Middle Successional Stages Research Articles

Nutrient cycling aspects as possible ecosystem functional indicators of successional stage in Semideciduous seasonal forest, Rio de Janeiro state, Brazil

Semideciduous Seasonal Forest is a phytophysiognomy of Atlantic Forest with high plant richness but low representativeness in few remnants areas in different successional stages. The assessment of the degree of conservation of those areas helps to indicate whether there is a need for taking strategies to favor forest succession. Thus, the aim of this study was to identify litterfall and its nutrient content, accumulated litter biomass on topsoil, leaf litter decomposition, and topsoil (0–10 cm) chemical attributes as possible indicators of successional stages in areas of Seasonally Semideciduous Forest. We collected available information in literature on CAPES Portal and Google Scholar (May/2021 to February/2022) for Pinheiral municipality, State of Rio de Janeiro, Brazil, which were evaluated by multivariate analysis. Accumulated litter biomass, nutrient content (N, P, K) in total litterfall, pH and P availability in topsoil, leaf litter decomposition constant, and half-life time of leaf litter were the most sensitive attributes to indicate the successional stage in the study area, according to Principal Component Analysis. This multivariate analysis indicated that areas in early successional stage were associated with higher values of leaves contribution, half-life of leaf litterfall, contents of Ca and K in total litterfall, whereas areas in middle successional stage were associated with higher values of pH, total organic carbon, exchangeable Ca2+, K+, and Mg+, sum of bases and cation exchange capacity, and lower values of extractable acidity and exchangeable Al3+ in the topsoil. Areas in advanced stages of succession were associated to higher values of total litterfall and its nutrient content (N, K, Mg), accumulated litter biomass, available P in topsoil, and leaf litter decomposition constant. The Cluster multivariate analysis revealed that the areas in advanced successional stage presented high dissimilarity in relation to the areas in early and middle successional stage.

Above- and Belowground Plant Functional Composition Show Similar Changes During Temperate Forest Swamp Succession.

Plant functional composition, defined by both community-weighted mean (CWM) traits and functional diversity, can provide insights into plant ecological strategies and community assembly. However, our understanding of plant functional composition during succession is largely based on aboveground traits. Here we investigated community-level traits and functional diversity for six pairs of analogous leaf and fine root traits of understory plants in a temperate forest swamp during succession with a decrease in soil pH and nutrient availability. CWMs of traits related to resource acquisition (including specific leaf area, specific root length, leaf N, leaf P, root N, and root P) decreased with succession, whereas those related to resource conservation (leaf dry matter content, root dry matter content, leaf tissue density, leaf C, and root C) increased along the forest swamp successional gradient. Multi-trait functional dispersion (FDis) of both leaf and fine root traits tended to decrease along the successional gradient, but functional richness and evenness were highest at the middle successional stage. Moreover, FDis of individual plant traits except N showed the same pattern as multi-trait FDis. Soil pH and nutrient availability were the main drivers of successional changes in both CWM traits and FDis. The changes of community-level traits along succession indicated a shift from acquisitive to conservative strategy of understory plants during forest swamp succession. Similar trends in leaf and fine root functional diversity along succession may indicate above- and belowground functional diversity are coordinated during the processes of plant community assembly. These findings of linkages between above- and belowground plant functional composition have important implications for plant community dynamics and assembly rules.

Effects of Soil Properties and Plant Diversity on Soil Microbial Community Composition and Diversity during Secondary Succession

