Sapling Abundance Research Articles

Spatial distribution of woody plants in relation to mistletoe-infected Vachellia karroo trees in a semi-arid African savanna

By increasing resource heterogeneity, mistletoe-infected trees can restructure plant community processes and distribution patterns. No information is available on how mistletoe-infected Vachellia (Acacia) karroo trees within V. karroo dominated stands are spatially distributed, and on how they influence the spatial patterns of their surrounding conspecifics and heterospecifics. Each woody plant was stem mapped using a cartesian plane (x, y) within three 50×50 m plots located in V. karroo dominated stands in a semi-arid savanna, South West Zimbabwe. Pair correlations g(r) were used for the univariate analysis and Poisson process null models were applied to quantify and detect overall departure from randomness. For the bivariate analysis, pair correlations g12(r) under the null model of independence were used, whilst the mark correlation function (kmm(r)) was used to analyse the correlation of tree canopy area and mistletoe infection intensity. For each plot, size class distributions, based on tree height and basal stem diameter displayed negative J curves, with steep negative regression slopes across the size classes, clearly indicating a strongly recruiting population of V. karroo. The univariate patterns of all trees (infected and non-infected) were consistent with a random pattern, which is attributed to unsystematic mistletoe seed dispersal by birds. The univariate analysis of all woody plants (adults and juveniles) exhibited aggregation at small spatial scales due to the high abundance of clustered seedlings and saplings. At small spatial scales, understory woody plants (both conspecifics and non-conspecifics) were positively associated with mistletoe-infected trees due to mistletoephily which is the facilitation (or nurse protégé interactions) within the more resource-rich mistletoe-infected tree subcanopies. These results provide strong evidence suggesting that the variations in spatial pattern modification by mistletoe-infected trees could further increase spatial heterogeneity in this semi-arid savanna. As such, by increasing heterogeneity, mistletoe-infected trees can increase the resilience of semi-arid savannas in the face of perturbations and stochastic events.

Elevation-Dependent Natural Regeneration of Abies georgei var. smithii Forest in Southeastern Tibet

The comprehensive impacts of biotic and abiotic factors on the natural regeneration of Abies georgei var. smithii (Abies) forests in Tibet are not thoroughly understood. To address this gap, our study focused on the regeneration densities of Abies seedlings, saplings, and small trees across 21 plots (each 20 m × 20 m) along an elevation gradient from 3730 m to 4330 m in the Sygera Mountains of Southeastern Tibet. We meticulously measured a suite of 11 variables that describe stand structures and ecological conditions. Through analyses using Spearman’s correlation analysis, hierarchical partitioning, and multiple linear regression, we identified key ecological drivers for successful Abies regeneration. Our results highlighted a peak in the abundance of seedlings, saplings, and small trees at an elevation of 3930 m. As the elevation rose from 3730 m to 4330 m, we observed an initial increase followed by a decrease in canopy cover (canopy), mother tree density (MotherT), 1000-seed weight (SeedW), litter thickness (LitterT), moss cover (MossC), moss thickness (MossT), soil moisture (SM), and soil bulk density, while mean annual temperature and soil depth to permafrost consistently decreased. The critical ecological drivers for Abies natural regeneration were identified as follows: MossT was pivotal for seedling density; canopy and MossC were influential for sapling density, and MotherT was the main factor affecting the density of small trees. This study suggests that a high density of mother trees and a thick and highly covered layer of moss are conducive to the natural regeneration of Abies in the Sygera Mountains. Understanding the current status of regeneration is vital for informing conservation and management strategies for Abies forests in Tibet.

