Woody Plant Density Research Articles

Understanding woody plant encroachment: A plant functional trait approach

AbstractThe increasing density of woody plants threatens the integrity of grassy ecosystems. It remains unclear if such encroachment can be explained mostly by direct effects of resources on woody plant growth or by indirect effects of disturbances imposing tree recruitment limitation. Here, we investigate whether woody plant functional traits provide a mechanistic understanding of the complex relationships between these resource and disturbance effects. We first assess the role of rainfall, soil fertility, texture, and geomorphology to explain variation in woody plant encroachment (WPE) following livestock grazing and consequent fire suppression across the Serengeti ecosystem. Second, we explore trait‐environment relationships and how these mediate vegetation response to fire suppression. We find that WPE is strongest in areas with high soil fertility, high rainfall, and intermediate catena positions. These conditions also promote woody plant communities characterized by small stature and seed sizes smaller relative to a comparative baseline within the Serengeti ecosystem, alongside high recruit densities (linked to a recruitment‐stature trade‐off). The positioning of species along this “recruitment‐stature axis” predicted woody stem density increase in livestock sites. Structural equation modeling suggested a causal pathway where environmental factors shape the community trait composition, subsequently influencing woody recruit numbers. These numbers, in turn, predicted an area's vulnerability to WPE. Our study underscores the importance of trait‐environment relationships in predicting the impact of human alterations on local vegetation change. Understanding how environmental factors directly (resources) and indirectly (legacy effects and plant traits) determine WPE supports the development of process‐based ecosystem structure and function models.

Abundance and Species Richness of Lianas in a Karst Seasonal Rainforest: The Influence of Abiotic and Biotic Factors

Lianas are a crucial component of karst seasonal rainforests, yet research on them has predominantly focused on non-karst regions. Consequently, their abundance and species richness remain relatively understudied within karst ecosystems. We aimed to document the abundance and species richness of lianas and investigate their relationships with abiotic and biotic factors, based on data from a fully mapped 15 ha plot in a karst seasonal rainforest of Nonggang (SW China). Structural equation models (SEMs) were employed to estimate the path coefficients and variation of dependent variables, enabling a comprehensive analysis of the factors affecting the abundance and species richness of liana. Within the 15 ha plot, a total of 23,819 lianas were identified, encompassing 113 species from 34 families. These lianas constituted 24.16% of the total woody plant density and 33.44% of the species present, but only 4.32% of the total woody plant basal area. Lianas are primarily influenced by abiotic factors, especially elevation and phosphorus (P), with less impact from biotic factors. Our findings reveal that lianas, despite constituting a relatively small percentage of the total woody plant basal area, significantly contribute to the density and diversity of the forest. Notably, abiotic factors such as elevation and phosphorus availability predominantly shape the distribution and richness of lianas, highlighting the importance of these environmental variables. The findings offer valuable insights for future liana studies and the preservation of karst forests’ biodiversity.

Finders' eaters: Increasing bush encroachment may shift carcass detection from diurnal avian to nocturnal mammalian scavengers

AbstractBush encroachment is increasingly becoming a problem for biodiversity conservation in African savannas. While this invasion by woody vegetation may hamper avian scavengers such as vultures, which primarily search by sight, it may benefit mammalian scavengers that search by smell. This study aimed to examine the ability of nocturnal mammalian and diurnal avian scavengers to locate carcasses at increasing vegetation densities. We successively placed 27 impala (Aepyceros melampus) carcasses five days apart in a 2000 ha fenced game camp that offered an extensive range of woody plant densities. Scavenger arrivals and first feedings were recorded with camera traps. The avian scavengers, mainly white‐backed Vultures (Gyps africanus), fed exclusively on carcasses during the day, and mammalian scavengers, predominantly brown hyenas (Parahyena brunnea), fed solely at night. The two guilds thus competed exploitatively without direct interaction between them. For vultures, the time taken to locate a carcass increased with woody plant density. The mean density of woody plants that avian scavengers located carcasses at was 2188 plants/ha, whereas mammalian scavengers located carcasses at appreciably higher densities of 5156 plants/ha. Resource managers need to understand the synergy between maintaining woody vegetation to benefit nocturnal mammalian scavengers and maintaining open savannas to benefit diurnal avian scavengers.

