“Forest sector underutilized, says World Bank report” is the title of the story ran by Kuensel on July 25, 2019. Dr. Tashi Wangchuk’s opinion in Kuensel, titled “cutting more forest is not the most expedient choice” (Wangchuk, 2019) sums up the need for looking at our forests as an asset at par with our built assets. I haven’t had an opportunity to read through World Bank’s report so I can’t comment much on it, however, if World Bank’s report read “forest sector underutilized”, it calls for a much broader debate.
Similar to Kuensel’s story on World Bank’s report, Dr. Phuntsho Namgyel’s talk on “Cut trees, save forest: a call for a new forestry thinking in Bhutan” delivered during the second BLISS Bhutan talks (BLISS, 2019) on 5th May 2019 in Thimphu drew many attentions. Dr. Phuntsho’s talk revolved around the two opinion piece he wrote in Kuensel (Namgyel, 2018, 2019). Having read through many comments on social media, both for and against the radical approach presented, I will make an effort to outline some of the intricate contributions forests makes.
I will also focus on the contribution of forests to landslides and also on maintaining the continental hydrological cycle. Owing to the dearth of literature from Bhutan and the region, I looked at the studies done elsewhere.
First, it is important to get the numbers straight. Many commentaries reflect that only 5% of the total forest area is currently under commercial management in Bhutan. This is not correct, as it should have read as “5% of the country” and not “forest area.” In Bhutan, Forest Management Units (FMU) are commercial forest management regimes and besides FMUs we have Local Forest Management Unit (LFMU), and Community Forests (CF). Thus, considering LFMU and CF together with FMU, almost 10% of the country or almost 14% of the total forest area in Bhutan is under forest management regimes.
According to Costanza et al. (1997), ecosystem services (ES) are understood as the ecological characteristics, functions, or processes that directly or indirectly contribute to human well-being: that is, the benefits that people derive from functioning ecosystems. Some example of the ES are soil erosion control; food production; waste treatment; raw materials; air; water; etc. (Coztanza et al., 2017). One of the well-recognized ES of forests is as stores of carbon. However, forests also provide a broad range of ‘less’ recognized benefits that are equally, if not more, important like the functioning of the hydrological cycle and associated cooling.
Rainfall is considered the major cause for most of the landslides. Landslides are commonly seen on steep slopes during or after an intense rainfall event, however, vegetation provides a natural bioengineering method to prevent slope failures (Fan & Su, 2008). Several scholars like (Bathurst, Bovolo, & Cisneros, 2015; Cohen & Schwarz, 2017; Fan & Su, 2008; Giadrossich et al., 2019; Moos et al., 2016; Preti, 2013) reported that forests can decrease the risk of shallow landslides by mechanically reinforcing the soil and positively influencing its water balance . To this line, Giadrossich et al. (2019) remarked that forests are part of risk reduction strategies and are an important aspect of ecosystem services. A simulation exercise performed by Cohen and Schwarz (2017) demonstrated the function of root to slope stabilization. Their simulation exercise demonstrated that higher root density with higher root reinforcement results in a more stable slope.
The effect of vegetation on slope stability is now well established. However, the contribution of roots on slope stability is effective only when the tree is living, as Preti (2013)’s study revealed that after tree death, the favourable effects on the soil water potential regime are lost immediately, increasing the potential landslide hazard. This is because, once the tree ceases to live, the roots are subjected to a progressive decomposition, eventually causing gaps in the interlocking root system of neighbouring individual trees reducing the root tensile strength and the cohesion provided by the root system to the soil.
While tree cover helps in reducing the landslide hazard, its contribution to groundwater recharge has remained still a subject of debate. This debate is applicable to Bhutan with ever-increasing forest cover, but increasing incidences of water scarcity reported from across the country.
Evapo transpiration and Ground Water
The interactions between forest change and water have been studied for over a century and many published works describe forests as ‘sponges’ storing rainwater and slowly releasing it to maintain groundwater and streams during dry periods (Calder et al., 2004). However, in recent decades, the ‘sponge’ theory lost credibility as studies increasingly showed that forest clearance generally leads to increase and afforestation to reduce water yields (Farley, Jobbágy, & Jackson, 2005; Jackson et al., 2005; Sandström, 1998). Therefore a contrasting trade-off theory–in which more trees means less water–has become the dominant paradigm (Ilstedt et al., 2016). The trade-off theory is the possibility that afforestation could cause or intensify water shortages in many locations but could sequester more atmospheric carbon. This trade-off theory predicts that as tree densities increase, water losses from transpiration and interception dominate their hydrological effects (Jackson et al., 2005).
