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Climatic variability and episodic Pinus ponderosa establishment along the forest-grassland ecotones of Colorado
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The primary objective of this study was the detection of possible climatic influences on the recent (i.e., past c. 40 years) establishment of ponderosa pine (Pinus ponderosa) at or near forest-grassland ecotones in the northern Front Range of Colorado. Germination dates were precisely determined for >500 juvenile ponderosa pine collected in six widely dispersed sample areas. All sites sampled were open areas lacking an overstory tree cover but located near seed sources. To evaluate the effects of recent climatic variation on recruitment and survival patterns, three types of climate data were used: (1) instrumental climate records from nearby local weather stations; (2) a multivariate index of El Nino/Southern Oscillation (ENSO); and (3) a regional, ponderosa pine tree-ring index sensitive to moisture variation. There is a strong association between episodic recruitment of ponderosa pine and years in which spring and fall moisture availability is high in the instrumental climate record. During the past 40 years, tree establishment was highly episodic and concentrated mainly in four years—1973, 1979, 1983, and 1990. These years are also associated with large-scale warming of sea-surface temperatures in the eastern tropical Pacific (i.e., El Nin ̃o events). These years of abundant seedling establishment also coincide with years of above average radial growth in mature ponderosa pine. Thus, at open sites suitable for the survival of shade-intolerant ponderosa pine, successful establishment of seedlings is highly episodic depending on local moisture availability related to broad-scale climatic variation. This study demonstrates the climatic sensitivity of ponderosa pine recruitment at low elevation sites along forest-grassland ecotones in the northern Colorado Front Range.
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Variability, contingency and rapid change in recent subarctic alpine tree line dynamics
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Summary
1 Boundaries between forest and tundra ecosystems, tree lines, are expected to advance in altitude and latitude in response to climate warming. However, varied responses to 20th century warming suggest that in addition to temperature, tree line dynamics are mediated by species-specific traits and environmental conditions at landscape and local scales.
2 We examined recent tree line dynamics at six topographically different, but climatic- ally similar, sites in south-west Yukon, Canada. Dendroecological techniques were used to reconstruct changes in density of the dominant tree species, white spruce (Picea glauca), and to construct static age distributions of willow (Salix spp.), one of two dominant shrub genera. Data were analysed to identify periods and rates of establish- ment and mortality and to relate these to past climate.
3 Tree line elevation and stand density increased significantly during the early to mid 20th century. However, this change was not uniform across sites. Spruce advanced rapidly on south-facing slopes and tree line rose 65 – 85 m in elevation. Tree line did not advance on north-facing slopes, but stand density increased 40–65%. Differences observed between aspects were due primarily to the differential presence of permafrost. Additional variability among sites was related to slope and vegetation type. Results were less conclusive for willow, but evidence for an advance was found at two sites.
4 Increases in stand density were strongly correlated with summer temperatures. The period of rapid change coincided with a 30-year period of above average temperatures, beginning in 1920. The highest correlations were obtained using a forward average of 30 – 50 years, supporting the hypothesis that tree line dynamics are controlled more by conditions influencing recruitment than by establishment alone.
5 The changes observed at several sites are suggestive of a threshold response and challenge the notion that tree lines respond gradually to climate warming. Overall, the results provide further evidence to support the idea that the pattern and timing of change is contingent on local, landscape, and regional-scale factors, as well as species’ biology.