Soil microbial communities play an important role in maintaining the ecosystem during forest secondary succession. However, the underlying mechanisms that drive change in soil microbial community structures during secondary succession remain poorly defined in species-rich subtropical coniferous forests. In this study, Illumina high-throughput sequencing was used to analyze the variations in soil microbial community structures during forest secondary succession in subtropical coniferous forests in China. The role of soil properties and plant diversity in affecting soil bacterial and fungal communities was determined using random forest and structural equation models. Highly variable soil microbial diversity was observed in different stages of secondary succession. Bacterial community diversity rose from early to middle and late successional stages, whereas fungal community diversity increased from early to middle successional stages and then declined in the late stage. The relative abundance of Acidobacteria, Gemmatimonadetes, Eremiobacterota(WPS-2), Rokubacteria, and Mortierellomycota increased during succession, whereas the relative abundance of Ascomycota and Mucoromycota decreased. The community composition and diversity of the soil microbial community were remarkably influenced by plant diversity and soil properties. Notably, tree species richness (TSR) displayed a significant and direct correlation to the composition and diversity of both bacterial and fungal communities. The carbon-to-nitrogen (C:N) ratio had a direct impact on the bacterial community composition and diversity, and pH had a marked impact on the fungal community composition and diversity. Furthermore, succession stage and plant diversity indirectly impacted the composition and diversity of soil bacterial and fungal communities via soil properties. Overall, it can be concluded that soil intrinsic properties and plant diversity might jointly drive the changes in soil microbial community composition and diversity during secondary succession of subtropical coniferous forests.

Development of Nutrient Uptake by Understory Plant Arrhenatherum elatius and Microbial Biomass during Primary Succession of Forest Soils in Post-Mining Land

The development of plant and soil microbial communities is one of the basic preconditions for the restoration of functional ecosystems. However, nutrients are concurrently used by plants and microbes, and the dynamics of this interaction during ecosystem development have seldom been studied. The aim of our study, thus, was to describe the dynamics of nutrient availability in soil and, at the same time, the nutrient accumulation in plant and microbial biomass along an unassisted primary succession heading toward broadleaf forest. The growth of the understory plant Arrhenatherum elatius on soils originating from three (16, 22, and 45 years’ old) successional stages of a post-mining area and the development of the microbial community in the presence or absence of this plant were studied in a pot experiment. Both, the plant biomass and carbon (C) in microbial biomass in intermediate and late middle successional stages were higher than those in the early stage. In soil, extractable organic C, extractable organic nitrogen (N), and inorganic N increased with proceeding succession, but Olsen phosphorus (P) peaked in the intermediate successional stage. The amounts of N and P in plant and microbial biomass increased during succession. In the late middle successional stage, the amount of P in microbial biomass exceeded that of plant bound P approximately twice, and this increase was higher in pots with plants than without. The results imply that the competition between plants and microbes for available P may increase microbial P uptake and, thus, hinder plant growth in later successional stages.

Changes in Plant Functional Groups during Secondary Succession in a Tropical Montane Rain Forest

Aggregating diverse plant species into a few functional groups based on functional traits provides new insights for promoting landscape planning and conserving biodiversity in species-diverse regions. Ecophysiological traits are the basis of the functioning of an ecosystem. However, studies related to the identification of functional groups based on plant ecophysiological traits in tropical forests are still scarce because of the inherent difficulties in measuring them. In this study, we measured five ecophysiological traits: net photosynthetic capacity (Amax), maximum stomatal conductance (gmax), water use efficiency (WUE), transpiration rate (Trmmol), and specific leaf areas (SLA) for 87 plant species dominant in a chronosequence of secondary succession, using four time periods (5 year-primary, 15 year-early, and 40 year-middle successional stages after clear cutting and old growth) in the tropical montane rainforest on Hainan Island, China. These species were grouped using hierarchical cluster analysis and non-metric multidimensional scaling. Finally, the changes in the composition of functional groups and species richness along the chronosequence were analyzed. Results showed that the plant species in the tropical montane rainforest could be classified into eight distinct functional groups. The richness of functional groups was low during the initial early stage and increased as the early and middle stages progressed, and then declined in the late successional stage. The dominant functional groups in the primary stages had the highest Amax, gmax, Trmmol, and SLA, as well as the lowest WUE, while those in the early and middle successional stages had functional traits at a moderate level, and at the late stage they had the lowest Amax, gmax, Trmmol, and SLA, and highest WUE. Our study showed that the diverse plant species in the tropical montane rainforest could be grouped into a few functional groups according to major ecophysiological traits, and the composition and relative abundance of different groups changed with the successional dynamics of the forest ecosystem.

