The Lifeblood of a Forest
For countless centuries, India's diverse forests have evolved in rhythm with the seasons, particularly the southwest monsoon. Predictable, steady rainfall is the engine of forest productivity. It replenishes soil moisture, enabling trees to absorb essential
nutrients and carry out photosynthesis, the process that fuels their growth. This consistent supply of water supports everything from the germination of seeds to the lush canopy that provides shade and habitat. In many regions, especially central India's tropical deciduous forests, this seasonal cycle is fundamental; trees shed their leaves during the dry months and burst back to life with the monsoon's arrival. Studies show that in years with adequate rainfall, most of India's forested areas exhibit a 'greening' trend, indicating healthy growth and vitality.
When the Blessing Becomes a Curse
The problem arises when rainfall patterns shift from steady showers to extreme downpours. Climate change is altering the monsoon, leading to more intense, concentrated rainfall events punctuated by longer dry spells. When rain falls faster than the ground can absorb it, the excess water becomes destructive runoff. This powerful flow of water can strip away the nutrient-rich topsoil, a process known as sheet erosion. On steeper slopes, such as those in the Himalayas and the Western Ghats, this can trigger devastating landslides that uproot entire sections of forest. The force of fast-moving water can expose tree roots, making them unstable, and even topple mature trees. Furthermore, in flatter areas, intense rain can lead to waterlogging, suffocating root systems that are not adapted to prolonged saturation.
A Tale of Two Extremes
The combination of longer droughts and more intense rainfall creates a particularly damaging 'double whammy' for forest ecosystems. During extended dry periods, trees become stressed, their growth slows, and their root systems may even die back in the upper soil layers as they search for deeper moisture. When a water-stressed forest is suddenly hit with a torrential downpour, its ability to cope is severely compromised. The dry, compacted soil is less able to absorb the deluge, leading to increased runoff and erosion. Trees that are already weakened by drought are more susceptible to being damaged or uprooted by the physical force of the storm. Studies have found that tree growth responds more negatively to dry years than it does positively to wet years, meaning the benefits of a wet year do not fully compensate for the damage from a drought.
Not All Forests Are Equal
India's varied landscapes mean that different forest types exhibit different vulnerabilities. Dry deciduous forests, which function closer to their moisture-stress limits, are more vulnerable to extended droughts and the intense rains that follow. In contrast, moist deciduous forests with deeper canopy cover may be slightly more resilient to short-term instability. Humid ecosystems and rainforests, which are accustomed to consistent moisture, often fare worse when subjected to the longer dry spells between intense rain events. Mountainous forests are particularly susceptible to landslides triggered by heavy rain, while coastal forests face the dual threat of storm surges and extreme precipitation from cyclones. Urban forests, like those in Delhi, face unique challenges where concretisation around tree bases chokes roots, making them structurally weak and prone to falling during heavy rain and wind.
The Foundation of Resilience
In the face of these challenges, the key to survival is resilience—the forest's ability to withstand and recover from disturbances. A forest's resilience is not accidental; it is built on several core factors. Biodiversity is paramount. A forest with a wide variety of plant species is more likely to have some that can tolerate changing conditions, helping the ecosystem as a whole remain intact. Healthy, undisturbed soil with plenty of organic matter acts like a sponge, absorbing rainfall, preventing erosion, and filtering water. An intact forest canopy intercepts rainfall, softening its impact on the ground below. These natural defences are crucial. When forests are fragmented by roads or cleared for agriculture, their resilience weakens, making them more vulnerable to the shocks of a changing climate.
