Aurelio Guevara-Escobar

Use of digital photography for analysis of canopy closure

The relationships between trees and understory crops are very important in agroforestry systems. Also, above ground interactions can be related to canopy structure. However, measurements of canopy structural parameters, either destructive or indirect, are time-consuming or prohibitively expensive. The present work explored the use of digital photography as a simple method to characterise the extent of canopy closure (CC), defined as the area of tree canopies projected onto the horizontal ground surface beneath, and expressed as a percentage of the ground covered. Measurements were made in two Eucalyptus (Eucalyptus nitens, Deane and Maiden) plantations and a subtropical mixed legume woodland dominated by Albizia (Albizia sp), Kidneywood (Eysenhardtia sp.) and Desert Fern (Lysiloma sp.). Images were captured at dawn to minimise light scattering and the number of sunlit foliage elements. Mean CC estimates provided by analysis of images obtained using digital cameras with contrasting performance, a Kodak DC-120 and a Canon EOS D1, were similar in precision and accuracy both between the two cameras and to those provided by a Li-Cor LAI-2000 canopy analyser. Bias between the estimates provided by the Kodak and Canon cameras was –0.02, between the Kodak and LAI-2000 was –0.07 and between the Canon and LAI-2000 was –0.05. Data from a pruning experiment using alder also demonstrated the repeatability of estimates obtained with a photographic method using the Kodak camera. The number of ring sensors within the LAI-2000 used to estimate CC affected agreement between the photographic method and the LAI-2000.

Soil properties of a widely spaced, planted poplar (Populus deltoides)pasture system in a hill environment

Planting poplars is an effective technology for controlling hill soil erosion in New Zealand pastureland. However, the effects of widely spaced poplars on soil properties are not documented. Soil was sampled from 3 soil depths (0-75, 75-150, and 150-300 mm) in poplar-pasture (PP) and adjacent open pasture (OP) systems. Four sites were examined, 3 unreplicated sites with mature poplars (>29 years, 37-40 stems/ha) and a replicated experiment with immature poplars (5 years, 50-100 stems/ha). Pastures at all sites were dominated by low fertility species and were grazed by sheep and cattle. Pasture species were used in a glasshouse experiment to assess the production potential of the topsoil media (0-20 mm) from the PP and OP soils, and the OP topsoil amended with 5% poplar leaf litter.

THE ROLE OF URBAN VEGETATION IN TEMPERATURE AND HEAT ISLAND EFFECTS IN QUERÉTARO CITY, MEXICO

Alteration of climatic conditions and the urban heat island effect (UHI) are consequences of increased human population and activities in urban zones. Determining the magnitude of the UHI is important to improve urban planning in medium-size cities like Queretaro. Increase and conservation of vegetated areas is a mitigation option for UHI. Here we characterized both the UHI and the role of vegetation cover over temperature regularization in urban zones. Four local climatic zones were defined: three urban and one rural, each with two plots with low and high canopy cover defined by their average leaf area index (0.5 and 2.0, respectively). Air temperature and relative humidity were measured with data loggers at a 30 min time step from June 2012 to May 2013. Climatic data from six weather stations was also analyzed. Daily mean temperature increased at a rate of 0.75 oC per decade ( r 2 = 0.38, P < 0.0001), and this was related to population dynamics ( r 2 = 0.52, P < 0.0001). Patterns of air temperature defined a cold and a warm season: July to March and April to June for maximum temperature, and November to March and April to October for minimum temperature. The difference between cold and warm seasons was 5 oC (P < 0.0001). The minimum temperature was similar between canopy cover levels. However, relative humidity was higher in high canopy cover plots. The relationship between UHI and the pervious surface fraction of the city was inversely proportional. The UHI ranged from 0.1 to 5 oC and this magnitude was similar between the warm and cold seasons. Vegetation with high canopy cover had lower temperature at 17:00 LT and higher at 9:00 to 10:00 LT during the warm season. Increasing the urban zone canopy cover by 50% would reduce the UHI by 2.05 oC. In conclusion, vegetation with higher canopy cover improved environmental conditions in terms of relative humidity and regularization of extreme temperatures during the warm season.