Variations of bacterial and fungal communities along a primary successional chronosequence in the Hailuogou glacier retreat area (Gongga Mountain, SW China)

New terrestrial habitats have emerged and a primary succession has developed in the retreat area (29A degrees 34'N, 102A degrees 00'E, 2951-2886 m) after the retreat of the Hailuogou glacier. To investigate soil microbial changes along the primary successional chronosequence, mixed soil samples were collected at six sites at different ages (2 young sites, 2 mid-aged sites, and 2 old sites). The RNA was extracted and amplified. Bacterial 16S rRNA and fungal 18S rRNA were analyzed using high-throughput 454 pyrosequencing analysis. Overall, pyrosequencing showed that Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria were the main bacterial phyla, and the fungal communities were strongly dominated by the phyla Ascomycota and Basidiomycota in the retreat area. The Shannon diversity index (H-shannon) of bacteria was 6.5-7.9, and that of fungi was 2.2-4.1 in these sites. For the bacterial communities, diversity and evenness values were highest on the mid-age sites and were relatively low on the young and old sites. A similar trend was observed for the fungal communities. In contrast, soil properties showed significant linear distributional trends (increase or decrease) with the age of the site. Combining the linear change patterns of soil properties, the highest values of bacterial and fungal evenness and diversity in the mid-aged sites indicated that there was less environmental stress and more niches for microbial communities in the middle successional stage compare with other stages. In addition, our analysis showed that microbial communities were the main drivers that build a soil organic matter pool to expedite pedogenesis for ecosystem succession. This primary succession in the Hailuogou glacier retreat area is developing rapidly compared with that in other glacier retreats.

Disturbance, complexity, and succession of net ecosystem production in North America's temperate deciduous forests

AbstractCentury‐old forests in the U.S. upper Midwest and Northeast power much of North America's terrestrial carbon (C) sink, but these forests' production and C sequestration capacity are expected to soon decline as fast‐growing early successional species die and are replaced by slower growing late successional species. But will this really happen? Here we marshal empirical data and ecological theory to argue that substantial declines in net ecosystem production (NEP) owing to reduced forest growth, or net primary production (NPP), are not imminent in regrown temperate deciduous forests over the next several decades. Forest age and production data for temperate deciduous forests, synthesized from published literature, suggest slight declines in NEP and increasing or stable NPP during middle successional stages. We revisit long‐held hypotheses by EP Odum and others that suggest low‐severity, high‐frequency disturbances occurring in the region's aging forests will, against intuition, maintain NEP at higher‐than‐expected rates by increasing ecosystem complexity, sustaining or enhancing NPP to a level that largely offsets rising C losses as heterotrophic respiration increases. This theoretical model is also supported by biological evidence and observations from the Forest Accelerated Succession Experiment in Michigan, USA. Ecosystems that experience high‐severity disturbances that simplify ecosystem complexity can exhibit substantial declines in production during middle stages of succession. However, observations from these ecosystems have exerted a disproportionate influence on assumptions regarding the trajectory and magnitude of age‐related declines in forest production. We conclude that there is a wide ecological space for forests to maintain NPP and, in doing so, lessens the declines in NEP, with significant implications for the future of the North American carbon sink. Our intellectual frameworks for understanding forest C cycle dynamics and resilience need to catch up to our more complex and nuanced understanding of ecological succession.

