History Of Vegetation Changes Research Articles

Analysis of non-cellulosic polysaccharides helps to reveal the history of thick organic surface layers on calcareous Alpine soils

Background and aimsWe investigated the potential of non-cellulosic polysaccharides (NCP) as biomarkers to identify the plant types that dominate present and past litter input into organic surface covers on calcareous Alpine soils and to reveal historic vegetation changes.MethodsAt two sites in the Alps, NCP monomers were quantified in different organs of site-dominating plants, the Oa horizon of four Folic Leptosols, and different sections of thick organic surface layers of four Folic Histosols on calcareous bedrock.ResultsThe dominating plant types at our study sites differ markedly in their NCP composition and (galactose + mannose)/(arabinose + xylose) [GM/AX] ratio (grasses and sedges: 0.2; dicots Fagus and Vaccinium: 0.2–0.6; conifers Abies, Picea, Pinus: 0.7–2.4; mosses: 5). For all except one soil, the NCP signature of the uppermost Oa horizon reflects the present vegetation. For all Histosol O horizons, NCP signatures indicate a dominance of conifer litter throughout their development (up to 1,500 years). Different NCP and GM/AX depth profiles reflect specific patterns of O layer genesis.ConclusionsNCP and GM/AX depth profiles in organic surface covers of soils provide important information about dominating litter sources in the past and can be valuable tools to reveal historic vegetation and/or land use changes.

Utilizing soil indicators to explain historical vegetation changes of a peatland subjected to flood inundation

Flooding and land use changes can be a significant source of nutrients to wetlands and contribute to ecosystem changes at a community level. We studied changes in vegetation composition and peat properties in a New Zealand wetland incorporated into a flood control scheme. Lack of hydrological records pre-development of the flood control scheme allowed the opportunity to use nutrient and physical indicators developed for restiad vegetation groups, to identify if increased flooding was the primary cause for ecological succession. Vegetation changes along a 2.3-km transect were related to hydrological processes, peat characteristics and atmospheric ammonia inputs. Measurements for peat and vegetation composition were taken from 27 sites, whereas hydrological analysis incorporated seven automated water level sites and a historical investigation of 46 years of river flood records. Ammonia deposition was higher on the farmland/wetland fringe (4.0 kg N ha−1 year−1) but decreased to background levels (2–2.5 kg N ha−1 year−1) 500 m into the wetland. Classification and ordination of vegetation data with environmental variables identified six main groups along a gradient from low nutrients and stable water tables (farthest from the river) to high nutrients and a dynamic water table near the river. Invasion over 50 years of the native scrub tree Leptospermum scoparium into restiad bog was linked to enhanced nutrient inputs and physical degradation from flooding, portrayed through levels higher than restiad indicator target ranges. This study shows that target ranges for vegetation indicators can be used as a tool to identify ecological succession and invasion. Copyright © 2012 John Wiley & Sons, Ltd.

Using sediment seed banks and historical vegetation change data to develop restoration criteria for a eutrophic lake in China

Restoration of submerged macrophytes to lake that have lost them can be difficult but can be helped by studies on historical vegetation data and remnant seed banks in the sediments. We analysed sediment seed banks and historical vegetation change data in Lake Dianchi, China, and aimed to develop a possible recovery trajectory of submerged vegetation. The results indicate that phosphorus concentrations have increased by 28 times in the lake since 1961 and macrophytes that used to grow at 5–6.5 m are now confined to water less than 3 m deep. Many species had disappeared by 1978 and a former 17 species and 88% cover in 1961 was reduced to 9 species in three turbidity-tolerant communities with only 2% cover by 2010. The remaining seed bank was dominated by two species, still present in the lake and many former species, which had been very abundant, were not found as seeds. We suggest that macrophytes can be restored to areas shallower than 3 m by using three turbidity-tolerant species, and that other formerly present species will need to be reintroduced when conditions have been further improved.

