Multiple disturbances accelerate clonal growth in a potentially monodominant bamboo

Organisms capable of rapid clonal growth sometimes monopolize newly freed space and resources. We hypothesize that sequential disturbances might change short-term clonal demography of these organisms in ways that promote formation of monotypic stands. We examined this hypothesis by studying the clonal response of Arundinaria gigantea (giant cane, a bamboo) to windstorm and fire. We studied giant cane growing in both a large tornado-blowdown gap and under forest canopy, in burned and unburned plots, using a split-block design. We measured density of giant cane ramets (culms) and calculated finite rates of increase (lamda) for populations of ramets over three years. Ramet density nearly doubled in stands subjected to both windstorm and fire; the high ramet densities that resulted could inhibit growth in other plants. In comparison, ramet density increased more slowly after windstorm alone, decreased after fire alone, and remained in stasis in controls. We predict that small, sparse stands of giant cane could spread and amalgamate to form dense, monotypic stands (called "canebrakes") that might influence fire return intervals and act as an alternative state to bottomland forest. Other clonal species may similarly form monotypic stands following successive disturbances via rapid clonal growth.     

The effects of forest harvest intensity in combination with wind disturbance on carbon dynamics in Lake States Mesic Forests

Total forest carbon (C) storage is determined by succession, disturbances, climate, and the edaphic properties of a site or region. Forest harvesting substantially affects C dynamics; these effects may be amplified if forest harvesting is intensified to provide biofuel feedstock. We tested the effects of harvest intensity on landscape C using a simulation modeling approach that included C dynamics, multiple disturbances, and successional changes in composition. We developed a new extension for the LANDIS-II forest landscape disturbance and succession model that incorporates belowground soil C dynamics derived from the CENTURY soil model. The extension was parameterized and calibrated using data from an experimental forest in northeastern Wisconsin, USA. We simulated a 9800 ha forested landscape over 400 years with wind disturbance combined with no harvesting, harvesting with residual slash left on site (‘standard harvest’), and whole-tree harvesting. We also simulated landscapes without wind disturbance and without eastern hemlock (Tsuga canadensis) to examine the effects of detrital quantity and quality on C dynamics. We estimated changes in live C, detrital C, soil organic C, total C, and forest composition. Overall, the simulations without harvesting had substantially greater total C and continued to sequester C. Standard harvest simulations had more C than the whole tree harvest simulations. Under both harvest regimes, C accrual was not evident after 150 years. Without hemlock, SOC was reduced due to a decline in detritus and a shift in detrital chemistry. In conclusion, if the intensity of harvesting increases we can expect a corresponding reduction in potential C storage. Compositional changes due to historic circumstances (loss of hemlock) may also affect forest C although to a lesser degree than harvesting. The modeling approach presented enabled us to consider multiple, interacting drivers of landscape change and the subsequent changes in forest C.     

Influences of season and water depth on the clonal biology of the seagrassThalassia testudinum

Ramet density, leaf relative growth rates, leaf chlorophyll levels, and proximate constituent levels were determined on three dates in 1988 at three water depths for aThalassia testudinum Banks ex Konig meadow in lower Tampa Bay, Florida, USA. Density varied seasonally in patterns unique to each depth. Leaf relative growth rates indicated a unimodal, rather than bimodal, growth pattern at this site. Leaf chlorophyll levels reflected both depth-related and seasonal influences, with levels at all depths increasing in times of high light attenuation. Based on results from leaf relative growth rates and proximate constituent levels, the degree of ramet interdependence appears to vary with sampling date and water depth. The degree of ramet interdependence appears to be maximal in times of genet expansion (June and August) and minimal in times of energy storage (November). Interdependence of ramets varies spatially as well; ramets are maximally integrated in shallow regions (on those dates when genet proliferation occurs), and minimally integrated at deep edges. Depth-related differences in ramet integration are probably due to the spatial heterogeneity of the primary resource limitation varying with water depth, and to depth-related differences in ramet population dynamics. Patterns of ramet physiological integration inT. testudinum are similar to the patterns reported for terrestrial clonal plants.     

