Adult Tree Species Research Articles

Positive interactions in shaping neighborhood diversity during secondary forests recovery: Revisiting the classical paradigm

Secondary forests recovery, following disturbances, plays a pivotal role in ecosystem dynamics and biodiversity recovery. Given the rising frequency and intensity of anthropogenic disturbances within forest ecosystems, understanding the mechanisms underlying secondary succession is vital for the effective restoration and conservation of compromised ecosystems. In the classical secondary succession paradigm, early-arriving species are gradually replaced by their later-arriving counterparts. However, over time, valuable historical insights into the involvement of pioneer species become obscured and challenging to discern, particularly in community-scale studies. Consequently, this obscurity has predominantly directed contemporary research predominantly towards examining the consequences of species replacement by later-arriving counterparts during secondary succession. Concurrently, the mechanisms by which pioneer species facilitate or impede the establishment of diversity among later-arriving species remain insufficiently clarified. In this study, we established a 6-ha dynamic forest plot within a secondary forest that has undergone nearly four decades of restoration. Specifically, we utilized the individual species-area relationship (ISAR) framework to evaluate the neighborhood diversity structure of 49 evergreen and 20 deciduous species identified within our evergreen broad-leaved forest plot. Our findings indicate that deciduous tree species undergo a transition from diversity accumulator to repeller in diversity structuring as they progress through different life history stages. On the other hand, evergreen trees either engage in diversity accumulator or neutral. Through repeated plot surveys, we established a comprehensive dataset encompassing the mortality and regeneration of evergreen and deciduous tree species from 2014 to 2020. Spatial covariance models were employed to quantify the distinct effects of density dependence on deciduous and evergreen tree species. The results demonstrate significant negative density dependence mortality and self-thinning in deciduous species at all life history stages. Conversely, adult evergreen tree species facilitate the survival of their seedlings and saplings. In contrast to the classical paradigm that primarily focuses on the replacement of pioneer species by successor species, our findings reveal: (i) self-inhibition mechanisms that shape the neighborhood diversity spatial patterns among deciduous tree species, (ii) self-promotion or neutral mechanisms that influence the diversity spatial patterns of evergreen tree species, and (iii) early-arriving tree species that play a role in facilitating the establishment and diversity of late-arriving counterparts. These results not only signify the significant role of late-arriving species in the natural recovery of secondary forests but also propose that integrating the mechanisms of facilitation, inhibition, and neutral interactions into the classic forest succession paradigm could reshape our interpretation of interactions within plant communities across historical, current, and future timeframes. Such comprehension holds implications for forest management policies and conservation practices.

Biodiversity consequences of long-term active forest restoration in selectively-logged tropical rainforests

Forest restoration figures prominently on climate action plans, both in the public and private sector. Restoration has the potential to enhance forest recovery and carbon storage, yet could cause unanticipated alterations of forest biodiversity and functioning. In particular little is known about the long-lasting effects of active forest restoration. We therefore evaluated the effects of such management on adult trees and seedlings of actively restored forest to comparable areas where forest regenerated naturally. We investigated a forest site in Sabah, Malaysian Borneo that is recovering from selective logging between 1981 and 1991. Some of the area has been left to naturally regenerate, and some areas have been actively restored for production purposes between 1994 and 2004 through climber cutting and enrichment-planting of exclusively indigenous tree species. We hypothesized that active forest restoration affects forest diversity and composition negatively (i.e., reduction in diversity and presence of pioneer species), and that the silvicultural interventions had long-lasting effects (i.e., higher density of species that were planted, fewer climbers).Surprisingly, our findings suggest that active forest restoration promoted the recovery of adult tree species diversity, expressed as Shannon Diversity Index, and in particular promoted rare species. In actively restored plots, the number of adult individuals of tree species that were planted was enhanced, and the density of liana seedlings was reduced, demonstrating that these silvicultural interventions were effective and had long-lasting effects on the forest structure. Nevertheless, we could not detect differences in the number of seedlings of species that were planted nor in the density of adult lianas between actively restored and naturally regenerating forest sites. We also did not find differences in the species diversity of seedlings, but we observed a compositional shift in the species community for seedlings that were younger than one year. Furthermore, we did not detect a difference between actively restored and naturally regenerating forest plots in the abundance of the present tree guilds (i.e., pioneer or late-succession species) for neither adult trees nor seedlings, as all of our forest plots were dominated by late-succession species.Our results show that active forest restoration can promote species diversity and highlight that active forest restoration focusing on biomass production does not need to adversely affect biodiversity. This work emphasizes the potential of active forest restoration on biodiversity and potentially other key ecosystem functions which are needed to be restored in order to mitigate climate change and the current ecological crisis.

