It’s 100% chemical change. The differentiating factor for Chemical change is that it will always and always forms a new substance whereas physical changes never does that.
So when you are burning leaves it is basically making the carbon present in it to react with oxygen. So you are forming a new substance that’s carbon dioxide and hence its a chemical change.
You might take into consideration whether or not it’s reversible. But keep it mind it’s not always true. There are many chemical reactions which are reversible. So always look for “New substances being formed” to decide if it’s physical or chemical changes.