Demographic Effects of Harvesting Epiphytic Bromeliads and an Alternative Approach to Collection

Abstract: Hundreds of epiphytic bromeliads species are harvested from the wild for trade and for cultural uses, but little is known about the effects of this harvest. We assessed the potential demographic effects of harvesting from the wild on 2 epiphytic bromeliads: Tillandsia macdougallii, an atmospheric bromeliad (adsorbs water and nutrients directly from the atmosphere), and T. violaceae, a tank bromeliad (accumulates water and organic material between its leaves). We also examined an alternative to harvesting bromeliads from trees—the collection of fallen bromeliads from the forest floor. We censused populations of T. macdougallii each year from 2005 to 2010 and of T. violaceae from 2005 to 2008, in Oaxaca, Mexico. We also measured monthly fall rates of bromeliads over 1 year and monitored the survival of fallen bromeliads on the forest floor. The tank bromeliad had significantly higher rates of survival, reproduction, and stochastic population growth rates (λ_s) than the atmospheric bromeliad, but λ_s for both species were <1, which suggests that the populations will decline even without harvest. Elasticity patterns differed between species, but in both, survival of large individuals had high elasticity values. No fallen bromeliads survived more than 1.5 years on the forest floor and the rate of bromeliad fall was comparable to current harvest rates. Low rates of population growth recorded for the species we studied and other epiphytic bromeliads and high elasticity values for the vital rates that were most affected by harvest suggest that commercial harvesting in the wild of these species is not sustainable. We propose the collection of fallen bromeliads as an ecologically and, potentially, economically viable alternative.     

A Multidisciplinary Approach to Assessing the Sustainability of Freshwater Crayfish Harvesting in Madagascar

Abstract:  There is growing interest among conservation decision makers in promoting harvesting of forest products as an incentive for communities to retain forest cover. Assessments of the sustainability of existing harvests are essential for implementing such policies. Madagascar's endemic freshwater crayfish, Astacoides spp., are harvested throughout their range. Despite their importance to human communities, Madagascar's crayfish, like much of the island's freshwater biodiversity, are poorly known, and there is concern that the harvest may be unsustainable. We investigated sustainability of the crayfish harvest in and around Ranomafana National Park in eastern Madagascar, focusing on the heavily harvested A. granulimanus. Several villages around the park have traditional taboos against selling crayfish, resulting in widely varying levels of crayfish exploitation. We used two approaches to assess sustainability of the harvest. First we used participatory mapping combined with a geographic information system analysis to produce a spatially accurate map of harvesting intensity. We then carried out mark-and-recapture sampling at 74 sites across a range of harvest intensities to test whether the level of harvesting was a significant predictor of crayfish density and structure. Second, we used size-structured matrix population models to estimate the forest area necessary to provide the observed annual harvest from one harvesting village and compared this estimate with the area available to the harvesters. Our findings show that the crayfish harvest in Ranomafana may be sustainable under current socioeconomic conditions, suggesting that A. granulimanus is less vulnerable to overexploitation than previously thought. We emphasize the importance of a multidisciplinary approach to assessing sustainability involving both ecological information about the harvested species and socioeconomic data about the level and spatial pattern of the harvest.     

Effects of Harvest of Nontimber Forest Products and Ecological Differences between Sites on the Demography of African Mahogany

Abstract: The demographic impacts of harvesting nontimber forest products (NTFP) have been increasingly studied because of reports of potentially unsustainable harvest. Nevertheless, our understanding of how plant demographic response to harvest is altered by variation in ecological conditions, which is critical for developing realistic sustainable‐use plans, is limited. We built matrix population models to test whether and how variation in ecological conditions affects population responses to harvest. In particular, we examined the effect of bark and foliage harvest on the demography of populations of African mahogany (Khaya senegalensis) in two contrasting ecological regions of Benin, West Africa. K. senegalensis bark and foliage harvest significantly reduced its stochastic population growth rates, but ecological differences between regions had a greater effect on population growth rates than did harvest. The effect of harvest on population growth rates (Δλ) was slightly stronger in the moist than in the drier region. Life‐table response experiments revealed that the mechanism by which harvesting reduced λ differed between ecological regions. Lowered stasis (persistence) of larger life stages lead to a reduction in λ in the drier region, whereas lowered growth of all life stages lowered λ in moist region. Potential strategies to increase population growth rates should include decreasing the proportion of individuals harvested, promoting harvester‐owned plantations of African mahogany, and increasing survival and growth by promoting no‐fire zones in gallery forests. Our results show how population responses to harvest of NTFP may be altered by ecological differences across sites and emphasize the importance of monitoring populations over the climatic range in which they occur to develop more realistic recommendations for conservation.     

