By James W. Kisekka, 2012
Paper mulberry (Broussonetia papyrifera) is a small or medium-sized tree usually growing to 10-15m tall, but occasionally reaching 20m. Native to Japan and Taiwan (Whistler and Elevitch, 2006), paper mulberry is now found in the southeastern USA, South America (Argentina), Africa (Ghana and Uganda) and Asia (Pakistan and the Philippines) (Technigro, 2011). In some of these regions, for example Ghana and Uganda, Haysom and Murphy (2003) report that paper mulberry has become naturalized and is regarded as invasive. Records point to the importance of the species in the Polynesian culture, more than 1500 years ago, where its bark was used to make tapa cloth; one of the most important materials in ancient Polynesia (Whistler and Elevitch, 2006).
In Uganda, Mr. Severest Ssekindi (a forester whose experience dates as back as the time of the Forest department), reports that paper mulberry was first introduced in Budongo Forest in the late 1950’s by William Julius Eggeling, who was by then the commissioner in charge of forests in the Forest Department. It was hoped that the tree species would be used for pulp production, but this was not achieved because the species did not attain the required diameter as had been expected. For the case of Mabira Forest, Mr. Ssekindi suspects that paper mulberry was among the species introduced between the late 1970s and early 1980s to restore areas that had been degraded due to human encroachment. Given its fast growth, paper mulberry would out-compete encroachers’ agronomic crops. Reports by the Uganda Forest Resources and Institutions Centre (UFRIC); a body housed in the School of Forestry, Environmental and Geographical Sciences of Makerere University, indicate that paper mulberry is now the dominant tree species in Wakisi the Eastern part of Mabira forest.
This raises many questions about our struggle and efforts to eliminate paper mulberry. If it is already naturalized, does it still make sense to fight it? Shall we ever win that battle, or should we rather invest our efforts in exploiting its “properties” to achieve sustainable development? This article seeks to address those questions. I present lessons drawn from observations made in Uganda and elsewhere and also suggest more questions that I believe if answered will help determine whether or not paper mulberry is good for Uganda.
Lessons from Uganda and elsewhere, and implications for development
UFRIC has, since the early 1990s, carried out research about how communities interface with forests in different parts of Uganda, and has studied two communities (Nakalanga and Kirugu) that access Wakisi. Findings from these two communities indicate that about 30% of the households own cattle and goats, which they either graze in the forest or keep in zero-grazing units with paper mulberry leaves as the main source of fodder. On average, a household owning two cows harvests 100kg of the leaves per day, while those with 2 goats harvest 10kg daily. This demonstrates the importance of paper mulberry to livestock production among the communities surrounding Wakisi.
Mr. Dan Kasujja, a resident of Nakalanga village, adds that the community uses paper mulberry (locally known as Nkulaidho) for firewood and charcoal production, both for subsistence purposes and for sale in the neighbouring towns like Jinja, Njeru and Kangulumira where it is said to be highly demanded. According to him, even though the charcoal is less dense than that from the traditionally preferred tree species in the forest, it is easy to ignite and burns properly. Freshly stacked, harvested or old kiln sites where paper mulberry was the main wood carbonized are a common sight in the forest.
To the community, paper mulberry has thus provided a nearly inexhaustible source of fodder and woodfuel, given its fast rate of growth, thereby cushioning the native tree species in the remaining parts of Mabira from further exploitation. It may be argued that forest cover in the Eastern part of Mabira forest would have been much lower had it not been for the presence of paper mulberry. While a pure stand of paper mulberry is not the desired status quo in this region, its presence may protect the native species from exploitation. Consequently, its absence might, in some cases, mean no more forest at all, further endangering the three pillars of sustainable development namely, the economy, society and the environment (Kayanja and Byarugaba, 2001).
In countries like the Lao PDR and Thailand, paper mulberry is one of the forest products local communities depend upon to earn an income (Aubertin, 2004; Watanabe et al. 2004; Neef et al., 2010). In these countries, the bark of the tree is used to make durable paper that is either sold and used locally (Neef et al., 2010) or exported to countries like Japan and South Korea where it is processed into various high-value products like special papers for banknotes, liturgical objects and luxury stationery (Aubertin, 2004). Reports from Lao PDR and Thailand (for example Neef et al., 2010) indicate that the tree has now been domesticated, with land-rich people growing it as a way of consolidating their income.
In Uganda, a country that relies on imports to satisfy most of its paper demands, establishing small-scale paper processing industries based on Broussonetia papyrifera as a raw material could lessen the reliance on foreign products while at the same time providing employment to the local population who may be involved in, among other activities, hand-made paper production. In addition, a developed and sustainable paper industry could reduce the reliance on polythene packing material, thereby reducing chemical byproducts and non-degradable waste. The successful domestication of paper mulberry in Lao PDR may suggest that new opportunities have emerged for developing sustainable agroforestry systems in Uganda. Whistler and Elevitch (2006) note that the species has no potential of becoming invasive once only male clones are introduced.
