Contemporary Forest Research Articles

Using perceptual maps to communicate concepts of Sustainable Forest Management – Collaborative research with the Office of the Wet'suwet'en Nation in British Columbia

This article discusses collaborative research with the Office of the Wet'suwet'en Nation on their traditional territories in north-central British Columbia, Canada, a forest-dependent region where contemporary and traditional forest resources management regimes overlap. In-depth personal interviews with the hereditary chiefs and concept mapping were used to identify social-ecological linkages in Wet'suwet'en culture to inform the development of culturally sensitive social criteria and indicators of sustainable forest management (SFM) in this region. The preliminary results demonstrate how the CatPac II software tool can be applied to identify key component concepts and linkages in local definitions of SFM, and translate large volumes of (oral) qualitative data into manageable information resources for forest managers and decision-makers. Key words: social criteria and indicators, sustainable forest management, qualitative research, Wet'suwet'en

Among- and within-patch components of genetic diversity respond at different rates to habitat fragmentation: an empirical demonstration

Habitat fragmentation is a ubiquitous by-product of human activities that can alter the genetic structure of natural populations, with potentially deleterious effects on population persistence and evolutionary potential. When habitat fragmentation results in the subdivision of a population, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulation, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulations and greater genetic divergence among them. Theoretical and simulation analyses predict that these two main genetic effects of fragmentation, greater differentiation among resulting subpopulation and reduced genetic diversity within them, will proceed at very different rates. Despite important implications for the interpretation of genetics data from fragmented populations, empirical evidence for this phenomenon has been lacking. In this analysis, we carry out an empirical study in population of an alpine meadow-dwelling butterfly, which have become fragmented increasing forest cover over five decades. We show that genetic differentiation among subpopulations (G(ST)) is most highly correlated with contemporary forest cover, while genetics diversity within subpopulation (expected heterozygosity) is better correlated with the spatial pattern of forest cover 40 years in the past. Thus, where habitat fragmentation has occurred in recent decades, genetic differentiation among subpopulation can be near equilibrium while contemporary measures of within subpopulation diversity may substantially overestimate the equilibrium values that will eventually be attained.

Modeling Historical Ecology, Thinking about Contemporary Systems

One way to make archaeological trajectories compelling to contemporary audiences is through detailed computer simulation with graphical interfaces that allow students or researchers to explore historical sequences and ask “what if” questions of them. We discuss progress on modeling coupled human systems and ecosystems over long periods in the Mesa Verde region of the U.S. Southwest, a project developed with both research and educational products in mind. The project has many foci, but here we concentrate on fuel‐wood availability and its pre‐Hispanic use in the pygmy forests of this region. Our preliminary results tend to indicate that wood for fuels became sufficiently limited in this sequence to become a factor of considerable importance in decisions about where to live, how to build, and even whether to remain in the region. The same logic of modeling can be used to study problems of contemporary forest use in other parts of the world.

Climatic influences on fire regimes in the northern Sierra Nevada mountains, Lake Tahoe Basin, Nevada, USA

