🌿 ecology

Impact of selective logging on the population dynamics and genetic diversity in the neotropical timber tree Dicorynia guianensis

This study demonstrates that while selective logging in French Guiana alters dispersal dynamics and reproductive patterns of *Dicorynia guianensis*, it does not cause immediate genetic erosion, highlighting the species' resilience under current management practices while underscoring the need for long-term monitoring to ensure sustainable recruitment.

Original authors: Bonnier, J., Traissac, S., Brunaux, O., Troispoux, V., Tysklind, N., Heuertz, M.

Published 2026-08-10

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CC BY 4.0

Original authors: Bonnier, J., Traissac, S., Brunaux, O., Troispoux, V., Tysklind, N., Heuertz, M.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine a giant, bustling city where the buildings are ancient trees and the citizens are seeds, pollen, and tiny saplings. In this city, life depends on a delicate dance of movement: pollen must travel from one tree to another to create new families, and seeds must drift away to find a sunny spot to grow. Scientists who study this world are called population geneticists. They act like detectives, looking at the "family trees" of plants to see how much variety exists in their DNA. Why does this matter? Think of DNA as a library of instructions. If a library has too few books, it can't adapt when a new disease or a change in weather hits. If the library is full of diverse books, the species has a better chance of surviving. When humans go into these forests to cut down specific trees for timber, they are essentially removing the tallest, most successful buildings from the city. The big question is: does this construction project ruin the city's future, or is the city resilient enough to keep its library full and its citizens happy?

This paper investigates that exact question in the rainforests of French Guiana, focusing on a famous timber tree called Dicorynia guianensis (locally known as Angélique). The researchers compared two neighboring forest plots: one that had been left completely alone (the "unlogged" plot) and one where loggers had carefully cut down a few large trees in 2012 (the "logged" plot). They treated the forest like a giant puzzle, using genetic markers to trace the parents of hundreds of trees and seedlings, effectively mapping out who mated with whom and how far their "children" traveled.

The team found that, surprisingly, the logging didn't immediately destroy the genetic library. The number of different genetic "books" (alleles) and the overall health of the DNA remained almost identical between the logged and unlogged forests. The trees in the logged area didn't suddenly become inbred or lose their genetic variety. However, the way the forest operates has changed. In the logged plot, the "pollen delivery service" (pollen flow) had to work a bit harder, traveling shorter distances on average, and the "father trees" became a bit more competitive, with a few males fathering a disproportionate number of offspring. Meanwhile, the "mother trees" shared the workload more evenly.

The study also discovered that baby trees (seedlings) love the mess created by logging. They sprouted much more often in the sunny, open gaps left behind by felled trees and the dirt tracks used by logging trucks. But here is the twist: even though these gaps are great for starting life, the seedlings growing there weren't genetically different from those growing in the dark, undisturbed forest. They were just as diverse and healthy. The researchers suggest that while the forest is bouncing back well for now, the changes in how pollen moves and how fathers reproduce might have subtle effects that won't show up for decades. The forest is resilient, but it's not invincible; it needs long-term monitoring to ensure that the next generation of trees can keep the city thriving for the next 65 years.

Problem Statement
Selective logging is a prevalent forest management strategy in the tropics, particularly in the Guiana Shield, aimed at reconciling timber production with conservation. However, the long-term impacts of even low-intensity logging on the demographic and evolutionary processes of timber species remain insufficiently documented. Specifically, there is uncertainty regarding how logging-induced disturbances—such as canopy openings, reduced adult density, and altered microhabitats—affect seedling recruitment, reproductive success, gene flow dynamics, and genetic diversity. The study focuses on Dicorynia guianensis (Angélique), a hyperdominant and economically critical timber species in French Guiana, to determine if current reduced-impact logging practices compromise the genetic resilience and regeneration capacity of this species.

Methodology
The study employed a comparative approach between two forest plots in the Régina-Saint Georges massif of French Guiana: a selectively logged plot (PAI74, logged in 2012) and an unlogged control plot (HKO50).