Decadal change of forest biomass carbon stocks and tree demography in the Delaware River Basin

Quantifying forest biomass carbon (C) stock change is important for understanding forest dynamics and their feedbacks with climate change. Forests in the northeastern U.S. have been a net carbon sink in recent decades, but C accumulation in some northern hardwood forests has been halted due to the impact of emerging stresses such as invasive pests, land use change and climate change. The Delaware River Basin (DRB), sited in the southern edge of the northern hardwood forest, features diverse forest types and land-use histories. In 2001–2003, the DRB Monitoring and Research Initiative established 61 forest plots in three research sites, using Forest Service inventory protocols and enhanced measurements. These plots were revisited and re-measured in 2012–2014. By comparing forest biomass C stocks in the two measurements, our results suggest that the biomass C stock of the DRB forest increased, and was thus a carbon sink over the past decade. The net biomass C stock change in the Neversink area in the north of the DRB was 1.94MgCha−1yr−1, smaller than the biomass C change in the French Creek area (2.52MgCha−1yr−1, southern DRB), and Delaware Water Gap Area (2.68MgCha−1yr−1, central DRB). An increase of dead biomass C accounted for 20% of the total biomass C change. The change of biomass C stocks did not correlate with any climatic or topographic factors, but decreased with increasing stand age, and with tree mortality rate. Mortality rates were highest in the smallest size class. In most of the major tree species, stem density decreased, but the loss of biomass from mortality was offset by recruitment and growth. The demographic changes differ dramatically among species. The living biomass of chestnut oak, white oak and black oak decreased because of the large mortality rate, while white pine, American beech and sweet birch increased in both biomass and stem density. Our results suggest that forests in the DRB could continue to be a carbon sink in the coming decades, because they are likely at a middle successional stage. The linkage between demography of individual trees species and biomass C change underscores the effects of species-specific disturbances such as non-native insects and pathogens on forest dynamics, and highlights the need for forest managers to anticipate these effects in their management plans.

Changes in soil respiration and its temperature sensitivity at different successional stages of evergreen broadleaved forests in mid-subtropical China

Aims Studies on the influences of forest succession on soil respiration (Rs) and its temperature sensitivity (Q10) are controversial, leading to uncertainties in the accuracy of global carbon budget. Our objectives were to deter- mine: (1) changes of Rs and Q10 in a succession series of mid-subtropical forests, (2) seasonal variations of Rs and its relationships with temperature and water content, and (3) the underlying mechanism of changes in Rs with suc- cession. Methods We selected stands of an evergreen broadleaved forest at the early successional stage (15 years), mid- dle successional stage (47 years), and late successional stage (110 years) under similar site conditions in Jian'ou, Fujian. Monthly Rs was measured by using an infrared gas exchange system from September 2009 through August 2010. Soil temperature and moisture were measured concurrently. The relationships of Rs with annual litterfall, fine root biomass, contents of soil organic carbon (SOC) and total nitrogen (TN) in the 0-20 cm soil layer were tested by linear regression analysis Important findings The average values of Rs were 2.38, 3.32 and 3.91 µmol·m -2 ·s -1 , and the average values of Q10 were 2.64, 1.97 and 1.79, respectively, in the early, middle, and late successional stages. Compared to in the early successional stage, Rs was increased significantly by 64.29% while Q10 was decreased by 32.30% in the late successional stage. The seasonal patterns of Rs were similar among the three successional stages; soil temperature and water content explained 69.5%, 81.9% and 61.3% of the seasonal variations. According to regression analysis, soil respiration was positively correlated with annual litterfall, fine root biomass, and contents of SOC and TN in the 0-20 cm soil layer. Succession promoted carbon emission and reduced soil respiration sensitivity in our study, which might be related to the increases in fine root biomass, carbon input and soil nutrient with forest succession.

Quantifying ecological memory during forest succession: A case study from lower subtropical forest ecosystems in South China