Understory plant growth forms respond independently to combined natural and anthropogenic disturbances

Natural disturbances can maintain forest diversity by creating a heterogeneous resource landscape, which can contribute to coexistence of early- and late-successional species. However, almost all forested ecosystems are also subject to multiple anthropogenic stressors, which could inhibit plant diversity and forest recovery after natural disturbances. Here, we present the first large-scale replicated field experiment testing the interactions among two natural and two anthropogenic disturbances in a mature secondary temperate forest. Specifically, we test the extent to which: 1. a natural windthrow (tornado), 2. deer browsing, 3. salvage logging, a common forestry practice to generate revenue after natural disturbances, and 4. mechanical removal of the understory, drive subsequent plant community assembly, diversity, and abundance. Our results have two clear messages. First, the combined disturbances, especially salvage logging, increased plant species richness and abundance; we found 65 more species in 0.1 ha of the disturbed areas versus the same area of reference forest. Second, we found that it was critical to analyze plant growth forms separately; each major plant growth form responded to the disturbances differently. Surprisingly, salvage logging, browsing, and vegetation removal had negligible effects on the diversity and abundance of tree seedlings or saplings. In contrast, salvaging increased herb richness by 30% (six extra species per 36 m2 plot), and shrubs were twice as abundant in salvaged versus unsalvaged plots. The combined disturbances created unique plant communities in comparison to adjacent undisturbed reference sites, but plant growth forms differed in which combination of disturbances shifted community composition the most. We did not find that non-native invasive species substantially increased in abundance in response to the disturbances, nor were invasive species unique to the salvaged areas. Together, our results demonstrate that a patchwork of combined natural and anthropogenic disturbances can promote plant diversity in a human-modified temperate forest. In particular, the combination of a natural wind disturbance and salvage logging benefited native herbaceous species, the plant group that represents the vast majority of vascular plant species (∼80%) in temperate forests across the world.

Tree regeneration potential in urban spruce-dominated forests is shaped by management history

With projected climate change, urban spruce-dominated forests are facing increasing risks of forest damages, encouraging management for mixed stand structures. In the major cities of southern Finland, forests are preferentially maintained continuously covered, and tree regeneration is mostly reliant on naturally emerging sapling stock. To understand the role of forest management in shaping natural tree regeneration in urban forests, we studied the occurrence and abundance of tree saplings in spruce-dominated tree stands on a management continuum ranging from partially logged to undisturbed near-natural stands. Study sites (N = 74) were located in three urban centers in southern Finland: Tampere, Lahti and Helsinki region. We analyzed the data by comparing tree regeneration potential between management classes reflecting the timing and intensity of past logging, and by relating the occurrence of saplings with current structures of the living tree stand.Compared to undisturbed stands, partially logged sites had increased regeneration of broad-leaved trees and repressed regeneration of spruce, while the most abundant sapling tree species across all management classes was rowan. We conclude that partial logging can be a successful way of directing tree regeneration towards lower dominance of spruce. However, when the canopy is only partially opened, created gaps may end up being filled primarily by rowans that are comparatively shade-tolerant. Because the ingrowth of rowan and many other broad-leaved tree species is strongly restricted by dense populations of large browsing animals in non-urban areas, urban forests may develop stand structures and tree species composition that are otherwise rare in the Fennoscandian boreal forests.

Grazing regime effects on bird biodiversity overwhelmed by an interference competitor

The majority of the world's mammal biomass is domestic livestock. Intensive livestock grazing can negatively impact some elements of biodiversity. We quantified the effects of grazing management on bird occupancy over a 10-year period in patches of Australian endangered temperate woodland within paddocks subjected to one of three grazing regimes: continuous set stocking, rotational, and total livestock exclusion. Grazing may affect birds through altering resource availability, influencing vegetation structure, or affecting the occurrence of noisy miners (Manorina melanocephala), a native honeyeater that engages in interference competition with other birds.Using Bayesian generalized linear mixed models and multispecies occupancy modelling, we quantified relative and interactive effects on bird biodiversity of grazing, vegetation structure, and noisy miner occupancy. We found only muted grazing regime effects on woodland birds. However, many species responded to vegetation structure. Small invertivorous woodland birds responded positively to sapling abundance, and some (larger) species responded positively to the abundance of trees >50 cm. Furthermore, species richness increased with increased sapling abundance and trees >50 cm. The largest effects were associated with noisy miner occurrence, which drove reductions in small-bodied, invertivorous birds, effectively “swamping” the positive effects of vegetation attributes on these species.The profound impacts of noisy miners present challenges for bird conservation in woodland ecosystems, especially those subject to grazing. Management to reduce grazing pressure by domestic livestock may eventually help limit the impacts of the noisy miner, in part by facilitating natural regeneration of temperate woodlands to which small-bodied woodland birds respond positively.