Exploiting sea otter populations: A simulation analysis

We used a Leslie matrix population model to investigate the impact of a range of harvest rates proposed for Alaskan sea otters (Enhydra lutris). The simulation included an analysis of several population mechanisms that might be important in the natural regulation of sea otter populations or in their reactions to harvesting. Significant differences in equilibrium population levels were found between compensatory mechanisms when fixed harvest rates were applied for 25-year periods. Adult harvests set at 2 and 4% of the total population showed that new stable population levels were rapidly attained. Harvest rates of 8 and 10%, however, resulted in marked population declines in simulated harvests. This analysis demonstrates that limited harvesting can be sustained by the population and that otter population compensation responses will be a critical determinant of sustainable harvest rates of sea otter populations.     

Variation in responses of late-seral herbs to disturbance and environmental stress

Clonal herbs that attain maximum development in late-seral forest are often assumed to have similar responses to disturbance and to be functionally equivalent. However, little is known about the demographic or physiological responses of these plants to disturbance or to the altered conditions of the post-disturbance environment. Following harvest of a mature coniferous forest, we compared abundance, demographic changes, and physiological acclimation of three clonal herbs (Asarum caudatum, Clintonia uniflora, and Pyrola picta) that differ in belowground morphology and leaf longevity. We measured ramet density, leaf area, and demographic variables (survival, clonal growth, flowering, and seedling establishment) before and for two years after harvest, and in adjacent undisturbed forest. Acclimation to increased solar radiation was assessed two years after harvest by measuring leaf mass per unit area (LMA) and chlorophyll a:b ratios of leaves produced in the current year. Although initial declines in abundance were similar, demographic responses indicate that patterns of recovery varied greatly among species. Two years after logging, ramet survival and clonal growth (production of new ramets) of Clintonia were greater in the harvest area than in the forest. Asarum had lower survival in the harvest area, but greater clonal growth, and Pyrola showed no difference in either survival or growth between environments. Only Asarum produced seedlings, although their survival was low in the harvest area. All species had higher LMA in the harvest area, but only Clintonia (with annual leaves) had a higher chlorophyll a:b ratio, suggesting the greatest potential for acclimation to increased light. Our results demonstrate that forest herbs with greater rhizome plasticity and shorter leaf duration have greater potential to acclimate after disturbance than those with rigid architectures and persistent leaves. Thus, species with comparable successional roles can vary substantially in their demographic and physiological responses to disturbance, with potential consequences for long-term recovery.     

野化培训大熊猫采食和人为砍伐对拐棍竹无性系种群生物量的影响

采用固定样方法和定位观察法连续测定了2003～2007年间卧龙自然保护区大熊猫野化培训圈内及其附近区域的拐棍竹无性系种群数量和生长发育特性等参数,运用收获法与非破坏性重量估测法建立了不同龄级和残桩的竹子种群和分株生物量估测模型,进而利用最佳模型计算并评估了野化培训大熊猫采食和人为砍伐对拐棍竹无性系种群生物量和植株个体生物量的影响.结果表明:在环境条件、种群密度、生长发育特征和种群生物量等基本相似的基础上,大熊猫采食和人为砍伐不仅降低实验期间的竹子生物生产力,而且影响到后期阶段实验种群的恢复与发展.大熊猫采食样方中的竹子种群生物量虽然较对照样方低,就竹笋生物量而言,约为对照的57.79%,这与野化培训圈的面积较小、竹种单一而使采食比重(67.07%)较大有关,但其各龄级植株个体生物量均能达到大熊猫的取食利用标准(仅2004年生竹除外),具有持续供给大熊猫食物资源的潜力;而人为砍伐措施与大熊猫采食相比,影响效果极为强烈,它严重降低了拐棍竹无性系的种群生物量,尤其是竹笋重量更是如此,仅为对照样方的14.69%,且植株个体鲜重远低于大熊猫的觅食条件.因此,竹笋和无性系植株的生物量是大熊猫采食标准的主要因素.     

