Topography is a well-known driver of changes in plant community organization in the tropics. However, we have a limited understanding of how the evolutionary history of component species shapes the organization of these plant communities along topographic gradients. We investigated how the phylogenetic structure of an understory plant community changes along a topographic gradient. We expect closely related species to occupy higher elevations along the gradient, leading to clustering, and to observe overdispersion at lower elevations. The study was conducted in a Neotropical Forest fragment in southeastern Brazil. Twenty plots (10 m x 10 m) were surveyed along a topographic gradient, distributed across four topographic habitats: valley, southwest slope, northwest slope, and ridge. We applied ordination methods to species abundance and soil data. We calculated phylogenetic diversity (PD), the mean pairwise distance (MPD), the mean nearest taxon distance (MNTD), and their SES (standardized effect sizes). Generalized linear models were fitted with phylogenetic metrics as outcomes and soil nutrients as predictors. We found 1,695 individuals belonging to 70 species, 53 genera, and 24 families. The valley was characterized by Rubiaceae, Piperaceae, Myrtaceae, and Lauraceae, while representatives of Lecythidaceae, Bignoniaceae, and Salicaceae were more abundant at the ridge. Notably, the valley habitat exhibited phylogenetic clustering, while the ridge habitat demonstrated phylogenetic overdispersion. Soil moisture was negatively associated with phylogenetic metrics, indicating clustering in the wetter valley and a tendency toward overdispersion on the ridge. Our findings suggest that environmental filtering plays a crucial role in structuring the understory of this tropical community.
Rural road verges are widespread semi-natural habitats in the intensively managed agricultural landscapes of the Inland Pampa, Argentina, where they can contribute to the conservation of plant diversity. Although wider linear habitats often support greater species richness, less is known about whether verge width is also associated with changes in species composition and in the representation of annual and non-native species. Here, we evaluate these complementary responses along a gradient of rural road verge width. We surveyed flowering non-graminoid plants across 20 rural road verges spanning a width gradient of 2–39 m in the Inland Pampa, Argentina. We analysed total species richness using a negative binomial generalized linear model, the proportions of non-native and annual species using binomial generalized linear models, and species composition using PERMANOVA based on Bray–Curtis dissimilarities. All analyses accounted for adjacent land use and landscape diversity. Verge width was positively associated with species richness (negative binomial GLM: β = 0.0146, p = 0.003) and with variation in species composition (PERMANOVA: R² = 0.120, p = 0.012). We found no evidence of an association between width and the proportion of non-native species, whereas the estimated association with the proportion of annual species was consistently negative but statistically uncertain. Neither adjacent land use nor landscape diversity showed clear associations with these response variables. Our results indicate that wider rural road verges are associated with higher richness and differences in species composition among flowering non-graminoid plants, whereas broad life-history and biogeographic proportions show little evidence of change along the width gradient. These findings highlight the value of considering species identity alongside richness when evaluating biodiversity patterns in non-crop habitats within agricultural landscapes.
Aboveground biomass (AGB) in tropical forests plays a fundamental role in the carbon cycle and in mitigating global warming. One of the main functional traits associated with tree biomass is species maximum height (Hmax). We used structural equation modeling to investigate local-scale variation in AGB in an Atlantic tropical forest (6.5-ha plot, 100 subplots of 10 × 10 m). Regarding the direct influence on variation in AGB among subplots, terrain elevation showed a negative effect, species richness had a null effect, the coefficient of variation of diameter (CVD) and the community-weighted mean of Hmax had positive effects. Functional dispersion based on Hmax (FDISHmax) had a positive effect on AGB only when CVD was replaced by MCVD, calculated as the mean of CVD values for understory and canopy species. MCVD is an alternative metric of structural complexity less sensitive to size inequalities among individuals of functionally distinct species, which minimizes redundancy with FDISHmax. Considering a single plot and only one functional trait (Hmax), our results were consistent with both the mass-ratio and niche complementarity hypotheses: AGB was associated with functional composition, reflecting the functional profile of dominant species, and with functional diversity, consistent with the optimized use of limited resources by functionally distinct species, namely understory and canopy species. We hypothesize that to maximize forest carbon stocks, the management and restoration of forests similar to the one studied should aim to increase structural complexity, dominance of taller species, and functional diversity associated with vertical forest stratification.
In many regions worldwide, Asteraceae exhibits the highest species richness among invasive alien plants (IAP). Notably, Asteraceae IAP frequently demonstrate co-invasion tendencies. Plant communities invaded by Asteraceae IAP may differ structurally and functionally from those invaded by non-Asteraceae IAP. More importantly, multiple IAP may coexist within the same habitat, and these species can be further differentiated as either Asteraceae IAP or non-Asteraceae IAP, potentially leading to significant differences in community structure under invasion by varying numbers of IAP species or by IAP with different species identities. This study aimed to evaluate the differences in IAP’ invasion intensity and community invasibility between communities invaded by Asteraceae IAP and those invaded by non-Asteraceae IAP. A comparative field survey approach was adopted, examining six distinct plant community types: uninvaded communities, communities invaded by a single Asteraceae IAP, communities invaded by a single non-Asteraceae IAP, communities co-invaded by two Asteraceae IAP, communities co-invaded by one Asteraceae and one non-Asteraceae IAP, and communities co-invaded by two non-Asteraceae IAP. Under single-IAP invasion scenarios, Asteraceae IAP triggered significantly higher invasion intensity and more pronounced community invasibility compared to non-Asteraceae IAP. However, under co-invasion conditions involving multiple IAP—whether two Asteraceae species, one Asteraceae and one non-Asteraceae species, or two non-Asteraceae species—no substantial differences were observed in invasion intensity or community invasibility. Thus, Asteraceae IAP exhibited stronger invasion intensity and greater impact on community invasibility only in single-IAP invasion contexts, with such differences diminishing under multi-IAP co-invasion conditions.
