Mesic Deciduous Forest Research Articles

Weak precipitation δ2H response to large Holocene hydroclimate changes in eastern North America

In eastern North America, annual precipitation increased by >40% over the Holocene, largely in response to melting of the Laurentide Ice Sheet. The change substantially raised lake levels and transformed conifer-dominated ecosystems into mesic deciduous forests. δ2H values of terrestrially derived leaf-wax n-alkanes can facilitate diagnoses of the climate dynamics involved by reconstructing δ2H values of mean annual precipitation (δ2HMAP). However, competing influences on δ2HMAP values in the mid-latitudes, such as changes in moisture sources and in the seasonal distribution of precipitation, can generate confounding effects. To test δ2HMAP sensitivity to potential changes associated with the final Holocene phases of deglaciation in eastern North America, we used 14 fossil-pollen records to reconstruct monthly precipitation changes and to model δ2HMAP values during the Holocene. The pollen-inferred precipitation increased by 100–200 mm during both cold and warm seasons, but modeled δ2HMAP values changed by only ∼10‰, because isotopically-heavy summer precipitation increased by nearly as much as the cold-season isotopically-light winter precipitation. Three new leaf wax n-C29-alkane (δ2HC29) records spanning the Holocene from Vermont, Pennsylvania, and Massachusetts closely follow modeled δ2HMAP trends and confirm only a small decline in δ2HMAP values over the Holocene. Because the shifts in precipitation seasonality accurately predict the n-alkane records, changes in moisture sources or pathways appear to play only a minor role in the regional δ2HMAP history despite the effects of deglaciation on atmospheric circulation. Soil evaporation also did not significantly alter δ2HC29 values from the values predicted using the pollen-derived reconstructions. The results affirm that δ2HC29 values faithfully detected anticipated isotopic changes in δ2HMAP values, but that important paleoclimate events may not always yield strong changes in δ2HMAP values.

Classification of European oak–hornbeam forests and related vegetation types

AbstractAimsOak–hornbeam forests and related vegetation types (phytosociological order Carpinetalia betuli) are widespread in temperate western Eurasia. However, their national classification systems are poorly compatible, and a broad‐scale classification based on numerical analyses is lacking. Therefore, we aimed to establish a unified formalized classification system based on a large data set of vegetation plots covering the entire range of these forests.LocationEurope, Anatolia, Caucasus and northern Iran.MethodsWe compiled a data set of 15,817 vegetation plots from the European Vegetation Archive and the Hyrcanian Forest Vegetation Database, using the formal definition of the EUNIS habitat type T1E Carpinus and Quercus mesic deciduous forest. We classified the data set using TWINSPAN. Biogeographically and ecologically similar plot clusters were merged into oak–hornbeam forest types, which were interpreted as alliances. We also developed expert systems for automatically classifying vegetation at the alliance level for both the EuroVegChecklist (EVC) system and the revised classification. In addition, we calculated ordinations to show the major gradients in the species composition of the data set.ResultsWe present a revised classification system of the order Carpinetalia betuli with nine alliances, including basic descriptions of their species composition, distribution, ecology and syntaxonomy. The analyses largely supported the biogeographic concept of classification, analogous to EVC. Compared to EVC, we recognized an additional alliance Physospermo verticillati‐Quercion cerridis (southern Italy) but found no support for the alliances Astrantio‐Carpinion, Erythronio‐Carpinion and Scillo‐Quercion. The greatest difference in species composition was found between the southern and northern‐northeastern Carpinetalia types. Expert systems for the revised classification system (~89% of plots classified) and the EVC system (~72%) are also included.ConclusionsWe provide the first comprehensive overview of alliances of the order Carpinetalia betuli across its whole distribution range. The associated expert systems allow consistent application of the classification of these forests in nature conservation, habitat monitoring, and biodiversity and ecological research.

