Yes, if a land receives Defend from multiple sources, the Defend values stack, and they apply to both Damage to the land and to Dahan in that land.

This is supported by the following points from the rulebook:

• "If multiple Defend effects are used in one land, they add together. Defend effects last for the entire turn."
  (Page 18)

• "‘Defend 2’ means ‘Whenever Invaders deal Damage in target land this turn, reduce by 2 the Damage done to the land and to Dahan.’"
  (Page 18)

Summary

• Multiple Defend effects in a land are added together.
• The total Defend value reduces Damage to both the land and the Dahan in that land.

Source: page 18.

Source: Core Rulebook (pp. 11, 16, 18, 19, 21)