Long-term exclusion of invasive ungulates alters tree recruitment and functional traits but not total forest carbon.

Forests are major carbon (C) sinks, but their ability to sequester C and thus mitigate climate change, varies with the environment, disturbance regime, and biotic interactions. Herbivory by invasive, nonnative ungulates can have profound ecosystem effects, yet its consequences for forest C stocks remain poorly understood. We determined the impact of invasive ungulates on C pools, both above- and belowground (to 30 cm), and on forest structure and diversity using 26 paired long-term (>20 years) ungulate exclosures and adjacent unfenced control plots located in native temperate rainforests across New Zealand, spanning 36-41° S. Total ecosystem C was similar between ungulate exclosure (299.93 ± 25.94 Mg C ha-1 ) and unfenced control (324.60 ± 38.39 Mg C ha-1 ) plots. Most (60%) variation in total ecosystem C was explained by the biomass of the largest tree (mean diameter at breast height [dbh]: 88 cm) within each plot. Ungulate exclusion increased the abundance and diversity of saplings and small trees (dbh ≥2.5, <10 cm) compared with unfenced controls, but these accounted for ~5% of total ecosystem C, demonstrating that a few, large trees dominate the total forest ecosystem C but are unaffected by invasive ungulates at a timescale of 20-50 years. However, changes in understory C pools, species composition, and functional diversity did occur following long-term ungulate exclusion. Our findings suggest that, although the removal of invasive herbivores may not affect total forest C at the decadal scale, major shifts in the diversity and composition of regenerating species will have longer term consequences for ecosystem processes and forest C.

Replace me if you can: Abundance of advance regeneration under canopy trees in a primeval beech forest

Tree replacement patterns strongly shape species coexistence and dominance in forest ecosystems. In mixed forests subject to a small-scale disturbance regime, dead canopy trees are often replaced by advance regeneration. We studied the abundance of saplings (6–10 cm dbh) and poles (10–25 cm dbh) under canopy trees based on four inventories on a 10-ha permanent plot in a large primary forest dominated by Fagus sylvatica in Ukraine. Saplings and poles of Fagus sylvatica, Acer platanoides, A. pseudoplatanus and Ulmus glabra were spatially linked to canopy trees (‘hosts’, dbh > 25 cm) based on their crown radius, and the hosts’ neighborhood was classified according to the presence of dead trees. The number of saplings and poles under hosts was modelled with a Bayesian approach. There was a higher number of advance regeneration under hosts with increasing host diameter. The abundance of advance regeneration was the lowest under hosts in the canopy (i.e., under shaded conditions) and highest for hosts growing in gaps. 1) Under the canopy, only F. sylvatica poles can replace heterospecific hosts > 80 cm dbh, while other pole species are clearly below the replacement threshold. 2) Near dead lying trees, Acer pseudoplatanus rarely achieved an abundance of one pole at a host dbh > 80 cm. 3) In gaps, Acer spp. poles were able to replace F. sylvatica hosts. The proximity to dead lying trees and gaps is crucial for Acer spp. and U. glabra saplings for recruitment to the pole stage. The higher rate of recruitment under hosts adjacent to dead lying trees suggests that the total length of gap edges may be as important as gap size or disturbance frequency. In gaps > 550 m2, advance regeneration without hosts (growing in gaps) of Acer spp. can recruit higher number of saplings than F. sylvatica, but not poles. We conclude that almost all canopy trees of Acer spp. and U. glabra are likely to be replaced by Fagus sylvatica if the current small-scale disturbance regime and single-tree mortality continue to prevail.