Compositional and Structural Diversity of Woody Stands in the Community Forests of Rogho and Boala in Central-West Burkina Faso

The biodiversity of community forests is poorly studied in Burkina Faso. This results in a lack of understanding of their ecological importance, which is characterized by neglect in their management. The main objective of this study is to characterize the flora and woody vegetation of the community forests of Rogho and Boala to demonstrate their importance. For this purpose, a forest inventory was conducted using stratified random sampling methods. Shannon, Simpson, Margalef, and Pielou diversity indices reveal significant biodiversity of the flora in both forests, with a better distribution of individuals within the species that make them up. The horizontal structure of the two woody populations is characterized by a predominance of individuals with small diameters (DBH € [5cm-25cm[) on either side, with respective regeneration rates of 58.36% and 22.46% for Rogho and Boala. Regarding the ecological importance of species, Lannea microcarpa has the highest Importance Value Index (IVI = 99.06) for the Rogho site, and Vitellaria paradoxa for the Boala site (IVI = 136.58). Phanerophytes dominate the flora of both forests with a strong presence of mesophanerophytes. The average density of woody plants is evaluated at 330.34 trees/ha and 742.01 trees/ha respectively in Rogho and Boala, with respective average land areas of 14.8 m2/ha and 119.78 m2/ha. This study highlights the strong ecological potential of the forests studied. Communal and regional authorities must develop strategies for the sustainable management of these forest areas.

Thresholds and alternative states in a Neotropical dry forest in response to fire severity.

Neotropical xerophytic forest ecosystems evolved with fires that shaped their resilience to disturbance events. However, it is unknown whether forest resilience to fires persists under a new fire regime influenced by anthropogenic disturbance and climate change. We asked whether there was evidence for a fire severity threshold causing an abrupt transition from a forest to an alternative shrub thicket state in the presence of typical postfire management. We studied a heterogeneous wildfire event to assess medium-term effects (11 years) of varying fire severity in a xerophytic Caldén forest in central Argentina. We conducted vegetation surveys in patches that were exposed to low (LFS), medium (MFS), and high (HFS) fire severities but had similar prefire woody canopy cover. Satellite images were used to quantify fire severity using a delta Normalized Burning Ratio (dNBR) and to map prefire canopy cover. Postfire total woody canopy cover was higher in low and medium than high severity patches, but the understory woody component was highest in HFS patches. The density of woody plants was over three times higher under HFS than MFS and LFS due to the contribution of small woody plants to the total density. Unlike LFS and MFS patches, the small plants in HFS patches were persistent, multistem shrubs that resulted from the resprouting of top-killed Prosopis caldenia trees and, more importantly, from young shrubs that probably established after the wildfire. Our results suggest that the Caldén forest is resilient to fires of low to moderate severities but not to high-severity fires. Fire severities with dNBR values > ~600 triggered an abrupt transition to a shrub thicket state. Postfire grazing and controlled-fire treatments likely contributed to shrub dominance after high-severity wildfire. Forest to shrub thicket transitions enable recurring high-severity fire events. We propose that repeated fires combined with grazing can trap the system in a shrub thicket state. Further studies are needed to determine whether the relationships between fire and vegetation structure examined in this case study represent general mechanisms of irreversible state changes across the Caldenal forest region and whether analogous threshold relationships exist in other fire-prone woodland ecosystems.

Fire frequency has a contrasting effect on vegetation and topsoil in subcoastal heathland, woodland and forest ecosystems, south‐east Queensland, Australia

