Response of overstory and understory vegetation 37 years after prescribed burning in an aspen-dominated forest in northern Minnesota,USA – A case study

Many studies have examined short-term changes in understory vegetation following prescribed burning. However, knowledge concerning longer term effects on both forest understory and overstory vegetation is lacking. This investigation was initiated to examine changes in understory (herbaceous and shrub) and overstory species composition almost four decades after logging and prescribed burning at the Pike Bay Experimental Forest in Minnesota. The experiment was established in 1964 with a randomized block design with four treatments: control (c); burned in spring 1967 (S0); burned in spring 1967 + repeat burn spring 1969 (S2); and burned in spring 1967 + repeat burn fall 1970 (F4). Overstory and understory species diversity indices and richness varied within and among treatments but were not strongly or consistently affected by the treatments. Multivariate analyses (multi-response block permutation procedures and non-metric multidimensional scaling) reveal some lingering effects of burning intensity and seasonal variation as well as some compositional differentiation among treatments, but only in the herb layer. In this environment, the effects of two repeated burnings (fire) have essentially disappeared for overstory and understory species diversity and community composition and have failed to convert an aspen-dominated stand to a coniferous stand (an original goal of the study).     

Nine years of climber community dynamics in a Nigerian lowland rain forest 31 years after a ground fire

Successional studies in tropical forests have generally emphasized the tree component, ignoring the community dynamics of non-tree life-forms, and so there is a limited understanding of how the plant community as a whole is changing during succession within forests. Thus, this study examined the changes in climber community composition and structure in a regenerating secondary lowland rain forest at Ile-Ife that was ravaged by a ground fire 31 years ago using six sample plots. All individual climbers in each sample plot were identified, enumerated and their girths at breast height were measured. The girths were measured at 1.3 m height or just before the point of branching. Our data were compared with those of previous studies in the forest to determine the changes in floristics and structure of climber community over the years using Sorenson’s similarity index. The mortality and recruitment rates in the forest during the course of succession were determined. Climber species increased from 49 (2005) to 61 (2014). Climber density increased astronomically from 448–1152 ha^?1 (2005) to 1712–4492 ha^?1 but basal area only increased slightly from 0.37–1.10 m² ha^?1 (2005) to 0.40–1.14 m² ha^?1. The recruitment rate (8%) was higher than the mortality rate (5.8%). The similarity of the climber species composition calculated using the Sorenson similarity index showed that the similarity between the two periods of study was 0.53 (53%). This study concluded that during the study period, the climber community changed, and climber species abundance and structure increased.     

Lignin properties in topsoils of a beech/oak forest after 8 years of manipulated litter fall: relevance of altered input and oxidation of lignin

Background and aims

We studied the response of lignin oxidation in soils of a beech/oak forest to changes in litter fall. Additionally we considered possible factors in lignin oxidation, including altered (i) input of fresh organic matter and (ii) fungi-to-bacteria ratios.

Methods

The field-based experiment included (i) doubling and (ii) exclusion of litter fall and (iii) controls with ambient litter fall. Soil (0–20 cm depth) was sampled after 8 years. We analyzed (i) lignin using the CuO oxidation method, (ii) stocks of free and mineral-bound organic carbon (OC), (iii) the response of soil organic matter (SOM) decomposition to addition of labile organic compounds in laboratory incubations, and (iv) ratios of fungal- vs. bacterial-derived amino sugars (F/B ratios).

Results

Litter exclusion increased stocks of free-light fraction OC, F/B ratios, the ability of the microbial community to use labile compounds for SOM decomposition, as well as acid-to-aldehyde ratios of vanillyl-type lignin phenols in A horizons. Litter addition had no such effects. We assume that litter exclusion caused enhanced transport of organic debris from lower forest floor horizons with rainwater into the A horizon. Enhanced input of organic debris might have increased (i) the availability of labile compounds and (ii) F/B ratios. Consequently, lignin oxidation increased.

Conclusions

Enhanced input of organic debris from forest floors can increase lignin oxidation in mineral topsoils of the studied forest. The expected gradual changes in litter fall due to climate change likely will cause no such effects.     

