Pioneer Tree Species Research Articles

Effects of logging on landscape-level tree diversity across an elevational gradient in Bornean tropical forests

Logging has caused a substantial loss of biodiversity and associated ecosystem services. Therefore, it is important to examine how logging affects biodiversity on a landscape scale to plan responsible management of a tropical forest. Although a number of plot-based studies have shown the effect of logging on local tree species richness (alpha diversity), the effect on species turnover along environmental gradients (beta diversity) remains largely unknown. In this study, we evaluated how logging disturbance affects alpha and beta diversity along an elevational gradient on the eastern slope of Mount Trus Madi in Borneo. We further investigated how pioneer and late-successional tree species differed in the habitat range to clarify the mechanism underlying the beta diversity pattern. We selected 90 plots, each with a radius of 20 m, with a range of disturbance intensity (five classes from highly degraded forests to pristine forests) in lower (285–600 m asl) and higher elevation areas (600–1105 m asl). The remaining above-ground biomass, which is an indicator of past disturbance intensity, strongly varied across the plots (5.4–570.6 and 3.1–771.6Mgha−1 in lower and higher elevation areas, respectively). Diameter at breast height (DBH) and species name were recorded for all trees with a DBH larger than 10 cm. We calculated the species number per 20 individual trees for each plot to represent alpha diversity. Beta diversity along the elevational gradient was calculated as the slope of the relationship between standardized compositional dissimilarity (beta deviation) and the elevational difference. Alpha diversity decreased in higher (17.3–12.3 species per 20 trees) and lower areas (16.8–11.3 species per 20 trees) with increasing logging intensity. Beta diversity along the elevational gradient also decreased to almost zero in highly disturbed areas. Pioneer tree species had a wider elevational range than late-successional species. These results suggest that the shift in dominant tree species after logging (from late-successional to pioneer species) was the main driver of the decline in beta diversity along the elevational gradient. We conclude that preserving and restoring beta diversity are important to sustain tropical production forests.

Demographic differentiation among pioneer tree species during secondary succession of a Neotropical rainforest

Abstract Early pioneer species share life histories enabling them to colonize disturbed sites, but how much they differ demographically and how such differentiation determines pioneer species turnover during succession are still open questions. Here, we approached these issues by comparing the demography of dominant pioneer tree species during the secondary succession of tropical rainforest in Southeast Mexico. We assessed changes in population density, population structure, vital rates and intrinsic population growth rate (r) of the pioneer species Trema micrantha, Cecropia peltata and Trichospermum mexicanum during the first 35 years of succession. For this, we combined chronosequence and long‐term (from 2000 to 2018) data from 14 abandoned cornfields with 0.5–35 years fallow age. Trema colonized and disappeared first during succession (<15 years), followed by Cecropia (<28) and Trichospermum (>31). All species exhibited hump‐shaped successional trajectories of population density and biomass with Trema reaching a peak first, followed by Cecropia and later Trichospermum. Species exhibited a fast reduction in r with fallow age, with Trema reaching negative growth rates (r < 0) in the third, Cecropia in the fourth, and Trichospermum in the seventh year of succession. Recruitment, growth and mortality rates of seedlings and juveniles defined the period of population increase and the age of succession at which each species reached maximum density and biomass. The mortality rate in mature stages determined how long each species persisted during succession. An important variation in species replacement occurred among study sites. In some sites, one species was abundant and the others were almost absent, while it was the opposite in other sites. We inferred that priority inhibitory effects operated among species during the field colonization. Synthesis. Although Trema, Cecropia and Trichospermum are considered typical pioneer trees, these species differed importantly in their demographic attributes during succession. The speed at which r declined with age of succession indicated the moment at which each species reached its maximum density and species replacement sequence during succession. However, inter‐specific priority inhibitory effects during field colonization may also be involved in the chance of colonization and replacement between species with similar regeneration strategies.