AbstractEcosystems managed with contrasting fire regimes provide insight into the responses of vegetation and soil. Heathland, woodland and forest ecosystems along a gradient of resource availability were burnt over four decades in approximately 3‐ or 5‐year intervals or were unburnt for 45–47 years (heathland, woodland), or experienced infrequent wildfires (forest: 14 years since the last fire). We hypothesized that, relative to unburnt or infrequent fires, frequent burning would favour herbaceous species over woody species and resprouting over obligate seeder species, and reduce understorey vegetation height, and topsoil carbon and nitrogen content. Our hypothesis was partially supported in that herbaceous plant density was higher in frequently burnt vegetation; however, woody plant density was also higher in frequently burnt areas relative to unburnt/infrequently burnt areas, across all ecosystems. In heathland, omission of frequent fire resulted in the dominance of fern Gleichenia dicarpa and subsequent competitive exclusion of understorey species and lower species diversity. As hypothesized, frequent burning in woodland and forest increased the density of facultative resprouters and significantly reduced soil organic carbon levels relative to unburnt sites. Our findings confirm that regular burning conserves understorey diversity and maintains an understorey of lower statured herbaceous plants, although demonstrates the potential trade‐off of frequent burning with lower topsoil carbon levels in the woodland and forest. Some ecosystem specific responses to varied fire frequencies were observed, reflecting differences in species composition and fire response traits between ecosystems. Overall, unburnt vegetation resulted in the dominance of some species over others and the different vegetation types were able to withstand relatively high‐frequency fire without the loss of biodiversity, mainly due to high environmental productivity and short juvenile periods.

Comparison of species composition and community characteristics of Quercus forests on south and north slopes of Taibai Mountain, China.

We examined species composition, community characteristics, diversity, and community similarity of five Quercus communities composed of three Quercus species (Q. variabilis, Q. aliena var. acutiserrata, Q. wutaishanica) on the altitudinal gradient on the south and north slopes of Taibai Mountain. The results showed that there was an altitudinal transition pattern from Q. variabilis pure forest to Q. variabilis-Q. aliena var. acutiserrata mixed forest, Q. aliena var. acutiserrata pure forest, Q. aliena var. acutiserrata-Q. wutaishanica mixed forest and Q. wutaishanica pure forest on the south and north slopes of Taibai Mountain. The main companion species of Quercus community on the north slope were Pinus armandii, Castanea seguinii, and Sorbus alnifolia, and were Pinus tabuliformis, C. seguinii, Carpinus cordata, and Q. spinosa on the south slope. Species richness, woody plant density, and Quercus species dominance on the north slope of Taibai Mountain were higher than those on the south slope. α diversity of tree layer in Quercus community on the south and north slopes of Taibai Mountain increased first, then decreased and then increased with altitude. α diversity of tree layer was higher in mixed forests than pure forests. α diversity of shrub layer was higher than that of tree layer and herb layer in Quercus community on south and north slopes. β diversity fluctuated greatly along the altitudinal gradient on the south and north slopes, indicating that species composition changed greatly with altitude. Results of redundancy analysis showed that mean warmest month temperature, altitude and tree height accounted for 79.0% of the community diversity on the north slope, and that soil water content, tree height, canopy density and mean annual temperature accounted for 79.6% of the community diversity on the south slope. Overall, Quercus dominance was higher on the north slope of Taibai Mountain, and the substitution distribution pattern of Quercus species was clearer than that on the south slope. Environmental factors related to temperature and precipitation jointly affected α diversity of Quercus communities.

Challenges, successes, and recommendations for management of coastal sandplain grasslands as regional biodiversity hotspots in the northeastern United States

A high proportion of regional plant biodiversity occurs in hotspots of species richness that cover small areas created and maintained by disturbance. Sustaining plant diversity in these areas requires region‐ and habitat‐specific management of disturbance and, increasingly, habitat expansion or restoration to offset species losses. Coastal sandplain grasslands are threatened, disturbance‐controlled plant biodiversity hotspots in the northeastern United States. We formed a network of grassland managers and scientists to review the published and unpublished sandplain grassland literature. Additionally, we conducted interviews with grassland managers about management challenges and successes. Principal concerns of managers were increases in woody plant cover, losses of rare species, increased cover and variety of invasive species, and constraints on the ability to use prescribed fire. The literature review and managers' experiences together led to the following recommendations: (1) increase applications of prescribed burning and mowing during the growing season when possible; (2) expand selective removal of woody plants including herbicide use; (3) test the application of harrowing or disking to reduce woody plant density especially in places where invasive plant densities are low; and (4) increase applications of combinations of disturbances in rotations with occasional fire. At regional scales, monitoring of management effects, identification of parcels for potential grassland expansion and restoration, and increased supplies of native seeds of plant ecotypes to use for restoration ahead of climate change are badly needed. Formation of networks of managers and scientists to share information and experiences has the potential to greatly improve land management within other biodiversity hotspots.

