I own a Case 1550 dozer. It's 170hp and weighs 40,000 pounds. If my soil is wet, as it is in Spring, I can pop 12 to 18 inch pines out of the ground fairly easily. If the soil is dry and hard, I struggle getting 6 inch stumps out of the ground. Stumps are ten times harder to get out then full sized trees. I also tear up the ground something crazy, and it usually takes more time to fix all the damage the ground then it takes to get the tree out. I've learned that it is faster and easier to just dig the entire tree out with my backhoe. An excavator would be even better at digging out trees or stumps.
With all equipment, HP is what you need to look at first. I learned on a 80 hp John Deere 450G that was fun and easy to operate, but too light for clearing the land. It's great for building house pads and spreading materials, but if the ground is hard, it's not very good at digging. My backhoe is 80 hp and I can take out any sized tree with it. Biggest have been close to four feet thick at the trunk. Pines are about the hardest to get out because of how deep their pat root runs. I would think that an 8 tonne excavator would be close to the same in digging ability as my full sized backhoe, but better because it's on tracks and it can spin 360 degrees.
The dozer in your picture would be fun as a toy, maybe most some light material with it, but never to be relied on to do any work.