AbstractAim The goal of this study was to understand better the role of interannual and interdecadal climatic variation on local pre‐EuroAmerican settlement fire regimes in fire‐prone Jeffrey pine (Pinus jeffreyiGrev. & Balf.) dominated forests in the northern Sierra Nevada Mountains.Location Our study was conducted in a 6000‐ha area of contiguous mixed Jeffrey pine‐white fir (Abies concolorGordon & Glend.) forest on the western slope of the Carson Range on the eastern shore of Lake Tahoe, Nevada.Methods Pre‐EuroAmerican settlement fire regimes (i.e. frequency, return interval, extent, season) were reconstructed in eight contiguous watersheds for a 200‐year period (1650–1850) from fire scars preserved in the annual growth rings of nineteenth century cut stumps and recently dead pre‐settlement Jeffrey pine trees. Superposed epoch analysis (SEA) and correlation analysis were used to examine relationships between tree ring‐based reconstructions of the Palmer Drought Severity Index (PDSI), Southern Oscillation Index (SOI), Pacific Decadal Oscillation (PDO) and pre‐EuroAmerican fire regimes in order to assess the influence of drought and equatorial and north Pacific teleconnections on fire occurrence and fire extent.Results For the entire period of record (1650–1850), wet conditions were characteristic of years without fires. In contrast, fire years were associated with drought. Drought intensity also influenced fire extent and the most widespread fires occurred in the driest years. Years with widespread fires were also preceded by wet conditions 3 years before the fire. Widespread fires were also associated with phase changes of the PDO, with the most widespread burns occurring when the phase changed from warm (positive) to cold (negative) conditions. Annual SOI and fire frequency or extent were not associated in our study. At decadal time scales, burning was more widespread during decades that were dryer and characterized by La Niña and negative PDO conditions. Interannual and interdecadal fire–climate relationships were not stable over time. From 1700 to 1775 there was no interannual relationship between drought, PDO, and fire frequency or extent. However, from 1775 to 1850, widespread fires were associated with dry years preceded by wet years. This period also had the strongest association between fire extent and the PDO. In contrast, fire–climate associations at interdecadal time scales were stronger in the earlier period than in the later period. The change from strong interdecadal to strong interannual climate influence was associated with a breakdown in decadal scale constructive relationships between PDO and SOI.Main conclusions Climate strongly influenced pre‐settlement pine forest fire regimes in northern Sierra Nevada. Both interannual and interdecadal climatic variation regulated conditions conducive to fire activity, and longer term changes in fire frequency and extent correspond with climate‐mediated changes observed in both the northern and southern hemispheres. The sensitivity of fire regimes to shifts in modes of climatic variability suggests that climate was a key regulator of pine forest ecosystem structure and dynamics before EuroAmerican settlement. An understanding of pre‐EuroAmerican fire–climate relationships may provide useful insights into how fire activity in contemporary forests may respond to future climatic variation.

IDENTIFYING FOREST REFERENCE CONDITIONS ON EARLY CUT-OVER LANDS, LAKE TAHOE BASIN, USA

Pre-Euro-American settlement forest structure and fire regimes for Jeffrey pine-white fir, red fir-western white pine, and lodgepole pine forests in the Lake Tahoe Basin (California and Nevada, USA) were identified using stand structural analysis and fire scars based on measurements of stumps of trees that were cut in the 19th century. Com- parisons of the presettlement reference with contemporary conditions were then used to determine how and why contemporary conditions deviate from presettlement conditions and to guide ecological restoration. Contemporary forests varied in different ways compared to the presettlement reference. Contemporary Jeffrey pine-white fir forests have more and smaller trees, more basal area, less structural variability, and trees with a more clumped spatial distribution than preset- tlement forests. The mean presettlement fire-return interval for Jeffrey pine-white fir forests was 11.4 yr, and most ( .90%) fires burned in the dormant season; no fire was recorded in the study area after 1871. Similar differences were identified in the structural characteristics of contemporary and presettlement red fir-western white pine and lodgepole pine forests. However, 19th-century logging changed the composition of red fir-western white pine forests, and these forests now have more lodgepole pine than red fir or western white pine. Comparison of contemporary forests with the presettlement reference suggests that resto- ration treatments in Jeffrey pine-white fir forests should include: (1) density and basal- area reduction, primarily of smaller diameter trees; (2) reintroduction of frequent fire as a key regulating disturbance process; and (3) increasing structural heterogeneity by shifting clumped tree distributions to a more random pattern. Restoration treatments in red fir- western white pine forests should include: (1) a shift in species composition by a density and basal-area reduction of lodgepole pine; and (2) increasing structural heterogeneity by shifting tree distributions to a more random pattern. In lodgepole pine forests the restoration emphasis should be: (1) a density and basal-area reduction of small-diameter trees; and (2) an increase in structural heterogeneity that shifts tree spatial patterns from clumped to a more random distribution. Reintroduction of fire as a regulating process into high-elevation red fir-western white pine and lodgepole pine forests can be viewed as a longer-term restoration goal. The method for quantifying presettlement reference conditions from stumps complements, or is an alternative to, methods based on dendroecology or repeat photog-

