Age Class Distribution Research Articles

Forest soil respiration across three climatically distinct chronosequences in Oregon

To assess the relative influence of edaphoclimatic gradients and stand replacing distur- bance on the soil respiration of Oregon forests, we measured annual soil respiration at 36 independent forest plots arranged as three replicates of four age classes in each of three climatically distinct forest types. Annual soil respiration for the year 2001 was computed by combining periodic chamber measurements with continuous soil temperature measurements, which were used along with site- specific temperature response curves to interpolate daily soil respiration between dates of direct measurement. Results indicate significant forest type, age, and type · age interaction effects on annual soil respiration. Average annual soil respiration was 1100-1600, 1500-2100, and 500- 900 g C m � 2 yr � 1 for mesic spruce, montane Douglas-fir, and semi-arid pine forests respectively. Age related trends in annual soil respiration varied between forest types. The variation in annual soil respiration attributable to the climatic differences between forest types was 48%(CV). Once weighted by the age class distribution for each forest type, the variation in annual soil respiration attributable to stand replacing disturbance was 15%(CV). Sensitivity analysis suggests that the regional variation in annual soil respiration is most dependent on summer base rates (i.e. soil respiration normalized to a common temperature) and much less dependent on the site-specific temperature response curves (to which annual rates are relatively insensitive) and soil degree-days (which vary only 10% among plots).

An economic and landscape evaluation of the green-up rules for California, Oregon, and Washington (USA)

Green-up constraints related to forest harvesting practices can be found in forest practices rules around the world. This research was aimed at evaluating the effects of green-up constraints on measures of economics and landscape structure in three western United States (USA). The green-up rules contained in the California, Oregon, and Washington forest practices laws were applied to two hypothetical forests with randomly generated age classes. Forest 1 contained a uniform distribution of age classes from 5 to 120 years and forest 2 was composed of mature forest primarily greater than 75 years. Spatially feasible 10-year timber harvest schedules were produced using a two-stage heuristic procedure that included a provision that the green-up constraint specified in each state's forest practices rules would not be violated. When modeled on both forests, the discounted net revenue and harvest volume were significantly lower under California rules than under Oregon or Washington rules. The forests modeled under California rules thus did result in a slightly more mature landscape than those modeled under the Oregon and Washington rules, yet one with more edge habitat than interior forest habitat. Otherwise, there seems to be little structural differences among the landscapes when the green-up rules from these three states are applied.

Disturbance and net ecosystem production across three climatically distinct forest landscapes

Biometric techniques were used to measure net ecosystem production (NEP) across three climatically distinct forest chronosequences in Oregon. NEP was highly negative immediately following stand‐replacing disturbance in all forests and recovered to positive values by 10, 20, and 30 years of age for the mild and mesic Coast Range, mesic West Cascades, and semi‐arid East Cascades, respectively. The response of stand‐level NEP to individual disturbance events is greater than that attributable to edaphoclimatic differences between forest type. However, regional age class distributions are such that the variability in landscape‐level NEP attributable to disturbance regimes is equivalent to that attributable to regional edaphoclimatic differences between forest types. Simulations of age class distribution under varying disturbance frequencies suggest that the sensitivity of landscape‐level NEP to changes in disturbance regime varies among forest types and is linked to both remnant detritus and photosynthetic recovery rate that are partly a function of edaphoclimatic differences.

Public Values for Biodiversity Conservation Policies in the Oregon Coast Range

Abstract This study uses a choice experiment framework to estimate Oregonians' willingness to pay (WTP) for changes in levels of biodiversity protection under different conservation programs in the Oregon Coast Range. We present biodiversity policy as an amalgam of four different conservationprograms: salmon and aquatic habitat conservation, forest age-class management, endangered species protection, and large-scale conservation reserves. The results indicate substantial support for biodiversity protection, but significant differences in WTP across programs. Oregonians indicatethe highest WTP for increasing the amount of forest devoted to achieving old-growth characteristics. On average, respondents indicate an annual household WTP of $380 to increase old-growth forests from 5% to 35% of the age-class distribution. Conversely, WTP for increasingconservation reserves peaks at $45 annually to double the current level to 20% of the landscape, whereas WTP is negative for any increase over 32%. We also find resistance to any change in conservation policy, which substantially offsets WTP for increases in all four conservationprograms. FOR. SCI. 50(5):589–602.