Functional trade-offs are driven by coordinated changes among cell types in the wood of angiosperm trees from different climates.

Wood performs several functions to ensure tree survival and carbon allocation to a finite stem volume leads to trade-offs among cell types. It is not known to what extent these trade-offs modify functional trade-offs and if they are consistent across climates and evolutionary lineages. Twelve wood traits were measured in stems and coarse roots across 60 adult angiosperm tree species from temperate, Mediterranean and tropical climates. Regardless of climate, clear trade-offs occurred among cellular fractions, but did not translate into specific functional trade-offs. Wood density was negatively related to hydraulic conductivity (Kth ) in stems and roots, but was not linked to nonstructural carbohydrates (NSC), implying a functional trade-off between mechanical integrity and transport but not with storage. NSC storage capacity was positively associated with Kth in stems and negatively in roots, reflecting a potential role for NSC in the maintenance of hydraulic integrity in stems but not in roots. Results of phylogenetic analyses suggest that evolutionary histories cannot explain covariations among traits. Trade-offs occur among cellular fractions, without necessarily modifying trade-offs in function. However, functional trade-offs are driven by coordinated changes among xylem cell types depending on the dominant role of each cell type in stems and roots.

Adaptation and mitigation capacity of wildland forests in the northeastern United States

Managing forests to mitigate climate change and increase their capacity to adapt to future climate-related disturbances and conditions typically involves protecting and enhancing forest carbon stocks and sequestration capacity while promoting structural diversity. While the focus has been on comparing active management approaches for meeting these objectives, there are few empirical assessments of passive management. Here we used quasi-experimental methods to compare carbon and structural complexity within “wildlands,” where harvesting and other land uses are prohibited, to environmentally comparable forests without protection from timber harvesting. Using USDA Forest Inventory and Analysis (FIA) plots from the Adirondack-New England region of the Northeastern U.S., we compared aboveground carbon, total forest basal area increment (our proxy for carbon sequestration), and six forest-level structural variables in forests. To help explain observed differences, we examined (1) the recent history of harvesting within unprotected forests, (2) stand age in wildland and unprotected forests, and (3) the carbon and structural attributes of protected and unprotected plots at the initiation of wildlands protection. Aboveground carbon was 20% higher in wildlands overall (P < 0.0001), with differences greatest in wildlands of New York (+32%; P = 0.0001) and in Maine (+34%; P = 0.01) where recent harvesting intensity and differences in stand age between protection categories were highest. Basal area increment did not differ between protected areas at the regional and sub-regional scale, but was 37% higher in wildlands (P = 0.03) than in recently harvested areas. Structural complexity was generally higher in wildlands, with four structural variables – large live (>60 cm DBH) and large dead (>45 cm DBH) tree density, maximum tree height, and diversity of diameter size classes) – greater in wildlands than in unprotected forests. Two variables (adult tree species richness and standard deviation of tree height) did not differ between protection categories. Both carbon and structural differences were amplified by recent harvesting in unprotected plots. For the subset of plots that allowed for comparison, wildlands did not differ in carbon and structural attributes from unprotected plots at the onset of wildlands protection, suggesting that subsequent management rather than initial differences was the driver of carbon and structural differences between protection categories. Our results highlight the adaptation and mitigation benefits of allowing natural processes to predominate in strictly protected areas.

