Regional Forest Composition Research Articles

Influence of climate zone shifts on forest ecosystems in northeastern United States and maritime Canada

Climate zones play a significant role in shaping the forest ecosystems located within them by influencing multiple ecological processes, including growth, disturbances, and species interactions. Therefore, delineation of current and future climate zones is essential to establish a framework for understanding and predicting shifts in forest ecosystems. In this study, we developed and applied an efficient approach to delineate regional climate zones in the northeastern United States and maritime Canada, aiming to characterize potential shifts in climate zones and discuss associated changes in forest ecosystems. The approach comprised five steps: climate data dimensionality reduction, sampling scenario design, cluster generation, climate zone delineation, and zone shift prediction. The climate zones in the study area were delineated into four different orders, with increasing subzone resolutions of 3, 9, 15, and 21. Furthermore, projected climate normals under Shared Socioeconomic Pathways 4.5 and 8.5 scenarios were used to predict the shifts in climate zones until 2100. Our findings indicate that climate zones characterized by higher temperatures and lower precipitation are expected to become more prevalent, potentially becoming the dominant climate condition across the entire region. Thes changes are likely to alter regional forest composition, structure, and productivity. In short, such shifts in climate underscore the significant impact of environmental change on forest ecosystem dynamics and carbon sequestration potential.

Comparison of paleobotanical and biomarker records of mountain peatland and forest ecosystem dynamics over the last 2600 years in central Germany

Abstract. As peatlands are a major terrestrial sink in the global carbon cycle, gaining an understanding of their development and changes throughout time is essential in order to predict their future carbon budget and potentially mitigate the adverse outcomes of climate change. With this aim to understand peat development, many studies have investigated the paleoecological dynamics by analyzing various proxies, including pollen, macrofossil, elemental, and biomarker analyses. However, as each of these proxies is known to have its own benefits and limitations, examining them in parallel allows for a deeper understanding of these paleoecological dynamics at the peatland and a systematic comparison of the power of these individual proxies. In this study, we therefore analyzed peat cores from a peatland in Germany (Beerberg, Thuringia) to (a) characterize the vegetation dynamics over the course of the peatland development during the late Holocene and (b) evaluate to what extent the inclusion of multiple proxies, specifically pollen, plant macrofossils, and biomarkers, contributes to a deeper understanding of those dynamics and interaction among factors. We found that, despite a major shift in the regional forest composition from primarily beech to spruce as well as many indicators of human impact in the region, the local plant population in the Beerberg area remained stable over time following the initial phase of peatland development up until the last couple of centuries. Therefore, little variation could be derived from the paleobotanical data alone. The combination of pollen and macrofossil analyses with the elemental and biomarker analyses enabled further understanding of the site development as these proxies added valuable additional information, including the occurrence of climatic variations, such as the Little Ice Age, and more recent disturbances, such as drainage.

Postglacial vegetation and fire history with a high-resolution analysis of tephra impacts, High Cascade Range, Oregon, USA

The postglacial history of vegetation, wildfire, and climate in the Cascade Range (Oregon) is only partly understood. This study uses high-resolution macroscopic charcoal and pollen analysis from a 13-m, 14,500 years sediment record from Gold Lake, located in a montane forest, to reconstruct forest vegetation and fire history. The occurrence of three tephra layers, including a 78-cm airfall Mazama tephra, as well as highly laminated segments, allows one to study tephra impacts on vegetation at a fine temporal resolution. From the Late Glacial through the Younger Dryas, pollen spectra vary little. The early Holocene is marked by a sudden increase in Pseudotsuga, indicating warmer conditions, while the late Holocene is marked by increasing Tsuga heterophylla and Tsuga mertensiana, indicating the onset of moist conditions in the region. High-resolution charcoal data show periods of large peaks during the Late Glacial, pre-, and post-Mazama eruption and since 4 ka (thousands of years before present). Low fire during the early Holocene is unexpected, given regional evidence of warmer and drier summers, but it may be the result of fuel limitation. After the Mazama tephra deposition (7.63 ka), the non-arboreal pollen composition was changed, with some taxa disappearing or reduced in abundance for 300 years. Arboreal taxa were little affected by the tephra, showing only a 20% increase in Pinus pollen and no discernible impact on the pollen accumulation rate (PAR).In contrast, the Mazama tephra was followed by ca. 70 years of very low charcoal input, followed by a large peak, consistent with the burial of surface fuels and decades of fuel accumulation. There was also increased fire frequency and peak magnitude at 1.5 ka, followed by very little fire after 0.4 ka, consistent with the current old-growth forest surrounding the lake. This detailed and high-resolution record adds significantly to understanding the impacts of climate change and the singular effect of the Mazama eruption, impacting watershed vegetation, and fire for centuries but with minimal impact on the regional forest composition.

