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BackgroundThe need for energy sources with low greenhouse gas emissions and sustainable production encourages the search for alternative biomass sources. However, the use of biomass fuels faces the problem of storage, transport and lower energy densities. Low-density values can negatively affect energy density, leading to an increase in transportation and storage costs. Use of pellets as alternative biomass source is a way to reduce the volume of biomass by densification, which improves their energy quality. They are produced by diverse biomass resources and mainly from wood materials. In all cases, it is important to evaluate the fuel characteristics, to determine their suitability on the heating system and handling properties.MethodsThe present study determines and compares data from proximate analysis, calorific values, physical and mechanical properties of wood pellets produced from the common tropical species Acacia wrightii, Ebenopsis ebano and Havardia pallens. Data were obtained from pellets produced from each species chips collected from an experimental plantation and analyzed through ANOVA and Kruskal–Wallis test at 0.05 significance level.ResultsThe results of diameter, length and length/diameter ratio didn’t show statistical differences (p > 0.05) among species. Acacia wrightii showed the highest density (1.2 g/cm3). Values on weight retained and compression test showed statistical differences (p = 0.05) among species. Havardia pallens was more resistant to compression strength than A. wrightii and Ebenopsis ebano. Statistical differences (p < 0.01) were also observed for the volatile matter and calorific value. E. ebano has the lowest volatile matter (72%), highest calorific value (19.6 MJ/kg) as well as the fixed carbon (21%).DiscussionThe pellets of the species studied have a high energy density, which makes them suitable for both commercial and industrial heating applications.A pellet with low compression resistance tends to disintegrate easily, due to moisture adsorption. The percentages obtained for the resistance index were higher than 97.5%, showing that the pellets studied are high-quality biofuels. Proximate analysis values also indicate good combustion parameters. Pellets of Acacia wrightii and Ebenopsis ebano are the more favorable raw material sources for energy purposes because of their high density, calorific value, low ash content and they also met majority of the international quality parameters.

Fifteen multipurpose tree species native and introduced to the matorral (low dry shrubland and forest) of the Gulf Coastral Plain in north-eastern Mexico were planted in monoculture in four randomized blocks. Measurements of various growth parameters and volume of trees over the first five years were evaluated. Eucalyptus camaldulensis, E. microtheca, Leucaena leucocephala (exotic species) and Parkinsonia aculeata (native species) performed best while Prosopis glandulosa, Helietta parvifolia and Acacia rigidula (native species) did not establish well due to biotic problems which arose under plantation conditions. Acacia farnesiana, A. wrightii and two Pithecellobium spp. (native species) showed high yields which is of great interest since their multipurpose potential is the best of all fifteen species. These species could be of great importance in rehabilitating badly degraded parts of the matorral before such areas deteriorate to an irreversible desertified condition.Resumen. Para cuantificar el crecimiento y la productividad de las plantas lefiosas, quince especies nativas e introducidas con caracteristicas multiprop6sito fueron plantadas en monocultivo en una zona de matorral de la Planicie Costera del Golfo Norte de MExico a partir de 1984. Durante cinco afios de medici6n continua sobre diferentes parfimetros de crecimiento, fueron evaluados los resultados sobre el comportamiento y productividad (volumen de la madera) de las especies. Eucalyptus camaldulensis, E. microtheca, Leucaena leucocephala (especies ex6ticas) y Parkinsonia aculeata (especie nativa) presentaron los mejores crecimiento en altura yen volumen en comparaci6n con Prosopis glandulosa, Helietta parvifolia y Acacia rigidula (especies nativas). E1 desarrollo de Acacia farnesiana, A. wrightii y ambos Pithecellobium spp. (especies nativas) se puede considerar bastante bueno. Estas ultimas especies son de gran interEs como potencial forestal y forrajero. Todas las especies ensayadas son de suma importancia en la rehabilitaci6n de matorral degradado yen el manejo silvicola de estos vastos recursos.

Leaf biomass over 20 native species from thornscrub canopies was evaluated by five nondestructive allometric methods and compared in order to determine the most accurate estimating procedure. Indirect relationships between leaf biomass and some ecological characteristics of the plants may be found by using regression models. Ecological and morphological characteristics of these species were determined using a structural analysis. No single standard method estimated leaf biomass for all species on site due to the diversity of geometric shapes in these species. However, Adelaide, double sampling and the dimensional methods were the most precise, practical and simplest methods for measuring the forage leaf biomass of many shrub species. The linear models gave a better estimate of tree biomass than the logarithmic functions. The regression equations showed a close relationship between foliar biomass and growth parameters.