Te. Fulbright et al., EFFECTS OF NURSE-PLANT CANOPY TEMPERATURES ON SHRUB SEED GEMINATION AND SEEDLING GROWTH, Acta oecologica, 16(5), 1995, pp. 621-632
Conversion of upland grasslands to thorn woodland in southern Texas ha
s occurred in part through initial colonization by Prosopis glandulosa
followed by establishment of Celtis pallida and other shrubs beneath
P. glandulosa. We tested the hypothesis that temperatures characterist
ic of the microenvironment under P. glandulosa enhance seed germinatio
n and seedling growth of C. pallida and inhibit germination and seedli
ng growth of Acacia smallii. Soil temperatures beneath P. glandulosa i
ndividuals and in adjacent herb-dominated interspaces between canopies
and effects of interspace and canopy temperatures on germination and
seedling growth of the 2 shrub species were determined. Greatest germi
nation of C. pallida seeds occurred at temperatures (25 and 30 degrees
C) within the range of mean monthly soil temperatures (25 +/- 0.3 to
31 +/- 5 degrees C, (x) over bar +/- SD) under P, glandulosa during Ma
y and June, the peak period of seedling emergence in the field, Exposi
ng unimbibed C. pallida seeds to 50 degrees C, similar to maximum temp
eratures (49 +/- 6 degrees C) beneath canopies during the peak period
of C. pallida seed dispersal by birds during July and August, increase
d germination 62%. Aggregation of C. pallida beneath P. glandulosa may
occur in part because birds disperse seeds beneath P, glandulosa wher
e maximum summer temperatures reduce seed dormancy and mean May-June t
emperatures favor germination. Absence of C. pallida in interspaces ma
y result in parr from lack of dispersal by birds and inhibition of ger
mination by high temperatures characteristic of interspaces.