SOIL ORGANIC MATTER AND SOIL PHYSICOCHEMICAL PROPERTIES ASSOCIATED WITH FOREST FIRES IN CENTRAL TAIWAN

Forest fires can disturb the evolution of plant communities and influence both soil organic matter (SOM) and soil physicochemical properties. The historic vegetation changes and the influences on soil properties and OM induced by fires are still not well known for central Taiwan. This study investig

Modeling the effects of historical vegetation change on near-surface atmosphere in the northern Chihuahuan Desert

Our goal was to evaluate effects of broad-scale changes in vegetation from grasslands to shrublands over the past 150 years on near-surface atmosphere over the Jornada Experimental Range in the northern Chihuahuan Desert, using a regional climate model. Simulations were conducted using 1858 and 1998 vegetation maps, and data collected in the field. Overall, the vegetation shift led to small changes in sensible heat (SH) and an increase in latent heat (LH). The impacts of shrub encroachment depended on shrubland type: conversion from grass to mesquite cools the near-surface atmosphere and from grass to creosotebush warms it. Higher albedo of mesquite relative to grasses reduced available energy, which was dissipated mainly as LH due to the deeper root system in mesquite. In creosotebush-dominated areas, a decrease in albedo, an increase in roughness length and displacement height contributed to the SH increase and warmer temperatures. Sensitivity simulations showed that an increase in soil moisture content enhanced shrub LH and a reduction in mesquite cover enhanced the temperature differences. The observed shift in vegetation led to complex interactions between land and surface fluxes, demonstrating that vegetation itself is a weather and climate variable as it significantly influences temperature and humidity.

Long‐term effects of climate change on vegetation and carbon dynamics in peat bogs

AbstractQuestions:What are the long‐term effects of climate change on the plant species composition and carbon sequestration in peat bogs?Methods:We developed a bog ecosystem model that includes vegetation, carbon, nitrogen and water dynamics. Two groups of vascular plant species and three groups of Sphagnum species compete with each other for light and nitrogen. The model was tested by comparing the outcome with long‐term historic vegetation changes in peat cores from Denmark and England. A climate scenario was used to analyse the future effects of atmospheric CO2, temperature and precipitation.Results:The main changes in the species composition since 1766 were simulated by the model. Simulations for a future warmer, and slightly wetter, climate with doubling CO2 concentration suggest that little will change in species composition, due to the contrasting effects of increasing temperatures (favouring vascular plants) and CO2 (favouring Sphagnum). Further analysis of the effects of temperature showed that simulated carbon sequestration is negatively related to vascular plant expansion. Model results show that increasing temperatures may still increase carbon accumulation at cool, low N deposition sites, but decrease carbon accumulation at high N deposition sites.Conclusions:Our results show that the effects of temperature, precipitation, N‐deposition and atmospheric CO2 are not straightforward, but interactions between these components of global change exist. These interactions are the result of changes in vegetation composition. When analysing long‐term effects of global change, vegetation changes should be taken into account and predictions should not be based on temperature increase alone.

Vegetation and fire history of a Chinese site in southern tropical Xishuangbanna derived from phytolith and charcoal records from Holocene sediments

