1. In the years that are to come,all trees in this forest will disappear if nothing is done to protect them

=>In the years to come all the trees will disappear if nothing is done to protect them.

2. They couldn't find a way that may help clean the polluted river

=>2. They couldn't find a way to clean the polluted river

3.The governments of many countries are discussing methods that can protect the environment

=> The governments of many countries are discussing methods to protect the environment

4. During a boat tour along the canals,tourists can see the birds are searching for food or the cranes are flying in flocks

=>
1. In the years coming all trees in this forest will disappear if nothing is done to protect them. 
2. The couldn't find a way to help clean the polluted river. 
3. The governments of many countries are discussing methods to protect the environment. 
4. During a boat tour along the canals,tourists can see the birds searching for food or the cranes flying in flocks.