The application of a hierarchical, decision-support system to evaluate multi-objective forest management strategies: a case study in northeastern British Columbia, Canada

Increases in the environmental awareness of global consumers coupled with pressure from regional stakeholders has forced forest managers to demonstrate the potential implications of forest management activities for a broad range of indicators. This paper describes the construction and application of a hierarchical decision-support system for evaluating multi-objective management options for a 288,000 ha forest in northeastern British Columbia. The decision-support system includes a stand-level model, a forest estate model, a habitat model and a visualization model. A set of criteria and indicators, developed in conjunction with a public advisory committee, were used to identify key economic, ecological and social objectives. Indicators include volume harvested, gross profit, active road density, ecosystem carbon storage, age-class distribution, patch-size distribution, snag density, visual aesthetics and backcountry recreation area. A natural disturbance baseline and two alternative harvest strategies that include natural disturbance are projected and assessed with the decision-support system. The first strategy represents a dispersed harvesting approach in which cut blocks are limited to sizes <60 ha. The second strategy represents an aggregated harvesting approach in which a range of cut block sizes (up to 2000 ha) and shapes is created that more closely follows the distribution of openings generated from natural disturbance events in the region. Spatial and temporal changes in each indicator are presented and evaluated for the harvest strategies, and compared to the natural disturbance baseline where appropriate. The application of the decision-support system for strategic analysis of management options is discussed, including a review of the importance of representing the impacts of natural disturbance and the benefits and risks associated with the use of visualization techniques for presenting results to stake holder groups.

Timber production versus old-growth preservation with endogenous prices and forest age-classes

This study combines timber production and environmental values, applying a dynamic forest-level economic model with any number of forest age-classes. The model includes endogenous timber price or nonlinear harvesting costs and various possibilities to specify the dependence of environmental values (related e.g. to species persistence) on the forest age-class structure. The nonlinearities in the net benefits from timber production have the consequence that fluctuations in optimal timber harvesting may totally vanish or at least become smaller than in forest scheduling models without ad hoc even flow constraints. If environmental values are specified to depend on the fraction of forest land preserved as old growth, the optimal long run allocation between timber production and old growth is represented by an equilibrium continuum. Thus the optimal long run allocation depends on the initial age-class distribution. The continuum and the dependence of initial age-class distribution vanish when the rate of discount approaches zero. If the environmental values of age-classes increase smoothly with age, the long run equilibrium may simultaneously include multiple rotation periods. The model determines the optimality of producing timber and environmental values separately at different parts of the forest or at the same piece of forest land. Numerical computation suggests that the optimal solution always converges toward some optimal long run stationary age-class distribution.

Growth and nutritional responses of western hemlock to fertilization: A review

Western hemlock (Tsuga heterophylla) dominates coastal forests of British Columbia. Current age-class distributions may reduce wood supply in the near term. Fertilization might improve growth and supply, but hemlock is considered unresponsive or erratic in its response. This paper reviews how hemlock has responded to fertilization in past studies and discusses some of the difficulties in interpreting those responses.Topics include (1) nutrient deficiencies (2) experimental designs used, and growth and nutritional responses measured, (3) relationships between nutrient availability and growth of hemlock and associated conifers, and fertilization effects as influenced (4) by site and (5) by tree and stand characteristics. Few generalizations can be drawn from the literature. Phosphorus (P) additions may enhance response to additions of nitrogen (N), although P-deficient stands remain difficult to identify without measuring a response to P fertilization. For older (mid-rotation) stands, it is not possible to separate possible effects of stand age, stand density, and site and treatment applied (e.g., N-only versus N+P) on response to fertilization. There is a need to better define constraints on growth responses (nutrients, moisture, light) to fertilization in mid-rotation stands on key site types. Field experiments should be initiated to better define the relationships among stand age, stand density, stem growth, stand productivity, and stand leaf area, and to determine how these parameters may be influenced by nutrient availability. New experiments should apply more nutrients than N alone and should be designed to better characterize how nutrient supply and stand nutrient demand change with stand development.

