Present-day Forest Composition Research Articles

Spatial patterns of light-demanding tree species in the Yangambi rainforest (Democratic Republic of Congo).

Most Central African rainforests are characterized by a remarkable abundance of light‐demanding canopy species: long‐lived pioneers (LLP) and non‐pioneer light demanders (NPLD). A popular explanation is that these forests are still recovering from intense slash‐and‐burn farming activities, which abruptly ended in the 19th century. This “human disturbance” hypothesis has never been tested against spatial distribution patterns of these light demanders. Here, we focus on the 28 most abundant LLP and NPLD from 250 one‐ha plots distributed along eight parallel transects (~50 km) in the Yangambi forest. Four species of short‐lived pioneers (SLP) and a single abundant shade‐tolerant species (Gilbertiodendron dewevrei) were used as reference because they are known to be strongly aggregated in recently disturbed patches (SLP) or along watercourses (G. dewevrei). Results show that SLP species are strongly aggregated with clear spatial autocorrelation of their diameter. This confirms that they colonized the patch following a one‐time disturbance event. In contrast, LLP and NPLD species have random or weakly aggregated distribution, mostly without spatial autocorrelation of their diameter. This does not unambiguously confirm the “human disturbance” hypothesis. Alternatively, their abundance might be explained by their deciduousness, which gave them a competitive advantage during long‐term drying of the late Holocene. Additionally, a canonical correspondence analysis showed that the observed LLP and NPLD distributions are not explained by environmental variables, strongly contrasting with the results for the reference species G. dewevrei, which is clearly aggregated along watercourses. We conclude that the abundance of LLP and NPLD species in Yangambi cannot be unambiguously attributed to past human disturbances or environmental variables. An alternative explanation is that present‐day forest composition is a result of adaptation to late‐Holocene drying. However, results are inconclusive and additional data are needed to confirm this alternative hypothesis.

Tree Age Distributions Reveal Large-Scale Disturbance-Recovery Cycles in Three Tropical Forests.

Over the past few decades there has been a growing realization that a large share of apparently ‘virgin’ or ‘old-growth’ tropical forests carries a legacy of past natural or anthropogenic disturbances that have a substantial effect on present-day forest composition, structure and dynamics. Yet, direct evidence of such disturbances is scarce and comparisons of disturbance dynamics across regions even more so. Here we present a tree-ring based reconstruction of disturbance histories from three tropical forest sites in Bolivia, Cameroon, and Thailand. We studied temporal patterns in tree regeneration of shade-intolerant tree species, because establishment of these trees is indicative for canopy disturbance. In three large areas (140–300 ha), stem disks and increment cores were collected for a total of 1154 trees (>5 cm diameter) from 12 tree species to estimate the age of every tree. Using these age estimates we produced population age distributions, which were analyzed for evidence of past disturbance. Our approach allowed us to reconstruct patterns of tree establishment over a period of around 250 years. In Bolivia, we found continuous regeneration rates of three species and a peaked age distribution of a long-lived pioneer species. In both Cameroon and Thailand we found irregular age distributions, indicating strongly reduced regeneration rates over a period of 10–60 years. Past fires, windthrow events or anthropogenic disturbances all provide plausible explanations for the reported variation in tree age across the three sites. Our results support the recent idea that the long-term dynamics of tropical forests are impacted by large-scale disturbance-recovery cycles, similar to those driving temperate forest dynamics.

Modern and fossil pollen assemblages reveal forest taxonomic changes in the Mexican subtropics during the last 1300 years

The usual approach to reconstructing long-term vegetation dynamics is through the use of fossil pollen records from sedimentary sequences. This requires, however, an understanding of the relationship between modern pollen and the species composition and distribution on landscapes. Since different taxa produce different amounts of pollen, with different dispersal characteristics, understanding this relationship can be complex. This research aimed to address the following questions: Is it possible to distinguish different high-altitude forests by modern pollen signature? Is modern pollen abundance related to forest structure, forest diversity or to differences in altitude? How well can modern and fossil pollen assemblages reveal changes in the forest composition over the past ~1300years?Data were collected on present-day forest composition and structure and diversity, paired with modern pollen samples in three high-altitude forest types: pine forest, cloud forest and a transitional forest (a mixture of Pinus–Quercus–Carpinus) in west-central Mexico. A sediment core was collected from each vegetation type for reconstructing past vegetation. Constrained and unconstrained ordination methods were used to discern patterns of variation and the correlates behind the datasets. To compare the fossil with the modern pollen assemblages, dissimilarity indexes were computed between each of the fossil pollen sequences and their modern assemblages at different altitudes using the chord distance.Results demonstrated that each of the three forests types was distinctive in composition, and modern and fossil pollen reflected local vegetation at stand level; mean diameter and altitude were the main variables related to differences among modern pollen signatures. When reconstructing high-altitude vegetation in the subtropics, it is important to consider all taxa, even if they are rare. Therefore, in order to reveal responses to climate change and human disturbances at stand level in forests at different successional stages; particularly from 102 to 104m2 and, at temporal scales from 102 to 103years, it is essential to combine modern and fossil pollen together with present-day vegetation records.

