ecosystem services to and from north american arid ... - Conabio

IV SIMPOSIO INTERNACIONAL DE PASTIZALES
San Luis Potosí, S.L.P. México; 22 al 24 de agosto de 2007
Artículos in extenso
Área temática: Productividad
Table 1. Seasons of NDVI measurements and forage harvest in pastures of the Eastern
Research Station, near Haskell, OK.
Season/Year † Pasture
Spring 2004-2005 1
Spring 2004-2005 2
Summer 2004-2005 1
Summer 2004-2005 2
Summer 2004-2005 3
Summer 2004-2005 4
Fall 2005-2006 1
Fall 2005-2006 2
Fall 2005-2006 3
Fall 2005-2006 4
Spring 2005-2006 1
Spring 2005-2006 2
Spring 2005-2006 3
Spring 2005-2006 4
Summer 2005-2006 1
Summer 2005-2006 2
† Two measurements in spring 2004-2005 and two in the
summer of 2005-2006 are missing because scanning of
pastures started after two pastures had been already grazed
and because of malfunction of the sensor, respectively.
Clippings were made with a flail harvester to a stubble height of 10 cm during the period of NDVI
readings. Fresh forage was weighed in the field and subsamples of approximately 0.5 kg from
each plot were weighed and dried to determine the percent dry matter. Dry matter yields per unit
area were calculated. Forage yields reported are the average of five plots (microreliefs) per
fertilizer strip.
Correlation coefficients (r) along with associated probability levels were obtained for all pairs of
yield-NDVI measurements for each season from spring 2004-2005 until the summer 2005-2006
(PROC CORR, SAS Institute, 2003). Number of pairs of observations per season was not equal
throughout this research because of measurements in the spring of 2004-2005 started after two
of the pastures had been already grazed and in the summer of 2005-2006 ten observations
were missing because of malfunction of the sensor.
RESULTS AND DISCUSSION
The relationship between forage yield and NDVI was inconsistent (Table 2). In four of five
seasons NDVI was significantly related with forage yield but from the four significant, the last two
had extremely low forage yield levels and had opposite sign relations, negative in the spring,
and positive in the summer. From these two seasons it is suggested that the relationship of yield
to NDVI under such of low yield levels, seems to be random. Taylor et al. (1998) reported that
under low forage yields, correlation coefficients between various radiance light spectrums
(including NDVI) with forage yields, decreased dramatically compared with those of high yields.
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