Quantifying the effect of chemical bush control of Senegalia mellifera on vegetation production in the Eastern Kalahari Bushveld, South Africa

Bush encroachment is the invasion of whole landscapes by indigenous and alien woody species. An imbalance in the ratio of grasses to bushes is a consequence of bush encroachment due to competition for moisture, nutrients and sunlight. This imbalance results in a decrease in grass cover, plant biodiversity and grazing capacity, leading to severe economic losses. Several methods exist to reduce high woody plant densities, including mechanical, manual, biological or chemical control. In this study, we assessed the structural and compositional attributes of the grass layer and compared these to the woody vegetation structure for herbicide-controlled rangelands and the no chemical control. The main objective was to evaluate the potential of chemical control to restore an open savanna system dominated by perennial grasses. Woody-dominated vegetation resulting from long-term overgrazing was assessed and compared to chemically controlled sites. Results revealed that chemical control treatment increased forage production and maintained woody-patch conservation. After the treatment, the sites were characterised by more productive and desirable woody species. The re-encroachment of woody species at all bush-controlled sites is possible. A follow-up control programme to manage and mitigate encroachment needs to be implemented when mitigating bush encroachment.

The Effects of Prescribed Dry Season Burning on Woody Species Composition, Mole National Park, Ghana

Fire use in protected savannas of Africa is a common practice. Fires in these savannas create many environmental benefits, such as reducing grass, brush and trees that can fuel large and severe wildfires and improving wildlife habitat. However, wrong timing of fire can threaten plants, animals and habitats. This study investigated the effects of time of burning on woody plant composition, diversity and density in the Mole National Park, Ghana. A total of twelve 300 m2 plots were systematically sampled in a 200 m × 200 m treatment plot established by Park Management each for early burn, late burn and no-burn plots. Twenty-seven different woody species belonging to fourteen families were recorded in all the treatments. Most of the species identified belonged to the families Fabaceae and Combretaceae. Vitellaria paradoxa (Shea), Terminalia avicennioides, Combretum adenogonium and Combretum molle were the most common and abundant in all treatments. A TWINSPAN on sites and species revealed four species groups based on affinity to burning time. A follow-up DCA showed a strong association between burning time and species composition, with the first two axes explaining 65% of variation. The late burn and no-burn treatments recorded the lowest diversity amongst the three treatments. Stem density was highest in no-burn treatment which had lowest species richness and diversity compared to early and late burn treatments. Early burn treatment had the highest diversity and the lowest density of woody species. The study revealed that the different times of prescribed burning influenced vegetation differently. Prescribed early dry season burning could contribute to the management of indigenous woody species in protected fire-prone savannas, because it can promote the diversity of species, as found in the Mole National Park in the Guinea savanna of Ghana.

A meta‐analysis of shrub density as a predictor of animal abundance

Facilitative interactions between shrub and animal species influence the structure and composition of communities. The benefits associated with woody shrub species can critically influence local animal populations, in particular. Here, we tested the relative importance of the density of shrub species on the local abundance of animal populations using a meta‐analysis. Full‐text review for shrub density, animal abundance or density and sampling effort, resulted in a total of 113 independent observations that reported both shrub density and animal abundance. A meta‐regression of shrub density on animal density with feeding functional group of the animal species as a moderator was used to test the predictive capacity of this simple vegetation measure on animal populations. Shrub density positively predicted animal abundance in these studies – particularly in deserts and grasslands. Shrub and woody plant density can thus be used as a potential rapid proxy for habitat in predicting local animal abundances. This method can support restoration and conservation of resident animal species in impacted ecosystems structured by woody shrubs globally.

Elephant rewilding affects landscape openness and fauna habitat across a 92-year period.

