Successional Gradient Research Articles

Identifying tropical dry forests extent and succession via the use of machine learning techniques

Information on ecosystem services as a function of the successional stage for secondary tropical dry forests (TDFs) is scarce and limited. Secondary TDFs succession is defined as regrowth following a complete forest clearance for cattle growth or agriculture activities. In the context of large conservation initiatives, the identification of the extent, structure and composition of secondary TDFs can serve as key elements to estimate the effectiveness of such activities. As such, in this study we evaluate the use of a Hyperspectral MAPper (HyMap) dataset and a waveform LIDAR dataset for characterization of different levels of intra-secondary forests stages at the Santa Rosa National Park (SRNP) Environmental Monitoring Super Site located in Costa Rica. Specifically, a multi-task learning based machine learning classifier (MLC-MTL) is employed on the first shortwave infrared (SWIR1) of HyMap in order to identify the variability of aboveground biomass of secondary TDFs along a successional gradient. Our paper recognizes that the process of ecological succession is not deterministic but a combination of transitional forests types along a stochastic path that depends on ecological, edaphic, land use, and micro-meteorological conditions, and our results provide a new way to obtain the spatial distribution of three main types of TDFs successional stages.

Effects of Haloxylon spp. of Different Age Classes on Vegetation Cover and Soil Properties on an Arid Desert Steppe in Iran

In arid regions, afforestation has been considered as a method for ecological revival in terms of vegetation enrichment and soil amelioration. In this study, the effects of afforestation with Haloxylon spp. on vegetation cover and soil properties were measured < 3, 3, 6, and 25 years after planting in an arid desert in Iran. Soil samples were collected at two depths (0–30 and 30–60 cm) under and between shrub canopies. Afforestation succession significantly affected plant community characteristics. In total, 16 species from 8 families and 15 genera were observed along the afforestation successional gradient. Plant species richness and diversity and vegetation cover increased slowly during the succession, and reached the maximum values in the area where Haloxylon had been planted for 25 years. Soil nutrient values gradually increased during the succession, and the levels of organic matter, total nitrogen, available potassium, and available phosphorus were significantly higher under Haloxylon canopies than between them. Afforestation reduced soil pH under and between Haloxylon canopies during the succession, while soil electrical conductivity followed an opposite pattern. Haloxylon planting increased the silt content in the 0–30 cm soil layer. Our results suggest that Haloxylon establishment plays an important role in the reestablishment of desertified ecosystems in arid regions.

Linkage of microbial residue dynamics with soil organic carbon accumulation during subtropical forest succession

It has been recognized that the formation and subsequent sequestration of soil organic carbon (SOC) during forest succession are primarily driven by soil microorganisms. However, the time-integrated microbial influence on long term SOC accumulation remains unknown. In a subtropical forest succession including three stages of early coniferous forest, middle mixed species forest and climax broad-leaved forest, we investigated changes in soil amino sugars, a biomarker of microbial residues, along a successional gradient to evaluate contributions of fungal and bacterial residues to SOC accumulation over time.Both the concentrations and stocks of SOC and amino sugars increased with forest succession in the 0–40 cm soil depth, suggesting a close association of microbial proliferation-mortality processes with the sequestration of SOC. In the early successional stage, the contribution of microbial residue-carbon to SOC was low due to the decomposition resistance of needle leaf litter. The later invasion of broad-leaved trees increased the contribution of microbial residues to SOC formation, but the accumulation of amino sugars was more rapid than SOC from early to middle stage, possibly implying that both the production and retention of microbial residues were the essential prerequisite for SOC sequestration. Given the preferences of bacteria to available substrate while the advantage of fungi in using the more recalcitrant part, the proportion of fungal residue-carbon in SOC was significantly larger in the middle stage (mixed forest) while bacterial residues were more prone to accumulate in SOC in the climax stage (broad-leaved forest). The sequestration of SOC along the subtropical forest succession possibly underwent a first stage of accumulation of fungal residues followed by the preferential accumulation of less recalcitrant bacterial residues.

