Afforesting savannas with Acacia mangium and eucalyptus improves P availability in Arenosols of the Congolese coastal plains

Basic information

• Case ID: INT-256-1
• Intervention type: Created habitats
• Intervention description:

  Mixed Eu- calyptus urophylla × grandis hybrid (18–52) and Acacia mangium stands were established in May 2004 (starter fertilization of 43 kg ha − 1 of N as ammoniumnitrate). Pure acacia (100A), mixed-species with 50% aca- cia and 50% eucalyptus trees (50A50E, the two species being alternately planted in the row and between adjacent rows) and pure eucalyptus (100E) stands were compared within a randomised block design with five replicates (planting density of 800 trees ha−1). Each stand (1250 m2) consisted of an inner plot comprising 36 trees (6 × 6) and two buffer rows (Fig. 1 adapted from Koutika and Mareschal, 2017). The first rotation ended after 7 years which is a full length rotation for euca- lyptus plantations established in the area. Trees were harvested in Jan- uary 2012. Using the same design, the second rotation was planted in March 2012, with a closely related Eucalyptus urophylla × grandis hybrid (18–147) and Acacia mangium but without any N fertilizer added, while potassium (K) was supplied three months after planting i.e., 50 kg ha−1 as KCl.

• Landscape/sea scape ecosystem management: No

• Climate change impacts	Effect of Nbs on CCI	Effect measures
  Reduced soil quality	Positive	Soil fertility: various measures of phosphorus in the soil in different size fractions of organic matter and total available P in the soil“"Introduction of nitrogen-fixing trees as a way to improve soil fertility led to an increase in standing wood biomass, soil C and N accretion in the mixed-species stands. It also resulted in a decrease of soil P availabil- ity relative to pure eucalyptus and acacia stands at the end of the first 7- year rotation on the Arenosols of the Congolese coastal plains. Even then, it must be noticed that overall soil P availability in afforested stands was still higher than those of natural savannas at year 3 of the second rotation. This study is showing that in the low input systems; such as the studied experimental site, afforesting savannas increases P availability of inherently nutrient-poor but low P fixing soil, along with an increase in N stock and a potential C sequestration in both soil and biomass."”

• Approach implemented in the field: Yes
• Specific location:

  The studied site is located on a plateau close to Tchissoko village in Congo (4°S, 12°E, 100 Alt.), on a deep Ferralic Arenosol laying on a bed- rock composed of thick detritic layers of continental origin dated from plio-pleistocene at about 35 km of Pointe-Noire city.

• Country: Congo, Rep.
• Habitat/Biome type: Created forest |
• Issue specific term: Not applicable
  

Evidence

• Notes on intervention effectivness: aim of study was to test different types of species and species mixures to see which was most effective but these are not coded as separate interventions. All options are also compared to a control natural savannah where no trees have been planted so that is how effectiveness is assessed. "Introduction of nitrogen-fixing trees as a way to improve soil fertility led to an increase in standing wood biomass, soil C and N accretion in the mixed-species stands. It also resulted in a decrease of soil P availability relative to pure eucalyptus and acacia stands at the end of the first 7- year rotation on the Arenosols of the Congolese coastal plains. Even then, it must be noticed that overall soil P availability in afforested stands was still higher than those of natural savannas at year 3 of the second rotation. This study is showing that in the low input systems; such as the studied experimental site, afforesting savannas increases P availability of inherently nutrient-poor but low P fixing soil, along with an increase in N stock and a potential C sequestration in both soil and biomass."
• Is the assessment original?: Yes
• Broadtype of intervention considered: Not applicable
• Compare effectivness?: No
• Compared to the non-NBS approach: Not applicable
• Report greenhouse gas mitigation?: Yes
• Impacts on GHG: Positive
• Assess outcomes of the intervention on natural ecosystems: No
• Impacts for the ecosystem: Not reported
• Ecosystem measures: N/A
• Assess outcomes of the intervention on people: No
• Impacts for people: Not reported
• People measures: N/A
• Considers economic costs: No
• Economic appraisal conducted: No
• Economic appraisal described:
• Economic costs of alternative considered: No
• Compared to an alternative: Not reported

Evaluation methodology

• Type of data: Quantitative
• Is it experimental: Yes
• Experimental evalution done: In-situ/field
• Non-experimental evalution done: Not applicable
• Study is systematic: