Towards the reconstruction of the Holocene vegetation history of Lower Provence: two new pollen profiles from Marais des Baux

Two new¹⁴C-dated Holocene pollen profiles from Marais des Baux, Bouches-du-Rhône, France, are presented. The record begins in the Younger Dryas, when the vegetation consisted mainly of grasses and mugwort (Artemisia). The Preboreal was marked by a transitory expansion of pine forests and was followed by the establishment of a rich deciduous oak-forest that included hazel (Corylus) and elm (Ulmus). During the Boreal, hazel played a dominant role within the oak-forest. The oak forests, which includedQuercus ilex, achieved a major expansion during the Atlantic period. The Subboreal was characterised by the regional establishment of, firstly, fir (Abies) and then beech (Fagus). The spread and expansion of beech coincides with the first clear evidence for farming. Agricultural activities brought about the decline of deciduous oak-forest. During the Subatlantic, forests in the vicinity of Marais des Baux were cleared for farming. Cereal growing, which included rye cultivation, was of considerable importance. Three noteworthy characteristics that serve to differentiate the Holocene vegetation history of the low-lying Provence region from other French regions are as follows: 1) the early establishment (from the onset of Preboreal) of low altitude mixed forest; 2) the expansion during the Subboreal of fir and beech in low altitude areas with a Mediterranean climate and, 3) the exceptional taxonomic richness of the pollen assemblages (120 identified taxa) and the presence of borealalpine and Euro-Siberian taxa that no longer exist in Lower Provence.     

Effectiveness of repeated autumn and spring fires for understorey restoration in weed‐invaded temperate eucalypt woodlands

Question. Can strategic burning, targeting differing ecological characteristics of native and exotic species, facilitate restoration of native understorey in weed‐invaded temperate grassy eucalypt woodlands? Location. Gippsland Plains, eastern Victoria, Australia. Methods. In a replicated, 5‐year experimental trial, the effects of repeated spring or autumn burning were evaluated for native and exotic plants in a representative, degraded Eucalyptus tereticornis grassy woodland. Treatments aimed to reduce seed banks and modify establishment conditions of exotic annual grasses, and to exhaust vegetative reserves of exotic perennial grasses. Treatments were applied to three grassland patch types, dominated by the native grass Austrodanthonia caespitosa, ubiquitous exotic annuals, or the common exotic perennial grass Paspalum dilatatum. Results. The dominant native grass Austrodanthonia caespitosa and native forbs were resilient to repeated fires, and target exotic annuals and perennials were suppressed differentially by autumn and spring fires. Exotic annuals were also suppressed by drought, reducing the overall treatment effects but indicating important opportunities for restoration. The initially sparse exotic geophyte Romulea rosea increased in cover with fire and the impact of this species on native forbs requires further investigation. There was minimal increase in diversity of subsidiary natives with fire, probably owing to lack of propagules. Conclusions. While fire is often considered to increase ecosystem invasibility, our study showed that strategic use of fire, informed by the relative responses of available native and exotic taxa, is potentially an effective step towards restoration of weed‐invaded temperate eucalypt woodlands.     

Nutritional status of soil and plant species in several clearings in coniferous woods compared to that in two related habitats

Summary The nutritional status of the soils of a series of coniferous woodland clearings in the Netherlands was found to be intermediate between that of the soil in a dune area with a climax population of Chamaenerion angustifolium and that of the edge (and undergrowth) of a Quercus robur stand. In the dune area the greater part of the NPK was present as an internal pool in the plant tissues of C. angustifolium enabling the population of this species to persist and inhibiting further succession through limiting the availability of NPK. It is suggested that succession in clearings might stagnate in the same way in the absence of new tree growth. Because C. angustifolium is capable of persisting as a population under poor N conditions, it is unsuitable as an indicator species for nitrate-rich soils. The same may be true for Senecio sylvaticus, the other character species of the association Epilobio-Senecionetum sylvatici.A comparison of species in clearings with those occurring on the edge of a wood seems to indicate that, when using field measurements only (i.c. N_total and NO₃-N in the soil and in the plant tissues, and the activity of nitrate reductase in the leaves), conclusions may indeed be drawn concerning the adaptability of the species to a particular habitat factor (i.c. the availability of nitrate), but not concerning their requirements for that factor or how the species utilize it.Nomenclature follows Heukels & Van Ooststroom (1973).The authors are indebted to Foresters of the different areas studied.     

