Contrasting shrub and grass hydraulic responses to experimental drought.

Whole-plant hydraulics provide important information about responses to water limitation and can be used to understand how plant communities may change in a drier climate when measured on multiple species. Here, we measured above- and belowground hydraulic traits in Cornus drummondii, an encroaching shrub within North American tallgrass prairies, and Andropogon gerardii, a dominant C grass, to assess the potential hydraulic responses to future drought as this region undergoes woody expansion. Shelters that reduced precipitation by 50% and 0% were built over shrubs and grasses growing in sites that are burned at 1-year and 4-year frequencies.

Trajectories and state changes of a grassland stream and riparian zone after a decade of woody vegetation removal.

Riparian zones and the streams they border provide vital habitat for organisms, water quality protection, and other important ecosystem services. These areas are under pressure from local (land use/land cover change) to global (climate change) processes. Woody vegetation is expanding in grassland riparian zones worldwide.

Intra-canopy leaf trait variation facilitates high leaf area index and compensatory growth in a clonal woody encroaching shrub.

Leaf trait variation enables plants to utilize large gradients of light availability that exist across canopies of high leaf area index (LAI), allowing for greater net carbon gain while reducing light availability for understory competitors. While these canopy dynamics are well understood in forest ecosystems, studies of canopy structure of woody shrubs in grasslands are lacking. To evaluate the investment strategy used by these shrubs, we investigated the vertical distribution of leaf traits and physiology across canopies of Cornus drummondii, the predominant woody encroaching shrub in the Kansas tallgrass prairie.

Stronger influence of growth rate than severity of drought stress on mortality of large ponderosa pines during the 2012-2015 California drought.

Forests in the western United States are being subject to more frequent and severe drought events as the climate warms. The 2012-2015 California drought is a recent example, whereby drought stress was exacerbated by a landscape-scale outbreak of western pine beetle (Dendroctonus brevicomis) and resulted in widespread mortality of dominant canopy species including ponderosa pine (Pinus ponderosa). In this study, we compared pairs of large surviving and beetle-killed ponderosa pines following the California drought in the southern Sierra Nevadas to evaluate physiological characteristics related to survival.

Historical changes in the stomatal limitation of photosynthesis: empirical support for an optimality principle.

The ratio of leaf internal (c ) to ambient (c ) partial pressure of CO , defined here as χ, is an index of adjustments in both leaf stomatal conductance and photosynthetic rate to environmental conditions. Measurements and proxies of this ratio can be used to constrain vegetation model uncertainties for predicting terrestrial carbon uptake and water use. We test a theory based on the least-cost optimality hypothesis for modelling historical changes in χ over the 1951-2014 period, across different tree species and environmental conditions, as reconstructed from stable carbon isotopic measurements across a global network of 103 absolutely dated tree-ring chronologies.

Visualization instructions enhance preschoolers' spatial problem-solving.

This study explores whether verbal instructions to visualize an event can improve children's ability to make predictions about a difficult spatial problem. Three-year-olds (N = 48) were introduced to two intertwined tubes, and prior to predicting how a ball would travel through a given tube, one group of children was told to imagine the ball rolling down the tube, one group was told an explicit rule about where the ball would land, and a third group was given no instructions. Children were prevented from interacting with the apparatus to investigate the effect of the different verbal instructions alone on their problem-solving.

The development of tool use: Planning for end-state comfort.

Some grips on the handle of a tool can be planned on the basis of information directly available in the scene. Other grips, however, must be planned on the basis of the final position of the hand. "End-state comfort" grips require an awkward or uncomfortable initial grip so as to later implement the action comfortably and efficiently.

Planning an Action: A Developmental Progression in Tool Use.

How children pick up a tool reveals their ability to plan an action with the end goal in mind. When presented with a spoon whose handle points away from their dominant hand, children between infancy and 8 years of age progress from using an awkward ulnar grip that causes food to spill from the spoon to consistently using a radial grip. At 4 years of age children's grip strategies are highly variable, including the awkward grips of infancy and use of the non-dominant hand, but they also employ adult-like grips never seen in infancy.

Age differences in online processing of video: an eye movement study.

Eye movements were recorded while sixty-two 1-year-olds, 4-year-olds, and adults watched television. Of interest was the extent to which viewers looked at the same place at the same time as their peers because high similarity across viewers suggests systematic viewing driven by comprehension processes. Similarity of gaze location increased with age.

Development of the coordination between posture and manual control.

Studies have suggested that proper postural control is essential for the development of reaching. However, little research has examined the development of the coordination between posture and manual control throughout childhood. We investigated the coordination between posture and manual control in children (7- and 10-year-olds) and adults during a precision fitting task as task constraints became more difficult.