Macro- and Micronutrient Contents in Soils of a Chronosequence of Naturally Regenerated Birch Stands on Abandoned Agricultural Lands in Central Poland

Abandoned agricultural lands in Central and Northern Europe undergo a quite rapid secondary succession of woody species, especially silver birch (Betula pendula Roth.) as a pioneer tree species. Such a process is desirable both from natural and economic point of views, as afforestation involves a change to the entire ecosystem and, in particular, the transformation of anthropogenic habitats typical for agriculture into habitats similar to a natural forest. In the present study, we report the chemical properties of soils under birch stands that naturally regenerated on abandoned agricultural lands and answer the question of whether silver birch modifies the chemical properties of soils over a (relatively short—17 years) time and with depth in the soil profile. The research investigated the natural secondary succession of silver birch on 28 study plots established as a chronosequence in seven locations in Central Poland. The age of the stands ranged from 2 to 17 years. We analysed the contents of selected micro- and macroelements and heavy metals at three depths in the soil profile. The chemical properties of former agricultural soils covered with newly established silver birch stands, taking into account the depth in the soil profile, demonstrated tendencies to change over the time. In the first age class of birch stands, the stock of investigated nutrients in the soil was higher compared to the following age classes. Statistically significant differences were noted in the case of Cu and Cr. Along with the age of birch stands (age class IV), there was a tendency for stock of the analysed nutrients to grow, which can be associated with an increase in aboveground biomass and root system development. The changes in the contents of the macro- and microelements, as well as heavy metals, were characterised by a gradual increase of the elements analysed in the upper layer of the soil that, in the years following the birch influence on the soil, starts having an effect on the deeper layers. In the case of Cu, Pb, Cd, Ni and Cr, there was a statistically significant change in the depth of the soil. Longer chronosequences should be observed to see a clear trajectory in soil chemistry changes with birch stand ages.

Growth and Potential of Lomatia hirsuta Forests from Stump Shoots in the Valley of El Manso/Patagonia/Argentina

Lomatia hirsuta (Lam.) Diels is a pioneer tree species that develops after wildfires, and in advanced successional stages, it is often found as a secondary species in Patagonian forests. However, in El Manso Valley, Province of Río Negro in Western Argentina, L. hirsuta forms mature pure stands, originated from stump shoots. The wood is very attractive for its colourful appearance and beautiful grain. Nevertheless, these forests are not managed for timber production, they are mostly strong thinned for grazing, and the wood is mainly used as firewood. The objective of this study was to evaluate the possibility to improve quality wood production in stands through silvicultural interventions in a sustainable way. Samples have been carried out in stands of different developmental stages. We evaluated the state and quality of the trees, and their growth has been studied by means of trunk analysis. The results indicate that there is significant potential to improve the production of quality wood in dense stands by thinning to release crop trees. Thinning should start in young stands. It also became apparent that forest management is first necessary to stabilise these nearly unattended forests.

Dynamics of ecosystem carbon stocks in a chronosequence of nitrogen‐fixing Nepalese alder (Alnus nepalensis D. Don.) forest stands in the central Himalayas

AbstractNitrogen‐fixing Nepalese alder (Alnus nepalensis D. Don.) is a rapidly‐growing pioneer tree species that often forms pure stands in areas affected by landslides, but also occurs mixed with other late‐successional species in the central Himalayas. In this study, we assessed the distribution of carbon in vegetation and soil in a chronosequence of A. nepalensis (3–270 years old) forest stands and evaluated its correlation with the stand and alder total basal area (TBA). The study was conducted in six different naturally occurring forest stands in a chronosequence, viz., alder‐early regenerating (AER), alder‐late regenerating (ALR), alder young‐mixed (AYM), alder mature‐oak (Quercus leucotrichophora) mixed (AMOM), alder mature‐rhododendron (Rhododendron arboreum) mixed (AMR), and alder old‐oak (Q. leucotrichophora) mixed (AOOM) forests. The chronosequence consisted of three young unreserved, AER, ALR, and AYM (age 3–25) and three older reserved, AMOM, AMR, and AOOM (age 80–270) stands. We used structural equation modelling (SEM) to quantify the contribution of various carbon pools on ecosystem carbon stock. Forest carbon stock significantly increased (p < 0.05) with forest age and TBA, indicating that succession is the driving factor of the forest ecosystem processes, carbon accumulation, and therefore, change in vegetation biomass carbon and soil carbon in the chronosequence of A. nepalensis forests. Total vegetation biomass carbon (tree, shrubs, herbs, and litter) contained ~12.54–289.85 Mg ha−1 (79.11–57.77% total carbon stock), and soil carbon (depths of 0–10 cm in AER, 0–30 cm in AYM, 0–100 cm in remaining forest stands) contained ~3.31–210.13 Mg ha−1 (20.8–42% total carbon stock) and positively increased with stand and A. nepalensis TBA. The tree layer biomass carbon stock was considerably higher than the understory (shrubs, herbs, and forest floor). The soil carbon stock was reported to be influenced by the successional stages. Therefore, these findings reflect that the A. nepalensis forest development in the central Himalayas lead to storage of large amount of carbon stock in both plant biomass and soil.

