Implementation of geophysical methods for spatial niche
description
In each of the 12 experimental plots, we determined the vertical extent
of soil, regolith, and massive rock, the presence of rock fractures, as
well as the horizontal and vertical distribution of different root
diameters using a ground penetrating radar (GPR, MALÅ RAMAC X3M –ProEx
system coupled to an inspection wheel and shielded antennas: 500 and 800
MHz). We also generated 12 profiles with the electric radar tomography
(ERT, SYSCAL KID SWITCH-24, IRIS instruments, with a 24-multi-electrode
switch box) (four for each stand type) on four dates (October 2013,
December 2013, February 2014 and May 2014). In each ecohydrological
period, we monitored the two-dimensional (20 x 5 m area) water
distribution at 5 points separated at equal distances along a 25 meter
transect considering the different substrate layers with ERT. The
geophysical methods employed in this study were described in detail in
Rodríguez-Robles et al. (2017). All roots
detected in the radar profile along each 25 m transect were grouped into
five root diameter classes (< 3.0, 3.0–4.0, 4.0–5.0,
5.0–6.0 and > 6.0 cm). Finally, for calibration purposes,
individual roots (total of 76) were excavated to determine their depth
and diameter in situ.