Açaí palm management disturbs seed rain and soil seed bank of an Amazonian estuarine forest

AbstractThe exploitation of non‐timber forest products has been proposed as a sustainable way to exploit tropical forests, but such an opportunity remains to be proved. Here, we examine the impact of intensive açaí palm (Euterpe oleracea) management on the seed rain and soil seed bank in an estuarine forest landscape with a long history of forest management by locals in the Amazon region. Seed rain (100 80 cm2 collectors) and soil seed bank (100 30 cm2 samples) were monitored through a year across 20 forest stands, covering a gradient of açaí stem density (50–3575 açaí stems per ha). Seed rain and bank were dominated by açaí seeds (85.5%–85.8%) and by excluding them, seed rain and bank were low density and species poor, capturing a tiny subset from the local (17.91%–19.40%) and landscape woody flora (11.82%–14.55%). Moreover, autochthonous and vertebrated‐dispersed predominated as well as those from tree species considered useful by locals. Overall, açaí stem density positively affected açaí seed abundance in the seed rain and negatively affected seed pools in the bank in relation to abundance of seeds and vertebrated dispersed, while adult tree species richness and density and accessibility to forest stands were associated with more diversified seed pools. Thereby, forest stands are exposed to different levels of açaí management (high vs. low intensity) supported taxonomically distinct seed pools. Our results suggest that açaí intensification disturbs seed rain and soil seed bank with potential impacts on forest regeneration and the forest integrity standards required to consider açaí fruit production as sustainable according to current legislation.

Natural plant revegetation on three reclaimed gold mined sites in South Western Ghana

Mining companies in Ghana have been encouraged by law and policy to reclaim degraded mined sites using native tree species. The study assessed stand structure, compositional dynamics, conservation and economic value of restored species after 20 years of reclamation. Eighty seedlings each of Amphimas ptericarpoides and Macaranga barteri were planted on the first reclaimed site (stand I); 160 seedlings each of Macaranga barteri and Amphimas ptericarpoides on the second (stand II) and third (stand III) reclaimed sites respectively. Each reclaimed site (1000 m 2 ) was inventoried and sampled using 400 quadrats (25 m × 25 m). In all, 123 ‘restored‘ species in 55 families (stand I), 103 species in 52 families (stand II) and 96 species in 49 families (stand III) were identified. Species composition of the reclaimed sites were moderately similar to the old - growth forest remnant. Pioneer species, zoophilous and zoochorous species were dominant in all the reclaimed sites. One hundred and twenty- four adult (DBH > 5 cm) tree species (stand I), 105 (stand II) and 128 (stand III) were obtained. The tree stand structure of the Amphimas reclaimed site had the highest basal area of 13.75 m 2 /ha and most of the adult tree species in all the reclaimed sites were in the lower diameter class (5 cm ≥ DBH < 20 cm). The Genetic Heat Index and Economic Index of trees – only were significantly (p < 0.05) higher in the Amphimas - Macaranga site. The mixed tree species of the Amphimas - Macaranga reclaimed site seem to perform better as almost all measured parameters were dominant on this site. The two tree species used have high potential for restoration of native species. Later studies will further establish the suitability of the two native tree species for reclamation in the study area. • Mined sites were reclaimed with Amphimas pteridocarpus and Macaranga bateri species. • Restored species in the mixed- tree site had higher conservation and economic values. • The tree stand -structure of the A. pteridocarpus site had the highest basal area. • The two tree species used have the potential for restoration of native species.