The Influence of Vegetation Structure on the Composition of the Seed Rain and Seedling Pool in AbandonedMolinion caeruleaeMeadows

The investigations of the effect of different habitat conditions on the composition of the seed rain and seedling pool were conducted in the years 2014 and 2015 in abandoned patches of Molinion caeruleae dominated by small-stature meadow taxa (patch I), tall-growing grasses (patch II), as well as shrubs and trees (patch III). Observations showed that along the successional gradient the seed rain and seedling pool diminishes. The prevalence of perennials and native taxa in the seed rain and seedling pool occurred in all the study sites. Moreover, in the propagule and seedling pools of all the patches hemicryptophytes and meadow taxa prevailed but their number decreased in successional sites. Also, the abundance of ruderal and grassland taxa decreased gradually, at expense of number of forest species. Zoochorous species prevailed in the seed rain and seedling pool of all patches. Number of hydrohorous species decreased in successional patches, while the abundance of species with other dispersal modes were similar. Irrespective of patch character, the species producing propagules with medium size dominated in the seed rain and seedling pools, whereas a significant decrease of number of small-seeded species was noticed only in the seedling pool. Despite the diminishing of the seed rain and seedling pool along the successional gradient, the gap creation might be a very effective way of active protection of Molinion caeruleae meadows. However, the gap colonisation requires permanent monitoring to avoid further spreading of undesired taxa.

Anurans Species Diversity and Composition along the Successional Gradient of the Evergreen Rainforest in Silago, Southern Leyte, Philippines

Anurans Species Diversity and Composition along the Successional Gradient of the Evergreen Rainforest in Silago, Southern Leyte, Philippines

Expansion Dynamics and Performance of the Dwarf Shrub Empetrum hermaphroditum (Ericaceae) on a Subarctic Sand Dune System, Nunavik (Canada)

ABSTRACTMany tundra plant species rely more heavily on clonal propagation than on sexual reproduction. However, if reproduction bottlenecks are alleviated, shifts in the balance between these strategies can occur. To better understand the colonization and expansion dynamics of clonal dwarf shrubs in a rapidly changing environment, we monitored a crowberry population (Empetrum hermaphroditum) on a sand dune system in subarctic Québec. Our objectives were to quantify survival, recruitment, and growth and to determine whether performance varied across a topographic and successional gradient. In 2012, we resurveyed a 6-ha plot where all individuals had been counted in 2007. Along the successional gradient, we measured vegetation cover, soil characteristics, shoot elongation, and seed germination. Over the 2007–2012 period, the population continued to experience abundant recruitment, fast growth, and low mortality, resulting in a 40% increase in population size and a 244 m2 increase in cover. Performance patterns did not match the dune successional gradient; instead, individuals at intermediate positions showed better growth and produced more viable seeds. The ability of crowberry to successfully establish from seed might have been enhanced by the regional warming observed since the 1990s and seems to be part of a dual strategy allowing crowberry to fill gaps while continuing to spread efficiently on the dune system via clonal growth.

Long-term changes in surface-active beetle communities in a post-fire successional gradient in Pinus brutia forests

Abstract: Fire is one of the most important ecological factors for many ecosystem types. Since prehistoric times, synergistic effects of fires and humans have led to changes in Eastern Mediterranean ecosystems. The effects of fire on different trophic levels, particularly regarding plants, have been examined intensively in fire-induced ecosystems. In this study, we aimed to study long-term changes in beetle community structure after fire in Pinus brutia Ten. forests. Five sites burned in different years and a control site unburned for at least 50 years were selected. Beetle sampling was conducted using four pit-fall traps in each of four transects in three replication plots at every successional site and in two plots at the control site. Microhabitat variables related to vegetation structure and litter layer were recorded and associated with abundances of beetles and feeding groups. The results showed that total, wood-eating, and predator beetles showed a decreasing trend of abundance along the successional gradient after fire. In contrast to these groups, herbivores tended to increase towards the late successional stages. Middle and late successional stages were important in terms of species richness, species diversity and evenness of beetle communities and feeding groups. The characteristics of vegetation and litter layer changed with successional gradient, playing a decisive role in the structure of beetle communities at successional sites. According to the data presented here, a mosaic structure consisting of different successional stages is very important to sustain high species diversity in beetle communities.

