Why is overall plant productivity usually low in scrublands?

Overall plant productivity in scrublands is typically low due to high environmental stress, primarily characterized by long periods of hot, dry weather where a lack of moisture acts as a limiting factor for growth. Additionally, soil nutrient levels in these regions are generally very low, which further restricts rates of photosynthesis.1

Structural adaptations of scrubland vegetation also contribute to slow biomass production. Many dominant shrubs are deciduous, losing their leaves during periods of water scarcity, or they are evergreen with small, tough leaves that result in a relatively low total leaf area. Furthermore, these plants allocate a substantial proportion of their biomass to extensive root systems or large underground organs, such as lignotubers, rather than to aboveground photosynthetic tissues. Consequently, only a small fraction of the plant's living material is dedicated to the green parts necessary for producing new plant material.12