Check out this remarkable tribute by John Vidal in the Guardian UK, which includes this quote from Maathai spoken in England in the late '80s:
The top of the pyramid is blinded by insatiable appetites backed by scientific knowledge, industrial advancement, the need to acquire, accumulate and over-consume. The rights of those at the bottom are violated every day by those at the top... the economic and political systems are designed to create more numbers, population pressures show no sign of waning, deforestation and desertification continue. The people at the top of the pyramid do not understand the limits to growth and they do not appreciate that they jeopardise the capacity of future generations to meet their own needs.World leaders are sending tributes of their own. Read them here.