Leaf silicon accumulation rates in relation to light environment and shoot growth rates in paper mulberry (Broussonetia papyrifera, Moraceae).

While increasing numbers of studies report wide variations of leaf silicon (Si) accumulation among plant species, within-species variations of leaf Si accumulation have scarcely been examined for tree species. As in crop plants, environmental factors that affect transpiration rates may influence passive transpiration-dependent transport of Si uptake in trees. Here, we tested a hypothesis that leaf Si accumulation rate should be higher in shoots that receive more light and thus achieve faster growth, using Broussonetia papyrifera, a pioneer tree species with successive leaf production and Si accumulation with leaf age. We marked individual leaves weekly throughout the growing season (June-September), and measured Si concentration and light availability in relation to the chronosequence of leaf age in September. In shoots that continued growing and successively produced leaves throughout the growing season, leaf Si content increased linearly with leaf age. In support of our hypothesis, leaf Si accumulation rate varied widely among shoots with positive correlations with shoot growth and light availability. In conclusion, both leaf age and microenvironment affect within-species variations in leaf Si concentration of this species, a moderate Si accumulator.

Ecological drivers of intraspecific variation in seed dispersal services of a common neotropical palm

AbstractThrough frugivory and seed dispersal, vertebrates influence plant demography and forest regeneration. Variation in local habitat surrounding fruiting plants can influence frugivore foraging decisions, thereby creating intraspecific variation in seed dispersal services. However, we have little knowledge of drivers of local variation in frugivory. Here, we investigate factors that may influence frugivore diversity and fruit removal at the level of individual plants. We focus on a common understory palm within a continuous Chocó forest with mixed land‐use histories in Ecuador. The density of pioneer tree species in the genus Cecropia around focal palms was negatively related to fruit removal and the diversity of frugivores visiting palms. This may relate to the fact that the presence and abundance of Cecropia species often indicate the existence and severity of past disturbances. Local Cecropia density was also related to an overall shift in the frugivore community that corresponded with an increase in fruit removal by lower‐quality seed dispersers (rodents). We also found that the local density of fruiting conspecifics was positively related to frugivore diversity, but not fruit removal. Our results provide information on drivers of intraspecific inequalities in plant populations across tropical forest landscapes. The reduction in fruit removal and frugivore diversity associated with local Cecropia abundance suggests that seed dispersal services can be sensitive to fine‐scale variation in habitat structure. Furthermore, because Cecropia are often indicative of past disturbances, this indicates that even small‐scale habitat degradation by humans can have lasting effects by creating localized pockets of forest unfavored by frugivores.Abstract in Spanish is available with online material.

Is there an effect of storage depth on the persistence of silver birch (Betula pendula Roth) and rowan (Sorbus aucuparia L.) seeds? A seed burial experiment

Sorbus aucuparia L. (rowan) and Betula spp. (birch) are the most common of the early successional pioneer tree species in central Europe with the ability to form a soil seed bank. Little is known about the reasons for the high variations observed in the persistence in the soil of rowan and birch seeds. The objective of this study was to assess the ability of buried birch and rowan seeds to form short-term persistent soil seed banks and to analyse the influence of burial depth on seed persistence. An artificial seed burial experiment was initiated to study the persistence of birch seeds and rowan seeds, with and without pulp, stored at depths of 2, 5 and 10 cm in mineral soil over 2.5 years. The predicted maximum storability periods for buried birch seeds was 13 years, compared to 4.5 years for rowan seeds with pulp and 3.5 years without pulp. The lower storage capacity of rowan seeds was demonstrated by germinations in the darkness within soil of 3-22% of seeds without pulp and 4-48% of seeds with pulp. Germination percentages of birch and rowan with and without pulp did not differ between depths. Only burial duration had an effect for either tree species. Birch and rowan seeds are able to form short-term persistent soil seed banks. Birch accumulates a seed reserve in the soil over time, until a change in conditions conducive to germination occurs, while rowan seeds germinate promptly after overcoming seed dormancy. The pulp provides no benefits in relation to the persistence of rowan seeds; rather, it appears to act as a physical inhibitor of germination. Therefore, annual input of fresh seeds is required for the success of rowan. Seed input every few years seems sufficient to guarantee a minimum number of viable birch seeds.