Differential responses of tree species to a severe ice storm and their implications to forest composition in the southeast United States

The unique terrain, geography, and climate patterns of the eastern United States encourage periodic occurrences of catastrophic ice storms capable of large-scale damage or destruction of forests. However, the pervasive and persistent effects of these glaze events on regional forest distribution and composition have rarely been studied. In the southeastern US, ice storm frequency and intensity increase with increasing latitude and along the complex gradients from the coast (low, flat, sediment controlled and temperature moderated near the ocean) to the interior (high, rugged, bedrock controlled, distant from warming ocean). To investigate the potential influence of this disturbance gradient on regional forest composition, we studied the differential responses of trees (canopy position, lifeform group, and species group) to a particularly severe ice storm. Our results indicated that tree mortality and damage (canopy damage, bent bole, snapped bole, and uprooted) varied significantly between overstory and understory trees, and among species and lifeform groups. Overstory trees were more prone to glaze damage than understory trees, and evergreen broadleaf species were the most susceptible to glaze damage, while deciduous species were the least susceptible. Among the pine species studied, slash pine (Pinus elliottii Engelm.) and longleaf pine (P. palustris Mill.) suffered more severe damage and mortality than loblolly pine (P. taeda L.). Further, ice damage was correlated with distribution-based differences in injury susceptibility among pine and deciduous tree species. The most ice storm-tolerant pine species, loblolly pine, had the most northerly distribution (39.51°N), while the least resistant species were those with more southerly distribution (e.g., 33.29°N for slash pine). These results support hypotheses that the distributions of evergreen tree species are regulated by periodic catastrophic ice storms. Therefore, predicting future distributions of tree species in response to climate change should consider the role of ice storms in shaping the forest composition.

Increasing numbers of wintering forest birds in Swedish Lapland 1986–2017 show stronger correlations with forest development than with local weather

After a long period of decline, the number of forest birds has increased in Sweden in recent decades. Whether this trend is due to an increase in forested area, forest quality, climate change, or a combination of these factors, remains unclear. Here, we compared forest bird data from a local winter point count route around Storuman in Swedish Lapland between 1986 and 2017, with the development of regional forest composition and local weather conditions. We suggest that rather than changes in average annual, winter, or summer local temperatures or precipitation, the main drivers behind increasing numbers of wintering forest birds in this part of Sweden are an increase in the area of denser forest and dead wood volume, and a decrease in open ground area without forest vegetation. While there may be supplementary explanations behind the increasing numbers of forest birds, such as reduced agriculture, decreasing local human population, or stronger photosynthesis, our results indicate that local land use has been favourable for forest birds in recent decades in this area.

Importance of succession, harvest, and climate change in determining future composition in U.S. Central Hardwood Forests

Most temperate forests in U.S. are recovering from heavy exploitation and are in intermediate successional stages where partial tree harvest is the primary disturbance. Changes in regional forest composition in response to climate change are often predicted for plant functional types using biophysical process models. These models usually simplify the simulation of succession and harvest and may not consider important species‐specific demographic processes driving forests changes. We determined the relative importance of succession, harvest, and climate change to forest composition changes in a 125‐million ha area of the Central Hardwood Forest Region of U.S. We used a forest landscape modeling approach to project changes in density and basal area of 23 tree species due to succession, harvest, and four climate scenarios from 2000 to 2300. On average, succession, harvest, and climate change explained 78, 17, and 1% of the variation in species importance values (IV) at 2050, respectively, but their contribution changed to 46, 26, and 20% by 2300. Climate change led to substantial increases in the importance of red maple and southern species (e.g., yellow‐poplar) and decreases in northern species (e.g., sugar maple) and most of widely distributed species (e.g., white oak). Harvest interacted with climate change and accelerated changes in some species (e.g., increasing southern red oak and decreasing American beech) while ameliorated the changes for others (e.g., increasing red maple and decreasing white ash). Succession was the primary driver of forest composition change over the next 300 years. The effects of harvest on composition were more important than climate change in the short term but climate change became more important than harvest in the long term. Our results show that it is important to model species‐specific responses when predicting changes in forest composition and structure in response to succession, harvest, and climate change.

