The science of planting (and nurturing) trees

Come every monsoon, civic-minded individuals, corporate social responsibility (CSR)-driven corporations and city entities set out to expand the urban green cover. Telanagana’s Haritha Haram programme, for instance, aims to increase green cover by 33 per cent and is even considering dropping at one crore seed balls in deforested areas using drones.

Meanwhile, in Mumbai, the Brihanmumbai Municipal Corporation has committed to a goal of 30-40 per cent green cover in the city by 2030.

Urban tree plantation efforts are largely centred around planting trees along roadsides and the perimeters of recreational grounds. Trees reduce soil erosion and stormwater run-off, bring down ambient temperatures, apart from providing shade and aesthetic appeal. They also help in climate change mitigation by sequestering atmospheric carbon dioxide as carbon in trunks, branches, leaves and the soil. 

Trees also absorb toxic chemicals (such as nitrogen oxide and sulphur dioxide) with leaf surfaces ‘filtering’ the air and removing particulate matter — the tiny particles of chemicals and dust emitted from vehicles and construction. So, it is not surprising that tree planting is instinctively considered the right thing to do. 

However, evidence shows that the survival rate of urban trees, planted during plantation drives, is poor. This is largely attributed to poor site judgement, polluted or unfavourable soil conditions, selection of non-native species and little to no sapling maintenance. 

It would augur well if corporations and government-aided programs could adopt a scientific approach to tree planting. 

Here are five ways to ensure best efforts do not wither away

Prioritise high-risk areas, site: The first step is to conduct a city-wide risk analysis to map areas that have lost maximum green cover over the past decade resulting in an increase in high land surface temperatures. Next, identify the ideal site and understand which city entity owns it and what are their prospective plans — with respect to zoning regulations, new infrastructure, road widening, laying of pipes among others. 

The plantation plan should ideally be discussed keeping in mind local biodiversity, soil characteristics, inclination and access to water. It should also take into consideration the potential canopy spread (will it touch existing electric wires) and how roots are likely to develop (will it crack the tarmac or be obstructed by underground utilities).

Seek expert advice to choose local species: Often well-meaning citizens select invasive and / or ornamental trees for their aesthetic appeal without considering its potential impact on the existing ecology and pollinators such as birds and butterflies.

Local saplings, while not as picturesque, are hardier and integral to local biodiversity. Engage with horticulture experts and local community members to identify native tree species that offer environmental benefits. Ecologists can suggest species based on site location, soil properties and local biodiversity. 

Nurture mixed groves: Often monoculture saplings are planted in rows but this can be detrimental to local biodiversity. Also, trees planted in layers, or in clusters, stand a stronger chance of survival as they form their own microclimate that helps in long-term survival. 

The aim should be to provide a mix of native trees, shrubs, herbs and creepers. Mixed groves, over time, create healthy biomass that sequesters more carbon and supports a healthier ecology than a single tree. 

The Miyawaki mini forest method of planting diverse local species close together, is slowly gaining traction as a space efficient nature-based solution for cities. Ecologists, however, cite biodiversity implications of improper implementation. 

Adopt water-positive planting for long-term maintenance

Saplings must be carefully watered at the time of planting and will need regular irrigation, at a slow rate to ensure penetration, for the first three dry seasons. Public parks are often watered using freshwater from the municipal water supply. 

Instead, greening projects should be water-wise and integrate rainwater harvesting and decentralised wastewater treatment systems that incorporate nature-based solutions to treat grey water.

Recycled water is nutrient rich with higher levels of phosphorus and nitrogen and is considered beneficial for plant growth. However, salinity levels of the treated water need to be checked for select plant species.

Engage with  local communities: Priority areas for planting often lie in vulnerable neighbourhoods. Once the monsoons abate and the heat sets in, watering plants regularly becomes a challenge. Here, engaging with local communities could prove beneficial.

This could be done by involving local community-based organisations and taking into account the priorities of local residents. Some neighbourhoods prefer having recreational areas, whereas others need areas for growing food for livelihood and sustenance. 

Involving citizens, from the get-go, ensures community ownership for long-term maintenance. In wealthier neighbourhoods, engaging resident welfare associations or broadening the appeal by urging citizens to join a plantation program and ‘adopt’ a tree in the name of a loved one, can be effective ways of strengthening community stewardship. 

While these arguments augment the case for planting more trees, it is critical to plant with a plan. Often you also see smaller species planted in areas that could support larger species and these represent a missed opportunity. In our rush to plant trees, we must not inadvertently put local ecosystems in peril, damaging the very systems that enhance our wellbeing.

Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth.

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