Anthropogenic interventions regulate forest structure and carbon stock in transitional dry forests of Similipal Biosphere Reserve, India

ABSTRACT Tropical dry forests play an important role in the storing of significant amounts of biomass and carbon. However, carbon storage in these forests is linked to biotic, edaphic and climatic factors as well as human interventions. The forest structure and carbon storage in relation to human interventions and soil properties were studied in tropical dry forest patches located in a transition region of the Similipal Biosphere Reserve, India. Random sampling of vegetation and soil was done in 30 plots of 50 × 20 m in size. A total of 41 adult tree species, 50 juvenile tree species and 28 climber species were recorded within the study area. The average carbon stock of the forest was 179.54 ± 9.56 Mg ha−1, of which adult trees were the highest contributors (55%) followed by soil organic carbon (36%), woody climbers (6%) and juvenile trees (3%). There was a significant effect of lopping, cutting of trees and soil properties on forest structure and carbon stock. This study confirms that anthropogenic disturbances and edaphic factors play a significant role in the variation of carbon stocks of biomass and soils in the forest.

Urban tree carbon density and CO2 equivalent of National Zoological Park, Delhi.

In a highly urbanized city like Delhi, the urban forest plays a vital role in climate change mitigation by capturing and storing carbon dioxide (CO2) from the atmosphere. Urban vegetation helps in increasing carbon sink and CO2 equivalent (CO2eq) and also provides other aesthetic and psychological environmental benefits. To understand how urban trees are vital for carbon sink, the present study aimed to quantify the carbon density and CO2eq in trees at National Zoological Park (NZP), New Delhi, a tropical semi-arid region of India. For this, we estimated tree biomass or dry matter content of 25 species with the help of allometric equations which are available in published literature and applicable for the tropical region. It was observed that the highest diameter at breast height (DBH) was contributed by Ficus sp. while the maximum density among adult tree species found in Albizia procera. The total mean dry matter content, C density, and CO2eq of NZP were 92.10Mgha-1, 43.61Mg-C ha-1, and 168.83Mgha-1, respectively. The highest biomass, C density, and CO2eq obtained in the species of Ficus benghalensis followed by Ficus racemosa and Azadirachta indica. The data indicates that the trees having the capacity to store carbon are essential for the maintenance of a sustainable environment. Thus, the study suggests that there is a substantial scope to increase the carbon density and CO2eq in urban city through adopting various management strategies viz. afforestation and reforestation program on degraded and abandoned land to maintain a clean and sustainable environment.

CAN ARAUCARIA FOREST REMNANTS REGENERATE AFTER 70 YEARS OF ANIMAL HUSBANDRY? A CASE STUDY ON CAÍVAS IN SOUTHERN BRAZIL

In Southern Brazil, forest fragments are commonly used for agroforestry systems (AFS) - called caívas - focused on erva-mate and livestock production. Although the caívas have helped maintain forest cover, there is a general lack of understanding of the effects of this system on species diversity and their potential for ecological restoration. Aiming to contribute to a better understanding of the forest dynamics (trees and regeneration) of these AFS, we present a six-year case study in which we monitored a caíva that has been used for animal husbandry for 70 years. We observe that forest management in the caíva modified the population structure mostly through reductions in the density of a few adult tree species. On the other hand, the potential regeneration shows consistent growth, including several species not found in the adult population. The caíva showed high levels of resilience in terms of regeneration, despite the extractive use of these remnants over several decades. This result demonstrates that the strategies used herein can help to restore forests with a dense and diverse forest cover within caívas. With the correct management of this regeneration potential, it is possible to maintain healthy and diverse forests that are being conserved through use.

Spatial distribution and interspecific associations in a deciduous broad‐leaved forest in north‐central China

