Keiiner Herrinotiti

REFER ENCES

I , BUDYKO, M. I. (1956): Tepluicioj ßar(crns Zenmoj Potverclinosri, Leningrad, 225 p. 2. BUDYKU, M.T. (1963): Atlas Teploiuugo Balnti.s.sa Zeninogo Schorci, Moskva. 3. FLOIIN, H. and OECKEL, H. (1956): Geopliys. Mag. (Tokyo) 27, 527-532. 4. FLOHN, H., HENNING, D. and Konm, H.C. (1956): Bunner Meteor. Aúh~indl., 6. 5. FLOHN, H. and FRAEDRICH, K. (1969): Meteor. Riiiidschuii, 19, 266-373. 6. FLOIIN, H. (1968): Wetter ritid Lehen 20, 181-191. 7. FLOHN, H. (1969): Erdkunde 23, 205-215. 8. FKAEDRICII, K. (1968): Arch. Meteor. Geophys. Biold., A 17, 157-166. 9. FRANKENHERGER, E. (1960): Ber. DI. Wetterdiemr, 73. 10. HAVLIK, D. (1969): Freibiirger Geogr. Hefte, 7. 11. HUTCHINCS, J.W. (1957): Qriart. Joiirn. Roy. Meteor. SOC., 83, 30-48. 12. KESSLER, A. and MONHEIM, F. (1968): Erdkritide, 22, 275-383. 13. KUNG, E.C., BRYSON, R.A. and LENSCHOW, D.H. (1964): Mo?ith/y Weather Review, 92,

14. MOLLER, F. and de DARY, E. (1951): Arch. Meteor. Geoph. Biold., A4, 142-155. 15. RASMUSSON, E. M. (1968): Monthly Weater Review, 96, 720-734. 16. SAKKER, R. P. (1966): Monthly Weather Review, 94, 555-572. 17. SCHNEIDER, H. J. Die Erde, Z. Ces. Erdk. Berlin. 100, 266-286. 18. STARR, V. P., PEIXOTO, J.P. and Coll.: Tellus, 10 (1958), 189-194; 37(1965), 463-475; Pageoplr.

19. STRUENING, J. O. (1970): Diss. Uniu., Bonn. 20. TROJER, H. (1959): Cenicafé, 10, 289-373. 21. TROLL, C. (1952): Bonner Geogr. Ahhandl., 9,124-182. 22. WErscHET, W. (1969): Die Erde, Z. Ces. Erdk., Berlin, 100, 287-306. 23. USSR Committee for the International Hydrological Decade (1967): Water Resources and

24. Secr. Gen. Est. Americanos (1969): Cuenca del Rio de la Plata. Investario de Datos Hidrolo-

25. WUNDT, W. (1953): Gewüsserkunde, Berlin, 320 p. 26. KELLEn, R. (1961): Gewü,rser und Wasserharishalt c h Festlandes, Berlin, 520 p.

543-564.

75 (1969), 300-331. I

Water Budget of the USSR Areu, Leningrad.

gicoc y Climatologicos, Washington D. C.

Vertically differentiated water balance in tropical high mountains - with special reference to the Sierra Nevada de Santa Marta/Colombia

Reimer Herrmann

SUMMARY: From the example of the northwestcrn Sierra Ncvada de Santa Marta/Colombia the vertical variation of thc water balance of tropical high mountains in lee of the trade wind can he sccn. The prccipitation increases according to height from sea level ( P = 350 mm) to a height of 1 660 m (P = 2 500 mm). Abovc this the precipitation measured in a raingage falls at less than P = I 800 mm in about 4 O00 m. By fog drip (P,.-220 nini) the height or maximuin prccipitation is assumed to bc raised to 2 300 rn. Thc runoff incrcaccs gradually from RO O min at sea levcl to ahout RO = 2 O00 mm at 2 200 in, then thc runoff decrcascs to RO = 1 400 inm at 3 600 m. The cvapotranspiratioii has its maximum A E = 1 260 mm at a height of I 300 ni. Both upwards

262

and downwards it decreases because of low tcmperature in Lhe first case and because of lack of moisture in the second case to AE= 400mm and AE= 350 mm respectively. The dry season runoff increases from DSq = O Is-’ km-* at sea level to DSq = 24-30 Is-’ km-2 at a height of 2 200 m and upwards it decreases to DSq = 5 Is-’ km-’.