Mid-term successional patterns after fire of mixed pine–oak forests in NE Spain

This study analyzes the factors affecting the current variability in density and age and size structure of mixed pine–oak forests of Pinus nigra and Quercus faginea in Central Catalonia (NE Spain), 37 years after a wildfire. The objective is to determine whether different post-disturbance responses may be obtained from the same pre-fire community and which factors can determine these different potential responses. The two factors analyzed were the distance to the unburned forest and site conditions (represented in this case by different aspects). The response of pines and oaks was different to the pattern expected for the Mediterranean Basin. Oaks resprouted immediately from stools already present before the fire and dominated during the first years, independent of both disturbance and site conditions. Pines established later, and their response depended on both factors: pine density decreased sharply from the forest edge to the burned area, and the number of pines was also higher in the more mesic than in the more xeric conditions. The age structure analysis for pines and oaks in the different aspects also revealed site-dependent rates of succession manifested by initial differences in post-fire establishment. In mesic plots, the establishment of pines occurred quite early, while in xeric plots, pine recruitment was delayed several years. These different patterns of post-fire recovery have led to pine dominance in more mesic sites and codominance of pines and oaks in more xeric ones, suggesting that different mid-term post-fire patterns can be identified for the same pre-fire forest type, depending on variations in environmental conditions.     

Contrasting responses of two Sitka spruce forest plots in Ireland to reductions in sulphur emissions: results of 20 years of monitoring

Long-term trends in ion concentrations of bulk precipitation, throughfall, forest floor leachate (humus water) and shallow and deep soil water were assessed at two Sitka spruce (Picea sitchensis) stands—one on an Atlantic peat bog in the west of Ireland (Cloosh), the other on the east coast on a peaty podzol (Roundwood). Deposition at Cloosh was dominated by marine ions (sodium, [Na⁺], chloride [Cl^?], and magnesium [Mg²⁺]), whereas bulk precipitation and throughfall at Roundwood was characterized by inputs of non-marine sulphate (nmSO₄ ^2?), acidity and inorganic nitrogen (NH₄ ⁺, NO₃ ^?). Significant declines in concentrations of nmSO₄ ^2? and acidity in bulk precipitation and throughfall were observed at both sites. The decline in throughfall nmSO₄ ^2? was significantly related to reductions in European sulphur dioxide (SO₂) emissions. At Roundwood, SO₄ ^2? declined significantly in humus, shallow and deep soil water. In deep soil water this was accompanied by a long-term increase in pH and a reduction in total aluminum (Al_tot). The recovery from acidification was delayed by high concentrations of NO₃ ^?, which strongly influenced acidity and Al_tot concentrations. At Cloosh, there was a significant decline in SO₄ ^2? in humus water but long-term trends were not evident in shallow or deep soil water; SO₄ ^2? concentrations at these depths fluctuated in response to drought-events. Marine ions strongly influenced soil water chemistry at both sites; at Cloosh soil water acidity was strongly related to Na⁺ and Cl^?, while at Roundwood, Na⁺, Cl^? and Mg²⁺ influenced Al_tot concentrations. Dissolved organic carbon increased significantly in humus and soil water at Roundwood, where it was associated with declining acidity. Soil water at both sites was influenced by a combination of anthropogenic sulphur (S) and nitrogen (N) deposition, drought and sea-salt events. The study highlights the value of long-term monitoring in assessing the response of forest soils to S and N deposition against a background of climate influences on soil water through drought and sea-salt events.     

Temporal dynamics and resilience of fine litterfall in relation to typhoon disturbances over 14 years in an old-growth lucidophyllous forest in southwestern Japan

