Why are more particles showing in the render than in the viewport? There is quite a difference between the 3D View and the render. In the viewport there are a few palm trees but when I hit 'Render' I can see a huge amount of trees that looks like a forest. I have no children setting activated.

Blend File (Palm Trees)

3D viewport:



Render: 



Any solution as to what's going on and why there are so many particles (trees) shown?
Your particle system is set to only show 10% of the total particles. 

In the 'Display' panel of the particle system change the 'Display Percentage' to 100%:



This will display all the particles in the viewport.