Maria Theresa of Austria established laws that determined how many trees you have to plant for every cut-down tree. Why?
Did the industry need so many trees because of the industrial revolution?
The industrial revolution obviously had nothing to do with it. Maria Theresa reigned from 1740 to 1780; the Industrial Revolution only began in Britain from around the 1760s and didn't come to Central Europe until much later.
Her laws on forestry were enacted over a period of decades. The measures you cited were clearly motivated by a concern for sustainability, which was a common theme in Habsburg forestry laws at the time.
In 1755, Maria Theresia placed the Viennese Forest into the ownership of the state. Nevertheless, the forest was managed in the same was as before. Forest laws of this time [were published] to avoid, generally, forest destruction and forest devastation.
-Johann, E. "17 Shaping the Landscape: Long-term Effects of the Historical Controversy about the Viennese Forest (Wienerwald)." *The Conservation of Cultural Landscapes (CABI, 2006): 242.
Maria Theresa issued similar laws in both Bohemia and Hungary, For example, her famous ordinances for the Carniola forests in 1771:
The Carniolan forest ordinance issued by the Empress Maria Theresa in 1771, represents a major progress in formal development and practice of sustained forest. Not only does it express a concern for public interest in sustainable forestry, it is also an interesting silvicultural guideline dealing - among other matters - with rejuvenation, reflecting the general spirit of the times.
- News of Forest History, Issue 13-21, 1984
This was by no means a suddenly new development. As early as 1565, Emperor Maximilian issued the landmark Constitutio Maximiliana which attempted to regulate forestry. However, it was under Maria Theresa's rule that population boom and environmental changes necessitated a more concerted effort to conserve and regenerate the forests of the Habsburg domains.
The forestry problem became a really pressing one only in the XVIIIth century, when the draining of the swamps deprived the soil of much of its humidity and the rapid increase of the population was followed by wholesale destruction of forests.
- International Bulletin of Agricultural Law, 1940.
It was the British (and later European) Agricultural Revolution of the 1700s, not the Industrial Revolution, that brought about this result.
The development of new seeding, hoeing, and weeding technologies made it far more possible to grow crops in "marginal" lands such as forests and swamps. The result was that after stagnating for four centuries from 1300-1700 (the Black Death, Hundred Year's War, various wars between the Hapsburgs and France, including the 30 Years' War), Europe's population resumed its growth in the 18th century.
The resulting use of "non-traditional" land for agriculture threatened the survival of the forests. A way to combat this threat was to require the planting of new trees for each one cut down; both "restoration" and a disincentive to cutting down trees.