We examined fine litterfall fluctuations on a seasonal and annual scale for 14 years (1992–2005) in a 1.2-ha plot in an old-growth lucidophyllous (evergreen broad-leaved) forest within the Aya Research Site, southwestern Japan. The average total litterfall input was 6.32 Mg ha^–1, of which leaf litter accounted for 60% of the total. Two high-impact typhoons struck the study area in 1993 (T9313) and 2004 (T0416) during the observation period; however, the subsequent pattern of litterfall after disturbance was different between the two typhoons. T9313 disturbance caused a reduction of biomass (ca. 10% of basal area (BA)) and a sharp decrease in litterfall input following a massive input in 1993. On the other hand, T0416 caused a minor decline in litterfall input, accompanied by a relatively small reduction of BA (5.2% of the 2001 BA). In spite of large fluctuations, litterfall input increased year by year after the T9313 disturbance. In 2000, 7 years after T9313, leaf input showed no significant differences and recorded more than 90% of pre-T9313 levels. Re-leafing from typhoon survivors may play an important role in the recovery of litterfall input in this forest. This study demonstrated how one high-impact typhoon can alter the temporal fluctuations in fine litterfall in lucidophyllous forest ecosystems.     

Sustained enhancement of photosynthesis in mature deciduous forest trees after 8 years of free air CO2 enrichment

Carbon uptake by forests constitutes half of the planet’s terrestrial net primary production; therefore, photosynthetic responses of trees to rising atmospheric CO₂ are critical to understanding the future global carbon cycle. At the Swiss Canopy Crane, we investigated gas exchange characteristics and leaf traits in five deciduous tree species during their eighth growing season under free air carbon dioxide enrichment in a 35-m tall, ca. 100-year-old mixed forest. Net photosynthesis of upper-canopy foliage was 48% (July) and 42% (September) higher in CO₂-enriched trees and showed no sign of down-regulation. Elevated CO₂ had no effect on carboxylation efficiency (V _cmax) or maximal electron transport (J _max) driving ribulose-1,5-bisphosphate (RuBP) regeneration. CO₂ enrichment improved nitrogen use efficiency, but did not affect leaf nitrogen (N) concentration, leaf thickness or specific leaf area except for one species. Non-structural carbohydrates accumulated more strongly in leaves grown under elevated CO₂ (largely driven by Quercus). Because leaf area index did not change, the CO₂-driven stimulation of photosynthesis in these trees may persist in the upper canopy under future atmospheric CO₂ concentrations without reductions in photosynthetic capacity. However, given the lack of growth stimulation, the fate of the additionally assimilated carbon remains uncertain.     

Changes in community structure and species–landform relationship after repeated fire disturbance in an oak-dominated temperate forest

Landform has long been considered one of the primary controls on forest community structure; however, it is still unclear how the strength of such species–topography couplings varies in response to recurring disturbance events. We evaluated this question in the context of repeated prescribed fire applied to a forest landscape in eastern Kentucky, USA. The landscape encompassed different areas of varying treatment frequencies: no fire, less frequent fires (two times, 6-year interval), and frequent fires (four times, 1 or 2-year interval) over 8 years. For each of 32 plots (10 m × 40 m), species–landform data were collected seven times between 2002 and 2010. Results of canonical correspondence analysis showed generally decreasing importance of terrain attributes to the overall tree species composition, during and after the period of fire disturbance. Before fire, species composition showed high fractal dimensions and low Moran’s I, implying that the complex terrain of the area provided local, site-specific topographic controls on community structure. As fire was repeatedly applied, fractal dimensions decreased and Moran’s I increased, indicating that plots possessed increasingly similar vegetation characteristics regardless of site-specific terrain conditions; that is, local topography no longer acted as the primary driver of species composition because such a short-range spatial control became overwhelmed by a longer-range variation dictated by fire. Following a period of fire disturbance, forest modelers are recommended to avoid species distribution modeling heavily based on topographic parameters and to explicitly take into account potentially increasing spatial autocorrelation in species composition.     

Formation of forest gaps accelerates C,N and P release from foliar litter during 4 years of decomposition in an alpine forest