Examining the effects of alternative management strategies on landscape-scale forest patterns in northeastern Minnesota using LANDIS

Spatial modeling of forest patterns can provide information on the potential impact of various management strategies on large landscapes over long time frames. We used LANDIS, a stochastic, spatially-explicit, ecological landscape model to simulate 120 years of forest change on the Nashwauk Uplands, a 328,000 ha landscape in northeastern Minnesota that lies in the transition between boreal and temperate forests. We ran several forest management scenarios including current harvesting practices, no harvests, varied rotation ages, varied clearcut sizes, clustered clearcuts, and landowner coordination. We examined the effects of each scenario on spatial patterns of forests by covertype, age class, and mean and distribution of patch sizes. All scenarios reveal an increase in the spruce-fir (Picea-Abies) covertype relative to the economically paramount aspen-birch (Populus-Betula) covertype. Our results also show that most covertypes occur in mostly small patches <5 ha in size and the ability of management to affect patch size is limited by the highly varied physiography and landuse patterns on the landscape. However, coordination among landowners, larger clearcuts, and clustered clearcuts were all predicted to increase habitat diversity by creating some larger patches and older forest patches. These three scenarios along with the no harvest scenario also create more old forest than current harvesting practices, by concentrating harvesting on some portion of the landscape. The no harvest scenario retained large, fire-regenerated aspen-birch patches. Harvests fragment large aspen-birch patches by changing the age structure and releasing the shade-tolerant understory species. More sapling forest, and larger sapling patches resulted from the shortened rotation scenario.     

Availability and Extraction of Forest Products in Managed and Primary Forest around a Dayak Village in West Kalimantan, Indonesia

We examined the density and abundance of marketable products in managed forest (rubber gardens, fruit gardens, and dry rice fallows) and in primary forest surrounding the Dayak village of Kembera, near Gunung Palung National Park, West Kalimantan, Indonesia. We calculated the proportion of trees that were marketable and useful for local consumption by counting and identifying trees in each managed forest type, and we documented extraction of products through interviews. Villagers harvested four marketable tree products: tengkawang seeds ( Shorea stenoptera ), durian fruits (various Durio spp.), rubber ( Hevea brasiliensis ), and timber, especially Bornean ironwood ( Eusideroxylon zwageri ). We inventoried trees at least 20 cm diameter at breast height (dbh) of marketed species from 0.4-ha plots in primary forest ( n = 8) and from 0.1-ha plots in each managed forest type ( n = 10–11). With the exception of timber, the density of trees producing a marketable product was significantly higher in the forest type managed for that product than the density of the marketed species, or of similar wild species, in primary forest. Total abundance (product of density and available area) of durian and tengkawang was greater in primary forest; however, villagers gathered these products only from managed forest. We infer from this choice a greater efficiency of harvesting from trees in dense stands near the village. Historically, this choice resulted in deliberate development of fruit gardens in preference or in addition to gathering from the more distant, primary forest. Because of low product density in primary forest, extractive forest reserves or buffer zones designed to encourage the production of fruits such as tengkawang or durian may not provide a sufficient incentive for the protection of primary forest around Kembera and other Dayak villages near Gunung Palung National Park.     

Tree mortality following partial harvests is determined by skidding proximity

Recently developed structural retention harvesting strategies aim to improve habitat and ecological services provided by managed forest stands by better emulating natural disturbances. The potential for elevated mortality of residual trees following such harvests remains a critical concern for forest managers, and may present a barrier to more widespread implementation of the approach. We used a harvest chronosequence combined with dendrochronological techniques and an individual-based neighborhood analysis to examine the rate and time course of residual-tree mortality in the first decade following operational partial "structural retention" harvests in the boreal forest of Ontario, Canada. In the first year after harvest, residual-tree mortality peaked at 12.6 times the preharvest rate. Subsequently, mortality declined rapidly and approached preharvest levels within 10 years. Proximity to skid trails was the most important predictor both of windthrow and standing death, which contributed roughly equally to total postharvest mortality. Local exposure further increased windthrow risk, while crowding enhanced the risk of standing mortality. Ten years after harvest, an average of 10.5% of residual trees had died as a result of elevated postharvest mortality. Predicted cumulative elevated mortality in the first decade after harvest ranged from 2.4% to 37% of residual trees across the observed gradient of skid trail proximity, indicating that postharvest mortality will remain at or below acceptable rates only if skidding impacts are minimized. These results represent an important step toward understanding how elevated mortality may influence stand dynamics and habitat supply following moderate-severity disturbances such as partial harvests, insect outbreaks, and windstorms.     