AbstractAim The aims of this paper are to reconstruct the vegetation and fire history over the past 2000 years in a well‐preserved rain‐forest area, to understand interactions between climate, fire, and vegetation, and to predict how rain forest responds to global warming and increased intensity of human activity.Location Xishuangbanna, south‐west China, 21–22° N, 101–102° E.Methods Phytolith (plant opal silica bodies) morphotypes, assemblages, and indices were used to reconstruct palaeovegetation and palaeoclimate changes in detail. Micro‐charcoal particles found in phytolith slides, together with burnt phytoliths and highly weathered bulliform cells, were employed to reconstruct a record of past fire occurrence. A survey of field sediments, lithology, and 14C dating were also employed.Results Phytoliths were divided into 11 groups and classified into 33 well‐described morphotypes according to their shape under light microscopy and their presumed anatomical origins and ecological significance. The phytolith assemblages were divided into six significant zones that reveal a complete history of vegetation changes corresponding to climate variation and fire occurrence. Phytolith assemblages and indices show that the palaeoclimate in the study area is characterized by the alternation of warm–wet and cool–dry conditions. Phytolith and charcoal records reveal that 12 fire episodes occurred. Comparison of burnt phytoliths with an aridity index (Iph) shows that fire episodes have a strong relationship with drought events.Main conclusions Our results indicate that fire occurrence in the tropical rain forest of Xishuangbanna is predominantly under the control of natural climate variability (drought events). Nearly every fire episode is coupled with a climatic event and has triggered vegetation composition changes marked by a pronounced expansion of grasses. This indicates that drought interacts with fire to exert a strong influence on the ecological dynamics of the rain forest. However, the impact of human activity in recent centuries is also significant. Our results are important for understanding the interactions between climate, fire, and vegetation, and for predicting how rain forest responds to global warming and increased human activity.

Phytolith evidence for the absence of a prehistoric grass understory in a Jeffrey pine – mixed conifer forest in the Sierra San Pedro Mártir, Mexico

Phytolith analysis was applied to several sites in a Jeffrey pine ( Pinus jeffreyi Grev. & Balf.) – mixed conifer forest in the Sierra San Pedro Mártir, Baja California, Mexico, to explore the hypothesis that the introduction of livestock in the late 18th century led to overgrazing of a prehistoric grass understory, resulting in changes to the prehistoric fire regime observed in the tree-ring fire-scar record. Stable soils in regions with extensive prehistoric grass cover retain a high concentration of total phytoliths and high percentage of grass phytoliths, regardless of historic vegetation changes. Phytoliths extracted from soil samples collected from several sites in the Sierra San Pedro Mártir revealed total phytolith concentrations in forest soils were generally <0.5% by mass, with most <0.1%, whereas grass phytoliths were generally <10% of the total, values consistent with the interpretation of a forest with sparse grass cover in the understory. Phytolith evidence suggests that there was minimal grass available for grazing in prehistoric Sierra San Pedro Mártir forests; overgrazing a grass understory was probably not a major driver of changes in the prehistoric fire regime.

Drivers of rain-forest boundary dynamics in Kakadu National Park, northern Australia: a field assessment

Understanding the causes of savanna–forest dynamics is vital as small but widespread changes in the extent of tropical forests can have major impacts on global climate, biodiversity and human well-being. Comparison of aerial photographs for 50 rain-forest patches in Kakadu National Park had previously revealed a landscape-wide monotonic expansion of rain-forest boundaries between 1964 and 2004. Here floristic, structural, environmental and disturbance attributes of the changes were investigated by sampling 588 plots across 30 rain-forest patches. Areas that had changed from savanna to rain forest were associated with a significantly higher abundance of rain-forest trees and less grasses, relative to stable savanna areas. Ordination analyses showed that overall floristic composition was not significantly different between newly established rain forest and longer established rain forest. Generalized linear models also indicated that contemporary levels of disturbance (fire and feral animal impact) and environmental variables (slope and soil texture) were poor predictors of historical vegetation change. We concluded that (1) the rain-forest boundaries are highly dynamic at the decadal scale; (2) rain-forest expansion is consistent with having been driven by global environmental change phenomena such as increases in rainfall and atmospheric CO2; and (3) expansion will continue if current climatic trends and management conditions persist.

