The population dynamics and productivity of Acacia pennatula in the pasturelands of the Nature Reserve Mesas de Moropotente, Estelí, Nicaragua

Abstract

Acacia pennatula trees are the most conspicuous woody species in the pasturelands of the Nature Reserve Mesas de Moropotente, Estelí, Nicaragua. Cattle ranchers keep A. pennatula because it produces fence posts, forage (pods) and firewood. A population projection matrix model was developed to: (1) estimate the sustainable harvest (H) of fence posts at different tree population densities, (2) explore the range of recruitment (R), and survival and growth of both saplings and small poles compatible with current population density, and (3) determine how much carbon is stored in the soil-pasture-tree system. Acacia pennatula trees take 40 years to reach H size (D₃₀ ≥ 30 cm). Estimated sustainable H from current tree population density is 1.8l7 trees ha⁻¹ year⁻¹, yielding 2.8 large and 11.2 regular size fence posts ha⁻¹ year⁻¹. This annual output easily satisfies the needs of a typical 100 ha cattle ranch in the study area. Current population density is congruent with very low R (<100 saplings ha⁻¹ year⁻¹), very low survival rates (<0.30%) and/or retarded D₃₀ growth of saplings and small poles. Total carbon in tree biomass was only 37 Mg ha⁻¹. Cattle ranchers have learned to harness the invasive nature of the species to obtain valuable tree products for farm use or sale.