Successional leaf traits of monsoon evergreen broad-leaved forest, Southwest China

Understanding the variation of functional traits of plant species along forest successional gradients may provides useful insights into community assemblages. However, species performance during forest succession is controversial. We explored the variation of leaf traits along a forest succession by examining ten leaf traits in four successional stages in a monsoon evergreen broad-leaved forest in Southwest China. Results showed significant differences in all leaf traits except leaf area and leaf carbon content among the successional stages. Five leaf traits were highly correlated to successional stage, while the first principal component showed no correlation with successional stage. The first principal component accounted for 56.1% of the total variation in all ten leaf traits. Almost 50% of the relationships between leaf traits differed along the examined successional gradient, indicating that leaf traits were affected by the successional stage.

Efecto de los estadios sucesionales del bosque tropical seco sobre el microhabitat usado por Agalychnis dacnicolor (Anura: Phyllomedusidae) y Smilisca fodiens (Anura: Hylidae)

Habitat disturbance can modify microhabitats and therefore have a significant effect on the abundance and distribution of anurans species, particularly those associated to specific microhabitats. In this study we evaluated changes in the use of microhabitat by two syntopic species of tree frogs, Agalychnis dacnicolor and Smilisca fodiens along a successional gradient of Tropical Dry Forest in the region of the Biosphere Reserve of Chamela-Cuixmala at the coast of Jalisco, Mexico. We hypothesized that because these two species are habitat generalists, microhabitat use would change in response to secondary forest succession and to the climatic season of the year. Although both species were registered in both secondary and mature forests, A. dacnicolor was associated to mature forest, whereas S. fodiens was more associated to disturbed sites. Neither species showed differences in biomass among successional stages (ES) or between climatic seasons. Unlike S. fodiens, A. dacnicolor presented larger sizes during the rainy season. Body temperature of both species varied between ES and climatic season. S. fodiens presented a more constant temperature among individuals in pastures, while A. dacnicolor in mature forests. Environmental and structural habitat variables that influenced the presence of both species in ES were substrate temperature, height of tree or shrub where the frog was perching and percentage cover of litter, grasses, shrubs, trees and bare soil. The variables that best explained biomass, snout-vent length (LHC) and body temperature of S. fodiens were cover of dry branches and substrate temperature, whereas biomass of A. dacnicolor was better explained by cover of herbs, LHC, height of the tree or shrub where the frog was perching, body temperature and the substrate temperature. Both species used differentially environmental and structural variables of microhabitats along the gradient of initial to late ES. The variables that separated the species were the height of the shelter or perch and the percentage of trees in different ES. Whereas A. dacnicolor was more associated to the lowest strata of vegetation, S. fodiens showed plasticity in microhabitat use, especially in height of shelter or perch. Our results suggested that even when both species are considered habitat generalists, in anthropic landscapes, A. dacnicolor is specialist in microhabitat use, whereas S. fodiens is a species with greater ecological plasticity in microhabitat use. These differences in microhabitat use in response to habitat disturbance may help explain the success of these species in these new landscapes, as well as the importance of secondary forests in different stages of succession to maintain adequate microhabitats for the permanence of species in anthropogenic landscapes.

Micro-arthropod community responses to ecosystem retrogression in boreal forest

Explaining the variation in communities of soil organisms across plant communities or ecosystems remains a major challenge for ecologists. Several studies have explored how soil communities are affected along ecosystem successional gradients but most of these are based on relatively short term chronosequences. To address the impact of ecosystem age on micro-arthropod communities, we utilized a 5000 year old post-fire chronosequence, which consists of thirty lake islands differing greatly in time since fire in the boreal forested zone of northern Sweden. The Acari community did not change along this chronosequence, indicating that Acari rapidly (<60 yr) reach equilibrium after forest fire and that they are relatively unresponsive to subsequent long term changes in plant community composition and soil quality. The Collembola community composition, however, showed greater responsiveness to the chronosequence and this was best explained through their functional traits. Notably, the youngest (most recently burned) islands, which had the highest ecosystem productivity and fungal mass turnover, were dominated by soil-dwelling (eu-edaphic) Collembola species that are best positioned to take advantage of resource input to the soil. Although plant community characteristics did not emerge as powerful drivers of the Collembola community, we found that Collembola community composition was related to the quality (N and P) of the soil substrate, which reflects a long term legacy of the plant community. Collembola life history characteristics proved to be important for understanding how abundances of different taxa varied relative to one another across the gradients of plant diversity and substrate quality gradients that occur across long-term chronosequences. The causal connection between vertical stratification of Collembola and substrate quality is at present unclear but is likely to be related to their feeding preferences and microhabitat conditions. Because the soil-dwelling Collembola showed a strong decline in abundance with ecosystem retrogression while surface-dwelling Collembola did not these two life history groups may operate as functionally distinct groups within the soil food web across these long-term chronosequences.

