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Title: Potential uses of red alder (Alnus rubra Bong.) in silvopastoral systems
Author: Mmolotsi, Ronnie M.
ISNI:       0000 0001 3412 8203
Awarding Body: University of Wales, Bangor
Current Institution: Bangor University
Date of Award: 2004
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Studies on Alnus rubra, Bong. (Red alder) were carried out at Henfaes agroforestry experimental site, in North Wales to asses its potentials for use as a component of silvopastural systems. The specific objectives were: 1) to study the nitrogen fixing capability of red alder using nitrogen-15 natural abundance method, 2) to investigate the dynamics of fine roots and root nodules in red alder and their contribution to organic matter and nitrogen balance under silvopastoral systems, 3) to assess the timber quality of red alder wood in comparison with sycamore and finally, 4) to study the firewood and biomass energy value of red alder in comparison with sycamore. Literature reviewed showed that red alder, as a nitrogen fixing tree species, inputs large amount of nitrogen into natural ecosystems where it occurs. Reports also showed that it provides the much needed nitrogen when it is grown with other crops. The wood of red alder was reported to be good for furniture, studs, panelling and for making household utensils. There is, however, no information on the use of red alder in silvopasture. In the present study, using nitrogen-15 natural abundance method 815N values close to zero were recoded in red alder plant parts except in root nodules. This indicates that a large proportion of nitrogen in red alder was fixed from the atmosphere. The highest fixed nitrogen was measured in leaves (91 %) and the least (78%) in wood of red alder. Fixed nitrogen was higher during the summer and autumn (90% and 99%, respectively) than in winter and spring (85% and 64%, respectively). The 815N values in root nodules were enriched with 15N and this indicates that soil was the source of nitrogen for root nodules of red alder. Overall, it was estimated that 63.45 and 329.53 kg N ha-1 was fixed by red alder in the agroforestry and forestry systems, respectively. Live and dead fine root weight densities of red alder were 2700 and 5400 kg ha-1 and 360 and 790 kg ha-1 in agroforestry and forestry, respectively. Live and dead root nodule weight density of red alder yielded 880 and 520 kg ha-1 in agroforestry in 800 and 310 kg ha-' in forestry, respectively. The amount of organic matter potentially added to the soil due to senescent leaves and dead roots and root nodules was estimated at 4.0 and 9.1 t ha-' yf 1, in agroforestry and forestry, respectively. These results showed that red alder has a potential to improve and maintain soil fertility in silvopasture. Fine root length density was also found to differ significantly between agroforestry and forestry treatments, between seasons and between depths but there was no difference between distances from the tree base of red alder. Overall, the results of the distribution of fine root length density showed that red alder is compatible with pasture. Wood mechanical properties of red alder were found to be significantly different from that of sycamore. Sycamore yielded higher wood density (0.64 g cm-3), modulus of rupture (90.24 MPa) and compression strength (36.49 MPa) than red alder (0.49 g cm- , 73 .48 MPa and 32.13 MPa, respectively). However, modulus of elasticity was higher in red alder (7614.64 MPa) than in sycamore (7430.05 MPa), although it was not significantly different. Based on the results of wood properties of red alder it was concluded that red alder is medium strength tree species with potential for furniture manufacturing and for ordinary non-structural uses such as panelling and studs. Although the calorific value of sycamore was higher than red alder, red alder wood gave significantly higher fuel value index (1637.77) than sycamore (1480.60) due to very high ash content of sycamore. Thus, it was concluded that red alder has a potential to provide a better bioenergy than sycamore for heating homes and generating electricity. On the basis of the findings of the present study it was finally concluded that red alder is a suitable tree species for incorporation in silvopasture.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available