Julian L. Hadley

Wind effects on needles of timberline conifers: seasonal influence on mortality

In the Rocky Mountains, USA, year—round wind exposure has been correlated with widespread needle dehydration and death in winter for alpine timberline conifers. Needle death may be due solely to the drying effects of winter wind or may also result from predisposition to winter injury associated with suboptimal summer growth conditions. Our experiments showed that in the lower timerbline ecotone in southwest Wyoming, needle mortality was primarily due to winter wind and cuticle abrasion; death was frequent only in wind—exposed needles of flagged trees and surface needles of krummholz mats. At higher elevations where only krummholz mats and a few flagged trees exist, mortality averaged ≥75% for needles unprotected by snow, regardless of wind exposure. Snow covered needles had low mortality throughout the timberline ecotone. Winter death of naturally wind—exposed needles of Picea engelmannii occurred at ≤—4.5 MPa water potential (≤60% relative water content). Cuticular resistance of wind—exposed needles declined from 100—250 ks/m in autumn to ≤30 ks/m by midwinter. Experimentally reversing the windward—leeward orientation of small, flagged trees in early winter resulted in lower xylem pressure potentials and needle viabilities for newly wind—exposed (originally leeward) compared to newly sheltered (originally windward) shoots. Also, sheltering exposed branches from winter wind on flagged trees in the lower timberline ecotone (3200 m) increased mean overwinter needle survival from near 0 to ≥50% in both Picea engelmannii and Abies lasiocarpa. Scanning electron micrographs of dehydrate wind—exposed needles collected in March at this site showed little cuticular surface wax, probably because of windborne ice crystal abrasion. However, winter dehydration and death in both experimentally and naturally wind—sheltered needles at higher elevation may have been due to inadequate needle maturation during summer, which could act to exclude flagged trees from the upper timberline ecotone.

Wind Erosion of Leaf Surface Wax in Alpine Timberline Conifers

Loss of leaf surface wax during winter could contribute to the extreme desiccation and leaf mortality previously observed for timberline conifers. For Picea engelmannii, leaf surface wax declined most rapidly for leaves above the snowpack as winter progressed, until there was approximately 60% less surface wax than for leaves protected by snow cover. Near the upper limit of the timberline ecotone (3400 m), leaves of P. engelmannii had less surface wax compared to individuals near the lower ecotone limit (3200 m), as well as smaller differences between windward versus leeward sides of the same shoot. Abies lasiocarpa leaves at 3400 m had the least amount of wax, while leaves of Pinus contorta at a lower, wind-exposed site (3100 m) had the greatest amount. Only small differences in wax quantities occurred on windward versus leeward leaves on P. contorta saplings, despite much higher mortality for windward leaves near the snow surface. From measurements on artificial wax cylinders placed in the field, an inc...

Soil respiration in a northeastern US temperate forest: a 22‐year synthesis

To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and inter-annual variations in soil respiration (R-s), we analyzed m ...

Water use by eastern hemlock (Tsuga canadensis) and black birch (Betula lenta): implications of effects of the hemlock woolly adelgid

Eastern hemlock (Tsuga canadensis (L.) Carr.) is a coniferous evergreen species found across the northeastern United States that is currently threatened by the exotic pest hemlock woolly adelgid (HWA; Adelges tsugae Annand). As HWA kills eastern hemlock trees, black birch (Betula lenta L.) has been found to be a dominant replacement species in the region. Seasonal changes in water use by eastern hemlock and black birch were investigated utilizing whole-tree tran- spiration measurement techniques. Annual evapotranspiration in an eastern hemlock and deciduous stand was also esti- mated. During the peak growing season, daily rates of transpiration were 1.6 times greater in black birch. Cumulative transpiration in black birch exceeded hemlock transpiration by 77 mm from June until October. During the dormant sea- son, evapotranspiration rates were higher in the hemlock stand; however, estimated annual evapotranspiration was 327 mm in eastern hemlock compared with 417 mm in the deciduous stand. Our results suggest that a transition from a hemlock- dominated to a black birch-dominated stand will alter the annual water balance with the greatest impact occurring during the peak growing season. Late in the growing season, flow may be unsustainable in streams that normally have light or moderate flow because ofincreased water use by black birch. Resume´ : La pruche du Canada (Tsuga canadensis (L.) Carr.) qui est une espece de conifere a feuilles persistantes pre´-

Effect of Daily Minimum Temperature on Photosynthesis in Eastern Hemlock (Tsuga canadensis L.) in Autumn and Winter

Most coniferous trees are capable of photosynthesis throughout the year, but low temperatures and frozen soil limit winter photosynthesis in many regions. In eastern hemlock (Tsuga canadensis L.) in central Massachusetts, U.S.A., midday light saturated photosynthesis (Pmax) in autumn was limited by subfreezing temperatures during the previous one to two nights. In autumn, minimum air temperature (Tm,n) during the previous 24 h had a strong effect on midday Pmax only if Tmn, was below -2?C. Pmax averaged about 5 ,umol m-2 s-~ after Tmin near -2?C, but fell to about 1 ,umol m-2 s-l after a Tni of -8?C. Maximum measured Pmax in winter was about 2.5 uxmol m-2 s-1 after a Tmin of 7?C in mid-March, and Pmax in winter was more strongly related to average Tmin during the previous week than to the Tmin just prior to measurement. However, no major mid-winter thaws, with several successive above-freezing minimum temperatures, occurred during this study. A model of annual carbon exchange for the hemlock forest showed that daily ecosystem carbon exchange in December through March was very sensitive to variation between -5 and 2?C in average daily Tmn during the past 2 d. Fewer autumn frosts and prolonged winter thaws could increase annual photosynthesis and carbon storage in eastern hemlock forests in the northeastern United States.

