Direct traffic can encompass a wide range of sources, including those you would have liked to have tracked in analytics. A drop in traffic from a particular source does not necessarily mean a drop in traffic. It could indicate a case in which that source ended up being categorized under Direct traffic. The best advice is - proactively use tracking parameters in cases where you may be risking not properly seeing traffic. There is actually a nice infographic showing the main factors impacting traffic. I use it sometimes to solve the current issues. Taking the right steps to address potentially miscategorized traffic, as well as being upfront with clients about the causes, can help to mitigate problems.
Yahoo Answers is one of my favorite traffic generation sources when it comes to answer sites. It has been one of my main traffic sources on a niche site for a long time, even after I haven’t used it for months. The main thing is to give your best when answering. If your answers are chosen as the best ones, you will have more respect in the eyes of the visitors so… yes, more of them will come to check out your blog.

The Google, Yahoo!, and Bing search engines insert advertising on their search results pages. The ads are designed to look similar to the search results, though different enough for readers to distinguish between ads and actual results. This is done with various differences in background, text, link colors, and/or placement on the page. However, the appearance of ads on all major search engines is so similar to genuine search results that a majority of search engine users cannot effectively distinguish between the two.[1]
And although has way more links than its competitor, it seems that is performing better for a lot of important keywords. Why, you might wonder. Well, the answer is simple: content. And although they are both offering good content, is a site offering general information about a lot of things while offers articles highly related to the topics, leaving the impression that this site really offers reliable content. We are not saying that the 5 mil links has do not matter, yet it seems that in some cases content weighs more.
Google claims their users click (organic) search results more often than ads, essentially rebutting the research cited above. A 2012 Google study found that 81% of ad impressions and 66% of ad clicks happen when there is no associated organic search result on the first page.[2] Research has shown that searchers may have a bias against ads, unless the ads are relevant to the searcher's need or intent [3]

If you publish whitepapers or offer downloadable PDF guides, for example, you should be tagging the embedded hyperlinks with UTM campaign parameters. You’d never even contemplate launching an email marketing campaign without campaign tracking (I hope), so why would you distribute any other kind of freebie without similarly tracking its success? In some ways this is even more important, since these kinds of downloadables often have a longevity not seen in a single email campaign. Here’s an example of a properly tagged URL which we would embed as a link:
The most common way a user can arrive at your website is by typing the URL into the address bar. This is known as direct traffic. Your visitor arrives directly without coming from anywhere else on the web. Other forms of direct traffic include clicking on a bookmark, or links from documents that don’t include tracking variables (such as PDFs or Word documents).

When a user follows a link on a secure (HTTPS) page to a non-secure (HTTP) page, no referrer data is passed, meaning the session appears as direct traffic instead of as a referral. Note that this is intended behavior. It’s part of how the secure protocol was designed, and it does not affect other scenarios: HTTP to HTTP, HTTPS to HTTPS, and even HTTP to HTTPS all pass referrer data.
Secure (https) to non-secure sites (http): Since Google began emphasizing the importance of having a secure site, more websites are securely hosted, as indicated by the “https” in their URLs. Per the security protocol, however, any traffic going from a secure site to a non-secure site will not pass referral information. For this issue, you can correct by updating your site to be secure through a third-party SSL certificate.