How does body language play a key role in effective leadership communication?

It doesn't.

Body language frequently plays no role whatsoever in leadership communication.  Some leadership roles exist only (or almost only) online or by telephone: there is no body language.

Some people study body language in order to use it better, but they usually end up behaving slightly weirdly.  This is because body language is a complex mixture of unconscious acts which are nearly impossible to replicate deliberately. 

Leadership and communication are both a mixture of complex things, and are specific to the situation.  There is nothing which has a "key role" in general.   (A particular thing, such as body language, may have a key role in a particular case.)  If there was a thing which had a general key role, it would probably be words. 

Body language carry out messages depends on the situation. There are instances where body language can help the leader to demonstrate or to give conviction on his word; other instances is body language can be used as a type of communication but sometimes leads to confusion of audiences. We cannot say its a key role on effective leadership but its a key role on effective communication. Body language adds confidence on a speaker while body language in leadership can somehow give the audience a wrong impression. 

Body language plays a major role in determining confidence and abilities to guide and motivate team leaders to work hard and acheive targets to run its organiszation

It doesn't play a key role in leadership communication. But doing a couple of moves in certain conditions, in the right way and for the right reasons may help the leader to dominate a situation and shows him as a persuasive character.

In recent communication studies, the body language constitute about 54%, the word 8% and the accent 38%; so you sould take care of you body language as you can attract people in your message that you'de like to tramsmet. Also, effective leadership communication needs these qualities. hence, there are another point when you interact with your body , this means that you believe in your words and people generally are infuenced by deeds and not words.

It plays partially part especially if you are already become the leader.

No communication without language.....if person didn't language of who dealing with him, then a problem will be

Body language plays an important role in communication.  A leader should always ensure that his body language causes any resentment to others.  A good leader should not get involved in unnecessary arguments or provocations. He should keep his calm and deal with the situations very judiciously.  Body language and the words used by a leader are very very important in leadership communication. 

Good body language is important, poor body language sends out mixed messages. However, in relation to leadership communication, it is important the messages are strategic, specific and concise. Keep it simple, short and to the point. The message must be clear and understood to be effective. This needs to be supported by the right body language in order to enforce your verbal communications.

body language plays a very important role in effective leadership communication. first impression is the last impression. whenever you try to communicate your team, you must have an active body. if you are showing laziness in you then it will effect your team less than your active body posture. your activeness play a motivational role for your team.

if you are not active then your words may not place a good impression on your team. 

Smile, confidence, gesture showing respect for others.

Be Positive,  calm and Stand with your team through thick & thin. Don't show Panic when things are getting tough but continue the fight to overcome.