AbstractQuestionsWhat are the primary types of intraspecific distribution patterns and interspecific associations of tree species in the temperate–subtropical transition region? Can potential ecological mechanisms such as habitat heterogeneity, dispersal limitation, density dependence, spatial segregation, and competition between species regulate these patterns?LocationThe Qinling Mountains, north‐central China.MethodsRipley's K‐function, D‐function and pair correlation function were applied to assess the spatial distribution of 15 dominant tree species in a fully mapped 25‐ha plot. Complete spatial randomness (CSR), heterogeneous Poisson (HP) and random‐labelling (RL) null models were used to reveal the potential process of community construction.Results(a) Thirteen of 15 adult tree species displayed an aggregation distribution at various scales. (b) Eleven adult species (73.3%) showed significant aggregation, especially at small distances, after removing the effect of habitat. (c) The percentage of species showing additional aggregation relative to adults decreased from saplings to juveniles. The maximum strength of density dependence was negative with species abundance. (d) Only 29 (13.8%) of the species pairs showed significant small‐scale interactions. Most of the significant small‐scale associations did not occur in abundant species pairs. (e) Negative interactions of interspecific associations were more prevalent than positive ones, yet there was no consistency of the characteristics among species pairs.ConclusionsHabitat heterogeneity and dispersal limitation likely contribute to the spatial pattern of tree species at different life stages. Density dependence remains the important factor in maintaining species diversity in this forest stand. Moreover, spatial segregation generates the interspecific spatial patterns of segregation and partial overlap. Unexpectedly, the species herd protection hypothesis and the low‐frequency hypothesis cannot well explain the mechanism of interspecific interaction at small distances. Resource competition might be responsible for negative associations being more frequent among species pairs.

Influencia del método de árboles padres en la diversidad de la regeneración de bosques mixtos de Durango, México

Introduction:Forest managers need to know the impact of regeneration cuts on tree species diversity in order to conserve it. Objective:To evaluate changes in tree species richness and diversity after applying the seed tree method in six communities. Materials and methods: The communities of Cienega Grande, Las Cienegas, La Colmena, El Venado, Los Bajios and Pino Gordo of the Pueblo Nuevo ejido, Durango, were divided into three plots called: a) regeneration in seed trees cuttings (RST); b) regeneration in adult trees (RAT); and c) adult trees (AT). Starting from the center of each RST plot, and following the cardinal and subcardinal points, eight sites of 25 m2 and 0.1 ha were located to record the regeneration and adult tree species, respectively. Species richness indicators (Shannon-Wiener, Simpson, Pielou and Sorensen) were estimated to characterize the plots by community and were compared with t-tests and rarefaction analysis. Results and Discussion. Twelve species were recorded in the study area, of which 11 are found as a renewal of seed trees. Species richness in the RST plots with respect to that of AT was equal in the Cienega Grande, El Venado and La Colmena communities, and higher in Las Cienegas and Los Bajios. The Shannon-Wiener and Simpson indices were higher in Pino Gordo, Los Bajios and El Venado. The Sorensen index ranges from 0.67 to 1.0, indicating high species similarity among plots. Conclusions. The seed tree method in a mixed forest ensures the continuity of tree species diversity.

Post-fire forest regeneration shows limited climate tracking and potential for drought-induced type conversion.

Disturbance such as wildfire may create opportunities for plant communities to reorganize in response to climate change. The interaction between climate change and disturbance may be particularly important in forests, where many of the foundational plant species (trees) are long-lived and where poor initial tree establishment can result in conversion to shrub- or graminoid-dominated systems. The response of post-disturbance vegetation establishment to post-disturbance weather conditions, particularly to extreme weather, could therefore provide useful information about how forest communities will respond to climate change. We examined the effect of post-fire weather conditions on post-fire tree, shrub, and graminoid recruitment in fire-adapted forests in northern California, USA, by surveying regenerating vegetation in severely burned areas 4-5yr after 14 different wildfires that burned between 2004 and 2012. This time period (2004-2016) encompassed a wide range of post-fire weather conditions, including a period of extreme drought. For the most common tree species, we observed little evidence of disturbance-mediated community reorganization or range shifts but instead either (1) low sensitivity of recruitment to post-fire weather or (2) weak but widespread decreases in recruitment under unusually dry post-fire conditions, depending on the species. The occurrence of a single strong drought year following fire was more important than a series of moderately dry years in explaining tree recruitment declines. Overall, however, post-fire tree recruitment patterns were explained more strongly by long-term climate and topography and local adult tree species abundance than by post-fire weather conditions. This observation suggests that surviving adult trees can contribute to a "biological inertia" that restricts the extent to which tree community composition will track changes in climate through post-disturbance recruitment. In contrast to our observations in trees, we observed substantial increases in shrub and graminoid establishment under post-fire drought, suggesting that shifts in dominance between functional groups may become more likely in a future with more frequent and intense drought.

