Sería bueno que se empezara a ... y endurecer

Hola Ελισάβετ 

You can of course continue the second sentence with the same structure:

y se endureciera....., because, as you said, it is a continuation of the first statement: Sería bueno que... We will add this option to that part.

We left it as an infinitive sentence because you could also have gone for a combination of the subjunctive in the first sentence and the infinitive in the second:

Sería bueno que se empezara a limpiar los montes

y [sería bueno] endurecer la ley.

We try to admit all possible interpretations whenever possible and when the English given is open to different options in Spanish. 

Saludos

Inma