Spanish term (edited): se constituye en la base de información cartográfica de la vegetación (en el país)

I fully agree with Charles’ interpretation of “se constituye en” as “forms” or “becomes” or “constitutes”, but I think it would be more natural to simply say that it “is” in English.

My interpretation of “base” in the sentence you’re asking about is “foundation”, which, after careful consideration, I feel could be rendered as “main source” for the purposes of that sentence. It would certainly make it clearer. However, I would translate “base de información” simply as “database” as it appears at the start of the passage (see below).

I also found from my research that “vegetation mapping data” is very commonly used in English, and I think this would cover “información cartográfica de la vegetación” nicely.

The US Geological Survey uses it:

“Several vegetation related studies are under way at Acadia National Park that will use the USGS-NPS vegetation mapping data. Objectives of these studies include determination of the threat to Park ecosystems by invasive non-native plants, the development of a rare plant monitoring program, and the current and future distributions of pitch and Jack pine (Pinus rigida, Pinus banksiana) in Maine.”
http://www.usgs.gov/core_science_systems/csas/vip/products_a...

As does the Department of Environment, Water and Natural Resources of the Government of South Australia:

“Native vegetation maps are continuously updated when additional data, error corrections and new data analysis based on emerging technologies become available.
Native Vegetation Mapping Data is available within NatureMaps, DEWNR's online mapping site.”
http://tinyurl.com/cfm6f5g

And there are many more examples of usage out there: http://tinyurl.com/ca9flbd

My suggestions are based on my understanding of the passage:

“Como base de información de carácter nacional, CONAF administra desde el año 1993 el Catastro de los Recursos Vegetacionales Nativos de Chile, destinando a la fecha un presupuesto que bordea los US$3 millones. Este catastro se constituye en la base de información cartográfica de la vegetación en el país y se configura como el soporte para toda acción de Niveles de Referencia y...”

“CONAF has managed the Cadastre of Chile’s Native Vegetation Resources in a national database since 1993, allocating a budget of some US$3 million to it to date. This cadastre is the country’s main source of vegetation mapping data and is designed to support all Reference Level actions and...”
___________________

Hope this helps :)