Process Of Secondary Succession Research Articles

A flash in the pan? The population dynamics of a dominant pioneer species in tropical dry forest succession

AbstractGlobally, around half of all tropical forests are secondary communities which are recovering from previous disturbances. In these communities, dominant pioneers play a critical role in the successional dynamics due their ability to modify the environment, and thus to facilitate or hinder the performance of other species. In this study, we examined the population dynamics of the dominant pioneer species, Mimosa acantholoba var. eurycarpa, in a tropical dry forest during the process of secondary succession. We collected data from permanent plots over a period of 13 years and used integral projection models to analyze the vital rates and changes in population size. Most vital rates were negatively related to successional age, with resprouting, survival and recruitment of individuals responding more strongly, and individual growth rate more weakly. These vital‐rate trends translated into significant variation of population size over succession, with a maximum size at year four and a rapid decline thereafter. Overall, our findings suggest that this species benefits from its ability to display a large number of resprouts in very early stages of succession, contributing to the rapid increase in population density. However, as succession unfolds, a lack of resprouting and a decline in survival reduce its population size, to the point of local extinction. These results highlight the importance of resprouting in the early dynamics of tropical dry forest communities recovering from disturbance.

Long-term vegetation responses to climate depend on the distinctive roles of rewilding and traditional grazing systems

ContextThe abandonment of traditional practices has transformed agro-pastoral systems, leading to a more frequent occurrence of passive rewilding of Mediterranean landscapes. Reconstructing ecosystem responses to climate under different grazing conditions (i.e., wild, and domestic ungulates) is important to understand the future of these ecosystems.ObjectivesHere we study the different roles of domestic and wild herbivory in defining the climate-vegetation interaction. Specifically, we evaluated (1) the effect of climate on primary productivity at the landscape scale and (2) the long-term trends of vegetation biomass in response to passive rewilding or maintenance of traditional grazing systems.MethodsThis study was carried out in South-eastern Spain. We used satellite images to generate NDVI time series that proxy primary productivity and vegetation biomass. We combined the NDVI and climate data from two key landscapes: one with wild ungulates and another predominantly with domestic ungulates.ResultsWe detected a secondary succession process in areas with only wild ungulates. In domestic herbivory areas, vegetation biomass remained constant throughout time (30 years). In domestic herbivory areas temperature and seasonal precipitation affected primary productivity. In areas with only wild herbivory, primary productivity was mainly driven by annual precipitation, and it was less dependent on seasonal precipitation.ConclusionThese results highlight the distinctive roles of herbivores in defining Mediterranean landscapes' adaptability to climate, through passive rewilding or traditional livestock use. Maintaining both ecosystems can enhance landscape heterogeneity and ecological sustainability in a context of climatic changes.

Impacts of wildfires and strategies to accelerate secondary succession: A comprehensive analysis

Wildfires pose a significant and growing threat to ecosystems, leading to loss of biodiversity, water contamination, and alteration of habitats. This paper examines the devastating impacts of wildfires, with a focus on California, and explores the natural process of secondary succession in coastal forests. It further presents a comprehensive set of solutions to accelerate this process and mitigate the effects of wildfires. Strategies include immediate interventions like mulching, controlling invasive species through geo-spatial mapping, utilizing artificial structures such as seed banks and erosion control matting, and strategic planting and seeding. The paper emphasizes the need for collaboration among governments, researchers, and communities to implement these solutions effectively. It offers a roadmap for creating resilient ecosystems that can recover more quickly and sustainably from wildfires, highlighting the importance of innovation, education, and commitment to safeguarding our natural environment.

How do acid or alkaline soil environments affect soil organic carbon stocks in a post-abandonment secondary succession process in Mediterranean mountain areas?