Understory microclimate and photosynthetic response of saplings in an old-growth eastern hemlock (Tsuga canadensis L.) forest.

Abstract I measured microclimate and photosynthesis of eastern hemlock (Tsuga canadensis L.) saplings in the understory of an old-growth eastern hemlock forest. About 14% of the canopy trees were deciduous. Daily maximum air temperature in the understory was 3-4°C lower than above the canopy in July through September, but only 1-2°C lower from October through June. Photosynthetic photon flux density (PFD) in the understory was typically less than 20 µmol m−2 s−1, or about 1% of full sunlight, and exceeded 200 µmol m−2 s−1 during < 1.2% of the daylight hours in July through September. Average PFD was higher in spring, with May having about twice as much total daily PFD as late June and early July. At 22°C, net photosynthesis by hemlock sapling foliage was 0 at ≈10 µmol m−2 s−1 PFD and reached light saturation (≈ 5 µmol m−2 s−1) at ≈ 350 µmol m−2 s−1 PFD. Net photosynthesis near light saturation increased slightly as air temperature changed from 11 to 15°C, but did not change significantly between 15 and 30°C. These microclimatic and physiological measurements indicate that net photosynthesis by hemlock saplings is probably little affected by temperature from late spring through early fall. Late spring is probably the time of greatest photosynthesis by eastern hemlock saplings in hemlock forests with deciduous trees in the canopy.

Ensuring reliable datasets for environmental models and forecasts

Abstract At the dawn of the 21st century, environmental scientists are collecting more data more rapidly than at any time in the past. Nowhere is this change more evident than in the advent of sensor networks able to collect and process (in real time) simultaneous measurements over broad areas and at high sampling rates. At the same time there has been great progress in the development of standards, methods, and tools for data analysis and synthesis, including a new standard for descriptive metadata for ecological datasets (Ecological Metadata Language) and new workflow tools that help scientists to assemble datasets and to diagram, record, and execute analyses. However these developments (important as they are) are not yet sufficient to guarantee the reliability of datasets created by a scientific process — the complex activity that scientists carry out in order to create a dataset. We define a dataset to be reliable when the scientific process used to create it is (1) reproducible and (2) analyzable for potential defects. To address this problem we propose the use of an analytic web , a formal representation of a scientific process that consists of three coordinated graphs (a data-flow graph, a dataset-derivation graph, and a process-derivation graph) originally developed for use in software engineering. An analytic web meets the two key requirements for ensuring dataset reliability: (1) a complete audit trail of all artifacts (e.g., datasets, code, models) used or created in the execution of the scientific process that created the dataset, and (2) detailed process metadata that precisely describe all sub-processes of the scientific process. Construction of such metadata requires the semantic features of a high-level process definition language. In this paper we illustrate the use of an analytic web to represent the scientific process of constructing estimates of ecosystem water flux from data gathered by a complex, real-time multi-sensor network. We use Little-JIL, a high-level process definition language, to precisely and accurately capture the analytical processes involved. We believe that incorporation of this approach into existing tools and evolving metadata specifications (such as EML) will yield significant benefits to science. These benefits include: complete and accurate representations of scientific processes; support for rigorous evaluation of such processes for logical and statistical errors and for propagation of measurement error; and assurance of dataset reliability for developing sound models and forecasts of environmental change.

Experience in using a process language to define scientific workflow and generate dataset provenance

This paper describes our experiences in exploring the applicability of software engineering approaches to scientific data management problems. Specifically, this paper describes how process definition languages can be used to expedite production of scientific datasets as well as to generate documentation of their provenance. Our approach uses a process definition language that incorporates powerful semantics to encode scientific processes in the form of a Process Definition Graph (PDG). The paper describes how execution of the PDG-defined process can generate Dataset Derivation Graphs (DDGs), metadata that document how the scientific process developed each of its product datasets. The paper uses an example to show that scientific processes may be complex and to illustrate why some of the more powerful semantic features of the process definition language are useful in supporting clarity and conciseness in representing such processes. This work is similar in goals to work generally referred to as Scientific Workflow. The paper demonstrates the contribution that software engineering can make to this domain.

Modeling acclimation of photosynthesis to temperature in evergreen conifer forests.

• In this study, we used a canopy photosynthesis model which describes changes in photosynthetic capacity with slow temperature-dependent acclimations. • A flux-partitioning algorithm was applied to fit the photosynthesis model to net ecosystem exchange data for 12 evergreen coniferous forests from northern temperate and boreal regions. • The model accounted for much of the variation in photosynthetic production, with modeling efficiencies (mean > 67%) similar to those of more complex models. The parameter describing the rate of acclimation was larger at the northern sites, leading to a slower acclimation of photosynthesis to temperature. The response of the rates of photosynthesis to air temperature in spring was delayed up to several days at the coldest sites. Overall photosynthesis acclimation processes were slower at colder, northern locations than at warmer, more southern, and more maritime sites. • Consequently, slow changes in photosynthetic capacity were essential to explaining variations of photosynthesis for colder boreal forests (i.e. where acclimation of photosynthesis to temperature was slower), whereas the importance of these processes was minor in warmer conifer evergreen forests.

Process technology to facilitate the conduct of science

This paper introduces the concept of an analytic web, a synthesis of three complementary views of a scientific process that is intended to facilitate the conduct of science. These three views support the clear, complete, and precise process documentation needed to enable the effective coordination of the activities of geographically dispersed scientists. An analytic web also supports automation of various scientific activities, education of young scientists, and reproducibility of scientific results. Of particular significance, an analytic web is intended to forestall the generation of scientific data that are erroneous or suspect, by using process definitions to prevent incorrect combinations of scientific results. The paper also describes experiences with a tool, SciWalker, designed to evaluate the efficacy of this approach.