In the Páramo (3 600 mj there occurs a dry period with soil moisture pressure of pF 2.5-3.6. Below in the tropical ombrophilous cloud forest (2 100 m) even in the dry season pF 2.5 is not surpassed. Further downward in the tropical ombrophilous montane forest ( 1 150 m) pF 2.5-3.6 occurs in the dry season. But under all these formations the period of < pF 2.5 is predominant. Under the drier formations down to the sea level high soil moisture pressure >. pF 4.2 occurs in lengthening periods. Even in the wet, season the dricst formations from the drought deciduous forest to the succulent drought deciduous shrublaiid show high soil moisture pressure of > pF 4.2 in periods extending from a few days to one month.

Capillary supported Aow occurs at positive pressure gradients in soils witli a high groundwater table in the alluvial plains.

BALANCE H YDRO L O GIQ UE VER TI CA LEMENT DIFFERENCIEE DANS LES HAUTES MONTAGNES TROPICALES - AVEC REFERENCE SPECIALE A LA SIERRA NEVADA DE SANTA MARTA (COLOMBIE) RESUME : De l’exemple dc la Sierra Nevada de Santa Marta (Colombie) du Nord-Ouest, la varia- tion verticale du bjlaii d’eau de hautes montagnes tropicales du côté opposé au vent alizé peut étre étudiée. La précipitation augmente avec la hauteur à partir du niveau de la mer (P = 350mm) jusqu’i une hauteur de I 660 ni (P = 2 500 mm). Au-dessus de cettc dernière hauteur, la précipitation mesurée à un pluviomètre tombe a moins de 1 800 min à environ 4 O00 ni. Par brouillard (PF-220 nun) la hauteur de la précipitation maxima est supposée s’élever à 2 300 nini. L’écoulement s’élève graduellement de RO = O mm au niveau de Ia mer i environ RO = 2 O00 inm à 2 200 m, alors l’écoulement diminue à RO = 1 400 mm à 3 600 m. L’évapotranspiration a son maximum AE = 1 260 mm à une hauteur de I 300 m. Tant vers le haut que vers le bas, eJle décroît par suite de la basse température dans le premier cas el du fait du maiique d’humidité dans le second, à AE = 400 mm et AE = 350 nim respectivement. L’écoulement resultant d’un mois sans précipitation croit de DSq = O Is-’ km-’ au niveau de la mer à DSq = 301s- ’km-’ a une hauteur de 2 200 m et plus haut, il décroît a 5 Is-’ km-’. Dans le Páramo (3 600 m) il se produit une saison sèche avec des pressions d’humidité du sol

de pF 2,5-3,6. Plus bas dans la forêt tropicale ombrophile de nuage (2 100 m), niéme en saison sèche pF 2,5 n’est pas dépassé. Plus bas encore, dans la forêt ombrophile de montagne (1 150 m) pF 2,5-3,6 se produit cn saison sèche. Mais en dessous de ces formations, la période de < pF 2,5 est prédominante. En dessous des formations sèches, jusqu’au niveau de la mer, une haute pression de I’humiditk du sol ; pF 4,2 se produit en périodes qui s’allongent. Même en saison humide, les formations les plus sèches, comme la forêt et les buissons à feuilles caduques, montrent de hautes pressions d’humidité du sol avec < p H 4.2 durant des périodes s’étendant de quelques jours à un mois.

U n écoulement supporté capillairement se produit pour des gradients de pression positifs dans des sols avec un niveau phrkatique élevé dans la plaine alluviale.

BALANCE HIDROLÓGICO VERTICALMENTE DIFERENCIADO

A LA SIERRA NEVADA DE SANTA MARTA - COLOMBIA

RESUMEN: Tomando como ejemplo la parte noroccidental de la Sierra Nevada de Santa Marta en Colombia, puede observarse la variación vertical del balance hidrológico de lx altas montañas tropicales, situadas a sotavento de los vientos aliseos. La precipitación aumenta’ en función de la altura a partir del nivel del mar (P = 350 mm) hasta una altura de 1 660 m (P = 2 500 mm). Por encima de dicha altura, la precipitación medida en el pluviómetro desciende a menos de P = I 800mm aproximadamente 4 000m. Mediante un goteo de la niebla (P, 220mm) la altura de la precipitación máxima se supone que alcanza 2 300 m. La escorrentia aumenta gradualmente a partir de RO = O mm al nivel del mar, hasta RO = 2 O00 mm a 2 200 m de altura, a partir de cuyo valor la escorrentia disminuye a RO = 1 400 mm a 3 600 m. La evapo- transpiración presenta su valor máximo AE = 1 260 mm a una altura de 1 300 m. Tanto hacia arriba como hacia abajo, los valores decrecen, debido a la baja temperatura en el primer caco

EN LAS ALTAS MONTAÑAS TROPICALES, CON ESPECIAL REFERENCIA

263

Reimer Herrmann

y a la falta de liuniedad en el segundo caso en que AE = 400 mm y A E = 350 mm rcspectiva- mente. La escorrentia dc la estación seca aumenta de DSq = O Is-' km2- al nivel del mar, hasta

DSq = 24- 30 Is-' km-z a una altura de 2200 m, y a partir de esa altura disminuye a DSq = 5 Is-' km-2.

En el Páramo (3 600 m) se produce un periodo seco con tina presión de humedad del suelo de pF 2.5 - 3.6. Más abajo, en la floresta tropical cubierta de nubes (2 100 m) no se sobrepasa el valor de pF 2.5, incluso durante Ia estación seca. Más abajo aún, en el bosque montañoso tropical (I 150 m) los valores pF 2.5 - 3.6 se producen durante Ia estación scca. Pcro, en todas esas formaciones, el periodo inferior a pF 2.5 es el predominante. A medida que se desciende hacia el nivel del mar, bajo formaciones más secas, se produce; durante periodos más largos una presión superior de la huniedad del suelo que sobrepasa pF 4.2. Incluso durante la estación de las lluvias, las formaciones más secas de los bosques de vegetación seca transitoria y las malezas transitorias secas conservan una presión de la humedad del suelo superior a pF 4.2, durante periodos de tiempo que se extienden de unos cuantos dias a un mes. EI flujo por capilaridad se produce en gradientes de presión positivas en suelos que tienen

un alto nivel de agua subterránea en las llanuras de los terrenos de aluviones.

PACEIPEAEJIEHHE BOAHOI'O BAJIAHCA lT0 BbICOTE B BbICOKOI'OPHbIX TPOIIHYECICHX PAHOHAX, B YACTHOCTEI B CbEPPA-HEBAZA-Re-CAHTA-MAPTA (KOJIyM6HH)

A H II o T a q n : Ha npuMepe Ce~epo-sana~aoCi YacTu Cbeppa-HeBaAa-Ae-CaHTa-

KoropHLIx Tponusecwm paüoaax c T~IJIOBOZI CTO~OH~I naccaToE. II0 Mepe noAzeMa Mapa (KOJIyM6EiR) no~a3a~o H3MeHeHHe EOAIIOï'O 6ajra~ca C EbICOTOk E EbICO-