PHYTOLITH EVIDENCE FOR THE LACK OF A GRASS UNDERSTORY IN A SEQUOIADENDRON GIGANTEUM (TAXODIACEAE) STAND IN THE CENTRAL SIERRA NEVADA, CALIFORNIA

ABSTRACT Tree ring fire-scars in Sequoiadendron giganteum (giant sequoia) stands record a high frequency, low intensity, prehistoric fire regime. Difficulties achieving short prehistoric fire return intervals with prescribed burns at a S. giganteum stand in Calaveras Big Trees State Park, California, currently characterized by dense tree cover with little understory vegetation due to over a century of fire suppression, suggest that a prehistoric grass understory provided fine fuel required for frequent fire spread. We used phytolith analysis to test this hypothesis. Phytoliths, microscopic silica bodies found in many plants but produced in large quantities with distinctive morphotypes in grasses, are preserved for thousands of years in the soil. Soils under vegetation with extensive prehistoric grass cover retain a high concentration of grass phytoliths regardless of historic vegetation changes. Phytoliths were extracted from soil samples taken from pits dug at 14 plots throughout a S. giganteum stand in ...

Eolian sand transport pathways in the southwestern United States: importance of the Colorado River and local sources

Geomorphologists have long recognized that eolian sand transport pathways extend over long distances in desert regions. Along such pathways, sediment transport by wind can surmount topographic obstacles and cross major drainages. Recent studies have suggested that three distinct eolian sand transport pathways exist (or once existed) in the Mojave and Sonoran Desert regions of the southwestern United States. One hypothesized pathway is eolian sand transport from the eastern Mojave Desert of California into western Arizona, near Parker, and would require sand movement across what must have been at least a seasonally dry Colorado River valley. We tested this hypothesis by mineralogical, geochemical and magnetic analyses of eolian sands on both sides of the Colorado River, as well as sediment from the river itself. Results indicate that dunes on opposite sides of the Colorado River are mineralogically distinct: eastern California dunes are feldspar-rich whereas western Arizona dunes are quartz-rich, derived from quartz-rich Colorado River sediments. Because of historic vegetation changes, little new sediment from the Colorado River is presently available to supply the Parker dunes. Based on this study and previous work, the Colorado River is now known to be the source of sand for at least three of the major dune fields of the Sonoran Desert of western Arizona and northern Mexico. On the other hand, locally derived alluvium appears to be a more important source of dune fields in the Mojave Desert of California. Although many geomorphologists have stressed the importance of large fluvial systems in the origin of desert dune fields, few empirical data actually exist to support this theory. The results presented here demonstrate that a major river system in the southwestern United States is a barrier to the migration of some dune fields, but essential to the origin of others.

