Impacts of Neltuma chilensis Invasion on Native Species Richness, Abundance and Forest Structure in Hyphaene thebaica (Doum Palm) Forests of Sudan’s Drylands

Neltuma chilensis (Mesquite) is one of the world’s most aggressive invasive woody species, and its ecological impacts have drawn increasing scientific attention, particularly in arid and semi-arid ecosystems. In Sudan, it is rapidly reshaping Hyphaene thebaica (Doum palm) forests, yet its effects on native forest ecosystems remain poorly quantified. This study aimed to: (i) assess tree species composition and structure; (ii) evaluate the impact of N. chilensis invasion on species richness and native species abundance in H. thebaica forests. A stratified random sampling approach was employed across 59 plots within three forests reserves, namely Alhelgi, Geli and Um Bashim. N. chilensis showed overwhelming dominance in Alhelgi and Geli forests, with the highest densities of 1314 and 605 trees ha−1, and accounting for 83% and 86% of total tree density, and relative abundance of 63% and 71% of total tree stems, respectively. In contrast, N. chilensis was absent in Um Bashim forest. H. thebaica was the dominant native tree species, with the highest Importance Value Index (IVI) of 137. A total of nine species, belonging to seven genera and six families, were recorded across the studied forests. Within the invaded forests, Pearson’s correlation showed that increasing in N. chilensis abundance significantly reduced species richness (R = −0.34, p = 0.021). While Kendall’s tau confirmed a significant decline in native species abundance at the community level (τ = −0.22, p = 0.036), increasing abundance of N. chilensis was associated with a reduction in native woody species abundance. At the individual species level, this negative effect was not statistically significant for most species, except for Vachellia nilotica, which showed a significant decline (τ = −0.28, p = 0.022). In addition, the findings reveal N. chilensis as a formidable and accelerating threat to Doum palm forests’ integrity. The study recommends integrated management strategies, including the control of N. chilensis and restoration of native vegetation, to safeguard these dryland ecosystems.