Journal of Vegetation Science最新文献

Aims

Lianas form an important component of tropical forests as they contribute to maintaining biodiversity. Thus, understanding the factors that control them is essential for forest management and biodiversity conservation. However, how topography and logging, as well as their interaction, affect liana community structure is not well understood. Therefore, we sought to evaluate the effects of topography and logging on the structure of liana communities in a tropical upland evergreen forest in Ghana.

Location

Tano Offin Forest Reserve, Ghana.

Methods

We assessed liana community structure by quantifying liana species diversity and composition, abundance, and basal area in nine 20 × 20 m plots, each of three topographic habitats (valley, slope, hilltop) in two land-use types (non-logged and logged-over forests) in the Tano Offin Forest Reserve, Ghana. We measured elevation and slope angle, and quantified host tree abundance and basal area for each plot.

Results

Topographic position influenced liana species diversity, abundance and basal area across the forest land-use types, with the valley habitat supporting a significantly greater values than the other habitats. In the same vein, topographic position was a significant predictor of liana species diversity, abundance and basal area in the logged-over forest, but not the non-logged forest. Selective logging also showed significant negative effects on liana species diversity, abundance and basal area, both across forest land-use types and within slope and hilltop habitats. Similarly, there were significant effects of topographic habitat and logging, and their interaction on liana species composition. Liana species composition was significantly driven by elevation, while liana abundance and basal area were predicted by elevation, slope angle, and tree abundance and basal area.

Conclusion

In view of our findings, forest managers should take into account the heterogeneity of topographic landscapes in their management operations and pay particular attention to areas that support higher plant assemblages, such as valleys. The findings further suggest that logging operations in topographic landscapes should be conducted in a manner that does not disrupt the topographic patterns of plant community structure.

Question

What are the reasons that tree gap dynamics are little found in conifer boreal and subalpine forests in upland small forest gaps (1 to 1.5 gap diameter/tree heights (D/H))? Location: High latitude conifer forests in western Canada.

Methods

We use a sample of 480 from 2103 small gaps created 40 years ago for forest water management to increase snow and delay melt to assess if tree gap regeneration occurs. We then used two published studies: a ray-trace model of solar irradiance into gaps (Musselman et al. 2015) and a Gap Radiation Model (GaRM) (Seyednasrollah and Kumar 2014) to explain the net short and long wave radiation and snow accumulation and melting in small forest gaps, in large forest clearings, and in closed canopy forests.

Results/Discussion

We find that tree regeneration is rare in high latitude conifer forests because small gaps (1–1.5 diameter gap/tree height) accumulate deep snow that persists into spring and prevents regeneration of trees. Besides the shorter growing season, the cause may be several species of parasitic snow fungi since seed sources are nearby, adjacent conifer trees do not reach into gaps, and the forest floor is not the best for tree regeneration. Finally, the short return time of large lightning-caused crown fires sets the existence time of these small gaps.

Conclusion

Low net short wave radiation in gaps at latitudes greater than ~40° North leads to deep accumulation and slow melt in the spring of snow in these small gaps compared to closed canopy conifer forests or larger clearings. The result is little or no tree regeneration and thus little or no tree gap dynamics.

Aims

Root traits are critical for resource acquisition, particularly in nutrient-limited environments such as open savannahs, and any changes in these traits can impact ecological processes. However, it is poorly understood whether invasive species outcompete natives by competitive superiority in nutrient acquisition (‘exploitation competition’) or by interfering with natives by space occupancy (‘interference competition’).

Location

Cerrado, south-eastern Brazil.

Methods

We selected five sites of open savannahs, each consisting of two paired subsites, that is, non-invaded or invaded by Urochloa grass species. We assessed community-level root biomass and depth distribution in the upper 1 m of soil. We measured root biomass and functional traits for fine roots (< 2 mm) classified as absorptive and transport roots in the uppermost soil layers (0–30 cm).

Results

Invaded and non-invaded plant communities differed primarily in root trait and biomass in the upper soil layer (0–10 cm). Invaded communities showed higher root biomass and root length density (RLD) compared to non-invaded communities, evidencing space occupancy through a larger root system. Species in invaded communities had roots with larger diameters, but lower root tissue density (RTD) and lower root dry mass content (RDMC), commonly associated with fast root spreading and expansion, compared to species in non-invaded communities. Contrarily, non-invaded communities presented a higher proportion of absorptive roots.

Conclusions

Functional dissimilarities in traits related to space occupancy indicate that interference competition plays a bigger role than exploitation competition in the invasion of Cerrado by Urochloa species. Invaded savannahs are characterized by root traits and biomass allowing effective neighbor suppression. As changes in root traits such as RTD can cause modifications in ecosystem functioning, our results suggest that invasive species may modify ecosystem processes that hamper the restoration of invaded savannahs.