Post-Glacial Climate–Fire Interactions Control Tree Composition of Mesic Temperate Forests in Eastern North America

Stand-scale gap-phase dynamics is generally viewed as the main driver of development in mesic deciduous forests of the temperate biome. Soil charcoal of temperate forests in eastern North America are unnoticed in most surveys, thus explaining why fire is undervalued as a driver of forest succession. The extent to which gap-phase, fire, or other processes are responsible for the regeneration and maintenance of mesic deciduous forests is unknown because paleoecological evidence is lacking. We tested the fire-driven succession hypothesis on the development of this major forest type. Based on charcoal 14C dates of two sites, 44 and 55 fires occurred since early Holocene, with a mean interval of 170 to 215 years. The vegetation of both sites followed comparable post-glacial trajectories consisting of three distinct periods. Conifers dominated the two first periods during 5200–6000 years and were replaced by hardwoods–conifers over the last 3500 years. The first period was represented by boreal conifers, whereas the second period, dominated by white pine (Pinus strobus) forests, persisted during 3000–4300 years. The third period marked the development of hardwood (sugar maple, Acer saccharum) forests. Fires occurred continuously on the sites since early Holocene likely under dry conditions during the conifer periods and cooler and moister conditions during the hardwood–conifer period. Recurrent fires appear with climate as key drivers of the long-term dynamics of several temperate forests in eastern North America. Similar studies on other temperate forests should be pursued to test the hypothesis of climate–fire interactions influencing tree composition change.

Value of large Quercus robur fallen logs in enhancing the species diversity of vascular plants in an old-growth mesic broad-leaved forest in the Central Russian Upland

Large old trees and decaying logs are key-retained structures for the retention forestry approach, but quantitative estimations of the role of fallen logs in the overall diversity and composition of forest vascular species are few and controversial. Particularly for mesic deciduous forests only a small number of such estimates are known. Our study aimed to partly fill this gap using data collected in the Reserve Kaluzhskie Zaseki where large Quercus robur individuals of more than 300 years old and fallen logs are frequent. We found 44 fallen oak logs supporting vascular plants within a 200-ha forest tract. The vegetation in plots of 1 m2 located on the fallen logs and on the forest floor adjacent to the logs was surveyed together with vegetation in fifteen 10 × 10 m plots randomly placed in patches without large fallen logs. NMDS and PERMANOVA were applied to examine differences in composition between fallen logs and forest floor. Generalized linear models were used to examine the relationships between environmental variables and species richness. Additive diversity partitioning was performed to examine differences in species richness and to estimate the contribution of the fallen logs to the general diversity in vascular species. In total, 71 vascular plant species in 108 1 m2-plots were identified. Twenty-five and 16 species were detected only on fallen logs and on the forest floor, respectively. More than 60% of the studied logs were in early stages of decomposition; their mean diameter was 75.4 ± 25.6 cm. Fallen logs significantly affected species richness and composition in terms of both woody seedlings and herbaceous species. The diameter of logs significantly and positively affected species diversity and composition. Large logs with cracked bark at the first two stages of decay were places of successful vascular plant establishment and growth. The abundance and frequency of tree seedlings were higher on the logs than on the forest floor and seven out of ten tree species appeared to be significant indicator species for the log-plots. Illumination varied over the observed sites and directly influenced the richness of herbaceous species and the overall species composition, but had no effect on woody species richness. We conclude that retention of large fallen logs can be an effective tool for maintaining and restoring the vascular species richness and composition in mesic broad-leaved forests.