0CaAY.H BO3paCTa€OT C 350 M M Ha YpOEHe MOPR AO 2500 M M Ha EhICOTe 1600 'C. BhIme 3TOg OTMeTKU, npU6JIH3IITeJIbHO Ha EbICOTe 4000 M, II3MepeHHbIe OCaAKU COCT3,EJIRH)T MeHee 1800 MM. ECJIK EbIYeCTb OCaAKH, oópa3y~oquec~ 3a CYeT TyMaHa (OKOJIO 220 MMI), TO MaKCUMaJILHOe KOJíIIYeCTBO OCanKOB COCTaEIIT OKOJIO 2300 31. CTOK IIOCTeneHHO yBenH~EaeTCR OT 0 MM Ha YpOBHe MOPR np116nu3mem~o 2000 MM Ha BbICOTe 2200 M, 3aTeM OH yMeHLIiIaeTCR AO 1400 M M Ha BbICOTe 3600 M. Ma1:CEiMaJILHaR EeJIII~NWa CYhlMapHOrO IlCIïapeHUR (1260 MM) Ha6~11aAaeTcR U R BbIcoTe 1300 M. Bbrme u H m e ~ T O Ü OTM~TKU OHO CHEIjKaeTcIi - B nepEoM cnyrae go 400 MM, B p e 3 y n ~ ~ a ~ e rroIiuxeHnx TeMnepaTypbI, EO BTOPOM - AO 350 MM U3-3a HeAOCTaTKa EnalTi. CTOK EO BpeMR CyXOFO Ce3OIIa BO3paCTaeT C 0 II& YpOEHe MOPR AO 24-30 JI/CBK/KM2 Ha EbICOTe 2200 M; BbIIiIe 3TOÜ OTMeTXH CTOY, YMeHb- ILIaeTCR AO 5 JI/CeK/KMz. B JIapaMo (3600 kl) AasneHHe IIOsEeHHOg maru B cyxoü nepHon pamo 2,5 - 3,6 p F

EbIcoKoropoHoro neca (2100 M) A m e B cyxok ce30~ EeJínma p F He npesbmaeT (IIOKa3aTeJm COCmeÜ CIIJIbI IIOYEbI) . Kuxe, E 30He ~narom6uEoro TpOnII4eCKOrO

2,5. E q e m e , B 30He TpOIIUYeCKOk FOpWOR PaCTUTeJIbHOCTU (1150 M) EeJIUYMHa pF B CyXOk Ce3OH COCTaEJIIieT 2,5 - 3,6. H O BCe X e EO ECeX BTIIX paCTUTeJILHbiX @OpMaqURX ~auóonee IIpOAOJIXUTWIhHbIM REJIReTCEI nepUOA C BeJIWIKHOB pF < 2,5. B boxee CyXUX C@OpMaqURX Ha MeHbUIIIX BbICOTaX BIIJiOTb AO YPOEHR MOPR B TEYeHUe AJIHTeJIbIlbIX nepHOAOE Ha6JI€OAaeTCR ELICOKOe AaBJieHHe IIOrIEeIIIIOk EJIaITi IIpU PF > 4,2. EO BJTaXHbIg Ce30H B 3aCyIiIJíUBbiX 30HaX, PAe npOIICXOAHT IIepeXOA OT 3aC~OyCTOk~€TBbIX JíKCTOIIanHhIX JIBCOB I: 3aCYXOYCTOÜ9IiEbIM JIIICT- EeIIHbIMl KYCTaPHIIKaM EbICOICOe AaEJIeHHe IIOrEeIIHOk BJIaFU (pF > 4,2) ~aónm- AaeTcx B TeyeHHe nepHoAoB, ~ ~ ~ a q u x c ~ OT xecKonIiI:m AHeü AO OAHOrO Mecnqa. H a aJImoEuaJImhIx pamimax p.rmHtearre maru E n o w e npoucxoAm npx nono- XUTCJIIbIIbIX rpaAUeHTaX AaBJIeHUii E n09BZL.X npII BJdCOKOM CTDRHIiH I'PYHTOEbIX BOA.

1. INTRODUCTION

The hydrological vertical zonation of tropical high mountains depends on their situation within the general circulation and on the climatic diflercntiatioii causcd by the local

2 64

Verticuliy diflerentiated water balunce in tropical high mountains

exposure. Thus there exists threedimensionally a variety of dïfferent hydrological altitu- dinal zones (C. Troll 1959: 17). In the following text the lee type sequence of the trade wind zone will be explained taking as an example the north western Sierra Nevada de Santa Marta/Colombia. The Sierra climbs steeply direct from sea level to a height of approx. 6 O00 in (fig. 1).