Questions

A non-random spatial distribution of species in relation to environmental factors is an important mechanism for maintaining high tree diversity in tropical forests. Niche theory predicts that competing species should use the environment differently. However, we have only limited information on the extent to which environmental dependence and the relative importance of different types of environmental factors vary between species. It is also unclear how the environmental dependence differs according to life stage and species.

Location

Here we investigate the environmental variables that determine the spatial distribution of tree species in a 25-ha plot of mixed-dipterocarp tropical rainforest in Sri Lanka.

Methods

We compiled data on the spatial distribution of recruits, saplings, and adults of 57 tree species, as well as topographic and soil variables, and applied methods of spatial point process theory to estimate parametric spatial intensity functions for each life stage of the species as a function of environmental variables.

Results

Most species distributions were significantly associated with at least one environmental variable, with elevation and the first principal component of soil nutrients being the most important ones. With few exceptions, species showed an intermediate strength of environmental dependence, and we observed a striking similarity in the intraspecific environmental dependence between life stages. Finally, only a few species showed for the same life stage strong positive or negative correlations in their intensity functions, while most species pairs showed only weak or no correlations at all.

Conclusions

Taking together, our results indicate that the distribution of most of the more abundant species in our forest plot is influenced by local heterogeneity in environmental conditions, and that their environmental preferences lead to a spatial arrangement where competing species use the environment somewhat differently. Overall, our study provides a nuanced understanding of the complex environmental dependencies that shape tropical rainforest ecosystems at local spatial scales.

Questions

Which components of the fire regime affect plant species diversity? Does pre-fire vegetation physiognomy influence the effect of the fire regime? Which species are favoured by different fire regimes?

Location

Natural Reserve of Monte Catillo (central Italy).

Methods

We sampled vegetation in 58 units across areas that underwent different fire regimes and were originally occupied by different vegetation physiognomies.

We used plot-level species diversity calculated through Hill numbers in (generalised) linear models with components of fire regimes (time since the last fire, fire frequency and severity) and pre-fire physiognomy as explanatory variables.

We identified species related to different levels of fire frequency, severity and time since the last fire through indicator species analysis.

Results

Species richness (q = 0) was negatively related to time since last fire, while Shannon (q = 1) and Simpson (q = 2) diversity were influenced by the severity of last fire, with positive and negative relationships, respectively. Shrubland pre-fire vegetation interacted significantly with severity effects on diversity.

All components of fire regimes favoured annual and chamaephytic species with a Mediterranean distribution, while areas subjected to older, less severe and less frequent fires were characterised by tree species, including deciduous ones, and paleotemperate herb species.

Conclusions

Recent fires increase vascular plant species richness, but only temporarily. Severe fires determine relevant shifts in community dominance. Frequent and severe fires favour the spread of Mediterranean herb species in areas potentially occupied by thermophilous forests dominated by a mix of deciduous and evergreen tree species.

Aims

Epiphytes distribute heterogeneously along their phorophytes, according to the microenvironmental gradient within them. Phorophyte leaf phenology (evergreen vs. deciduous) determines the microenvironment experienced by epiphytes, their diversity and vertical stratification. No studies have evaluated the effects of phorophyte leaf phenology on the phorophyte—vascular epiphyte network metrics. We compare the phorophyte—vascular epiphyte global- and per stratum-network in phorophyte species with contrasting leaf phenology within a fragment of cloud forest in central Mexico.

Location

Fragment of cloud forest in Amatlán de Quetzalcóatl, Morelos State, in central Mexico.

Methods

Epiphyte species and their abundance on each phorophyte and per vertical stratum were determined. Grouping phorophytes with different leaf phenology (evergreen vs. deciduous), we estimated true diversities (⁰D, ¹D, and ²D) and network metrics both for the whole communities and per stratum.

Results

Evergreen phorophytes hosted a greater diversity (¹D, and ²D) of epiphyte species and interactions, and a greater network size and nestedness than deciduous phorophytes. In both types of phorophytes, connectance, specialization, and modularity had similar values; vulnerability was greater than generality; niche overlap was greater for phorophytes than epiphytes, whereas robustness was greater for epiphytes than phorophytes.

Conclusions

Our results suggest that evergreen phorophyte networks are more stable than those in deciduous phorophytes. Different epiphyte species have adaptations to the microenvironmental conditions offered by each type of phorophyte, allowing the coexistence of a great diversity of epiphytes typical of cloud forests. To our knowledge, this is the first study comparing the phorophyte—epiphyte networks between phorophytes with contrasting leaf phenology. Understanding how leaf phenology affects the interactions between phorophytes and epiphytes is fundamental for species and ecosystem management and preservation.

