The water and energy exchange of a shaded coffee plantation in the lower montane cloud forest zone of central Veracruz, Mexico

Holwerda, F., L.A. Bruijnzeel, V.L. Barradas, J. Cervantes. 2013. The water and energy exchange of a shaded coffee plantation in the lower montane cloud forest zone of central Veracruz, Mexico. Agricultural and Forest Meteorology 173: 1-13. PDF

Abstract: The water and energy fluxes of a shaded coffee plantation in the lower montane cloud forest (LMCF) zone of central Veracruz, Mexico, were measured over a two-year period (September 2006–August 2008) using the eddy covariance method. Complementary measurements of throughfall and stemflow were made to study rainfall interception. The sum of the observed sensible (H) and latent (E) heat fluxes was almost 95% of the net radiation (Rn) minus the canopy heat storage fluxes, indicating very good energy balance closure. The mean annual evapotranspiration was 1066 mm, and 95% of the corresponding FAO Penman-Monteith reference evapotranspiration (ET0) of 1117 mm yr−1. Interception loss was 8% of annual rainfall (1386 mm). Both the eddy covariance, and the throughfall and stemflow measurements showed average wet-canopy evaporation rate to be very low (0.05 mm h−1) compared to the corresponding rainfall rate (3.06 mm h−1). As a result, and despite the low canopy storage capacity of the coffee plantation (Cm, 0.50 mm), interception was dominated by post-event evaporation of intercepted water rather than by within-event evaporation. Comparing the results for the coffee plantation with interception data from mature and secondary LMCFs in the study area suggests that the conversion of LMCF to shade-coffee may lead to a decrease in interception loss of 8−18% of incident rainfall. This decrease is caused by a three to seven-fold decrease in Cm, probably due to the lower leaf area and smaller epiphyte biomass of the coffee plantation. The mean annual dry-canopy evaporation was 992 mm, and 89% of ET0. Comparing the eddy covariance-based estimate of dry-canopy evaporation for the coffee plantation with sapflow-based estimates of transpiration for the LMCFs did not show any clear differences.

La niebla y la ecohidrología del Bosque Mesófilo de Montaña en México

Un articulo nuevo desde Profesores Friso Holwerda y Sybil Gotsch en el boletin del Centro de Ciencias de la Atmosfera (UNAM). (PDF)

La ecohidrología es un área de trabajo novedosa e interdisciplinaria, que busca entender las interacciones entre el ciclo hidrológico y los ecosistemas terrestres. La niebla es simplemente una nube en contacto con la superficie terrestre. Su presencia en forma de numerosas y muy pequeñas gotas de agua produce una visión limitada de los objetos. Por tanto, no es sorprendente que la densidad de la niebla se exprese en términos de la visibilidad, que es la distancia a la cual se puede observar claramente un objeto o una luz.

Incidence and Implications of Clouds for Cloud Forest Plant Water Relations

Goldsmith, G.R., N.J. Matzke and T.E. Dawson. In Press. Incidence and Implications of Clouds for Cloud Forest Plant Water Relations. Ecology Letters DOI: 10.1111/ele.12039

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Abstract: Although clouds are the most recognisable and defining feature of tropical montane cloud forests, little research has focussed on how clouds affect plant functioning. We used satellite and ground-based observations to study cloud and leaf wetting patterns in contrasting tropical montane and pre-montane cloud forests. We then studied the consequences of leaf wetting for the direct uptake of water accumulated on leaf surfaces into the leaves themselves. During the dry season, the montane forest experienced higher precipitation, cloud cover and leaf wetting events of longer duration than the pre-montane forest. Leaf wetting events resulted in foliar water uptake in all species studied. The capacity for foliar water uptake differed significantly between the montane and pre-montane forest plant communities, as well as among species within a forest. Our results indicate that foliar water uptake is common in these forest plants and improves plant water status during the dry season.

Where Does The Water Go?

Project scientist Conrado Tobón, who also carries out extensive research on tropical montane ecohydrology in South America. He has recently been featured in a series of great videos about his research on the website What if We Change? Click below to learn more:

What If We Change: Conrado Tobón

Runoff generation in a steep, tropical montane cloud forest catchment on permeable volcanic substrate

Muñoz-Villers, L. E., and J. J. McDonnell (2012), Runoff generation in a steep, tropical montane cloud forest catchment on permeable volcanic substrate, Water Resour. Res., 48, W09528, doi:10.1029/2011WR011316. PDF

