Placemaking for the pedestrian: generative design & the street

This paper evaluates the influence of placemaking design concepts and historical development processes on the pedestrian experience of three different neighbourhood commercial streets in Toronto. Placemaking is an urban design movement that proposes walkable, pedestrian-­‐oriented environments in reaction to Modern planning's "placeless" car-­‐dominated landscapes. To explore if placemaking design theories relate to actual pedestrian experiences, I conducted qualitative case studies of three Toronto streets using spatial analyses, interviews, photographic observation, and archival research. I found that placemaking design concepts did correlate to positive pedestrian experiences, but the theories were lacking when it came to explaining pedestrian accounts of the age and storied character of the street. This led me to investigate the historic formation and evolution of each street, where I discovered that, more than conceptual design theories, changes in the scale of street design practices—particularly involving techniques of construction and finance—have played a key role in shaping pedestrian experiences. My findings support Christopher Alexander's process-­‐based design theory, and the critical spatial theories of political economy. In my conclusion I suggest some ways that these theories might dovetail into a more holistic approach to design based on adaptive, egalitarian processes. My research shows that consideration of process is essential to any urban design theory that aims to account for the pedestrian experience of streets

The influence of canopy structure and epiphytes on the hydrology of Douglas-fir forests

Canopy structure has a significant impact on the canopy hydrology of Douglas-fir forests in the Pacific Northwest (PNW). Whole canopy rainfall interception was measured for young Douglas-fir forest and compared to an old-growth Douglas-fir forest. The old-growth forest had significantly greater canopy water storage capacity (5) and direct throughfall fraction (p). However, the interception loss (la) for the old-growth forest was only slightly larger than the young forest due to the similar ratios of evaporation to rainfall intensity (E/R). The spatial distribution of throughfall was more right-skewed in the old-growth forest; with many locations receiving throughfall in excess of gross precipitation (PG). Despite differences in the spatial distribution of throughfall, the spatial distribution of soil moisture did not differ between the two forests. Because the S was significantly greater in the old-growth forest, the influence of epiphytic lichens and bryophytes on S was examined. The maximum water content (MWC) of individual samples of fruticose lichens, foliose lichens, and bryophytes from an old-growth Douglas-fir forest were measured in the laboratory and the field. The laboratory results indicate that typical epiphytic fruticose lichens, foliose lichens and bryophytes for old-growth Douglas-fir forests in the PNW could store 2.23, 3.42 and 9.99 times their dry weight in water, respectively. Although these values could be used to predict the maximum epiphyte-laden branch water storage under laboratory conditions, they were unable to do so under field conditions. In the field the biomass on the branch could not predict the maximum branch water storage because the branches: 1) were partially saturated for most of the measurement period; and 2) required greater than 30 mm of rain to saturate due to preferential flow routing water through the epiphyte mats. The frequent storms and the slow saturation of the canopy resulted an underestimation of S and an overestimation of E/R by standard regression based techniques for estimating canopy variables. Lastly, the water stored on epiphyte-laden branches after exposure to natural rainfall was positively associated with rainfall intensity. The absorption of atmospheric water vapor by epiphytes in old-growth Douglas-fir forests in the PNW may have facilitated carbon uptake by green lichens and altered the energy budget of the forest during the seasonal summer drought. During the summer months the green lichens absorb sufficient quantities of atmospheric water to reactivate their photosystems. The diurnal absorption/evaporation of atmospheric water will result in significant uptake of water at night and may account for 5 to 21 % of the canopy latent heat flux in the early morning (600 to 1000 h)

Shifting environmental controls on CH4 fluxes in a sub-boreal peatland

We monitored CO2 and CH4 fluxes using eddy covariance from 19 May to 27 September 2011 in a poor fen located in northern Michigan. The objectives of this paper are to: (1) quantify the flux of CH4 from a sub-boreal peatland, and (2) determine which abiotic and biotic factors were the most correlated to the flux of CH4 over the measurement period. Net daily CH4 fluxes increased from 70 mg CH4 m−2 d−1 to 220 mg CH4 m−2 d−1 from mid May to mid July. After July, CH4 losses steadily declined to approximately 50 mg CH4 m−2 d−1 in late September. During the study period, the peatland lost 17.4 g CH4 m−2. Both abiotic and biotic variables were correlated with CH4 fluxes. When the different variables were analyzed together, the preferred model included mean daily soil temperature at 20 cm, daily net ecosystem exchange (NEE) and the interaction between mean daily soil temperature at 20 cm and NEE (R2 = 0.47, p value \u3c 0.001). The interaction was important because the relationship between daily NEE and mean daily soil temperature with CH4 flux changed when NEE was negative (CO2 uptake from the atmosphere) or positive (CO2 losses to the atmosphere). On days when daily NEE was negative, 25% of the CH4 flux could be explained by correlations with NEE, however on days when daily NEE was positive, there was no correlation between daily NEE and the CH4 flux. In contrast, daily mean soil temperature at 20 cm was poorly correlated to changes in CH4 when NEE was negative (17%), but the correlation increased to 34% when NEE was positive. The interaction between daily NEE and mean daily soil temperature at 20 cm indicates shifting environmental controls on the CH4 flux throughout the growing season

