This study focuses on the southern provinces of Loja and Zamora-Chinchipe (Fig. 1). These regions feature marked gradients in mean annual precipitation within a relatively short distance. Figure 2 shows mean annual precipitation in Loja and Zamora-Chinchipe, varying between 200-400 mm in Loja to 3200-6400 mm in Zamora-Chinchipe. Thus, a transect of relatively limited length transversing these two provinces is appropriate for the study of ecohydroclimatological relations.

Fig. 2   Mean annual precipitation in Ecuador (Click --here-- to expand).

This study is part of a research program in ecohydroclimatology carried out jointly by San Diego State University (San Diego, California, USA) and the Technical University of Loja (Loja, Ecuador). The logistical support for the field studies was provided by the Technical University of Loja.

2.  GEOGRAPHICAL SETTING

The provinces of Loja and Zamora are located in southern Ecuador (Fig. 3). Wolf (1892) has described the geology, geomorphology, and hydrography of Ecuador, including Loja and Zamora. The Andes Mountain Range transverses the study region, from the Sabanilla Knot, to the south of Loja, to the moorlands of Zaraguro, toward the north.

From the Sabanilla Knot, the Santa Rosa Range takes off to the northwest and the Condor Range to the southeast. The Santa Rosa Range is narrow, low, and relatively small. From the Condor Range, several large branches take off toward the northeast.

Fig. 3   Location of Loja and Zamora-Chinchipe in southern Ecuador (Click --here-- to expand).

From 4° 8' S latitude, south of the city of Loja, the Western Range runs parallel to the Eastern Range in a general northern direction. The Western Range is narrow, with short branches on both sides, rising up to 3000 m through most of its length. In contrast, the Eastern Range rises up to 4000 m. These two branches of the Andes are united by two transversal knots, the Cajanuma Knot to the south of Loja (Fig. 4), and the Guagra-uma Knot to the north. The region comprised between the knots constitutes the valley of Loja.

Fig. 4   The Cajanuma Knot at close range.

The valley of Loja, oriented from north to south, is divided into two different sections. The northern section is narrow, resembling a canyon. The southern section, properly the valley of Loja, is oval-shaped, with a total length comprising about 6 km and a maximum width of about 3 km.

The Malacatos river has its headwaters in the Cajanuma Knot, flowing north to meet the Zamora river at Loja proper, where it takes the name of the latter. Continuing to flow north through the Guagra-uma Knot, the Zamora river meets several tributaries along its course, eventually discharging into the Santiago river in the eastern lowlands of Zamora-Chinchipe province.

The interandean valley of Loja is small and low, at 2150 m altitud, with the city of Loja occupying the entire valley. The lowest point on the road (pass) from Loja through Cajanuma Knot to the south is at 2525 m altitude (Fig. 5). The lowest point on the road from Loja to Catamayo to the west is at 2786 m (Fig. 6). This pass is next to Villonaco peak, which rises to about 3000 (Wolf 1892).

Fig. 5   The lowest point on the road (pass) from Loja to Malacatos.

Fig. 6   The lowest point on the road (pass) from Loja to Catamayo.

3.  CONCEPTUAL FRAMEWORK

This study sets the foundations to describe the characteristics of vegetative communities, using the interdisciplinary perspective of ecohydroclimatology. Several factors condition the type and density of vegetative communities across the landscape. The most important are:

1. Mean annual precipitation

   Mean annual precipitation determines the humidity provinces (arid, semiarid, subhumid, or humid) (Holdridge 1947). Plants respond readily to the presence of environmental moisture, including that in the air, land surface, vadose zone (unsaturated soil), and that flowing underground. Low relative humidity in the air is usually associated with low moisture levels on land surface and soil, together with the presence of ephemeral streams and relatively deep groundwater. Conversely, high relative humidity is usually associated with high moisture levels on the land surface and soil, coupled with perennial streams and shallow groundwater. In practice, these elements of the landscape are all related, with a common denominator: high environmental moisture means humid, while low moisture means arid.

2. Terrain geology and geomorphology

   Next to climate type, terrain geology and geomorphology are generally a good indicator of vegetation type (Cole 1960a; Ponce and da Cunha 1993). Notwithstanding other factors, terrain geology and geomorphology determine the relation between surface water and groundwater. Plants may transpire either vadose water, groundwater, or both (Ponce 2006). Land surface slope and rock/soil type determine the quantity of surface flow, surface detention and retention, infiltration rate, depth to water table, and groundwater replenishment. In addition, drainage conditions, either exorheic, endorheic, or mixed exorheic-endorheic, by interacting with soil and groundwater salinity, determine the type and density of vegetative communities that prevail across the landscape.

3. Proximity to groundwater

   Vegetative communities referred to as phreatophytes specialize in satisfying their water needs directly from the underlying groundwater. In essence, shallow groundwater supports the growth of plants that habitually feed on groundwater (Meinzer 1927). Thus, the presence of phreatophytes is a good indicator of shallow groundwater in the vicinity.

4. Speed of surface drainage

   Land slopes vary widely, from larger than 30% in certain mountainous landscapes (Ponce, 2008), to near zero in some geologically controlled depositional landscapes or broad river valleys undergoing geologic subsidence (Ponce 1995). Very mild terrain slopes lead to swamps and wetlands and their characteristic vegetative community structures, including the dynamics imposed by seasonal variations, floods and droughts, and more recently, anthropogenic climate change.

5. Mean annual temperature

   Plants are naturally adapted to either wide (desert) or narrow (rainforest) variations in temperature. Mean annual temperature conditions the liveability and survivability of diverse vegetative communities across the landscape, from arid to humid.

6. Seasonal variations in temperature

   Plants are naturally adapted to seasonal variations in temperature, which are conditioned by latitude, altitude, and continental location relative to the nearest moisture source. Desert plants readily adapt to wide variations in seasonal temperature, while rainforest plants do not.

4.  ANNUAL PRECIPITATION

The transect chosen for this study comprises the section between Catacocha, in central Loja province, to Zamora, in western Zamora-Chinchipe (Fig. 7).

Fig. 7   General location of the study transect in the Loja and Zamora-Chinchipe provinces. (Click --here-- to expand).

Figure 8 shows a map of mean annual precipitation for the study transect. Data from ten (10) climatological stations were used to develop this map. The stations are, from west to east: (1) Chaguarpamba, (2) Catacocha, (3) Nambacola, (4) El Cisne, (5) Catamayo, (6) El Tambo, (7) La Argelia (in Loja), (8) Cajanuma, (9) San Francisco, and (10) Zamora. The locations of the stations are shown in Fig. 8.

Fig. 8   Mean annual precipitation isohyets for the Catacocha-Zamora transect. (Click --here-- to expand).

Mean annual precipitation varies from 400 mm in Catamayo to 2200 mm in San Francisco, depicting a marked precipitation gradient. The straight distance between Catamayo and San Francisco is about 40 km, while the straight distance between Catacocha and Zamora is about 80 km. Significantly, the city of Loja, capital of the province of Loja, is located at midrange along the Catamayo-San Francisco subtransect.

Figure 9 shows an image of the Catacocha-Zamora transect, revealing the marked diferences in vegetation along the transect. Albedo, a reliable indicator of the presence or absence of vegetation is estimated to vary between as high as 0.30 near Catamayo, to as low as 0.05 near San Francisco (Ponce et al. 1997). Figure 10 shows a longitudinal profile of the Catacocha-Zamora transect, corresponding to Fig. 9. The Catacocha, Catamayo, Loja, and Zamora valleys are indicated in the profile. Figure 11 shows a topographic map comprising the study transect.

Fig. 9   Image of the Catacocha-Zamora transect (Click --here-- to expand).

Fig. 10   Longitudinal profile of Catacocha-Zamora transect (Click --here-- to expand).

Fig. 11   Topographic map comprising the Catacocha-Zamora transect (Click --here-- to expand).

Figure 12 shows an image of the Catamayo-Zamora transect, at somewhat larger scale that the previous image, again revealing the marked diferences in vegetation type and density along the transect. Pulgar et al. (2010) have noted that mean annual precipitation at an isolated spot at Cerro El Consuelo, near San Francisco, has been measured at 6,259 mm. Also, they have documented the number of rainy months to vary from 1-2 for Catamayo (a hyperarid climate) to 11-12 for San Francisco (a hyperhumid climate) (Ponce et al. 2000). Thus, the Catamayo-San Francisco subtransect appears to be optimal for the study of tropical ecohydroclimatological relations.

Fig. 12   Image of the Catamayo-Zamora transect (Click --here-- to expand).

Figure 13 shows an image focused on the Loja valley, showing the marked differences in vegetation density from the mountains west of Loja to those east of Loja, a distance of less than 20 km. Mean annual precipitation (Fig. 8) varies from 800-1000 mm to the west and 1600-1800 mm to the east.

Fig. 13   Image of the vicinity of Loja (Click --here-- to expand).

5.  VEGETATIVE LANDSCAPES

Figures 14 and 15 show the contrast between typical landscapes and associated vegetative communities in Catamayo and Zamora, respectively. Figure 14 shows a hilly landscape covered with short semiarid shrubs and grasses, while Fig. 15 shows a dense tropical montane humid forest, featuring relatively tall trees. Ongoing field research is aimed at identifying the spatial distribution, density, size, and other relevant characteristics of vegetative species and communities along the study transect.