Change from pre-settlement to present-day forest composition reconstructed from early land survey records in eastern Québec, Canada

Questions: What was the tree species composition of forests prior to European settlement at the northern hardwood range limit in eastern Québec, Canada? What role did human activities play in the changes in forest composition in this region? Location: Northern range limit of northern hardwoods in the Lower St. Lawrence region of eastern Québec, Canada. Methods: We used early land survey records (1846–1949) of public lands to reconstruct pre-settlement forest composition. The data consist of ranked tree species enumerations at points or for segments along surveyed lines, with enumerations of forest cover types and notes concerning disturbances. An original procedure was developed to weigh and combine these differing data types (line versus point observations; taxa versus cover enumerations). Change to present-day forest composition was evaluated by comparing survey records with forest decadal surveys conducted by the government of Québec over the last 30 years (1980–2009). Results: Pre-settlement dominance of conifers was strong and uniform across the study area, whereas dominance of maple and birches was patchy. Cedar and spruce were less likely to dominate with increasing altitude, whereas maple displayed the reverse trend. Frequency of disturbances, especially logging and fire, increased greatly after 1900. Comparison of survey records and modern plots showed general increases for maple (mentioned frequency increased by 39%), poplar (36%) and paper birch (31%). Considering only taxa ranked first by surveyors, cedar displayed the largest decrease (19%), whereas poplar (15%) and maple (9%) increased significantly. Conclusions: These changes in forest composition can be principally attributed to clear-cutting and colonization fire disturbances throughout the 20th century, and mostly reflected the propensity of taxa to expand (maples/aspen) or decline (cedar/spruce) with increased disturbance frequency. Québec's land survey archives provide an additional data source to reconstruct and validate our knowledge of North America's pre-settlement temperate and sub-boreal forests.

Current distribution of older and deciduous forests as legacies from historical use patterns in a Swedish boreal landscape (1725–2007)

We combine historical maps and satellite derived data to reconstruct the development of a Swedish boreal landscape over the past 300 years. The aim is to understand legacies from past use patterns in present-day forest composition and consequences for conservation objectives from a landscape perspective. We analyze landscape development in cross-tabulation matrixes, building change trajectories. These trajectories are tested in linear models to explain the distribution of present-day landscape composition of coniferous, mixed, and deciduous forests >110 years. Of 49 tested change trajectories, 11 showed a significant association. Associations for mixed and coniferous forests were similar and linked to characteristics such as forest continuity, which characterized the studied landscape. Deciduous older forests did not show any association to forest continuity but were more likely to occur on areas that specifically shifted from forests with grazing in the 1720s to open impediment (likely indicating low tree coverage) in the 1850s. There were large shifts and spatial redistribution in ownerships over time. Use patterns and legacies varied between small- and large-scale ownership categories as well as within small-scale categories. The legacies found in the study indicate a complex origin of heterogeneous landscape elements such as older deciduous forests. Additionally, the origin of the legacies indicates a potential need to diversify conservation management based on the influence of past use patterns. Despite large inconsistencies in historical and contemporary data we argue that this type of analysis could be used to further understand the distribution of landscape elements important for conservation objectives.