Therefore, in contrast to the prevailing view of tree cover contributing the more groundwater recharge, Ilstedt et al. (2016) found that moderate tree cover increases groundwater recharge. For example, the groundwater recharge increased from 36 to 55 mm when the average canopy area for an individual tree was reduced from 130 to 40 m2. Similar results were also found by Farley et al. (2005), wherein they reported of annual runoff reducing on average by 44% (±3%) and 31% (±2%) when grasslands and shrub lands were afforested, respectively. Jackson et al. (2005) synthesized more than 600 observations, and climate economic modeling to document substantial losses in stream flow with afforestation. They found a decrease in stream flow by 227 mm per year globally (52%), with 13% of streams drying completely for at least a year after the plantation programs. In a yet another study conducted to study the effect of timber harvest on water quantity in North Carolina, US found that discharge in watersheds increased dramatically, averaging anywhere between 200% – 240% when 33% of watershed was harvested (Boggs, Sun, & McNulty, 2016).
The reason for inverse relations between tree cover and stream flow is attributed to transpiration and there is a good number of empirical evidence suggesting groundwater depletion due to an excessive rate of transpiration from trees. For example, in an experiment performed by (Dawson, 1996), small trees were found to use only soil water and did not carry out hydraulic lift, whereas large trees were found to use groundwater through a hydraulic lift. This hydraulic lift replenishes the soil water pool each night with groundwater, thereby increasing the water available to small trees. Sandström (1998, p. 138) remarked that “when a forest is defined as a mass of trees, each one pumping water from the soil to the atmosphere, it is obviously impossible to state that forests can provide water”. Thus, it is likely that transpiration may be contributing to depletion on groundwater, but on the flip-side, transpiration also helps build-up cloud-cover contributing to the hydrological cycle.
With regards to the contribution of transpiration to the hydrological cycle, existing literature recognizes that trees transpire moisture at higher rates than they can draw it from the ground for periods of several hours. According to Sheil (2014), plant scientists estimate that transpiration produces 80–90% of the atmospheric moisture derived from continents. The moisture from transpiration is important, as it contributes to a larger share of atmospheric water vapour available for rainfall. On average, at least 40% of rainfall over land originates from moistures contributed by transpiration, with greater contributions in some regions such as the Amazon forest contributes more than 70% of rainfall (Ellison et al., 2017).
Though water is lost through transpiration, forests may be particularly important for high altitude areas as forests have a special ability to intercept fog and cloud droplets (Ellison et al., 2017). Condensation on plant surfaces, including on dense, epiphytic lichen and moss communities – which are plenty in Bhutan’s forests, provides additional moisture for tree growth, infiltration, and groundwater recharge. High altitude forest loss may thus have disproportionate, negative implications for water availability, however, this warrants a localized and much deeper study.
According to the 2017 Forestry Facts and Figures, there were 31 recorded forest fire incidences, burning an area of about 5249 hectares (DoFPS, 2017a), and similarly, 39 forest fires were recorded in 2018 (DoFPS, 2018). However, in 2016 Bhutan witnessed 72 forest fire incidences burning an area of about 10,900 hectares of forests (DoFPS, 2016). The number tells that in 2016, Bhutan witnessed one forest fire every fifth day, sending a clear sign of Bhutan grappling with the incidences of forest fires. Though a trend of forest fire incidences can’t be deduced from three years data, 2017 Forestry Facts and Figures stated that “forest fire poses a major threat to the sustainability of the forests and is one of the major drivers of deforestation and degradation in Bhutan” (DoFPS, 2017a, p. 21).
Several scholars like (Finkral & Evans, 2008; Mason et al., 2006) have argued that failure to remove small logs through performing thinning operations results in retention of ladder fuels that support crown fires. Crown fires are the most destructive kind forest fires. Mason et al. (2006) commented that not only irreplaceable habitats for threatened and endangered species may be lost when forests burn but smoke from the forest fire increases atmospheric carbon. Finkral and Evans (2008) demonstrated from their study in northern Arizona ponderosa pine forests that the thinning treatment resulted in stand structural changes that make the stand less likely to support a crown fire and therefore more likely to avoid the carbon releases associated with crown fires, even under extreme fire conditions.
