Why Poson is considered the second most important event in the Sri Lankan Buddhist calendar 

Poson (Marked on the full moon day in June) is a day of great significance to Sri Lankan Buddhists. It commemorates the day on which Buddhism was introduced to SL from India in BC 306. 
Legend has it that King Devanampiyatissa was out hunting on the Missaka rock in north-eastern Sri Lanka, as was his usual popular pastime. The God in charge of the Missaka Rock changed himself into a deer, crossed the path of the king and started to graze. 

The king who thought that it was not appropriate that he should kill a grazing deer, made a noise to make it run. The deer started to run and the king gave chase to shoot at it. 
It was then that the king heard the call, “Tissa, Tissa.’ He was surprised and looked up to find a saffron-robed monk looking down at him. It was Arahath Mahinda, the son of the emperor of India, who then said “ “O’ great king, the beasts that roam the forest and birds that fly the skies have the same right to this land as you. The land belongs to the people and all other living things, and you are not its owner but only its guardian.”  
The king threw down his bow and arrows, and so did his retinue. Then they sat to listen to the first sermon of Arahath Mahinda, and after listening to the king and his retinue became Buddhists.

So Poson is considered the second most important event in the Buddhist calendar. 
However, I see another significance of this event. It was while the King was hunting and going to kill an animal that he was interrupted by this holy man. The very foundation of Buddhism in Sri Lanka was thus firmly laid, 
when the King’s hunt was disrupted, and in a place, he was converted to Buddhism.
So I think this gives the story an additional important and powerful message about Buddhism and Conservation. True, Buddhist scriptures forbid the killing of any living thing. But the fact that the very moment of the introduction of Buddhism to this country is firmly bonded to the prevention of killing animals, is symbolically very significant. 

The five precepts “pansil pada “The most basic and prime precepts of the Buddhist given to human beings embody the panathipatha veramani sikkhapadamasamadhiyami ” I shall refrain from taking any life of another living being’
Therefore, it is indeed heart wrenching to see this island’s rich tapestry of fauna, being cruelly destroyed daily. In this predominantly Buddhist country, we have seen close upon 350 wild elephants killed last year, many in a gruesome and torturous manner. (ironically the elephant figures very prominently in Buddhist worship and festivals). Every day we hear of the leopards being killed due by snares. Poaching is rampant in several areas, including within wildlife parks and protected areas. 
It is therefore important that some serious self-evaluation has to be done about the very foundation of our beliefs of this great religion.