DEVELOPMENTAL PATTERNS AND NUTRITION IMPACT RADIATION USE EFFICIENCY COMPONENTS IN SOUTHERN PINE STANDS

A number of contemporary forest productivity models use some variation of a growth efficiency (ε) approach. Typically, these models predict production (aboveground net primary production, ANPP, in units of dry mass biomass per unit of area per unit of time) as the product of two terms: radiation use efficiency (ε, in units of dry mass biomass per megajoule of photosynthetically active radiation [PAR] intercepted or absorbed by the plant canopy) and the sum of PAR intercepted or absorbed by the canopy (Φpar, in units of megajoules per unit of radiation area per unit of time). Predicting productivity in a biologically realistic manner requires an understanding of how model components are affected by natural and anthropogenic environmental factors, as well as other influences such as aging or stand development. We measured or calculated all components of the ε model (aboveground woody biomass increment, IWB; foliage biomass increment, IFB; aboveground net primary production, ANPP; leaf area index, LAI; Φpar; and aboveground radiation use efficiency, εA) from ages 4 to 18 yr in loblolly and slash pine stands in north-central Florida grown under replicated fertilizer and understory vegetation control treatments that induced a large gradient in soil nutrient availability. Treatments impacted all measured components, which in turn led to strong responses in aboveground radiation use efficiency. Age 6–9 yr εA, averaged across species, ranged from 0.78 g/MJ to 0.83 g/MJ in treatments receiving fertilizer or vegetation control vs. 0.53 g/MJ in untreated plots. Stand developmental processes modified these responses, however, with εA declining by over 40% in treated plots from age 6–9 yr to age 15–16 yr. Variation in εA in both species was linked to development of stand basal area (BA), with a positive, linear relationship between εA and BA for values of BA < 18 m2/ha and a declining, linear relationship for values of BA > 18 m2/ha. Loblolly pine εA was positively correlated with foliar nitrogen concentration, [N]. These data highlight the dynamic nature of εA and suggest that both stand developmental and nutritional processes drive changes in ANPP and εA in southern pines.

Comparison of Historical and Contemporary Forest Structure and Composition on Permanent Plots in Southwestern Ponderosa Pine Forests

Abstract We compared historical (1909–1913) and contemporary (1997–1999) forest structure and composition on 15 permanent plots in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests of Arizona and New Mexico. We used the same sampling methods as in the early 1900s and compared stand density, diameter distributions, species composition, and broad age classes from the two periods. Stand density (trees ≥9.14 cm dbh) significantly (P &amp;lt; 0.001) increased on plots from an average of 77.4 trees per plot (s = 49.9) at plot establishment in 1909–1913 to 519.1 trees per plot (s = 252.3) at remeasurement in 1997–1999. Basal area significantly (P &amp;lt; 0.001) increased from 8.0 m2 per plot (s = 3.5) to 28.5 m2 per plot (s = 10.1). Contemporary tree diameter distribution shifted toward smaller size classes as demonstrated by a significant (P = 0.001) decrease in quadratic mean diameter from 38.5 cm (s = 7.5) in 1909–1913 to 28.6 cm (s = 7.1) in 1997–1999. Broad age classes yielded an average of 61.5 (s = 49.5) residual live trees classified as “blackjack” ponderosa pine (P. ponderosa &amp;lt;150 years) and 13.3 (s = 11.9) “yellow pine” (P. ponderosa ≥150 years) in 1909–1913. In 1997–1999, 416 live trees (s = 229.6) were “blackjack” and 57.2 (s = 28.5) trees on average were “yellow pine.” Twelve of the 15 plots were not invaded by other tree species (remained pure ponderosa pine type), while composition shifted slightly on three plots toward more shade-tolerant and fire-intolerant species. Ninety-one percent of the historically (1909–1913 or older) mapped tree structures (live trees, snags, logs, stumps, etc.) were relocated, which suggested that the forest reconstruction field techniques are reliable within 10%. Dramatic increases in tree densities may represent an increased potential for bark beetle epidemics and stand replacing wildfire over large areas in the Southwest. FOR. SCI. 50(2):162–176.