High-latitude boreal and arctic surface/inland waters contain sizeable reservoirs of dissolved organic matter (DOM) and trace elements (TE), which are subject to seasonal freezing. Specifically, shallow ponds and lakes in the permafrost zone often freeze solid, which can lead to transformations in the colloidal and dissolved fractions of DOM and TE. Here, we present results from experimental freeze-thaw cycles using iron (Fe)- and DOM-rich water from thaw ponds situated in Stordalen and Storflaket palsa mires in northern Sweden. After ten cycles of freezing, 85% of Fe and 25% of dissolved organic carbon (DOC) were removed from solution in circumneutral fen water (pH 6.9) but a much smaller removal of Fe and DOC (< 7%) was found in acidic bog water (pH 3.6). This removal pattern was consistent with initial supersaturation of fen water with respect to Fe hydroxide and a lack of supersaturation with any secondary mineral phase in the bog water. There was a nearly two- to threefold increase in the low-molecular-weight (LMW) fraction of organic carbon (OC) and several TEs caused by the repeated freeze-thaw cycles. Future increases in the freeze-thaw frequency of surface waters with climate warming may remove up to 25% of DOC in circumneutral organic-rich waters. Furthermore, an increase of LMW OC may result in enhanced carbon dioxide losses from aquatic ecosystems since this fraction is potentially more susceptible to biodegradation.     

Celebrating 20 years of historical papers in Photosynthesis Research

This Editorial has four goals: (1) to inform the readers of ‘Photosynthesis Research‘ about the past of the ‘Historical corner’; which began 20 years ago; (2) to encourage photosynthesis researchers and historians of science to contact me for publishing papers of historical interest; these include: (a) Obituaries and Tributes; (b) historical papers on current and past discoveries and controversies; (c) history of research in specific laboratories, or in specific countries, or at specific conferences; (d) Personal perspectives (not discussed any further); (3) to encourage researchers not to discard, but to save correspondence and data of their discoveries for the future historians by donating them to their Archives, when appropriate (not discussed any further); and (4) to reinforce to the readers that the concept of two-light reaction and two-pigment system was already there in 1959. I mention here three key papers presented at the IX^th International Botanical Congress, held at Montreal Canada (in August, 1959) prior to the famous April 9, 1960 paper by Robert Hill and Fay Bendall on the ‘Z-scheme’ of photosynthesis, that was based on thermodynamic and energetic considerations. ^★ This Historical corner Editorial is dedicated to Bessel Kok (1918–1978).     

Speedy blooming in Cerrado after fire is not uncommon: New records of Cyperaceae species flowering 24 h after burning

Fire-stimulated flowering has long been a subject of investigation in tropical grasslands and savannas. Still, speedy blooming (i.e. flowering in <24 h after fire) had only been recently described for a single species of Cyperaceae common in Cerrado open ecosystems. Here, we described two new species displaying this unique feature of producing flowers <24 h after fire, suggesting that this fast phenological response might be more common than previously thought. Rhynchospora confusa F.Ballard and Rhynchospora terminalis Nees ex Steud. var. terminalis are two widely distributed species in grasslands and savannas at Chapada dos Veadeiros (a World Natural Heritage by UNESCO). Yet, there is a paucity of herbarium collection for both species and no registration of the quick bloom after fire passage or other aspects of their ecology. Understanding the diversity of phenological patterns and vegetation responses to fire is key to uncovering the functioning and singularities of the tropical open ecosystems.     

Potential for marker-assisted selection for forest tree breeding: lessons from 20 years of MAS in crops

For the most part, molecular markers and detection of quantitative trait loci have been developed for forest tree species in view to performing marker-assisted selection (MAS). However, MAS has not been applied to forest trees until now. In parallel, some success stories of MAS in crop breeding have been reported. Recently, genotyping techniques have undergone a tremendous increase in throughput, moving the trend from MAS to genomic selection. We analyzed 250 papers reporting the use of MAS in plant breeding and found that the most popular schemes used were gene pyramiding and marker-assisted backcross manipulating a single or very few genomic regions which have a major impact on crop value. We reviewed theoretical and simulation studies to identify the parametric space in which MAS is expected to bring about significant advantages over phenotypic selection. Then, we tried to explain why MAS has not been applied to forest trees and discuss the opportunities offered by recent advances in these species.     

