(Re)designing urban parks to maximize urban heat island mitigation by natural means

Urban trees play a key role in mitigating urban heat by cooling the local environment. However, the cooling benefit that trees can provide is influenced by differences in species traits and site-specific environmental conditions. Fifteen dominant urban tree species in parks from Mexico City were selected considering physiological traits (i.e., transpiration and stomatal conductance) and aesthetic and morphological characteristics. Species’ physiological performance was measured to explore the potential of trees to reduce urban heat load. Data were collected over a 4-week period in the months of April and May 2020, the warmest and driest months of the year in Mexico City. We used the Thermal UrbaN Environment Energy (TUNEE) balance model to calculate the cooling benefit of each species and the number of individuals necessary to reduce local air temperature. The highest midday transpiration was registered for Liquidambar styraciflua L. (0.0357 g m−2 s−1) and the lowest for Buddleja cordata H.B.K (0.0089 g m−2 s−1), representing an energy consumption and cooling potential of 87.13 and 21.69 J m−2 s−1, respectively. Similarly, the highest stomatal conductance was recorded for L. styraciflua., whereas the lowest was recorded for B. cordata. Based on the species transpiration rates and aesthetic characteristics, we developed a proposal and outline for a 50 X 50 m urban park (i.e., park community) consisting of six species with 19 individuals, and according to the TUNEE model, the proposed arrangement can reduce air temperature up to 5.3 °C. Our results can help urban planners to (re)design urban parks to mitigate urban heat while increasing urban tree diversity in parks

How important are fog and the cloud forest as a water supply in Eastern Mexico?

The water balance is the volume of water flowing through the hydrological cycle, and one of its main components is fog. Fog is considered a type of low-lying cloud and is heavily influenced by water bodies, topography, and wind conditions. Fog incorporates water from the atmosphere to the terrestrial surface and for some ecosystems (e.g., cloud forests) represents a great water contribution. In this work, we aimed to answer the following questions: (1) What is the fog-water contribution to the water balance? (2) How does the presence of vegetation affect the water supply to the ecosystem? We took as a case study the Central Mountain Region of Veracruz, in eastern Mexico, and measured components of the water balance; this included precipitation (gross and net), fog water, interception, transpiration, evapotranspiration, and condensation, and we estimated water gain and loss of the water balance. We registered 510 precipitation events distributed throughout the year with three peaks (October, May, and January). Of these, 386 were fog events, 41 were rain events, and 83 were events combining fog and rain. Fog had a substantial contribution of water to the system, with a volume 22 times greater than that of rain (4311.14 mm vs. 197.5 mm). From the total water gain, the highest proportion (91%) was contributed by fog interception. Fog was considered a constant source of moisture throughout the year; however, water intercepted during the dry season was higher (56%) compared with the wet season (36%). Our results highlight the importance of the fog as a source of water for the region

Tree traits and microclimatic conditions determine cooling benefits of urban trees

Trees play a key role in mitigating urban heat by cooling the local environment. This study evaluated the extent to which street trees can reduce sub-canopy air temperature relative to ambient conditions (DT), and how DT relates to tree traits and microclimatic variables. Air temperature under the canopies of 10 species was recorded within residential areas in Western Sydney, Australia, during summer 2019–2020. Tree and canopy traits, namely tree height, specific leaf area, leaf dry matter content, leaf area index, crown width and the Huber value (the ratio of sapwood area to leaf area) were then measured for all species. Species differed significantly in their DT values, with peak cooling (maximum DT 3.9 C) observed between 9–10 am and sub-canopy warming (i.e., positive DT values) typically occurring during afternoon and overnight. Trees with high LAI and wider canopies were associated with the greatest daytime cooling benefits and lower levels of nighttime warming. DT was also negatively related to windspeed and vapor pressure deficit, and positively to solar irradiance. This study provides valuable information on how tree characteristics and microclimate influence potential cooling benefits that may aid planning decisions on the use of trees to mitigate heat in urban landscapes

Potential vulnerability to climate change of four tree species from the central mountain region of Veracruz, Mexico

We define vulnerability here as the extent to which climate change may damage or harm a system, depending not only on a system's sensitivity, but also on its ability to adapt to new climatic conditions. Current climate change has already affected the Earth's biodiversity, and the rate of change is likely to accelerate in the future. It is expected that climate change will affect the performance, structure and distribution of ecosystems, species and genetic constituents. Changes in temperature and precipitation, and in the frequency and intensity of extreme events, can directly influence ecosystem functioning. To determine the vulnerability or fragility of different species to climate change, we used the envelope function method, because of its capacity to analyze the variables that directly affect different species; by measuring the effect of climate variables on stomatal conductance, this provided an effective analysis of the diversity of eco-physiological responses. Using this method to assess vulnerability helped us predict the extreme values that the species could tolerate; and also gave information about the species' sensitivity. We analyzed the effects of air temperature, photosynthetically active radiation, vapor pressure deficit and leaf water potential on the stomatal conductance in 4 tree species (Alnus acuminata, Quercus xalapensis, Liquidambar styraciflua and Pinus ayacahuite) from different altitudinal ranges in the central region of Veracruz, Mexico, in Las Grandes Montanas. Knowing how vulnerability affects the species and ecosystems is a key element of maintaining regional biodiversity

Stomatal responses of tree species from the cloud forest in central Veracruz, Mexico

