DENDROLOGY

Detailed explanation-1: -D is correct. The first species to occupy a barren area that has no existing community due to volcanic explosions and retreating glaciers are called pioneer species.

Detailed explanation-2: -In ecology, a pioneer species is the first organism to live in a new area.

Detailed explanation-3: -The settling of a pioneer community marks the start of the colonizing phase of primary succession. Examples of pioneer species are lichens, algae, and fungi. These species are more tolerant and eventually contribute to the formation of the soil by breaking down rocks into smaller particles.

Detailed explanation-4: -Lichens (the pioneer species) are able to survive because they are specialised to cope with the hostile abiotic conditions. Lichens can grow in cracks to avoid the wind and they secrete acids that erode rock to release minerals. The pioneer species have now changed the abiotic conditions.