Question asked:
Can you explain how the rating system works? How would someone get more stars, leafs, twigs...?

The system is designed by the amount of activity (posts) on the site.  Kinda like, your experience here.
[table]
[tr]
[td]Total posts              [/td]
[td]Stars displayed              [/td]
[td]Membergroup[/td]
[/tr]
[tr]
[td]00          [/td]
[td]1 [Image Can Not Be Found][/td]
[td]Bud[/td]
[/tr]
[tr]
[td]01[/td]
[td]1 [Image Can Not Be Found][/td]
[td]Leaf[/td]
[/tr]
[tr]
[td]50[/td]
[td]2 [Image Can Not Be Found][Image Can Not Be Found][/td]
[td]Twig[/td]
[/tr]
[tr]
[td]100[/td]
[td]2 [Image Can Not Be Found][Image Can Not Be Found][/td]
[td]Branch[/td]
[/tr]
[tr]
[td]250[/td]
[td]3 [Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][/td]
[td]Limb[/td]
[/tr]
[tr]
[td]500[/td]
[td]3 [Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][/td]
[td]Trunk[/td]
[/tr]
[tr]
[td]750[/td]
[td]4 [Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][/td]
[td]Roots[/td]
[/tr]
[tr]
[td]1000[/td]
[td]5 [Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][Image Can Not Be Found][/td]
[td] :-X[/td]
[/tr]
[/table]

It is common for members to join a forum and never post.  Members who aren't logged on for a period of time (maybe 6 months or 1 year) with no posts will be purged so we aren't representing our membership count inflated.