A Comprehensive Emission Inventory of Bbiogenic Volatile Organic Compounds in Europe: Improved Seasonality and Land-cover

Biogenic volatile organic compounds (BVOC) emitted from vegetation are important for the formation of secondary pollutants such as ozone and secondary organic aerosols (SOA) in the atmosphere. Therefore, BVOC emission are an important input for air quality models. To model these emissions with high spatial resolution, the accuracy of the underlying vegetation inventory is crucial. We present a BVOC emission model that accommodates different vegetation inventories and uses satellite-based measurements of greenness instead of pre-defined vegetation periods. This approach to seasonality implicitly treats effects caused by water or nutrient availability, altitude and latitude on a plant stand. Additionally, we test the influence of proposed seasonal variability in enzyme activity on BVOC emissions. In its present setup, the emission model calculates hourly emissions of isoprene, monoterpenes, sesquiterpenes and the oxygenated volatile organic compounds (OVOC) methanol, formaldehyde, formic acid, ethanol, acetaldehyde, acetone and acetic acid. In this study, emissions based on three different vegetation inventories are compared with each other and diurnal and seasonal variations in Europe are investigated for the year 2006. Two of these vegetation inventories require information on tree-cover as an input. We compare three different land-cover inventories (USGS GLCC, GLC2000 and Globcover 2.2) with respect to tree-cover. The often-used USGS GLCC land-cover inventory leads to a severe reduction of BVOC emissions due to a potential miss-attribution of broad-leaved trees and reduced tree-cover compared to the two other land-cover inventories. To account for uncertainties in the land-cover classification, we introduce land-cover correction factors for each relevant land-use category to adjust the tree-cover. The results are very sensitive to these factors within the plausible range. For June 2006, total monthly BVOC emissions decreased up to −27% with minimal and increased up to +71% with maximal factors, while in January 2006, the changes in monthly BVOC emissions were −54 and +56% with minimal and maximal factors, respectively. The new seasonality approach leads to a reduction in the annual emissions compared with non-adjusted data. The strongest reduction occurs in OVOC (up to −32 %), the weakest in isoprene (as little as −19 %). If also enzyme seasonality is taken into account, however, isoprene reacts with the steepest decrease of annual emissions, which are reduced by −44% to −49 %, annual emissions of monoterpenes reduce between −30 and −35 %. The sensitivity of the model to changes in temperature depends on the climatic zone but not on the vegetation inventory. The sensitivity is higher for temperature increases of 3K (+31% to +64 %) than decreases by the same amount (−20 to −35 %). The climatic zones “Cold except summer” and “arid” are most sensitive to temperature changes in January for isoprene and monoterpenes, respectively, while in June, “polar” is most sensitive to temperature for both isoprene and monoterpenes. Our model predicts the oxygenated volatile organic compounds to be the most abundant fraction of the annual European emissions (3571–5328 Gg yr−1), followed by monoterpenes (2964–4124 Gg yr−1), isoprene (1450–2650 Gg yr−1) and sesquiterpenes (150–257 Gg yr−1). We find regions with high isoprene emissions (most notably the Iberian Peninsula), but overall, oxygenated VOC dominate with 43–45% (depending on the vegetation inventory) contribution to the total annual BVOC emissions in Europe. Isoprene contributes between 18–21 %, monoterpenes 33–36% and sesquiterpenes contribute 1–2 %.We compare the concentrations of biogenic species simulated by an air quality model with measurements of isoprene and monoterpenes in Hohenpeissenberg (Germany) for both summer and winter. The agreement between observed and modelled concentrations is better in summer than in winter. This can partly be explained with the difficulty to model weather conditions in winter accurately, but also with the increased anthropogenic influence on the concentrations of BVOC compounds in winter. Our results suggest that land-cover inventories used to derive tree-cover must be chosen with care. Also, uncertainties in the classification of land-cover pixels must be taken into account and remain high. This problem must be addressed together with the remote sensing community. Our new approach using a greenness index for addressing seasonality of vegetation can be implemented easily in existing models. The importance of OVOC for air quality should be more deeply addressed by future studies, especially in smog chambers. Also, the fate of BVOC from the dominant region of the Iberian Peninsula should be studied more in detail

Measurement methods and variability assessment of the Norway spruce total leaf area: implications for remote sensing

Estimation of total leaf area (LAT) is important to express biochemical properties in plant ecology and remote sensing studies. A measurement of LAT is easy in broadleaf species, but it remains challenging in coniferous canopies. We proposed a new geometrical model to estimate Norway spruce LAT and compared its accuracy with other five published methods. Further, we assessed variability of the total to projected leaf area conversion factor (CF) within a crown and examined its implications for remotely sensed estimates of leaf chlorophyll content (Cab). We measured morphological and biochemical properties of three most recent needle age classes in three vertical canopy layers of a 30 and 100-year-old spruce stands. Newly introduced geometrical model and the parallelepiped model predicted spruce LAT with an error \u3e5 % of the average needle LAT, whereas two models based on an elliptic approximation of a needle shape underestimated LAT by up to 60 %. The total to projected leaf area conversion factor varied from 2. 5 for shaded to 3. 9 for sun exposed needles and remained invariant with needle age class and forest stand age. Erroneous estimation of an average crown CF by 0. 2 introduced an error of 2-3 μg cm-2 into the crown averaged Cab content. In our study, this error represents 10-15 % of observed crown averaged Cab range (33-53 μg cm-2). Our results demonstrate the importance of accurate LAT estimates for validation of remotely sensed estimates of Cab content in Norway spruce canopies