Sampling: A total of 703 D. guianensis individuals were sampled across both plots, categorized into three life stages based on diameter at breast height (DBH): juveniles (<4 cm), intermediates (4–30 cm), and adults (>30 cm). Notably, the logged plot included pre-logging adult data from 2009, allowing for a direct comparison of genetic composition before and after extraction.
Genotyping: Individuals were genotyped using 66 nuclear SSR markers and 26 chloroplast SSR markers via high-throughput sequencing (SSR-SEQ). Rigorous quality control was applied to remove duplicates and potential contaminants.
Analytical Framework:
- Genetic Diversity & Structure: Metrics such as allelic richness, heterozygosity, inbreeding coefficients ( $F_{IS}$ ), and spatial genetic structure (SGS) were calculated using SPAGeDi. Bayesian clustering (STRUCTURE) and spatial principal component analysis (sPCA) assessed population differentiation.
- Parentage & Dispersal: Parentage analysis was conducted using CERVUS and COLONY to infer seed and pollen dispersal distances, reproductive skew (Gini index), and effective population sizes ( $N_e$ ).
- Regeneration Dynamics: The spatial association between seedling establishment and logging features (felling gaps, skid trails, log landings) was analyzed using logistic regression. Genetic metrics were compared for seedlings established inside versus outside canopy openings.

Key Results

Genetic Diversity: No evidence of immediate genetic erosion was found. Genetic diversity indices (allelic richness, heterozygosity) were broadly similar between the logged and unlogged plots and across life stages. The logged plot did not show a significant decline in diversity compared to its pre-logging state or the unlogged control.
Spatial Genetic Structure (SGS): SGS was slightly stronger in the unlogged plot ($Sp = 0.019$) than in the logged plot ($Sp = 0.016$). However, significant SGS was detected in both, indicating fine-scale genetic clustering.
Dispersal Dynamics:
- Seed Dispersal: Remained short-range and localized in both plots (mean ~25–32 m), with almost no cross-plot seed movement.
- Pollen Dispersal: While long-distance pollen flow was substantial in both plots, mean pollen dispersal distances were shorter in the logged plot (148 m) compared to the unlogged plot (291 m). Despite this reduction, high rates of pollen immigration from outside the plots were observed, maintaining genetic connectivity.
- Reproductive Success: Maternal reproductive success was evenly distributed in both plots. In contrast, paternal reproductive success was skewed in the logged plot (higher Gini index), with a lower effective number of fathers ( $N_{e\_f} = 12.2$ ) compared to the unlogged plot ( $N_{e\_f} = 30.9$ ).
Regeneration in Canopy Openings: Seedling establishment was significantly associated with logging-induced canopy openings (felling gaps and skid trails). However, genetic diversity metrics (heterozygosity, inbreeding) for seedlings inside these openings were not significantly different from those outside. Interestingly, chloroplast markers (tracing seed flow) indicated weaker spatial structure inside gaps compared to outside, suggesting gaps facilitate recruitment from a broader set of maternal sources.

Key Contributions
The paper provides empirical evidence that D. guianensis exhibits short-term resilience to low-intensity selective logging in French Guiana. It demonstrates that while logging alters dispersal dynamics (reducing pollen distances and increasing reproductive skew among males), it does not immediately erode genetic diversity or compromise the genetic quality of the regenerating cohort. The study highlights the critical buffering role of long-distance pollen flow in maintaining genetic cohesion between logged and unlogged stands, even when seed dispersal remains localized.

Significance and Claims
The authors conclude that the current management regime, characterized by low extraction intensity (4–5 stems/ha) and long rotation cycles (65 years), has successfully avoided strong genetic erosion in the short term. The findings underscore the resilience of D. guianensis but caution that the observed shifts in reproductive dynamics (skewed male contribution) and the transient nature of regeneration in canopy gaps warrant long-term monitoring. The paper emphasizes that while immediate genetic impacts are minimal, the sustainability of regeneration and evolutionary potential across multiple logging cycles remains uncertain and requires evaluation beyond the first decade post-logging. The study advocates for integrating demographic and genetic metrics into long-term monitoring frameworks to ensure sustainable forest management.

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