Preparation of lipid-free tissue extracts for chromatographic determination of thyroid hormones and metabolites

We have developed a new method of preparing tissues for analysis of thyroid hormones and metabolites which eliminates troublesome lipids and proteins. Frozen tissue is homogenized by grinding with dry ice in a Waring blender, and the moist powder obtained is extracted with chloroform:methanol (2:1). In a modification of the Folch procedure for the total separation of lipids, the filtered extracts then are partitioned into polar and nonpolar layers by the addition of 0.05% aqueous calcium chloride. The upper phase contains the iodocompounds of interest as well as all salts and small polar molecules. The lipids remain dissolved in the lower phase after it is back-extracted with pure upper phase. The combined upper or aqueous methanol layers are lyophilized and the residue is taken up in methanol to yield a concentrated solution ready for analysis of iodocompounds. The greater clarity of the extract permits application of larger samples for two-dimensional paper chromatography than has been customary. For gradient analysis by reverse-phase ion-pair high-performance liquid chromatography (HPLC), the nitrogen-evaporated methanol extract is dissolved in the initial mobile phase, 0.1% H₃PO₄, for injection onto the column. Using these methods we have achieved the first reported separation of ¹²⁵I-labeled tissue iodothyronine metabolites by HPLC. The new method of extraction is of general applicability to any biological sample which might be analyzed in thyroid hormone metabolism research.     

Closed forest or open woodland as natural vegetation in the surroundings of Linearbandkeramik settlements?

Deciduous woodland can be reconstructed as the potential vegetation cover of most parts of the Chernozem (black earth) loess areas settled by the early Neolithic farmers of the Bandkeramik culture in the sixth millennium b.c. The character of the woodland as closed, with few light-demanding plants, or more open is very important for the potential of an agricultural system. Botanical results are not able to indicate the composition of the woods quantitatively, but they can give indirect hints. It is discussed whether these archaeobotanical results, in combination with the characteristics of the wild and domesticated herbivores identified, can be interpreted with regard to the density of the woodland cover in Neolithic times. The use of the floodplains as pasture is interpreted from pollen analytical results.     

Characteristics of free air carbon dioxide enrichment of a northern temperate mature forest

In 2017, the Birmingham Institute of Forest Research (BIFoR) began to conduct Free Air Carbon Dioxide Enrichment (FACE) within a mature broadleaf deciduous forest situated in the United Kingdom. BIFoR FACE employs large‐scale infrastructure, in the form of lattice towers, forming ‘arrays’ which encircle a forest plot of ~30 m diameter. BIFoR FACE consists of three treatment arrays to elevate local CO₂ concentrations (e[CO₂]) by +150 µmol/mol. In practice, acceptable operational enrichment (ambient [CO₂] + e[CO₂]) is ±20% of the set point 1‐min average target. There are a further three arrays that replicate the infrastructure and deliver ambient air as paired controls for the treatment arrays. For the first growing season with e[CO₂] (April to November 2017), [CO₂] measurements in treatment and control arrays show that the target concentration was successfully delivered, that is: +147 ± 21 µmol/mol (mean ± SD) or 98 ± 14% of set point enrichment target. e[CO₂] treatment was accomplished for 97.7% of the scheduled operation time, with the remaining time lost due to engineering faults (0.6% of the time), CO₂ supply issues (0.6%) or adverse weather conditions (1.1%). CO₂ demand in the facility was driven predominantly by wind speed and the formation of the deciduous canopy. Deviations greater than 10% from the ambient baseline CO₂ occurred <1% of the time in control arrays. Incidences of cross‐contamination >80 µmol/mol (i.e. >53% of the treatment increment) into control arrays accounted for <0.1% of the enrichment period. The median [CO₂] values in reconstructed three‐dimensional [CO₂] fields show enrichment somewhat lower than the target but still well above ambient. The data presented here provide confidence in the facility setup and can be used to guide future next‐generation forest FACE facilities built into tall and complex forest stands.     