Tropical Rainforest Successional Processes can Facilitate Successfully Recovery of Extremely Degraded Tropical Forest Ecosystems Following Intensive Mining Operations

Reforestation is an effective way to alleviate deforestation and its negative impacts on ecosystem services. In tropical rainforest ecosystem, however, frequent typhoons and heavy rainfall can result in landslides and uprooting of many seedlings, making reforestation efforts very difficult, especially within extremely degraded sites where soil conditions cannot support any plant life. Here, we described a reforestation protocol which is based on tropical rainforest successional processes to not only prevent landslides and tree uprooting due to frequent typhoon and heavy rain, but also accelerate tropical forest succession. This protocol first used the slope and soil layer of the undisturbed old-growth tropical rainforest as a reference to reconstruct slope and soil layers. Then multiple tropical tree species with high growth and survival rate were separately monocultured in the reconstructed soil layers. In the year of 2015 and 2016, we tested the effectiveness of this protocol to recover a 0.2 km2 extremely degraded tropical rainforest which consists of bare rock and thus does not support any plant life, in Sanya city, China. Our results showed that, both typhoons and heavy rains did not result in landslide or any tree damages in the area this reforestation protocol was used. Moreover, our separately monocultured eight fast-growing tree species have much higher fast-growing related functional traits than those for tree species in the adjacent undisturbed tropical seasonal forest, which in turn resulted in large soil water and nutrient loss within 3 years. This seemed to simulate a quick transition from primary succession (consist of bare rock and cannot support any plant life) to mid-stage of secondary tropical rainforest succession (many fast-growing pioneer tree species induced high soil water and nutrient loss). Thus, mixing the late-successional tropical tree species with each of the separately monocultured eight fast-growing tree species can accelerate recovery to the undisturbed tropical rainforest as soon as possible. Overall, based on tropical rainforest successional processes, our research provides an effective protocol for quickly and effectively restoring an extremely degraded tropical rainforest ecosystem. We expect that this work will be important for the future recovery of other extremely degraded tropical rainforest ecosystems.

Morphometrical Variation of Carob tree (Ceratoniasiliqua L) in Algeria.

Mediterranean ecosystems are subject to the influence of particular climatic conditions characterized by scarcity or irregular rainfall and long dry summer periods. These climatic restrictions generally disturb the vegetation. In order to overcome these problems. The use of pioneer tree species, adapted to climatic hazards, remains the most recommended solution. The carob tree (C.siliqua) is an agro-sylvo-pastoral species with enormous socio-economic and ecological interests. This Mediterranean tree is favourably established in semi-arid and arid areas. For the success of reforestation projects, the management and preservation of this species requires prior assessment and characterization of their variability. This approach is based on multidisciplinary studies involving the analysis of the diversity of agro-morphological, adaptive traits. In this context, the present study aims to explore, using agro-morpho-metric markers of the carob tree in central and north-western Algeria. We use the pods and leaves to identify, label or characterize the different collections or germplasm of the carob tree in the world. This study was carried out on the variability of nine morpho-metric traits related to fruits (pods) and leaves through a comparative study at the level of provenances (Larabaa, BordjBounaama, Aflou, Remchi and Ain Sefra). Carob plants from three contrasting ecotypes of Ceratoniasiliqua (Remchi ecotype from the sub-humid stage, Tissemsilt and BordjBounaama ecotype from the semi-arid stage and Ain Sefra and Aflou ecotype from the arid stage) were subjected to a thorough biometric study of the leaves and pods collected after a field survey in June-July 2013. The results showed the highest mean values for the majority of the traits studied, thus indicating the importance of the provenance factor. Based on the analyses of variance and their decomposition, and depending on the biometric traits studied, the carob resource management strategy can be chosen either for the pod factor (pod weight, pod length, number of seeds per pod and number of infested seeds per pod) or the leaf factor (petiole length and leaf area). In the case of our collections, the longest size was recorded in the Bordj Bounaama population (16.66 cm ± 2.36) and Remchi (16.10 cm ± 2.78) and the smallest in the Aflou population (9.40 cm ± 1, 27). Indeed, a positive correlation between the measured parameters (length, width, thickness and weight of the pod) was observed. Differences between ecotypes were observed for all morphological traits studied.