Questions

Community-level stability includes both temporal and spatial dimensions, yet most research has focused on temporal aspects. While considerable progress has been made in understanding community-level temporal stability (α temporal stability), including its interactions with temporal stability at smaller scales (e.g., population or species level) and broader spatial scales (β and γ temporal stability), our understanding of spatial stability at the same community level (α spatial stability or spatial autocorrelation) and its connections to species-level spatial stability and spatial asynchrony remains limited.

Location

An alpine meadow on the Tibetan Plateau, China.

Methods

Using 5 years of data from a nitrogen addition experiment conducted in an alpine meadow on the Tibetan Plateau, we examine the impacts of nitrogen addition on both temporal and spatial stabilities of community biomass, considering species richness, asynchrony, and stability of all species, as well as of dominant and other non-dominant species.

Results

Nitrogen addition influenced the temporal and spatial stability of community biomass by altering the temporal and spatial asynchrony of dominant species and of the overall species level. In this alpine meadow with high species richness, temporal stability of community biomass increased despite a decline in species richness, while spatial stability of community biomass remained unaffected. These results suggest that dominant species dynamics can enhance temporal stability under nutrient enrichment, even as diversity decreases.

Conclusion

Dominant species play a key role in regulating the temporal and spatial stability of community biomass, and the two dimensions of stability respond differently to nitrogen addition. These findings emphasize the importance of incorporating both spatial and temporal facets of stability into ecological theory and ecosystem management under global change.

Question

How do fire and flooding, acting as ecological filters separately and in combination, influence species richness, taxonomic diversity, functional diversity, and phylogenetic diversity in tree communities along a flood gradient with varying fire histories?

Location

Pantanal, Mato Grosso do Sul, Brazil.

Methods

We sampled trees in 45 forest patches along a flood gradient, assessing species richness, alpha and beta taxonomic diversity, functional diversity, and phylogenetic diversity. Fire histories were categorized as 25, 13, and 2 years without fire (1997, 2009, 2020, respectively). Alpha diversity was estimated using Hill numbers, beta diversity via the Sørensen Index, and functional and phylogenetic diversity through the standardized effect size of mean pairwise distance (SES-MPD). A total of 321 plots were analyzed.

Results

Functional diversity increased along the flood gradient, promoting environmental heterogeneity. However, in recently burned areas, species richness, alpha taxonomic diversity, and functional diversity declined. The positive effect of flooding on functional diversity was reduced in recently burned areas, suggesting fire selectively removes flood-adapted but fire-sensitive species. Beta diversity analysis revealed a nested pattern, with species in recently burned areas forming subsets of older communities, indicating strong environmental filtering. Phylogenetic diversity remained stable across fire and flood gradients, suggesting fire filters species within lineages rather than altering evolutionary relationships.

Conclusions

Fire and flooding shape species richness, taxonomic diversity, and functional diversity in the Pantanal. Flooding enhances functional diversity, while fire reduces alpha and functional diversity, leading to species loss and functional homogenization. Strong adaptive trade-offs limit species' tolerance to both disturbances. Recently burned areas contain subsets of older communities, emphasizing the role of fire-free intervals in biodiversity recovery. As fire frequency increases due to climate change and human activity, conservation strategies should prioritize fire management and integrate hydrological dynamics into conservation planning to maintain wetland resilience.

Question

Native and invasive species interact simultaneously with each other and with their species-specific soil biota, yet the relative importance of native plant–soil feedback (PSF) on the outcome of competition between these species with different origins is poorly understood. Therefore, we studied the influence of native PSF on the performance of two invasive and two native target species in two situations: (1) when the species were grown alone, and (2) when the target species were grown in pairwise competitive setup with the native conditioning species. We also tested the importance of phylogenetic relatedness between target and conditioning species on the simultaneous effect of PSF and competition.

Location

Cluj-Napoca, Romania.

Methods

We used native species from a semi-dry grassland dominated by Brachypodium pinnatum and Festuca rupicola to study how their species-specific PSFs affect the performance of invasive (Solidago canadensis, Erigeron canadensis) and native (Centaurea jacea, Crepis foetida) Asteraceae species. In the first year, soil was conditioned by six native grassland species (three Asteraceae and three species from other families); while in the second year, we performed a pairwise competition experiment in pots between the four target and six native species in conditioned and control soils.

Results

We found that although the native species exerted a strong negative PSF on the performance of the target species, this effect mostly disappeared in the real presence of the native competitors. We also showed that the identity of native resident species is more important in determining PSF and competitive outcome than whether it is dominant or subordinate, or whether it is phylogenetically related to the target species.

Conclusions

We showed that PSF of native species may not influence the competitive outcome between invasive and resident native species, thus PSF does not significantly contribute to the invasion resistance of the studied grassland community.