Environment

Keeping Track of How Plants Move Across Changing Landscapes

Looking over Sarmoli... Credit: Soumya Prasad

Looking over Sarmoli… Credit: Soumya Prasad

One morning in mid May, I trekked a few hundred metres uphill to watch birds in Sarmoli, a remote village in the Indian Himalayas. We had driven over 500 km from Delhi to Sarmoli the previous week. Exiting the grey maze of Delhi, we entered green sugarcane fields in the terai plains. After crossing the shaggy Shiwalik ranges, we ascended slowly through winding Himalayan roads. Movement, short and long, is part of everyone’s life. A ride to get to school or work; a holiday in the Himalayas. Similar to us, most animals travel short distances daily and occasionally undertake long hauls, be it elephants, bees or bats. Among the most incredible journeys are the ones undertaken by migratory birds. The tiny greenish warbler, which weighs less than 10 g, flies hundreds of kilometres from their summer home high in the mountains to spend winters in warmer parts of India.

A century back, someone wanting to travel from Delhi to Sarmoli would have taken weeks to get here, on foot or on a mule. Thanks to all the smart science and engineering in the last few decades, it took us around 22-hour to drive from Delhi to Sarmoli. However, we are not the first species to use transport vectors to move ourselves around. Plants have been using transport vectors for millions of years to move their seeds. In tropical regions like India, most plants produce nutritious fruits which attract animals. Some plants have sweet sugar rich fruits which are bird favourites. Fruits like amla have high fibre content, which attracts deer. The animals that eat fruit transport seeds away from parent plants, ensuring the latter’s survival. Besides, several plants also use mechanical vectors such as wind or water. Plants with winged seeds like the sal tree (Shorea robusta) can fly several kilometres when they latch on to wind uplifts. There are seeds that float – such as coconut’s that has been transported across continents by ocean currents. Surely, all of us have transported those incredible hooked seeds that fasten to our clothing or skin when we’re walking through grassy areas.

Adult plants stay rooted in a place all through their lives. Parent plants invest heavily in transporting their seeds away from themselves. This process of movement of offspring away from the parent is called “dispersal”. If seeds do not disperse, plant populations can soon become inbred due to pollination between closely related individuals. Another very important reason driving the evolution of seed dispersal strategies are the changing environmental contexts. Across Earth’s 4.5-billion year history, environmental conditions have been changing constantly. A species that cannot move to find suitable habitats when climates change faces huge extinction risks.

I went to Sarmoli in May 2015 to escape Delhi’s extreme summer temperatures. I cannot think or write when temperatures are beyond 40° celsius. Species and even individuals vary in their physiological tolerances. The maximum and minimum limits for various environmental variables that govern the functioning of our bodies determine where we can live. A plant or bird which fares poorly over 45° celsius has a slim chance of surviving in places such as Delhi where temperatures are predicted to increase by over 5° celsius in the coming decades.  Birds and bats can fly to find cooler spots. Animals like elephants and civets can walk miles and miles to escape the heat. The only way plants can find a cooler spot, is to pack their seeds off with someone headed towards a cooler spot.

For example, we know from studies of fossil pollen that several plant species and the forest habitats extended their range rapidly when environmental conditions were favourable.  In the last 2.5 million years, the earth went through several cold phases (referred to as glacial periods) which alternated with warm periods (or interglacials). During the interglacial periods, plant species and forests extended pole-wards very rapidly as the earth warmed. Compared to past climate change events, plant species face a very different world today. Firstly, natural habitats exist in a highly fragmented condition. Plants and animals need to move across highly inhospitable habitats such as cities and villages to find suitable habitats. The second problem that many plants face today is the lack of transport vectors in human-dominated landscapes. This is especially true for animal-dispersed plants, whose vectors are missing or have become extremely rare in cities and villages, and often inside several forests as well.  

Animals as dispersers of seeds

A photo of the oriental pied hornbill feeding on putijia fruit in a forest at the foothills of the Himalayas, within the Rajaji National Park, Uttarakhand. Credit: Mohan Chandra Joshi

A photo of the oriental pied hornbill feeding on putijia fruit in a forest at the foothills of the Himalayas, within the Rajaji National Park, Uttarakhand. Credit: Mohan Chandra Joshi

In the Himalayan foothill tropical forests, where we work, elephants, deer, hornbills, bulbuls and barbets disperse seeds of the plant communities. As it warms up over the next few decades, it is expected that the tropical plants and animals found in the foothill Shivalik forests will need to move up into the higher altitudes of the Himalayas. Outside forest reserves such as the Rajaji or Corbett National Parks, large fruit-eating animals such as elephants, deer and hornbills are rare. Plant species such as our berda (Terminalia bellirica) or kumbhi (Careya arborea), which depend entirely on large animals for seed dispersal, are likely to have limited ability to move. Even plants that are dispersed by both small and large animals such as putijia (Drypetes roxburghii) or ber (Ziziphus mauritiana) could be impacted by large animal declines.  Large animals often move longer distances than smaller animals. Large animals are the only ones who may be able to provide that extra long dispersal service which is required to keep pace with rapidly changing climatic conditions.