The profile bcgins with the region of the driest climate on the Caribbean coast. This dry cli- mate is caused by dry, hot katabatic winas (R. Herrmann 1970b), stress-differential induced divergence (R.A. Bryson and P. M. Kuhn 1961) and leeside divergence (F. Lahey 1958). As the dry katabatic winds are limited to the coastal heights and the floodplain of the Río Gaira in the profile, and as at growing distance from the coast the stress-differential induced divergence and the leeside divergence diminish, there develops strong slope convergence connected with higher tendency for rainfall. By means of the least square method the vertical variation of rainfall may be described by a parabola (R. Herrmann 1970a: 64):

P = 40f26H-0,8H2

P = precipitation (cmj

H = height (100 m) ,

which makes it easy to find the height of maximum rainfall at 1 660 m. BLI~ above this in the zone of tropical ombriphilous cloud forest there is additional rainfall by fog drip, which indicates that the hydrological effective maximum may be at a height of about 2 300 m. The whole survey was made among natural plant formations or among secondary

plant formations similar to the natural ones. The description of plant formations is in accordance with the physiognomic-ecological classification of H. Ellenberg and D. Mueller Dombois (1965/1966: 21-55). During the water year 1967 (March 1967-February 1968) rainfall and runoff were

measured in 5 small river basins in the course of the hydrological profile. Because of the marked dry season it is possible to solve the water balance equation

AE = P-RO+AS

where theIexpression AS =:O AE actual evapotranspiration; P precipitation; RO runoff; +AS storage.

Besides this in two meteorological stations at 23 m (Sta Marta) and 2 100 m (CVM- San Lorenzo) above sea level, measurements were taken of rainfall, class A pan evapora- tion, minimum and maximum temperature, relative humidity, windvector, and potential evapotranspiration (PE) in a lysimeter (only at Sta Marta). In addition, soil moisture pressure was measured every week among typical plant formations using the method of McQueen and Miller (1966, la-10: 1-11). In a column of soil with a free water surface at the base and no evaporation, the mois-

ture distribution will be in equilibrium when:

$ , = g e h

265

Reimer Herrniutiri

th, soil moisture potential at equilibrium; g acceleration of gravity; h height.

FIGlJKh I . Locution of the frofik

266

If under natural conditions, at the height h there is a measured potential I/,,, the following relations will result: I), < the soil moisture is moving downward; I), > IC/, soil moisture is moving upward; ihm = I)e equilibrium.

These relations may also be expressed in terms of soil moisture pressure. In all accessible rivers one month after the last rainfall the dry season runoff (DSq in

Is-' km-') was measured. The verlical zonation of the water balance follows the vertical zonation of plant

formations beginning at sea level. The soil moisture pressure dynamics are explained by means of isopleths (fig. 3) and in an abbreviated version used by A.A. Rode (1966, B: 14).

2. THE WATER BALANCE OF THE ALTITUDINAL ZONES OF THE NORTH- WESTERN SlERRA NEVADA

2.1 SUCCULENT DROUGHT-DECJDUOUS SHRUBLAND

In figure 3, H soil moisture pressure dynamics are shown in a 30 c m deep soil above shists with a cleavage parallel to the surface. The plant formation is a low Haernntoxycylon- Melochia-Lippia semidesert shrubland of 80 c m height (described by R. Schnetter J 969: 289-302). Because of the low water capacity of the soil (detritus and rock are practically impervious) merely a few intensive showers are able to fill the soil. Thus in August there appears in short periods soil moisture pressure of < pF 1.8 and because of $," < the there occurs downward flow of water. In the main wet season with soil moisture pressure at < pF 2.5 there is downward flow, partly as overland runoff. Ih the dry season dry conditions with > pF 4.2 follow quickly after. Some plants maintained their turgescent leaves even up to the high pressure of pF 4.8.

