The mid-Holocene (ca. 8000–4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000–7000 yr ago) and out of (ca. 5000–2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼ 5–36 yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7–4.0 vs. 0.6–1.7 mm2 cm− 2 yr− 1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming.

This study investigated the structure, diversity and composition of the regenerating shrub-tree species community along a stretch of riparian vegetation in relation to environmental heterogeneity. In the Environmental Protection Area of Pandeiros River, southeastern Brazil, the regenerating stratum on 70 plots (25 m2) divided into four groups according to their soil characteristics and natural barriers was sampled. For each plot observations were made of variables related to several soil properties, canopy openness and flooding regime. In addition to the traditional calculation of phytosociological parameters and diversity, a canonical correspondence analysis (CCA) to examine the existing relationships between environmental variables and species distribution was performed. The families with the highest species richness were Fabaceae and Myrtaceae and the species with the highest importance value indices were Zygia latifolia, Tapirira guianensis, Butia capitata, Bauhinia rufa and Hirtella gracilipes. The CCA largely confirmed the groups that were originally proposed. The stretch of riparian vegetation studied was highly heterogeneous with regard to both the abiotic variables tested and floristic structure and composition.

The testate amoeba, ciliate and rotifera communities living in interstitial waters in peatbog in eastern Poland were studied. Sampling was done on a monthly basis from April to November 2007–2008. Microbial communities were examined in a transect including three sites: (1) pine forest (site located 5 m from the lagg/forest contact zone), (2) lagg, (3) open peatbog (the centre of the peatbog). At each of the sites, interstitial water was sampled by means of piezometric wells placed to a depth of 1 m. The species richness and abundance of protozoa and rotifers significantly differed between the studied stations, with the lowest numbers in the pine forest and the highest in the lagg. These differences between macro-habitats may be due to differences in environmental conditions. The distribution of samples in ordination space led to conclude that studied habitats are distributed along the falling gradient of pH and rising gradient of total organic carbon, water table depth and nitrate nitrogen. Assemblages of all three groups showed a strong compositional gradient correlated with water-table depth, conductivity and total phosphorus. However, species composition of ciliates and rotifers was explained by nitrate nitrogen and/or phosphates concentrations. The results suggest that lagg zone of a raised bog can fulfil the function of an ecotone zone, distinguished by a significant increase in biodiversity, abundance and species specificity of micro-organisms. It can also be a place of very efficient matter and energy flow in a peat bog ecosystem.

The dry grasslands of the Mediterranean Basin have been traditionally managed since ancient times, but have been drastically degraded by recent human activities such as cultivation. Cultivated plots in a dry grassland of Southern France were abandoned more than 20 years ago, but their vegetation and ground-active beetle community structure and composition differ considerably from neighbouring uncultivated grassland plots. Because these formerly cultivated plots are adjacent to an uncultivated grassland area, they constitute a model system for examining beetle recolonization patterns on field margins. No edge effect or ecotone was identified on the margins between two of the formerly cultivated plots and the uncultivated dry grassland; there was no significant peak of beetles species richness in this area. All the most common dry grassland beetle species (mainly saprophagous and predatory species, which are less habitat-specialist than phytophagous species) had already recolonized the formerly cultivated plots. However, although uncultivated dry grassland was adjacent to the formerly cultivated plots it was insufficient for complete regeneration of dry grassland beetle communities on formerly cultivated plots, indicating habitat quality remained lower even after 20 years. Understanding the causes of spatial variation in active-ground beetles at the species level is important before the ecological restoration of habitat quality to its prior state, using the adjacent steppe as a reference.

Although it is well known that riparian zones can contribute strongly to between-habitat beta diversity, for most taxa it is not clear how far this ‘zone’ extends, and whether it corresponds to easily recognizable topographic features. Forty 200-m2 plots were installed in a terra firme tropical forest to detect compositional variation in terrestrial herbs from the margins of small streams to the uplands. Plots were ordinated by their dissimilarity in species composition with non-metric multidimensional scaling. The riparian zone around streams was distinct in understorey herb composition from upland areas for about 100 m from the streams, or about 70 m asl in elevation, the exact distance depending on the size of the stream valley. However, the only assemblage that was almost completely distinct occurred as a narrow band a few metres wide along the streams. The rest of the riparian zone appears to represent an ecotone with continuous change, most of which occurs out to a distance of about half the width of the riparian zone as we defined it. Although riparian zones are legally protected in Brazil, they are frequently degraded. The complex factors leading to zonation around streams need to be understood to effectively manage these areas.

The photosynthetic light response of Amazonian semi-deciduous forest trees of the rain forest–savanna transition near Sinop Mato Grosso, Brazil was measured between July 2000 and September 2003 to test the hypothesis that the photosynthetic capacity of trees acclimated to different growth light environments will decline during the dry season. Maximum photosynthesis (Amax) and stomatal conductance (gmax) were significantly higher during the wet season; however, the physiological response to drought was not a clear function of growth light environment. For some species, such as Psychotria sp. growing in the mid-canopy, internal leaf CO2 concentration (Ci) was >30% lower during the dry season suggesting that declines in Amax were caused in part by stomatal limitations to CO2 diffusion. For other species, such as Brosimum lactescens growing at the top of the canopy, Tovomita schomburgkii growing in the mid-canopy, and Dinizia excelsa growing in the understorey, dry season Ci declined by <20% suggesting that factors independent of CO2 diffusion were more important in limiting Amax. Dry-season declines in gmax appeared to be important for maintaining a more consistent leaf water potential for some species (T. schomburgkii and D. excelsa) but not others (Psychotria sp.). These results indicate that while seasonal drought exerts an important limitation on the physiological capacity of semi-deciduous Amazonian forest trees, the mechanism of this limitation may differ between species.

As part of the programme Écosystèmes et Paléoécosystémes des Forêts Intertropicales (ECOFIT,France),we are engaged in multisite comparative studies of how forests regenerate across ecotones such as those between forests and savannas (Vincens et al. 2000).One such ecotone comprises the forest succession from bare soil that occurs naturally on beach successions along meandering rivers. To gauge the development of foliar layers during succession and quantify changes of efficiency of the vegetation in capturing the available solar energy, we are measuring the Leaf Area Index (LAI) of transects within forests and across their edges.