Key-words: climate change, dendroecology, ecotones, forest-tundra, non-linearity, Picea glauca, Salix glauca, stand dynamics, timberline, Yukon
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Phylogenetic trees and the future of mammalian biodiversity
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Phylogenies describe the origins and history of species. However, they can also help to predict species’ fates and so can be useful tools for managing the future of biodiversity. This article starts by sketching how phylogenetic, geographic, and trait information can be combined to elucidate present mammalian diversity patterns and how they arose. Recent diversification rates and standing diversity show different geographic patterns, indicating that cra- dles of diversity have moved over time. Patterns in extinction risk reflect both biological differences among mammalian lineages and differences in threat intensity among regions. Phylogenetic com- parative analyses indicate that for small-bodied mammals, extinc- tion risk is governed mostly by where the species live and the intensity of the threats, whereas for large-bodied mammals, eco- logical differences also play an important role. This modeling approach identifies species whose intrinsic biology renders them particularly vulnerable to increased human pressure. We outline how the approach might be extended to consider future trends in anthropogenic drivers, to identify likely future battlegrounds of mammalian conservation, and the likely casualties. This framework could help to highlight consequences of choosing among different future climatic and socioeconomic scenarios. We end by discussing priority-setting, showing how alternative currencies for diversity can suggest very different priorities. We argue that aiming to maximize long-term evolutionary responses is inappropriate, that conservation planning needs to consider costs as well as benefits, and that proactive conservation of largely intact systems should be part of a balanced strategy.
extinction risk latent risk mammals
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DOES WOOD SLOW DOWN “SLUDGE DRAGONS?” THE INTERACTION BETWEEN RIPARIAN ZONES AND DEBRIS FLOWS IN MOUNTAIN LANDSCAPES
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Conservation measures for aquatic species throughout the Pacific Northwest rely heavily on maintaining forested riparian zones. A key rationale for this strategy is that the presence of standing and downed trees next to streams will provide a continuous source of wood, which is an important structural component of aquatic habitat. Yet little is known about the interactions between wood and debris flows, which are an important way that wood enters streams.Researchers from the PNW Research Station and Oregon State University created a physics-based simulation of debris flow dynamics in a headwater basin within the Oregon Coast Range. They found that the presence of wood funda- mentally changes the behavior of debris flows by reducing the momentum and distance that they travel. Because debris flow deposits are primary storage sites for sediment within headwater catchments, a shift toward shorter flows means that more sediment is stored higher up in watersheds. In addition, they found that zones with high densities of wood and sediment are relatively fixed in space and do not migrate downstream. This suggests that management strategies could specifically target achieving habitat objectives within these high accumulation zones, and there may be multiple management pathways for achieving these objectives.
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Exponential Decline of Deep-Sea Ecosystem Functioning Linked to Benthic Biodiversity Loss
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Here, we present a global-scale study based on 116 deep-sea sites that relates benthic biodiversity to several independent indicators of ecosystem functioning and efficiency. We show that deep-sea ecosystem functioning is exponentially related to deep-sea biodiversity and that ecosystem efficiency is also exponentially linked to functional biodiversity. These results suggest that a higher biodiversity supports higher rates of ecosystem processes and an increased efficiency with which these processes are performed. The exponential relationships presented here, being consistent across a wide range of deep-sea ecosystems, suggest that mutually positive functional interactions (ecological facilitation) can be common in the largest biome of our biosphere.Conclusions: Our results suggest that a biodiversity loss in deep-sea ecosystems might be associated with exponential reductions of their functions. Because the deep sea plays a key role in ecological and biogeochemical processes at a global scale, this study provides scientific evidence that the conservation of deep-sea biodiversity is a priority for a sustainable functioning of the worlds’ oceans.
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Spatial relationship between climatologies and changes in global vegetation activity
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Vegetation forms a main component of the terrestrial biosphere and plays a crucial role in land-cover and climate- related studies. Activity of vegetation systems is commonly quantified using remotely sensed vegetation indices (VI). Extensive reports on temporal trends over the past decades in time series of such indices can be found in literature. However, little remains known about the processes underlying these changes at large spatial scales. In this study, we aimed at quantifying the spatial relationship between changes in potential climatic growth constraints (i.e. temperature, precipitation and incident solar radiation) and changes in vegetation activity (1982–2008). We demonstrate an additive spatial model with 0.5° resolution, consisting of a regression component representing climate-associated effects and a spatially correlated field representing the combined influence of other factors, including land-use change. Little over 50% of the spatial variance could be attributed to changes in climatologies; conspicuously, many greening trends and browning hotspots in Argentina and Australia. The nonassociated model component may contain large- scale human interventions, feedback mechanisms or natural effects, which were not captured by the climatologies. Browning hotspots in this component were especially found in subequatorial Africa. On the scale of land-cover types, strongest relationships between climatologies and vegetation activity were found in forests, including indications for browning under warming conditions (analogous to the divergence issue discussed in dendroclimatology).