Distribution, Abundance and Population Status of Four Indigenous Threatened Tree Species in the Arba Minch Natural Forest, Southern Ethiopia

The study on distribution, abundance and population structure of four indigenous threatened tree species in the Arba Minch natural forest, southern Ethiopia. The objective of this study was to assess the use of this species by local communities and its current population structure and status in its natural habitat in southern Ethiopia where it is poorly known. The study approach was categorized in to three; market survey, informant interview and species population inventory in the surrounding natural habitat. Market survey was mainly focused on market observation to estimate the amount of fruits, charcoal, timber, firewood and pole sold in the market. Informant interview was focused on the uses of the species and its availability in the surrounding forest fragments. The adult tree species abundance and regeneration status in the existing forest was estimated. The result indicates that the species are used source of food, charcoal production, timber production, house constriction, fuel- wood and farm implement. Local communities supplement their livelihood by selling wild collected ripe fruit, charcoal, timber, fuel-wood of these species for income. These species are locally very useful plant that needs attention for future research that benefits communities. Current over harvesting of mature tree influenced the regeneration of the species. If this unsustainable harvesting by local people continues, the capacity of the species to maintain its wild population is significantly reduced. Therefore, management and conservation strategies that incorporate this factor is required.

Do Eugenia hiemalis seedling leaves under different light conditions develop phenotypic plasticity?

Leaf light responses, especially structural aspects, are well studied in adult tropical tree species. However, there is still a gap in the knowledge of these plastic responses on first developed leaves, which may be important to seedling survival in variable environments. An experimental approach was used to test the hypothesis that phenotypic plasticity is expressed in first leaves in response to different light intensities. This study was conducted in the Upper Parana River floodplain, near Porto Rico city (22°55′S, 53°10′W), Southeast Brazil. We quantified the responses of 40 morphological and anatomical traits in first leaves of Eugenia hiemalis Cambess. (Myrtaceae), a riparian shrub that occurs in deep shade and full sun exposure. Seedlings were grown under four treatments: 100, 50, 30, and 0.3 % of full sunlight. Lamina and petiole size was larger in leaves exposed to 0.3 % of full sunlight than in full sun leaves, which have greater leaf thickness, palisade parenchyma, stomatal density, xylem area, and vascular density. Intermediate values were found in 50 and 30 % of full sunlight. The morphological and anatomical variability of E. hiemalis first leaves results from plasticity onset and is regarded as an advantage to seedlings exposed to different light conditions.

Nutrient resorption efficiency and proficiency in economic wood trees irrigated by treated wastewater in desert planted forests

Little is known about the impacts of recycled wastewater irrigation on adult tree species, especially the nutrient resorption efficiency (RE) and proficiency (RP) during leaf senescence and whether trace metals are resorbed or not during this process. Here, we present a study on the concentrations of nutrients and trace metals in green and senesced leaves, collected from Eucalyptus camaldulensis and Casuarina spp., in four planted forests irrigated by wastewater (or groundwater as control). Stoichiometric ratios (C:N, C:P, and N:P), RE and RP from senesced leaves of the trees were investigated. The concentrations of trace metals showed normal levels and were below phytotoxic concentrations in green and senesced leaves except for Mn. The intra-specific variations in nutrient concentrations in senesced leaves showed larger differences among the sites than those found in green leaves. The studied tree species excluded excess elements by decreasing its proficiency. The RE for N and P was high under poor soil nutrient conditions, but very low under high availability of nutrients. Resorption of trace metals from senesced leaves was low and presented negative mean values for most metals at all sites. RP values were low or equal to zero for the estimated elements. C:N and C:P ratios were high at low nutrient availability i.e. control site, while N:P ratios were non-significant among sites in green or senesced leaves. Our results illustrate that forest trees have highly variable nutrient resorption capacities that vary under high nutrients availability and indicate that under continuous wastewater irrigation, low or negative resorption efficiency for trace metals and other nutrients is an efficient protective strategy.