An Integrated Model of Two Fire Regimes

Casual observers of chaparral in southern California(SCA) quickly learn two key facts about fires: they maybe started in a variety of weather conditions—windy orcalm, dry or humid—and the most spectacular modernburns occur during Santa Ana winds. Serious research-ers who seek to understand ecosystems and guide landmanagers must ask whether this has always been true.Readers should be surprised that Keeley and Fothering-ham (2001 [this issue]) answer yes. First, the chaparralecosystem has certainly not been static: it has experi-enced major changes in fire management as southernCalifornia’s population has increased. Second, observa-tions of the chaparral in nearby Baja California (BCA)immediately reveal a very different dynamic that surelydeserves serious consideration as a model for SCA, onethat precedes the establishment of modern suppressionpractices and dense population. The chaparral of BCA ischaracterized by smaller stands and a propensity forlow-intensity fires in relatively calm, humid weather.The sharp transition between the two regimes cannotbe explained by natural gradients in flora or weather; itfollows the international border, an artificial line drawnby human beings. Vegetation maps show that Californiaecosystems extend 200 km into BCA (Minnich & Franco-Vizcaino 1998).Climatic gradients including temperature and meanannual precipitation cross the border at right angles, andprevailing winds are everywhere westerly. Open-rangecattle grazing is practiced in BCA, but chaparral is unpal-atable to livestock (Minnich & Bahre 1995). Without dis-tinctive suppression systems, changes in fire regime shouldbe expressed in a continuum along environmental gradi-ents, not the discontinuity seen along the border. Theprimary difference is that BCA has not experienced thesame protectionist management policies as SCA, and thedivergence in chaparral fire ecology may provide insightinto the nature of historical vegetation change in SCA.The seminal question is how fires shaped ecosystemswithout management interference. Suppression is un-precedented in ecological history.Keeley and Fotheringham are obviously aware of theneed to balance the BCA and SCA models in any plausi-ble account of chaparral history. Yet their analysis fo-cuses on a 1983 account of the cross-border contrastand ignores a substantial body of more recent publica-tions, including a 52-year transborder fire history (1920–1971; Minnich & Chou 1997), a study of transborder post-fire chronosequences (Minnich & Bahre 1995), and stud-ies of presuppression fire regimes in SCA (Minnich 1987,1988). To evaluate their case for dismissing the BCAmodel, I must review the key findings they ignore. Thesefindings concern the following sequence of topics: (1)the nonrandom turnover of fire patches, (2) the over-abundance of natural ignitions compared with fuel pro-duction; (3) the dominance of landscape burning by rel-atively few fires (most fire starts fail), and (4) therandom phasing of fires with normal weather in the ab-sence of fire control. This is not just an intellectual exer-cise: these are serious implications for fire management.Both the original and subsequent studies (Minnich1983; Minnich & Chou 1997) show that, in the absenceof suppression, the chaparral of BCA is a diverse, fine-grained patch mosaic. With fire suppression in SCA, thechaparral comprises unbroken carpets of mature vegeta-tion interspersed with a few extensively denuded water-sheds (Fig. 1). There are ample data to suggest differ-ences in fire management, including the number of firesof 15 ha (BCA, 2000 events; SCA 350 events), maxi-mum fire size (BCA, 3,000 ha; SCA 59,000 ha), and dif-ferences in fire weather (BCA, onshore flows; SCA, off-shore flows). The only similarity is that fire-return intervalsare 50–70 years in both countries. Our integrated modelexplains the disparate fire outcomes that have existed inthe two countries since the 1920s, Keeley and Fother-ingham do not.An important aspect in developing fire-disturbancetheory is choosing an incontrovertible starting point thatleads in directions productive for research. The modelby Minnich and Chou (1997) is based on the fact that

Patterns of intraspecific diversification in the Piriqueta caroliniana complex in southeastern North America and the Bahamas.

We use chloroplast DNA (cpDNA) variation and nested clade phylogeographic analyses to infer the historical processes that have contributed to the high level of morphological and ecological diversification present in a group of herbaceous perennials (the Piriqueta caroliniana complex) in North America and the Bahamas. The presence of morphologically distinct and intercompatible varieties (morphotypes) that can be distinguished based on suites of taxonomic characters (e.g., leaf shape, pubescence type, stature) and contrasting habitat affinities (from marshes to dry pinelands and sand scrub) makes this group particularly appropriate for studies of intraspecific diversification. To examine the distribution of haplotypes among populations, we sampled 467 individuals from 55 locations in Florida, Georgia, and the northern Bahamas (Grand Bahama and Abaco) and screened each individual for cpDNA variation using restriction fragment length polymorphism (RFLP) and heteroduplex analyses. We develop a one-step haplotype phylogeny for this group and use the geographic distributions of haplotypes and clades to test specific phylogeographic hypotheses using the methods developed by Templeton and his colleagues (Templeton 1998). In general, the distribution of haplotypes was strongly influenced by limited dispersal distances, with the more recently derived haplotypes having much lower levels of dispersion and lower frequencies in populations than the ancestral haplotypes. The patterns of clade and haplotype dispersion and displacement and the distribution of morphotypes imply at least three cases of long-distance dispersal and one case of historical fragmentation. The historical patterns inferred for populations of Piriqueta are consistent with known biogeographical events, historical vegetation change, and the concordant patterns of multiple Pleistocene refugia that have been observed for a number of other taxa in southeastern North America.