Aurbertin (2004) notes that paper mulberry grows rapidly, reaching maturity at between six months and one year, at an average height of 3 m and diameter of 5 cm).It is adapted to all kinds of soil although it prefers moist alluvial soils. For any invasive species, such abilities reflect its potential to outcompete the native vegetation. This property can be exploited to address the current energy situation in Uganda where a majority of the population owes their energy supplies to biomass. Reports (e.g. MEMD, 2007; Khundi et al., 2011) are that 93% of the total energy supplied is from biomass (mainly in two forms; firewood and charcoal - with charcoal being used mainly in urban centres), and this is expected to continue in the foreseeable future. The use of charcoal is estimated to increase at 6% per year, which is proportional to the rate of urbanization (MEMD, 2002; Kuteesakwe and Tumuhimbise, 2003; NEMA, 2006), while firewood consumption is estimated to be growing at a rate of 3% per annum (MEMD, 2007), yet a negative trend in the availability of tree resources from which these two forms of wood fuel are extracted has been observed. The current increase in hydroelectricity tariffs coupled with the increased shortage of Liquefied Petroleum Gas (LPG) has worsened the situation even further. The scarcity of woodfuel has pushed the "rural poor” in areas like Manafwa, on the slopes of Mt. Elgon, to using plastic material as a source of fuel (NTV, 2012). This is harmful to the atmosphere as well as to the people because of the carcinogenic substances in the fumes from burning plastics.
To many researchers (for example Banana and Turiho-habwe, 1998; Kataki and Konwer, 2002; Arnold et al., 2003; Buyinza and Teera, 2008), establishing woodlots or plantations specifically for energy production could sustain the raw material for both charcoal and firewood production while at the same time cushioning trees in natural forests against the pressure of extraction for fuel, but still, that can best be achieved if the tree species selected for such plantations are fast-growing, which makes Broussonetia papyrifera a potential candidate. Kayanja and Byarugaba (2001) reported that managing the species on a 4-5 year rotation in Uganda could yield 90 –100 tonnes of woody biomass per hectare, as opposed to approximately 13 tonnes per hectare from woodlands. Going by this estimate, one hectare of paper mulberry could shield 6 hectares of woodland from exploitation for woodfuel production.
There is a common belief, backed by no empirical evidence, that paper mulberry negatively affects soil health. However, the few studies conducted point to the contrary. The tree species has been observed to improve soil fertility (Watanabe et al., 2004; Sakurai et al., 2005), probably by drawing nutrients from deeper layers and then returning it to the top layers in form of organic matter (Forsen et al., 2001). Reports from Laos (Aubertin, 2004) indicate that paper mulberry trees accelerate the regeneration of soil fertility, and their rapid growth results in rapid canopy closure which in turn suppresses weeds. In the perspective of Uganda whose soils are losing fertility, paper mulberry can thus be used to rejuvenate soil fertility, especially on land under fallow, and therefore boost agricultural productivity.
Ecological principles of “light demanders” vis a vis “shade tolerants” suggest that the diversity of shade tolerant tree species would be low in a young forest dominated by paper mulberry which is a light demander, but this changes over time. Observations in Mabira forest on either side of the Kampala-Jinja road are that the high-light areas immediately along the road were dominated by paper mulberry, which has now been displaced by native tree species by apparently regenerating in its shade, where its seedlings don’t survive. Thus, paper mulberry can be used to aid natural regeneration in previously deforested areas provided the soil seed bank is rich in seeds of the tree species in the “previous” forest. Further, it may be argued that paper mulberry does not displace the late-successional native forest species. Hence its introduction in an area could have no effect on secondary or climax forests.
Paper mulberry (like other woody invasives) is biomass waiting to be converted to fuel. Exploiting it as such could either keep its population in check or provide a more or less sustainable source of fuel to the community. Accordingly, it could be domesticated and grown in woodlots as a way of increasing the raw material for woodfuel production thereby reducing pressure on forests. However, only male clones of the species should be introduced if its invasive potential is to be curbed.
Further, its leaves can support livestock production while its bark can provide a sustainable source of raw material for hand-made paper production. This would contribute to improvement of rural incomes while at the same time ensuring environmental health through reducing reliance on packaging materials of polythene origin.
However, research is needed about how paper mulberry affects the animals on which it is fed; how it affects the soil physical, chemical and biological properties; and which other plant species are associated with it, if we are to make more logical conclusions.
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