With reference to Open Natural Ecosystems (ONEs) in India, consider the following statements:
- Naturally occurring grasslands can exist without having resulted from deforestation.
- Open Natural Ecosystems may include savannas, grasslands, alpine meadows and saline landscapes.
- Low tree cover necessarily indicates that an ecosystem is degraded.
- Excessive tree plantation in naturally open ecosystems can alter their ecological characteristics.
Which of the statements given above are correct?