Farmland abandonment has become one of the most important land use and land cover (LULC) changes threatening mountain areas in the Mediterranean. The concomitant natural revegetation process brings with it a series of ecosystem services and disservices for these marginal areas. Secondary succession can improve soil environment properties; however, its effects can be influenced by the specific characteristics of the site (topography, climate, vegetation, etc.). Thus, the main objective of this research was to study how soil quality and carbon sequestration are affected by post-abandonment secondary succession depending on the environment (delimited from the bedrock and the typical vegetation communities of the area. Soil sampling was carried out in a representative area of the Mediterranean mid-mountains (Leza Valley, Spain) for two soil environments (acid and alkaline), at different depths (0–40 cm) and in 5 stages of the abandonment process: cropland (CRL); shrubland (SH); bushland (BS); young forest (YF); and old forest (OF). Soil physico-chemical parameters were analysed and data analysis carried out with the following results: (i) significant differences were detected between environments for most LULCs; (ii) LULC, depth and soil environment significantly affected most of the soil variables studied; (iii) alkaline soil environments showed a progressive increase of soil organic carbon (SOC) and total nitrogen (N) stocks as the revegetation process and age of abandonment advanced (from 101.16 Mg ha−1 SOC (CRL) to 181.68 Mg ha−1 SOC (OF); (iv) in acid soil environments, the highest stocks were observed in the YF (161.56 Mg ha−1 SOC) with an irregular evolution pattern.Our study showed that secondary succession can improve soil quality and SOC sequestration. However, factors such as soil environment may be of great importance in selecting the best post-abandonment management strategy in a bid to gain recovery of ecosystem services and mitigate the effects of Global Change.

The Changes in the Forest Vegetation on the Danube River Aggradation Mound Affected by Water Regime Changes

Abstract This article is focused on the specific vegetation, which has formed from the floodplain forests on the aggradation mound (elevated sediment deposition) along the original Danube river in Slovakia in the part affected by Gabčíkovo waterworks that was put in operation in 1992. As a result of water regime changes, when a major part of the Danube water flow was redirected to the Gabčíkovo hydroelectric power plant, original floodplain forests on the aggradation mound began to suffer from a water deficit, which is also supported by shallow soils formed mostly on the gravel sediments with limited capillary rise of groundwater. It has triggered successional processes leading to the degradation of forest with changes in all layers. To identify these changes and development trends, we analyzed vegetation data from 2002, 2012, and 2022. The results indicate that the process of secondary succession of the original floodplain forest continues. This includes mainly an increase in the number of species, especially those typical for grasslands and synanthropic habitats. From an environmental point of view, the spread of some invasive species is striking. Ordination method (canonical-correlation analysis [CCA]) confirmed light, moisture, number of species, and Shannon–Wiener index as the main factors determining relevés’ variability.

Assessing plant diversity change in logged and unlogged dense semi-deciduous production forest of eastern Cameroon

This study was carried out in the dense semi-deciduous production forest of East Cameroon. The objective of this work of this study was to provide comparative floristic knowledge that can serve as a basis for the planning and sustainable management of ligneous plant resources in Communal Forests before and after logging. Sampling was done in unlogged and logged forest. Data collection was carried out using the linear transects subdivided into 10 plots of 25 m × 20 m (500 m2) with an equidistance of 225 m for the inventory of all trees with dbh ≥10 cm installed measured at 1.3 m above ground level. Nested quadrats 5 m × 5 m, oriented south-west and north-east were set up in each plot for the counting and identification of all individuals with a diameter less than 10 cm. The analysis of inventory data showed that the floristic composition was higher in the unlogged forest. The individuals were more evenly distributed in the logged (Pielou's equitability index = 0.83) than in the unlogged forest. The study of the functional spectra showed that the flora of the two forest types was dominated by Guinean-Congolese species (67.57% in the unlogged forest and 63.07% in the logged forest) and Phanerophytes, particularly Mesophanerophytes. The dominance of sarcochorous species reveals that the main mode of dissemination in this forest is zoochory, particularly endozoochory. The presence of pleochroic species in the logged forest reveals the importance of dissemination by water in the environment. The plants surveyed were divided into five plant assemblages (three for logged forest and two for unlogged forest) based on ecological parameters. The findings of this study suggest that forest management which combines assisted natural regeneration with the natural process of secondary succession facilitates the reconstitution of the vegetation cover and, by extension, the conservation of biodiversity in post-logging forest concessions.