Morphometrical Variation of Carob tree (Ceratoniasiliqua L) in Algeria.

Mediterranean ecosystems are subject to the influence of particular climatic conditions characterized by scarcity or irregular rainfall and long dry summer periods. These climatic restrictions generally disturb the vegetation. In order to overcome these problems. The use of pioneer tree species, adapted to climatic hazards, remains the most recommended solution. The carob tree (C.siliqua) is an agro-sylvo-pastoral species with enormous socio-economic and ecological interests. This Mediterranean tree is favourably established in semi-arid and arid areas. For the success of reforestation projects, the management and preservation of this species requires prior assessment and characterization of their variability. This approach is based on multidisciplinary studies involving the analysis of the diversity of agro-morphological, adaptive traits. In this context, the present study aims to explore, using agro-morpho-metric markers of the carob tree in central and north-western Algeria. We use the pods and leaves to identify, label or characterize the different collections or germplasm of the carob tree in the world. This study was carried out on the variability of nine morpho-metric traits related to fruits (pods) and leaves through a comparative study at the level of provenances (Larabaa, BordjBounaama, Aflou, Remchi and Ain Sefra). Carob plants from three contrasting ecotypes of Ceratoniasiliqua (Remchi ecotype from the sub-humid stage, Tissemsilt and BordjBounaama ecotype from the semi-arid stage and Ain Sefra and Aflou ecotype from the arid stage) were subjected to a thorough biometric study of the leaves and pods collected after a field survey in June-July 2013. The results showed the highest mean values for the majority of the traits studied, thus indicating the importance of the provenance factor. Based on the analyses of variance and their decomposition, and depending on the biometric traits studied, the carob resource management strategy can be chosen either for the pod factor (pod weight, pod length, number of seeds per pod and number of infested seeds per pod) or the leaf factor (petiole length and leaf area). In the case of our collections, the longest size was recorded in the Bordj Bounaama population (16.66 cm ± 2.36) and Remchi (16.10 cm ± 2.78) and the smallest in the Aflou population (9.40 cm ± 1, 27). Indeed, a positive correlation between the measured parameters (length, width, thickness and weight of the pod) was observed. Differences between ecotypes were observed for all morphological traits studied.

Pinus massoniana population dynamics: Driving species diversity during the pioneer stage of ecological restoration

As a dominant and active component across ecological restoration processes, the population dynamics of pioneer tree species significantly affect species composition and community assemblage. To assess the effect of pioneer populations on species diversity, this study investigated species diversity and population characteristics in five secondary forests dominated by Pinus massoniana in southeastern China. For 40 years, all anthropogenic activities (e.g., logging, farming, etc.) have been banned on the hillsides of these five secondary forests to promote afforestation, for which these forests have thereafter been left to grow naturally. We found that: (1) the basal area (BA) of P. massoniana drove changes in species diversity across forest plots, explaining 31.6% of total variation. The species richness of the herb layer was negatively correlated to BA, while the diversity and evenness of the tree and shrub layers were both positively correlated to the BA. (2) As the size of individual P. massoniana specimens increased, the trend in species richness of the shrub layer and the diversity indexes of both the tree and shrub layer was first to increase and then to decrease once again, while the species richness of the tree layer stabilized after reaching a certain threshold. (3) Species diversity of the forest plots did not improve over time along with an increase in the density of the pioneer species. When the P. massoniana population density was low, the diversity indexes of both the tree and shrub layer increased with an increase in population density. Conversely, when the P. massoniana population density reached 2800 plants/ha, species diversity began to decline. However, when the P. massoniana population density increased to 3733 plants/ha, species diversity of the plant community exhibited an upward trend. Our results indicated that forest species diversity was extremely sensitive to P. massoniana population dynamics during the pioneer stage of ecological succession. Moreover, the pioneer population was the driving factor for both development and change in species diversity, and it did so through habitat adjustment of its ecological relationships.