At Santa Marta the following water balance was measured:

M A M J J A S O N D J F Year

P O I I I 40 136 26 50 62 25 O O O 351 (mmj PE 267 222 189 240 257 248 231 226 252 219 282 269 2971 (mmj

It is supposed that there is no groundwater flow and only a short distance overland flow. As there is PE> P for each month it should be P = A E = 351 m. This is sup- ported by a DSq = O Is-' km-*.

2.2 OPEN HALOPHYTIC ALLUVlAL FOREST AND SHRURLAND

Southeast of the coastal heights follows the floodplain of the Río Gaira where the water balance is governed by the depth of the water table and the capillary conductivity of the sediments. Should water flow in liquid phase to lhe surface, then there is a salt concentra- tion in the top soil. Because of this íhere are electrical conductivities (L) of the saturation extract of L > IO4 pS cm-' and a pH (KCl) > 8.5. Thus only open stand of shrubs with halophilous plants (Bnris ~nuiirima L.) grow here. With smaller capillary conductivity

267

Reirtrer Herrmann

(or deeper groundwater table) therc occurs a salinization in the lower soil profile and an open alluvial forest with a few halophilous plants will grow there.

? .

E Y

Frc;unE 2. FíydroloRical Profile ofllie Sierra Nevudo de Saritci MrrrtnlCalomhiri, S. A. 15/67/58

268

Vertically differentiated waler balance in tropical high mouri~oins

0 -

3 -

6 -

9 -

17 - 15 - 78 -

A depth [dm] A S 0 N n J F ''

. . . . .. . 1 . '. ........

< 1,a

B

_.._.. 1.8 ___- 2.5 - 3.6 I 4.2 pF

FIGURE 3A-D Soil inoisriire pressrire dvnrrntics (Aiigrst 1967-March 1968 in pF, depth in drn) A Soil developed froni luiid slide muterial [inder tropical ombrophilous cloiidforest

B Soil developed froin Imid slide material under tropiccil onibrophiloils montane forest

C Colluviril soil deueloped from grtriiodiorite detriliis cinder tropical euergreen seasonal

D Soil deoeloped/rorn grccriodiorite detriíiis under tropical seniidecidiioris loialnnd fores

(2 100 m)

( I 150 m)

submontane Jorest

The soil nioisture pressure dynamics of figure 3F are measured in soil salinized to a depth of 60 cm (L > 0.5. 103pS cm-'). Even at full saturation in the wet season there occurs in addition to a matric suction

of < pF 2.5, also a solute suction of n > pF 4.2. This was computed by the empirical formula of K. Kreeb (1964: 101):

x = 0.036.L

L electrical conductivity of the saturation extract (pS cm-'); n solute suction (at).

The short phases of downward movement when II/,,, < t,be and < pF 2.5 are clearly to be seen after storms. In the rest of the time with $, > t,úe there occurs upward movement. Figure 3G shows that under open alluvial forest the flow of capillary supported water

stops at the lower soil where the salinization occurs. In the upper soil the movement goes on in the gas phase because of the high pressure in the dry season, which also causes wilting of the forbs.

269

Reinirr Herrniaii

3 -

6 -

7.3 DROuGwr DECIDUOUS TROPICAL LOWLAND IOl<F,ST (up lo - 150 ill) This formation covers the lower bordering heigh ts of the Sierra. The soil moisture pressure was measured in a colluvial soil of granodiorite dctritus under drought deciduous low- land forest with Pereskiu colombiana Br. LI. R (fig. 3E). The low rainfall of P = 450 mm could only lower the soil moisture pressure of the

subsoil for a short time, thus and < pF 2.5 causing downward movemenl of water. Most of the time the soil moisture was bound with > pF 4.2 not allowing trans- piration of the plants. Even in the wet season in the lower soil profile there was a high soil moisture pressure of > pF 4.2 for a long time. There was very little runoff and also the DSq = 0.5 Is-' kmP2 was very low. The

class-A pan evaporation (E) in the same plant formation but outside the profile has a mean of E = 4.2 mm day- in the wet season, in the dry season of E = 6.2 mm day- ' . By means of the soil moisture pressure increase and the desorption curve mean daily

A E = 1.3 rnm day-' was calculated at the beginning of the dry season (30.11-28.12.67).

