What factors could lead to an increased likelihood of tree failure?

The likelihood of tree failure increases due to a combination of pest infestations, diseases, severe weather, and poor structural integrity.

Pest infestations can weaken a tree by damaging its foliage, bark, or roots, ultimately impacting its overall health and stability. Diseases can affect various parts of a tree, leading to decline and increased susceptibility to physical failure. Severe weather events, such as high winds or heavy snowfall, can place excessive stress on trees, particularly if they are already compromised by pests or diseases. Moreover, poor structural integrity – which may be due to defects in the trunk, branches, or root system – directly influences the tree's ability to withstand external pressures. Hence, these factors collectively contribute to an increased risk of tree failure.

The other options do not directly relate to increased likelihood of failure. Planting trees in clusters can enhance ecosystem benefits and provide mutual support but doesn’t inherently increase failure risk. Using organic fertilizers generally promotes healthy growth and can strengthen trees, reducing the risk of failure. Providing sufficient sunlight is essential for tree health and growth; adequate sunlight supports photosynthesis, which is crucial for a tree's vitality and resilience against failure.