Imagining a way out of the gravity bias: preschoolers can visualize the solution to a spatial problem.

Can young children visualize the solution to a difficult spatial problem? Forty-eight 3-year-olds were tested in a spatial reasoning paradigm in which they were asked to predict the path of a ball moving through 1 of 3 intertwined tubes. One group of children was asked to visualize the ball rolling down the tube before they made their predictions, a second group was given identical instructions without being asked to use visual imagery, and a third group was given no instructions. Children in the visualization condition performed significantly better than those in the other conditions, suggesting that encouraging young children to use visual imagery may help them to reason through difficult problems.

Manipulations of listeners' echo perception are reflected in event-related potentials.

To gain information from complex auditory scenes, it is necessary to determine which of the many loudness, pitch, and timbre changes originate from a single source. Grouping sound into sources based on spatial information is complicated by reverberant energy bouncing off multiple surfaces and reaching the ears from directions other than the source's location. The ability to localize sounds despite these echoes has been explored with the precedence effect: Identical sounds presented from two locations with a short stimulus onset asynchrony (e.

Preschoolers search for hidden objects.

The issue of whether young children use spatio-temporal information (e.g., movement of objects through time and space) and/or contact-mechanical information (e.

Movement planning reflects skill level and age changes in toddlers.

Kinematic measures of children's reaching were found to reflect stable differences in skill level for planning for future actions. Thirty-five toddlers (18-21 months) were engaged in building block towers (precise task) and in placing blocks into an open container (imprecise task). Sixteen children were retested on the same tasks a year later.

The development of problem solving in young children: a critical cognitive skill.

Problem solving is a signature attribute of adult humans, but we need to understand how this develops in children. Tool use is proposed as an ideal way to study problem solving in children less than 3 years of age because overt manual action can reveal how the child plans to achieve a goal. Motor errors are as informative as successful actions.

Young children's representations of spatial and functional relations between objects.

Three experiments investigated changes from 15 to 30 months of age in children's (N = 114) mastery of relations between an object and an aperture, supporting surface, or form. When choosing between objects to insert into an aperture, older children selected objects of an appropriate size and shape, but younger children showed little selectivity. Further experiments probed the sources of younger children's difficulty by comparing children's performance placing a target object in a hole, on a 2-dimensional form, or atop another solid object.

Release and re-buildup of listeners' models of auditory space.

When listeners hear sound presented repeatedly in a room with reflections, echo threshold rises. The current experiments tested how long this buildup in echo threshold would last when exposure to a different simulated space (designated as room B) intervened before returning to the original space (designated room A). Stimuli were trains of lead-lag click pairs (room A) and trains of clicks with no reflections (room B) in an ABA sequence.

Self-directed action affects planning in tool-use tasks with toddlers.

Toddlers grasp a tool more effectively when it is self-directed (e.g., spoon) than other-directed (e.

Preschoolers' oculomotor behaviour during their observation of an action task.

Adult and child oculomotor behaviour was measured during the observation of a naturalistic action task. Adult and 4-year-old participants viewed a video presentation of an actor making a root-beer float. Eye movements were monitored to examine fixation patterns during a series of means-end action sequences.

One sound or two? Object-related negativity indexes echo perception.

The ability to isolate a single sound source among concurrent sources and reverberant energy is necessary for understanding the auditory world. The precedence effect describes a related experimental finding, that when presented with identical sounds from two locations with a short onset asynchrony (on the order of milliseconds), listeners report a single source with a location dominated by the lead sound. Single-cell recordings in multiple animal models have indicated that there are low-level mechanisms that may contribute to the precedence effect, yet psychophysical studies in humans have provided evidence that top-down cognitive processes have a great deal of influence on the perception of simulated echoes.

Conflicting cues in a dynamic search task are reflected in children's eye movements and search errors.

Three-year-olds were given a search task with conflicting cues about the target's location. A ball rolled behind a transparent screen and stopped behind one of four opaque doors mounted into the screen. A wall that protruded above one door provided a visible cue of blockage in the ball's path, while the transparent screen allowed visual tracking of the ball's progress to its last disappearance.

Vision and action: the effect of visual feedback on infants' exploratory behaviors.

The role of visual feedback during object exploration and manipulation was examined in 8-month-old infants. Infants appeared to maximize the stimulating properties of objects by producing sound when possible, and engaged in more activities in the light compared to the dark.

Object and event representation in toddlers.

Mental representation of absent objects and events is a major cognitive achievement. Research is presented that explores how toddlers (2- to 3-year-old children) search for hidden objects and understand out-of-sight events. Younger children fail to use visually obvious cues, such as a barrier that blocks a moving object's path.