<

O

6 .

9

12.

2.4 TROPICAL SEMIDECIDUOUS LOWLAND AND EVERGREEN SEASONAL SUBMONTANE FOREST (150-800 m)

--< 3 -

--- --- ________- -------_ ................................... -._ ........... ..... .....

------a\-

In this altitudinal zone there have developed deeply weathered granodiorites and medium weathered schists with sufficient storage capacity for the precipitation. For both plant formations the water balance is P = 1 i80 mm, RO = 274 mm, AE = 906 mm.

u .

12 -

A C II N O J F M

> 4.2

q7 J L _ _ _ - - _ _ _ _ _ _ _ _ _ - -- _ _ _ _ _ _

............................................................

-w

15 J

....... 1.8 _ _ _ _ 2.5 - 3.6 - 4,2 PF

Fiaii~~ 3E-lì Soil nioislure pressure dynamics (Aiigrrsl 1967-Murcli 1968) in pF, deptli in dm. E Colliroicil soil ùeoeloped froiii grriiiocliorite detritri,s wider droriglit decidi~~ir.r loiulu nd

F Alliioirrl .scilinized .soil under Batis maritima L. C AlIrroicil soil irtider crlkiuicrl forest H SIr(r1Ioii; soil obove schists iriidcr ci .seniirleser/ sliriih foriwiiotr

Jorest

270

Vertically differeritinted tvuter holritice iiz /rupictrl hgii rnurrrirriiils

In the upper moister region of the submontane forest there was measured a DSq = 5 - 10 Is- ’ k m - ’, whereas in the lower and drier region of the semideciduous forest only DSq = 0.5- 1 Is-’ km-’ was measured. Under this semideciduous forest in a soil developed from granodiorite detritus the

following soil moisture pressure dynamics were measured (fig. 3D): during the “short dry season” in August the soil was dried to a depth of > 150 cni with > pF 4.2. The sub- sequent less intensive rains up to the beginning of October only lowered the pressure to pF 3.6-4.2. But even in the main wet season the moisture supply was never sufficient to cause ibn, < lhe for the whole profile, thus there was no groundwater recharge. From December onward the soil dried very quickly reaching > pF 4.2 in January. By means of the soil moisture pressure increase and the desorption curve the mean

daily A E was computed as follows: 1. beginning of dry season (2.17.-25.12.67) AB = 4.6 mm day-’; 2. 3/4 of dry season (2.12.67-10.2.68) AB = 1,7 mm day-’. Under the submontane forest in a colluvial soil developed from granodiorite detritus

during the wet season lb,,, < $e was frequently observed with < pF 2.5 indicating down- ward movement of soil moisture. In contrast to the dynamics under semideciduous forest the phase > pF 4.2 is much longer. Inspite of the measuring site being the middle slope, at the end of October soil groundwater appears in the lower profile. Beginning in mid January and starting in the top soil high soil moisture pressure of > pF 4.2 occurs. Because of IC/, > $e there follows an upward movement of soil moisture mostly in the gas phase. The forbs are wilted during this part of the year and about 20% of all trees lose their leaves.

A E = 3.7 mm day-’ is computed (30.11.67-10.1.68). From the soil moisture pressure increase and the desorption curve mean daily

2.5 TROPICAL OMBROPHILOUS MONTANE FOREST (800-1 800 ln)

According to whether schists or granodiorities form the slopes, a thick or thin layer of land slide material lies on the detritus, but not lower than 1 500 m. The natural plant formation on wide stretches is transformed into coffee plantations with shading trees (Inga spriria cf., Willd). Jn a small river basin the following water balance was measured:

M A M J J A S O N D J F Year

RO 32 42 45 57 84 56 96 81 73 62 69 69 718 m m P 1 114 139 359 318 210 382 252 167 26 6 9 1983 mm AE 1265 rnm

For January and February a mean daily AE = 2.6 mm day- was computed by means of soil moisture pressure increase and the desorption curve. Together with the above balance there is a mean daily AE = 3.6 mm day- for the rest of the year. The soil moisture pressure dynamics (fig. 3B) show that the conventional wilting point

,of pF 4.2 is not surpassed. In the wet season with < tbc and < pF I .8 there is rapid .downward movement of water. In the dry season for a short period with ibn, > iI/, water moves upward. At the high pressure of pF around 3.6 some of the hygrcphilous forbs appeared to be wilting. At this time the DSq = 10-15 Is-’ km-’ was still higher than in .the altitudinal zones below.