Most studies to date in the humid tropics have described a similar pattern of rapid
translation of rainfall to runoff via overland flow and shallow subsurface stormflow.
However, study sites have been few overall, and one particular system has received
very little attention so far: tropical montane cloud forests (TMCF) on volcanic substrate.
While TMCFs provide critical ecosystem services, our understanding of runoff generation
processes in these environments is limited. Here, we present a study aimed at identifying
the dominant water sources and pathways and mean residence times of soil water and
streamflow for a first-order, TMCF catchment on volcanic substrate in central eastern
Mexico. During a 6-week wetting-up cycle in the 2009 wet season, total rainfall was
1200 mm and storm event runoff ratios increased progressively from 11 to 54%. With the
increasing antecedent wetness conditions, our isotope and chemical-based hydrograph
separation analysis showed increases of pre-event water contributions to the storm
hydrograph, from 35 to 99%. Stable isotope-based mean residence times estimates showed that soil water aged only vertically through the soil profile from 5 weeks at 30 cm depth to 6 months at 120 cm depth. A preliminary estimate of 3 years was obtained for base flow residence time. These findings all suggest that shallow lateral pathways are not the controlling processes in this tropical forest catchment; rather, the high permeability of soils and substrate lead to vertical rainfall percolation and recharge of deeper layers, and rainfall-runoff responses appeared to be dominated by groundwater discharge from within the hillslope.

Variability of the radial profile of sap velocity in Pinus patula from contrasting stands within the seasonal cloud forest zone of Veracruz, Mexico

Alvarado-Barrientos, M.S., Hernández-Santana, V. & H. Asbjornsen. 2013. Variability of the radial profile of sap velocity in Pinus patula from contrasting stands within the seasonal cloud forest zone of Veracruz, Mexico. Agricultural and Forest Meteorology 168: 108–119. 

Abstract: Characterizing the variability of the radial profiles of sap velocity (vS) is a critical step to improve upscaling point measurements of vS to whole-tree sap flow. One promising approach is the use of a probability distribution function (pdf) to model radial profiles of vS, because shape parameters could potentially be generalized to trees of the same species based on the premise that the shape remain consistent regardless of the tree size and age, and over time, even though the magnitude of vS may vary with environmental conditions. The objective of this study was to characterize and assess the variability of the radial profile and to examine the validity of the premises underlying this approach by applying it to Pinus patula, one of the most widely planted tree species in the uplands of central- eastern Mexico. We measured vS with the Heat Ratio method at various sapwood depths in 18 P. patula trees with a dbh between 7.3-59.7 cm and age between of 10-34 years, over a period of 1.5 years. Trees were growing in two stands: a mature forest stand and a young plantation. By fitting the Beta-pdf to hourly radial profiles of vS, we derived a lumped shape parameter (ρ) to denote the radial position relative to sapwood depth with average vS and a scaling parameter (cS). The typical radial profile was unimodal, asymmetrical and with peak vS generally within the outermost 20-33% of the sapwood depth. However, tree-to-tree variability in ρ was considerable among trees within the same stand and also across stands. Long-term and day-to-day variation of ρ was marginal. The hourly dynamics of the radial profile, characterized by cS, can be explained by a linear combination of incoming shortwave radiation, vapor pressure deficit, the hour of day and their interaction (r2=0.74). An independent field evaluation confirmed that a radial profile of fixed shape can be effectively used to estimate whole-tree sap flow with relatively low bias (4-26% underestimation) relative to cut-tree water uptake, particularly for trees for which vS observations covered at least 60% of the sapwood depth. Our findings emphasize the importance of conducting multiple vS point measurements covering most of the sapwood depth for accurate characterization of the radial profile, and demonstrate the utility of fitting a pdf to point vS measurements in order to assess the variability of vS radial profiles as well as to compute sap flow at the whole-tree level.

Evaluating the environmental impact of payments for ecosystem services in Coatepec (Mexico) using remote sensing and on-site interviews

Scullion, J., C.W. Thomas, K.A. Vogt, O. Perez-Maqueo, & M.G. Logsdon. 2011. Evaluating the environmental impact of payments for ecosystem services in Coatepec (Mexico) using remote sensing and on-site interviews. Environmental Conservation 38: 426-434. (PDF)

Abstract: Over the last decade, hundreds of payments for ecosystem services (PES) programmes have been initiated around the world, but evidence of their environmental benefits remains limited. In this study, two PES programmes operating in the municipality of Coatepec (Mexico) were evaluated to assess their effectiveness in protecting the region’s endangered upland forests. Landsat satellite data were analysed to assess changes in forest cover before and after programme implementation using a difference-in- differences estimator. Additionally, surveys and interviews were conducted with local residents and a subset of PES programme participants to evaluate the programmes’ social and environmental impacts, particularly the effect of the programmes on landowner behaviour. The remote-sensing data show that deforestation was substantially lower on properties receiving PES payments compared to properties not enrolled in the programmes, but the programmes did not prevent the net loss of forests within Coatepec. Moreover, the on-site interviews suggest that the payments may have had little impact on deforestation rates, and that other factors contributed to the conservation of forests in PES properties. These findings suggest that risk-targeted payments, robust monitoring and enforcement programmes, and additional conservation initiatives should be included in all PES schemes to ensure environmental effectiveness.