Trophic rewilding aims to promote biodiverse self-sustaining ecosystems through the restoration of ecologically important taxa and the trophic interactions and cascades they propagate. How rewilding effects manifest across broad temporal scales will determine ecosystem states; however, our understanding of post-rewilding dynamics across longer time periods is limited. Here we show that the restoration of a megaherbivore, the African savannah elephant (Loxodonta africana), promotes landscape openness (i.e., various measures of vegetation composition/complexity) and modifies fauna habitat and that these effects continue to manifest up to 92 years after reintroduction. We conducted a space-for-time floristic survey and assessment of 17 habitat attributes (e.g., floristic diversity and cover, ground wood, tree hollows) across five comparable nature reserves in South African savannah, where elephants were reintroduced between 1927 and 2003, finding that elephant reintroduction time was positively correlated with landscape openness and some habitat attributes (e.g., large-sized tree hollows) but negatively associated with others (e.g., large-sized coarse woody debris). We then indexed elephant site occurrence between 2006 and 2018 using telemetry data and found positive associations between site occurrence and woody plant densities. Taken alongside the longer-term space-for-time survey, this suggests that elephants are attracted to dense vegetation in the short term and that this behavior increases landscape openness in the long term. Our results suggest that trophic rewilding with elephants helps promote a semi-open ecosystem structure of high importance for African biodiversity. More generally, our results suggest that megafauna restoration represents a promising tool to curb Earth's recent ecological losses and highlights the importance of considering long-term ecological responses when designing and managing rewilding projects.

The vegetation cover dynamics and potential drivers of habitat change over 30 years in the Free State National Botanical Garden, South Africa

As a conservation strategy, the South African National Biodiversity Institute (SANBI) establishes biodiversity gardens in areas with unique vegetation types that are vulnerable to extinction. The study aimed to (1) determine the vegetation cover dynamics of the Free State National Botanical Garden (FSNBG) over a 30-year period (1987–2017), focusing on different vegetation classes; (2) evaluate the ecological integrity of the Critical Biodiversity Area 1 (CBA1) vegetation using species abundance and vegetation cover; and (3) quantify potential conservation threats that may be drivers of vegetation cover changes. The “moderate vegetation cover” and “dense vegetation cover” had increased by 25.1 ha and 8.6 ha respectively in the FSNBG. Woody vegetation cover expanded significantly over the past 30-year period, suggesting “bush” encroachment. Shannon–Wiener diversity indices showed high overall plant species diversity of CBA1 vegetation type (H = 3.5), with the vegetation cover remaining high (79.6 ± 15.9%), 50 plant species no longer existing, suggesting reduced taxonomic richness. Major conservation threats included the presence of 27 alien and invasive plant species interspersed within different vegetation patches and anthropogenic habitat fragmentation in the past 19 years (i.e. covering ~ 18% of the buffer zone). We conclude that increased vegetation cover is associated with bush encroachment and we recommend interventions to reduce the population density of woody plants and establish permanent vegetation monitoring plots.

Early ecosystem establishment using forest floor and peat cover soils in oil sands reclamation

ABSTRACT Early trends of plant community development provide the basis of ecosystem function and reclamation success of oil sand extraction sites. However, few studies have explicitly investigated species-level interactions with different cover soil types, placement depths, and time since reclamation during early plant community development in boreal forests. We investigated effectiveness of forest floor mineral mix (FMM) and peat mineral mix (PMM) cover soils and placement depths (10 and 20 cm) at four research sites 4 to 13 years after reclamation. Outcomes of this study indicate FMM had a more positive influence on woody plant densities, vegetation cover, and species richness than PMM. Species assemblage, composition, dominance, and types (successional stages, habitat types, competitive-stress tolerant-ruderal strategies) also showed FMM cover soil performed better than PMM. Greater vegetation cover and richness on deeper (20 cm) cover soil placements were evident. However, this effect of cover soil depth would likely decrease with time. Dominant and subdominant species on FMM were native and early to late successional, thus trajectory community development on FMM followed typical early succession of boreal forests (from ruderal and annual to perennial communities), while PMM was dominated by non-native and annual forbs which could slow succession and ecosystem recovery.

Palm density and grazing effects on plant communities: implications for livestock management in a Butia palm grove.

