Restoration of Riparian Ecosystems Post Tin Mining in the Central Amazon

Authors and Affiliations

• Rodrigo de Souza Barbosa (Mineraçao Taboca, Brazil)

• Julia Isabella de Matos Rodrigues (Federal Rural University of Amazonia, Brazil)

• Victor Pereira de Oliveira (National Institute of Amazon Researches, Brazil)

• Walmer Bruno Rocha Martins (Federal Rural University of Amazonia, Brazil)

• Carlos Alexandre Costa Coelho (Mineraçao Taboca, Brazil)

• Wyler Frank Siqueira do Carmo (Mineraçao Taboca, Brazil)

• Nonato Junior Ribeiro dos Santos (Mineraçao Taboca, Brazil)

• Wagner Varanda de Sousa (Mineraçao Taboca, Brazil)

• Eliezer Augusto Litaiff de São Paulo Aguiar (Mineraçao Taboca, Brazil)

Article Info

Keywords:

• Environmental recovery

• Forest revegetation

• Periodic monitoring

• Ecological indicators

• Restoration of mining environments

Abstract

• Riparian forests play a critical role in protecting water and soil and creating gene flow corridors between forest remnants.

• Restoration via seedling planting can accelerate ecological succession but is rarely assessed in post-mined areas of the Amazon.

• This study evaluated the restoration trajectory of riparian forests after tin mining, focusing on compositional and structural indicators for species selection based on height and DBH (Diameter at Breast Height) increments.

• Eight riparian forests were examined, with ages ranging from ≤1.5 years to 8.5 years.

• Plots established for assessment were 30 m × 30 m, with at least three plots in each forest.

• Results showed an increase in individual and species density over time, particularly in RF6.5 and RF1.5 areas.

• Species with the highest Importance Value Index (IVI) accounted for more than 60% of total species in the restored ecosystems.

• Most suitable species for planting:

  • P. pendula across all assessed forests

  • C. guianensis, H. courbaril, E. precatoria, and M. flexuosa as structuring species.

1. Introduction

• The Amazon hosts the largest tropical forest globally, with about 11% of terrestrial biodiversity and an estimated 15,000 tree species.

• Global climate change and biodiversity loss necessitate the restoration of degraded forest ecosystems, with a goal to restore 350 million hectares by 2030 under initiatives like the Bonn Challenge.

• Brazil aims to restore 12 million hectares by 2030 via the National Policy for the Recovery of Native Vegetation (PROVEG).

• Riparian forests play an essential role in protecting waterways from pollutants and supporting regional biodiversity through seasonal dynamics of water.

• Approximately 5 million hectares remain degraded in Brazil, primarily in Amazonia, due to activities like tin mining.

• Tin Mining:

  • Tin's industrial applications necessitate its extraction, leading to significant environmental degradation by modifying landscapes and disrupting ecosystems.

  • Brazil has approximately 9% of world tin reserves, with the Amazon accounting for over 90% of national production.

• Restorative efforts require active engagement due to total disturbance from mining impacts, focusing primarily on soil restoration and species selection.

2. Material and Methods

2.1. Study Area

• Conducted at Mineraçao Taboca SA, Presidente Figueiredo, Amazonas, Brazil, 320 km from Manaus.

• Climate: Aw (rainy tropical) with average monthly temperatures above 18°C and relative humidity around 96%.

2.2. Methods

2.2.1. Sampling of Riparian Forests

• Covering 1239 ha, 40% are riparian ecosystems now in recovery.

• Eight areas chosen based on recovery initiation (2014-2021) and grouped by age for monitoring.

• Plantation Methodology:

  • Spacing of 3 m × 3 m, fertilized with superphosphate and N-P-K.

  • Planting occurs during the rainy season (December to April).

  • Permanent plots (30 × 30 m and 30 × 5 m) used for assessing tree metrics.

2.2.2. Phytosociological Analysis

• Utilized the Importance Value Index (IVI) calculated from Relative Dominance (RD), Relative Frequency (RF), and Relative Density (RD).

• Equation for IVI:
  IVIi = \frac{RDoi + RFi + RDi}{3}

2.2.3. Analysis of Species Suitability for Restoration

• Species categorized into groups based on mortality and growth increments:

  • Very Low (VL), Low (LO), High (HI), Very High (VH).

  • Weighted values (WV) calculated for species fitness based on these classifications.

  • Sequential growth measures using:

    • Mortality:
      Mi(\%) = \left(1 - \frac{Nt2}{Nt1}\right) \left(\frac{1}{t}\right) \times 100

    • Mean Annual Increment in Diameter (MAI_DBH):
      MAIDBH = \frac{DBH}{T}

    • Mean Annual Increment in Height (MAI_Ht):
      MAIHt = \frac{Ht}{T}

2.2.4. Data Analysis

• Testing for normality and sphericity, applying ANOVA for density comparisons.

• Species richness analyzed through rarefaction curves, comparing sampling efforts across ecosystems.

• Multivariate analysis (NMDS) assessed floristic-structural patterns.

3. Results

3.1. Floristic Composition and Richness of Species

• Density of Individuals:

  • Ranged from 473.02 to 667.46 ind ha−1 across three measurements.

• Significant differences in species density observed in the third measurement.

• Statistical differences (ANOSIM: R = 0.34) indicated floristic-structural disparities between ecosystems.

3.2. Horizontal Structure

• Top 10 species (with high IVI) constituted over 60% of the ecosystems.

• V. guianensis predominated except for RF_1.5 where S. alata was prevalent.

• A total of 79 species identified, with 35 classified as efficient for restoration.

• Highlight: P. pendula had lower mortality rates and higher growth increments.

4. Discussion

• Selection of appropriate species is critical for restoration success, significantly affecting structure recovery in riparian ecosystems.

• Factors such as proximity to watercourses and water dynamics essential for plant health and species abundance.

• Importance of ongoing monitoring and adaptive management to address ecological challenges and enhance restoration efforts.

• Key Species Recommended:

  • P. pendula as ideal due to adaptability and growth characteristics.

  • Other bioeconomically valuable species like C. guianensis and M. flexuosa.

5. Conclusions

• Species selection significantly impacts restoration trajectories and the success of ecological indicators in riparian forests.

• P. pendula identified as the optimal species for planting in degraded areas, promoting recovery while minimizing costs and mortality rates.

Declaration of Competing Interest

• The authors have no known competing interests that could influence the reported work.

Data Availability

• Data will be available upon request.

Acknowledgments

• Thanks to Taboca Mining Company for logistical support and the Federal Rural University of Amazonia for professional assistance.

References

• A comprehensive list of studies and reports related to the restoration ecology, mining impacts, and biodiversity in the Amazon region, including sources on climate change and ecological restoration strategies.