Conrado Tobón

Biomass and water storage dynamics of epiphytes in old-growth and secondary montane cloud forest stands in Costa Rica

Epiphytic biomass, canopy humus and associated canopy water storage capacity are known to vary greatly between old-growth tropical montane cloud forests but for regenerating forests such data are virtually absent. The present study was conducted in an old-growth cloud forest and in a 30-year-old secondary forest (SF) on wind-exposed slopes in the Cordillera de Tilarán (Monteverde area) in northern Costa Rica. Epiphytic vegetation in both forests was dominated by bryophytes. Epiphyte mat weight (epiphyte biomass and canopy humus) at the stand level was 1,035xa0kgxa0ha−1 in the SF and 16,215xa0kgxa0ha−1 in the old-growth forest (OGF). The water contents of epiphytic bryophytes in the OGF were determined gravimetrically in situ and showed maximum values of 418%xa0±xa074 (SD)% of dry weight and minimum values of 36%xa0±xa010 (SD)%. Maximum stand water storage of non-vascular epiphytes and canopy humus at Monteverde was estimated at 0.36xa0mm for the SF and 4.95xa0mm for the OGF. Epiphytic bryophytes exhibited more dynamic wetting and drying cycles compared to canopy humus. Maximum water loss through evaporation was 251% of dry weight (bryophytes) and 117% of dry weight (canopy humus) within 3xa0days of sunny weather without precipitation. Despite the high potential water storage capacity of epiphytic bryophytes and canopy humus the actually available storage is likely to be much smaller depending on antecedent rainfall and evaporative conditions.

Effects of Land Use in the Hydrology of Montane Catchments in Central-eastern Mexico

The La Antigua river upper watershed (1,325 km2), located on the eastern slopes of the Cofre de Perote-Pico de Orizaba volcano (central Veracruz, Mexico), is a region of high biodiversity and great hydrological importance. The watershed plays a key role supplying water to main urban areas, such as the capital of Veracruz (Xalapa) and Coatepec, and providing downstream water for agricultural purposes and local fisheries, among others. The tropical montane cloud forest (TMCF) is a high value ecosystem because of the hydrological services it provides. Although many of the forests in this region have been disturbed or converted to crops and grasslands (112 km2) in the last 30 years, the hydrological effects of these changes at the catchment scale are still largely unknown, particularly in the case of the Mexican TMCF. This chapter addresses this knowledge gap by studying three headwater catchments (<50 ha) covered with, respectively, old-growth TMCF, 20-year old regenerating TMCF, and pasture, with the following objectives: 1) to evaluate the hydrological effects of TMCF disturbance and its conversion to pasture, with emphasis on annual and seasonal distribution of streamflow (baseflow and stormflow), and 2) to determine the effects of land use on stream-suspended solids exportation. The study period covered two years (2005–2007) during which continuous rainfall and streamflow data were collected. The results showed a higher stormflow (run-off produced by rainfall) in the regenerating forest and pasture (4.5 and 6.2 per cent of the rainfall, respectively) as compared with the old-growth forest (2.2 per cent), most likely because of a combination of lower canopy water interception and reduced soil infiltration. Nevertheless, the stormflow values observed across the different land cover types were very low (<6 per cent of rainfall) as a result of the very high infiltration capacity of the volcanic soil. The bedrock characteristics underlying the catchments appeared to be a key factor controlling their annual streamflow, particularly the baseflow. The pasture stream showed the highest concentrations of total suspended solids (10 mg l-1) compared with the forests (3.2 mg l-1), presumably due to higher surface run-off causing soil erosion. It is concluded that the TMCF disturbance and conversion to pasture modifies the eco-hydrological functioning of the catchments. However, the results also suggest that 20 years of natural regeneration following cloud forest disturbance in eastern Mexico is capable of producing near-original hydrological behaviour.

Ecophysiology of frailejones ( Espeletia spp.), and its contribution to the hydrological functioning of páramo ecosystems

Páramos are high elevation tropical ecosystems in northern Andes, with large water yield and water regulation. One of the main and representative species growing in these páramos is the genus Espeletia, known as frailejones. There is a lack of knowledge of Espeletia ecophysiology, maybe due to its unusual anatomical modifications and the specific climatic conditions of these ecosystems. Therefore, it is important to determine the relationships between the anatomical modifications of Espeletia, its physiological functioning, and its contribution to the ecohydrologic functioning of páramos. Consequently, we studied the physiology of frailejones in two Colombian páramos, focused on the identification of conductive tissues inside the stems, calculated the age, and measured sapflow, using the heat ratio method. Results show that Espeletia spp. have a central pith that increases with height, as the size of secondary xylem decreases. Frailejones respond quickly to the changing conditions of weather factors controlling transpiration such as solar radiation, temperature, and fog presence. However, although environmental factors favor transpiration, the sapflow tends to decrease—a particular behavior of the Espeletia transpiration processes—since this occurs chaotically over time, including sapflow at night. The transformation of sapflow velocity to depth of water in a basin shows that the water lost through their transpirationxa0is very low, which contributes to the high runoff ratio of páramo ecosystems. For the first time, we determine by radiocarbon the real ages of three E. hartwegiana, and their mean growth rates to range between 3.8 and 6.9xa0cmxa0year−1.

Contribution of occult precipitation to the water balance of páramo ecosystems in the Colombian Andes

Doctoral Candidate in Engineering— Hydraulic Resources, Universidad Nacional de Colombia, Calle 56 N°78A‐59 (801), Medellín 050034, Colombia Postgraduate Department of Forestry and Environmental Conservation, National University of Colombia, Calle 59A, No. 63‐20, Medellín 050034, Colombia Faculty of Engineering, Department of Civil and Environmental Engineering, Imperial College, 403A Skempton Building South Kensington Campus, London SW7 2AZ, UK Correspondence Maria Fernanda Cárdenas, Doctoral Candidate in Engineering—Hydraulic Resources, Universidad Nacional de Colombia, Calle 56 N°78A‐59 (801), Medellín 050034, Colombia. Email: mfcarden@unal.edu.co

Defining, Managing and Coping with Weather and Climate Related Risks in Forestry

Risks of weather and (changing) climate in forestry are large and vary considerably in time and space. Among them, most observed risks relate to altitudinal shifts (Peters and Darling 1985; Kariuki et al. 1997; Scheffer et al. 2001; Zhao et al. 2005), changes in productivity, standing biomass and species composition and fire damages (Dixon et al. 1996; Dale et al. 2001; Flannigan et al. 2005; Scholze et al. 2006; FAO 2007), tree health and extinction (Thomas et al. 2004), and migration (Kienast et al. 1998; Stocks et al. 1998; Dale et al. 2001; Bush et al. 2004; Phillips et al. 2009; Jimenez et al. 2009). Weather and climate exert strong effects on herbivore and pathogen dynamics (Coley 1998; Matthew et al. 2000). These changes affect species composition and species richness (Kienast et al. 1998), ecosystem functions and socioeconomic values of forests (Keller et al. 2002).