In the last decade we have made massive advances in the science of predicting the impacts of ongoing climate change on biodiversity. Yet, we do not have time left for a complete understanding of the directions and paths along which every species will move to start planning management strategies. Today, our research group and a few others have assembled datasets which we are using to understand how to align green spaces in urban and rural areas to facilitate plant and animal movements. This would allow both plant and animal species to move around and sort themselves out in changing landscapes.

In this context it is truly inspiring to see efforts such as those initiated by the Nature Conservation Foundation (NCF). In the Valparai plateau of Tamil Nadu, the NCF team has been planting native plants to connect forest patches. Across India, there are several ongoing ecological restoration efforts. Over half a dozen ecological restoration programs have been initiated within the National Capital Region itself.  Hopefully, these attempts to reconnect fragile forest patches in the National Capital Region can help the eastern Aravalli belt to cope with environmental variability in the coming decades.  

A seedling in a nursery of forest plants that are used for restoration, in Valparai. Credit: Soumya Prasad

A seedling in a nursery of forest plants that are used for restoration, in Valparai. Credit: Soumya Prasad

However, the real challenge that we face today is whether we can scale up efforts to reconnect the habitat dots across India. The massive infrastructure challenges for human movement across India pale in comparison to the movement challenges faced by other species that share this nation with us. Can we integrate ecological thinking into the planning of urban and rural green spaces? The government of India aims to plant of trees across millions of hectares annually under various afforestation programs. Afforestation programs have been dominated by a few exotic species, notably Eucalypts from Australia. Afforestation programs, by the government’s own admissions (here and here), have very low survival rates for plants. Can we bring about rapid policy changes in our afforestation programs to prioritise our own native plant species, especially those that will face a dispersal crunch? Can we invest the vast CAMPA funds using sound ecological principles and maximise benefits to both nature and society?

The Valparai landscape. Credit: Soumya Prasad

The Valparai landscape. Credit: Soumya Prasad

The government of India has recently announced an ambitious program to develop green roads by planting trees with the help of various government and non-government agencies.  Green roads will also keep roads cooler, and make travel more comfortable.  These linear connections that transport us could also help transport our native animal and plant species as well.  

Reconnecting the habitat dots across India’s vast landscapes is indeed very challenging. Using ecological approaches to restore habitat connectivity would offer some of the cheapest and quickest solutions to help us adapt and align with ongoing climate change. If we fail to restore the ecological connectivity in changing landscapes, we will weaken the capacity of our natural habitats to inhale carbon dioxide, exhale oxygen, and provide us water, food and medicines. In the end, truly smart cities and smart villages will be those that can rejuvenate and sustain their eco-spaces.

Soumya Prasad is an ecologist based at the Jawaharlal Nehru University. She researches seed dispersal in changing landscapes.

  • Reader

    A fantastic read. Thank you.

  • Vinay Tandon

    A good read, limited perhaps by no mention of the BIGGEST threat to India’s native flora, from Invasive Alien Species (IAS). The vast areas already ‘conquered’ by IAS and their rate of spread, even to the casual observer, pose a major threat to our ecology. What is more worrisome is that there is little or no research going on to understand (leave alone challenge) the spread, diversity and impact of IAS on various habitats and in turn on forest and natural resources based livelihoods of rural India. Many of the potential wildlife ‘corridors’ are now heavily infested with alien weeds that effectively ‘choke’ all native vegetation.

    A major, major reason for the very low survival rate of forest plantations is that little or no money is spent on raising good nursery stock. The plants planted out in the field are so pathetic that they do not survive even the first six months or one year. Of course, ‘targets’ are invariably achieved or exceeded. Yet, despite all our ‘scientifically’ trained foresters, there is no mention of poor nursery stock being the prime culprit behind criminal survival rates of plantations. And there is no dearth of money, thanks to CAMPA!