Short trees & grasses in moderate rainfall
Explanation
The growth of vegetation depends primarily on temperature and moisture. The major vegetation types of the world are grouped as forests, grasslands, scrubs, and tundra. The amount of precipitation directly influences the size, density, and type of vegetation found in a region.
Statement-wise Analysis:
- Grasslands in heavy rainfall is Incorrect: Areas with heavy rainfall support huge trees and dense forests (such as Tropical Evergreen Forests). Grasslands typically develop in regions where rainfall is insufficient to support closed-canopy forests.
- Trees grow larger with less moisture is Incorrect: Moisture is a critical factor for tree growth. As the amount of moisture decreases, the size of trees and their density reduce. Consequently, trees do not grow larger with less moisture; they become stunted or sparse.
- Short trees & grasses in moderate rainfall is Correct: In regions with moderate rainfall, the vegetation transitions from dense forests to short stunted trees and grasses. These climatic conditions are characteristic of the world's major grasslands.
- Thorny shrubs in polar regions is Incorrect: Thorny shrubs and scrubs are adapted to dry regions with low rainfall (hot or cold deserts) to minimize water loss. Polar regions are characterized by Tundra vegetation, which consists of mosses and lichens, rather than thorny shrubs.
Key Takeaway:
Vegetation zones follow a gradient based on precipitation: heavy rainfall supports dense forests, moderate rainfall supports grasslands, and low rainfall results in thorny shrubs and scrubs.