27 1

Reimer Herrmunti

2.6 TROPICAL OMBKOPHILOUS CLOUD FOREST (1 800-2 800 m)

In landslide material over schist and granodiorite detritus, soil types similar to pseudo- gleys have developed. The thick evergreen cloud forest, which is at the upper limit about 2-3 m high and at the lower limit 15-20 m is partly cleared and then covered with thick “Kikuyu ” -grass. During the wet season with I),,, < I) e and < pF 1.8 the soil is percolated by free gravitational water. Only for short periods in the dry seasons a higher soil moisture pressure of pF 1.8-2.5 occurs in the top soil (fig. 3A). In a small river basin the following water balance was measured: RO = 2 O08 mm, P = 2 316 m m . If one estimates the PE from G. Stanhill’s (I 958) formula: PE = 0.83.B (mm); E = class A pan evaporation, it fallows PE = 0.83.636 = 529 rnni. As under these moisi condition PE = AE, the computed PE = AE is higher than the difference of P- RO. There are two possible ways of explaining this discrepancy: first f AS + O, or secondly there is a higher rainfall as measured by the rain gage in form of log drip. There are reasons for accepting the latter explanation and then the balance shows as follows: RO = 2 008, AE = 529 111111, P = 2 537 mrn. Of course, these are rough estimates. Because of the low AE the DSq = 24- 30 1s- km-2 is very high. The monthly balance of RO (measured in a weir), P (rain gage) and E (class A pan)

is a follows:

M A M J J A S O N D J E Year

RO 35 60 101 386 264 200 396 202 150 118 61 35 2008 mm P 2 138 174 462 321 229 496 281 166 22 12 13 2316 mm E 71 39 38 42 45 64 40 41 36 77 83 60 636 rnm

2.7 PARAMO (> 2 800 m)

Under the influence of man lhe plant formation of the páramo has spread downward to 2 800 m above sea level. O n the steep slopes flat podsolic “rankers” have developed above granite without a deep detritus. Outside the profile there are raw soils on moraines. Taking into consideration the mean annual temperature of 5,572 (measured 50 c m deep in the soil) and the mean annual rainfall of P = 1 800 mm (estimated by means of the regression parabola) the water balance was estimated by means of L. Turc’s formula (R. Keller 1961: 350): P = 1 800 mm, RO = 1375 mm, AE = 425 mm. The formula of C. W. Thornthwaite (1957) gives PE = 412 mm. Because of the high relative humidity the computed values of AE and PE may be too high. Thus the estimated water balance would probably be RO = 1 400 mm, AE = 400 mm and P = I 800 mm. Contrary to the description of Colombian páramos by J. Quatrecasas (1968: 163) the soil is not all the time fully “soaked”, but there is a distinct dry phase of pF 2.5-3.6 when > I)~. By means of the desorption curve and the soil moisture pressure increase at the end of January A E = 1,l mm day-’ was computed. The comparatively high soil moisture pressure of the dry season and the good drainage of the soils are held responsiblc for the absence of Espeletia spp., which J. Quatrecasas considers to be the essentially typical plant of the páramo. The DSq< 5 Is-’ km-’ is by no means as high as in thealtitudinal zoneof the cloud

jorest.

212

Verticuily diflerentierted iuuîer baleince in iropicui high muiriitains

ACKNOWLEDGEMENT

The author gratefully acknowledges the receipt of a grant from the German Research Association in respect of this work and the hospitality of the Instituto Colombo-Alemàn in Santa Marta.

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