However, there exists another group of literature which are not in sync with the argument of thinning and logging operations minimizing the risk of the forest fire. Ray, Nepstad, and Moutinho (2005) said, logging operations not only alter micro-climatic conditions, but also can change stocking densities and patterns of trees, inter crown spacing, and other forest attributes such as plant species composition. These changes can influence fire regimes. For example, logging in moist forests in southeastern Australia shifted the vegetation composition towards characteristic of drier forests that tend to be more fire-prone (Mueck & Peacock, 1992). Studies from western North America indicated that logging related alterations in stand structure increase both the risk of occurrence and severity of subsequent wildfires through changes in fuel types and conditions (Thompson, Spies, & Ganio, 2007). Similarly, in Asian rain forests, post-fire salvage logging changed the vegetation composition towards more fire‐prone grassland taxa (Van Nieuwstadt, Sheil, & Kartawinata, 2001).
Timber harvest in Bhutan
According to the recently conducted National Forest Inventory (NFI) of Bhutan, the country is blessed with 1001 million cubic meters of growing stock (DoFPS, 2017b). Growing stock is defined as the standing volume of all living trees in a given area of forests by the forest management code of Bhutan. Growing stock is different from ‘economically’ harvestable timber and not all trees in Bhutan are of ‘economic’ value and those that are harvestable and possessing ‘economic’ value are either on a geographically precarious terrain or, are already within the forest management regimes: Forest Management Unit (FMU), Community Forestry, and Local Forest Management Area (Outside FMU).
As per the forest facts and figure, Annual Allowable Cut (AAC) in 2017 was 218,046 cubic meters of timber (DoFPS, 2017a). However, 244,233 cubic meters of timber was supplied in 2017 (DoFPS, 2017a). AAC is the total maximum sustainable harvestable timber supply for each year of the plan period. That’s about 0.02% of the growing stock. Don’t get swathed by this figure as there exists no data on the stock of economically harvestable timber, let alone data on illegal timber poaching and trees lost in natural disasters.
The annual report of Natural Resources Development Corporation Ltd. reported of increased timber production in 2018 from 2017 by 24,947 cubic meters surpassing the target of 52,725 cubic meters (NRDCL, 2018). Besides timber, NRDCL also produced 3,727.70 MT of wood chips and 32,949.91 cubic meters of firewood (NRDCL, 2018).
This being said, timber shortage in Bhutan hit the headlines of the country’s media for quite some time now. A study was undertaken by Jadin, Meyfroidt, and Lambin (2016) and found that from 1996 – 2011, 59% of the total volume of wood consumed in Bhutan was met by domestic production, however, the remaining 41% of wood came from India. Their study also revealed that, in 2009 and 2011, 75 and 77 % respectively, of the volume of wood consumed domestically was imported from India.
Forest is the only abundant resources Bhutan has, and the domestic demand for wood could be met from the country. However, Bhutan is geographically located in one of the fragile landscapes on earth, prone to landslide hazards. This is further aggravated by the fact that some of our forests are too distant from roads, in fragile ecosystems, or essential for the subsistence of local communities.
The potential use of protection forests to combat shallow slope instabilities is increasingly important and relevant and should be seriously considered. Bhutan is geographically located in one of the fragile landscapes on earth, prone to landslide hazards triggered by rain; earthquakes; and even infrastructural development. A landslide brings many ecological disasters which are intricately linked to economics, social and cultural landscapes of Bhutanese. For example, an increase in the incidence of landslides and debris flows leads to injection of sediment into river systems. This not only deteriorates an aquatic habitat but also impacts hydropower, tourism, and agriculture, all of which are the major contributor to Bhutan’s GDP. The landslide also blocks transport corridors, it poses threats to human life and can have major social, economic and environmental repercussions.
