Demographic processes in forest trees in the Rocky Mountains

2017 Summer.Includes bibliographical references.Forests provide numerous ecological and economic services including regulation of biogeochemical cycles, fiber production, watershed protection, as well as less tangible aesthetic and recreational benefits. Forests are being substantially altered by a range of consumptive uses related to expanding human population and economies. Superimposed on other anthropogenic impacts is global climate change. Global circulation models unambiguously reveal the role of greenhouse gas forcings associated with industrial processes in driving global temperature trends (Hanson et al. 2005). Meteorological observations indicate that global mean temperature has increased by approximately 0.6 C over the past century relative to a base 1951 to 1980 period, with record high temperatures occurring in 2010. Paleoclimatic reconstructions based on proxy data indicate that modern rates of warming may be unprecedented in the context of the past 1000 years. Rates of warming are geographically heterogeneous. Temperature anomalies in the Rocky Mountain ecoregion, for example, are 2‒3 times higher than the global mean temperature increase. Some models and observational data suggest that temperature trends are elevation dependent with greater warming at high altitudes and with greater increases in daily minimum temperatures than maximum temperatures. Documented increases in minimum temperature is associated with earlier spring thaw events, driven by minimum temperatures that exceed 0 °C and a lengthening of the growing and fire seasons. In the Rocky Mountains, an altered climate system is projected to result in a higher frequency and intensity of drought events. Precipitation over the previous 100 years lacks clear trends across the region as a whole, but models of snow water equivalent (SWE) indicate declining moisture availability since the mid-20th century. Early spring snowmelt and warming driven increases in rates of evapotranspiration may correlate with reduced stream flow and declines in effective soil moisture late in the growing season. Warming temperatures and reductions in moisture availability have been associated with significant increases in area burned by wildfire in some forest systems, particularly at high elevations where climate variability rather than fuel conditions is the primary driver of fire activity. Changing climate may also be expanding the ranges and altering the dynamics of forest insects, such as the mountain pine beetle (Dendroctonus ponderosae), resulting in extensive tree mortality. The recent widespread acceptance of climate change has highlighted the need for regional and species specific adaptation strategies. However, a lack of reliable projections describing the responses of organisms and communities to climate change has been identified as a major impediment to the development and implementation of climate adaptation strategies within federal agencies. Potential vegetation responses include migration to track preferred habitats or adaptation through phenotypic or genetic plasticity. Heat stress and prolonged drought have been associated with rapid shifts in the range limits of ponderosa pine (Pinus ponderosa) and in significantly elevated rates of background tree mortality for tree species and forest environments worldwide. Mortality events associated with physiological stress or environmental disturbances may accelerate changes in the distributions of long-lived tree species that might otherwise persist in sub-optimal environments. The distribution and abundance of plants are largely determined by physiological, life history, and ecosystem processes, and how these processes interact or respond to climate. A mechanistic understanding of these processes and their physiological thresholds is required to accurately predict forest response to climate change. The 2007 Intergovernmental Panel on Climate Change working group has argued that current predictive vegetation models are limited by a failure to adequately quantify relationships between climate, critical life history processes, and disturbance regimes. The main objective of this research is to quantify life history processes for select tree species in the Rocky Mountain ecoregion. Specifically, non-linear regression models will be developed to quantify variation in both tree fecundity and growth as a function of climate variables, edaphic gradients, and competition. Comprehensive field data will be used to train flexible functions in a maximum likelihood framework. Competing models representing alternative hypotheses will be evaluated using information theory. The overarching objective of this project is to provide detailed quantitative life history information that may subsequently be used to parameterize dynamic simulation models for the prediction of forest response to alternative future climate scenarios. An additional component of this research involves the reconstruction of historical temperatures in the southern portion of the Rocky Mountain ecoregion using chronologies of radial growth from several high elevation tree species occurring in northern Colorado and southern Wyoming. Historical temperatures have been reconstructed for northern portions of the Rocky Mountain ecoregion. A comparable reconstruction for the southern portion of the region has not been developed. Global climate models predict that parts of the Rockies may experience future climates with no previous analogs. Historical temperature reconstructions based on proxy indicators will provide historical context for both modern climate variation and simulations of future conditions

Wnt/Frizzled Signaling Requires dPRR, the Drosophila Homolog of the Prorenin Receptor

