Restoration of degraded pastures using agrosilvopastoral systems with native trees in the Neotropics 2nd.World Congress in Agroforestry, Nairobi, Kenya, August 23-28, 2009 Session 14: "Agroforestry as a Tool For Landscape Restoration" Florencia Montagnini Professor in the Practice of Tropical Forestry Director, Program in Tropical Forestry Global Institute of Sustainable Forestry
Conversion of forests to pastures is one of the most widespread land-use changes in the Latin American tropics. Between 30% and 60% of these pastures have been degraded by inadequate management. Degraded pastures in Quindio, Colombia. Photos: Alicia Calle
Native tree species, in pure or mixed plantations, as well as in silvopastoral combinations, can contribute to restore soils, productivity and environmental services of degraded pastures. • We present results of long-term studies on rehabilitation of degraded pastures using native tree species that are well suited to silvopastoral systems in Costa Rica. Degraded pasture, dominated by non-productive ferns and grasses more than 20 years after abandonment. Photo: Daniel Piotto
Methods • Native tree species were planted in mixed and pure plantations in 1991-1992 on degraded pastures. Twelve species were planted, 4 of which were eliminated by pests and disease; the 8 following remained: • Plantation 1: Vochysia guatemalensis (Vochysiaceae) and Jacaranda copaia (Bignoniaceae); • Plantation 2: Dipteryx panamensis (Fabaceae), Terminalia amazonia (Combretaceae) and Virola koschny (Myristicaceae); • Plantation 3: Balizia elegans (Mimoseaceae), Hyeronima alchorneoides (Euphorbiaceae) and Vochysia ferruginea (Vochysiaceae). • Height and diameter at breast height (dbh) were measured annually. • Basal area, volume, aboveground biomass, and carbon storage were measured/calculated. • Litterfall was measured using litter traps for 12 months in each plot. • Soil was sampled below each of the pure and mixed plots, in unplanted abandoned pastures, and adjacent 20 year old secondary forest.
Young mixed plantation of native species (Jacaranda copaia, Calophyllum brasiliense “Cedro Maria”, and Vochysia guatemalensis “Mayo/Chancho”, on degraded pasture. La Selva, Costa Rica (10 22'N, 83 59'W, 35-137 masl, 24°C, mean annual precipitation 4000 mm). Soils are Fluventic Dystropepts, deep, well-drained, stone-free, with low or medium amounts of organic matter (2.5%-4.5%), acidic (pH in water <5.0), and low fertility.
Terminalia amazonia, 10 years, timber price comparable to teak in Panama Mixed plantation, product diversification and environmental benefits.
Vochysia ferruginea , 14 years, controls erosion, increases soil N and OM content. Virola koschnyi, 14 years, medium timber quality, dense crown.
Vochysia guatemalensis: 27.4 cm dbh in pure plantation and 37.9 cm in mixed plantation at 16 years. Reduces soil erosion. Adapted to soils of very low fertility and poor drainage. Harbors diversity. Calculated NPV at 16 yrs: $16,000/ha (Montagnini and Piotto, 2010) Photo: Daniel Piotto
Tree density and volume in 16-year-old pure and mixed plantations. La Selva, Costa Rica. Source: Montagnini and Piotto, 2010
Carbon storage in 16-year-old pure and mixed plots, La Selva. Source: Montagnini and Piotto, 2010.
At 16 years, mixed species plots were more productive than pure plantations in wood volume and carbon sequestration. • Vochysia guatemalensis is preferred by farmers for its good growth on poor, acid, poorly-drained soils and high-value timber, grew particularly well. • Virola koschnyi, Terminalia amazonia, Vochysia ferruginea, and Hyeronima alchorneoides all grew well and are preferred by farmers for their good growth and high quality timber (Redondo-Brenes 2007). • Rotation lengths are 10 years for J. copaia, 20 yrs for V. guatemalensis, 25 yrs for T. amazonia, V. ferruginea, H. alchorneoides, V. koschnyi, and B. elegans; and 40 yrs for D. panamensis.
Soil Organic Matter and Nitrogen in 15-16 year old mixed and pure plantations. La Selva, Costa Rica. Source: Montagnini 2008.
Impacts on soil fertility • At 3 years, plantations soils had already improved: in the top 15 cm, total N was 0.23% - 32% and SOM was 5.5% - 6.6%, while abandoned pastures had only 0.23% N and 4.8% OM. • Soil in adjacent 20-year-old secondary forest was similar to that of 3-year-old plantations: 0.33% (N) and 7.6% (MO). • The highest OM, N, Ca, and P values were below Vochysia ferruginea, the species that produced the greatest quantity of litter. • Mixed plots had intermediate levels of OM and nutrients.
Annual litterfall and accumulation in pure and mixed plantations. La Selva, Costa Rica.
Litterfall, decomposition, and accumulation • Litterfall was greatest in V. guatemalensis, T. amazonia, H. alchorneoides and V. ferruginea • Decomposition was fastest in T. amazonia, D. panamensis and B. elegans, where litter decomposed completely in 12 months. • Decompositon was slowest in V. guatemalensis, J. copaia and V. koschnyi. • Litterfall, decomposition, and accumulation were intermediate in mixed plantations.
Hyeronima alchorneoides in a silvopastoral system. Photo: Alvaro Redondo
Use of these tree species in silvopastoral systems • T. amazonia, D. panamensis, and Balizia elegans provide rapid liberation of soil nutrients through litter, encouraging growth of natural or seeded grass species. • Hyeronima alchorneoides forms a open crown, and its nutrient cycling makes it an appropriate choice for agroforestry systems. • Virola koschnyi and Terminalia amazonia form denser crowns, but can be included in lower-density silvopastoral systems. • These trees are used in silvopastoral combinations with beef cattle when the trees are 2-3 years old, when damage by cattle is expected to be minimal. • Native grasses such as Paspalum fasciculatum, and the exotic Cynodon nlenfuensis, Panicum maximum, Pennisetum purpureum, Brachiaria spp., Melinis minutiflora, and Ischaemun indiana grow well beneath these species.
Conclusions • Degraded pastures can be replaced with plantations of native trees that improve soils, control erosion, and produce high-quality timber, providing both restoration and productivity. • Farmers can also benefit from tree plantations with payments for environmental services (PES), due to the C sequestration performed by these species. • By adding cattle in silvopastoral systems, short-term economic products are also obtained, thereby accelerating returns on investment, providing an added incentive for reforesting degraded sites. • In these systems, the cattle feed on grasses that grow naturally below the plantation. Future research should seek more productive silvopastoral systems using grasses and other species better fit to these conditions. • Plantations that include multiple tree species may offer the benefits of each species, as well as the advantage of providing a diversity of products, an important factor to local farmers.
Thank you!Questions? Photos: Alicia Calle
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