EFFECTS OF LAND COVER, WATER REDISTRIBUTION, AND TEMPERATURE ON ECOSYSTEM PROCESSES IN THE SOUTH PLATTE BASIN

Over one‐third of the land area in the South Platte Basin of Colorado, Nebraska, and Wyoming, has been converted to croplands. Irrigated cropland now comprises 8% of the basin, while dry croplands make up 31%. We used the RHESSys model to compare the changes in plant productivity and vegetation‐related hydrological processes that occurred as a result of either land cover alteration or directional temperature changes (−2°C, +4°C). Land cover change exerted more control over annual plant productivity and water fluxes for converted grasslands, while the effect of temperature changes on productivity and water fluxes was stronger in the mountain vegetation. Throughout the basin, land cover change increased the annual loss of water to the atmosphere by 114 mm via evaporation and transpiration, an increase of 37%. Both irrigated and nonirrigated grains became active earlier in the year than shortgrass steppe, leading to a seasonal shift in water losses to the atmosphere. Basin‐wide photosynthesis increased by 80% due to grain production. In contrast, a 4°C warming scenario caused annual transpiration to increase by only 3% and annual evaporation to increase by 28%, for a total increase of 71 mm. Warming decreased basin‐wide photosynthesis by 16%. There is a large elevational range from east to west in the South Platte Basin, which encompasses the western edge of the Great Plains and the eastern front of the Rocky Mountains. This elevational gain is accompanied by great changes in topographic complexity, vegetation type, and climate. Shortgrass steppe and crops found at elevations between 850 and 1800 m give way to coniferous forests and tundra between 1800 and 4000 m. Climate is increasingly dominated by winter snow precipitation with increasing elevation, and the timing of snowmelt influences tundra and forest ecosystem productivity, soil moisture, and downstream discharge. Mean annual precipitation of \u3c500 mm on the plains below 1800 m is far less than potential evapotranspiration of 1000–1500 mm and is insufficient for optimum plant productivity. The changes in water flux and photosynthesis from conversion of steppe to cropland are the result of redistribution of snowmelt water from the mountains and groundwater pumping through irrigation projects

Leaf Area of Mature Northwestern Coniferous Forests: Relation to Site Water Balance

Leaf area of nature coniferous forest communities of western Oregon appears to be related primarily to site H2O balance rather than characteristics of tree species composing the community. Leaf areas were determined for stands in communities ranked along measured gradients of precipitation and evaporative potential. Nine coniferous and 1 deciduous tree species were found in the various stands along these gradients. Leaf areas of these stands were linearly correlated with a simple site H2O balance index computed from measurements of growing season precipitation, open pan evaporation, and estimates of soil H2O storage. Species composition had no apparent influence on the relation between community leaf area and site H2O balance

Assessing the Role of Climate Change and Land Cover Change in Eco-Hydrologic Modeling (Snowmelt Timing and Dissolved Organic Carbon Fluxes)

This study explores temporal trends in snowmelt timing, dissolved organic carbon (DOC) concentrations, and DOC fluxes in the large forested Penobscot watershed of Maine. The spatially-distributed process-based Regional Hydro-Ecological Simulation System (RHESSys) model was used to simulate streamflows and DOC fluxes and concentrations from 2004-2013 with peak transport generally associated with snowmelt. Results were evaluated with field measurements (streamflow, DOC concentrations and fluxes) and remotely sensed products (Net Primary Production (NPP) and Leaf Area Index (LAI)). The annual and inter annual variability in the amount of fluvial DOC export was further explored under future climate change scenarios and predicted land cover compositions of the watershed

Modeling ecosystem services of urban trees to improve air quality and microclimate

Städte beherbergen mehr als die Hälfte der Weltbevölkerung und sind für 70% der gesamten Energie- und Treibhausgasemissionen verantwortlich. Luftschadstoffe und Bodenversiegelung verschlechtern die Umweltqualität der Städte und verursachen ernsthafte Gesundheitsprobleme. Eine Vergrößerung der Grünflächen in den Städten kann die Luftqualität und das Mikroklima verbessern. Modelle ermöglichen eine Maximierung der Ökosystemleistungen auf der Grundlage aktueller und zukünftiger Szenarien

Understory Growth Dynamics and Mensuration Techniques in Uneven-Aged, Mixed-Species Northern Conifer Stands

