This is the 15102nd most frequent German word.
starker
"Starker" means "stronger" in English.
In this sentence, "starken" (a form of "stark") is an adjective describing the noun "Baum" (tree), meaning it is strong or sturdy.
Ich sehe einen starken Baum im Park.
I see a strong tree in the park.
Here, "starken" is used to describe the noun "Willen" (will), indicating determination or resilience.
Er hat einen starken Willen, Probleme zu lösen.
He has a strong will to solve problems.
"Stärker" in this case is the comparative form of "stark", used to show improvement or increase in strength in comparison to her earlier state.