The effect of temperature, soil nitrogen and gastropods on _Thuja plicata_ growth and reproduction

Humans are changing the environment. For example, nitrogen deposition, rising temperatures, and non-native species are influencing plant communities. These changes have and will continue to affect trees, thus, understanding the response of species to global change will help conservationists plan for the future. Urban areas already experience higher temperatures, elevated CO~2~, greater nitrogen levels, and more non-native species compared to rural areas. The response of trees to urban parks and park edges can therefore be used as a proxy for the net effects of global change on trees. We investigate the growth and reproduction of _Thuja plicata_, a native Pacific Northwest conifer, in both urban and rural forest fragments to understand global change impacts. Data collected from sites include hourly temperature, soil NO~3~^-^, seedling counts, and an increment core. After observing extremely low conifer germination rates across sites, we concluded that factors such as herbivory might be important. Gastropods have been shown to impact communities through consumption of plants at the seedling stage, and to limit seedling survival of a European conifer. The effects of soil moisture, soil nitrogen, and gastropod herbivory on _Thuja plicata_ seedlings was analyzed experimentally to determine the relative effect each might be having on the observed germination rate. Our results suggest that urban forest edges resemble future global change conditions of higher temperature and nitrogen. These global change factors appear to be positively influencing tree growth, suggesting that _Thuja plicata_ will benefit from future conditions. However, low seedling recruitment may be a concern, because it appears that urban and rural forests are currently failing to regenerate on their own. Introduced gastropods could play a role, as they have the ability to reduce seedling biomass significantly. The relative impacts of invasive slug herbivory and other global change factors on native conifer recruitment should be prioritized in future study

Shifting phenology of an apex/specialist predator tracks changes in its favored prey

Phenology, or the timing of biological activities such as migration, growth, and reproduction, can have dramatic implications for fitness; consumer phenology that is out of step with its resource phenology can cause increased mortality or reduced reproductive success. The timing of southern resident killer whale (SRKW, Orcinus orca) movements in the Salish Sea is thought to be related to seasonal migrations of their prey. In recent decades, the abundance and phenology of the favored prey of SRKWs, salmon, has shifted in many locations across the western United States. Here, we use the OrcaMaster Database to quantify seasonal variation in SRKW activity in the Salish Sea, the extent to which these seasonal patterns have shifted in recent decades, and how potential shifts compare to shifts in their prey. Since 1994, we find that SRKWs are arriving later, leaving earlier, and spending fewer days at one well-monitored location adjacent to San Juan Island, and that the timing of SRKW activity corresponds to the timing and abundance of Fraser River Chinook salmon. Across the broader Central Salish Sea region, we find that shifts in SRKW phenology vary by pod. Phenology of J pod has shifted later in the Central Salish Sea, with estimates of peak probability of occupancy delaying at a rate of 5.5 days per year since 2001. Our estimates of phenology of K and L pods, on the other hand, have not shifted dramatically across the dataset. To better understand the extent to which prey availability controls the timing of SRKW activity in inland waters, there is a need for quantification of seasonal variation in salmon abundance throughout the Salish Sea

Testing the Limits: Understanding How Climate and Competition Affect Species' Ranges in a Warming World

Thesis (Ph.D.)--University of Washington, 2013What factors determine where species occur, known as their geographic range limits? This classic ecological question has fascinated scientists for centuries, and is even more relevant today, in the face of anthropogenic climate change. Unfortunately, despite decades of research, we still lack a full understanding of the ecological processes driving range limits. Of particular interest, given forecasted global warming, is the extent to which climate determines species' range limits. If climate is important in controlling species' range limits, then ranges will likely shift up in elevation, as temperatures rise. This research examined how climatic factors, including temperature and precipitation, interact with biotic factors (specifically, competition between plants) to determine the distributions of common conifers on Mt. Rainier. I conducted observational studies of adult and sapling tree rings, as well as an experiment, in which seeds and seedlings were transplanted across species' altitudinal ranges and beyond their range limits, into different competitive environments. Taken together, my studies suggest that climate limits growth and survival at high elevations, while competition is more important at low elevations. These results support a classic, but little tested, hypothesis: biotic factors, such as competition, are more important at lower range limits, while abiotic factors, such as temperature, control upper range limits. Furthermore, these results suggest that climate change will lead to increased tree growth and upward expansion of Mt. Rainier's forests, beyond current high elevation treeline. Climate change will likely have less dramatic effects at low elevations, where climate does not appear to strongly limit growth and survival of focal tree species, but competitive dynamics between plants do limit growth and survival. More experimental studies of other biotic interactions, diverse species, and widespread locations are necessary to better understand effects of climate change, and to prioritize conservation and natural resource management efforts

MicroClimate from Climate Change Experiments (doi:10.5063/F17P8WNT).

Database of daily microclimate data (above-ground and soil temperature, and soil moisture) from warming experiments, information on experimental sites included in database, and definitions of warming and precipitation treatments applied to each plot are available in Knowledge Network for Biocomplexity (KNB) at https://doi.org/10.5063/F17P8WN

Data from: How do climate change experiments alter plot-scale climate?