Managing uneven-aged, mixed-species stands requires balancing the need for high leaf area allocation in the overstory where it is most efficient versus the need to allow for sufficient growth of younger cohorts in the understory. To help forest managers make informed decisions to maintain this balance, the understory growth dynamics of northern conifer species in stands managed under uneven-aged silvicultural systems were studied. Sapling height growth of Picea rubens Sarg., Abies balsamea (L.) Mill, and Tsuga canadensis (L.) Carr. were modeled as a function of overstory canopy openness (gap fraction) using regression analysis. Research was conducted in four uneven-aged northern conifer stands on the Penobscot Experimental Forest in eastern Maine; two replicates each of selection cutting on five- and ten-year cycles. Gap fraction estimates were obtained directly above 167 sample trees between 0.5-6.0 m in height, using a LI- COR LAI-2000 plant canopy analyzer. These estimates were tested in several model forms along with initial tree height to predict sapling height growth. The effect of different vertical distributions of foliage on sapling height growth was also explored using analysis of covariance. Using cluster analysis, plots were grouped into one of three categories based on similar vertical leaf area structure. Species-specific height growth was then compared between groups of similar vertical structure using initial tree height as a covariate. An innovative method employing vertical point sampling was used to obtain leaf area estimates to quantify plot-level vertical leaf area structure. To validate the use of vertical point sampling, plot-level leaf area index (LAI) and basal area (BA) estimates based on vertical point sampling were compared with conventional horizontal point sampling using a 2 m2/ha basal area factor (BAF) prism. Tree-level LA1 estimates were replaced with specieslspecific constants based on projected leaf area (PLA)-height squared and PLA-DBH\u27 linear regression coefficients in an effort to develop a quick and accurate method to estimate LA1 in the field using both vertical point sampling and prism sampling. Leaf area index measurements, BA, and tree tallies from vertical point sampling were also related to gap fraction measurements to determine if an efficient method for in-the-field gap fraction estimation could also be developed. Regression modeling demonstrated that sapling height growth of all three species followed a monotonically increasing pattern with respect to decreasing canopy closure. Abies balsamea appeared to be the most aggressive competitor demonstrating the greatest response to changes in gap fraction while Tsuga canadensis appeared to be the least responsive to changes in gap fraction. Although total plot-level LA1 was not significant in predicting height growth in these complex stands, the vertical distribution of leaf area was. While height growth of Abies balsamea and Tsuga canadensis were not significantly different between vertical leaf area structures, height growth of Picea rubens was significantly higher in plots with well-developed understories with high LAI, regardless of overstory LAI. Vertical point sampling showed strong promise in providing LA1 estimates, and in particular facilitating in-the-field LA1 estimation with the use of species-specific tree- level LA1 constants that remove the need for individual tree measurements. More field- testing of this technique needs to be done. Simple vertical point sample measures were not successful in accurately predicting gap fraction

Crop Tree Growth and Quality Twenty-five Years after Precommercial Thinning in a Northern Conifer Stand

Growth characteristics of selected Picea rubens Sarg. (red spruce) and Abies balsamea (L.) Mill. (balsam fir) crop trees were studied in a northern conifer forest to determine the effects of precommercial thinning (PCT) 25 years after initial treatment. Two measures of growth efficiency (GE, growth per unit of growing space) were examined: stemwood increment (dm3) per unit of projected leaf area (PLA) (m2) and stemwood increment (dm3) per unit of crown projection area (CPA) (m2). Stem form differences were evaluated by comparing stem taper between species and treatments. Branch diameters were measured between 1 .O - 2.0 meters above breast height (BH, 1.37 m (4.5 ft)) for each crop tree, and the number and size of branches and the ratio of knots were determined. Volumes of all crop trees were calculated using Smalian\u27s formula (Avery and Burkhart 1994) applied to different geometric forms of the tree to estimate total cubic foot volume from diameter measurements up the tree bole. The efficacy of Honer\u27s (1967) volume equation for estimating total cubic foot volume from diameter at BH (DBH) and total height (THT) was tested by comparing measured values to the estimated values. Differences in tree stability were determined by comparing height to diameter ratios (IUD) of all the crop trees by species and treatment. GE did not differ between treatments using either definition, although average PLA and CPA per tree were higher in the spaced plots. As expected, balsam fir was more growthefficient than red spruce using both GE definitions. There were no significant differences in average PLA between the two species, but red spruce had a larger average CPA than balsam fir. Crop trees in the spaced plots had more stem taper than the unspaced plots and a lower (WD) ratio. Stem taper differed between species; red spruce crop trees had more stem taper than balsam fir. The crop trees in the spaced plots had significantly more volume than those in the unspaced; total stand volume including non-crop trees was not measured. Balsam fir trees contained significantly more volume than red spruce in both treatments. Crop trees in the spaced plots had more and larger branches and also a higher percentage of knot volume than in the unspaced plots. There were no differences in the number and size of branches between balsam fir and red spruce, although red spruce crop trees had a greater knot volume than balsam fir trees. Results of this study are important for managers wanting to use PCT as a silvicultural tool to increase volume growth of selected crop trees without losing value or productivity