Erosion of insect diversity in response to 7000 years of relative sea-level rise on a small Mediterranean island

We have investigated the potential effects of global sea-level rise on Mediterranean coastal wetlands by studying the Coleoptera and pollen fossil remains in a 7000-year sedimentary record, which we obtained from a coastal marshy area on a small Mediterranean island (Cavallo, southern Corsica). Using beetle structural diversity and plant composition as recorded prior to marine and human influences as a ‘past analogue’, we reconstructed the impact of the Holocene relative sea-level rise on the coastal ecosystem. Our results show that beetle species richness and diversity were highest when freshwater was predominant, which was the case until about 6200 years ago. We also found that a major increase in salinity had occurred over the last 5300 years, experiencing a peak rate of increase at about 3700 years ago. These changes are clearly reflected in the fossil records of the following key taxa: halophilous beetles (Ochthebius sp., Pterostichus cursor), halophilous plants (Chenopodiaceae, Tamarix) and non-pollen palynomorphs (microforaminiferal linings). In particular, we note that the majority (60%) of wetland beetle fauna became locally extinct in response to the salinity changes, and these changes were exacerbated by the recent aggravation of human pressures on the island. The major part of this diversity loss occurred 3700 years ago, when the relative Mediterranean sea-level rose above ?1.5 ± 0.3 meters. These findings demonstrate the value of fossil beetle assemblage analysis as a diagnostic for the response of coastal wetland biodiversity to past salinity increases, and serve as a means of forecasting the effects of sea-level rise in the future. The conservation of inland freshwater bodies could ultimately prove essential to preserving freshwater insect diversity in threatened coastal environments.     

Seasonal dynamics of shoot biomass of dominant clonal herb species in an oak–hornbeam forest herb layer

Seasonal fluctuations of light availability, nutrient concentrations, and moisture affect plant population traits like density, standing biomass, and flowering. We analyzed seasonal changes of density and shoot biomass of the four most frequent herb species growing in an oak–hornbeam forest community, i.e., Anemone nemorosa, Ficaria verna, Galeobdolon luteum, and Galium odoratum. In 2010 and 2011 plant biomass was harvested from 7 to 10 randomly situated square sample plots (0.36 m²) in the homogenous oak–hornbeam forest community every week in the spring and every two weeks in the summer and autumn. The highest abundance of Anemone nemorosa reached over 1000 shoots per m², of Ficaria verna 459.5 shoots per m², of Galium odoratum 83.6 shoots per m², and of Galeobdolon luteum 98.4 shoots per m² (means for 2010 and 2011, based on all sample plots). We did not observe negative correlation between density and shoot biomass. Growth rates of vegetative shoot biomass amounted to 0.857 mg day^?1 for Anemone nemorosa, 0.467 mg day^?1 for Ficaria verna, 0.722 mg day^?1 for Galium odoratum, and 0.448 mg day^?1 for Galeobdolon luteum (means for 2010 and 2011). Spring ephemerals had much higher densities of shoots than summer-greens. Summer-greens reached higher biomass of individual shoots than spring ephemerals. Flowering shoots constituted only 4, 2, and 11% of all shoots for A. nemorosa, F. verna, and G. odoratum, respectively. More resource availability resulting in high shoot biomass did not translate to higher share of flowering shoots.

     

Molecular-level changes in soil organic matter composition after 10 years of litter,root and nitrogen manipulation in a temperate forest

With climate change, forests are expected to receive increased inputs of carbon (C) and nitrogen (N) but it is unclear how this will modify forest C cycling and storage at the molecular-level. To investigate the response of forest soil organic matter (SOM) to changes in soil inputs, a study area was established in a Michigan hardwood forest as part of the Detrital Input and Removal Treatments (DIRT) network. Experimental treatments were comprised of both exclusions of detrital inputs (No Litter, No Roots, No Inputs) and additions of C and N (Double Litter, N-Addition, Double Litter?+?N, Wood). After 10 years of treatment, the soils were characterized using elemental analysis, molecular biomarker techniques, nuclear magnetic resonance spectroscopy, and microbial biomass C measurements. Although manipulation of detrital inputs did not significantly change the soil C and N content after 10 years, alterations in the cycling and distribution of SOM components were observed. Root exclusion enhanced SOM degradation, while doubling litter favoured the degradation of more labile forms of soil C such as unsaturated n-alkanoic acids and simple sugars. N-Addition and Double Litter?+?N increased the concentrations of extractable biomarkers, including aliphatic and cyclic lipids and compounds derived from cutin, suberin, and lignin. Microbial biomass C also varied with experimental litter input manipulations and N addition, and these data were consistent with the observed changes in SOM composition. Overall, the observed shifts in SOM chemistry after 10 years of manipulating ecosystem inputs highlight the sensitivity of natural systems to changes in amounts of C and N inputs from roots and litter, and N inputs from external sources.     