The forest planning system in relation to the forest resource and forestry policies

The current forest planning system of Japan has been in place since the formulation of the Forest Law back in 1897. During this time, although addressing specified forests as demonstrated in the system for protection forests, in a more general sense, the execution of the forest planning system has placed “forestry management” at the core. In other words, it has instead been forest administration delivered in a manner relevant to forestry management. This trend is exhibited in, for instance, policies for the reorganization of common forest, the forest management planning system, forest owners' associations, the proceeds-sharing reforestation system, cooperative silviculture management, and valley forestry revitalization; which have all been implemented.In this paper I review the results of these practices and explore the contemporary forest owner's pattern of behavior. I also discuss the passive attitudes among forest owners, especially in comparison with the attitudes prevalent during the postwar reforestation era, continuing up to the 1960s, and the current tendency towards neglect in the afforested areas, as well as the increasing number of forest owners giving up forestry practice.In the postwar era (up to the 1960s), forestry had been following an upward trend of development that motivated forest owners to afforest, as this was the optimal choice for increasing the family's stocks for future generations (in the manner of holding an asset), and thus a rapid expansion of plantation forests resulted. By the 1970s, when domestic wood supply became less than a half of all domestic wood demand (it is still declining now), forest owners gradually began to lose interest in reforestation and care of the forest as a method of increasing assets. The current share of domestic wood supply in total consumption has dropped to 20%, and the annual cut volume is only 23% of the annual volume increment.Forests are as much a public property as they are private and, moreover, represent a globally significant resource. Active stewardship, such as materializing internationally agreed notions of sustainable forest management, promoting forest certification systems, and complying with the Kyoto Protocol, are now important issues, both domestically and internationally.The paradoxical gap between current forestry trends and public aspirations for forests is widening with each year, thus creating a grave social problem. I have been focusing on forestry revitalization as the primary step towards the resolution of this issue. As the logical basis for executing this policy, I review the relations between forest resource policies and forestry policies.At the same time, by reviewing the forest planning system and its developmental process, I sought to investigate what new policies would fulfill the need to realize the public functions of forests while revitalizing forestry, form the point of view of forestry policies and their influence on the forest planning system. I have concluded that there is a case for separating forest management from forest ownership in units of forest compartments; namely to establish an incorporative management system by which forest owners can invest in their stands.

Diversity in Ponderosa Pine Forest Structure Following Ecological Restoration Treatments

Abstract We tested the effectiveness of ponderosa pine forest restoration by comparing forest restoration treatments to untreated forest and to reconstructed forest structure in 1870 (date of Euro-American settlement) using an experimental block design at the Grand Canyon-Parashant National Monument in northwestern Arizona. Forest tree density averaged more than 20 times the historical tree density, and basal area was 4 to 6 times higher in contemporary forests than in historical forests. Restoration treatments consisted of thinning young trees to emulate the forest density, tree composition, and spatial distribution in 1870, followed by prescribed burning. Following restoration treatment, tree density was significantly reduced but remained 6 times higher than historical forests. Basal area in restored forests was still 2.5 times greater than reconstructed basal area values. Ponderosa pine dominance changed little from pretreatment data across the four blocks, averaging 60% of stems and 87% of the basal area prior to treatment and 56% of stems and 85% of the basal area following treatment. Ninety-eight percent of contemporary forest trees were less than 100 yr old prior to restoration treatment; this proportion was reduced to 82% following treatment. Restoration treatment also significantly reduced canopy cover and increased total tree regeneration. However, treatment effects on forest fuels were highly variable. Litter and duff fuel layers were significantly reduced by prescribed fire but woody debris increased. Overall forest structural diversity following treatment implies that fire behavior, wildlife habitats, and other ecological attributes will vary relatively widely in the future landscape.

Same Forest, Different Countries

SUMMARY In the Gran Sabana of Venezuela and the North Rupununi Savannah of Guyana, protected areas have been established primarily for purposes of conservation. However, both Canaima National Park in Venezuela and the Iwokrama International Centre for Rainforest Conservation and Development in Guyana are multiple use areas where a variety of resource use occurs and/or is planned. Shifting cultivation by the indigenous population is currently both the most common use of the forest and the use of longest duration in both areas. Surveys were conducted of paired primary and secondary forests in order to test the hypothesis that traditional, dispersed shifting cultivation with long fallows and no post-cultivation disturbance is sustainable, resulting in the eventual re-establishment of diverse secondary forests. Interviews and observations of agricultural practices and surveys of agricultural fields were conducted to determine the contemporary forest use practices and the extent to which traditional practices have changed. Results indicate that even dispersed, long fallow shifting cultivation requires careful management and several disturbance-free decades before diversity levels in secondary forests approach those in old growth. Further, that the process of integration and cultural “development” has destabilized this traditionally sustainable system in some areas. A central assumption of the paper is that with an understanding of the impacts of shifting cultivation and of the conditions under which it is sustainable, informed decisions about protected area management can be made. The data provide valuable and hitherto missing information on the levels of forest disturbance that can be sustained in the two protected areas while still meeting conservation goals.