Winter Abundance of the American Oystercatcher in South Carolina

Abstract South Carolina winters a large proportion (over 1/3) of the eastern race of the American Oystercatcher (Haematopus palliatus), a declining species. During December of 1999-2002 ground surveys were conducted to provide baseline data on the abundance, age class partitioning and distribution of wintering American Oystercatchers in South Carolina. The number of oystercatchers in South Carolina was stable during this study (3,536, 95% CI: 3,030, 4,042). A single comprehensive survey can estimate the number of oystercatchers with enough precision to detect changes in the population of 13% and greater, but location of flocks and the range of tidal heights needed to concentrate flocks must be known prior to conducting the survey. About 89% of the birds in 2002 roosted on washed shell rakes and 9% had immature bill coloration. Winter surveys of the proportion of immature oystercatchers may provide an index of regional reproductive success, an important parameter for conservation plans. Because South Carol...

Consequences of various landscape-scale ecosystem management strategies and fire cycles on age-class structure and harvest in boreal forests

At the landscape scale, one of the key indicators of sustainable forest management is the age-class distribution of stands, since it provides a coarse synopsis of habitat potential, structural complexity, and stand volume, and it is directly modified by timber extraction and wildfire. To explore the consequences of several landscape-scale boreal forest management strategies on age-class structure in the Mauricie region of Quebec, we used spatially explicit simulation modelling. Our study investigated three different harvesting strategies (the one currently practiced and two different strategies to maintain late seral stands) and interactions between fire and harvesting on stand age-class distribution. We found that the legacy of initial forested age structure and its spatial configuration can pose short- (&lt;50 years) to medium-term (150–300 years) challenges to balancing wood supply and ecological objectives. Also, ongoing disturbance by fire, even at relatively long cycles in relation to historic levels, can further constrain the achievement of both timber and biodiversity goals. For example, when fire was combined with management, harvest shortfalls occurred in all scenarios with a fire cycle of 100 years and most scenarios with a fire cycle of 150 years. Even a fire cycle of 500 years led to a reduction in older forest when its maintenance was not a primary constraint. Our results highlight the need to consider the broad-scale effects of natural disturbance when developing ecosystem management policies and the importance of prioritizing objectives when planning for multiple resource use.

Functionality of riparian forest ecotones in the context of former Soviet Union and Swedish forest management histories

Abstract Forest management in Central and Eastern Europe, under direct or indirect Soviet influence, for a long time followed different management objectives and strategies as compared to the forest management in countries with market economies in Western Europe located in the same biogeographic zones. In the light of the appearing paradigms of natural disturbance regimes and ecosystem-based forest management we evaluate forest management in the former Soviet Union and Sweden with respect to conservation of riparian forest ecotones. We studied the site and forest age class distribution both along watercourses and at randomly selected locations in the surrounding terrain in managed landscapes in Sweden and the former Soviet Union, respectively. Along watercourses in the former Soviet Union 20% of the overall forest cover was classified as old-growth compared with 6% in the surrounding landscape. By contrast, although the proportion of site type distribution was similar, such forests were neither found along watercourses nor in the surrounding landscape in Sweden. The results hence show that the Soviet management policy resulted in better conditions from the biodiversity conservation perspective. We conclude that the forestry decision-making environment does matter for practical forest conservation. We also make the following recommendations to forest and environmental planners and decision-makers: (1) protect existing and restore and re-create riparian corridors in general; (2) maintain riparian forests along streams of all orders, because small rivers are as important for conservation of biodiversity as large rivers; (3) designate riparian corridors for protection not focusing on a single width, but rather based on vegetation site type appropriate for stand types with a continuous forest cover.