Signatures of an abiotic decomposition pathway in temperate forest leaf litter

Photodegradation helps explain why leaf litter mass loss rates are comparable between mesic environments and drylands, despite water availability limiting decomposer activity in drylands. With photodegradation, light energy directly mineralizes photoreactive organic molecules such as lignin, which contrasts with biotically-driven decomposition where lignin persists in decomposing leaf litter relative to other compounds. Photodegradation of leaf litter has largely been studied in dryland systems, but whether it occurs in mesic, deciduous forest systems is uncertain. As such, we examined potential photodegradation in maple and oak litter in the Southern Appalachian Mountains (USA) during the non-growing season, when newly fallen leaves are exposed to maximum solar radiation without deciduous canopies. The proportion of oxidized lignin in the leaf litter relative to other carbon compounds decreased with maximum solar radiation during the non-growing season. With a closed canopy, however, the proportion of total lignin relative to other compounds in the leaves increased. This pattern was particularly strong for the syringyl- S6 and guaiacyl-G6 lignin monomers. The relative proportion of S6 and G6 in the litters was reduced by 10–65% in the first 5 months. The largest reductions in lignin occurred on south-facing mountain slopes where solar radiation was highest (relative to north-facing slopes) in the Northern Hemisphere. Overall, however, the changes in lignin did not alter cumulative litter mass lost. Our results suggest that photodegradation promotes the transformation and relative loss of lignin in the early stages of litter decomposition in mesic deciduous forests.

The Flora of a Mesic Forest Remnant in Iowa's Paleozoic Plateau: Malanaphy Springs State Preserve (Winneshiek County, Iowa)

We present the results of a floristic inventory and qualitative descriptions of the forest communities occurring in Malanaphy Springs State Preserve (MSSP), located in the Paleozoic Plateau of northeastern Iowa. Most of the 25.9-ha preserve is a mature mesic to dry-mesic deciduous forest community occurring on a steep slope adjacent to the Upper Iowa River. The preserve also contains a small floodplain forest as well as a small highly disturbed forest on the upland. We documented 422 plant taxa in our surveys, including 52 non-vascular taxa, 14 seedless vascular taxa, 3 gymnosperms, and 353 angiosperms. Eighty-seven percent of the vascular plant taxa are native, and 21% of the species have an Iowa coefficient of conservatism score of 7 or higher. Five species are listed by the Iowa Department of Natural Resources as endangered, threatened, or of special concern in the state. This survey provides critical baseline data needed to document future changes in the plant communities of MSSP. We conclude that this preserve is an important example of high-quality mesic deciduous forest communities in Iowa. We further conclude that the species diversity of the preserve is threatened by the cumulative impacts of habitat loss, high levels of deer herbivory, invasive species, nitrogen deposition, and climate change and that active management and strategic policy decisions will be needed to preserve native plant species diversity.

How will a drier climate change carbon sequestration in soils of the deciduous forests of Central Europe?

Global warming is accompanied by increasing water stress across much of our planet. We studied soil biological processes and changes in soil organic carbon (SOC) storage in 30 Hungarian oak forest sites in the Carpathian Basin along a climatic gradient (mean annual temperature (MAT) 9.6–12.1 °C, mean annual precipitation (MAP) 545–725 mm) but on similar gently sloped hillsides where the parent materials are loess and weathered dust inputs dating from the end of the ice age. The purpose of this research was to understand how a drying climate, predicted for this region, might regulate long-term SOC sequestration. To examine the effects of decreasing water availability, we compared soil parameters and processes in three categories of forest that represented the moisture extremes along our gradient and that were defined using a broken-stick regression model. Soil biological activity was significantly lower in the driest (“dry”) forests, which had more than double the SOC concentration in the upper 30 cm layer (3.28 g C/100 g soil ± 0.11 SE) compared to soils of the wettest (“humid”) forests (1.32 g C/100 g soil ± 0.09 SE), despite the fact that annual surface litter production in humid forests was ~ 37% higher than in dry forests. A two-pool SOM model constrained to fit radiocarbon data indicates that turnover times for fast and slow pools are about half as long in the humid soil compared to the dry soil, and humid soils transfer C twice as efficiently from fast to slow pools. Enzyme activity and fungal biomass data also imply shorter turnover times associated with faster degradation processes in the soils of humid forests. Thermogravimetry studies suggest that more chemically recalcitrant compounds are accumulating in the soils of dry forests. Taken together, our results suggest that the predicted climate drying in this region might increase SOC storage in Central European mesic deciduous forests even as litter production decreases.