Effects of competition and facilitation on species assemblage in two types of tropical cloud forest.

Competition and facilitation between tree individuals are two kinds of non-random processes influencing the structure and functioning of forest communities, but how these two plant-plant interactions change along gradient of resources or environments remains very much a matter of debate. We developed a null model to test the size-distance regression, and assessed the effects of competition and facilitation (including interspecific interactions, intraspecific interactions and overall species interactions) on each adult tree species assemblage [diameter at breast height (dbh) ≥5 cm] across two types of tropical cloud forest with different environmental and resource regimes. The null model test revealed that 17% to 27% tree species had positive dbh-distance correlations while 11% to 19% tree species showed negative dbh-distance correlations within these two forest types, indicating that both competition and facilitation processes existed during the community assembly. The importance of competition for heterospecific species, and the intensity of competition for both heterospecific and overall species increased from high to low resources for all the shared species spanning the two forests. The importance of facilitation for conspecific and overall species, as well as that the intensity of facilitation for both heterospecific and conspecific species increased with increasing low air temperature stress for all the shared species spanning the two forests. Our results show that both competition and facilitation processes simultaneously affect parts of species assemblage in the tropical cloud forests. Moreover, the fact that nearly 50% species assemblage is not detected with our approaches suggest that tree species in these tropical forest systems are assembled with multiple ecological processes, and that there is a need to explore the processes other than the two biotic interactions in further researches.

Secondary forests of central Panama increase in similarity to old‐growth forest over time in shade tolerance but not species composition

AbstractQuestionDoes species and functional composition of secondary tropical forests more closely follow a deterministic or a stochastic model of succession?LocationThe Barro Colorado Nature Monument (BCNM), central Panama. The BCNM comprises Barro Colorado Island (BCI) and five adjacent mainland peninsulas and is a mosaic of tropical old‐growth (OG) and secondary forests (SF).MethodsWe studied the species and functional composition of seedling, sapling and adult tree communities in a chronosequence of SF stands ranging in age from 20 to 100 yrs since abandonment, as well as two OG stands for comparison. Functional composition was defined as the representation of species with different degrees of shade tolerance. We also examined patterns of species diversity and dominance to better understand processes driving compositional changes.ResultsSpecies diversity recovered rapidly, and, by 20 yrs, species richness for all size classes was equivalent if not higher in SF compared to OG. Species diversity tended to be lower and species dominance higher for seedlings than saplings or adults. Seedling, sapling and adult tree species composition did not clearly increase in similarity to OG with forest age. Instead, differences in species composition among stands reflected variation in dominance by particular species. Light‐demanding species became less common and shade‐tolerant species more common over stand age, with the functional composition of older secondary forests converging on that of OG. The seedling and sapling communities across the chronosequence were composed of a shade‐tolerant subset of those species found in the stands as adults.ConclusionOur results suggest that recruitment into the seedling community of SF is determined by both predictable (e.g. selection for shade‐tolerant species) and unpredictable factors (e.g. species‐specific reproduction events and dispersal limitation). Recruitment into the sapling and tree communities reflects stronger, and potentially compounded, selection for shade‐tolerant species. Therefore, changes in the species composition of regenerating forests in this area appear to be unpredictable, even though the functional composition follows a more deterministic and predictable trajectory with convergence on OG over time.

Root anoxia effects on physiology and emissions of volatile organic compounds (VOC) under short-and long-term inundation of trees from Amazonian floodplains