Forgotten forest relics: Apple trees (Malus spp.) in eastern U.S. forests

One potential legacy of the widespread deforestation of the 1700-1800s and subsequent agricultural abandonment and reforestation across the eastern United States (U.S.) during the 1900s is the establishment of introduced apple trees (Malus domestica) exclusive of naturally occurring native crab apple species. As these apple trees might provide ecological services and a genetic reserve of long-forgotten apple cultivars, a region-wide forest inventory was used to estimate the current extent, condition, and changes in the population of apple trees across eastern forests of the U.S. It was found that hundreds of millions of apple trees currently exist in the forests of the northern U.S. with indications of population senescence as the abundance of seedlings and saplings decline while the abundance of the largest-sized trees and standing dead trees increase. The distribution of forest apple trees is only aligned with native crab apple distributions in limited areas, suggesting distinct feral apple populations derived from agricultural abandonment decades ago. As these extant apple trees are likely relics of former orchards and/or their naturally dispersed progeny, these populations may serve as an in-situ gene bank representing hundreds, if not thousands, of apple cultivars forgotten long ago but adapted to local conditions and perhaps of importance to ensuring the future resilience of domestic apple production in the context of global change.

Population structure, aggregation, and dispersal of Euterpe edulis Mart. at two sites of interior atlantic forest.

Habitat destruction and fragmentation can change environmental conditions and disrupt mutualistic interactions, leading to impacts on natural populations. Here we checked how plant population structure responds to environmental degradation by quantifying effective seed dispersal and patterns of population distribution for the animal-dispersed palm Euterpe edulis Mart. (Arecaceae). Thus, we assessed E. edulis population structure at two locations with different degrees of fragmentation in the Interior Atlantic Forest (west of the State of Paraná, Brazil), where we registered the density of saplings at increasing distances from adults palms and from large trees in the vicinity (perch-trees). We found differences between locations, with aggregated saplings and highest densities at the most fragmented site, although in this site Immature individuals were almost absent. We also identified patches of saplings under perch-trees canopies, in a way which suggests these individuals originate from dispersal events. In both sites, the abundance of Immature saplings was similar either nearby adult palms or perch-trees, pointing to perch-trees being relevant to E. edulis population dynamics. Thus, while conservation of E. edulis in the Interior Atlantic Forest can benefit from such new data, it is still necessary to check whether our findings are recurring and consistently found elsewhere.

Tree regeneration response to a shifting soil nutrient economy depends on mycorrhizal association and age

Atmospheric nitrogen (N) deposition has led to an increase in N cycling and N availability. This increase in inorganic N is likely to impact forest ecosystems, although the responses remain uncertain. Most tree species are associated with one of two mycorrhiza types – arbuscular mycorrhizae (AM) or ectomycorrhiza (ECM). Due to functional differences in their ability to access soil nutrients, we might expect that increased N cycling and availability of inorganic N would benefit AM associated species, with negative or neutral impact for ECM associated species. This study addresses how the abundance of the regeneration layer responds to those shifting soil conditions, based on their mycorrhizal association. We used a long-term experiment located in a temperate deciduous forest, where the native acidic soils are low in nutrients. Soil treatments began in 2009, by adding lime and/or phosphate to raise pH and increase the availability of N and P. All trees ≥ 6.0 cm in 2010 were tagged and have been monitored with annual censuses. To quantity the density of the regeneration layer, seedlings and saplings were recorded in the control and limed plots in 2019. Trees that had recruited into the canopy (DBH ≥ 6.0 cm) were measured in 2020 in all treatment plots. Seedlings older than one year responded to the treatments as predicted, as AM seedlings increased by 42 % in the lime treatment (1.53 ± 0.38 individuals per m2 in control, to 2.17 ± 0.56 in lime) and ECM seedlings decreased by 49 % in response to liming (0.61 ± 0.14 individuals per m2 in control, to 0.31 ± 0.04 in lime). AM saplings also responded positively to liming, increasing 254 % from control to lime (from 0.013 ± 0.003 to 0.046 ± 0.018 individuals per m2), while ECM sapling abundance was neutral (0.063 ± 0.015 individuals per m2 in control, and 0.054 ± 0.009 in lime). The highest number of ECM recruits was found in the control plots (34.4 %), followed by phosphate (25.8 %), lime + phosphate (21.5 %), then lime (18.3 %). For AM associated tree species, the number of trees recruiting into the canopy was substantially higher in the phosphate treatment (39.4 %), with lower numbers in the other three treatments (26.8 % in control, 19.7 % in lime, and 14.1 % in lime + phosphate). Overall, we found a positive regeneration response in AM associated species to increasing nutrient availability which has important consequences for species composition in forests experiencing chronic N deposition.