Retrospective monitoring of rangeland vegetation change: ecohistory from deposits of sheep dung associated with shearing sheds

AbstractThis paper explores the potential of a new method of reconstructing historical vegetation change in the Australian rangelands. Historical monitoring of rangeland vegetation has been so deficient that it is not possible to determine whether a long‐term trend toward degradation has occurred (as is often assumed) or, indeed, if it is continuing to occur. Because long‐term records are unavailable any attempt to monitor vegetation retrospectively must be based on proxy measures rather than direct observation. Where historical data are lacking an integration of palaeoecological, archaeological and ecological methods is required to reconstruct the past. Our research is based on a detailed analysis of sheep faeces deposited near a shearing shed in the semiarid rangelands of south‐west Queensland between the late 1930s and the mid‐1990s. The faeces in these deposits represent the diet of sheep in the days leading up to the property’s annual shearing and as such are a potentially useful index to changes in vegetation. Results indicate significant changes in the diet of sheep since the late 1940s. The potential of this method, and its limitations, are discussed. Long‐term records are critical in understanding issues of sustainability in land management and it is intended that this paper will stimulate further research into historical vegetation change in rangelands.

Temporally-explicit models of fire and forest

Pollen and charcoal data from varved sediments of Lake Ahvenainen, southern Finland, were examined through ordination analyses to determine temporal groupings of vegetation. The ordination `continually' changed throughout the pollen profile, indicating nonequilibrium system dynamics. However, temporal associations that were stationary existed during the history of vegetation change at Lake Ahvenainen, and these temporal associations were nested in a hierarchy. Weighted averaging regression and calibration were used to model the relationship between fire and vegetation within each temporal association. Fire was significantly related to the vegetation for nearly all temporal associations. Community dynamics within temporal associations were examined with cross-correlation analysis. Taxa were correlated with fire occurrence (charcoal fragments) within the temporal associations and classic successional recovery was confirmed. In addition, two temporal associations showed evidence of chaotic behavior. The long-term pollen-charcoal analysis supported three theories of system dynamics: (1) nonequilibrium long-term dynamics, (2) hierarchical structuring of temporally stationary associations, and (3) chaotic dynamics in stationary associations. These theories are not necessarily contradictory, but are scale dependent.

PATTERNS OF INTRASPECIFIC DIVERSIFICATION IN THE PIRIQUETA CAROLINIANA COMPLEX IN SOUTHEASTERN NORTH AMERICA AND THE BAHAMAS

We use chloroplast DNA (cpDNA) variation and nested clade phylogeographic analyses to infer the historical processes that have contributed to the high level of morphological and ecological diversification present in a group of herbaceous perennials (the Piriqueta caroliniana complex) in North America and the Bahamas. The presence of morphologically distinct and intercompatible varieties (morphotypes) that can be distinguished based on suites of taxonomic characters (e.g., leaf shape, pubescence type, stature) and contrasting habitat affinities (from marshes to dry pinelands and sand scrub) makes this group particularly appropriate for studies of intraspecific diversification. To examine the distribution of haplotypes among populations, we sampled 467 individuals from 55 locations in Florida, Georgia, and the northern Bahamas (Grand Bahama and Abaco) and screened each individual for cpDNA variation using restriction fragment length polymorphism (RFLP) and heteroduplex analyses. We develop a one-step haplotype phylogeny for this group and use the geographic distributions of haplotypes and clades to test specific phylogeographic hypotheses using the methods developed by Templeton and his colleagues (Templeton 1998). In general, the distribution of haplotypes was strongly influenced by limited dispersal distances, with the more recently derived haplotypes having much lower levels of dispersion and lower frequencies in populations than the ancestral haplotypes. The patterns of clade and haplotype dispersion and displacement and the distribution of morphotypes imply at least three cases of long-distance dispersal and one case of historical fragmentation. The historical patterns inferred for populations of Piriqueta are consistent with known biogeographical events, historical vegetation change, and the concordant patterns of multiple Pleistocene refugia that have been observed for a number of other taxa in southeastern North America.Corresponding Editor: M. Dudash

Palynological evidence for 19th century grazing-induced vegetation change in the southern Sierra Nevada, California, U.S.A.

