I think at this point it is pretty clear that the dramatic population decline in Europe (started late 20th century but has accelerated since the 60s) is not something that can be solved by money nor does it seem to have to do with life style choices (the first and second world war did not do much to change the overall trend[1]).

One fascinating book I read a couple of years ago compared Western European nations with each other vs the "European counterparts that settled America", i.e. the Caucasians in North America. It's interesting that in this particular comparison America (main difference: less social welfare, more individualism, more religion) still has the highest of all ethnic Caucasian birthrates approx. 2.4 [2]

One economist's work that is very interesting to follow on this topic is Gunnar Heinsohn[3] who publishes his findings in intriguing essays usually backed by a lot of statistics and numbers.

But back to the article: the whole topic raises a couple of important fundamental questions:
What do you mean by "Germany's" birth rate plummeting? The population overall, of course, has been steady for the most part and was recently admitted publicly by the ministry of federal statistics (a few years back) [4] Germany itself will be a majority Muslim country by 2050. So the population itself will probably not change or not much, it will rather turn into a different cultural entity, one with a small and shrinking "original" ethnic group (similar to the Japanese, for instance) but being replaced by a (mainly) Turkish/Middle Eastern cultural group that will incorporate their own beliefs and traditions into the aging German society and probably eventually dominate it (it is, after all, just a number's game).
It's also not really a workforce problem as the article alluded - some here have already pointed out increases in productivity and automation that might offset these issues. The whole notion of population decline is inherently a cultural/ethnic question IMHO - even if a desire to shrink the population to improve the quality of life is your goal and immigrant birth rates fall over time: the fact of the matter remains this that you might be looking at a new "Voelkerwanderung" and all that comes with it.

Personal anecdote: I used to work for an IT company in Germany about 10 years ago - I had roughly 40 co-workers in an age-range of 20 to 40 (I was 25 at that time). I was the only one with 2 kids - nobody else had kids! Zero. My colleges had dogs, cars, expensive vacations and lived for the most part in those parts of town that shielded them nicely from the mass immigration taking place in what they called "(immigrant) ghettos". The life style benefits were non-negotiable for most of them but left not much for kids either (taxation is tough if you have to fund healthcare and mass immigration :-). The girls were brought up to loathe the idea of being a mother (and all the single mothers at the edge of society were an effective warning sign). So they were all headed for their careers, making it near impossible to have their first child before the age of 30-35. Not much time left after that. The climate in the bigger German cities that attract all those young and bright Germans looking for work is quite detrimental to raising children as well: very often our experience was that kids were seen as nuisance (in the US we had quite the opposite experience which might be one reason for the difference in birth rates - the US provides (in many emotional daily interactions) a way more supportive place to raise children than Western Europe).

At this point, sadly, it seems to me that population growth is linked to (a lack of) education and / or religious indoctrination. It does not seem to make much of a difference when some European countries pump millions into their social projects to support families (Sweden, France) or when they do not (Germany, Britain) - the birth rate decline is almost the same for all of these countries (again, I am talking native population, not immigrants) [5].

Conclusion: Religion might be one(?) way that natural selection ensures a population's continued growth - I like to be proven wrong, but I can't think of a nation where the growth rate is high and Atheism and Enlightenment reigns the day. A positive outcome would be a gently declining population overall on planet Earth that becomes supported by automation and a growing population on Mars while leaving violent fanaticism in the past...

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[1] http://www.trykkefrihed.dk/interview-a-continent-of-losers.h... (could not find a better one, but there are numerous essays describing his theory of "youth bulge" on the web
[2] http://www.pop.org/content/fertility-decline-in-western-euro...
[3] http://en.wikipedia.org/wiki/Gunnar_Heinsohn
[4] http://www.lifesitenews.com/news/german-population-plunge-ir...
[5] http://www.pewforum.org/files/2012/07/MDII-graphics-webready...