Abstract
Grass senescence estimation in rangeland is particularly important for monitoring the conditions of forage quality and quantity. During senescence, grasses lose their nutrients from the leaves to the root and thereby affecting forage productivity. Studies on the remote sensing of grasslands have been conducted during the senescent phenological stage. However, despite the efforts made in previous remote sensing studies on grass senescence, its role in estimating grass senescence is rudimentary. More so, the strengths and limitations presented by the newly developed remote sensing instruments in grass senescence estimation are not well documented. This work, therefore, provides a detailed overview on the progress of remote sensing applications in characterizing grass senescence. The review further highlights the challenges and opportunities presented by these techniques. Overall, the review indicates that studies on remotely sensed grass senescence are focused on understanding biophysical and biochemical properties, and these studies identify the leaf area index, biomass, and chlorophyll content, among others, as the key indicators of grass senescence. Nonetheless, recent scientific research highlights a mismatch between studies on the grass senescence and the development in remote sensing technologies. The use of sophisticated and robust time-series analysis techniques together with improved sensing characteristics from the new generation sensors seem to present new opportunities for the optimal quantification of grass senescence at resolutions complementary to the spatial extents of the rangelands. We, therefore, recommend further research in this field through the adoption of new satellite technologies and advanced spatial data analytics to enhance the monitoring of rangeland resources.
Highlights
The understanding of grass senescence in rangeland environments is of great importance as it informs the knowledge on availability status, condition, distribution and allocation of forage (Xu et al 2019; Fuhlendorf and Engle 2001; Pickup 1996)
The present study has provided an overview of remote sensing techniques for characterizing grass senescence with associated challenges and opportunities
Remote sensing efforts of grass senescence depends on the use of changes in biochemical and physiological components of the grass at this phenological stage as proxies
Summary
The understanding of grass senescence in rangeland environments is of great importance as it informs the knowledge on availability status, condition, distribution and allocation of forage (Xu et al 2019; Fuhlendorf and Engle 2001; Pickup 1996). 2009), chlorophyll content (Liu et al 2013), aboveground grass biomass (Guerini Filho et al 2020; Butterfield and Malmström 2009; Asner et al 2004), among others Despite this knowledge, only a handful of studies have reviewed remote sensing applications of vegetation with an element of senescence in general. The potential of remote sensing in characterizing senescence has been noted, such studies have largely focused on croplands or forested vegetation instead of grass species This highlights the need for the state of the art review in the literature to understand the contributions of remote sensing methods in estimating grass senescence. This information will serve as a baseline for highlighting critical knowledge gaps for future improvements. The study highlighted the common challenges in remote sensing of grass senescence together with possible directions for future studies in remote sensing of grass senescence
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