Some grasslands in ecotones with forests tend to be encroached by woody species, because of changes in climate and land use. Such structural changes in vegetation can be facilitated when the grassland community presents an autochthonous arboreal component, like Butia palms. We aim to identify the responses of taxonomic and functional diversity on grassland community with the occurrence of arborescent/arboreal species (autochthonous and encroaching) to palm density and grazing intensity. The study was conducted in a Butia odorata palm grove under cattle management, in Southern Brazil. To assess the taxonomic and functional composition we performed ordinations analysis with the vegetational data and using path analysis we assessed the causal relationships between variables of interest. Density of Butia odorata and woody plants were strongly positive related, suggesting a facilitation process in the establishment of arborescent plants on the grassland matrix. The abundance of less palatable plants and grazing pressure were inversely related, indicating a selection process induced by higher grazing intensity. We suggest that the grazing intensity management must be based on the autochthonous tree density, applying higher grazing intensity in areas with higher density of encroaching plants, in addition to maintaining other regions conducive to Butia palm regeneration through fallows.

Diversity of Agroforestry Systems Associated with Vegetable Plots in the Municipality of Thionck-Essyl (Bignona Department, Senegal)

In Senegal, as in the sub-Saharan zone, tree and shrub species are generally introduced into the fields and thus constitute an integral part of agricultural, forestry, and pastoral production systems called agroforestry systems. With a view to better management of these systems, this study aimed to contribute to a better understanding of these agrarian systems in Lower Casamance. To this end, surveys of woody vegetation were conducted in seven (07) of the 14 market garden blocks in the commune of Thionck-Essyl. On the basis of a survey rate of 25% in relation to the surface area, 15 square plots of 2500 m2 each were installed. The woody flora of these agroforestry systems included 31 species divided into 25 genera belonging to 14 botanical families. The basal area, the cover rate, and the observed density of woody plants are respectively 6 m2·ha-1; 46% and 67% individuals ha-1. The most frequent species in these agroforestry systems are Elaeis guineensis Jacq. (85%), Citrus sinensis (L.) Osbeck (71%) and Mangifera indica L. (71%). The dominant height class is [2 - 4 m] with 23% of the woody stand in these agroforestry systems. The horizontal structure is characterized by a good representation of individuals with a diameter between 5 and 15 cm (31%). This study constitutes the basis of information necessary for more rational management of these agrarian systems so important in the life of the populations of the commune of Thionck-Essyl.

Carbon-dioxide-driven increase in foliage projective cover is not the same as increased woody plant density: lessons from an Australian tropical savanna

Carbon accounting in tropical savannas relies on a good understanding of the effects of atmospheric carbon dioxide (CO2) and land management on foliage projective cover (FPC) and vegetation structure. We used generalised additive modelling to track changes in Autumn Persistent Green (APG, a satellite-image-derived measure of FPC) in six vegetation types on Cape York Peninsula, Australia, over an 18-year period, and examined the influence of fire and grazing land tenure. We then used field monitoring and variography (analysis of spatial autocorrelation) in a smaller study area to determine whether changes in APG reflected vegetation structural change. APG increased through the 18-year study period and was significantly influenced by vegetation type, recent fire history and grazing land tenure. Residual year-on-year increases suggest CO2 fertilisation was the main driver of APG increase. APG was reduced by fires in the previous year, with early dry season fires having greater impact than late dry season fires, particularly in grassland and rainforest. This is consistent with leaves being most fire sensitive early in the year, when they are actively growing, than in the late dry season, when they are dormant. As seedlings and suckers would be particularly fire-sensitive, early fires may therefore be more effective than late fires at preventing woody encroachment. We demonstrated that variography provides a good indication of whether APG increases are caused by increases in FPC alone, or by an increase in tree density. We found support for increased woody plant density in grasslands, and that this increase was most pronounced on grazing lands. Conversely, we found no support for stem density increases in the dominant eucalypt woodland, despite APG increases being highest in this vegetation type. Hence, increases in FPC cannot always be equated to increases in woody biomass, and may occur in their absence. This conclusion has serious implications for global carbon accounting.