Response Characteristics of Soil Organic Carbon Pool and Its Chemical Composition During Secondary Forest Succession in the Loess Plateau

In order to explore the characteristics of the soil organic carbon(SOC)pool and its chemical composition during the succession of secondary forests in the Loess Plateau, samples of the primary stage (Populus davidiana forest), transition stage (Populus davidiana and Quercus wutaishansea mixed forest), and top stage (Quercus wutaishansea forest) of secondary forest succession in the Huanglong Mountain forest area of the Loess Plateau in Northern Shaanxi were selected as the research object. The variation characteristics of SOC content, storage, and its chemical composition at different soil depths (0-10, 10-20, 20-30, 30-50, and 50-100 cm) were analyzed. The results showed that:① the contents and storage of SOC increased significantly with the secondary forest succession process (P<0.05). The content of SOC decreased significantly with the increase in soil depth, and the storage of SOC increased from 64.8 Mg·hm-2 in the primary stage to 129.2 Mg·hm-2 in the top stage, with an increase of 99%. ② During the succession of secondary forests, in the surface (0-30 cm) soil organic carbon, the relative content of aliphatic carbon components that have a simple structure and can be decomposed more easily decreased, and the relative content of aromatic carbon components that have a complex structure and cannot be decomposed easily increased, indicating that the chemical composition of organic carbon stability of surface-layer soil increased significantly with the process of secondary forest succession. However, the stability of the chemical composition of SOC in the deep layer (30-100 cm) first increased and then decreased, that is, the transition stage>the top stage>the primary stage. ③In the process of secondary forest succession, the stability of SOC chemical composition in the primary stage and transition stage increased significantly with the increase in soil depth. The top stage tended to be stable, and the deep soil carbon stability decreased slightly. ④ Pearson correlation analysis showed that during the secondary forest succession process, SOC storage and chemical composition stability were significantly negatively correlated with soil total phosphorus content. In general, the content and storage of SOC in the 0-100 cm soil increased significantly during the secondary forest succession, playing the role of a "carbon sink." The stability of the chemical composition of SOC in the surface layer (0-30 cm) increased significantly, but in the deep layer (30-100 cm), it increased first and then decreased.

LiDAR Point Clouds Usage for Mapping the Vegetation Cover of the “Fryderyk” Mine Repository

The paper investigates the usage of LiDAR (light detection and ranging) data for the automation of mapping vegetation with respect to the evaluation of the ecological succession process. The study was performed for the repository of the “Fryderyk” mine (southern Poland). The post-flotation area analyzed is a unique refuge habitat—Natura2000, PLH240008—where a forest succession has occurred for several dozen years. Airborne laser scanning (ALS) point clouds were used for deriving detailed information about the morphometry of the spoil heap and about the secondary forest succession process—mainly vegetation parameters i.e., height and canopy cover. The area of the spoil heap is irregular with a flat top and steep slopes above 20°. Analyses of ALS point clouds (2011 and 2019), confirmed progression in the forest succession process, and land cover changes especially in wooded or bushed areas. Precise vegetation parameters (3D LiDAR metrics) were calculated and provided the following parameters: mean value of vegetation height as 6.84 m (2011) and 8.41 m (2019), and canopy cover as 30.0% (2011) and 42.0% (2019). Changes in vegetation volume (3D area) were shown: 2011—310,558 m3, 2019—325,266 m3, vegetation removal—85,136 m3, increasing ecological succession—99,880 m3.

Soil legacy effects and plant—soil feedback contribution to secondary succession processes

Secondary succession is the process by which a community develops into a climax community over time. However, knowledge on the mechanisms, relating to soil legacy effects (soil chemistry and enzyme activity) and plant—soil feedback (PSF), driving community succession remains limited. In this work, we examined the PSF associated with three succession stage species through a 2-year greenhouse experiment. Setaria viridis, Stipa bungeana, and Bothriochloa ischemum were selected to represent dominant and representative early-, mid-, and late-successional stage species, respectively, of semiarid grasslands on the Loess Plateau. In response to the different soil origin, the shoot biomass of early-, mid-, and late-species were all higher when grown in their own soil than in other species’ soils, which indicated that the PSF of three species were positive. Over two growth periods, the early-species experienced a negative PSF, but the mid- and late-species experienced negative, neutral and positive PSF in the soil of early-, mid- and late-species, respectively. Our study demonstrates that soil legacy effects and PSF have a significant impact on community succession processes.