A field experimental study on the impact of Acer platanoides, an urban tree invader, on forest ecosystem processes in North America

BackgroundInvasive species affect community dynamics and ecosystem functions, but the mechanisms of their impacts are poorly understood. Hypotheses on invasion impact range from Superior Competitor to Novel Function, from Enemy Escape to Microbial Mediation. In this study, we examined the effects of an urban tree invader, Acer platanoides (Norway maple, NM), on a mesic deciduous forest in contrast to its native congener Acer rubrum (red maple, RM) with a split-plot design experiment. A total of 720 maple seedlings were transplanted to 72 plots under 24 trees of three canopy types. The three experimental treatments were removal of resource competition at above- and belowground and removal of leaf-litter effect. Soil moisture and nitrogen-related microbial activities were followed for each plot.ResultsWe found that partial canopy removal increased canopy openness and light transmission to the forest floor, but to a greater extent under NM than under RM trees. NM seedlings were more shade tolerant than RM seedlings in height growth. During the reciprocal transplantation in the mixed forest, biomass accumulation of NM seedlings under RM trees were twice as much as under NM, while that of RM seedlings under NM trees was 23.5% less than under RM. Soil net nitrification and relative nitrification were significantly higher, but mineralization rate was much lower under NM than under RM trees, which would lead to faster N leaching and lower N availability in the soil. Plots with litter removal had significantly higher seedling mortality due to herbivory by the end of 2 years, especially for NM seedlings under NM trees. Trenching enhanced soil water availability but there was no difference among canopy types.ConclusionsOur results demonstrated that invasion of NM not only altered forest canopy structure but also changed herbivory rate for seedlings and N dynamics in the soils. NM seedlings were more shade tolerant under NM canopies than RM seedlings and were more protected by NM litter under NM canopies than under RM canopies. These altered biotic and abiotic environments will likely facilitate further invasion of NM in the forests, hence positive feedbacks, and make it an increasingly serious tree invader in North America.

Distribution and habitat preferences of the stag beetle Lucanus cervus (L.) in forested areas of Poland

The incorporation of Lucanus cervus (L.) in Annex 2 of the EU Habitats Directive imposed on EU member countries the obligation to prepare protection plans and undertake adequate measures aimed at the preservation of this species. A necessary precondition for their implementation was connected with the identification of current localities of L. cervus. This paper presents the distribution of L. cervus localities in Poland, identified on the basis of a survey conducted in the areas administered by the State Forests. Habitat preferences for the selection of biotopes by stag beetles were evaluated in terms of forest-site types. This will facilitate effective protection of L. cervus by indicating potential biotopes for this species, particularly in areas with high abundance. The survey showed the presence of L. cervus in 176 localities distributed in 47 forest districts. Most of them were found in three main areas comprising forests in the areas of Zielona Góra, Wrocław and the Świętokrzyskie Mts. They constitute large-scale refuges. In 98% of cases the development of L. cervus was associated with oaks Quercus robur and Quercus petraea. Other host plants included Fagus sylvatica and Acer pseudoplatanus. The age of trees colonised by stag beetles ranged from 70 to 248 years, 134 years on average. Lucanus cervus was most frequently found in deciduous mesic forest sites (41% of localities) and deciduous mixed mesic forest sites (24% of localities). Over 90% of recorded localities are situated in forested areas, understood to include stands, residual trees and stumps, as well as localities at forest edges and along roads in the vicinity of forests.

Drought sensitivity of an N2 -fixing tree may slow temperate deciduous forest recovery from disturbance.

