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Environment 2. Biodiversity and climate gradients. Altitudinal gradient on the Andean western slope (Central Peru).

Irma Franke

Forest

Lindsay, Rimac River valley. Aerial photograph showing the importance of slope orientation for the development of woody vegetation. Orientation depends on the amount of radiation received. Trees only develop on the slopes receive less radiation and are due more humid.

is considered one of the most important biologically rich areas in Andean region is the compression of life zones along climatic gradients weather. In addition, d entered the large climatic gradients, variable terrain and slope and aspect of the slopes and the microrelief create a diverse topography that interacts with solar radiation, wind and precipitation, creating a multitude of habitats called "geodiversity" .

Due to its geographical location and topography, the Peruvian territory is dominated by climatic gradients, both latitudinal and altitudinal. Altitudinal gradients tend to have greater influence than latitudinal gradients biodiversity is developed along it.

Although s and have been several analysis of the distribution of organisms that live along climatic gradients (Pearson & Pearson, Ralph 1978, Patterson et al. 1996, Patterson et al. 1998), the main characteristics of these gradients are rarely reported. For this region of Peru, l to western slopes of the Andes in central Peru have analyzed the major gradients of climatic variables, having found interesting relationships between weather conditions and location of more complex habitats of the western slopes

Climate Elevational Gradient in Western Slope (Central Peru).

climate variables that most clearly represent the climatic gradients of temperature and precipitation. As these variables are presented in the elevation of the western slope of Peru Central?

temperature

The temperature value generally used to characterize an area's average temperature. Mentioned in a previous review of climatic gradients on the western slopes (Franke 2010) that the altitudinal gradient of mean temperature is relatively strong and similar in all the area between Piura and Lima, consisting of a reduction 0.4 º C each 100 m altitude (Valencia 1990). The temperatures of the bottom of the slope to 1500 m are influenced frequently between June and October by the inversion of the coast (Prohaska 1973). In these times the temperature gradient is reversed and this area increases with altitude. It is however important to analyze in detail the characteristics of the temperature regime under which develops a certain biodiversity. This requires reviewing several aspects of temperature: the mean temperature, minimum and maximum daily variation or range of temperatures prevailing.

Average temperature

The review of monthly mean temperature values \u200b\u200bshows that in the lower western slope of the annual oscillation of the average temperature is quite marked, with a difference of 7 ° C between higher temperatures that occur between January and April and the lowest, that occur in the central months of the year. The magnitude of the annual oscillation decreases with altitude, with very little between 2000 and 3000 m . Towards higher altitudes the annual oscillation gradually increases to values \u200b\u200bnear 3 º C to 4450 m . Unlike the lowlands, the highlands of higher average temperatures do not correspond to the initial months of the year but the central months of the year, between March and August (Figure 1).

Figura 1. Variación de la oscilación anual de   la Temperatura  Media   con la altitud en el Perú Central. Regresiones obtenidas a partir de los     datos de las estaciones meteorológicas de las estaciones de Ñaña ( 566 m ), Chosica ( 850 m ), Matucana ( 2378 m ) y Milloc ( 4350 m ) en Rimac River valley, Sing ( 2832 m) in the Chillon River Valley and Huarochirí ( 3154 m) in the Mala River Valley (Franke and Valencia 1984).

Minimum Temperature.

In contrast to the oscillation observed in mean temperature, mean minimum temperatures are the lowest values \u200b\u200bin the central months of the year and its highest values \u200b\u200bat the beginning of the year across the range of altitudes. However, the magnitude of the oscillation varies along the gradient. In the bottom of the slope, 1000 m , there is a difference of approximately 7 º C between the lowest values \u200b\u200b and higher values. In the middle altitudes, 2000 to 3000 m , the oscillation is greatly reduced a difference of 0.5 to 2 º C . At the top the annual oscillation is increased again to about 3 º C . (Figure 2).

Figure 2. Variation of the annual oscillation Minimum Temperature Media with altitude in central Peru. Regressions from the weather station data Ñaña stations ( 566 m), Chosica ( 850 m), Matucana ( 2378 m) and Milloc (4350 m ) in the Rimac River valley, Sing ( 2832 m) in the Chillon River Valley and Huarochirí ( 3154 m) in the Mala River Valley (Franke and Valencia 1984 .)

Maximum temperatures. The annual oscillation of mean maximum temperatures follows a pattern similar to the average temperature, but the reverse pattern of the average minimum temperature. In the lower area the highest values \u200b\u200boccur in the middle months and in the upper pattern is reversed and the highest values \u200b\u200bare at the beginning of the year. In the lower the annual oscillation is 6 to 8 º C . At medium altitudes the oscillation decreases sharply to values \u200b\u200bbetween 1.5 and 2.5 º C without a defined period of higher temperatures. At high altitudes increases the annual oscillation again until 4 to 5 º C .

The altitudinal strip between 2000 and 3000 is the transition zone between high summer temperatures in the lower and the area of \u200b\u200bhigher winter temperatures in the upper part and has the lowest oscillation annual mean maximum temperatures on the western slopes of central Peru (Figure 3) .

Figure 3. Variation of the annual oscillation Maximum Temperature Media with altitude in central Peru. Regressions from the weather station data Ñaña stations (566 m ) Chosica ( 850 m), Matucana ( 2378 m) and Milloc ( 4350 m) in the Rimac River valley, Sing (2832 m) in the Chillon River Valley and Huarochirí ( 3154 m) in the Mala River Valley (Franke and Valencia 1984).

average daily variation of T

The annual average daily variation the temperature difference between the daily values \u200b\u200bof maximum and minimum temperatures is similar, 9 to 10 º C in the bottom of the slope and medium altitudes, but is markedly higher altitudes high, 18 º C . The average daily variation does not increase steadily with altitude, but extends just above 3000 m . The band between 2000 and 3000 m is the area of \u200b\u200bsmaller daily temperature range.