A Comparison of Presettlement and Present-Day Forests in Two Northern Michigan Deer Yards

Deer yards are wintering areas used by white-tailed deer in the northern part of their range. In northern Michigan, deer yards typically consist of extensive stands of cedar- dominated (Thuja occidentalis) or mixed conifer swamps where thick evergreen overstories provide shelter from winter conditions. Forest and wildlife management in and around cedar- dominated swamps of the upper Great Lakes have created a nearly optimal interspersion of early-seral summer range and mature conifer winter range. For a variety of reasons which include favorable habitat changes, deer populations are today larger than those of presettle- ment conditions. We used General Land Office survey records from the 1840s to compare presettlement forest composition with present-day forest composition in two important deer yarding areas in Michigan's Upper Peninsula. Except for tamarack (Larix laricina), woody plant species that are unpalatable to deer or tolerant of browsing have increased. Species that are palatable and intolerant of browsing have decreased. Ages of extant mature cedars indicate establishment during a period of low deer populations in Michigan. Change in forest composition has many causes, but deer populations encouraged by forest and wildlife man- agement may contribute to a changing ecology in northern Michigan's conifer swamp com- munities, and may change the structure of plant communities in areas where deer use is concentrated.

Vegetation–site relationships of witness trees (1780–1856) in the presettlement forests of eastern West Virginia

Witness tree data from 1780–1856 for the Monongahela National Forest in eastern West Virginia were analyzed with respect to physiographic unit (Ridge and Valley versus Allegheny Mountains) and landform, and compared with present-day forest composition. Contingency table analysis and standardized residuals were used to quantify the preference or avoidance of common tree species with various landforms. Pre-European settlement forests in the Ridge and Valley were dominated by mixed oak (Quercusalba L., Quercusprinus L., Quercusvelutina Lam. and Quercusrubra L.), Pinus spp., Castaneadentata (Marsh.) Borkh., and Carya on ridge sites and Q. alba, Acersaccharum Marsh., Pinus, Tiliaamericana L., and Tsugacanadensis (L.) Carr. on valley floors. The original forests in the Allegheny Mountains were dominated by Fagusgrandifolia Ehrh., T. canadensis, A. saccharum, Acerrubrum L., Betula spp., and Pinus, with predominantly Fagus–Tsuga–Pinus forests on mountain tops and Tsuga–Acer–Betula forests on valley floors. Compared with the presettlement era, present-day forests on both physiographic units lack overstory C. dentata and have decreased Pinus and (or) Q. alba. Species that have increased substantially following Euro-American settlement include Q. prinus, Q. rubra, Quercuscoccinea Muenchh., and A. rubrum in the Ridge and Valley and Prunusserotina Ehrh., A. rubrum, and Betula spp. in the Allegheny Mountains. These dramatic changes in forest composition were attributed to the chestnut blight (caused by Endothiaparasitica (Murrill) P.J. Anderson & H.W. Anderson), widespread logging, intensive wildfires, and more recently, fire exclusion.

Physiographic analysis of witness-tree distribution (1765–1798) and present forest cover through north central Pennsylvania

This study analyzed witness-tree data recorded from 1765 to 1798 with respect to landform in four major physiographic provinces represented through north central Pennsylvania. These data were also compared with present-day forest composition to evaluate broad changes that occurred 200 years after European settlement. In the Allegheny High Plateau, Tsugacanadensis (L.) Carr. represented 40–47% of witness trees in mountain coves and stream valleys, but only 9% on plateau tops, which comprised 45% Fagusgrandifolia Ehrh. Pinusstrobus L. represented ≤4% frequency across all landforms. The original forests of the Allegheny Mountains were dominated by mixed Quercus, Acer, Castaneadentata (Marsh.) Borkh., and Pinus and had significant T. canadensis only in stream valleys. The presettlement forests of the Allegheny Front and the Ridge and Valley provinces had a similar mix of Quercus, Pinus, Castanea, and Carya, with increased P. strobus on the more mesic sites and Pinusrigida Mill, on the xeric ridges. Comparisons of presettlement with present-day forest composition indicate a dramatic reduction of T. canadensis (32% to 4%) and F. grandifolia (33% to 12%) in the High Plateau and increases in Acer (11% to 37%), Quercusrubra L. (0% to 10%), Prunusserotina Ehrh. (1% to 6%), and Betula (5% to 10%). Other units exhibited reductions in P. strobus, P. rigida, Quercusalba L., and Carya spp. and increases in Quercusprinus L., Q. rubra, Acerrubrum L., and P. serotina. Castaneadentata had its greatest abundance on higher elevation sites in each physiographic unit, and the elimination of this species this century apparently facilitated the increase in Q. prinus and Q. rubra on ridge sites. South of the Allegheny Plateau, increases in A. rubrum, P. serotina, and other mixed-mesophytic species may be in response to fire exclusion this century. The results of this study indicate the importance of landform and physiography on presettlement forest composition as well as the dramatic changes that have occurred as a result of altered disturbance regimes following European settlement.