The concept of ecological memory provides a new perspective for research on forest succession by including historical factors and the initial state of ecological processes. However, there are still significant gaps between the concept and its application. We selected nine proxy indicators (plant species, soil seed banks, soil microbes, soil animals, birds, soil age, soil pollen, soil mineral distribution, and light environment) and developed a method to quantify ecological memory and succession in a subtropical forest succession in South China. Taking the climax-monsoon evergreen broad-leaved forest as the reference ecosystem, we found that ecological memory increased nonlinearly and accumulated following a specific assembly rule during succession. Memory concerning major soil microbes and soil animals, which improve the soil substrate, mainly accumulated from the initial to the early successional stage. Memory concerning the number of bird species and the availability of light, which ensure a source of regenerative seeds and the survival of understory seedlings, mainly accumulated from the early to middle successional stages. Memory concerning vegetation and soil seed banks mainly accumulated late in succession, guaranteeing that the ecosystem would reach the regional climax stage. Prospective memory was greater than retrospective memory in every successional stage except the late stage, which indicated that all stages but the late stage were undergoing progressive succession. Our study demonstrates that the concept of ecological memory and the proposed evaluation framework are useful for guiding research on succession and restoration, and especially for assessing how “far” a restored ecosystem is from a reference ecosystem or how far a restored ecosystem has deviated from its natural succession trajectory.

Fitossociologia de uma floresta secundária com Araucaria angustifolia (Bertol.) O. Kuntze na Estação Ecológica de Bananal, Bananal, SP

In the present work, we aimed to evaluate successional forest stage and horizontal, vertical and diametric structures of upper and under strata on a secondary forest stretch under Araucaria angustifolia on the Bananal Ecological Station, Sao Paulo state, Brazil. During upper stratum survey (circumference at breast height (CBH) > 15 cm), 43 permanent plots of 10 × 20 m were established. In each plot, five sub-plots of 1 × 1 m were randomly allocated for under stratum (total height > 30 cm and CBH <15 cm) survey. Regarding upper stratum, density and dominance were estimated on 2142 ind./ha and 32.49 m2/ha, respectively, in absolute total values. Concerning under stratum, total absolute density was estimated on 48,302 ind./ha. The diametric structure of the community follows the J-invert pattern, which was not observed for Brazilian Pine population, compromising its maintenance in the community. The auto-ecology of the species supports the catalyzation of secondary succession under its crown, which was classified at middle successional stage.

Plant diversity patterns in subtropical evergreen broad‐leaved forests of Yunnan and Taiwan

AbstractThe subtropical evergreen broad‐leaved forests of Yunnan and Taiwan were compared along environmental and successional gradients with the aim of identifying important taxon and species diversity as well as the drivers of mountain biodiversity patterns. A detrended correspondence analysis of an exhaustive set of data collected from 105 and 223 plots for Yunnan and Taiwan, respectively, was applied to classify natural mature forest types. Additional data from 72 and 68 plots for Yunnan and Taiwan, respectively, were used for analyses of secondary succession. The floristic richness and diversity index were calculated for each type of forest. In Yunnan, the monsoon forests in mesic‐humid sites had more taxa and tended to show higher species diversity than the other two forest types. In Taiwan, species diversity values were significantly higher in the Machilus–Castanopsis zone in the middle altitudes (500–1500 m) than for the other three forest zones. For both Yunnan and Taiwan, the forests at the middle successional stage showed significantly higher species diversity than those at the early successional stage. Differences in diversity between the middle and late stages were not significant. These findings highlight the high species diversity of the natural mature evergreen broad‐leaved forests of both Yunnan and Taiwan. In the secondary forests, as succession proceeds, species diversity comes to resemble that of the natural mature forests. In both ecosystems, the drivers of species diversity patterns are moisture, altitude, and succession/disturbance.

Contrasting genetic diversity and differentiation of populations of two successional stages in a Neotropical pioneer tree (Eremanthus erythropappus, Asteraceae)

Eremanthus erythropappus, commonly known as "candeia", is an abundant pioneer tree species, forming dense populations known as "candeial", but it is also found in forests at middle stages of succession. Trees from forests are bigger and occur in lower density than in the "candeial". The objectives of the present study were to investigate if the decrease in population density during successional process is accompanied by 1) changes in within-population genetic diversity, and 2) differentiation of populations. Eight populations, four of early successional stage ("candeial") and four of middle successional stages (forest), were analyzed with RAPD markers. The genetic diversity found was high compared to other tree species analyzed with RAPD markers. AMOVA revealed that most of the genetic variations of E. erythropappus were found within populations (85.7%), suggesting that this species is predominantly outcrossing. The relatively low differentiation among the populations can be attributed to small distances among the populations analyzed (0.2 to 10.8 km). No indication that populations from middle successional habitats show lower genetic variation than populations from early successional stages was found. The percentage of polymorphic fragments (82.8 and 84.8%) and the Shannon indexes (0.442 and 0.455) were similar in "candeial" and forest, respectively. These results suggest that if an increase in selection intensity occurred during succession, it did not result in a decrease in genetic diversity or that the selection effect was balanced by other factors, such as gene flow. Higher significant differentiation among E. erythropappus populations from "candeial" in relation to that among populations from forest was also not detected.