Increased drought intensity and frequency due to climate change may reduce the abundance and activity of nitrogen (N2 )-fixing plants, which supply new N to terrestrial ecosystems. As a result, drought may indirectly reduce ecosystem productivity through its effect on the N cycle. Here, we manipulated growing season net rainfall across a series of plots in an early successional mesic deciduous forest to understand how drought affects the aboveground productivity of the N2 -fixing tree Robinia pseudoacacia and three co-occurring nonfixing tree species. We found that lower soil moisture was associated with reduced productivity of R.pseudoacacia but not of nonfixing trees. As a result, the relative biomass and density of R.pseudoacacia declined in drier soils over time. Greater aboveground biomass of R.pseudoacacia was also associated with greater total soil N, extractable inorganic N, N mineralization rates, and productivity of nonfixing trees. These soil N effects may reflect current N2 fixation by R.pseudoacacia saplings, or the legacy effect of former trees in the same location. Our results suggest that R.pseudoacacia promotes the growth of nonfixing trees in early succession through its effect on the N cycle. However, the sensitivity of R.pseudoacacia to dry soils may reduce N2 fixation under scenarios of increasing drought intensity and frequency, demonstrating a mechanism by which drought may indirectly diminish potential forest productivity and recovery rate from disturbance.

Resurrection of Carex ignota (Cyperaceae, section Laxiflorae), a long overlooked sedge of the southern U.S.A.

Since its publication in 1849, Carex ignota has been overwhelmingly ignored or treated as a synonym of C. striatula. Here, I present results of statistical analyses that support C. ignota as morphologically distinct from C. striatula and designate a lectotype for C. ignota. I also present the geography of C. ignota and C. striatula from over 750 examined and georeferenced specimens and results of maximum likelihood phylogenetic reconstruction of ddRAD loci. Carex ignota is distinguished from C. striatula by its narrower leaves on vegetative shoots, more loosely-flowered pistillate spikes, staminate spike with longer peduncles, and narrower perigynia. Based on strong morphologic and molecular evidence, C. ignota should be resurrected and treated as a distinct species. Carex ignota occurs on the Coastal Plain in the southeastern United States, as well as northern Alabama, the Ouachita in Arkansas, and the Piedmont in Georgia, where it grows in sandy to loamy soils in ravines and on slopes in mesic deciduous or mixed hardwood-conifer forests.

Managing fire in the mesic deciduous forest when fire history is unknown: response to Stambaugh et al.

Thanks to Stambaugh et al. (2015) for their close reading of my review (Matlack 2013) and thoughtful comments, criticisms, and suggestions. I hope this exchange is the beginning of a much-needed discussion on the use of fire in moist and mesic deciduous forests of the eastern United States (hereafter, MDF). The purpose of Matlack (2013) is to emphasize the fine-grained nature of fire as an ecosystem process and to call attention to gaps in our understanding. My concern is that we are rushing to subcontinent scale generalization on the basis of sparse and idiosyncratic data.

The relative controls on forest fires and fuel source fluctuations in the Holocene deciduous forests of southern Wisconsin, USA

AbstractReconstructing fire regimes and fuel characteristics is an important aspect of understanding past forest ecosystem processes. Fuel sources and fire regimes in the upper Midwestern United States have been shown to be sensitive to regional climatic variability, such as drought periods on millennial timescales. Yet, records documenting the connections between disturbance activity and the corresponding fuel source fluctuations in mesic deciduous forests and prairie/oak savanna in this region are limited. Thus, it has been difficult to provide a framework to evaluate changes in moisture availability on fire activity and the relationships with fuel source fluctuations in this region. We present high‐resolution charcoal analyses of lake sediments from four sites in southern Wisconsin (USA) to characterize fire activity and fuel source fluctuation in mesic deciduous forests and prairie/oak savanna over the last 10 000 years. We found that fire occurrence across the four study sites has been asynchronous throughout the Holocene, because of site‐specific differences that have strongly influenced local fire regimes. Additionally, we found that during periods of high fire activity the primary fuels were from arboreal sources, and during periods of low fire activity the primary fuels were from non‐arboreal sources. However, fluctuations in fuel sources did not always correspond to changes in vegetation, or changes in fire frequency.