Arbuscular mycorrhizal fungi improve the growth of pioneer tree species of tropical forests on savanna and tropical rainforest soils under nursery conditions

Background: Tropical rainforests and savannas are often spatially distributed at close distances. The combined effects of soil type and arbuscular mycorrhizal fungi (AMF) might contribute to explain the preference of tropical rainforest tree species for forest areas over those of savannas. However, few studies have examined such effects on pioneer tropical tree species.
 Objective: Evaluate the effects of soil type and inoculation with an AMF consortium on the growth of seedlings of pioneer tree species of tropical rainforest.
 Methods: A factorial 2 x 2 experiment was conducted to evaluate the role of soil type (rainforest or savanna) and native AMF consortium on growth (height and stem diameter) of four native pioneer tree seedling species under tree nursery conditions.
 Results and conclusions: The highest growth was detected on rainforest soils inoculated with AMF. Uninoculated plants growing on savanna soils rendered the lowest performance. AMF inoculation could be a valuable procedure in ecological restoration projects of tropical forests.

Predicting ecological impacts of invasive termites.

There are 28 invasive termite species, most belong to two families, the Kalotermitidae (esp. Cryptotermes spp.) and Rhinotermitidae (esp. Coptotermes spp.). Six invasive termite species are known to have spread into natural habitats, but little direct research has been conducted into their ecological impacts. Predictions based on indirect research (natural durability of commercial wood species) suggest fast-growing, pioneer tree species with low density wood, perhaps notably legumes, are most vulnerable to invasive termites, but even slow growing climax tree species may succumb. Cryptotermes will likely have less ecological impact, due to small colonies attacking dead branch stubs in the canopy. Coptotermes will likely have greater impact, due to large colony sizes and nesting in living trees, which they hollow out and can kill. There are no studies of invasive termites on native termites, other wood-eating insects, or predators, such as ants, showing considerable scope for future research.

The annual rhythmic differentiation of Populus davidiana growth–climate response under a warming climate in The Greater Hinggan Mountains

The stability and balance of forest ecosystems have been seriously affected by climate change. Herein, we use dendrochronological methods to investigate the radial growth and climate response of pioneer tree species in the southern margin of cold temperate coniferous forest based on Populus davidiana growing on the Greater Hinggan Mountains in northeastern China. Correlations of P. davidiana growth with temperature and precipitation in a year (October–September) were rhythmically opposed: while temperatures in previous October–June (winter and spring) and in May–September (growing season) respectively inhibited and promoted radial growth on P. davidiana (p < 0.01), precipitation in the same periods respectively promoted and inhibited of growth (p < 0.01). High temperature or less rain/snow in winter and early spring, and low temperature or excess rainfall in summer, are inconducive to P. davidiana growth and vice versa (p < 0.01). In addition, in March–April, when air temperature was above 0 °C and ground temperature below 0 °C, physiological drought caused significant growth inhibition in P. davidiana (p < 0.05). In general, temperatures play a driving and controlling role in the synergistic effect of temperature and precipitation on P. davidiana growth. Under current conditions of available water supply, changes of temperature, especially warming, are beneficial to the growth of P. davidiana in the study area. The current climate conditions promote the growth of P. davidiana, the pioneer species, compared with the growth inhibition of Larix gmelinii, the dominant species. Thus, the structure and function of boreal forest might be changed under global warming by irreversible alterations in the growth and composition of coniferous and broadleaf tree species in the forest.

