Dear Chornedsnorkack,
The pool of settlers is a few thousand settlers through 11th century, not yet dozens of thousands.
Welllll, I believe that in order a population boom to occur, there must be a minimum critical mass of population. If it is too little ( like these 4-5 000 Norse acting from their base in Greenland ) the fate of the settlement ( if it is sealed from new immigrants import ) would be the same as in OTL N American Norse. The colony would fade away. I can not estimate how much the "critical mass" must be, but I wild-guess that a ( connected with appropriate transport means, i.e. NOT necessary occuptying single "town" ) "population enough" must comprise at least small 5-figure number. May be 10-15 000 people?
Whatever the "critical mass" X of number of people is ( with proper gender and age distro ) the dynamics of this populaton are two-ways:
1. Under X = comparativelly quick population crunch ( die out ).
OR
2. Over X = exponential growth ( population explosion ).
"My" number of 50-60 000 people "initial investment" is guesstimated to be several times bigger then this hypothetical X.
The realisticity of 50-60 000 people as religious persecution immigrants ( and as a cause for the consequential "seal off" of the Norse N American society from Europe ), finds its support in the Eric's Greenlanders - virtually instant relocation of 4-5 thousand people, on as s.o. wisely noted, purely private basis. With serious reason, organization and funding, to move not 5 000 but 50 000 would be piece of cake.
And most of these a few thousands stay back in Newfoundland.
I do not believe that Newfoundland will remain more than a gateway and commersial hub with the presence of these far far richer lands south and southwest. The Ann'es Medows site shall develop into a city, but it will feed upon its geography - between iron and other things rich Greenland ( which may remain to be the "capital" of the Commonwealth of commonwealths for historical and other reasons... ) and the wood, food, etc. richer south. Initially not more than few thousands of people will remain in Newfoundland - eventually more than 80% of the immigrants / refugees will directly head to the bordertowns of the St. Lawrence-Great Lakes shores and to the Maritimes and New England and even more south Atlantic shoreline places.
The few tens of initial settlers of Montreal settle there BECAUSE the region is not "empty" for them.
Tens with the prep missions of Leif-Bijarni in 985-1001 AD period, and thousands there on waves from the Exodus. Thus up to Niagara falls the river will be dotted with settlements comprising of thousands and thousands of Norse, settling on places which already have been marked, utilized and started during the period between Discovery and Exodus.
They are not after farmland (enough of it back at Newfoundland)
Well, Newfoundland even in this warmer climatic period can not compete in agriculture with the St. Lawrence system lands. There shall be food production on Newfoundland - fish, sheep, goats ... but the more intensive agriculturally ( and thus populationally ) areas will be down south and up-river. ( Specialization in fact will strenghten a lot the Commonwealth - the different places of colonization are "strong" in various aspects which automatically leads to TRADE. Per instance Greenland will export not only the best Lawyers and Justice, and to profit from housing the Allthing, but also products from the native iron of Disko Island, processed with southern fuel - wood and even shallow coal from Maritimes ... )
- their aim is trading with the Indians all around. Who are local hunter-gatherer Montagnais - plus the route up to Great Lakes, and Mississippi culture.
The total native population of locals within the drainage basin of the Great Lakes, i.e. mainly on the shores was 50-60 000 people in OTL 17-18th century. In Newfoundland lived about 5000 in total of Beotuks. The Inuit population of the North ( the area of concern of Greenland and Helluland "governments" ) is in nowadays OTL 150 000 due to recent sharp increase. ITTL 1000 AD Inuit should've been not more than 20 000 people in total from Chukotka to Greenland. SO, what locals? They'll be pretty quickly integrated/absorbed/die out ...
It took the French a few decades before Montreal was populous enough to spare the settlers to send up to lake Ontario. It would take the Norse a few decades, too.
Yes, but French were sending comparativelly few colonists. Their demographic base was an ocean away. ITTL case with 50 000 total influx of which ( realistic ) distro at say ITTL 1020es:
- Greenland - 5000
- Helluland - 2000
- Markland - ( coinciding with OTL French N America of 17-18 cent. ) - 25 000
- Vinland - ( coinciding with OTL British N America of 17-18 cent ) - 25 000
will manage to take control over the territories and explosivelly to expand inland...
I believe given the pagan Icelandic Commonwealth's "anarcho-democratic-capitalism" the colonies multiplication will share 99% of the characteristics of the modes of the OTL
http://en.wikipedia.org/wiki/Colonies_in_antiquity#Greek_colonies.
The mother-of-all-mother-cities ( the Prime Metropolis, grandmother-city ) shall be Greenland's first settlement from 980es. From there on via the first three colonization vectors' points - 1. Newfoundland ( Markland, and up St.Lawrence system -> Great Lakes -> Mississippi, MCKenzee, etc. ), 2. Helluland ( Inuit ), 3. Vinland ( OTL Canadian Maritimes, New Enlgand, and down the Atlantic coast of N America -> Carribean basin... -> the big watersheds of South America ... ) will breed colonies-of-colonies-of-colonies ... in doubling rate coinciding with the population doubling rate ( of say, 20-25 years ).
As in OTL Greek colonization every colony will be formally independent, the colonies will be "anarchistic in the Icelandic way" and will form commonwealth of colonies the way the colonies themselves are commonwealths of their citizens / borgaranna and will have certain hinterland of 3-4 digit number of square miles like per instance the Black sea colonies had such, they did have the notion of polis territory.
Thus we have ( number of colonies ) - ( year AD ):
1 - 982
3 - 985
10 - 1010
25 - 1025
50 - 1050
100 - 1075
200 - 1100
400 - 1125
800 - 1150
1600 - 1175
3200 - 1200
...