Impact of forest management on the diversity of corticolous bryophyte assemblages in temperate forests

This study aimed at comparing the composition, the structure and the organisation of corticolous bryophyte assemblages (recorded within a 400 m 2 plot) between three silvicultural managements widely conducted in Europe: Even-Aged pure beech Forest (EAF), Coppice With Standards system (CWS) and Selective Cutting systems (SC). The stands used for the study were located in two neighbouring regions of northern France. Comparisons were performed using a functional approach based on species’ ecological requirements and life traits combined with multivariate analyses. Along the silvicultural cycle of the EAF, stand age and canopy opening were the main ecological factors influencing corticolous bryophyte assemblages. Old stands with a low canopy cover contained all the functional groups, with a preponderance of late successional and obligatory shade species. The regeneration stage appeared to be an outlier because of its lowest species richness. Although the same functional groups occurred in CWS and SC as in EAF, the bryophyte assemblages shared compositional and structural characteristics similar to those of EAF early and middle successional stages. This indicates that successional processes are not maintained by these management types and that the latter do not seem to favour late successional-obligatory shade species. EAF successional stages, CWS and SC did not exhibit differences in the relative species richness (i.e. the ratio between the number of species within the 400 m 2 plot (SR) and the richness of the local species pool) except for EAF regeneration stands. The results are used to propose practical ecological background information for the elaboration of forest management policies.

SPECIES DIVERSITY OF BUTTERFLIES IN TURKISH PINUS BRUTIA FOREST ECOSYSTEMS AFTER FIRE

This study aimed to determine changes in the species diversity of butterflies after fire in Pinus brutia forests. At four study sites representing different successional stages, butterflies were sampled by line transect method using sweep nets and by visual observation. In total, 18 species and 114 individuals were found at all sites. Although the species richness and species diversity of butterflies were higher in middle successional stages, abundance decreased with successional age. The changes in butterfly abundance, species richness and diversity with successional age resulted mostly from structural differences in the vegetation.

Effects of a nutrient pulse supply on nutrient status of the Mediterranean trees Quercus ilex subsp. ballota and Pinus halepensis on different soils and under different competitive pressure

Nutrient availability is a key factor in Mediterranean ecosystems that affects the primary productivity and the community structure. The great variability of its natural availability is now increasing due to frequent fires, pollution events and changes in rainfall regime associated to climate change. Quercus ilex ssp. ballota and Pinus halepensis are the most abundant tree species in the NW Mediterranean basin. They frequently compete in the early and middle successional stages. We investigated the effects of N and P pulse supplies on nutrient uptake capacity in these two species in an after-fire field area and in nursery conditions on different soil types and competing conditions. In the field, N fertilisation had weak effects on nutrient concentration and mineralomass likely as a consequence of this nutrient not being limiting in this field site whereas P fertilisation increased the P mineralomass and the Mg, S, Fe, K and Ca concentrations and mineralomass in the different biomass fractions of both species 1 and 3 years after fertilisation application. In the nursery experiments, P fertilisation increased the mineralomass and concentrations of P, Mg, S, Fe, K and Ca in all biomass fractions including the roots in both species and in different soils and competition conditions. The increment of nutrient mineralomass was due to both the increase of growth and of nutrient concentrations. Both species were able to absorb significant amounts of the P applied by fertilisation (between 5 and 20%) in short time (18 months). Competing vegetation decreased the positive effects of P fertilisation, and in many cases the negative effect of competing vegetation on nutrient mineralomass was stronger when P availability was increased by fertilisation. Q. ilex subsp ballota showed a greater competitive ability for P than the more pioneer species Pinus halepensis in the field but not in the nursery conditions. Pinus halepensis had greater nutrient mineralomass in calcareous than in siliceous soils. Q. ilex subsp. ballota had a higher root biomass allocation and root nutrient allocation than P. halepensis, but both species showed a high capacity to increase their nutrient uptake when its availability increased by fertilisation, thus assuring a great nutrient reserve for future growth periods and contributing to retain nutrients in the ecosystem.

