Study Notes on Forest Restoration in the Southern Amazon

Alexandre Ferreira do Nascimento
Embrapa Wheat, Rodovia BR 285, km 294, Rural Area, Passo Fundo, RS 99050-970, Brazil
Ingo Isernhagen
Embrapa Forests, Ribeira Road, Km 111 – Bairro da Guaraituba, Colombo, PR 834111-000, Brazil
Jorge Lulu
Embrapa Territorial, Campinas, SP, Brazil
Antonio Okada
REM FUNBIO Scholarship, Embrapa Agrossilvipastoril, Rodovia MT 222, km 2.5, Rural Area, Sinop, MT 78550-000, Brazil
Jussane Antunes Fogaça dos Antunes
Sustainable Rural Project Scholarship, IABS, Embrapa Agrossilvipastoril, Rodovia MT 222, km 2.5, Rural Area, Sinop, MT 78550-000, Brazil
Austeclínio Lopes de Farias Neto
Embrapa Cerrados, Rodovia BR 020, km 18, Planaltina, DF 73310-970, Brazil

Keywords: Natural regeneration, Carbon sequestration, Active restoration, Tropical ecosystems

The Amazon rainforest faces severe environmental effects due to forest degradation.
Active restoration, involving mixed plantings of native/exotic tree seedlings, is essential for ecosystem recovery.
This study aimed to assess soil organic carbon (SOC) and total nitrogen (TN) stocks in legal reserve (LR) restoration treatments in the southern Amazon after 10 years (2012 - 2022).
The experiment utilized randomized block design with 5 treatments and 4 replicates to analyze soil samples for SOC and TN.
Active restoration significantly outperforms passive regeneration, achieving SOC stocks up to $120 ext{ Mg ha}^{-1}$ .
Native species are recommended for effective restoration strategies.

Forest Degradation Impact: A key concern over environmental debt in the southern and eastern Amazon biome; reduced native vegetation in legally protected areas has been noted.
Legal Framework: Brazilian Forest Code mandates maintaining ecological processes and biodiversity conservation within legal reserves (LRs).
Restoration Strategies: Involves both passive (natural regeneration) and active (planting native species along with strategic use of exotic species) techniques.
Biodiversity Recovery: Restoration of forest through mixed methods has implications for human well-being and ecosystem service sustenance.
Research Objective: Investigate how species composition affects SOC and TN in the first decade of restoration to align findings with UN goals for ecosystem restoration.

Koppen Climate Classification: The region exhibits a tropical monsoon climate (Am) with an average annual temperature of $25^{ ext{°C}}$ , annual relative humidity of 83%, and accumulated precipitation of $2250 ext{ mm}$ .

Experiment Site: Installed in December 2012, located in Sinop, MT, Brazil, latitude 11°51’S, longitude 55°35’W, altitude 384 m.
Soil Type: Classified as Plinthic Dystrophic Red Yellow Latosol (Brazilian Soil Classification System).

Treatments Evaluated:
- Nat+Euca: Regional native seedlings intercropped with eucalyptus (Eucalyptus urograndis).
- Nat+Rubber: Native seedlings planted with rubber tree seedlings.
- Passive: Area left for natural regeneration without interference.
- Native (Nat): Only regional native species seedlings.
Native Species Selection: A total of 17 native species based on regional adaptation, ecological role, and economic interest were used.
Plot Specifications: Each plot measures 0.48 ha (60 × 80 m) with specific plant spacing and unique maintenance treatments depending on the methodology.

Soil Sampling: Conducted to a depth of 1 m for SOC and TN analysis using both disturbed and undisturbed samples.
PAR (Photosynthetically Active Radiation): Monitored from 2015-2019 using sensors to investigate microclimate effects from treatments.

Restoration treatments resulted in variable PAR levels over time, with significant decreases noted in active treatments.
Best Fitting Trends for PAR: Logistic models showed strong correlation (4) with Nat treatment.

SOC and TN Content: Evaluated across different soil layers with notable trends observed.
- Surface layers showed highest SOC in the secondary forest, Nat, and Nat+Rubber treatment with active treatments outpacing passive.
- Native treatments resulted in annual SOC accumulation rates of $1.4 - 2.5 ext{ Mg ha}^{-1} ext{ year}^{-1}$ .

C:N ratios indicated highest values in Nat with lower values in passive treatments. Significant and distinct patterns were found among the different treatments and the secondary forest, as determined by Principal Components Analysis (PCA).

Study highlights that the inclusion of native species promotes faster accumulation of SOC compared to passive regeneration, reinforcing active restoration's role.
The correlation between SOC dynamics and structural variables demonstrates the complexity of soil recovery relative to plant growth.

Results emphasize the importance of species selection, local land-use history, and environmental conditions in restoration effectiveness.

Significant C credits from LR restoration treatments pave the way for their potential incorporation into carbon credit projects and payments for environmental services.

Active restoration using native species significantly increases SOC stocks, underscoring the importance of tailored strategies to the biome's conditions. Passive restoration showed limited efficacy within the timeline of the study.