One of the reasons for a traffic drop can also be due to your site losing links. You may be seeing a direct loss of that referral traffic, but there could also be indirect effects. When your site loses inbound links, it tells Google that your site isn't as authoritative anymore, which leads to lower search rankings that in turn lead to traffic drops (because fewer people are finding your site if it's not ranked as highly and more).
So much traffic sources here, that I have not even come across. While there are the "most popular" ones, half of the sites you mentioned here are relatively new to me, so they all will be worth checking out. You are right about "forums" though, and although I am basically stuck with two (warrior and another that is unrelated), it does provide you some traffic provided as always, that you provide good feedback, help people, engage effectively with the community and of course, having a good and well structured signature :) Finally published :) Hopefully on your way to 300+ RTs, LOL

The first step to digging into organic traffic is to analyze what content on your website is performing best in this area. For obvious reasons, the homepage is almost certainly the landing page for most organic traffic, but the other top pages are often revealing. To view this data, we’re going to head over to the Behaviour section in the Analytics sidebar, then choose Site Content and finally Landing Pages.
To find the right people I downloaded a list of some of the most popular users within the community. To do this, I used Screaming Frog SEO Spider to gather a list of all the URLs on the website. I then exported this list into an Excel spreadsheet and filtered the URLs to only show those that were user profile pages. I could do this because all of the profile pages had /user/ within the URL.
At our agency, we work with sites of varying sizes, from very large to quite small, and recently, we have noticed a trend at the enterprise level. These sites aren’t relying as much on Google for traffic any more. Not only are they not relying on Google traffic, but also, the sites are getting less than 10 percent (or slightly more) of their organic traffic from the search giant.
For a long time, digital marketers summed up the properties of direct and organic traffic pretty similarly and simply. To most, organic traffic consists of visits from search engines, while direct traffic is made up of visits from people entering your company URL into their browser. This explanation, however, is too simplified and leaves most digital marketers short-handed when it comes to completely understanding and gaining insights from web traffic, especially organic and direct sources.