To understand and forecast biological responses to climate change, scientists frequently use field experiments that alter temperature and precipitation. Climate manipulations can manifest in complex ways, however, challenging interpretations of biological responses. We reviewed publications to compile a database of daily plot‐scale climate data from 15 active‐warming experiments. We find that the common practices of analysing treatments as mean or categorical changes (e.g. warmed vs. unwarmed) masks important variation in treatment effects over space and time. Our synthesis showed that measured mean warming, in plots with the same target warming within a study, differed by up to 1.6 urn:x-wiley:1461023X:media:ele13223:ele13223-math-0001C (63% of target), on average, across six studies with blocked designs. Variation was high across sites and designs: for example, plots differed by 1.1 urn:x-wiley:1461023X:media:ele13223:ele13223-math-0002C (47% of target) on average, for infrared studies with feedback control (n = 3) vs. by 2.2 urn:x-wiley:1461023X:media:ele13223:ele13223-math-0003C (80% of target) on average for infrared with constant wattage designs (n = 2). Warming treatments produce non‐temperature effects as well, such as soil drying. The combination of these direct and indirect effects is complex and can have important biological consequences. With a case study of plant phenology across five experiments in our database, we show how accounting for drier soils with warming tripled the estimated sensitivity of budburst to temperature. We provide recommendations for future analyses, experimental design, and data sharing to improve our mechanistic understanding from climate change experiments, and thus their utility to accurately forecast species’ responses

Forest restoration thinning accelerates development of old‐growth characteristics in the coastal Pacific Northwest, USA

Abstract A century of industrial‐scale management has transformed vast swaths of forest land across the Pacific Northwest (PNW), USA, from ancient forests with complex structure and diverse habitats to young forests with simple structure and dominated by few species. Consequently, there have been calls to restore ecosystem integrity and resilience. Here, we apply data from a watershed‐scale experiment to determine if restoration treatments have achieved our management goal of accelerating the development of old‐growth forest characteristics. We provide empirical evidence of how restoration treatments have affected key old‐growth forest indicators resulting in larger trees, more complex vertical and horizontal forest structure, reduced stand density, and increased understory plant richness. Our study also demonstrates that some restoration indicators responded in counter‐intuitive ways contingent on interactions between stand age and restoration treatment. Through this work, we learned two important lessons: (1) more time and monitoring may be needed to fully understand the effects of restoration treatments and (2) a “one and done” approach of implementing restoration treatments may not achieve a full suite of old‐growth characteristics. Moreover, long‐term management for wildlife habitat and climate resilience will likely require an adaptive approach, with ongoing monitoring continually informing and adjusting management practices

Site- and Species-Specific Influences on Sub-Alpine Conifer Growth in Mt. Rainier National Park, USA

Identifying the factors that influence the climate sensitivity of treeline species is critical to understanding carbon sequestration, forest dynamics, and conservation in high elevation forest/meadow ecotones. Using tree cores from four sub-alpine conifer species collected from three sides of Mt. Rainier, WA, USA, we investigated the influences of species identity and sites with different local climates on radial growth–climate relationships. We created chronologies for each species at each site, determined influential plant-relevant annual and seasonal climatic variables influencing growth, and investigated how the strength of climate sensitivity varied across species and location. Overall, similar climate variables constrained growth on all three sides of the mountain for each of the four study species. Summer warmth positively influenced radial growth, whereas snow, spring warmth, previous summer warmth, and spring humidity negatively influenced growth. We discovered only a few subtle differences in the climate sensitivity of co-occurring species at the same site and between the same species at different sites in pairwise comparisons. A model including species by climate interactions provided the best balance between parsimony and fit, but did not lead to substantially greater predictive power relative to a model without site or species interactions. Our results imply that at treeline in moist temperate regions like Mt. Rainier, the same climatic variables drive annual variation in growth across species and locations, despite species differences in physiology and site differences in mean climates

Spatial heterogeneity in ecologically important climate variables at coarse and fine scales in a high-snow mountain landscape.

Climate plays an important role in determining the geographic ranges of species. With rapid climate change expected in the coming decades, ecologists have predicted that species ranges will shift large distances in elevation and latitude. However, most range shift assessments are based on coarse-scale climate models that ignore fine-scale heterogeneity and could fail to capture important range shift dynamics. Moreover, if climate varies dramatically over short distances, some populations of certain species may only need to migrate tens of meters between microhabitats to track their climate as opposed to hundreds of meters upward or hundreds of kilometers poleward. To address these issues, we measured climate variables that are likely important determinants of plant species distributions and abundances (snow disappearance date and soil temperature) at coarse and fine scales at Mount Rainier National Park in Washington State, USA. Coarse-scale differences across the landscape such as large changes in elevation had expected effects on climatic variables, with later snow disappearance dates and lower temperatures at higher elevations. However, locations separated by small distances (∼20 m), but differing by vegetation structure or topographic position, often experienced differences in snow disappearance date and soil temperature as great as locations separated by large distances (>1 km). Tree canopy gaps and topographic depressions experienced later snow disappearance dates than corresponding locations under intact canopy and on ridges. Additionally, locations under vegetation and on topographic ridges experienced lower maximum and higher minimum soil temperatures. The large differences in climate we observed over small distances will likely lead to complex range shift dynamics and could buffer species from the negative effects of climate change

Relationships between vegetation characteristics and microclimate.

<p>(A–D) Percent cover by tree canopy at sites near the lower limit of the subalpine biome and (E–H) percent cover by ground vegetation at sites near the upper limit of alpine meadows plotted against the four microclimate variables (snow disappearance date and average daily mean, maximum and minimum soil temperature) on each of the three sides of the mountain. The <i>r</i>² values are for models that included the microclimate variable and side of the mountain as explanatory variables, while the <i>p</i> values indicate the significance of the microclimate variable in these models. Regression lines are shown for significant <i>p</i> values (<0.05).</p