Early responses of regeneration to weeding and herbicide application to control Guinea‐grass in a 20‐year‐old Atlantic Forest undergoing restoration

Among the invasive grasses harming natural ecosystems in Brazil, Guinea‐grass (Megathyrsus maximus) has received significant attention due to its high invasive potential and damage it causes to restoration sites. Here, we show the response of seedlings (10 cm to 1 m) and saplings (&gt;1 m) one year after Guinea‐grass removal in a 20‐year‐old restoration site in the Atlantic Forest. Thirty 10 × 20 m plots were installed and assigned into three treatments: control, mechanical removal using gas‐trimmers, and mechanical removal followed by the application of Roundup Transorb R (glyphosate). Forest canopy and grass cover were also assessed. Guinea‐grass was negatively correlated with woody species richness and abundance. Forest canopy cover was positively related to species richness and abundance, and negatively related to Guinea‐grass. Treatments applied were successful in controlling the plant invader and did not cause any significant reduction in the total abundance or richness of saplings after one year. For seedlings, however, the abundance and richness of pioneer woody species increased over time with mechanical removal, while the abundance and richness of non‐pioneer woody species decreased in plots treated with herbicide. We expect regeneration responses to continue to improve with time. Our results support the use of both herbicide and mechanical removal to reduce Guinea‐grass in Atlantic Forest sites undergoing restoration, although the use of herbicide lowers native seedling richness in the short‐term, while mechanical removal may be better for small sites, where it is more feasible and less demanding.

Sapling growth gradients interact with homogeneous disturbance regimes to explain savanna tree cover discontinuities

AbstractSavanna tree cover often exhibits sudden discontinuities across space. It has been proposed that local spatial processes imposed by variation in tree cover itself (as opposed to by external drivers such as edaphic variation) can reinforce such discontinuities. Despite this, we generally lack data on tree demography and the environmental drivers affecting the former as a function of tree neighborhoods in these systems. Given the importance of disturbance traps in savannas, spatial processes affecting the likelihood of escape from the seedling/sapling stage to the adult tree stage are likely to be critical. In a longitudinal survey of 800 saplings distributed along eight 1‐km transects spanning woodland–grassland transitions in Serengeti National Park, we found a positive association between tree cover and sapling growth and survival, but no relationship with sapling abundance, maximum tree height, disturbance, or topkill. Based on microclimate and soil moisture dynamics data, we found no evidence to suggest that tree cover itself drives variation in growth. Based on a prior analysis of soil properties along these transects, we hypothesized that underlying edaphic conditions may be responsible for variation in growth. Regardless of the underlying mechanism, we used simulations to show that subtle growth rate gradients interacted with intense disturbance regimes to produce sharp discontinuities in tree cover, with strong demographic bottlenecks where growth is slowest, explaining the observed patterns of tree cover along the transects. Our results indicated that disturbance and herbivory are equally intense in areas of high and low tree cover, and that although trees have the potential to successfully establish and reach adulthood in open, grassy sites, they grow too slowly to escape disturbance traps there. Importantly, we showed that although herbivory and fire are fundamental for explaining savanna structural patterns, their effects are not necessarily reinforced by tree cover itself.

Upward Treeline Shifts in Two Regions of Subarctic Russia Are Governed by Summer Thermal and Winter Snow Conditions