The Last Glacial–Interglacial Transition (LGIT) in south Westland, New Zealand: paleoecological insight into mid-latitude Southern Hemisphere climate change

High resolution pollen stratigraphy from three peat cores located within 20 km of Lateglacial moraines in south Westland, New Zealand provide detailed records of climate change during the Last Glacial–Interglacial Transition (LGIT). The pollen record shows the replacement of grassland by shrubland prior to ca 15,300 14C yr BP (18,300 cal. yr BP) followed by the progressive development of broadleaf shrubland and scattered forest prior to ca 12,000 14C yr BP (14,400 cal. yr BP). Local vegetation changes around the time of the Younger Dryas chronozone (11–10 ka 14C BP) are evident, but are not necessarily a result of regional climate cooling. Vegetation changes between ca 12,000 and 10,000 14C yr BP (14,400 and 11,400 cal. yr BP) indicate a period of increased precipitation. Tall podocarp forest, similar to that of the contemporary forest, was well established by ca 10,000 14C yr BP (11,400 cal. yr BP). A period of increased westerly circulation over southern New Zealand is considered to be the most likely mechanism for causing the increased precipitation between ca 12,000 and 10,000 14C yr BP (14,300 and 11,400 cal. yr BP). Increased precipitation would also provide a mechanism for initiating LGIT ice advance in the area. Data from these records show some support for global climate change models that propose inter-hemispheric linkage, but may be more supportive of a climate change model that incorporates an increased westerly circulation over southern New Zealand during the LGIT.

Participation and societal values: the challenge for lawmakers and policy practitioners

Participation is about finding consensus in diversity and reflects a normative shift towards multiple-use values that recognise that forest management should blend multiple management objectives into a coherent set of practices. A framework to incorporate interest groups’ values and needs into functional forest management systems has yet to be institutionalised in contemporary forest policy and management. Participation is not just a means but also a model for involving those concerned. It should be understood as a pro-active approach for creating an enhanced understanding of objectives, problems and their solution. Optimally any participative process will help to create more informed operative decisions, and thus provide a more solid base for policy outputs, increasing the chance of reaching ‘sustainable’ decisions that consider long-term effects. The analytical framework of this paper draws on theoretical traditions within the sociology of law and legal theory, and analyses some recent national legislation and international law with respect to participation. It proposes a set of guidelines that aim to facilitate participation (as opposed to merely pro forma consultation) with particular reference to the formulation and implementation of National Forest Programmes (NFPs).

