In interior Alaska’s 115 million acres of boreal forest, white and black spruce are the dominant tree species. Climate models suggest that the region is becoming warmer and drier, resulting in declining growth of black and white spruce, according to some researchers. These drier conditions also may lead to greater risk of stand-replacing wildfires, resulting in forests dominated by birch and aspen, which are early-successional tree species.
To compare long-term growth trends of the dominant coniferous and deciduous tree species, a team of researchers with the USDA Forest Service Pacific Northwest Research Station and the University of Alaska Anchorage analyzed tree cores collected from the Tanana Valley and measured tree-ring widths of these four tree species over the past 150 years. They also compared growth against monthly temperature and precipitation data to determine if there is a correlation between climate and growth.
The team found that white and black spruce have not experienced as rapid a growth decline as earlier studies suggested; instead, their annual growth remains near the long-term mean. Of the four species examined, aspen showed the greatest recent growth decline, likely reflecting a widespread insect outbreak. Among the climate variables that will affect the future growth of these species, summer rainfall was identified as a significant factor.
Microsites, local features having the potential to alter the environment for seedling regeneration, may help to define likely trends in high-elevation forest regeneration pattern. Although multiple microsites may exist in any alpine treeline ecotone (ATE) on any continent, some microsites appear to enhance density of seedling regeneration better than others. Known seedling regeneration stresses in the ATE include low temperature, low substrate moisture, high radiation, drought, wind, and both high and low snowfall amount. Relationships among various microsite types, annual temperature, annual precipitation, and tree genera groups were assessed by synthesizing 52 studies from 26 countries spanning six continents. By categorization of four main microsite types (convex, concave, object, and wood) by mean annual precipitation and temperature, four major climatic zone associations were distinguished: cold & dry, cold & wet, warm & dry, warm & wet. Successful tree recruitment varied among microsite types and by climatic zones. In general, elevated convex sites and/or decayed wood facilitated earlier snow melt for seedlings located in cold & wet climates with abundant snowfall, depressions or concave sites enhanced summer moisture and protected seedlings from wind chill exposure for seedlings growing in cold & dry locations, and objects protected seedlings from excessive radiation and wind in warm & dry high locations. Our study results suggest that climate change will most benefit seedling regeneration in cold & wet locations and will most limit seedling regeneration in warm & dry locations given likely increases in fire and drought. Study results suggest that high-elevation mountain forests with water-limited growing seasons are likely to experience recruitment declines or, at best, no new recruitment advantage as climate warms. Climate envelope models, generally focusing on adult trees rather than seedling requirements, often assume that a warming climate will move tree species upward. Study results suggest that climate models may benefit from more physically-based considerations of microsites, climate, and current seedling regeneration limitations.
Natural areas are tracts of land with little or no evidence of past human influence and designated for research, education, and conservation. Many sites were selected to represent high-quality examples of both common and rare plant association groups. However, the extent to which natural areas characterize regional environmental conditions or gradients important for measuring and understanding the effects of climate change has not been examined. We compared the current collection of natural areas in Oregon and Washington to the broader natural ecosystems found in the region using four ecological parameters derived from existing datasets: forest structure, dominant tree species, vegetation formation classes, and elevation. We evaluated these data sets at both the regional and ecosystem scales and looked at the influence of land ownership in representing these parameters. Our results suggest that the Pacific Northwest natural areas network is well representative of all four parameters at the regional level. There were some gaps in representation at the ecoregion scale and across some land ownerships. Results from this study further support using natural areas for monitoring long-term climate change effects in the Pacific Northwest.
Monitoring vegetation phenology is important for managers at several scales. Across decades, changes in the timing, pattern, and duration of significant life cycle events for plant groups can foreshadow shifts in species assemblages that can affect ecosystem services. In the shorter term, managers need phenological information to time activities such as grazing, ecological restoration plantings, biocontrol of pests, seed collection, and wildlife monitoring. However, tools to deliver timely seasonal development have been limited either spatially (data from a single tower or weather station, or on a single species, or both) or temporally (annually, quarterly, or monthly summaries). We developed another option called PhenoMap. This is a weekly assessment of land surface “greenness” across the continental United States that employs the Normalized Differential Vegetation Index (NDVI) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. Here we present the PhenoMap Web map and its validation by using 54 in situ PhenoCam camera sites representing six vegetation structure types and 31 different ecoregions. We found that PhenoMap effectively tracks phenology on grasslands, shrublands, deciduous broadleaf and mixed forests. Results for evergreen needleleaf sites were poor owing to the low green-up signal relative to the total amount of foliage detected by NDVI. Issues of extent and field of view were critical when assessing remotely sensed data with in situ oblique camera imagery.
The Arctic and boreal regions are warming more than twice as rapidly as the rest of the world. The timing of plants’ flowering and fruiting is changing, with implications for insects, wildlife, and people who rely on these resources for food and livelihoods in Alaska. Alaska’s boreal forest will undergo significant functional and structural changes within the next few decades that are unprecedented in the past 6,000 years. The Bonanza Creek Long-Term Ecological Research program is critical to Forest Service research because it is the only Forest Service outpost in the boreal forest, which is the biggest forest in the world. Pacific Northwest Research Station scientists are contributing groundbreaking climate research in Alaska, with global implications.
Many climate change models predict increases in frequency and magnitude of temperature fluctuations that might impact how ectotherms are affected by disease. Shifts in temperature might especially affect amphibians, a group with populations that have been challenged by several pathogens. Because amphibian hosts invest more in immunity at warmer than cooler temperatures and parasites might acclimate to temperature shifts faster than hosts (creating lags in optimal host immunity), researchers have hypothesized that a temperature shift from cold-to-warm might result in increased amphibian sensitivity to pathogens, whereas a shift from warm-to-cold might result in decreased sensitivity. Support for components of this climate-variability based hypothesis have been provided by prior studies of the fungus Batrachochytrium dendrobatidis (Bd) that causes the disease chytridiomycosis in amphibians. We experimentally tested whether temperature shifts before exposure to Batrachochytrium dendrobatidis (Bd) alters susceptibility to the disease chytridiomycosis in the larval stage of two amphibian species–western toads (Anaxyrus boreas) and northern red legged frogs (Rana aurora). Both host species harbored elevated Bd infection intensities under constant cold (15˚ C) temperature in comparison to constant warm (20˚ C) temperature. Additionally, both species experienced an increase in Bd infection abundance after shifted from 15˚ C to 20˚ C, compared to a constant 20˚ C but they experienced a decrease in Bd after shifted from 20˚ C to 15˚ C, compared to a constant 15˚ C. These results are in contrast to prior studies of adult amphibians highlighting the potential for species and stage differences in the temperature-dependence of chytridiomycosis.
Shorelines in Alaska are changing, with significant consequences for the animals and people in this region. Organizing a series of student-led discussions with community leaders and Alaskan Native elders, Pacific Northwest Research Station scientists Adelaide Johnson and Linda Kruger have identified which coastal resources are of most concern to local communities and how coastal changes may impact these valued resources.
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The iso/anisohydry concept characterizes plants according to their water status regulation. Coexisting definitions and misconceptions have recently led to considerable criticism. Here, we discuss reasons for the misconceptions and propose a robust definition of iso/anisohydry using the leaf turgor loss point to integrate the complex interplay of plant hydraulic traits.