In the bottom of the slope oscillation Variation Daily Media during the year is reduced because the periods of maximum and high minimum temperatures coincide. At the top times of high minimum temperatures and different resulting in a wide range of temperatures in the central months of the year, May to October. In the middle zone the annual oscillation is generally low (Figure 4).

Figure 4. variation Thermal Amplitude with altitude throughout the year in Central Peru) Average Minimum Temperature b) Average temperature c) mean maximum temperature. theoretical values \u200b\u200bobtained from the weather station data Ñaña stations (566 m ) Chosica ( 850 m), Matucana (2378 m ) and Milloc ( 4350 m) in the Rimac River valley, Sing ( 2832 m) in the Chillon River Valley and Huarochirí ( 3154 m) in the Mala River Valley (Franke and Valencia 1984).

As a result of annual patterns of the various aspects of temperature, altitudinal strip between 2000 and 3000 m has a high thermal stability during the whole year.

Precipitation

On the western side of Central Peru precipitation increases with altitude to about 4300 - 4500 m (Franke and Valencia 1984, SENAHMI 1976). At the bottom to 1000 m total annual rainfall is very low, less than 100 mm year and is restricted to 4 months from December to March. With increasing altitude, not only increases the total annual precipitation, but also its annual distribution or duration of the rainy season, although the wettest months are December to March provided with the highest value in February or March (Figure 5) .

Figure 5. Precipitation variation with altitude throughout the year in Central Peru theoretical data obtained with rainfall information Ñaña stations (566 m ) Chosica ( 850 m), Santa Eulalia ( 1030 m), Matucana ( 2378 m), Carampoma ( 3272 m), Bellever ( 3950 m), Casapalca ( 4143 m) and Milloc ( 4350 m) in the Rimac River valley (Franke and Valencia 1984).

Another aspect of precipitation have important modifications, especially for effects on vegetation and soils are the precipitation frequency and amount of precipitation per rainy day . In the bottom of the slope precipitation is very low. In the highlands the rains are usually relatively short and strong. In the middle parts of the watershed is dominated by relatively prolonged rain droplets, usually accompanied by a significant amount of fog (Franke and Valencia 1984).

seasonal climate

The combination of features regime of temperatures and precipitation creates a gradient that goes from warm and dry lower in cold, damp environments, with a time increased duration to wet the upper parts where the rooms are cold and humid with a short dry period in the middle months of the year. These features are clearly represented in the diagrams ombrothermal (Figure 6).

Figure 6. Altidudinal gradient of seasonality of climate on the western slope of central Peru.

Elevational Gradient of Biodiversity

altitudinal gradient of vegetation

The existence of a gradient of vegetation on the western slope was recognized by several authors. Weberbauer (1945) described a series of altitudes. The division was reviewed by M. Weberbauer Koepcke (1954), coining the term "mountain steppe" to describe the area between my 3500/4000 1400/1600 m. Within the mountainous steppe recognizes "vital areas", making a division higher than Weberbauer and adding sparse evergreen forest mist or dry forests (Figure 7). The sequence of altitudinal or vital areas is often described in general terms to a wide region. The altitudinal or vital areas present in a particular slope is necessarily limited because it depends on local conditions (Figure 8).

Figure 7. Vital areas of habitat or Western Slope of Central Peru as M. Koepcke (1954).

Figure 8. Vegetation gradient on the slope of the margin Right Seco River (Franke and Valencia 1984).

It reflects the altitudinal gradient of vegetation or habitats in an altitudinal gradient in the distribution of wildlife?

Studies on altitudinal distribution of the various groups of wildlife are more numerous to the eastern slopes of the Andes (Patterson et al. 1996, Patterson et al. 1998) that the western slopes (Pearson and Ralph Person, 1978). The greatest richness of the fauna of the western slopes is undoubtedly most attractive couple this type of study.

In Western Slope, the northernmost habitat has more complex and greater wealth of wildlife. Have not been conducted, however, further studies in this area. A study in the 90's in the Sana River Valley was in the collection of data unfortunately were never published.

Central in Peru is likely that this vegetation gradient has a low correlation with the distribution of organisms, especially birds and other fauna, as was emphasized by M. Koepcke (1954). This is mainly due to the limited amount of resources that provide these environments predominantly xerophytic.

has a stable climate of the middle zone influence on the location of the further development of the vegetation of the western slopes?

is interesting to note the coincidence of the stability zone climate between 2000 and 3000 m found by Franke and Valencia (1984) with the most developed area of \u200b\u200bthe vegetation of the western slope. Weberbauer (1945) notes that between 2500 and 3200 m are the places with dense vegetation on the western slopes and all of the dry forests of fog are known as isolated remnants (Koepcke HW 1961, Valencia 1990, Franke 1994) are located in this altitude range.

These dry forests of fog, which have been visited most in one hand and wn many cases no one has returned in the last 29 years are: Department of Huancavelica: Canchina and Manzanallo, Department of Lima: Zárate (Figure 9), Lindsay (Figure 10) and Groove, Department of Ancash: Yana , Colcabamba, San Damiano, Wiñapajatun, Noqno (Figure 11) and Cochabamba (Figure 12), Department of La Libertad : sores (Figure 13) and the Department of Lambayeque: Chinaman (Figure 14).