GENETIC RESPONSES TO CLIMATE INPINUS CONTORTA: NICHE BREADTH, CLIMATE CHANGE, AND REFORESTATION

Fundamental plant–environment relationships were revealed by analyses of 20-yr height and survival of 118 populations representing two subspecies of Pinus contorta growing in common gardens at 60 environmentally disparate test sites in British Columbia. The approach involved (1) preparing models that described the general climate of British Columbia, (2) developing population-specific response functions driven by predicted climate variables, (3) developing general transfer functions that predict performance from the climatic distances over which populations were transferred, and (4) interpreting the results in terms of niche breadth, effects of climate change on adaptedness of populations, and reforestation in a changing environment. Polynomial regression models used physiographic descriptors to predict seven climate variables from normalized records of 513 weather stations. Values of R2 ranged over 0.80–0.97 for thermal variables and 0.54–0.61 for precipitation variables. Validations with independent data from 45 stations were strong and suggested that the models were generally free of bias within the limits of the original data. Response functions describing the height or survival of each population were developed from quadratic regressions using predicted climate variables for each test site. Mean annual temperature and mean temperature in the coldest month were the most effective variables for predicting population height, while the ratio of summer temperature to summer moisture was the best predictor of survival. Validation of the response functions with independent data from two additional test sites produced values of R2 between actual and predicted values that were as high as 0.93 for height and 0.73 for survival. The results demonstrated that natural populations have different climatic optima but tend to occupy suboptimal environments. Nevertheless, the general transfer functions showed that optimal growth and survival of the species as a whole is associated with the null transfer distance. These seemingly anomalous results suggest that the same processes thought to determine the distribution of species control the distribution of genotypes within species: (1) environmental selection to produce a broad fundamental niche, and (2) density-dependent selection to produce a relatively narrow realized niche within which most populations are relegated to suboptimal environments. Consequently, the steep geographic clines typical of P. contorta seem to be driven more by density-dependent selection than by environmental selection. Asymmetric gene flow from the center of distribution toward the periphery is viewed as a primary regulator that provides the fuel for both environmental and density-dependent selection and thereby indirectly perpetuates suboptimality. The response functions predict that small changes in climate will greatly affect growth and survival of forest tree populations and, therefore, that maintaining contemporary forest productivities during global warming will require a wholesale redistribution of genotypes across the landscape. The response functions also provide the climatic bases to current reforestation guidelines and quantify the adjustments necessary for maintaining adaptedness in planted trees during periods of small (∼1°C) temporal temperature shifts.

DETERMINING REFERENCE CONDITIONS FOR ECOSYSTEM MANAGEMENT OF SOUTHWESTERN PONDEROSA PINE FORESTS

The fire disturbance regime and forest structure prior to Euro-American settlement (AD 1883) of a southwestern ponderosa pine (Pinus ponderosa) landscape were quantified in order to establish reference conditions as a baseline for ecosystem management. The mean presettlement fire interval between 1637 and 1883 was 3.7 yr for all fires and 6.5 yr for widespread fires, but fire has been excluded from the study area since 1883. Forest density increased under fire exclusion from an average of 148 trees/ha in 1883 (65 pines, 80 oaks, three other species), an open forest dominated by relatively large ponderosa pines, to 1265 trees/ha in 1994/1995 (720 pines, 471 oaks, 74 others), a dense forest characterized by relatively small and young trees. Species composition has shifted toward greater dominance by Gambel oak (Quercus gambelii) and conifers less adapted to frequent fires: white fir (Abies concolor) and Douglas-fir (Pseudotsuga menziesii). The reference presettlement conditions can be applied to management of this ecosystem in two ways. First, reference conditions are a benchmark against which to evaluate contemporary conditions and future alternatives. The comparison shows that the contemporary forest is well above the range of presettlement variability in forest density, and both live and dead fuel structures have developed that can support high-intensity wildfire. Second, reference conditions can serve as a goal for ecological restoration treatments.

Elements of 19th-Century Romanticism in Contemporary Forest Management Practices

Elements of 19th-Century Romanticism in Contemporary Forest Management Practices

4. The Meaning of the Forest Multiple Use in the Contemporary Forest Policy (On the Multiple Use of Forest (II))

4. The Meaning of the Forest Multiple Use in the Contemporary Forest Policy (On the Multiple Use of Forest (II))

Trees and their response to wind: mid Flandrian strong winds, Severn Estuary and inner Bristol Channel, southwest Britain

