Trends and land surface phenological responses to climate variability in the Argentina Pampas

Abstract

Understanding the interaction between land surface and atmosphere processes is fundamental for predicting the effects of future climate change on ecosystem functioning and carbon dynamics. The objectives of this work were to analyze the trends in land surface phenology (LSP) metrics from remote sensing data, and to reveal their relationship with precipitation and ENSO phenomenon in the Argentina Pampas. Using a time series of MODIS Normalized Difference Vegetation Index (NDVI) data from 2000 to 2014, the start of the growing season (SOS), the annual integral of NDVI (i-NDVI, linear estimator of annual productivity), the timing of the annual maximum NDVI (t-MAX) and the annual relative range of NDVI (RREL, estimator of seasonality) were obtained for the Argentina Pampas. Then, spatial and temporal relationships with the Multivariate ENSO Index (MEI) and precipitation were analyzed. Results showed a negative trend in annual productivity over a 53.6% of the study area associated to natural and semi-natural grassland under cattle grazing, whereas a 40.3% of Argentina Pampas showed a significant positive trend in seasonality of carbon gains. The study also reveals that climate variability has a significant impact on land surface phenology in Argentina Pampas, although the impact is heterogeneous. SOS and t-MAX showed a significant negative correlation with the precipitation indicating an earlier occurrence. 23.6% and 28.4% of the study area showed a positive correlation of the annual productivity with MEI and precipitation, respectively, associated to rangelands (in the first case) and to both rangeland and croplands, in the second case. Climate variability did not explain the seasonal variability of phenology. The relationships found between LSP metrics and climate variability could be important for implementation of strategies for natural resource management.

Ecosystem stability of temperate grasslands in response to variability of hydrological conditions

“…In particular, waterlogging in the Flooding Pampa is a disturbance process that impacts plant community structure (Chaneton et al, 1988; Entraigas et al, 2017; Entraigas et al, 2019). Our results indicate that, independently of changes in vegetation structure, periods of excess water modify a central element of grassland functioning at the landscape scale, such as the dynamics of their net primary productivity, something that has already been demonstrated at a regional scale in previous work (Lara et al, 2020).…”

“…Since the index values are normalized, positive SPI values indicate precipitation is higher than average and negative values indicate precipitation is lower than average. In this work, the 3‐month SPI was used because it reflects short‐ and medium‐term moisture conditions, providing an accurate estimate of the seasonal variability of precipitation (WMO, 2012) that has been shown to have a considerable impact on the functioning of ecosystems in much of the Pampas region (Lara et al, 2020). Thus, the SPI was used for December 2010–December 2015, the same time scale as the floristic surveys.…”

“…The possibility of being estimated by remote sensing makes it essential to relate before records of species diversity. The Normalized Difference Vegetation Index (NDVI), a linear estimator of the fraction of photosynthetically active radiation intercepted by vegetation (Wang et al, 2004), has been one of the most widely used proxies to describe local and regional patterns of net primary productivity (Lara et al, 2018(Lara et al, , 2020Pettorelli et al, 2016). Therefore, NDVI anomalies are used as an estimator of the stability of ecosystem functioning, that is, the long-term variability of ecosystem functions or processes.…”

Unveiling the increasingly altered patterns of wetland ecosystem functional diversity in the lower Delta of the Paraná River

“…In the context of global change, ecosystem functioning represents a useful tool in environmental management and conservation through monitoring terrestrial ecosystems as well as exploring LULCC and climate change dynamics (Fischer et al, 2006; Piao et al, 2019; Zarei et al, 2020). The net primary production (NPP) and its seasonal dynamics acquire particular relevance since it comprises both vegetation phenology and productivity (Lara et al, 2020). Its increasing significance relies on the fact that ecosystems can be grouped, according to their carbon gain dynamics and phenological parameters, into functionally homogeneous entities (Lara et al, 2018; Paruelo et al, 2001).…”

Impacto de los cambios en el uso del suelo sobre el balance hídrico en zonas de llanura

“…Además, se usaron solo las bandas reflectivas con resolución espacial de 30 m (azul, verde, rojo, infrarrojo cercano y dos bandas de infrarrojo medio). Las bandas térmicas fueron descartadas debido a que las coberturas a identificar tienen un rango dinámico mayor en las bandas reflectivas y no en las bandas térmicas (Lara y Gandini, 2014). Cómo las imágenes LANDSAT-8 se encuentran a partir del año 2013, para los periodos 2006-2007 y 2010-2011, se hizo la identificación de áreas misceláneas (bajos y lagunas, afloramientos rocosos y montes) a partir de 4 imágenes Landsat 7 con una serie de imágenes históricas de alta resolución.…”