The question is asking in which region you would typically find open, stunted forests that include bushes and small trees, known for their long roots and sharp thorns or spines.

Option 1, Eastern Orissa, is generally quite lush and receives sufficient rainfall, making it unsuitable for such vegetation.

Option 2 implies the North-Eastern part of Tamil Nadu. This region is known for its more tropical forests and would not foster the growth of such types of vegetation.

Option 3, the Siwaliks and Terai region, lies in the foothills of the Himalayas. It is known for its high rainfall and dense forests, and does not contain the described vegetation.

Option 4, Western Andhra Pradesh, is indeed the right answer. This region is characterized by a drier, arid climate which is suitable for open and stunted forests with bushes and small trees having long roots. The sharp thorns or spines are a typical adaptation to prevent water loss in such arid conditions.