Climate warming impacts on alpine treeline dynamics. However, we still lack robust assessments of the long-term impacts of climate on tree recruitment at the treeline, particularly in remote areas such as the subarctic regions of Russia subjected to different climate influences. We expected that the treelines in two regions may have different features and dynamics patterns. We analyzed climate variables and assessed treeline dynamics by quantifying recruitment using the tree rings of ca. 7000 trees of four species (Betula pubescens Ehrh. ssp. tortuosa, Pinus sylvestris L., Picea abies Ledeb. ssp. obovata, Larix gmelinii Rupr.) along 14 altitudinal transects (series of study plots). We compared the Khibiny Massif (Kola Peninsula) and the western Putorana Plateau, subjected to oceanic and continental influences, respectively. In both regions, summers became warmer, and winters became snowier during the past century. At the low part of the treeline ecotone, tree recruitment has slowly increased since the mid-18th century at the Putorana Plateau and the mid-19th century at the Khibiny but accelerated in the early 20th century at both regions and reached a maximum peak in the second half of the past century. Treeline encroachment intensified in the 1930s at the Khibiny and the 1950s at the Putorana Plateau. Trees encroached in the tundra leading to upward treeline shifts in the late 20th century. The slope exposure affected the rates of treeline shift with higher upward advances on southern-oriented slopes. Tree recruitment and early-winter precipitation were positively correlated. The differences in species composition, treeline altitude and influences of slope orientation on treeline dynamics can be explained primarily by differences in the degree of continentality. The abundance of saplings in both regions allows the future encroachment of trees into tundra and further treeline upward shifts to be forecast.

Forest management, site characteristics and climate change affect multiple biotic threats in riparian forests

In a changing world, riparian forests are coming under more and more stress from biotic threats. This impacts all stages from saplings to older trees. One of the most dominant biotic threats are alien species and eruptive pest species. Sustainable silvicultural methods are required to reduce the risk of such biotic threats. We investigated the influence of climate, site, tree, and silvicultural characteristics on leaf damage by insect pests or fungal pathogens, herbaceous alien plant species, browsing, and the abundance of native tree saplings. Transects across the Danube-Mura-Drava biosphere reserve from Austria in the northwest to Serbia in the southeast, each containing 7–8 plots, were established to assess tree and site characteristics, regeneration, as well as fungal and insect leaf damage. We found that the horizontal stand structure affected insect leaf damage in different ways. Insect leaf damage was positively correlated with fungal leaf damage and tree height, and negatively correlated with intensity of forest management (from natural forests to coppice/plantations), temperature and precipitation during the vegetation season. Fungal leaf damage was negatively associated with intensity of forest management, and negatively with public ownership and tree species richness. Browsing was positively influenced by the number of saplings. The abundance of alien herbaceous plant species was negatively associated with distance to the watercourse, mean tree height, mean temperature of the vegetative period (MTVP), competition level, and the number of trees per layer, and positively associated with the DBH.

Regeneration Status and Role of Traditional Ecological Knowledge for Cloud Forest Ecosystem Restoration in Ecuador

The importance of forests for biodiversity conservation has been well recognized by the global community; as a result, conservation efforts have increased over the past two decades. In Ecuador, the lack of integrated information for defining and assessing the status of local ecosystems is a major challenge for designing conservation and restoration plans. Thus, the objectives of this study were (1) to examine the regeneration status of cloud forest remnants, some of which had experienced past human disturbance events, (2) to explore a local rural community’s traditional ecological knowledge (TEK) relevant for restoration and (3) to investigate the integration between TEK and ecological science-based approaches. A survey of regeneration status was conducted in four remnants of cloud forests (n = 16) in Cosanga, Napo Province, in the Andes of northeastern Ecuador. The species of young trees (0.5–5 m height) were identified over 0.16 ha. In-depth interviews of individuals from local communities (n = 48) were conducted to identify socio-ecologically important native species. The results showed significant differences (p &lt; 0.001) in species richness and the stem density of seedlings and saplings in gaps. The stem density of Chusquea sp., a bamboo species, explained 63% of the variation in species richness and 48% of the variation in the abundance of seedlings and saplings between plots. Informants cited 32 socio-ecologically important species, of which 26 species were cited as sources of food and habitats for wildlife. The ranking of species based on a relative importance index and a cultural value index—taking into account both the spread of knowledge among local informants and the multiplicity of uses—revealed that Hyeromina duquei, Citharexylum montanum, Eugenia crassimarginata and Sapium contortum were traditionally the most valuable species for both humans and wildlife. Informants also recommended 27 species for future planting, of which 19 species were amongst the rarest species in the regeneration survey. In conclusion, the results demonstrate a synergy between TEK and ecological science-based approaches (regeneration survey) to natural ecosystem research. Thus, traditional ecological knowledge can provide insights into ecosystem–plant–animal interaction, and to identify native species useful for both humans and wildlife for forest restoration projects to reconnect isolated cloud forest fragments.