Oak trees decline; a sign of climate variability impacts in the west of Iran

The Persian oak, Quercus brantii, trees in the Zagros region of Western Iran have been in decline since 2000. The decline is assumed to be highly connected with changes in meteorological parameters. Our objectives were to quantify the long-term trends in meteorological parameters and reference evapotranspiration (ET0) in the Zagros region and estimate ecohydrological parameters highly affected by climate variability and related to rainfall interception (I) process (i.e., canopy storage capacity (S), the ratio of mean evaporation rate from the wet canopy to the mean rainfall intensity (E/R), and the free throughfall coefficient (p)). Long-term (1961-2010) changes in air temperature (T), precipitation (P), and wind speed (WS) were obtained from six synoptic meteorological stations located in the region. Throughfall (TF) was measured using the sixteen rain gauges randomly located underneath the crown of the five individual trees. P was measured using rain gauges fixed in an open space nearby to the oak trees .I was computed as the difference between P and TF. From 2000 to 2010, meteorological parameters and ET0 changed slightly; T, WS, and ET0 increased (+0.6 ˚C, +0.4 m.s -1, +0.25 mm.day-1, respectively), while P decreased (-60 mm).When climate patterns between 1961-2010 were analyzed for 6 synoptic weather stations, P significantly decreased significantly at one station, whereas T significantly increased at two stations and significantly decreased at another. I was estimated to be 40% and 25% within in-leaf and leaf-less periods, respectively. During the in-leaf period, the mean values of S, E/R, and p were roughly estimated to be 1 mm, 0.22, and 0.23, respectively. Our results indicate that the Zagros region is getting warmer and oak trees will indisputably experience reduction in the available water because of increased evaporative loss

Water level controls on sap flux of canopy species in black ash wetlands

Black ash (Fraxinus nigra Marsh.) exhibits canopy dominance in regularly inundated wetlands, suggesting advantageous adaptation. Black ash mortality due to emerald ash borer (Agrilus planipennis Fairmaire) will alter canopy composition and site hydrology. Retention of these forested wetlands requires understanding black ash’s ecohydrologic role. Our study examined the response of sap flux to water level and atmospheric drivers in three codominant species: black ash, red maple (Acer rubrum L.), and yellow birch (Betula alleghaniensis Britt.), in depressional wetlands in western Michigan, USA. The influence of water level on sap flux rates and response to vapor pressure deficit (VPD) was tested among species. Black ash had significantly greater sap flux than non-black ash at all water levels (80–160% higher). Black ash showed a significant increase (45%) in sap flux rates as water levels decreased. Black ash and red maple showed significant increases in response to VPD as water levels decreased (112% and 56%, respectively). Exploration of alternative canopy species has focused on the survival and growth of seedlings, but our findings show important differences in water use and response to hydrologic drivers among species. Understanding how a replacement species will respond to the expected altered hydrologic regimes of black ash wetlands following EAB infestation will improve species selection

Response of black ash wetland gaseous soil carbon fluxes to a simulated emerald ash borer infestation

The rapid and extensive expansion of emerald ash borer (EAB) in North America since 2002 may eliminate most existing ash stands, likely affecting critical ecosystem services associated with water and carbon cycling. To our knowledge, no studies have evaluated the coupled response of black ash (Fraxinus nigra Marsh.) wetland water tables, soil temperatures, and soil gas fluxes to an EAB infestation. Water table position, soil temperature, and soil CO2 and CH4 fluxes were monitored in nine depressional headwater black ash wetlands in northern Michigan. An EAB disturbance was simulated by girdling (girdle) or felling (ash-cut) all black ash trees with diameters greater than 2.5 cm within treated wetlands (n = 3 per treatment). Soil gas fluxes were sensitive to water table position, temperature, and disturbance. Soil CO2 fluxes were significantly higher, and high soil CH4 fluxes occurred more frequently in disturbed sites. Soil CH4 fluxes in ash-cut were marginally significantly higher than girdle during post-treatment, yet both were similar to control sites. The strong connection between depressional black ash wetland study sites and groundwater likely buffered the magnitude of disturbance-related impact on water tables and carbon cycling

