The dark side of Bamboo

 Dr Anjani Ganase, marine ecologist, takes a look at the land and specifically one plant that can overgrow areas where forests are cleared. Alongside the cultural utility of bamboo, there is significant cost to the environment as bamboo spreads rapidly, edging out other plants and depleting the soil.

Bamboo is the backdrop for picturesque scenes across our island landscapes. They create the settings of perfect postcard wedding photos; and they shape many scenes of Cazabon paintings. Bamboo is literally intertwined into our culture: essential for the celebrations of Divali, the stalks are split and bent and displayed with deyas. Bamboo is also used to make furniture and jewellery. Clumps of bamboo line many roadsides in north Trinidad, and can easily be spotted on the rolling hills of central and south Trinidad. In Tobago, bamboo may be less obvious, but take a closer look at the forests you pass along the windward roads; you will see clumps of bamboo among the canopy of the forest.

 

Bamboo grove at Plymouth (Photo by Pat Ganase)

Detail of bamboo

The presence of large clumps of bamboo tells a story of forest degradation and transition. Bamboo plants naturally occur throughout the tropics and subtropics but a higher presence is often associated with human activities. As forests are cleared, for wood or agriculture, through slash and burn activities, the faster growing colonizing vegetation will occupy the unused land. These fast colonizers are typically the grasses. In Trinidad and Tobago, bamboo is a very common grass but it’s also one of the fastest growing grasses on earth. It can easily establish itself on any cleared landscape. Unlike other grass and weeds that may then be eventually out-competed by other more aggressive plants and forest trees, bamboo has advantages in the air and under the earth.  Its vertical growth and rhizome root system that can spread to large areas, tend to prevent other trees or forest vegetation from re-acquiring space after bamboo sets in. As a result, the ecology of the area is permanently changed by bamboo.

Scientists have identified exactly how bamboo changes their surrounding habitat and the consequences of bamboo-invaded forests; and what it means for the integrity of the forest in the long term. In general, bamboo is also considered hardy, where large well-established stand can be resistant to disturbance such a low intensity forest fires or prolonged flooded conditions (Franklin et al 2009).  The bamboo clump forms a monoculture through the spread of the rhizomes in the top layer of the soil; and is thought to directly out-compete neighbouring tree seedlings. Scientists have also discovered that bamboo changes the soil conditions. As a grass, bamboo tends to suck the water from the soil, drying it out. Bamboo leaf litter and stems are naturally lower in nutrients, and high in lignin (good for building and furniture-making). Therefore bamboo leaf litter is harder to break down, and also poor in restoring organic matter and nutrients to the soil. The combination of the bamboo dominant leaf litter and the lack of other nutrient rich forest leaves around the monoculture stands may also limit the establishment of other tree seedling (Larpkern et al 2011).

Think about the ground underneath of bamboo patches, instead of rich soil there is a compact mat of bamboo leaf litter that doesn’t readily decompose. Large bamboo clumps may actually form canopies that may be suitable for shaded plants, but often the earth below would typically be bare. Consider that forests around the world are the major method of sequestering carbon since leaf litter is the biggest form of carbon sequestration on the planet. However, comparing the leaf litter of established forests to areas invaded and dominated by bamboo, the carbon storage capacity and nutrient quality of bamboo leaf litter is 50 % lower in the top soil (Zaninovich et al 2017). Clearly, allowing forest trees to be replaced by bamboo will dramatically reduce the carbon storage capacity in subtropical forests.

 

Bamboo catches easily along fertile river valleys, such as Arima-Blanchisseuse  (Photo by Pat Ganase)

Add caption

While certain areas in Trinidad and Tobago have been well established as bamboo forest, it is important to understand how human activities of land clearing leads to bamboo invasion and encroachment into forested areas, and the resulting forest degradation.

Our Main Ridge Forest Reserve has for centuries remained the most natural store of biodiversity, nutrients and the source and protection of our waterways.  We need to actively continue to care about the quality of our forests: it’s not just bush. Here in Tobago, the Main Ridge is the second most important contributor to the air, water and health of this pleasant island paradise. The first, of course, is the ocean.

REFERENCES

Franklin DC, Prior LD, Hogarth NJ, McMahon CR. Bamboo, fire and flood: consequences of disturbance for the vegetative growth of a clumping, clonal plant. Plant Ecology. 2010 Jun 1;208(2):319-32.

Larpkern P, Moe SR, Totland Ø. Bamboo dominance reduces tree regeneration in a disturbed tropical forest. Oecologia. 2011 Jan 1;165(1):161-8.

Zaninovich SC, Montti LF, Alvarez MF, Gatti MG. Replacing trees by bamboos: Changes from canopy to soil organic carbon storage. Forest ecology and management. 2017 Sep 15;400:208-17.