Environmental and biological factors affecting the abundance of Prosopis flexuosa saplings in the central-west Monte of Argentina

Trees and forests in drylands help mitigate the challenges through provision of economic products and vital environmental services such as habitat for biodiversity, prevention of erosion and desertification, regulation of water, microclimate, and soil fertility. The condition and changes in dry forests can be assessed by using ecological indicators able to quantify spatial and temporal changes in vegetation. One of the ways to determine the condition of the forest is to study the dominant tree species and its regeneration. Our study aimed to assess whether the abundance of Prosopis flexuosa saplings is affected by environmental and biological factors. To evaluate the first variables we used data from remote sensing such as satellite images and Aster Global Digital Model (GDEM). The second set of variables was about exotic and native ungulates and we used feces of these animals and camera traps to take data. We found that sapling abundance related positively to sandy substrates and negatively to Wetness Index. On the other hand, in relation to biological variables, the abundance of saplings was positively affected by density of adult trees and by number of seeds dispersed by equines, but space use by Lama guanicoe had a negative relationship with saplings. This research shows that P. flexuosa saplings are benefited from sandy substrates and the conditions around adult trees. In addition to this, we found that exotic ungulates in low densities have neutral (i.e. cattle) or positive (i.e. equines) effects on sapling abundance. Based on these findings, we conclude that regeneration of the population of P. flexuosa in our study area has no major problems. In addition, we corroborated that the presence of exotic and domestic ungulates in low densities does not have deleterious consequences for saplings of the dominant tree, P. flexuosa .

Interactive effects of chronic anthropogenic disturbances on Prosopis woodland structure in the Central Monte, Argentina

In drylands all over the world, chronic anthropic disturbances are relevant factors for woodland degradation. Different disturbances can potentially interact to change vegetation structure. Knowing woodland structure is crucial for better predicting forest dynamic because trees of different sizes significantly affect the regeneration processes, number of saplings and young trees, crown traits and competition attributes. Throughout the Monte biogeographic region, grazing and wood extraction are the main anthropogenic disturbances on Prosopis dry woodlands that can generate modifications in key ecosystem processes. First, we aimed to assess woodland structure at sites under chronic anthropic disturbances. Subsequently, we explored how the combination of grazing and wood extraction affected the population structure of P. flexuosa considered by classes: seedlings, saplings and adults. We found that sites under disturbances presented a high density of trees of smaller sizes. Besides, the interaction effect between grazing and wood extraction depended on the intensities of each of the disturbances. The combination of high intensities of both grazing and wood extraction negatively affected the abundance of all classes, but low or moderate grazing intensities combined with high wood extraction had a positive effect on the abundance of saplings and adults. High intensities of co-occurring disturbances decreased seedling abundance affecting forest recruitment which also was negatively reflected in sapling and adult abundance. However, the combination of low or moderate grazing and high wood extraction generated a woodland structure characterized by few seedlings, and many saplings and adult trees of small size. Application of management options (e.g., spatial or temporal separation of human use, programmed management of grazing and wood extraction intensities or planned practices as wood removal for local use) should contribute to enhance the provision of ecosystem services in Prosopis sp. woodlands without risking regeneration persistence and improving the woodland structure.

Elevation gradient distribution of indices of tree population in a montane forest: The role of leaf traits and the environment

To disentangle the controls on species distribution in the context of climate change is a central element in proposed strategies to maintain species diversity. However, previous studies have focused mainly on the roles of abiotic factors (e.g., climate and soil properties), with much less attention given to the roles of biotic factors such as functional traits. Here, we measured eight leaf traits for 240 individual trees of 53 species and analyzed the variation in traits and population composition indices and their relationships with soil properties, climate factors, and leaf traits. The tree density, frequency and species importance values of the overall species and saplings significantly increased with increasing elevation, while the same indices (except for species frequency) of adults did not significantly change. The largest percentage of variation of species importance value (greater than 50%) was explained by climate, but leaf traits played a critical role in driving elevation distribution patterns of both saplings and adults; the abundance of saplings significantly increased with elevation, with increased leaf carbon contents, while the abundance of adults did not change in accordance with a nutrient conservation strategy associated with the leaf economic spectrum. Our results suggest that the elevation gradient distribution of woody plant species is dependent on tree size and that local atmospheric humidity and leaf traits cause considerable variation in species distribution along subtropical mountain elevations. We provide evidence of which leaf traits play a key role in the elevation gradient distribution of different sizes of woody tree species.