Different variations in soil CO2, CH4, and N2O fluxes and their responses to edaphic factors along a boreal secondary forest successional trajectory

Forest succession is an important process regulating the carbon and nitrogen budgets in forest ecosystems. However, little is known about how and extent by which vegetation succession predictably affects soil CO2, CH4, and N2O fluxes, especially in boreal forest. Here, a field study was conducted along a secondary forest succession trajectory from Betula platyphylla forest (early stage), then Betula platyphylla-Larix gmelinii forest (intermediate stage), to Larix gmelinii forest (late stage) to explore the effects of forest succession on soil greenhouse gas fluxes and related soil environmental factors in Northeast China. The results showed significant differences in soil greenhouse gas fluxes during the forest succession. During the study period, the average soil CO2 flux was greatest at mid-successional stage (444.72 mg m-2 h-1), followed by the late (341.81 mg m-2 h-1) and the early-successional (347.12 mg m-2 h-1) stages. The average soil CH4 flux increased significantly during succession, ranging from -0.062 to -0.036 mg m-2 h-1. The average soil N2O flux was measured as 17.95 μg m-2 h-1 at intermediate successional stage, significantly lower than that at late (20.71 μg m-2 h-1) and early-successional (20.85 μg m-2 h-1) stages. During forest succession, soil greenhouse gas fluxes showed significant correlations with soil and environmental factors at both seasonal and successional time scales. The seasonal variations of soil GHG fluxes were mainly influenced by soil temperature and water content. Meanwhile, soil MBN and soil NO3--N content were also important factors for soil N2O fluxes. Structural equation modelling showed that forest succession affected soil CO2 fluxes by changing soil temperature and microbial biomass carbon, affected soil CH4 fluxes mainly by changing soil water content and soil pH value, and affected soil N2O fluxes mainly by changing soil temperature, microbial biomass nitrogen, and soil NO3--N content. Our study suggests that forest succession mainly alters soil nutrient and soil environment/chemical properties affecting soil CO2 and N2O fluxes and soil CH4 fluxes, respectively, in the secondary forest succession process.

The challenge of participatory restoration in rural areas

Restoration is a prominent field of research and of restoration projects that seek to recover degraded and dysfunctional ecosystems and the services they provide. Humanity’s environmental crisis has increased awareness of the urgent need to conserve ecosystems and their biodiversity. Many countries and international organizations have set ambitious plans and restoration targets. This paper emphasizes on current themes such as landscape restoration, invasive species, novel ecosystems, and the necessary involvement of local communities in ecological restoration. It is focused mainly on tropical forest ecosystems. Another aim of this paper is a review of the results obtained in diverse restoration practices that concentrate on inducing secondary succession processes in tropical forests. It draws heavily on case studies from Mexico. Members of society should play an active role in restoration planning and implementation. Social participation is central to the success and sustainability of restoration projects. Traditional ecological knowledge is essential in many projects, and there should be careful consideration of the ethics involved. In the coming years, we will probably see a surge in the unassisted revegetation and reforestation of many abandoned rural areas making the understanding and managing of these restoration processes necessary and crucial. Finally, a set of guidelines that view restoration as a long-term social and ecological process is given.

Soil microbes-mediated enzymes promoted the secondary succession in post-mining plantations on the Loess Plateau, China