Nutrient addition, fire and grass competition affects biological nitrogen fixation in Vachellia sieberiana, and associated soil respiration

Biological nitrogen fixation (BNF) by woody legumes is likely to vary due to factors such as nutrient availability, fire and grazing. BNF may also alter soil properties by increasing soil fertility, consequently affecting rates of soil respiration. Given the widespread increase in woody plant density in southern African savannas, we investigate the factors influencing BNF in a common encroaching woody legume, Vachellia sieberiana. We conducted a pot experiment using a matrix of grass and seedlings of V. sieberiana. We then assessed the effects of increased nutrient availability (nitrogen (N) and phosphorous (P)) through fertilizer addition, as well as simulated fire and grazing on the rate of BNF, the number and weight of root nodules, and soil respiration. We found a significant decrease in BNF with fertilizer addition, and increases in BNF after fire application. Soil respiration increased with fertilizer addition and decreased after fire application. Grazing had no independent effect on any of the response variables. However, decreased grass biomass, and therefore reduced competitive interactions between tree seedlings and grasses, resulted in increased BNF across all treatments. Furthermore, we found that larger woody seedlings achieved higher rates of BNF, with a positive correlation between the rate of BNF and both the number and weight of root nodules. We conclude that BNF in V. sieberiana is facultative and strongly influenced by grass competition, with differing responses to varying environmental factors. Fertilizer addition suppresses BNF because the presence of readily available N negates the costs of fixation. V. sieberiana seedlings compensated for N lost by fire application by increasing BNF. Soil respiration was found to increase with fertilizer addition, possibly due to higher carbon (C) inputs into the soil. Conversely, fire reduced soil respiration by removing biomass, and thus reduced C input into the soil.

Ecological apparency, ethnobotanical importance and perceptions of population status of wild-growing medicinal plants in a reserve of south-central Mexico

BackgroundThe apparency hypothesis in ethnobotany (common plants are used more than less frequent ones) has been studied mostly by comparing usefulness with woody plant density, or large plants (trees) with herbs, with uneven results. Here, we explore the hypothesis for wild-growing medicinal plants, separately for different life forms. Two methodological subjects relevant for testing the hypothesis are also treated: We compare various importance indicators, including recent use, and evaluate active healers’ knowledge of plant population size. The study area was the Tenancingo-Malinalco-Zumpahuacán Protected Natural Area in central Mexico in the upper part of the Balsas River Basin, a biogeographic region with a long tradition of using wild medicinal species.MethodsPrevious work on the vegetation of the protected area contributed information from 100 survey plots and a species list, which included preliminary data on the medicinal plants. Then, in 2019–2020, we held in-depth and repeated interviews with 13 traditional healers in three rural communities. They were interviewed on uses and population size of a selection of 52 medicinal species of different life forms and abundance (number of individuals in survey plots). The data were analyzed with descriptive statistics, use values and linear regression models.ResultsFor all species, use value correlated significantly with abundance. When separated by life forms, only herbs and shrubs/lianas showed this association, though with statistical limitations. Trees did not, perhaps because some of the most useful trees have been overcollected. We found a good correlation of recent use with frequency of mention and most other importance indicators; the correlation was weakest for number of uses. Also, active healers had a good estimation of population of their collected species.ConclusionsThe apparency hypothesis should be studied separating life forms to reduce the influence of this variable. To measure importance for the study of this hypothesis, the data show that frequency of mention is a good indicator and correlated with actual use. Also, local plant users’ appreciations of population size are quite accurate in the aggregate and may be more efficient than costly vegetation surveys.

Factors of population dynamics of Vitellaria Paradoxa (Karite) in the commune of N'dali in Northeast Benin

The shea tree (Vitellaria paradoxa) is a woody plant species, very useful for the populations of the commune of N'Dali. However, this species suffers from degradation, which jeopardizes its sustainability. The objective of this study is to determine the factors of the population dynamics of Vitellaria paradoxa in the commune of N'Dali. To this end, 340 households in 18 villages were surveyed on their perception of Vitellaria paradoxa dynamics. In addition, 72 square plots (36 in shea parks and 36 in fields) were set up to collect dendrometric data on Vitellaria paradoxa as well as elements relating to the pressure on the species. These data were processed using descriptive statistics methods. The density of woody plants is 25 feet per hectare in the fields and 141.66 feet per hectare in the open forests. The density of shea is 16 feet per hectare in the fields and 19 feet per hectare in the open forest. In general, the Vitellaria paradoxa population is in decline in the commune of N'Dali. The factors of its dynamics are: agriculture, wood exploitation, drought and winds. It is essential to train people in Vitellaria paradoxa based agroforestry.