Fig. 14   Mountainous semiarid landscape in the vicinity of Catamayo, Loja province.

Fig. 15   Vegetative communities along the road to Zamora, Zamora-Chinchipe province.

6.  BIOCLIMATOLOGICAL INDEXES

Three indexes are used to study bioclimatological relations (Rivas-Martínez 2007):

1. Continentality index

   This index is equal to the average temperature of the hottest month T_hot minus the average temperature of the coldest month T_cold .

   I_c = T_hot - T_cold

   The following procedure is used to calculate T_hot :

   • The maximum daily temperature, for each month and year of record is identified, and the mean maximum monthly temperature is calculated.

   • The mean of the mean maximum monthly temperature is calculated for the entire record.

   • The month with the highest mean of the mean maximum monthly temperature is selected as the hottest month.

   A similar procedure is applied to calculate T_cold.

   The continentality index varies between I_c = 0 for an extreme oceanic influence, to I_c = 65 for an extreme continental influence.

2. Thermicity index

   This index is equal to the mean annual temperature T_mean plus the mean of the monthly minimum temperatures T_min plus the mean of the monthly maximum temperatures T_max. The sum is multiplied by 10.

   I_t = 10 (T_mean + T_min + T_max)

   The mean annual temperature is the mean of the (12) mean monthly average temperatures. The mean of the monthly minimum temperatures in the mean of the (12) mean monthly minimum temperatures. The mean of the monthly maximum temperatures in the mean of the (12) mean monthly maximum temperatures.

3. Positive temperature index

   This index is equal to the sum of all positive (nonnegative) mean monthly temperatures. The sum is multiplied by 10.

   T_p = 10 ( ∑ T_pos )

Table 1 shows the classification of climates as a function of the continentality index. Table 2 shows the classification of climates as a function of the thermicity and positive temperature indexes. Table 3 shows the indexes calculated for the following stations: (1) Catacocha, (2) Catamayo, (3) La Argelia, and (4) Zamora. Table 4 shows the climatic classification for the stations considered in this study.

The low continentality index of the stations along the study transect justifies its classification as hyperoceanic (Table 1). This is attributed primarily to its geographical location near the Equator, and secondarily to its near proximity to the Pacific Ocean.

7.  SUMMARY

Ongoing ecohydroclimatological research along the Catacocha-Zamora transect in the provinces of Loja and Zamora-Chinchipe, Ecuador, is reported. Mean annual precipitation varies between 400 mm in Catamayo, along the study transect, to 2200 mm in Zamora, toward the eastern limit. Precipitation data indicates that mean annual precipitation may reach 6259 mm in an isolated point at Cerro del Consuelo, in the Podocarpus National Park, near Loja. Altitudinal variations are also quite marked, between 1230 m in Catamayo, to 2930 m in Cerro del Consuelo, to 900 m in Zamora. Ecohydrological and hydroclimatological data are examined with the aim of underpinning research in the nascent field of ecohydroclimatology.

REFERENCES

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Holdridge, L. R. 1947, Determinations of world plant formations from simple climatic data. Science, Vol. 105 (2727), 367-368.

Meinzer, O. E. 1927. Plants as indicators of ground water. U.S. Geological Survey Water Supply Paper 577, Washington, D.C.

Ponce, V. M., and C. N. da Cunha. 1993. Vegetated earthmounds in tropical savannas of Central Brazil: A synthesis; with special reference to the Pantanal of Mato Grosso. Journal of Biogeography, Vol. 20, 219-225.

Ponce, V. M., 1995. Hydrologic and environmental impact of the Parana-Paraguay Waterway on the Pantanal of Mato Grosso. Report, San Diego State University, San Diego, California, August.

Ponce, V. M., A. K. Lohani, and P. T. Huston. 1997. Surface albedo and water resources: Hydroclimatological impact of human activities. Journal of Hydrologic Engineering, ASCE, Vol. 2, No. 4, October, 197-203.

Ponce, V. M., R. P. Pandey, and S. Ercan. 2000. Characterization of drought across climatic spectrum. Journal of Hydrologic Engineering, ASCE, Vol. 5, No. 2, April, 222-224.

Ponce, V. M., 2006. Impact of the proposed Campo landfill on the hydrology of the Tierra del Sol watershed. Online report.

Ponce, V. M., 2008. Flood hydrology of the La Leche river, Lambayeque, Peru. Online report.

Pulgar, I., J. Izco, and O. Jadan. 2010. Flora selecta de los pajonales de Loja, Ecuador. Ediciones Abya-Yala, Quito, Ecuador. 175 p.

Rivas-Martínez, S. 2007. Mapa de series, geoseries, y geopermaseries de vegetación de España. Memoria del mapa de vegetación potential de España. I. Itinera Geobotanica, Vol. 17, 5-435.

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