In tropical humid Africa, sandy soils in herbaceous savannas—often exposed to periodic burning—typically exhibit low carbon (C) content and nitrogen (N) availability. Savanna afforestation has the potential to improve soil functionality, but its effects remain underexplored. This study examines whether changes in soil micro-food web composition contribute to increased C and N cycling following afforestation. A 7-year experiment in Congo assessed Eucalyptus monocultures, N₂-fixing Acacia monocultures, and mixed Eucalyptus-Acacia plantations on former savanna landscapes. Soil attributes analyzed included organic C and N levels, pHH₂O, nitrate, ammonium, mineralization and nitrification rates, as well as bacteria, fungi, nematodes, and ammonia-oxidizing archaea (AOA) and bacteria (AOB) abundances in the top 10 cm of soil. Afforestation with Eucalyptus monocultures increased soil carbon by 1.7 times, net nitrogen mineralization rates by 1.9 times, and soil inorganic nitrogen levels by 2.5 times. Mixed Eucalyptus-Acacia and Acacia monocultures further enhanced nitrogen mineralization by 1.4 times and inorganic nitrogen by 2.3 times compared to Eucalyptus monocultures. These changes correlated with a progressive increase in AOA abundance, peaking in Acacia monocultures. Additionally, afforestation significantly boosted bacterial-feeding nematode abundance by 678%, while fungal-feeders, omnivores, and predators declined. Enhanced nitrogen cycling was positively linked to AOA and bacterial-feeding nematode abundances, emphasizing the necessity of monitoring micro-food web structures to better understand how land use changes shape soil biogeochemical cycles in tropical afforestation contexts.
Tag: Afforestation
Assessing conditions to scale up private investment in forest restoration
Forest restoration (FR) in low- and middle-income countries (LMICs) requires private investment. We estimated the area of degraded forestland with investment conditions favoring private FR in 115 LMICs. We examined a base scenario, with FR driven by wood markets and influenced by seven investment conditions, and a “natural climate solutions” (NCS) scenario, with FR driven by carbon markets and influenced by six conditions. We have found that barely half of the restorable area in the base scenario, and barely a third in the NCS scenario, has at least four favorable investment conditions (i.e., at least half of the total number). In both scenarios, less than 1% of the restorable area has all conditions favorable. Locations with more favorable conditions tend to have greater potential to generate local livelihood benefits than global carbon or biodiversity benefits. Of the 59 LMICs that have made national commitments to restore forestland under the Bonn Challenge, which has a global goal to restore 350 million hectares by 2030, more than half have made a commitment whose area exceeds our estimate of the country’s restorable area with at least four favorable investment conditions. This discrepancy implies that those countries cannot rely solely on private investment to achieve their commitments. Scaling up private FR in LMICs requires coordinated public-sector investments and policy interventions to improve investment conditions and ensure that private FR generates both local and global environmental benefits.
Performance of forest plantations in small and medium-sized farms in the Atlantic lowlands of Costa Rica
Exotic tree species predominate in reforestation in tropical regions worldwide. However, some native species are suitable for plantations, providing a wider variety of products. Adequate government programs of incentives, coupled with good technical advice to farmers, are needed to stimulate reforestation, especially among small and medium-sized farmers with limited financial resources. This project evaluates growth of native and exotic tree species on plantations in small and medium-sized farms in the Atlantic humid lowlands of Costa Rica, Central America. A total of 210 pure plantations, ranging in age from 6 to 11 years, were evaluated on 123 farms that had used government incentives for reforestation, and had received technical advice from local non-government organizations. For each species, seven plantations were chosen at random for study. In each plantation, plots of 15 trees each were chosen systematically for evaluation of diameter at breast height (dbh), total height, number of trees per hectare, tree form and spacing. Terminalia amazonia (J.F. Gmel) Exell, Hieronyma alchorneoides Allemao, and Vochysia guatemalensis Donn. Sm. were the most frequent species found in plantations in the region of study. Gmelina arborea Roxb. (exotic) and V. guatemalensis (native) had the highest mean annual diameter increment with 2.90 and 2.59 cm, respectively. Calophyllum brasiliense Cambess. (native) had the lowest mean annual diameter increment (1.48 cm). G. arborea and V. guatemalensis had the highest mean annual volume increment, followed by Tectona grandis (L.f) Lam. (exotic), and T. amazonia and Cordia alliodora (R&P) Cham. (both native). Although G. arborea had the greatest mean annual diameter increment, it had the lowest plantation density and problems with form. V. guatemalensis and T. amazonia, two native species, were the most promising species for reforestation, due to good growth in volume, good form, and adaptability to a variety of sites. The poor form of exotic species was related to the low intensity management methods of small farmers. Exotic species had the highest performance variability between sites, while native species showed relatively high growth homogeneity. Therefore, native species seem more promising than exotics for general use across varying ecological conditions.