The response of contemporary trees to strong winds (gale force and greater) is repeatable and well defined, as shown by field studies in south east Britain after the October 1987 and January 1990 events, combined with awide-ranging literature survey. It involves the general processes of windprune, windsnap, windtilt and windthrow. Windprune depends on a range of physical and physiological mechanisms and leads to the loss of axial symmetry by a tree, especially where open-grown at an exposed site. Windsnap, windtilt and windthrow see the fall of a tree, as the result of either the breaking of the trunk or partial to full uprooting. Damage of this sort in a forest or woodland ranges from single trees, to scattered groups (swathes), to general devastation. In the main, perfectly healthy trees in youth or early maturity are affected by windsnap, windtilt and windthrow during strong wind events. Their fall-direction is readily established using the position of the rootball or snapped end of the trunk, the alignment of a broken trunk and stump, the taper of the trunk, the position on the trunk of relatively crowded branches (tree crown), and the position of the typically upward acute angle between branch and trunk. Contemporary trees overthrown by wind fall in a direction close to the wind. The variance of fall-directions in a sample due to a single wind event is observed to increase with the size of the woodland area from which the sample is drawn, but appears to become constant for sample areas in excess of 102- 103ha. Because this constant variance is relatively small, the mean fall-direction becomes, in contemporary woodlands and forests, a trustworthy indicator of the general direction of the strong wind which felled the trees. Rooted peats of mid Flandrian age (ca. 6000-2500 conventional radiocarbon years) which include prostrate trees are widely present among the post-glacial estuarine silts exposed along the shores of the Severn Estuary and the inner Bristol Channel. The trees when overthrown appear in the main to have been perfectly healthy and in youth to early maturity. Oak and alder are the predominant species, and their fall-directions, as judged from the criteria listed from contemporary forests and woodlands, and measured at 18 horizons distributed over 14 sites, are highly coherent both locally and over the area as a whole. Using a model in which the variance of fall-directions observed for a single event is combined with a probability density for event mean directions, it appears that the trees fossilized in the peats were felled by strong winds which blew chiefly toward a range of directions from N.N.W . clockwise to S.S.E. A westerly zonal air-flow is indicated but, compared to the contemns than now, with a greater emphasis on both southerly and westerly to northwesterly blows.

A global perspective on forest decline

—,;Carbon dioxide, the major plant food, is on the rise, but forests on both sides of the Atlantic are known to be declining, and industrial pollution is widely suspected to be the principal cause. However, significant contemporary forest declines also are occurring in several Pacific forests, in areas completely unaffected by industrial pollution. This paper focuses on researched forest declines in the Pacific area (New Zealand, Japan, and the Hawaiian and Galapagos islands), where canopy dieback was found to be a natural aspect of forest dynamics. It then summarizes characteristics of forest decline in central Europe (Czechoslovakia and Germany), where decline relates mostly to anthropogenic causes. Commonalities among the natural causes in the Pacific and anthropogenic causes in the European forests are emphasized through recognition of a third factor complex, the demographic component, which so far has been largely neglected in the European forest decline research. The natural cause complexes identified as demographic, disturbance, and biotic components are placed into a causal hierarchy theory based on cohort senescence. It is suggested that this may serve as a framework for comparative ecosystem research of forest declines at the global level, which includes a consideration of ongoing biotic impoverishment and climate change.

A commentary on: A synopsis of climatic and vegetational change in Southeast Asia

In this interesting review, Lawrence Heaney contrasts the features of the tropical forest of Southeast Asia with those in Latin America and Africa. Such forests originated across the entire southern fringes of Asia, Arabia, Africa, and ultimately India during Upper Cretaceous time, but, as I have pointed out in numerous reviews, they existed under a more equable climate and contained a mixture of elements that I now think of as being typical of warm temperature, subtropical, and full tropical biota. As the fringing islands of southern Asia were formed, they were occupied by a forest derived from the extensive forests of the mainland, and as Neogene time (25 million years ago) proceeded, these forests became progressively more like those of the present day. In other words, the equator-to-pole temperature gradient is sharper today than it has been in the past, and contemporary tropical forests exist under much more extreme temperatures than those into which they originally evolved, just as do polar tundra and taiga formations. Certainly the sorts of warm-temperate to subtropical forests that ultimately gave rise to today’s tropical forests occupied a much broader belt geographically prior to the middle Miocene epoch (15 million years ago), when the commencement of world climatic deterioration accompanied the expansion of the polar ice caps, first in the south.

Responses of tree populations to climatic change

The influence of climate on the population dynamics of trees must be inferred from indirect sources of information because the long lifespans of trees preclude direct observation of population growth and decline. Important insights about these processes come from 1) observations of the life histories and ecologies of trees in contemporary forests, 2) evidence of recent treeline movements in remote areas unaffected by human disturbance, and 3) results of experiments performed on forest simulation models. Each line of evidence indicates that tree population responses are influenced by many factors: including lifespans, seed productivity and dispersibility, phenotypic plasticity, genetic variability, competition, and disturbance. Some population characteristics should allow rapid changes in population sizes, while others should confer stability in times of environmental fluctuation. Interactions between controlling factors should result in a wide array of possible responses to climatic change. Interpretations of late-Quaternary forest dynamics must be based on an understanding of the biological processes involved in population responses to environmental variations.