Land-use history (1720–1992), composition, and dynamics of oak–pine forests within the Piedmont and Coastal Plain of northern Virginia

Woody vegetation was surveyed in 58 forest stands in northern Virginia to examine the effects of previous land-use history on past and present-day forest composition and dynamics. Stands were separated using detrended correspondence analysis (DCA) and overstory importance values into three forest groups: (i) white oak (Quercusalba L.)–tulip-poplar (Liriodendrontulipifera L.) (ii) white oak–scarlet oak (Quercuscoccinea Muenchh.) and (iii) Virginia pine (Pinusvirginiana Mill.) The first DCA axis represents a successional continuum from more recently disturbed areas containing young pine forests to less disturbed mature oak stands, and is negatively correlated with stand age and species diversity. White oak and red oak (Quercusrubra L.) dominated presettlement forests in the area. Following European settlement, forests experienced intense logging associated with the charcoal iron industry, large-scale clearing for agriculture, and subsequent land abandonment. By coupling radial growth analysis with age–diameter figures, we evaluated the responses of stands to disturbances associated with various land-use practices. This analysis indicated that many Virginia pine stands resulted from agricultural abandonment during the early 1900s, while a majority of oak stands experienced peak recruitment and radial growth following periodic logging disturbances in the 1800s. Canopy closure, forest protection, and reduced fire and logging disturbance this century led to increases in dogwood (Cornusflorida L.) and blackgum (Nyssasylvatica Marsh.) in area forests. The oldest stands exhibited a lack of tall oak regeneration; however, they also contained a scarcity of potential oak replacement species. Therefore, oak will seemingly share future dominance with several mixed-mesophytic species, although the exact successional status of these stands is unresolved.

A Comparison of Presettlement and Present-day Forests on Two Bigtooth Aspen-dominated Landscapes in Northern Lower Michigan

-Forest composition within a local landscape is influenced by physical site characteristics and prevailing disturbance regime. In many areas of eastern North America, the natural disturbance regimes that influenced presettlement forest composition have been altered by human activities associated with European settlement. These alterations have led to substantial changes in composition and the development of successional pathways markedly different from presettlement conditions. In this study we examined presettlement and presentday forest composition of two bigtooth aspen-dominated landscapes in northern Lower Michigan. Our objectives were to: (1) reconstruct and relate presettlement forest composition to the potential natural disturbance regime of each landscape; (2) compare presettlement and present-day forest composition of each landscape; and (3) assess the influence of postsettlement disturbance history on the development of the current forests and the potential successional pathways of the two landscapes. Presettlement forest composition, reconstructed using General Land Office survey records, differed substantially between the two landscapes. Landscape 1 was dominated by firesensitive eastern hemlock and American beech, while landscape 2 was dominated by firedependent red pine, white pine and jack pine. Compositional differences may have been related to differences in presettlement fire frequency, or to differences in physical site characteristics or regional climates. The present-day overstories of both landscapes were dominated by bigtooth aspen, red oak and red maple species that were of minor importance in the presettlement forests of the study areas. Compositional convergence was attributed to the similar influence of postsettlement disturbance history on each landscape. Logging and wildfires eliminated advanced regeneration and many remnant seed sources of hemlock, beech and pines and favored the development of forests dominated by bigtooth aspen, red oak and red maple. Individuals.of the latter species survived the disturbance and proliferated vegetatively in the postsettlement landscape. Differences in seed source availability in the present-day forests have led to marked differences in species recruitment in the understories of the two landscapes. Changes in seed rain and fire exclusion in the two landscapes are apparently leading to development of forest types markedly different from the presettlement conditions. The results illustrate how human-induced changes in disturbance regimes can have important, long-lasting effects on forest composition.

The Beech Forests of Wisconsin: Changes in Forest Composition and the Nature of the Beech Border

The forests of Wisconsin in which beech (Fagus grandifolia Ehrh.) is a component are of particular interest because of the limitation of this species to the eastern part of the state. Although touched upon in several earlier studies, these forests have not been examined throughout their range in the state. A phytosociological study was undertaken to gain information on three primary considerations: the status of the beech forest composition since the early 1800s; the nature of the beech border; and the relationship of present-day forests to other forests of the state without beech. The last of these three is to be reported on in a later paper, with the first two being taken up in the present paper. For these aspects of the study, the records of the original land survey were of primary value in providing information on the resettlement conditions of the forest. Presentday forest composition was compared with that of the past and species behavior along transects across the beech border was studied.