Bird Community Dynamics along Primary Successional Gradients of an Amazonian Whitewater River

We used spot-map methods to census birds in two plots (40 ha and 80 ha) representing the early and middle stages of primary succession generated by the meandering of the Manu River in southeastern Peru in 1983 and 1985. We distinguished seven distinct successional stages beginning with the first plant communities growing on open beaches (Tessaria: stage 1) and proceeding through mature floodplain forest (stage 7). Each successional stage was more structurally and floristically complex. One plot was dominated by early successional vegetation (stages 1-5) and the other was domi- nated by middle-to-late stages (5-6). We supplemented spot-map data with mist netting to census nonterritorial species, principally nectarivores and frugivores. Because the ear- liest successional stage (Tessaria) covered only small (<3 ha) areas on any given me- ander tongue, we censused six additional stands to characterize their bird communities. Species richness increased along the successional gradient, but not uniformly. Struc- turally simple Tessaria stands (stage 1) contained more diverse communities of breeding birds than the next two successional stages, which appeared to have few resources avail- able to birds. After stage 3, breeding species richness increased by 31-71 species per successional stage as a distinct canopy layer formed (stage 4), fruiting trees became more available (stages 5-6) and the vertical structure of the forest became fully developed (stage 7: 71 more species than stage 6). Early successional bird communities (stages 1- 3) were dominated by a few very abundant insectivores and omnivores, but wanderers from the adjacent forest plus Nearctic and austral migrants seasonally outnumbered breeding residents. Many species that breed in Tessaria stands were restricted to just one or two of the seven stands censused. The middle stages of succession had the highest estimated richness, abundance, and biomasses of nectarivores and frugivores. Nectarivore abundance reflected the huge stands of Heliconia that dominate the understory of mid- successional stages. Bark foragers reached their highest abundance in late successional stages as the dominant canopy tree species of middle successional stages (e.g., Cedrela odorata) began to die off, but remained standing. Middle successional stages lacked many of the insectivores characteristic of more structurally complex mature forest. Among the missing species were understory Mockers, ant-followers, ground foragers, and many arboreal insectivores that participate in canopy flocks. Species of early and middle stages tended to be more abundant on average than those of mature forest. Early-/and late-successional bird communities had few species in common, and many congeners segregated along this successional gradient. Most species characteristic of early successional vegetation, however, were also found in many other kinds of natural and anthropogenic disturbances. The Tessaria beaches of the Manu lacked most species endemic to the same successional stage on the larger rivers in the Amazon system. Mid-successional stages had relatively fewer species restricted to them, but some of these species are rare and endemic to southwestern Amazonia. Many char- acteristic species of floodplains reached their peak abundances in stages 4-6. Mid-suc- cessional stages, therefore, may play a greater role in contributing to the unusually high species richness of western Amazonia than had previously been recognized. These results point to the importance of preserving natural, undammed meandering rivers in conserving the avian diversity of Amazonia. Logging and agricultural devel- opment of mid-successional floodplain forests probably has a negative impact on regional bird communities. Not all species of the early and middle stages of succession have adapted to human-generated secondary succession. Recovery of the full diversity and richness of tropical bird communities following disturbance may take several hundred

Seasonal and successional dietary shifts of two sympatric rodents in coastal heathland: A possible mechanism for coexistence