Land cover change on the Isthmus of Karelia 1939–2005: Agricultural abandonment and natural succession

The Isthmus of Karelia is located in North-West Russia, between Lake Ladoga and the Baltic Sea. At the end of World War II (WWII), Finland ceded the western part of the Isthmus to the Soviet Union. In 1991 the Soviet Union ceased to exist. The Isthmus became a part of the Russian Federation. Using land cover data from the years 1939, 1987 and 2005 we document and analyze land use change on the Isthmus during and after the Soviet era. Large-scale agricultural abandonment was observed during the Soviet era. The landscape share of agriculture halved from 18 to 9%, as only a part of the land vacated by Finnish farmers during WWII was incorporated into the Soviet agricultural system. Forest expanded onto farmland and its landscape share increased from 72 to 77%. Another observed trend was the recovery from previous forest degradation. As logging on the Isthmus was banned, the development of the forest mosaic followed patterns of natural succession. Some deciduous forests were transformed into mixed forests and spruce forests. Clear cuts and sapling stands became rare. After the collapse of the Soviet Union, logging in old growth forests was resumed. However, its impacts on the regional forest composition remained modest. The recent forest history of the Isthmus is an extreme example of recovery from earlier forest degradation in boreal conditions. To illustrate the magnitude of the changes, we contrast our findings with the contemporary development in Southern Finland, where land use remained stable and forests were intensively utilized for timber production.

Legacies of historical land use on regional forest composition and structure in Wisconsin, USA (mid‐1800s–1930s–2000s)

Historical land use can influence forest species composition and structure for centuries after direct use has ceased. In Wisconsin, USA, Euro-American settlement in the mid- to late 1800s was accompanied by widespread logging, agricultural conversion, and fire suppression. To determine the maximum magnitude of change in forest ecosystems at the height of the agricultural period and the degree of recovery since that time, we assessed changes in forest species composition and structure among the (1) mid-1800s, at the onset of Euro-American settlement; (2) 1930s, at the height of the agricultural period; and (3) 2000s, following forest regrowth. Data sources included the original U.S. Public Land Survey records (mid-1800s), the Wisconsin Land Economic Inventory (1930s), and U.S. Forest Service Forest Inventory and Analysis data (2000s). We derived maps of relative species dominance and tree diameters for the three dates and assessed change using spatial error models, nonmetric multidimensional scaling ordination, and Sørenson distance measures. Our results suggest that since the mid-1800s, hemlock and white pine have declined in absolute area from 22% to 1%, and the proportion of medium (25-<50 cm) and large-diameter (> or = 50 cm) trees of all species has decreased from 71% to 27% across the entire state. Early-successional aspen-birch is three times more common than in the mid-1800s (9% vs. 3%), and maple and other shade-tolerant species are increasing in southern areas formerly dominated by oak forests and savannas. Since the peak agricultural extent in the 1930s, species composition and tree size in northern forests have shown some recovery, while southern forests appear to be on a novel trajectory of change. There is evidence of regional homogenization, but the broad north-south environmental gradient in Wisconsin constrains overall species composition. Although the nature of the future forests will be determined in part by climate change and other exogenous variables, land use is likely to remain the driving factor.

Spread of beech bark disease in the eastern United States and its relationship to regional forest composition

Beech bark disease (BBD) is an insect–fungus complex involving the beech scale insect ( Cryptococcus fagisuga Lind.) and one of two canker fungi. Beech scale was introduced to Halifax, Nova Scotia around 1890, presumably with the fungus Neonectria coccinea var. faginata Lohm. The disease has subsequently spread through a large portion of the range of beech. We used historical maps of the extent of the advancing BBD front (defined by presence of scale insects) in North America to estimate its rate of spread as 14.7 ± 0.9 km/year. This estimate did not account for stochastic “jumps” by the scale insects to several disjunct locations; therefore, this rate is a conservative estimate. Comparison of the year of scale colonization with beech density did not suggest a relationship between the scale spread rate and beech density. Our analyses also indicated that BBD has invaded less than 30% of regions where beech is present, but it has invaded most of the regions where beech is a dominant component of stands. Despite regional increases in beech mortality following invasion, considerable amounts of live beech remain in invaded areas. Moreover, the volume of beech has increased in most areas, though generally at lower rates than that observed for associated tree species.