Interactive effects of chronic deer browsing and canopy gap disturbance on forest successional dynamics

The interaction of browsing by white‐tailed deer (Odocoileus virginianus) and canopy gap disturbances may affect long‐term tree composition and lead to significant changes in forest structure. We used an individual‐based forest gap model (ZELIG) to better understand the aggregate and interactive impacts of these processes on the long‐term (200 years) successional dynamics of a mesic deciduous forest. We parameterized ZELIG to: (1) simulate successional dynamics within a temperate deciduous secondary forest typical of eastern North America; (2) simulate browsing impacts by white‐tailed deer; and (3) simulate gap‐scale disturbance of variable size and frequency. Our estimates of browsing impacts by species were derived from a 20‐year, four‐hectare deer exclusion study. Model calibration matched observed tree species composition, density by size class, and total basal area (39.92 m2 ha−1 vs. 37.13 m2 ha−1). Simulated deer browsing had little impact on total basal area over two centuries. However, deer browsing had substantial impacts on community composition, creating a less diverse understory, lower species richness, and decreased abundance of Quercus species, while retaining the dominance of Liriodendron tulipifera. Simulated gap disturbances exacerbated the impacts of chronic deer browsing and these impacts became stronger over time. Our analyses suggest that recent increases in white‐tailed deer density within many forests of eastern North America will result in altered community dynamics that persist beyond the sapling level, and that any increases in overstory disturbance frequency will exacerbate these impacts.

Plant—animal interactions and climate: Why do yellow pine chipmunks (Tamias amoenus) and eastern chipmunks (Tamias striatus) have such different effects on plants?

Climate can shape the nature of plant-animal interactions. The yellow pine chipmunk (Tamias amoenus), which occupies semi-arid pine forests of western North America, engages in mutualistic relationships with its food plants by dispersing seeds. These chipmunks scatter hoard seeds during spring, summer, and early autumn in soil; unrecovered seeds germinate in the spring. The eastern chipmunk (Tamias striatus) of eastern North America occupies mesic deciduous forests. These chipmunks primarily larder hoard seeds and nuts. Seeds in burrow larders cannot establish seedlings, so these chipmunks have not been documented to be involved in mutualistic plant-animal interactions. The differences in behaviour and the roles that these 2 species play in their communities appear to be caused by differences in precipitation. Scattered caches are more secure from pilferers in the dry western environment because olfaction is moisture dependent. In the more mesic eastern forests, scattered caches are quickly pilfered, causing chipmunks to store most food in larders, which they defend. Climate (i.e., amount of precipitation) also influences many other aspects of the ecology of these species, including home range size, the size and role of the home burrow, mode of foraging, and diet.

Variation in dormancy and germination in three co-occurring perennial forest herbs

Mesic deciduous forest herbs often disperse seed with morphophysiological dormancy (MPD) that prevents germination during unfavorable periods for seedling survival. However, for seeds of some species with MPD, seasonal separation of root and shoot emergence and variation in dormancy levels can complicate interpretation of seedling emergence timing in the field. We tested whether dormancy-break and germination requirements differed among co-occurring perennial forest herbs, Actaea racemosa, Hydrastis canadensis, and Sanguinaria canadensis, which are wild-harvested for their medicinal properties and known to have MPD. Seeds of all species exhibited a summer → autumn → winter requirement for seedling emergence in spring. However, species differed in seed-bank persistence due to variation in primary dormancy levels and stratification requirement of seeds. A. racemosa and H. canadensis can form short-term persistent seed bank, whereas S. canadensis can form a long-term persistent seed-bank, regardless of whether elaiosomes were removed from seeds prior to burial. A. racemosa seeds are dispersed in autumn with weak physiological dormancy, as seeds germinated to high rates at 15/6°C after 8 weeks. In contrast, most seeds of the summer dispersed species, H. canadensis and S. canadensis, require summer temperatures to overcome physiological dormancy. Consequently, seedling emergence is reduced and delayed by 1 year if seeds are not sown immediately following the period of natural dispersal. Seedling emergence was much lower in the field than in controlled conditions for all species, especially in the small-seeded A. racemosa. Interspecific variation in dormancy levels and germination traits must be considered when establishing populations for conservation purposes and in understanding recruitment limitation in perennial forest herbs.