The diversity of vegetation configuration is the key to ecological restoration in open-pit coal mine dump. However, the recovery outcomes of different areas with the same vegetation assemblage pattern are completely different after long-term evolution. Therefore, understanding the causes of differential vegetation recovery and the mechanism of plant succession is of great significance to the ecological restoration of mines. Three Pinus tabulaeformis plantations with similar initial site conditions and restoration measures but with different secondary succession processes were selected from the open-pit coal mine dump that has been restored for 30 years. Soil physicochemical properties, enzyme activities, vegetation and microbial features were investigated, while the structural equation models were established to explore the interactions between plants, soil and microbes. The results showed that original vegetation configuration and soil nutrient conditions were altered due to secondary succession. With the advancement of the secondary succession process, the coverage of plants increased from 34.8% to 95.5% (P < 0.05), soil organic matter increased from 9.30 g kg−1 to 21.13 g kg−1 (P < 0.05), and total nitrogen increased from 0.38 g kg−1 to 1.01 g kg−1 (P < 0.05). The activities of soil urease and β-glucosidase were increased by 1.7-fold and 53.26%, respectively. Besides, the secondary succession also changed the soil microbial community structure and function. The relative abundance of Nitrospira genus which dominates the nitrification increased 5.2-fold. The results showed that urease and β-glucosidase promoted the increase of vegetation diversity and biomass by promoting the accumulation of soil organic matter and nitrate nitrogen, which promoted the ecological restoration of mine dumps.

Seed Rain in a Degraded Mining Area: The Role of Bird Perches and Pioneer Trees

Mining causes changes in natural areas, from the elimination of vegetation and the seed bank to physical changes in the soil and water dynamics. The recovery of such impacted areas depends on both the natural process of secondary succession and the use of techniques that assist the return of the flora. Aiming to evaluate the seed rain in an area of basaltic rock mining, 18 seed collectors of 0.5 m2 were installed placed under artificial perches, pioneer trees (natural perches) and control collectors. After 12 months, 8976 seeds of 33 plant species were quantified with an average density of 997 seeds m2 year-1 that differed statistically between the different perches. Artificial perches were more efficient in facilitating the seed rain, the most abundant of which were Cecropia pachystachya Trécul (n=3218), Andropogon bicornis L. (n=1417), Urochloa plantaginea (Link) R.D.Webster (n=1179), and Leucaena leucocephala (Lam.) de Wit (n=1138) were more abundant and represented 77.4% of total collected seeds and 12.1% of species richness. The installation of artificial perches should be encouraged in degraded areas, because they facilitate the visitation of birds and seed dispersal, contributing both to the arrival of seeds and to an increase in seed richness in the area.

Secondary succession and parent material drive soil bacterial community composition in terraced abandoned olive groves from a Mediterranean hyper-humid mountainous area

Mediterranean humid mountains are ecological hotspots with high water availability that may accelerate their recovery after farmland abandonment, a widespread phenomenon in marginal areas of the European Mediterranean Region. This land use change led to secondary succession processes triggering changes in soil properties and soil microorganisms. This is the first study in assessing the environmental influence of both ecological succession and parent material over soil properties and soil bacterial communities in these habitats. To examine the effects of secondary succession and elucidate the role of parent material in soil bacterial communities, six soil plots were sampled from the combination of abandoned and rainfed olive groves, terraced or non-terraced, and over four parent materials in Lluc Valley, a Mediterranean hyper-humid mountainous area on the island of Mallorca, Spain. Soil bacterial diversity and taxonomic composition at phylum and family level in each field were analyzed by rRNA 16 S amplicon sequencing. In addition, a series of soil physicochemical and microbiological properties, together with enzyme activities were assessed. Results showed that secondary succession and parent material significantly affected soil physicochemical and microbiological properties, soil enzyme activities and soil bacterial communities’ diversity and taxonomic composition. Secondary succession following farmland abandonment triggered higher total organic carbon (TOC), microbial biomass carbon (Cmic), basal soil respiration (REB), alkaline phosphatase activity (Php) and dehydrogenase activity (DHA), thus enhancing soil quality. In contrast, parent material significantly shaped pH, specific surface area (SSA), TOC, Cmic, REB and soil enzyme activities, playing a key role in land use effects modulation. According to the distance-based redundancy analysis (db-RDA), SSA, TOC, REB, Cmic, urease activity (Ur) and Php were the soil properties that contributed to significant changes in bacterial communities’ composition at the family level. This study evidenced that farmland abandonment led to improve soil quality in Mediterranean humid mountains, with positive feedbacks provided by parent material.