Abstract Using microscopic analysis of faecal pellets, we compared the seasonal and successional patterns of food resource use of two Australian native rodents, the eastern chestnut mouse (Pseudomys gracilicaudatus) and the swamp rat (Rattus lutreolus) in a coastal heathland at Myall Lakes National Park, New South Wales. Using the Mantel test, the diets of the two mammal species were significantly different in autumn and winter but not in spring and summer. Further, the two species showed differential use of resources at the young and middle‐aged stages of vegetation succession following fire. The mean dietary overlaps for pairs of individuals between the two species were relatively high in all seasons and successional stages, but they were significantly lower than those for pairs of individuals within each species in autumn and winter, and at the young and middle successional stages. Analysis of dietary niche position (γ) and breadth (β) showed lower γ and larger β for P. gracilicaudatus than for R. lutreolus, confirming previous observations that R. lutreolus is more specialized, and less opportunistic in diet than P. gracilicaudatus. Overall, the dietary separations of the two species were less marked in canonical space than they were for specific seasons and successional stages. These results, together with previous studies, indirectly suggest that while these two mammal species may be partitioning diet in autumn and winter in the middle stages, for spring and summer in the old successional stage they might need to partition habitats to facilitate their coexistence. Our results indicate that the local community is more dynamic and complex than previously thought and that other mechanisms of coexistence (e.g. temporal rotation of food resources) may be operating rather than traditional habitat and diet separation.

Competitive effects of Rattus lutreolus presence on food resource use by Pseudomys gracilicaudatus

Abstract We examined faecal samples of the eastern chestnut mouse (Pseudomys gracilicaudatus) that were collected during a removal experiment conducted in a coastal heathland at Myall Lakes National Park to see whether removal of the swamp rat (Rattus lutreolus) had any effects on food resource use by P. gracilicaudatus. The results showed that, at the young successional stage of vegetation (1. 5 years since last fire), the diet of P. gracilicaudatus changed significantly after the number of R. lutreolus was significantly reduced on the experimental sites. Two months after the removal treatment was terminated there were no significant differences between the control and experimental sites. Factor analysis showed that seasonal change was significant for all three food factors on the control sites, whereas on experimental sites the change was significant only for factor 1. At the middle successional stage (3.5 years since last fire), P. gracilicaudatus showed relatively small seasonal changes on both control and experimental sites, and significant differences between the control and experimental sites did not occur until after the removal manipulation was completed, showing a delayed response. Comparisons of the young and the middle successional stages on both control and experimental sites showed that P. gracilicaudatus used proportionally different food when R. lutreolus was present, but consumed similar food when R. lutreolus was removed. These results suggest that R. lutreolus might have restricted the access of P. gracilicaudatus to better microhabitats, and hence to a better food supply. The ecological implication of these results is that the interpretation of observed population and community patterns must take into account the direct effects of species interactions.

Diet of the eastern chestnut mouse (Pseudomys gracilicaudatus). II Seasonal and successional patterns

The seasonal and successional changes of the diet of P. gracilicaudatus was examined by microscopic analysis of faecal pellets collected in a coastal heathland of New South Wales. Overall, five major dietary items (leaf, stem, seed, fungi and insect), which accounted for more than 95% of the total diet, showed significant seasonal changes. The Mantel test demonstrated that the diet of P. gracilicaudatus significantly differed between all seasons. At different successional stages of the habitat, the consumption of the dietary items leaf, stem and insect were significantly different. The overall diet at the middle successional stage was significantly different from those at the other two stages, between which the diet was not significantly different. However, when the comparison was made in summer, the differences between the young and old stages were significant for most dietary items and overall. As a result, a significant interaction of season and regeneration age on the diet of P. gracilicaudatus occurred. Such an interaction also extended to dietary diversity and among-individual variation. These results indicate that P. gracilicaudatus possesses an opportunistic foraging strategy that has evolved in a variable environment. They also have important take-home messages that any interpretation of observed ecological patterns and the design of future research for any species that appear to have evolved with such fire regimes must take into account such an interaction of season and vegetation succession.