A general allometric equation for estimating biomass in Acacia mangium plantations
Acacia Mangium Willd. is one of the most important tree species grown in commercial plantation in Monsoon Asia. Recently, the need for accurate information in the biomass in plantations has become more urgent, especially since the amount of carbon sequestered in afforestation/reforestation Clean Development Mechanism (AR-CDM) projects in developing countries can be included under the Kyoto Protocol. We present here a general allometric equation for estimating aboveground biomass (AGB) of A. mangium plantations from the diameter of the trees recorded at the respectives sites. Destructive samplings were conducted in Papua New Guinea, Vietnam, and Indonesia. At each site, 4-12 trees were felled, their trunks, branches and leaves were separately weighed, and allometric models for estimating AGB was determined. A general allometric equation (A log-log model) was developed from an overall total of 26 sample trees from sampled sites. No significant differences were found between the biomass estimations derived from the site-specific and the general allometric equations. The general allometric equation may allow us to estimate AGB of A. mangium plantations in Monsoon Asia without destructive sampling.
Forest plantations in Costa Rica and Nicaragua: performance of species and preferences of farmers
The area of forest plantations in the tropics worldwide is increasing as a response to the expansion of degraded lands. Rural farmers of many regions of the dry and humid areas are responding to government and other incentives, dedicating portions of their land to native and exotic tree plantations with varied uses and objectives.We evaluated the success of reforestation efforts in a dry region of Nicaragua and in a humid region of Costa Rica where reforestation has been promoted by the governments with local assistance of technical personnel and non-governmental organizations. In all farms, the survival, diameter at breast height (dbh), height, form, and health of the tree plantations were evaluated. In addition information regarding the farmer’s preferences and characteristics of the farms and the farmers was gathered through a survey including socioeconomic and silvicultural aspects. In both countries farmers used more native than exotic species for reforestation. Farmers are willing to continue reforesting as long as they continue to receive government incentives. In Costa Rica the plantations had better silvicultural management than in Nicaragua. In Nicaragua the species preferred by farmers for their growth were Azadirachta indica, Caesalpinia eriostachys, Eucalyptus spp., Gliricidia sepium, Leucaena leucocephala, and Tectona grandis. In Costa Rica the preferred species for their growth were Cordia alliodora, Gmelina arborea, Terminalia amazonia, Tectona grandis, Vochysia guatemalensis, and Virola koschnyi. The implementation of incentive programs for reforestation was a key factor in encouraging the participation of small and medium farmers.
Current trends of reforestation in the tropical countries of Asia and the Pacific
Notwithstanding the global trend, Asia and the Pacific region has recorded several years of strong economic growth. The economic potential of the region has steadily increased over the past quarter of a century and most analysis agree that this trend will continue in the years ahead. With the rapid rise of living and education standards the per capita consumption of wood and wood-derived products is increasing at well above the estimated average world rate. Presently the timber production of the tropical countries of Asia and the Pacific is, for the most part, from the natural forests and is still steeply and steadily increasing. However because of the rapid depletion of the resource and increasing environmental concern this trend is expected to reserve as it has in tropical Africa and tropical America. This situation poses new challenges and opportunities for the region to develop a competitive source of wood from plantations. This paper examines the comparative advantages of the Asia-Pacific tropical countries in this respect.
Forest management and terraced agriculture: case study of Hani of Ailao mountains, Yunnan
This case study of the Hani in the Ailao mountains of Yunnan, China, highlights the importance of forests in providing local ecological services that are essential for the system of terraced agriculture. The paper investigates local people’s knowledge of these ecological services, including water regulation and nutrient recycling, as well as the gender differences in the local knowledge of these services. The paper notes that the Hani have maintained the forest condition quite irrespective of its tenurial status. Contemporary forest policies and reforestation in the area are also discussed.