The solution is pretty simple and consists in cutting along the veins of the wood, in this way: it cracks open very quickly.
Then prying open the first crack it's cut really effortlessly!
Keep doing the same procedure...
...until you end up with lots of manageable sticks that now can be chopped sideways or even broken by hand!
I was very proud of myself when I learnt this simple trick as it helped me a lot on my biomass chopping duties. It works on round and really chunky pieces, until of course you reach the maximum opening of your scissors and your hand cannot make it anymore. Try it out!