Patterns and drivers of species composition of epiphytic bryophytes and lichens in managed temperate forests

Epiphytic bryophytes and lichens are an important component of the endangered forest biota in temperate forests, their diversity and composition patterns being regulated by tree, stand and landscape scale factors. The aim of this study is to improve ecological understanding of such factors in managed coniferous– deciduous mixed forests of Hungary in the context of forest management. In particular, this study investigate the effect of tree species composition, stand structure (tree size distribution, shrub layer and dead wood), microclimate (light, temperature and air humidity), landscape and historical factors on the stand level and tree level composition of epiphytic bryophytes and lichens. The relationships were explored by multivariate methods (redundancy analysis, canonical correspondence analysis and variation partitioning) and indicator species analysis. Tree species is among the most important driver of species composition in both organism groups. For bryophytes, the continuity of forest microclimate and the presence of shrub layer are also important, while lichen assemblages are influenced by light availability. Landscape and historical variables were less influential than stand scale factors. On the basis of our results, the main strategy of management focusing on epiphyte diversity conservation should include: (1) the maintenance of tree species diversity in mixed stands; (2) increasing the proportion of deciduous trees (mainly oaks and hornbeam); (3) the maintenance of large trees within the stands; (4) the presence of shrub and regeneration layer; (5) the creation of heterogeneous light conditions

Can carbon isotopes be used to predict watershed-scale transpiration?

The Penman‐Monteith equation is often used to estimate transpiration, but an important limitation to this approach, especially for mountainous forested sites, is an accurate estimate of canopy conductance averaged over the area of interest (Gs). We propose a method for estimating watershed‐scale transpiration using estimates of Gs derived from measurements of stable isotopes. To estimate Gs, we first determined the isotopic composition of ecosystem respiration (δ¹³CER) as derived from the ¹²C:¹³C ratio of respired CO₂ entrained within nocturnal cold air drainage flows exiting the base of the watershed. An isotope‐derived estimate of recent canopy conductance over the entire watershed (Gs‐I) was derived using biophysical models. To estimate daily average transpiration, we applied Gs‐I and other measured environmental variables to the Penman‐Monteith equation. The results were compared with an independent measure of transpiration using the heat dissipation method at four locations within the watershed. Considering the large number of assumptions required for both estimates of transpiration, the two estimates were remarkably similar. The relationship between the values derived by the two techniques was statistically significant (p value 0.1), but the standard error was large (SE = 0.48). The results demonstrate that this technique holds promise, but the effects of potential limitations require further attention. The future research necessary to fully demonstrate the validity of this potentially promising method is discussed

Ecosystem Carbon Stock Influenced by Plantation Practice: Implications for Planting Forests as a Measure of Climate Change Mitigation

Uncertainties remain in the potential of forest plantations to sequestrate carbon (C). We synthesized 86 experimental studies with paired-site design, using a meta-analysis approach, to quantify the differences in ecosystem C pools between plantations and their corresponding adjacent primary and secondary forests (natural forests). Totaled ecosystem C stock in plant and soil pools was 284 Mg C ha−1 in natural forests and decreased by 28% in plantations. In comparison with natural forests, plantations decreased aboveground net primary production, litterfall, and rate of soil respiration by 11, 34, and 32%, respectively. Fine root biomass, soil C concentration, and soil microbial C concentration decreased respectively by 66, 32, and 29% in plantations relative to natural forests. Soil available N, P and K concentrations were lower by 22, 20 and 26%, respectively, in plantations than in natural forests. The general pattern of decreased ecosystem C pools did not change between two different groups in relation to various factors: stand age (<25 years vs. ≥25 years), stand types (broadleaved vs. coniferous and deciduous vs. evergreen), tree species origin (native vs. exotic) of plantations, land-use history (afforestation vs. reforestation) and site preparation for plantations (unburnt vs. burnt), and study regions (tropic vs. temperate). The pattern also held true across geographic regions. Our findings argued against the replacement of natural forests by the plantations as a measure of climate change mitigation