Volatile organic compound (VOC) emissions are affected by a variety of biotic and abiotic factors such as light intensity, temperature, CO2 and drought. Another stress factor, usually overlooked but very important for the Amazon region, is flooding. We studied the exchange of VOCs in relation to CO2 exchange and transpiration of 8 common tree species from the Amazonian floodplain forest grown up from seeds using a dynamic enclosure system. Analysis of volatile organics was performed by PTR-MS fast online measurements. Our study confirmed emissions of ethanol and acetaldehyde at the beginning of root anoxia after inundation, especially in less anoxia adapted species such as Vatairea guianensis, but not for Hevea spruceana probably due to a better adapted metabolism. In contrast to short-term inundation, long-term flooding of the root system did not result in any emission of ethanol or/and acetaldehyde. Emission of other VOCs, such as isoprenoids, acetone, and methanol exhibited distinct behavior related to the origin (igapó or várzea type of floodplain) of the tree species. Also physiological activities exhibited different response patterns for trees from igapó or várzea. In general, isoprenoid emissions increased within the course of some days of short-term flooding. After a long period of waterlogging, VOC emissions decreased considerably, along with photosynthesis, transpiration and stomatal conductance. However, even under long-term testing conditions, two tree species did not show any significant decrease or increase in photosynthesis. In order to understand ecophysiological advantages of the different responses we need field investigations with adult tree species.

Ectomycorrhizal symbiosis of tropical African trees

The diversity, ecology and function of ectomycorrhizal (EM) fungi and ectomycorrhizas (ECMs) on tropical African tree species are reviewed here. While ECMs are the most frequent mycorrhizal type in temperate and boreal forests, they concern an economically and ecologically important minority of plants in African tropical forests. In these African tropical forests, ECMs are found mainly on caesalpionioid legumes, Sarcolaenaceae, Dipterocarpaceae, Asterpeiaceae, Phyllantaceae, Sapotaceae, Papilionoideae, Gnetaceae and Proteaceae, and distributed in open, gallery and rainforests of the Guineo-Congolian basin, Zambezian Miombo woodlands of East and South-Central Africa and Sudanian savannah woodlands of the sub-sahara. Overall, EM status was confirmed in 93 (26%) among 354 tree species belonging to EM genera. In addition, 195 fungal taxa were identified using morphological descriptions and sequencing of the ML5/ML6 fragment of sporocarps and ECMs from West Africa. Analyses of the belowground EM fungal communities mostly based on fungal internal transcribed spacer sequences of ECMs from Continental Africa, Madagascar and the Seychelles also revealed more than 350 putative species of EM fungi belonging mainly to 18 phylogenetic lineages. As in temperate forests, the /russula-lactarius and /tomentella-thelephora lineages dominated EM fungal flora in tropical Africa. A low level of host preference and dominance of multi-host fungal taxa on different African adult tree species and their seedlings were revealed, suggesting a potential for the formation of common ectomycorrhizal networks. Moreover, the EM inoculum potential in terms of types and density of propagules (spores, sclerotia, EM root fragments and fragments of mycelia strands) in the soil allowed opportunistic root colonisation as well as long-term survival in the soil during the dry season. These are important characteristics when choosing an EM fungus for field application. In this respect, Thelephoroid fungal sp. XM002, an efficient and competitive broad host range EM fungus, possessed these characteristics and appeared to be a good candidate for artificial inoculation of Caesalps and Phyllanthaceae seedlings in nurseries. However, further efforts should be made to assess the genetic and functional diversity of African EM fungi as well as the EM status of unstudied plant species and to strengthen the use of efficient and competitive EM fungi to improve production of ecologically and economically important African multipurpose trees in plantations.

Composition and spatio-temporal distribution of tree seedlings in an evergreen broad-leaved forest in the Ailao Mountains, Yunnan

2 and is one of the largest tracts of ever- green broad-leaved forests in China. A 6-ha plot was established in the reserve in 2008 by Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, for the purpose of monitoring long-term dynamics of the forest. Tree seedlings were sampled in this plot to understand their composition and spatio-temporal distribution. Five of the top 10 seedling species in terms of importance values were the same as 5 of the top 10 adult tree species with the highest importance values. Both abundance and species richness of tree seed- lings dropped between the end of the rainy season and the end of dry season, likely due to drought stress. Seedlings in canopy gaps were richer in species, more abundant in terms of density, and experienced lower mortality compared with those under the forest canopy, suggesting that forest gaps facilitate the recruitment