Summary Aim Stratigraphic pollen records are used to assess historic vegetation changes that have transpired in a North American mountain meadow since the introduction of Old World livestock species in the middle 1800s. Location Monache Meadows is located on the Kern Plateau in the Sierra Nevada mountain range, California, U.S.A. It is situated along the upper reaches of the South Fork Kern River in the southernmost drainage basin of the Sierra Nevada. Methods Short core samples of meadow sediments were extracted from five locations throughout Monache Meadows. These five samples are classified according to topographic position within the meadow – two upper meadow sites and three lower meadow sites. Stratigraphic analyses of fossil pollen from each core were used to assess vegetation composition before the introduction of European livestock (pre1850) and throughout the historic period (1850–present). The historic period geochronology is based on 210Pb dating of selected strata from each core. ResultsRiccia was a dominant taxon in the upper meadow before the introduction of grazing; Salix seems to have been more abundant in the lower meadow. Both Riccia and Salix decreased dramatically by c.1900, coeval with marked increases in Artemisia (upper meadow) and Cyperaceae (upper and lower meadows). Main conclusions Changes in meadow vegetation occurring during the latter part of the 19th century at Monache Meadows are attributed primarily to the introduction of European livestock (sheep and cattle). Other factors that may have contributed to the observed shifts in composition and dominance include changes in native herbivore populations and decreased fire frequency as a result of 20th century fire suppression policies.

Historical Vegetation Change in Oakland and Its Implications for Urban Forest Management

The history of Oakland, California's urban forest was researched to determine events that could influence future urban forests. Vegetation in Oakland has changed drastically from a preurbanized area with approximately 2% tree cover to a present tree cover of 19%. Species composition of trees was previously dominated by coast live oak (Quercus agrifolia), California bay {Umbellularia californica), and coast redwood (Sequoia sempervirens) and is currently dominated by blue gum [Eucalyptus globulus), Monterey pine {Pinus radiata), and coast live oak. Many forces throughout the history of Oakland have shaped the current urban forest structure. These forces include the gold rush of the 1840's, the San Francisco earthquake of 1906, massive afforestation of the early 1900's, and various fires from 1923 to 1991. These historical forces and the impact they had on Oakland's urban forest are explored. Future forces that can alter any urban forest are presented and discussed.

A case history of vegetation changes on the Meridean Islands of West-Central Wisconsin, USA

The history of the vegetation of the Meridean Islands on the Chippewa River in Wisconsin is presented. Land office survey data from 1845–1849 indicate that about 60% of the island was prairie and oak openings, while most of the remaining area was swamp-hardwood forest at the time of settlement. Farms, small industry and a small village developed on the islands but were abandoned in the early 1900s. Land economic inventories from 1937, aerial photographs taken from 1951 to 1981 and sample plots were used to trace the changes in vegetation that have occurred in the interim. The early settlers established their farms on the open land, much of which was converted to pine plantations after abandonment. Little change was found to occur in the location, extent and composition of the forests. Overall, the vegetation pattern present on the islands today is very similar to that present prior to settlement.

Historical vegetation change in the Kananaskis Valley, Canadian Rockies

This study compares the vegetation composition in the Kananaskis Valley from a forest survey in 1883 to another survey in 1972 and reconstructs the fire frequency for the period 1783 – 1882 and the period 1883 – 1972. A comparison of the 1883 to 1972 forest surveys using transition probabilities revealed that sites populated mostly by lodgepole pine (Pinus contorta) or Englemann spruce (Picea Englemannii) tended to remain the same in both surveys. The fire reconstructions for the period 1730 – 1972 showed no change in fire frequency after the beginning of European activity in 1883. Further, for the periods both before and after 1883, the valley burned, on average, once every 150 years. The distribution of the fire sizes for the 100-year period before 1883 was slightly larger than the period after 1883. It appears that in 1972 natural processes (site differences and fire occurrence) still dominated the changes in the vegetation composition and age.