Changes in Species Diversity, Aboveground Biomass, and Distribution Characteristics along an Afforestation Successional Gradient in Semiarid Picea crassifolia Plantations of Northwestern China

Changes in Species Diversity, Aboveground Biomass, and Distribution Characteristics along an Afforestation Successional Gradient in Semiarid <i>Picea crassifolia</i> Plantations of Northwestern China

Determinants of litter decomposition rates in a tropical forest: functional traits, phylogeny and ecological succession

Plant litter decomposition is one of the most important processes in terrestrial ecosystems, as it is a key factor in nutrient cycling. Decomposition rates depend on environmental factors, but also plant traits, as these determine the character of detritus. We measured litter decomposition rate for 57 common tree species displaying a variety of functional traits within four sites in primary and four sites in secondary tropical forest in Madang Province, Papua New Guinea. The phylogenetic relationships between these trees were also estimated using molecular data. The leaves collected from different tree species were dried for two days, placed into detritus bags and exposed to ambient conditions for two months. Nitrogen, carbon and ash content were assessed as quantitative traits and used together with a phylogenetic variance– covariance matrix as predictors of decomposition rate. The analysis of the tree species composition from 96 quadrats located along a successional gradient of swidden agriculture enabled us to determine successional preferences for individual species.Nitrogen content was the only functional trait measured to be significantly positively correlated with decomposition rate. Controlling for plant phylogeny did not influence our conclusions, but including phylogeny demonstrated that the mainly early successional family Euphorbiaceae is characterized by a particularly high decomposition rate. The acquisitive traits (high nitrogen content and low wood density) correlated with rapid decomposition were characteristic for early successional species. Decomposition rate thus decreased from early successional to primary forest species. However, the decomposition of leaves from the same species was significantly faster in primary than in secondary forest stands, very probably because the high humidity of primary forest environments keeps the decomposing material wetter.

Effects of Spartina alterniflora Invasion on the Abundance, Diversity, and Community Structure of Sulfate Reducing Bacteria along a Successional Gradient of Coastal Salt Marshes in China

Little is known about consequences of Spartina alterniflora invasion on soil sulfate-reducing bacteria (SRB). This study compared the abundance, diversity, and community structure of SRB in S. alterniflora and in native plant communities along a successional gradient (bare mudflat, young/mature S. alterniflora, Suaeda salsa, and Phragmites australis) in coastal salt marshes of Eastern China. Quantitative polymerase chain reaction of dissimilatory sulfite reductase (dsrB) gene was applied to assess SRB abundance, and the diversity and composition of SRB was analyzed by 454 pyrosequencing of partial dsrB gene. We found that S. alterniflora had a significantly higher abundance and diversity of SRB than native plant species. For all plant covers, Desulfobacteraceae was the largest soil SRB group, with a relative abundance of 33.6%, followed by Desulfobulbaceae (29.2%). S. alterniflora showed a higher relative abundance of Desulfobacteraceae (42.5%) than native species (29.5%) did. Notably, S. alterniflora invasion decreased the relative abundance of a SRB branch clustering with the thermophilic Thermodesulfovibrio yellowstonii. In conclusion, S. alterniflora invasion of the eastern coast of China has greatly increased the abundance and diversity of SRB communities and altered their structure. This might further influence carbon mineralization and inhibit the production of methane in China’s coastal marshes.

Temporal segregations in the surface community of an ephemeral habitat: Time separates the potential competitors of coprophilous Diptera