Decaying villages in the centre of Europe with no population decline: Long-term analysis using historical aerial images and remote sensing data

Agricultural land abandonment and depopulation of rural areas are a problem observed in numerous regions of the world, especially in Europe. Effectively counteracting this phenomenon requires the development of tools adapted to its nature in a given area as well as the origin and dynamics of observed changes. The article presents a study on the dynamics of land abandonment in central Poland, which has resulted in the complete abandonment of land cultivation of an area of hundreds of square kilometres. Historical stereometric aerial photographs from 1973 and the results of ALS measurements taken in 2012 were used in the study. The historical data was used to generate point data clouds representing the three-dimensional, historical structure of vegetation height in a specific year, with an accuracy similar to that of contemporary ALS measurements. The results obtained were quite surprising because, unlike many other studies of this issue, no intensive depopulation was found, and the change in the age structure, although noticeable, does not differ significantly from the changes observed in the entire population of Poland during the period in question. This approach allows for a very accurate assessment of changes in land use, in particular the process of the abandonment of land use, combined with secondary forest succession and self-reforestation processes. Such an analysis may cover a period of several decades and its results allow a precise diagnosis of the duration and dynamics of abandonment.

Caracterización de la vegetación en sitios con evidencias de antropización en Delta Frontal del Río Paraná

Anthropization is one of the main structuring factors of plant communities at a global scale. In particular, in the Paraná River Frontal Delta there was a strong process of settlement and transformation of the territory by productive activities during the 20th century with a process of depopulation and partial abandonment of the productive plots in recent decades. The original vegetation of the Frontal Delta was made up of flooding grasslands (“Pajonales”), open woodlands (“Ceibales”) and closed riparian forest (“Montes Blancos”), replaced in large areas by crops that after their abandonment gave rise to a secondary succession process. In this work we aimed to characterize the flora and plant communities in plots with evidence of current or past anthropization in the Frontal Delta. A total of 202 sampling plots of 25 m2 were established in which the species of vascular plants were recorded and their coverage was estimated. Taken together, 167 taxa were recorded of which 81% were native. Through multivariate analysis, 15 communities with different physiognomy and degree of invasion were identified and characterized. Some of these presented a great similarity with the original communities of the region, others were similar to secondary communities described in the bibliography and novel situations were identified. The results highlight the great local richness of the vegetation and the great diversity of plant communities, highlighting the importance of the study area for conservation.

Vascular plants and plant habitats of Brush Creek Island, Lewis County, Kentucky, U.S.A.

A descriptive survey of the vascular flora and plant habitats of Brush Creek Island, a 6.7-ha Ohio River island in Lewis County, Kentucky, was conducted during 1995–1996 and 2012. Brush Creek Island (BC), one of three Ohio River islands politically a part of Kentucky, is currently under private ownership and projected as a future part of the Ohio River Islands National Wildlife Refuge. Two major habitats in 2012 were Vegetated Unconsolidated Shoreline and Bottomland Hardwood Forest, a final sere of Late Old Field and Immature Bottomland Hardwood Forest. Two additional 1996 habitats, a seasonal Riverine Emergent Wetland and Late Old Field, were altered through fluvial action and secondary succession processes by 2012. An annotated list consists of 330 species in 220 genera from 82 families. Taxa are composed of one Monilophyte, four Magnoliids, 76 Monocots, and 249 Eudicots. Ninety-three taxa (28.2%) are non-native adventive or naturalized spe-cies. Forty-eight taxa (54%) are classified as Kentucky invasive plants. A total of 189 species (57.3%) are hydrophytes. Ninety-five native or non-native taxa (28.8%) are Lewis County distribution records.

What is the future of abandoned agricultural lands? A systematic review of alternative trajectories in Europe