Bhutan has just witnessed a series of landslides due to the heavy monsoon across the country. Studies say it is aggravated by man-made climate change and the consequences of landslides are destructive. In such a scenario, forest cover is required to reduce landslide hazards. If we continue with our argument, it will ultimately funnel to one conclusion: we need to conserve the forest. Conserving forest means conserving biodiversity – biodiversity plays a functional role in providing ecosystem services such as air, water, food, shelter, sequestering carbon, etc. This means we secure our future so long as we have forests – the very reason why life on the desert is scant!
There is much scientific evidence of the inverse relations between tree cover and stream flows. However, this relation stands valid only in places with good tree cover and the definition of “good” varies with species; aspects; region; latitude; longitude; and other factors. For example, a study conducted in the US found coniferous species transpiring more than broad-leave species, but a similar study from Japan concluded other way-round. The rate of transpiration and stream flow generally has inverse relations.
Considering our fragile landscape and increasing incidences of water scarcity reported throughout the country, it is the call of an hour to embark on a study to understand the “true” value of Bhutan’s forest cover. There are many empirical studies suggesting that an increase in forest area does not necessarily imply an increased provision of ecosystem services when landscapes are reforested with mono-culture plantations. It is an irony that the most abundant resources in the country come pricey and one of the most difficult to obtain: timber and freshwater. Bhutan definitely needs to re-look at the conservation and timber markets to make the most abundant resources in the country affordable to its own people but ensuring to maintain the forest cover status quo.
While maintaining forest cover and also making timber available appears to go in tangent, Bhutan offers an opportunity for these two opposite components to cross the path. This may be achieved by looking at Bhutan’s timber market through the timber harvesting modalities and market structure and not by prescribing to cut more trees or increasing forest area under commercial forest management regimes. Bhutan cannot go on, for long, with some obsolete machineries and keep on accepting the timber recovery volume for broad-leaves species to be only little over 50%. Investing in state-of-the-art machinery to harvest and convert logs to timber will not only achieve in producing timber but will also ensure in maintaining forest cover with rich biodiversity in perpetuity.
The existence of a contradictory array of literature calls for a localized study to understand the best practices for Bhutan’s forests and ecosystems. It is about time to invest in policy-driven research. Well, whatsoever, viewing our forests from the economics lens or bankers’ perspective would lead to an ecological disaster and the economies of the Earth would grind to a halt without the services of ecological life-support.
I shall leave it up to you all to decide how you would prefer to view our forest cover: as natural capital or as an exploitable resource.
Acknowledgment: My appreciation to Mr. Ugyen Penjor, DPhil Student – the University of Oxford for taking time to review the first draft of the article.
Click here for an opinion piece in Kuense(August 10, 2019) – http://www.kuenselonline.com/forests-natural-capital-or-exploitable-resources/
Bathurst, J. C., Bovolo, I., & Cisneros, F. (2015). Modelling the effect of forest cover on shallow landslides at the river basin scale. Ecological Engineering(1497), 1-11. doi:10.1016/j.ecoleng.2009.05.001
Boggs, J., Sun, G., & McNulty, S. (2016). Effects of Timber Harvest on Water Quantity and Quality in Small Watersheds in the Piedmont of North Carolina. Journal of Forestry, 114(1), 27-40. doi:10.5849/jof.14-102
Calder, I., Amezaga, J., Aylward, B., Bosch, J., Fuller, L., Gallop, K., . . . Wilson, V. (2004). Forest and water policies. The need to reconcile public and science perception. Geologica Acta, 2, 157-166. doi:https://doi.org/10.1344/105.000001436
Costanza, R., D’Arge, R., De Groot, R., Farber, S., Grasso, M., Hannon, B., . . . Van Den Belt, M. (1997). The value of the world’s ecosystem services and natural capital. Nature, 387(6630), 253-260. doi:10.1038/387253a0
Coztanza, R., Groot, R. d., LBraat, L., Kubiszewski, I., Fioramonti, L., Sutton, P., . . . Grasso, M. (2017). Twenty years of ecosystem services: how far have we come and how far do we still need to go? Ecosystem Services, 28(2017), 1-16.
