If using trees for grounding: plants do have emotional responses and memories. If you collect their energy for special methods, you are robbing them of their life essence for your self-interest.
When you are doing this you are injuring a life form and building up negative karma. So, most orthodox schools of Qi-Gong utterly forbid methods of plant energy gathering, as some techniques are desirable and some are immoral! Understand the differences and draw the distinctions between them. Be aware that gathering and collecting energy from another living being is stealing and the usurper will loose virtue by doing this!
Although, orthodox Qi-Gong schools do advocate energy interchange and exchange between humans and plants that have a vast storage, such as trees.
Exchanging energy while practicing Qi-Gong under trees, such as pine trees, in the prime of their lives or in the apex of the trees life is very healthy for people. Different trees will give off different energies. Some are too yang or harbor an energy that may exacerbate the issue and will therefore be unhealthy for the practitioner!
If you are looking to cool your heat built up within the body, look into evergreen arbors for their water nature.
Trees are also divided into five categories related to the five elements theory.
So, in order to correctly exchange energy with a tree we must know the root issue to exchange with the right family of tree.
So, basically, the trees energy will adjust the function of the corresponding internal organ that is creating the imbalance.