AbstractTemporal separations among species greatly enhance the species' coexistence, especially in insect communities inhabiting temporally unstable, yet resource‐rich, ephemeral habitats like dung or carrion. The insect communities inhabiting ephemeral habitats consist of two components, the internal community dwelling within the substrate (mostly Coleoptera), and the surface community inhabiting the habitat's outer rim (mostly adult Diptera). In contrast to the internal community, the surface community is very rarely studied. We present here the first quantitative study of temporal trends in the surface community of coprophilous dipteran adults. Using artificially created 1.5 L cow dung pats, we studied the succession and seasonality in the surface community during six sampling periods in 2011 and 2012. In total, we sampled 13579 adults of dung‐visiting Diptera. Both the abundance and species richness decreased rapidly throughout the succession, and were highest during summer. Along the successional gradient, the community was separated into two main groups (early and late) and four subgroups: (i) species occurring during the first few hours (mainly Calyptratae: Diptera); (ii) species occurring between the first and second days; (iii) species occurring between the second and third days (mainly Acalyptratae: Diptera); and (iv) species with optima after the third day of dung pat existence (mainly Nematocera). The earliest and latest successional groups, occurring mainly during spring–autumn, were seasonally separated from the two mid‐successional groups, occurring during summer. The ecologically similar species displayed detectable seasonal micro‐optima, which likely facilitate their coexistence. There was a high overall similarity in temporal patterns between dung and carrion surface communities.

Comparisons of Canyon Grassland Vegetation and Seed Banks along an Early Successional Gradient

Abstract The seed bank represents the future trajectory of plant communities following disturbance and is vital to their regeneration. Worldwide, grassland seed banks have been well studied. However, there are no examinations of the seed bank for the Pacific Northwest Bunchgrass Prairie system found in the Pacific Northwest of the United States. This absence may arise from the limited amount of intact grasslands in this type following decades of agricultural development and cultivation. In this study, we examined the seed bank from grasslands sites along an early successional gradient to evaluate how they relate to above ground vegetation, successional stage, and historical cultivation. We found that similarities between above ground vegetation and the seed bank were the strongest in the earliest successional stages, when annual grasses dominate. Surprisingly, this relationship was driven by the presence of a relatively new introduced annual grass, Ventenata dubia. Finally, the seed bank within cultivated...

Decoupled diversity dynamics in green and brown webs during primary succession in a saltmarsh.

Terrestrial ecosystems are characterized by a strong functional connection between the green (plant-herbivore-based) and brown (detritus-detritivore-based) parts of the food web, which both develop over successional time. However, the interlinked changes in green and brown food web diversity patterns in relation to key ecosystem processes are rarely studied. Here, we demonstrate changes in species richness, diversity and evenness over a wide range of invertebrate green and brown trophic groups during 100years of primary succession in a saltmarsh ecosystem, using a well-calibrated chronosequence. We contrast two hypotheses on the relationship between green and brown food web diversity across succession: (i) 'coupled diversity hypothesis', which predicts that all trophic groups covary similarly with the main drivers of successional ecosystem assembly vs. (ii) the 'decoupled diversity hypothesis', where green and brown trophic groups diversity respond to different drivers during succession. We found that, while species richness for plants and invertebrate herbivores (green web groups) both peaked at intermediate productivity and successional age, the diversity of macrodetritivores, microarthropod microbivores and secondary consumers (brown web groups) continuously increased towards the latest successional stages. These results suggest that green web trophic groups are mainly driven by vegetation parameters, such as the amount of bare soil, vegetation biomass production and vegetation height, while brown web trophic groups are mostly driven by the production and standing stock of dead organic material and soil development. Our results show that plant diversity cannot simply be used as a proxy for the diversity of all other species groups that drive ecosystem functioning, as brown and green diversity components in our ecosystem responded differently to successional gradients.

A shift from arbuscular mycorrhizal to dark septate endophytic colonization in Deschampsia flexuosa roots occurs along primary successional gradient.

Soil fungal community and dominant mycorrhizal types are known to shift along with plant community changes during primary succession. However, it is not well understood how and why root fungal symbionts and colonization types vary within the plant host when the host species is able to thrive both at young and at old successional stages with different light and nutrient resource availability. We asked (i) how root fungal colonization of Deschampsia flexuosa (Poaceae) by arbuscular mycorrhizal (AM) fungi and dark septate endophytes (DSE) changes along a postglacial primary successional land uplift gradient. As neighboring vegetation may play a role in root fungal colonization, we also asked (ii) whether removal of the dominant neighbor, Empetrum nigrum ssp. hermaphroditum (Ericaceae), affects root fungal colonization of Deschampsia. We also studied whether (iii) foliar carbon (C) and nitrogen (N) concentration of Deschampsia is related to successional changes along a land uplift gradient. AM colonization decreased (-50%), DSE colonization increased (+200%), and foliar C declined in Deschampsia along with increasing successional age, whereas foliar N was not affected. Empetrum removal did not affect AM colonization but increased DSE sclerotial colonization especially at older successional stages. The observed decrease in foliar C coincides with an increase in canopy closure along with increasing successional age. We suggest that the shift from an AM-dominated to a DSE-dominated root fungal community in Deschampsia along a land uplift successional gradient may be related to different nutritional benefits gained through these root fungal groups.

