8, tnx ON4UN) We can conclude that the effects of absorption over poor ground are pronounced with low horizontally polarized antennas and become less pronounced as the antenna height is increased. Artificial improvement of the ground conditions by the installation of ground wires is only practical if one wants maximum gain at a 90°-wave angle (zenith) from a low dipole (1/8 to 1/4 λ height). This can be done by burying a number of wires (1/2 to 1 λ long) underneath the dipole, spaced about 60 cm apart, or by installing a parasitic reflector wire (1/2 λ long plus 5%) just above ground (2 meters high) under the dipole. Improving the efficiency of the reflecting ground for low-angle signals produced by high horizontal dipoles is impractical and yields very little benefit. The active reflection area can be as far as 10 or more wavelengths away from the antenna! Horizontal dipoles, unlike verticals, do not suffer to a great extent from poor ground conditions. The reason is that for horizontally polarized signals, when reflected by the ground, the phase shift remains almost constant at 180° (within 25°), whatever the incident angle of reflection (equal to the wave angle) may be. For verticals, the phase angle varies between 0° and 180°. For vertical antennas, the pseudo-Brewster angle is defined as the angle at which the phase shift at reflection is 90°. This means that there is no pseudo-Brewster angle with horizontally polarized antennas such as a dipole, because there never will be a 90° phase shift at the reflection point.

The effects are proved daily by the fact that on the low bands big signals from areas with poor ground conditions (mountainous, desert, etc) are always generated by horizontal antennas, while from areas with fertile, good RF ground, we often hear big signals from verticals and arrays made of verticals.