Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

Ecological Studies of Chaparro (Curatella americana L.) and Manteco (Byrsonima crassifolia H.B.K.) in Venezuela

Ernesto Foldats and Edgars Rutkis
Journal of Biogeography
Vol. 2, No. 3 (Sep., 1975), pp. 159-178
Published by: Wiley
DOI: 10.2307/3037988
Stable URL: http://www.jstor.org/stable/3037988
Page Count: 20
  • Download ($42.00)
  • Subscribe ($19.50)
  • Cite this Item
Ecological Studies of Chaparro (Curatella americana L.) and Manteco (Byrsonima crassifolia H.B.K.) in Venezuela
Preview not available

Abstract

The principal physical factors determining the phenology of Curatella americana (chaparro) are the annual variation of the water table, the periodic fires of the savanna grassland and the herbivorous insects, which constitute a serious plague each year beginning in the month of July. The high water table during the months of August and September, and its quick rise to such levels (in 2 months), induce anaerobic conditions, and give rise to high mortality rates in most of the young absorbing roots of chaparro. This phenomenon is transmitted in the plant in the form of senescence of the leaves, visibly characterized by the chlorosis of their blades. The most active leaf fall of chaparro occurs during the months of November and December. During December, the principal floration occurs, along with an intensive production of new shoots. The maturation and the sclerosis of the leaves is over in 30-40 days, and the mature size of the shoots is reached in 60-80 days. In July, the production of new shoots is hindered because of the damage to tender sprouts by herbivorous insects. The chaparro change all their leaves yearly. Fire induces the production of a juvenile form of shoots in the trees. These shoots are about double the normal length, with the leaves approximately twice as big as those in shoots produced without the influence of fire. The total annual transpiration (by unit of surface or weight) of the individual leaves is higher in manteco (Byrsonima crassifolia) than in chaparro, however chaparros transpire more from the end of May to the first half of July. In the Biological Station, chaparros and mantecos live in the same macroclimate. Thus the different patterns of their annual transpiration rates (for individual leaves) are not climatically induced; the dominant control is variation in soil water table. There is generally a direct relationship between diurnal variations in transpiration rates of the two species and the intensity of daylight, mantecos being more sensitive to this than chaparros. However, the actual amount of diurnal transpiration is determined by water conditions in the soil. In addition, chaparro, during the driest months (December-April), controls its transpiration, and during the hours of brightest daylight, its transpiration is lower than before and after those hours. The annual transpiration curves for both trees have two maxima and two minima. In the case of chaparros the two peaks are almost of the same magnitude, but there is a notable difference between the two in the case of mantecos. The second annual decline of transpiration rates for the two species is not the result of lack of water in soil, but is due to an excess of it, which creates anaerobic conditions and retards water uptake in the roots. Since the total leaf surface in chaparro is considerably larger than that of manteco, the transpiration rates of whole chaparros are higher, despite the lower transpiration rates of the individual leaves of chaparro. The leaves of chaparro generally have more water and less dry weight than those of manteco.

Page Thumbnails

  • Thumbnail: Page 
159
    159
  • Thumbnail: Page 
160
    160
  • Thumbnail: Page 
161
    161
  • Thumbnail: Page 
162
    162
  • Thumbnail: Page 
163
    163
  • Thumbnail: Page 
164
    164
  • Thumbnail: Page 
165
    165
  • Thumbnail: Page 
166
    166
  • Thumbnail: Page 
167
    167
  • Thumbnail: Page 
168
    168
  • Thumbnail: Page 
169
    169
  • Thumbnail: Page 
170
    170
  • Thumbnail: Page 
[171]
    [171]
  • Thumbnail: Page 
[172]
    [172]
  • Thumbnail: Page 
173
    173
  • Thumbnail: Page 
174
    174
  • Thumbnail: Page 
175
    175
  • Thumbnail: Page 
176
    176
  • Thumbnail: Page 
177
    177
  • Thumbnail: Page 
178
    178