Keywords: climate- and human-induced change, climatologies, Gaussian random field, growth constraints, regression, spatial additive model, vegetation-activity trends
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WHY FORESTS ARE PIVOTAL IN PLANNING FOR CLIMATE CHANGE
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17 slides show carbon-forest relationships including logging and carbon in US forests
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Public land, timber harvests, and climate mitigation: Quantifying carbon sequestration potential on U.S. public timberlands
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Scientists and policy makers have long recognized the role that forests can play in countering the atmospheric buildup of carbon dioxide (CO2), a greenhouse gas (GHG). In the United States, terrestrial carbon sequestration in private and public forests offsets approximately 11% of all GHG emissions from all sectors of the economy on an annual basis. Although much of the attention on forest carbon sequestration strategy in the United States has been on the role of private lands, public forests in the United States represent approximately 20% of the U.S. timberland area and also hold a significantly large share (30%) of the U.S. timber volume. With such a large standing timber inventory, these forested lands have considerable impact on the U.S. forest carbon balance. To help decision makers understand the carbon implications of potential changes in public timberland management, we compared a baseline timber harvest scenario with two alternative harvest scenarios and estimated annual carbon stock changes associated with each. Our analysis found that a ‘‘no timber harvest’’ scenario eliminating harvests on public lands would result in an annual increase of 17–29 million metric tonnes of carbon (MMTC) per year between 2010 and 2050—as much as a 43% increase over current sequestration levels on public timberlands and would offset up to 1.5% of total U.S. GHG emissions. In contrast, moving to a more intense harvesting policy similar to that which prevailed in the 1980s may result in annual carbon losses of 27–35 MMTC per year between 2010 and 2050. These losses would represent a significant decline (50–80%) in anticipated carbon sequestration associated with the existing timber harvest policies. If carbon sequestration were valued in the marketplace as part of a GHG offset program, the economic value of sequestered carbon on public lands could be substantial relative to timber harvest revenues. Public timberland; Forestry; Climate change; Carbon sequestration
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Climate change hotspots in the United States
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We use a multi-model, multi-scenario climate model ensemble to identify climate change hotspots in the continental United States. Our ensemble consists of the CMIP3 atmosphere-ocean general circulation models, along with a high-resolution nested climate modeling system. We test both high (A2) and low (B1) greenhouse gas emissions trajectories, as well as two different statistical metrics for identifying regional climate change hotspots. We find that the pattern of peak responsiveness in the CMIP3 ensemble is persistent across variations in GHG concentration, GHG trajectory, and identification method. Areas of the southwestern United States and northern Mexico are the most persistent hotspots. The high-resolution climate modeling system produces highly localized hotspots within the basic GCM structure, but with a higher sensitivity to the identification method. Across the ensemble, the pattern of relative climate change hotspots is shaped primarily by changes in interannual variability of the contributing variables rather than by changes in the long-term mean
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Negative density-dependent dispersal in the American black bear (Ursus americanus) revealed by noninvasive sampling and genotyping
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Although the dispersal of animals is influenced by a variety of factors, few studies have used a condition-dependent approach to assess it. The mechanisms underlying dispersal are thus poorly known in many species, especially in large mammals. We used 10 microsatellite loci to examine population density effects on sex-specific dispersal behavior in the American black bear, Ursus americanus. We tested whether dispersal increases with population density in both sexes. Fine-scale genetic struc- ture was investigated in each of four sampling areas using Mantel tests and spatial autocorrelation analyses. Our results revealed male-biased dispersal pattern in low- density areas. As population density increased, females appeared to exhibit philopa- try at smaller scales. Fine-scale genetic structure for males at higher densities may indicate reduced dispersal distances and delayed dispersal by subadults.
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