Stomatal conductance is considered as a key plant response because it plays an important role in plant physiology by controlling transpiration (water status) and CO2 assimilation, regulating plant productivity. As stomatal conductance is affected by micro-environmental and physiological variables, changes in an altitudinal gradient will have a direct effect on stomatal conductance, which can explain their ecophysiological responses. In this work we used the envelope function method to assess the effect of three climate variables (air temperature, vapor pressure difference, photosynthetically active radiation), and two physiological (leaf water potential, transpiration) on the stomatal conductance response of four tree species (Alnus acuminata, Liquidambar styraciflua, Pinus ayacahuite, and Quercus xalapensis) from the central mountain region of Veracruz, Mexico. We found that all variables influenced stomatal conductance. We also found differential stomatal conductance responses among species, where A. acuminata had the highest stomatal conductance. We also estimated the optimal temperature when the highest stomatal conductance occurs, and among the species, optimal temperature varied from 26 to 29 C. The most sensitive species to changes in photosynthetically active radiation, leaf water potential and transpiration was L. styraciflua, and for vapor pressure difference was A. acuminata. We also proposed that the stomatal conductance response could help to explain ecophysiological responses along the elevation gradient

Juvenile and subadult feeding preferences of the Guadalupe fur seal (Arctocephalus townsendi) at San Benito Archipelago, Mexico

The feeding ecology of juvenile and subadult Guadalupe fur seals (Arctocephalus townsendi) at San Benito Archipelago, Baja California, Mexico, was investigated to determine if dietary differ-ences exist between these two age classes. During the summer of 2007, 108 scats of fur seals were collected from areas used mainly by juveniles (n = 54 scats) or subadults (n = 54 scats). Cephalopod beaks and/or otoliths were found in all samples collected. Only 702 squid beaks of 1,144 were identified to species level (61.3%). Only four of eight otoliths found were identified to species level (50%). Six squid species and two fish spe-cies were identified. Both juveniles and subadults showed similar dietary composition; however, differences between prey selection were found. The California market squid (Loligo opalescens) was the most common squid species for both age classes in the summer of 2007

(The re-colonization of the Archipelago of San Benito, Baja California, by the Guadalupe fur seal)

The aim of this paper is to analize the re-colonization process of the San Benito Archipelago by the Guadalupe fur seal (Arctocephalus townsendi). The archipelago is of great importance for the species, since it can be consolidated in the future as a breeding colony, which would imply a great achievement for the fur seal's natural recovery. Population growth, population structure, feeding behavior, foraging trips duration (which shows an important feeding area near), behavior and pup attendance, are characteristics that help analyze and study this process; where San Benito grows as a colony and, therefore, is established as a new breeding colony. Furthermore, this expansion of the breeding territory might reflect the gregarious nature of the species, and fidelity to breeding areas as well. The importance of this work is that it is an initial description of the re-colonization of a species that almost disappears. It can be expected to continue increasing the number of individuals at the archipelago, since it is unlikely that in a short period of time, the breeding territory and the food availability limit the birth of offspring and the population growth

Analysis of the re-colonization of San Benito Archipelago by Guadalupe fur seals (Arctocephalus townsendi) = Analisis de la recolonizacion del archipielago de San Benito por el lobo fino de Guadalupe (Arctocephalus townsendi)

Exploitation of the Guadalupe fur seal (GFS) during the XVIII and XIX centuries almost extirpated the species. GFS were distributed from the Revillagigedo islands (Mexico) to the gulf of Farallones (USA). At present, reproductive colonies are found at Guadalupe Island and San Benito Archipelago (SBA). The aim of this work was to analyze the process of re-colonization and the current status of GFS at SBA. The first births and the occupation of the west island of the SBA are also reported. Census data from 1997 to 2007 indicated an annual growth rate for the population of 21.6%. The population size, growth tendency of the colony, reproductive biology, and food preferences were also studied. A total of 2,227 GFS were counted at SBA. Three squid species (Loligo opalescens, Onychoteuthis banksii, Dosidicus gigas) were found to be the main dietary components. Territoriality, activity patterns, and reproductive behavior were similar for the seals from Guadalupe Island and SBA. The mean growth rate for pups from SBA was calculated and compared to that of the pups at Guadalupe Island (SBA: 6.7 +_ 1.4 kg, 68.9 +_ 2.64 cm; Guadalupe Island: 5.9 +_ 0.5 kg, 67.29 +_ 4.3 cm). The length of food foraging trips by females was measured, suggesting that the SBA colony is probably near an important feeding area. Maternal care patterns could indicate different strategies of nursing-foraging trips between the SBA and Guadalupe Island. The population of fur seals at SBA is expected to increase as there are no limitations in terms of reproductive space or available food resources in the area

Estimating evapotranspiration in the central mountain region of Veracruz, Mexico = Estimacion de la evapotranspiracion en la region montanosa central de Veracruz, Mexico

The global, regional and local hydrological cycle is strongly linked to vegetation distribution. The hydrological cycle is composed by precipitation, infiltration, runoff, transpiration and evaporation. Evaporation is influenced by high temperatures, high winds and low relative humidity. This work is focused on the study of evapotranspiration (ET) as the main variable of water loss in the water balance in the central mountain region of Veracruz, Mexico. ET was estimated using the Penman-Monteith model, which requires environmental (net radiation, vapor pressure deficit, air temperature and wind intensity) and physiological (stomatal and canopy resistances and leaf area index) variables. These variables were measured in two sites within the region: La Joya and La Orduña, comparing different ecosystems: pine-oak, pine forests and grassland, and cloud forest and sugarcane crop, respectively. Results show that both, the estimated and real ET, are high; although, we found net surplus related to precipitation at both sites (533.8 and 526.5 mm) from September 2006 to August 2007. Apparently, no water deficits in either location were found; however, in the dry season water gain was very low, zero or negative. March and April were the months presenting the lowest water contribution to the system. The forests in the central mountain region of Veracruz can provide ecosystem services favoring evapotranspiration and regulating water balance, although the lack of information on the magnitude and value of this variable has hindered recognition and understanding of these forests