Agricultural land abandonment and its impacts on landscape features have been a striking characteristic of many European rural areas over the last decades. Although previous research identified drivers and environmental impacts of abandonment, few described the post-agricultural abandonment trajectories. However, examining the driving forces leading to different post-agricultural abandonment trajectories is key to understand how alternative uses of these lands can be developed to address the environmental, economic, and social challenges faced in these areas. This paper reviews the literature of the different trajectories observed after agricultural abandonment and the related drivers and processes. Based on the literature evidence, we proposed a novel categorisation of different abandonment trajectories, with their drivers and landscape outcomes. In most reported cases, lands transitioned towards semi-natural landscapes and few returned to different agricultural uses after abandonment. The most common driving force of the landscape trajectory was the absence of land management where secondary succession processes led to semi-natural landscapes. Quality and state of these landscapes were variable. Alternative trajectories were essentially driven by institutional and socio-economic drivers within biophysical constraints and opportunities for (re-)afforestation, re-farming, and multifunctional uses of the land after abandonment. While abandoned lands can bring opportunities to respond to biodiversity and other environmental policy goals, the evidence across case studies suggests that adequate resources with institutional and socio-economic incentives are required to stimulate favourable development, mitigate, potential trade-offs, and support land management.

When Forests Take Over After Land Abandonment: Dissolved Organic Matter Response in Headwater Mountain Streams

Dissolved organic matter (DOM) represents the largest pool of organic carbon in fluvial ecosystems. The majority of DOM in rivers is of terrigenous origin—making DOM composition highly dependent on vegetation cover and soil properties. While deforestation is still a worldwide anthropogenic phenomenon, current land cover change in temperate regions is often characterized by secondary succession processes following the abandonment of agricultural activities including grazing on pasturelands. This results in (secondary) forest expansion with a consequent, time-lagged transformation of soil properties. Predicting the time scale and spatial scale (i.e., location in the catchment: riparian vs. upslope areas) at which such land cover changes affect the terrestrial-aquatic carbon linkage and concomitantly alter properties of fluvial DOM as drivers of carbon cycling in freshwater ecosystems represents a new scientific challenge. In an attempt to identify potential legacy effects of land cover, i.e., reaction delays of fluvial DOM to changes in land cover, we here investigate the influence of specific current and historic (2 decade-old) land cover types on molecularly resolved fluvial DOM composition in headwater mountain streams. Our analysis is based on a scale-sensitive approach weighing in the distance of land cover (changes) to the stream and ultrahigh-resolution mass spectrometric analyses. Results identified the dominance of terrigenous DOM, with phenolic and polyphenolic sum formulae commonly associated to lignins and tannins, in all the studied streams. DOM properties mostly reflected present-day gradients of forest cover in the riparian area. In more forested catchments, DOM had on average higher molecular weight and a greater abundance of O-rich phenols and polyphenols but less aliphatics. Besides the modulation of the DOM source, our results also point to an important influence of photodegradation associated to variation in light exposition with riparian land cover in defining fluvial DOM properties. Despite expectations, we were unable to detect an effect of historic land cover on present-day DOM composition, at least at the investigated baseflow conditions, probably because of an overriding effect of current riparian vegetation.

Floristic and structure of different strata in an urban Semideciduous Forest in Jataí, Goiás state, Brazil

Estudos comparativos entre diferentes estratos de florestas em sucessão ecológica são importantes para entender a dinâmica florestal. O estudo avaliou aspectos florísticos, fitossociológicos e ecológicos entre os estratos adulto e regenerante de um fragmento urbano de floresta estacional semidecidual, em Jataí, Goiás. Nas últimas décadas, a vegetação que era tipicamente savânica tem se tornado uma floresta. As árvores adultas (diâmetro a altura do peito, DAP ≥ 5 cm) foram amostradas em 12 parcelas permanentes de 200m². Em cada uma delas, sub-parcelas de 25m² foram amostradas para o estrato regenerante, que compreendeu indivíduos com DAP 5cm e altura ≥ 1m. Regenerantes tiveram maior riqueza (31 espécies), com duas espécies a mais do que os adultos. Houve baixa similaridade florística e estrutural entre os estratos, indicando uma substituição de espécies ao longo do tempo. A diversidade de Shannon foi significativamente menor para o estrato arbóreo (teste t), visto que apresentou baixa equabilidade, com dominância ecológica de poucas espécies. Ambos os estratos tiveram elevada proporção de espécies pioneiras, quando comparado com outros estudos. Zoocoria e espécies de ambientes florestais foram expressivamente mais abundantes no estrato regenerante. O estudo revelou um fragmento em franco processo de sucessão secundária e vulnerabilidade diante de pressões antrópicas, sendo importante os cuidados quanto à sua conservação.