Solving the area-restricted harvest-scheduling model using the branch and bound algorithm

There are two broad approaches to the discrete optimization problem of harvest scheduling with adjacency constraints: the unit-restricted model and the area-restricted model. In this paper two formulations of the area-restricted model are solved using the branch and bound algorithm. These formulations are tested on a set of approximately 30 tactical planning problems that range in size from 346 to 6093 polygons scheduled over three time periods. Our results show that these formulations can be used to solve small- and medium-sized harvest-scheduling problems optimally, or near-optimally, within reasonable periods of computing time. Solution quality and computing time were found to be sensitive to the initial age-class distribution of the forest and the mean polygon size relative to the maximum opening size. In addition, computation of the opening size constraints was found to be very sensitive to the maximum number of polygons in an opening constraint.

Can mature patch constraints mitigate the fragmenting effects of harvest opening size restrictions?

AbstractHarvest scheduling models often include maximum harvest opening size constraints, a restriction generally imposed for legal or policy reasons. The maximum harvest opening size restriction can greatly affect the spatial layout of the forest, with the dispersed harvesting increasing forest fragmentation. Because they can offset the negative impacts of maximum harvest opening size constraints, mature patch size constraints, which require a certain amount of the forest to be in patches meeting both minimum size and age requirements, have also been included in these models. This paper looks at the economic and spatial effects of ten harvest scheduling formulations with these two constraint sets on 21 hypothetical forest landscapes. Analyses of their age‐class distributions, border distributions, and patch size distributions at the end of a 60‐year planning horizon confirm that maximum harvest opening size constraints tend to fragment forest landscapes and that mature patch constraints can significantly reduce these effects.

Large carbon uptake by an unmanaged 250-year-old deciduous forest in Central Germany

Unmanaged forests at a late stage of successional development are considered to be insignificant as carbon sinks, since in theory, assimilation is thought to be balanced by respiration. However, little experimental evidence for this hypothesis exists so far for forests at the ecosystem level. Therefore, we performed continuous eddy covariance measurements of carbon dioxide over an unmanaged beech forest in the Hainich National Park in Central Germany as part of the EU project CARBOEUROFLUX. This forest shows typical characteristics of an ‘advanced’ forest with large dead wood pools, a diverse stand structure and a wide tree age class distribution, up to 250 years. This forest was a large carbon sink over 2 years, with 494 g C m −2 per year in 2000 and 490 g C m −2 per year in 2001. Daytime summer fluxes were strongly controlled by photosynthetic photon flux density ( R 2=0.7–0.9), with minor effects of the ratio of diffuse to total downward radiation or the vapor pressure deficit. Nighttime CO 2 fluxes were mainly controlled by soil temperature ( R 2=0.8) and soil moisture. In addition, high nighttime CO 2 fluxes (4–6 μmol m −2 s −1) were found directly before and during bud break in spring as well as just after leaf fall of both years (2000 and 2001), reflecting stand physiology corresponding to phenological changes, independent of soil temperature. Additional wind profile measurements at five heights within the canopy revealed a decoupling of above and below canopy air flow under conditions of low friction velocity ( u *<0.4 m s −1), probably indicating down slope drainage. In conclusion, unmanaged forests at a comparatively late stage of successional development can still act as significant carbon sinks with large implications for forest management practice and negotiations about biological sinks within the Kyoto Protocol.

Predicting the potential for old-growth forests by spatial simulation of landscape ageing patterns

