In general, species-rich ecosystems have exhibited greater resilience to extreme environmental conditions and greater potential to recover from disturbance than less diverse ecosystems. This makes less diverse ecosystems inherently more susceptible to future changes and stressors. Conversely, ecosystems that have low species diversity or low functional diversity (where multiple species occupy the same niche) may be less resilient to climate change or its associated stressors. Forest stands with low diversity of species, age classes, and genotypes have been more vulnerable to insect and disease outbreaks than diverse stands. Genetic diversity within species is also critical for the ability of populations to adapt to climate change, because species with high genetic variation are more apt to have individuals that can withstand a wide range of environmental stressors.