Aboveground and belowground effects of single-tree removals in New Zealand rain forest

There has been considerable recent interest in how human-induced species loss affects community and ecosystem properties. These effects are particularly apparent when a commercially valuable species is harvested from an ecosystem, such as occurs through single-tree harvesting or selective logging of desired timber species in natural forests. In New Zealand mixed-species rain forests, single-tree harvesting of the emergent gymnosperm Dacrydium cupressinum, or rimu, has been widespread. This harvesting has been contentious in part because of possible ecological impacts of Dacrydium removal on the remainder of the forest, but many of these effects remain unexplored. We identified an area where an unintended 40-year "removal experiment" had been set up that involved selective extraction of individual Dacrydium trees. We measured aboveground and belowground variables at set distances from both individual live trees and stumps of trees harvested 40 years ago. Live trees had effects both above and below ground by affecting diversity and cover of several components of the vegetation (usually negatively), promoting soil C sequestration, enhancing ratios of soil C:P and N:P, and affecting community structure of soil microflora. These effects extended to 8 m from the tree base and were likely caused by poor-quality litter and humus produced by the trees. Measurements for the stumps revealed strong legacy effects of prior presence of trees on some properties (e.g., cover by understory herbs and ferns, soil C sequestration, soil C:P and N:P ratios), but not others (e.g., soil fungal biomass, soil N concentration). These results suggest that the legacy of prior presence of Dacrydium may remain for several decades or centuries, and certainly well over 40 years. They also demonstrate that, while large Dacrydium individuals (and their removal) may have important effects in their immediate proximity, within a forest, these effects should only be important in localized patches containing high densities of large trees. Finally, this study emphasizes that deliberate extraction of a particular tree species from a forest can exert influences both above and below ground if the removed species has a different functional role than that of the other plant species present.     

Values Associated with Management of Yellowstone Cutthroat Trout in Yellowstone National Park

Recent emphasis on a holistic view of natural systems and their management is associated with a growing appreciation of the role of human values in these systems. In the past, resource management has been perceived as a dichotomy between extraction (harvest) and nonconsumptive use, but this appears to be an oversimplified view of natural-cultural systems. The recreational fishery for Yellowstone cutthroat trout ( Oncorhynchus clarki bouvieri ) in Yellowstone National Park is an example of the effects of management on a natural-cultural system. Although angler harvest has been drastically reduced or prohibited, the recreational value of Yellowstone cutthroat trout estimated by angling factors (such as landing rate or size) ranks above that of all other sport species in Yellowstone National Park. To maintain an indigenous fishery resource of this quality with hatchery propagation is not economically or technically feasible. Nonconsumptive uses of the Yellowstone cutthroat trout including fish-watching and intangible values, such as existence demand, provide additional support for protection of wild Yellowstone cutthroat trout populations. A management strategy that reduces resource extraction has provided a means to sustain a quality recreational fishery while enhancing values associated with the protection of natural systems.     

Synergistic Effects of Subsistence Hunting and Habitat Fragmentation on Amazonian Forest Vertebrates

Abstract: Subsistence game hunting has profound negative effects on the species diversity, standing biomass, and size structure of vertebrate assemblages in Amazonian forests that otherwise remain largely undisturbed. These effects are likely to be considerably aggravated by forest fragmentation because fragments are more accessible to hunters, allow no (or very low rates of  ) recolonization from nonharvested source populations, and may provide a lower-quality resource base for the frugivore-granivore vertebrate fauna. I examined the likelihood of midsized to large-bodied bird and mammal populations persisting in Amazonian forest fragments of variable sizes whenever they continue to be harvested by subsistence hunters in the aftermath of isolation. I used data from a comprehensive compilation of game-harvest studies throughout Neotropical forests to estimate the degree to which different species and populations have been overharvested and then calculated the range of minimum forest areas required to maintain a sustainable harvest. The size distribution of 5564 Amazonian forest fragments—estimated from Landsat images of six regions of southern and eastern Brazilian Amazonia—clearly shows that these are predominantly small and rarely exceed 10 ha, suggesting that persistent overhunting is likely to drive most midsized to large vertebrate populations to local extinction in fragmented forest landscapes. Although experimental studies on this negative synergism remain largely unavailable, the prospect that increasingly fragmented Neotropical forest regions can retain their full assemblages of avian and mammalian species is unlikely.     