Planning for old-growth forests requires answers to two large-scale questions: How much old-growth forest should exist? And where can they be sustained in a landscape? Stand-level knowledge of old-growth physiognomy and dynamics are not sufficient to answer these questions. We assert that large-scale disturbance regimes may provide a strong foundation to understand the spatio-temporal ageing patterns in forest landscapes that determine the potential for old growth. Approaches to describe large-scale disturbance regimes range from scenarios reconstructed from historical evidence to simulation of landscapes using predictive models. In this paper, we describe a simulation modelling approach to determine landscape-ageing patterns, and thereby the landscape potential of old-growth forests. A spatially explicit stochastic simulation model of landscape fire–forest cover dynamics was applied to a 1.8 million-ha case study boreal forest landscape to quantify the spatio-temporal variation of landscape ageing. Twenty-five replicates of 200-year simulation runs of the fire disturbance regime, at a 1-ha resolution, generated a suite of variables of landscape ageing and their error estimates. These included temporal variation of older age cohorts over 200 years, survivorship distribution at the 200th year, and spatial tendencies of ageing. This information, in combination with spatial tendency of species occurrence, constitutes the contextual framework to plan how much old-growth forest a given landscape can sustain, and where such forest could be located. Key words: landscape management, old growth, spatial simulation modelling, landscape ecology, boreal forest, Ontario, fire regime simulation, natural forest disturbances, stochastic models, age-class distribution

Les communautés d'oiseaux des vieilles forêts de la pessière à mousses de la ceinture d'argile : Problèmes et solutions face à l'aménagement forestier

In Canada, there are still extensive tracts of boreal forest consisting of stands that have resulted from natural disturbances. The country's forests are a mosaic made up to a large extent of old-growth forest that is beyond commercial harvesting age, especially in the boreal forest of eastern Canada. As areas of boreal forest under management steadily expand, as demand for forest products continues to grow and as rotation periods become shorter in response to silvicultural practices, the forest cover will inevitably become younger, causing changes to the structure and composition of the mosaic of forest stands that will affect the aspect of entire landscapes. These changes may have an adverse impact on biological diversity. Forest birds are one group of living organisms that may respond quickly to the advent of younger forest landscapes, thereby acting as a biological indicator. In this paper, we discuss some of the problems that birds face as a result of the truncation of the age-class distribution of managed forest landscapes in eastern Canada's coniferous boreal forest, using data obtained from our research in the Clay Belt region of Quebec and Ontario. More specifically, we look at how birds respond to changes in forest structure and composition in terms of time since natural disturbances, and to variation in dead trees availability. We then consider the impact of the prospective rejuvenation of the forest cover in managed forest landscapes, and possible solutions aimed at mitigating that impact through new management strategies based on the maintenance of forest ecosystem diversity. The ability of these new management strategies to maintain the ecological integrity of bird communities provides an indication of their potential as tools for contributing to the maintenance of biological diversity in a broader sense. Key words: bird communities, old black spruce forests, natural landscape age structure, stand structure, dead wood, multicohort management

The eastern box turtle at the Patuxent Wildlife Research Center 1940s to the present: another view

Several long-term mark recapture studies have been conducted on box turtles ( Terrapene c. carolina) providing valuable information on life span, basic demography, home range, and apparent effects of environmental changes on box turtle survival. One of the longest studied populations was first marked in 1942 on the Patuxent Wildlife Research Center in Maryland, and has been surveyed every 10 years until 1995. The age structure and gender ratio of these turtles in the field may support differential habitat use and survival estimates. A few of the turtles first marked during the 1945 study are still observed throughout the Center. Data collected from turtles marked in the more upland habitats during 1985–2002 indicate a younger age class distribution than that observed in the more protected biota of the bottomland floodplain study area. Extrapolating ages of turtles described in data collected throughout the long-term study, it was estimated that turtles, both males and females, can show reproduction-intent behaviors at ages greater than 54 years old. It is suggested that count data collection be continued on a more frequent cycle, extending over a larger part of the Center.

Preliminary assessment of habitat characteristics of woodland caribou calving areas in the Claybelt region of Québec and Ontario, Canada