Conservation zones increase habitat heterogeneity of certified Mediterranean oak woodlands

Forest certification is a conservation tool, which aims to promote the sustainable management and conservation of forest ecosystems. Establishing set-aside or lower intervention conservation zones to promote biodiversity conservation is a requisite of forest certification. We tested the effects of conservation zones on the tree biometrics and regeneration, as well as on the taxonomic, functional, and structural diversity of the shrub and herb understory, in Mediterranean oak woodlands. We also assessed how oak biometrics, regeneration and understory diversity varied among conservation zones established 10, 14, and 20 years before our sampling dates. Oak regeneration tended to be higher in conservation zones than in controls, but results varied with the age of conservation zones. For example, the abundance of oak seedlings and saplings was higher in 10-year-old conservation zones than in those established 20 years ago. Abundance of young oak trees was higher in 14-year-old conservation zones than in 10- and 20-year-old conservation zones. The understory vertical diversity was significantly higher in 14- and 20-year-old conservation zones than in controls. Functional diversity differed significantly between conservation zones and controls, with a higher abundance of late-successional shrubs, namely fleshy-fruited species in 20-year-old conservation zones. The plant species composition of the shrub and the herb understory was most dissimilar between older conservation zones and controls. Additionally, the cover and diversity of the understory herb species decreased with the age of conservation zones. Conservation zones implemented under forest certification increase habitat structural complexity of oak woodlands, which may benefit wildlife species, but there will be trade-offs with the cover and diversity of the herb understory. Forest managers must evaluate such trade-offs when establishing conservation zones in cork oak woodlands under forest certification schemes.

Large wild herbivores slow down the rapid decline of plant diversity in a tropical forest biodiversity hotspot

Abstract The UN declaration of the Decade of Ecosystem Restoration 2021–2030 emphasizes the need for effective measures to restore ecosystems and safeguard biodiversity. Large herbivores regulate many ecosystem processes and functions; yet, their potential as a nature‐based solution to buffer against long‐term temporal declines in biodiversity associated with global change and restore diversity in secondary forests remains unknown. By means of an exclusion experiment, we tested experimentally the buffering effects of large wild herbivores to avert against long‐term biodiversity collapse in old‐growth and secondary tropical forests in the Atlantic Forest of Brazil where sapling abundance and species richness declined c. 20% over the course of 10 years. The experiment comprised 50 large herbivore exclosure‐open control plot pairs (25 at the old‐growth forest and 25 at the secondary forest), where 2 m2 were monitored in every plot during a 10‐year period. Large herbivores were able to decelerate diversity declines and compositional change in the species‐rich old‐growth forest, but only decelerated compositional change in the secondary forest. In contrast, declines in species richness and abundance were unaffected by large herbivores on either forest. The buffering effects of large herbivores were strongly nonlinear and contingent on the initial level of diversity at the patch scale: highly diverse communities suffered the strongest collapse in the absence of large herbivores. Thus, larger buffering effects of large herbivores on the old‐growth forest are the logical consequence of large herbivores buffering the many high diversity plant communities found in this forest. Conversely, as the secondary forest held fewer high diversity patches, buffering effects on the secondary forest were weak. Synthesis and applications. Our study indicates that large herbivores have moderate yet critical effects on slowing down community change and diversity loss of highly diverse plant communities, thus suggesting that the conservation of (and potentially trophic rewilding with) large herbivores is a fundamental nature‐based solution for averting the global collapse of the strongholds of biodiversity. Its buffering effects on biodiversity loss operate at very small spatial scales, are likely contingent on successional stage and are most effective in old‐growth or high diversity secondary forests.