The development of secondary industries through the sustainable utilisation of reeds and forest timber in the Tembe Elephant Park,Maputaland, South Africa

The harvesting of Phragmites australis reeds in the Tembe Elephant Park has to be managed pro-actively. Solutions to potential problems should be sought before they arise. This paper offers a potential solution to the problem of instating a winter-only reed harvest in the Muzi Swamp. The potential for manufacturing finished products such as prefabricated huts from sustainably harvested reeds and forest timber is examined and a cost estimate is presented. A prefabricated reed hut is three-times cheaper than a similarly-sized house made of bricks and cement. The manufacturing of finished products from the harvested material will add secondary value to the resource and also offer an alternative employment to harvesting reeds in the summer. The higher prices obtained for a processed article will also, hopefully, reduce the demand for the resource in its raw form, thereby increasing the perceived value of the resource and reducing wastage from raw materials that are not sold.     

Effect of Harvest on Leaf Development of the Asian Palm Livistona rotundifolia

Although palms are the most commonly harvested tree family in the world, they are susceptible to overexploitation, and many harvest schemes are not sustainable. We assessed the impact of leaf harvesting of the Asian palm, Livistona rotundifolia , in North Sulawesi, Indonesia, to determine the effect of harvest intensity on subsequent growth and to determine if current harvest practices are ecologically sustainable. We conducted experimental harvests of two intensities and compared results with a control. Leaf emergence, expansion, opening, and maturation were monitored for 1 year. Leaves in heavy and light harvest treatments grew and opened significantly faster than control leaves. Final leaf size was a function of harvest intensity: control leaves were larger (4.06 m) than light-harvest leaves (3.62 m) and heavy-harvest leaves (2.62 m). Census results for palms in harvested and unharvested areas indicated that palm density was twice as high and reproductive-sized palms were 10 times more common in the unharvested area. We judged current harvest practices to be nonsustainable. Recommendations for sustainable harvesting include reduction of harvest intensity and waste and preservation of reproductive-sized palms.     

Tree species diversity and composition in logged and unlogged rainforest of Kudremukh National Park, South India

Species composition and diversity in logged and unlogged forests were assesed to understand the regeneration of the residual stand twenty years after logging in Kudremukh National Park, South India. Relative density, frequency and basal area were measured by Point Centered Quarter method to calculate the diversity and stand quality. The logged forest harbored lower stem density of mature trees (508 ha(-1)) than unlogged ones (630 ha(-1)). Indeed, logging operations increased the species diversity in the regenerative phase (seedling phase) due to the creation of larger canopy gaps. The extra radiation reaching the ground, facilitated the colonization of early and late secondary species. Ramakrishanan Index of Stand Quality (RISQ) values in logged forest was higher in comparison with unlogged forest, indicating the dominance of early and late secondary species, especially at sapling phase. The light demanding secondary forest species contribute higher percentage to the overall tree population in logged forest. It is observed from the study that a sufficient period of felling cycle should be practiced to reinstate the same set of species prevailed before logging.     

Optimization model for a wolf-ungulate system

Public outcries against predator control create a need to devise management policies that optimally balance the cost (managerial and environmental) of predator control against the benefit of ungulate harvesting. To address this problem, an optimization procedure utilizing stochastic dynamic programming is described. Through this approach, optimal feedback strategies for a wolf-ungulate system in Alaska are estimated. The dynamic predator-prey model used in the analysis is based on parameter estimates from data collected over an eight-year period in Denali (Mt. McKinley) National Park. Stability analysis of the system revealed that stability properties depend on predator search efficiency. The effects of random fluctuations in winter severity and alternative objective functions are considered in the estimation of optimal feedback strategies. Optimal moose harvesting strategies appear to be dependent on wolf control costs. If no wolf control cost is assessed, optimal moose harvest is independent of wolf density. Optimal wolf control strategies are completely insensitive to moose density. The strategies are compared to current and simplified management policies.