Mid to late Holocene vegetation and land use history in the Weald of south-eastern England: multiple pollen profiles from the Rye area

The High Weald is an unusually well-wooded area in southern England. A high proportion of this woodland is ancient, being formerly exploited as seasonal pasture and coppice. Multiple pollen profiles from the Rye area have been used to elucidate the origins of this cultural landscape. By combining sites with small and large pollen source areas, both local and regional patterns of vegetation change have been determined. The mid-Holocene Tilia-dominated woodlands were subjected to temporary clearance as early as the Neolithic. This woodland was more extensively exploited over a ca. 700 year period from the beginning of the Bronze Age. The main elements of the modern landscape (woodland, pasture and limited cultivation) can be traced back to a more intensive phase of human activity, which commenced in the late Bronze Age. A regional increase in Fagus sylvatica pollen ca. 750 B.C. probably reflects the use of the Wealden woods for pasturage. There is no palynological evidence that the fuel demands of the Roman iron industry resulted in widespread woodland destruction. The early Anglo-Saxon period appears to have been one of land-use continuity, with a second increase in Fagus pollen at ca. A.D. 700 corresponding to historical evidence for the presence of wood-pastures in the Weald.     

Response of the soil seed‐bank of Cumberland Plain Woodland to heating

Abstract Soil was investigated in a Cumberland Plain Woodland community to determine the presence of a soil seed‐bank and whether species richness and abundance of plants germinating from it were affected by heating such as that experienced in a fire. Soil samples were taken from the Holsworthy Military Area, in the south‐eastern region of the Sydney Basin, New South Wales, Australia, and one of four treatments was applied; soil was heated to 80°C, 40°C, unheated or unheated with litter not removed. Sixty‐eight species, representing 26 families including 11 exotic and 57 native species germinated from the soil. Herbs and grasses dominated and were in similar proportions to those surveyed in the above‐ground vegetation, suggesting that the soil seed‐bank reflected the current structure of the vegetation, although species composition differed. Species responded differently to heating. The seeds of some species germinated when heated at a higher temperature (80°C), particularly those from the family Fabaceae, whereas other species were more common in unheated or lightly heated samples (40°C). This suggests that fire is likely to change the species composition of the above‐ground vegetation and indicates that management must ensure that species that do not germinate when heated are maintained, as well as those species that germinate following heating. A large proportion of soil seed‐bank species showed low germination rates in the trials, and 112 above‐ground species did not germinate in the soil samples. We do not understand whether species of these two sets do not produce a soil‐stored seed‐bank or whether the seed‐bank has been depleted by past practices at Holsworthy. Further research is needed.     

黄土高原林草水土保持有效盖度分析

根据黄土高原缓德,延安、安寨和离石等地林、草地径流小区降雨侵蚀资料,对不同降雨和坡度下林、草地水土保持有效盖度进行了分析,建立了林地、草地水保持临界有效盖度与降雨坡度的关系式,在土壤和植被类型相对稳定的条件下,林、草地的有效盖度随着降雨和坡度的增大而增大,当临界有效盖度达到一定程度时,降雨和坡度的影响减弱;在其它条件相同时,同一水土保持作用所需求的有效盖度草地比林地大。并结合降雨频率分析,得出了林     

Competition between Quercus petraea and Carpinus betulus in an ancient wood in England: seedling survivorship

Abstract. Age structures of populations of canopy trees in Wormley Wood are consistent with reports that successional change is occurring, with Carpinus betulus replacing Quercus petraea as the dominant species. TWINSPAN analysis of data from a vegetation survey identifies three communities (described in earlier work), the ‘Bracken’, ‘Bramble’, and‘Bareground’ societies, characterized by increasing prominence of C. betulus and loss of species diversity. An experiment was set up in which C. betulus, Q. petraea and Betula pendula seedlings were explanted into each of the communities. Survival of seedlings was monitored over 860 days and differences investigated. Cohort survivorship differed between species and sites. C. betulus seedlings survived longer than Q. petraea in Bracken and Bramble communities. Species- and site-specific variation in the types and effects of herbivory were found. Herbivory did not appear to be a critical factor in the survival of Q. petraea seedlings. The photosynthetic light response of the seedling species was measured in the field. The light compensation point for Q. petraea seedlings (77 μmol photon m^-2 s^-1) is higher than the maximum available light under the main tree canopies in the wood. In contrast, seedlings of C. betulus have a lower light compensation point (15 μmol photon m² s^-1) and the mature tree casts a deeper shade than Q. petraea. It is suggested that the invasion of the canopy by C. betulus, following the cessation of coppicing, is creating light levels too low for Q. petraea seedling banks to persist.