Identification of glacial refugia in south‐eastern North America by phylogeographical analyses of a forest understorey plant, Trillium cuneatum

AbstractAim We examine several hypotheses emerging from biogeographical and fossil records regarding glacial refugia of a southern thermophilic plant species. Specifically, we investigated the glacial history and post‐glacial colonization of a forest understorey species, Trillium cuneatum. We focused on the following questions: (1) Did T. cuneatum survive the Last Glacial Maximum (LGM) in multiple refugia, and (if so) where were they located, and is the modern genetic structure congruent with the fossil record‐based reconstruction of refugia for mesic deciduous forests? (2) What are the post‐glacial colonization patterns in the present geographical range?Location South‐eastern North America.Methods We sampled 45 populations of T. cuneatum throughout its current range. We conducted phylogeographical analyses based on maternally inherited chloroplast DNA (cpDNA haplotypes) and used TCS software to reconstruct intraspecific phylogeny.Results We detected six cpDNA haplotypes, geographically highly structured into non‐overlapping areas. With one exception, none of the populations had mixed haplotype composition. TCS analysis resulted in two intraspecific cpDNA lineages, with one clade subdivided further by shallower diversification.Main conclusions Our investigation revealed that T. cuneatum survived the LGM in multiple refugia, belonging to two (western, eastern) genealogical lineages geographically structured across south‐eastern North America. The western clade is confined to the south‐western corner of T. cuneatum’s modern range along the Lower Mississippi Valley, where fossil records document a major refugium of mesic deciduous forest. For the eastern clade, modern patterns of cpDNA haplotype distribution suggest cryptic vicariance, in the form of forest contractions and subsequent expansions associated with Pleistocene glacial cycles, rather than simple southern survival and subsequent northward colonization. The north–south partitioning of cpDNA haplotypes was unexpected, suggesting that populations of this rather southern thermophilic species may have survived in more northern locations than initially expected based on LGM climate reconstruction, and that the Appalachian Mountains functioned as a barrier to the dispersal of propagules originating in more southern refugia. Furthermore, our results reveal south‐west to north‐east directionality in historical migration through the Valley and Ridge region of north‐west Georgia.

Pollen, plant macrofossils and microvertebrates from mid-Holocene alluvium in east-central Iowa, USA: Comparative taphonomy and paleoecology

Pollen, plant macrofossils, and micromammals are commonly used in paleoecological interpretations, but rarely are found associated because of distinctly separate taphonomic pathways into the fossil record. The Lilienthal local biota, dating between 5920 ± 60 and 6300 ± 80 14C B.P., is a rare exception as the site contains all three proxies juxtaposed in alluvium, impounded upstream from a fossil log near the headwaters of Mud Creek, east-central Iowa, U.S.A. A variety of taphonomic processes can strongly influence the composition of fossil assemblages. This paper compares the taphonomic framework for each fossil group, interprets the paleoecologic signal from each, and then compares the three interpretations. Pollen and plant macrofossils are found in organic silts, indicating deposition in a quiet water environment. Microvertebrates ordinarily occur in sand-sized sediments and show evidence of fluvial transport. Despite these different pathways, all Lilienthal assemblages indicate that a largely closed mesic deciduous forest grew along Mud Creek in mid-Holocene time. Therefore, a narrow north–south ecotone must have existed between the forest and tall-grass prairie biomes in eastern Iowa. This robust data set provides a detailed picture of the paleoecology and paleogeography of this past environment.