Woodland caribou (Rangifer tarandus caribou) require a diversity of forested habitats over large areas and may thus be particularly affected by the large-scale changes in the composition and age-class distribution of forest landscapes induced by the northern expansion of forest management. In this study we examine habitat characteristics associated to the use of calving areas by woodland caribou females and calves at different spatial scales. Thirty females were captured and collared with Argos satellite transmitters that allowed to locate 14 calving areas. Field surveys were conducted at each of these areas to measure the landscape composition of forest cover types and local vegetation characteristics that are used for both forage conditions and protection cover. At the scale of the calving area, univariate comparisons of the amount of forest cover types between sites with and without calves showed that the presence of calves was associated to mature black spruce forest with a high percent cover of terrestrial lichens. Within calving grounds, univariate comparisons showed that vegetation features like ericaceans and terrestrial lichens, that are important food resources for lactating females, were more abundant in calving areas where females were seen with a calf in mid-July than in areas where females were seen alone. The protection of the vegetation cover against predators was however similar between calving areas with or with&amp;not;out a calf. Logistic regression results also indicated that vegetation characteristics associated to forage conditions were positively associated to calf presence on calving grounds. Our results suggest that foraging conditions should be given more attention in analyses on habitat requirements of woodland caribou.

Species composition and vegetation structure of an upper montane forest at the summit of Mt. Doi Inthanon, Thailand

Upper montane forest (UMF) within Doi Inthanon National Park, Northern Thailand, was investigated by means of fifty, 40 × 40 m stratified random plots situated between 2080 and 2565 m altitude. The aim was to address a number of community ecological questions concerning woody species composition and structural heterogeneity of the forest. A total of 7474 individuals of trees and woody climbers ≥ 15 cm gbh (girth at breast height) were included in the study and these were identified to 47 species, 39 genera and 26 families. The average density was 934 individuals/ha and the average stem basal area was 71.8 m2/ha. The most important species were: Quercus eumorpha, Sjzygium angkae, Litsea martabanica, Helicia nilagirica, Lindera caudata, Schima wallichii, Osmanthus fiagrans, Eurya acuminata, Myrsine semiserrata and Ilex umbellulata and the most important families were Fagaceae, Lauraceae, Theaceae and Myrtaceae. Altitude was the most important environmental variable explaining species composition and vegetation structure. Most of the calculated vegetation variables showed significant correlation with altitude: species richness, family richness, diversity, density and crown cover declined with altitude, average tree height was uncorrelated with altitude and basal area increased with altitude. An analysis of size class distributions indicated good forest conditions and reverse‐J‐shaped age class distribution of most species.

Distribution of whitemouth croaker Micropogonias furnieri in relation to environmental factors at the Río de la Plata estuary, South America

The age-class distribution of the whitemouth croaker Micropogonias furnieri and its relationship to environmental factors was evaluated from 278 stations sampled between 1993 and 1999 during early winter and spring within the Rio de la Plata estuary (36° S, 56° W). A detrended canonical correspondence analysis (DCCA) was used to define sampling station groups based on age structure of whitemouth croaker, and to estimate their association with depth, type of substrate, tem- perature and salinity of surface and bottom waters. Complementary information for surface temper- ature and location of the turbidity fronts was derived from NOAA-14-AVHRR imagery obtained in 1999. Results indicated that bottom salinity has a major influence on the spatial distribution pattern of M. furnieri, and that distinct preferences for different salinities by the various age-classes of this species result in a differential distribution pattern along the main axis of the estuary. In both seasons, turbidity fronts were located at the inner central area of the estuary and showed a close fit with the distribution of the youngest age-classes.

Western Sandpipers (Calidris Mauri) During the Nonbreeding Season: Spatial Segregation on a Hemispheric Scale

Abstract The nonbreeding distribution of Western Sandpipers (Calidris mauri) was documented using 19 data sets from 13 sites along the Pacific and Atlantic coasts of the Americas. Western Sandpipers showed latitudinal segregation with regard to sex and age. Females wintered farther south than males. A “U” shaped pattern was found with respect to age, with juveniles occurring at higher proportions at both the northern and southern ends of the range. Distribution of sexes might be affected by differences in bill length and a latitudinal trend in depth distribution of prey. For age class distribution, two different life-history tactics of juveniles might exist that are related to the higher cost of feather wear for juveniles compared to adults. Most juveniles complete three long-distance migrations on one set of flight feathers whereas adults complete two. Juveniles may winter either far north, thereby reducing feather wear induced by ultraviolet light, migration, or both, or far south and spend the summer on the nonbreeding area.