Términos relacionados

3 resultados encontrados para: AUTOR: Holwerda, Friso
  • «
  • 1 de 1
  • »
1.
- Artículo con arbitraje
*Solicítelo con su bibliotecario/a
Reduced dry season transpiration is coupled with shallow soil water use in tropical montane forest trees
Muñoz Villers, Lyssette Elena ; Holwerda, Friso (coaut.) ; Alvarado Barrientos, María Susana (coaut.) ; Geissert, Daniel R. (coaut.) ; Dawson, Todd E. (coaut.) ;
Contenido en: Oecologia Vol. 188, no. 1 (September 2018), p. 303-317 ISSN: 1432-1939
Nota: Solicítelo con su bibliotecario/a
Resumen en: Inglés |
Resumen en inglés

Tropical montane cloud forests (TMCF) are ecosystems particularly sensitive to climate change; however, the effects of warmer and drier conditions on TMCF ecohydrology remain poorly understood. To investigate functional responses of TMCF trees to reduced water availability, we conducted a study during the 2014 dry season in the lower altitudinal limit of TMCF in central Veracruz, Mexico. Temporal variations of transpiration, depth of water uptake and tree water sources were examined for three dominant, brevi-deciduous species using micrometeorological, sap flow and soil moisture measurements, in combination with oxygen and hydrogen stable isotope composition of rainfall, tree xylem, soil and stream water. Over the course of the dry season, reductions in crown conductance and transpiration were observed in canopy species (43 and 34%, respectively) and mid-story trees (23 and 8%), as atmospheric demand increased and soil moisture decreased. Canopy species consistently showed more depleted isotope values compared to mid-story trees. However, MixSIAR Bayesian model results showed that the evaporated (enriched) soil water pool was the main source for trees despite reduced soil moisture. Additionally, while increases in tree water uptake from deeper to shallower soil water sources occurred, concomitant decreases in transpiration were observed as the dry season progressed. A larger reduction in deep soil water use was observed for canopy species (from 79 ± 19 to 24 ± 20%) compared to mid-story trees (from 12 ± 17 to 10 ± 12%). The increase in shallower soil water sources may reflect a trade-off between water and nutrient requirements in this forest.


PDF PDF
Resumen en: Inglés |
Resumen en inglés

Payments for Hydrologic Services (PHS) programs are increasingly used as a policy tool to provide incentives for upstream landowners to adopt land use activities that favor sustainable provision of high-quality water to downstream areas. However, the effectiveness of PHS programs in achieving their objectives and the potential for unintended (often undesirable) consequences remain poorly understood. We integrate results from ecohydrological and socioeconomic research to explore the impact of Mexico’s PHS program on the target hydrologic services and people’s decisions, behavior, and knowledge regarding forest conservation and water. Using central Veracruz as our case study, we identify areas of both synchrony and disconnection between PHS goals and outcomes. Mature and regenerating cloud forests (targeted by PHS) were found to produce enhanced hydrologic services relative to areas converted to pasture, including reduced peak flows during large rain events and maintenance of dry-season base flows. However, unexpectedly, these hydrologic benefits from cloud forests were not necessarily greater than those from other vegetation types. Consequently, the location of forests in strategic watershed positions (e.g., where deforestation risk or hydrologic recharge are high) may be more critical than forest type in promoting hydrologic functions within watersheds and should be considered when targeting PHS payments. While our results suggest that participation in PHS improved the level of knowledge among watershed inhabitants about forest–water relationships, a mismatch existed between payment amounts and landowner opportunity costs, which may contribute to the modest success in targeting priority areas within watersheds.

Combined, these findings underscore the complexity of factors that influence motivations for PHS participation and land use decisions and behavior, and the importance of integrating understanding of both ecohydrological and socioeconomic dynamics into PHS design and implementation. We conclude by identifying opportunities for improving the design of PHS programs and recommending priority areas for future research and monitoring, both in Mexico and globally.


3.
- Artículo con arbitraje
*Solicítelo con su bibliotecario/a
Surface energy exchange in a tropical montane cloud forest environment: flux partitioning, and seasonal and land cover-related variations
Holwerda, Friso ; Alvarado Barrientos, María Susana (coaut.) ; González Martínez, Teresa Margarita (coaut.) ;
Contenido en: Agricultural and Forest Meteorology Vol. 228–229 (November 2016), p. 13–28 ISSN: 0168-1923
Nota: Solicítelo con su bibliotecario/a
Resumen en: Inglés |
Resumen en inglés

Relationships between seasonal climate, land cover and surface energy exchange in tropical montanecloud forest environments are poorly understood. The goal of this study was to investigate the seasonality of flux partitioning in lower montane cloud forest (LMCF), shaded coffee (CO) and sugarcane (SU) in central Veracruz, Mexico, as well as to evaluate the changes in surface energy exchange associated with the conversion of LMCF to CO or SU. Sensible (H) and latent heat (λE) fluxes were measured duringthe late dry and wet seasons using eddy covariance (CO and SU) and sap flow (LMCF) methods. Other measurements included: meteorological parameters, radiation balance, soil heat flux, soil moisture andvegetation characteristics. During the wet-season month of July, average midday Bowen ratios (βs) forsunny conditions were lowest and least variable among land covers: 0.4 ± 0.2 (SE) in LMCF, 0.5 ± 0.1 inSU and 0.7 ± 0.1 in CO. In contrast, during the late dry-season months of March and April, s were higher(i.e. higher H and lower E) and more variable. The highest values of were observed in LMCF, reflecting effects of partial leaf-shedding by dominant deciduous species (2.4 ± 0.8, March) and increased stomatalcontrol (1.4 ± 0.3, April). There was also evidence of stomatal limitation of E in CO and SU, having sof up to 1.0 ± 0.1 in April and March, respectively. As compared to LMCF, the average midday availableenergy (Ae) for sunny conditions was very similar in CO (−3 ± 7%) and 15 ± 8% lower in SU. Although not all results were statistically significant, they suggest that for the wet season conversion of LMCF to shaded coffee or sugarcane led to a decrease of 15 ± 14% or 15 ± 17% in midday E under sunny conditions, respectively, where as corresponding values of H increased by 37 ± 38% or remained about the same(−4 ± 40%).

In contrast, for the late dry season, conversion of LMCF to shaded coffee or sugarcane appearsto have resulted in higher E and lower H, with changes of, respectively, +79 (±32)%/–45 (±16)% (CO) or+39 (±32)%/–43 (±16)% (SU) for a partially leafless LMCF in March, and +17 (±16)%/–11 (±16)% (CO) fora fully-leafed LMCF in April. In order to more accurately quantify the changes in surface energy fluxesassociated with LMCF conversion, future work should focus on reducing the errors in the flux estimates. Nevertheless, for sunny days during the wet season, potential changes in the moisture and heat content ofthe local atmosphere due to the conversion of LMCF to CO or SU seem to have been in the same directionas those induced by increased greenhouse gases (drying and warming), where as for the late dry season the effects appear to have been opposite (moistening and cooling).