SummaryWnt/Wg signaling pathways are of key importance during development and disease [1–4]. Canonical and noncanonical Wnt/Frizzled (Fz) pathways share a limited number of signaling components that are part of the membrane proximal signaling complex. In Drosophila, Fz [5–7] and Dishevelled (Dsh) [8, 9] are the only two components known to be involved in both Wnt/β-catenin and planar cell polarity (PCP) signaling. PCP signaling is required for the planar polarization of epithelial cells [10, 11], which occurs, for instance, during hair orientation and gastrulation in vertebrates [12]. Both pathways have been studied intensively in the past years. However, it still remains unresolved whether additional components are required at the receptor complex. Here we identify the Drosophila homolog of the mammalian prorenin receptor (dPRR) as a conserved modulator of canonical Wnt/β-cat and Fz/PCP signaling. We show that dPRR depletion affects Wg target genes in cultured cells and in vivo. PRR is required for epithelial planar polarity in Drosophila and for convergent extension movements in Xenopus gastrulae. Furthermore, dPRR binds to Fz and Fz2 receptors. In summary, our data suggest that dPRR has an evolutionarily conserved role at the receptor level for activation of canonical and noncanonical Wnt/Fz signaling pathways

Classification of oak vegetation in the Willamette Valley

A plant community classification was developed describing the comprehensive variation of oak vegetation currently occupying the Willamette Valley Ecoregion of western Oregon. Multivariate statistical analyses were used to classify field collected floristic and habitat data. Field sampling targeted minimally managed, homogenous vegetation stands with a significant oak component occupying at least 0.5 ha. Potential habitat locations were identified from local expert knowledge, data from The Nature Conservancy’s previous conservation planning efforts, and an interpretation of high resolution NAIP imagery. Potential oak habitats were digitized in a GIS and a random selection of sites stratifying significant environmental gradients was generated in order capture the range of oak habitat variability. Precise sample plot locations were predetermined and established at digitized stand centroids. Field sampling was based on relevé plot data collection methods and included ocular estimates of species cover. A total of 350 stands of oak vegetation were sampled over two field seasons. Two-way indicator species analysis (TWINSPAN) was used as an exploratory tool to identify potential patterns in species cover data and Detrended Correspondence Analysis (DCA) was used to delimit final plant community types. Nine vegetation classes were described from ordinations including seven forest / woodland types and two savanna

The Last Trees Standing: Climate modulates tree survival factors during a prolonged bark beetle outbreak in Europe

Plant traits are an expression of strategic tradeoffs in plant performance that determine variation in allocation of finite resources to alternate physiological functions. Climate factors interact with plant traits to mediate tree survival. This study investigated survival dynamics in Norway spruce (Picea abies) in relation to tree-level morphological traits during a prolonged multi-year outbreak of the bark beetle, Ips typographus, in Central Europe. We acquired datasets describing the trait attributes of individual spruce using remote sensing and field surveys. We used nonlinear regression in a hypothesis-driven framework to quantify survival probability as a function of tree size, crown morphology, intraspecific competition and a growing season water balance. Extant spruce trees that persisted through the outbreak were spatially clustered, suggesting that survival was a nonrandom process. Larger diameter trees were more susceptible to bark beetles, reflecting either life history tradeoffs or a dynamic interaction between defense capacity and insect aggregation behavior. Competition had a strong negative effect on survival, presumably through resource limitation. Trees with more extensive crowns were buffered against bark beetles, ostensibly by a more robust photosynthetic capability and greater carbon reserves. The outbreak spanned a warming trend and conditions of anomalous aridity. Sustained water limitation during this period amplified the consequences of other factors, rendering even smaller trees vulnerable to colonization by insects. Our results are in agreement with prior research indicating that climate change has the potential to intensify bark beetle activity. However, forest outcomes will depend on complex cross-scale interactions between global climate trends and tree-level trait factors, as well as feedback effects associated with landscape patterns of stand structural diversity

Natural disturbance impacts on trade-offs and co-benefits of forest biodiversity and carbon

With accelerating environmental change, understanding forest disturbance impacts on trade-offs between biodiversity and carbon dynamics is of high socio-economic importance. Most studies, however, have assessed immediate or short-term effects of disturbance, while long-term impacts remain poorly understood. Using a tree-ring-based approach, we analysed the effect of 250 years of disturbances on present-day biodiversity indicators and carbon dynamics in primary forests. Disturbance legacies spanning centuries shaped contemporary forest co-benefits and trade-offs, with contrasting, local-scale effects. Disturbances enhanced carbon sequestration, reaching maximum rates within a comparatively narrow post-disturbance window (up to 50 years). Concurrently, disturbance diminished aboveground carbon storage, which gradually returned to peak levels over centuries. Temporal patterns in biodiversity potential were bimodal; the first maximum coincided with the short-term post-disturbance carbon sequestration peak, and the second occurred during periods of maximum carbon storage in complex old-growth forest. Despite fluctuating local-scale trade-offs, forest biodiversity and carbon storage remained stable across the broader study region, and our data support a positive relationship between carbon stocks and biodiversity potential. These findings underscore the interdependencies of forest processes, and highlight the necessity of large-scale conservation programmes to effectively promote both biodiversity and long-term carbon storage, particularly given the accelerating global biodiversity and climate crises

Wnt secretion and gradient formation.