MESIC DECIDUOUS FOREST AS PATCHES OF SMALL-MAMMAL RICHNESS WITHIN AN APPALACHIAN MOUNTAIN FOREST

Forests of Southern Appalachia are critical habitats with respect to biodiversity, with a large portion of these forests residing on public multiuse lands. With pressure to extract timber from maturing forests, there is a need to identify the relative importance of forest types within the larger forest matrix. We examined small-mammal populations at 350 sample points across 157 km 2 of forested habitat in the George Washington and Jefferson National Forests, Virginia, to determine landscape and habitat correlates of species abundance and richness. A total of 3,955 individuals representing 20 species were captured using live trap and pitfall sampling at each point during 1996 and 1997. Nine species were sufficiently common to examine their abundance relative to landscape and habitat features. We found species abundance and richness to be highest in mesic deciduous forest types, with the exception of Peromyscus leucopus. Soil moisture capacity and the proportion of mesic habitat within 100 m of the sample point were also important for several species. If mesic deciduous forest can be considered patches within a matrix of xeric forest, then the abundance of 4 species and species richness could be predicted based on the distance of the sample point to the nearest mesic patch and the abundance of 3 species inside mesic patches was related to patch size. At least 73% of mesic patches within this forest were ,25 ha and separated from other patches by .100 m. Our results indicate that mesic forest patches contain the bulk of the species richness for small mammals in the Southern Appalachian ecotype. Designing timber harvests that minimize use of mesic deciduous forest type and that does not decrease patch numbers would achieve the largest benefits to small mammals within the region.

Living stands and dead wood in the Białowieża forest: suggestions for restoration management

The Białowieża Primeval Forest (BPF) is the only forest area in temperate Europe where forest communities have developed a natural stand structure and a natural distribution of coarse woody debris ((CWD)=standing dead trees (SDT)+down woody material (DWM)). Stand and dead wood characteristics are influenced by ancient and recent historical factors and current processes, such as fires, competitive exclusion, storms, insect outbreaks, and forest management. The aim of the present study was to relate CWD to stand characteristics in mesic deciduous forest ( Tilio– Carpinetum (TC)) and riparian forest ( Circaeo– Alnetum (CA)). Direct comparison of managed forest to protected forest provides information about the impact of the forestry practices on TC stand and CWD characteristics. Approximately two-fold larger volume of trees was found in the Białowieża National Park (BNP) TC stands (from 336 to 555 m 3 ha −1) than in the commercial forest ((CF), from 239 to 279 m 3 ha −1). Irregular distribution of “legacy trees” (DBH>90 cm) accounted for most of the variability among the TC BNP stands. Even stronger differences within TC stands were revealed among the various developmental phases (from 147 m 3 ha −1 in degradation phase to 630 m 3 ha −1 in biostatic-optimal phase). Difference in rate of stand development was responsible for the variability of tree volume within CA (338 m 3 ha −1 in early succession stand versus 634 m 3 ha −1 in close-to-climax stand). CWD (mostly DWM) contributed about one-quarter of the total above ground wood biomass in BNP TC and CA ecosystems, ranging from 87 to 160 m 3 ha −1. Higher relative abundance of spruce in DWM than in living stand volume and more spruce in old debris than in fresh debris suggests that the end of the spruce mortality wave was imminent. As a consequence, structural and dynamic changes in favour of smaller regeneration units are expected. A mere vestige of CWD was found in the CF ecosystem. Both stand and CWD data show a negative impact of former management on the forest ecosystems. In conclusion, special measures aimed at the restoration of ecological capacity of forest communities, including legacy retention and management for decadence, have been recommended. There is an urgent need for complementary studies to supply information necessary for successful adaptive management of the Białowieża Primeval Forest.