Shifts in bacterial community structure during succession in a glacier foreland of the High Arctic.

Primary succession after glacier retreat has been widely studied in plant communities, but bacterial succession is still poorly understood. In particular, few studies of microbial succession have been performed in the Arctic. We investigated the shifts in bacterial community structure and soil physicochemical properties along a successional gradient in a 100-year glacier foreland of the High Arctic. Multivariate analyses revealed that time after glacier retreat played a key role in associated bacterial community structure during succession. However, environmental filtering (i.e. pH and soil temperature) also accounted for a different, but substantial, proportion of the bacterial community structure. Using the functional trait-based approach, we found that average rRNA operon (rrn) copy number of bacterial communities is high in earlier successional stages and decreased over time. This suggests that soil bacterial taxa with higher rrn copy number have a selective advantage in early successional stages due to their ability of rapidly responding to nutrient inputs in newly exposed soils after glacier retreat. Taken together, our results demonstrate that both deglaciation time and environmental filters play key roles in structuring bacterial communities and soil bacterial groups with different ecological strategies occur in different stages of succession in this glacier foreland.

Body mass distributions along successional gradients in epigeic carabid beetle fauna (Coleoptera: Carabidae)

Background and purpose: Body mass distributions may be related to the stage of succession of a habitat and provide with information for assessing successional processes. Therefore, body mass distributions of carabid assemblages were studied in three research areas, which were post-industrial areas near the city of Belchatow (Central Poland) planted with different tree and shrub species, moist and wet forest stands in the Puszcza Knyszynska forest (Northeastern Poland), and beech stands in the Ruhr valley (Western Germany) in order to analyze the changes in body mass distributions within single assemblages along successional gradients. Materials and Methods: For each carabid assemblage, the mean individual biomass (MIB) as well as MIB standard deviation (SD) and coefficient of variation (CV) were calculated. SD and CV were plotted against the age of study sites and MIB values, respectively. Analyses of Covariance (ANCOVA) were carried out with SD and CV as dependent variables and the age of study sites and MIB as covariates. Results: SD was low at young stages of succession, but increased rapidly and plateaued at advanced stages in beech but not in wet forest stands. Accordingly, CV was low at very young stages of succession, showing a rapid increase and subsequent decrease in the beech stands, whereas in the wet stands it stayed on a constant level. ANCOVA revealed significant differences in SD and CV between the research areas and significant changes with age or MIB, but, with the exception of CV as dependent variable and MIB as covariate, interactions were also significant. Conclusions: The results of the study suggest that data on body mass distributions within single carabid assemblages may be useful in the assessment and comparison of successional stages and processes between different habitat types.

Tree succession across a seasonally dry tropical forest and forest-savanna ecotone in northern Minas Gerais, Brazil

Aims: Understanding succession in tropical forest is an important aspect of vegetation science, but to date, successional processes in seasonally dry tropical forests (SDTFs) have received much less attention than evergreen humid tropical forests. We aim to fill this knowledge gap. Methods: We investigated vegetation succession in SDTF areas consisting of three different successional stages (early, intermediate, late), and a SDTF-savanna ecotone in the municipal district of Juramento, north of Minas Gerais State, Brazil. Using twelve 400 m(2) plots in each area, we compared vegetation parameters and structural variables (absolute density and basal area) and examined the floristic composition of the tree component to find gradients of change. Important Findings: We found evidence of species turnover along a successional gradient, with the intermediate stage showing the highest species richness and diversity. This was accompanied with a significant increase in the number of tree individuals and basal area from the early to intermediate successional stage. However, the intermediate and late SDTF successional stages were more similar in structure and floristics. The ecotone was the most species rich and was similar to the intermediate SDTF and early successional stage in species richness and floristic composition respectively. These results will have implications for guiding SDTF management and recovery programs.