Concentration gradients formed by the lipid-modified morphogens of the Wnt family are known for their pivotal roles during embryogenesis and adult tissue homeostasis. Wnt morphogens are also implicated in a variety of human diseases, especially cancer. Therefore, the signaling cascades triggered by Wnts have received considerable attention during recent decades. However, how Wnts are secreted and how concentration gradients are formed remains poorly understood. The use of model organisms such as Drosophila melanogaster has provided important advances in this area. For instance, we have previously shown that the lipid raft-associated reggie/flotillin proteins influence Wnt secretion and spreading in Drosophila. Our work supports the notion that producing cells secrete Wnt molecules in at least two pools: a poorly diffusible one and a reggie/flotillin-dependent highly diffusible pool which allows morphogen spreading over long distances away from its source of production. Here we revise the current views of Wnt secretion and spreading, and propose two models for the role of the reggie/flotillin proteins in these processes: (i) reggies/flotillins regulate the basolateral endocytosis of the poorly diffusible, membrane-bound Wnt pool, which is then sorted and secreted to apical compartments for long-range diffusion, and (ii) lipid rafts organized by reggies/flotillins serve as "dating points" where extracellular Wnt transiently interacts with lipoprotein receptors to allow its capture and further spreading via lipoprotein particles. We further discuss these processes in the context of human breast cancer. A better understanding of these phenomena may be relevant for identification of novel drug targets and therapeutic strategies

Response to Mechanical Stress Is Mediated by the TRPA Channel Painless in the Drosophila Heart

Mechanotransduction modulates cellular functions as diverse as migration, proliferation, differentiation, and apoptosis. It is crucial for organ development and homeostasis and leads to pathologies when defective. However, despite considerable efforts made in the past, the molecular basis of mechanotransduction remains poorly understood. Here, we have investigated the genetic basis of mechanotransduction in Drosophila. We show that the fly heart senses and responds to mechanical forces by regulating cardiac activity. In particular, pauses in heart activity are observed under acute mechanical constraints in vivo. We further confirm by a variety of in situ tests that these cardiac arrests constitute the biological force-induced response. In order to identify molecular components of the mechanotransduction pathway, we carried out a genetic screen based on the dependence of cardiac activity upon mechanical constraints and identified Painless, a TRPA channel. We observe a clear absence of in vivo cardiac arrest following inactivation of painless and further demonstrate that painless is autonomously required in the heart to mediate the response to mechanical stress. Furthermore, direct activation of Painless is sufficient to produce pauses in heartbeat, mimicking the pressure-induced response. Painless thus constitutes part of a mechanosensitive pathway that adjusts cardiac muscle activity to mechanical constraints. This constitutes the first in vivo demonstration that a TRPA channel can mediate cardiac mechanotransduction. Furthermore, by establishing a high-throughput system to identify the molecular players involved in mechanotransduction in the cardiovascular system, our study paves the way for understanding the mechanisms underlying a mechanotransduction pathway

Climate warming disrupts mast seeding and its fitness benefits in European beech

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. Many plants benefit from synchronous year-to-year variation in seed production, called masting. Masting benefits plants because it increases the efficiency of pollination and satiates predators, which reduces seed loss. Here, using a 39-year-long dataset, we show that climate warming over recent decades has increased seed production of European beech but decreased the year-to-year variability of seed production and the reproductive synchrony among individuals. Consequently, the benefit that the plants gained from masting has declined. While climate warming was associated with increased reproductive effort, we demonstrate that less effective pollination and greater losses of seeds to predators offset any benefits to the plants. This shows that an apparently simple benefit of climate warming unravels because of complex ecological interactions. Our results indicate that in masting systems, the main beneficiaries of climate-driven increases in seed production are seed predators, not plants

Microtopographic drivers of vegetation patterning in blanket peatlands recovering from erosion

Blanket peatlands are globally rare, and many have been severely eroded. Natural recovery and revegetation (‘self-restoration’) of bare peat surfaces are often observed but are poorly understood, thus hampering the ability to reliably predict how these ecosystems may respond to climatic change. We hypothesised that morphometric/topographic-related microclimatic variables may be key controls on successional pathways and vegetation patterning in self-restoring blanket peatlands. We predicted the occurrence probability of four common peatland plant species (Calluna vulgaris, Eriophorum vaginatum, Eriophorum angustifolium, and Sphagnum spp.) using a digital surface model (DSM) generated from drone imagery at a pixel size of 20 cm, a suite of variables derived from the DSM, and an ensemble learning method (random forests). All four species models provided accurate fine-scale predictions of habitat suitability (accuracy > 90%, area under curve (AUC) > 0.9, recall and precision > 0.8). Mean elevation (within a 1 m radius) was often the most influential variable. Topographic position, wind exposure, and the heterogeneity or ruggedness of the surrounding surface were also important for all models, whilst light-related variables and a wetness index were important in the Sphagnum model. Our approach can be used to improve prediction of future responses and sensitivities of peatland recovery to climatic changes and as a tool to identify areas of blanket peatlands that may self-restore successfully without management intervention