Dawson, T. E. (1996). Determining water use by trees and forests from isotopic, energy balance and transpiration analyses: the roles of tree size and hydraulic lift. Tree Physiology, 16(1-2), 263-272. doi:10.1093/treephys/16.1-2.263
DoFPS. (2017b). National Forest Inventory Report: Stocktaking Nation’s Forest Resources. Retrieved from Thimphu: http://www.dofps.gov.bt/wp-content/uploads/2017/07/National-Forest-Inventory-Report-Vol1.pdf
Ellison, D., Morris, C. E., Locatelli, B., Sheil, D., Cohen, J., Murdiyarso, D., . . . Sullivan, C. A. (2017). Trees, forests and water: Cool insights for a hot world. Global Environmental Change, 43, 51-61. doi:https://doi.org/10.1016/j.gloenvcha.2017.01.002
Fan, C.-C., & Su, C.-F. (2008). Role of roots in the shear strength of root-reinforced soils with high moisture content. Ecological Engineering, 33(2), 157-166. doi:https://doi.org/10.1016/j.ecoleng.2008.02.013
Farley, K. A., Jobbágy, E. G., & Jackson, R. B. (2005). Effects of afforestation on water yield: a global synthesis with implications for policy. Global Change Biology, 11(10), 1565-1576. doi:10.1111/j.1365-2486.2005.01011.x
Finkral, A. J., & Evans, A. M. (2008). The effects of a thinning treatment on carbon stocks in a northern Arizona ponderosa pine forest. Forest Ecology and Management, 255(7), 2743-2750. doi:https://doi.org/10.1016/j.foreco.2008.01.041
Giadrossich, F., Cohen, D., Schwarz, M., Ganga, A., Marrosu, R., Pirastru, M., & Capra, G. F. (2019). Large roots dominate the contribution of trees to slope stability. Earth Surface Processes and Landforms, 44(8), 1602-1609. doi:10.1002/esp.4597
Ilstedt, U., Bargués Tobella, A., Bazié, H. R., Bayala, J., Verbeeten, E., Nyberg, G., . . . Malmer, A. (2016). Intermediate tree cover can maximize groundwater recharge in the seasonally dry tropics. Nature, 6, 21930. doi:10.1038/srep21930
Jackson, R. B., Jobbágy, E. G., Avissar, R., Roy, S. B., Barrett, D. J., Cook, C. W., . . . Murray, B. C. (2005). Trading Water for Carbon with Biological Carbon Sequestration. Science, 310(5756), 1944. doi:10.1126/science.1119282
Jadin, I., Meyfroidt, P., & Lambin, E. F. (2016). Forest protection and economic development by offshoring wood extraction: Bhutan’s clean development path. Regional Environmental Change, 16(2), 401-415. doi:10.1007/s10113-014-0749-y
Mason, C. L., Lippke, B. R., Zobrist, K. W., Bloxton, T. D., Jr., Ceder, K. R., Comnick, J. M., . . . Rogers, H. K. (2006). Investments in Fuel Removals to Avoid Forest Fires Result in Substantial Benefits. Journal of Forestry, 104(1), 27-31. doi:10.1093/jof/104.1.27
Moos, C., Bebi, P., Graf, F., Mattli, J., Rickli, C., & Schwarz, M. (2016). How does forest structure affect root reinforcement and susceptibility to shallow landslides? Earth Surface Processes and Landforms, 41(7), 951-960. doi:10.1002/esp.3887
Mueck, S., & Peacock, R. (1992). Impacts of intensive timber harvesting on the forests of East Gippsland, Victoria. VSP Technical Report No. 15. Department of Conservation and Environment, Melbourne. In.
Preti, F. (2013). Forest protection and protection forest: Tree root degradation over hydrological shallow landslides triggering. Ecological Engineering(61P), 633-645. doi:dx.doi.org/10.1016/j.ecoleng.2012.11.009
Ray, D., Nepstad, D., & Moutinho, P. (2005). MICROMETEOROLOGICAL AND CANOPY CONTROLS OF FIRE SUSCEPTIBILITY IN A FORESTED AMAZON LANDSCAPE. Ecological Applications, 15(5), 1664-1678. doi:10.1890/05-0404
Thompson, J. R., Spies, T. A., & Ganio, L. M. (2007). Reburn severity in managed and unmanaged vegetation in a large wildfire. Proceedings of the National Academy of Sciences, 104(25), 10743. doi:10.1073/pnas.0700229104
Wangchuk, T. (2019, August 3). Cutting more forest is not the most expedient choice, Opinion. Kuensel. Retrieved from http://www.kuenselonline.com/cutting-more-forest-is-not-the-most-expedient-choice/