Holocene vegetation and climate change in southern New Zealand: linkages between forest composition and quantitative surface moisture reconstructions from an ombrogenous bog

AbstractThis paper presents a Holocene pollen record from an ombrotrophic bog in Southland, New Zealand, together with multiproxy data (testate amoebae, peat humification and plant macrofossils) from the same core to establish an independent semiquantitative record of peatland surface moisture. Linkages between reconstructed peatland surface moisture and regional forest composition are investigated using redundancy analysis of the forest pollen data constrained with predicted bog water‐table depths. Over 32% of the pollen data variance can be explained by surface moisture changes in the bog, suggesting a common cause of water‐table and regional vegetation change. Water tables were higher during the early to mid‐Holocene when the forest was dominated by podocarp taxa. Water tables lowered after about 3300 cal. yr BP coevally with the expansion of Nothofagus species, culminating with the dominance of Nothofagus subgenus Fuscospora in the past 1200 cal. yr BP. This is in apparent opposition to the warm/dry to cool/wet trend suggested by subjective interpretation of pollen data alone, from this and other studies. We suggest that during the late Holocene, drier summers associated with shifts in solar insolation caused reduced surface wetness and summer humidity, which together with a trend to cooler winters, apparently favoured the regeneration of Nothofagus species. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Impact of Human Activity on Regional Forest Composition and Dynamics in Central New England

Historical and ecological data from north-central Massachusetts suggest that widespread and intensive human disturbance after European settlement led to a shift in forest composition and obscured regional patterns of species abundance. A paleoecological approach was required to place recent forest dynamics in a long-term context. Pollen and charcoal data from 11 small lakes in north-central Massachusetts were used to reconstruct local vegetation dynamics and fire histories across the region over the past 1000 years. The sites are located across an environmental gradient. Paleoecological data indicate that prior to European settlement, there was regional variation in forest composition corresponding to differences in climate, substrate, and fire regime. Oak, chestnut, and hickory were abundant at low elevations, whereas hemlock, beech, sugar maple, and yellow birch were common at high elevations. Fire appears to have been more frequent and/or intense at lower elevations, maintaining high abundances of oak, and archaeological data suggest Native American populations were greater in these areas. A change in forest composition at higher elevations, around 550 years before present, may be related to the Little Ice Age (a period of variable climate), fire, and/or activity by Native Americans, and led to regional convergence in forest composition. After European settlement, forest composition changed markedly in response to human disturbance and there was a sharp increase in rates of vegetation change. Regional patterns were obscured further, leading to homogenization of broad-scale forest composition. There is no indication from the pollen data that forests are returning to pre-European settlement forest composition, and rates of vegetation change remain high, reflecting continuing disturbance on the landscape, despite regional reforestation.

Modern Pollen Assemblages and Vegetation in the Myrtle Lake Peatland, Minnesota

Pollen grains and spores in moss polsters are compared with vegetation along transects across vegetational gradients in a large peatland in northern Minnesota. The distribution, percentage values, and source of 135 pollen and spore types are traced and related to the broad—scale vegetation pattern in the midwestern United States, and to the fine—scale vegetation pattern in the peatland. The pollen assemblages of taxa presently not growing in the peatland constitute the regional pollen deposition, with nearly constant proportions of pollen types distributed across the study area. Regional pollen values are compared for several peatlands in northern Minnesota and with the regional forest composition. The fine—scale pattern of peatland vegetation types corresponds well with the spatial pattern of the local pollen assemblages. Peatland vegetation types are characterized on the basis of these pollen assemblages. Conclusions on development of peatland vegetation can be drawn from local pollen assemblages preserved in sediment cores. Pollen transport for wind—pollinated Abies, Pinus, Betula, Alnus, Fraxinus, and Typha is discernible in the peatland only within 200 m from their source in local plant populations. The dispersal pattern of Abies pollen from an Abies balsamifera stand is related to wind speed and direction and sky cover for as much as 5 yr preceding sample collection. Most peatland pollen types are restricted in distribution to their corresponding vegetation types.