Impact of Robinia pseudoacacia stand conversion on soil properties and bacterial community composition in Mount Tai, China

BackgroundRobinia pseudoacacia is a widely planted pioneer tree species in reforestations on barren mountains in northern China. Because of its nitrogen-fixing ability, it can play a positive role in soil and forest restoration. After clear-cutting of planted stands, R. pseudoacacia stands become coppice plantations. The impacts of shifting from seedling to coppice stands on soil bacterial community and soil properties have not been well described. This study aims to quantify how soil properties and bacterial community composition vary between planted seedling versus coppice stands.MethodsNine 20 m × 20 m plots were randomly selected in seedling and coppice stands. The bulk soil and rhizosphere soil were sampled in summer 2017. Bulk soil was sampled at 10 cm from the soil surface using a soil auger. Rhizosphere soil samples were collected using a brush. The soil samples were transported to the laboratory for chemical analysis, and bacterial community composition and diversity was obtained through DNA extraction, 16S rRNA gene amplification and high-throughput sequencing.ResultsThe results showed that, compared to seedling plantations, soil quality decreased significantly in coppice stands, but without affecting soil exchangeable Mg2+ and K+. Total carbon (C) and nitrogen (N) were lower in the rhizosphere than in bulk soil, whereas nutrient availability showed an opposite trend. The conversion from seedling to coppice plantations was also related to significant differences in soil bacterial community structure and to the reduction of soil bacterial α-diversity. Principal component analysis (PCA) showed that bacterial community composition was similar in both bulk and rhizosphere soils in second-generation coppice plantations. Specially, the conversion from seedling to coppice stands increased the relative abundance of Proteobacteria and Rhizobium, but reduced that of Actinobacteria, which may result in a decline of soil nutrient availability. Mantel tests revealed that C, N, soil organic matter (SOM), nitrate nitrogen (NO3−-N) and available phosphorus positively correlated with bacterial community composition, while a variation partition analysis (VPA) showed that NO3−-N explained a relatively greater proportion of bacterial distribution (15.12%), compared with C and SOM. Surprisingly, N showed no relationship with bacterial community composition, which may be related to nitrogen transportation.ConclusionsThe conversion from seedling to coppice stands reduced soil quality and led to spatial-temporal homogenization of the soil bacterial community structure in both the rhizosphere and bulk soils. Such imbalance in microbial structure can accelerate the decline of R. pseudoacacia. This may affect the role of R. pseudoacacia coppice stands in soil and forest restoration of barren lands in mountain areas.

Effects of sewage sludge and other wastes application on the growth and element uptake of Jatropha curcas in abandoned rare-earth mine soil.

The wastes such as sewage sludge (SS) can be used to amend soil of abandoned rare-earth mine land (ARL). The energy plant Jatropha curcas could be used as a pioneer tree species in the ARL. In a pot experiment to address the responses of growth and element uptake of J. curcas, three treatments were established: adding SS to the soil of ARL (T1), adding SS and bagasse to the soil of ARL (T2), adding SS, bagasse and passivator to the soil of ARL (T3), with the untreated soil of the ARL as the control (CK). The results showed that compared with CK, T1 only significantly increased the plant height of J. curcas, T2 and T3 significantly increased the plant height, ground diameter and dry biomass of J. curcas, of which the total dry biomass increased by more than 184.7%. All the three treatments significantly increased the contents of N, P, K and Cu in J. curcas. T1 and T2 significantly increased the proportion of exchangeable Zn, Cd and Ni in the substrates, while T3 showed the opposite effects. T3 significantly decreased the migration factor (M) and mobility factor (MF) of Zn, Cd, Ni in the substrates, and significantly reduced the contents of Zn, Pb, Cd, Ni in J. curcas, with an inhibition rate of over 36.1%. The comprehensive evaluation of the membership function showed that the order of growth promotion effects on J. curcas was T2>T3>T1>CK, while the order of capacity of inhibiting J. curcas to accumulate Cu, Zn, Pb, Cd, Ni was T3>CK>T2>T1. The combined application of SS and bagasse significantly promoted the growth and element accumulation of J. curcas, and the addition of passivator significantly reduced heavy metals uptake without affecting the growth of J. curcas.