Initial pedogenesis in a topsoil crust 3 years after construction of an artificial catchment in Brandenburg, NE Germany

Cyanobacteria and green algae present in biological soil crusts are able to colonize mineral substrates even under extreme environmental conditions. As pioneer organisms, they play a key role during the first phases of habitat colonization. A characteristic crust was sampled 3 years after installation of the artificial water catchment “Chicken creek”, thus representing an early successional stage of ecosystem development. Mean annual rainfall and temperature were 559 mm and 9.3°C, respectively. We combined scanning electron microscopy (SEM/EDX) and infrared (FTIR) microscopy to study the contact zone of algal and cyanobacterial mucilage with soil minerals in an undisturbed biological soil crust and in the subjacent sandy substrate. The crust was characterized by an approximately 50 μm thick surface layer, where microorganisms resided and where mineral deposition was trapped, and by an approximately 2.5 mm thick lower crust where mineral particles were stabilized by organo-mineral structures. SEM/EDX microscopy was used to determine the spatial distribution of elements, organic compounds and minerals were identified using FTIR microscopy and X-ray diffraction (XRD). The concentration of organic carbon in the crust was about twice as much as in the parent material. Depletion of Fe, Al and Mn in the lower crust and in the subjacent 5 mm compared to the geological substrate was observed. This could be interpreted as the initial phase of podzolization. Existence of bridging structures between mineral particles of the lower crust, containing phyllosilicates, Fe compounds and organic matter (OM), may indicate the formation of organo-mineral associations. pH decreased from 8.1 in the original substrate to 5.1 on the crust surface 3 years after construction, pointing to rapid weathering of carbonates. Weathering of silicates could not be detected.     

Determination of the gas exchange phenology in an evergreen coniferous forest from 7 years of eddy covariance flux data using an extended big-leaf analysis

We defined gas exchange phenology as the seasonality of the gas exchange characteristics of a forest canopy, and investigated how the gas exchange phenology could be directly detected from an eddy covariance (EC) dataset and its influence on the canopy fluxes within an evergreen Japanese cypress forest. For the detection of gas exchange phenology, we derived three bulk parameters of the extended big-leaf model (Kosugi et al. 2005) inversely from EC flux data over a 7-year period: surface conductance (g _c), maximum rate of carboxylation of the “big leaf” (V _CMAX), and intercellular CO₂ concentration of the “big leaf” (C _I). The relationship between g _c and the vapor pressure deficit declined in winter and spring. The relationship between the daily ecosystem respiration and air temperature was greater in the spring than in the other seasons. The temperature dependence curve of V _CMAX decreased substantially in the winter and was different from that of an evergreen broadleaved forest. A decrease in C _I was occasionally coupled with the decrease in canopy gross primary production during April and August, indicating that stomatal closure was responsible for a decline in canopy photosynthesis. Gas exchange phenology should be quantified when understanding the determining factors of the seasonality of canopy fluxes at evergreen coniferous forests.     

Invasive rats and seabirds after 2,000 years of an unwanted coexistence on Mediterranean islands

In the Mediterranean, the survival of endemic long-lived seabirds despite the long-standing introduction of one of the most damaging alien predator, the ship rat (Rattus rattus), on most islands constitutes an amazing conservation paradox. A database gathering information on approximately 300 Western Mediterranean islands was analyzed through generalized linear models to identify the factors likely to influence ship rat presence and to account for how ship rat presence and island characteristics may have driven the presence and abundance of seabirds. Our review showed that few Mediterranean islands remain rat-free. At the regional scale, rat presence was only a limiting factor in the abundance of the smallest seabird, the storm petrel (Hydrobates pelagicus), while the distribution and abundance of the three shearwaters were more influenced by island characteristics. We hypothesized that the long-term persistence of these seabirds may have been facilitated by the various biogeographical contexts of Mediterranean islands, likely to provide intra-island refuges.