The influence of microsite conditions on early performance of planted Nothofagus nitida seedlings when restoring degraded coastal temperate rain forests

Widespread impacts of changes in land use, climate, and disturbance regimes continue to affect mature forests and their subsequent post-disturbance recovery. In South American temperate rainforests, the recovery of the original composition, structure, and ecological services of now-degraded old-growth forests is additionally hampered by the aggressive competition that the native Chusquea bamboo understory exerts on juvenile trees, thus arresting ecological succession. In this study, we aim to evaluate the early performance of Nothofagus nitida seedlings (pioneer tree species that tolerate shade) planted beneath nurse canopy following removal of the understory, and to define which microsite conditions can facilitate N. nitida growth. For this, we monitored 45 N. nitida plantings established in 2014 in Chiloé Island (North Patagonia, Chile) for five years. After this period, planted seedlings presented relatively good indicators of performance with low mortality (~30% of dead seedlings), good vitality (~60% of healthy seedlings), and relatively high mean periodic annual increments in root collar diameter and height (~1.7 mm/year and ~17.4 cm/year, respectively). Furthermore, our results show that the planted N. nitida seedlings can tolerate and grow under low-light conditions, though their diameter and height increase significantly with higher light availability. However, physiological stress of planted seedlings increased in open areas with more available light and planted seedlings were most stressed during the summer season. Increased summer-season stress was attributed to the months with highest depth of the water table, highest maximum and mean photosynthetic active radiation (PAR) values, highest temperature, and lowest precipitation. Our results show for first time with field-based data that different microsite and canopy conditions facilitate the initial performance of N. nitida plantings after removal of the Chusquea bamboo understory. In this context, we conclude that the removal of the Chusquea bamboo understory is the key to overcome arrested succession of coastal temperate rain forests Furthermore, supplementary planting of pioneer tree species that tolerate shade, like N. nitida, assists natural forest recovery, especially in humid and open sites with some protection of a nurse canopy.

Rodent suppression of seedling establishment in tropical pasture.

Grasses are recognized as a critical regeneration barrier in tropical pastures, yet the effects of rodents and rodent-grass interactions are not well understood. As selective foragers, rodents could shape tree communities, moderating biodiversity in regenerating tropical landscapes. We utilized a fully crossed two-way factorial design to examine the effect that grasses, rodents, and their interaction had on tree seedling establishment in pasture habitat. We followed two separate tree cohorts for 1year each within the experimental framework. Multiple cohorts were used to better represent successional tree species variation and responses. Trees species were characterized by a gradient of seed masses and as pioneer or persistent successional type. Both cohort seedlings were altered when rodents were present compared to control treatments. In Cohort 1, rodents adversely affected seedlings of persistent tree species only in the absence of grass. In Cohort 2, seedlings of persistent tree species were decimated by rodents in the absence or presence of grass. In both cohorts, seedlings of persistent species established better in grass treatments, while seedlings of pioneer tree species were strongly suppressed. Tree species seed mass positively correlated with seedling establishment across all treatments except no grass-rodent treatments. Strong suppression of tree seedlings by rodents (Sigmodon toltecus) is a novel result in tropical land recently released from agriculture. One implication is that selective foraging by rodents on large-seeded persistent tree species may be facilitated by the removal of grass. Another implication is that temporary rodent control in pastures may permit higher establishment of deep-forest persistent species.

Can variation in seed removal patterns of Neotropical pioneer tree species be explained by local ant community composition?

AbstractMany plants depend on animals for seed dispersal, and ants commonly fill this role. We examined whether heterogeneity in ant community composition among sites, between above‐ and belowground foraging guilds, or between seasons predicts observed variation in seed removal rates for 12 nonmyrmecochorous Neotropical pioneer tree species on Barro Colorado Island, Panama. We also investigated whether ants associated with removing seeds differed in specific morphological characters from the larger ant community. We observed ant–seed interactions at caches to determine which ants removed seeds of 12 tree species. We also sampled ant community composition by placing 315 pitfall traps and 160 subterranean traps across the five sites where seed removal rates were quantified. Aboveground ant community composition varied by site but not season. Among‐site variation in ant composition did not predict seed removal patterns at these same sites. Belowground ant communities differed from aboveground ant communities but were not structured by either site or seed cache type. Finally, ants that removed seeds did not differ morphologically from the broader ant community. Overall, our results suggest ant communities vary over relatively small spatial scales but exhibit a high degree of functional redundancy in terms of seed removal services provided for Neotropical pioneer tree species.Abstract in Spanish is available with online material.