Abstract
Given the close association between climate change and vegetation response, there is a pressing requirement to monitor the phenology of vegetation and understand further how its metrics vary over space and time. This article explores the use of the Envisat MERIS terrestrial chlorophyll index (MTCI) data set for monitoring vegetation phenology, via its estimates of chlorophyll content. The MTCI was used to construct the phenological profile of and extract key phenological event dates from woodland and grass/heath land in Southern England as these represented a range of chlorophyll contents and different phenological cycles. The period 2003–2008 was selected as this was known to be a period with temperature and phenological anomalies. Comparisons of the MTCI-derived phenology data were made with ground indicators and climatic proxy of phenology and with other vegetation indices: MERIS global vegetation index (MGVI), MODIS normalized difference vegetation index (NDVI) and MODIS enhanced vegetation index (EVI). Close correspondence between MTCI and canopy phenology as indicated by ground observations and climatic proxy was evident. Also observed was a difference between MTCI-derived phenological profile curves and key event dates (e.g. green-up, season length) and those derived from MERIS MGVI, MODIS NDVI and MODIS EVI. The research presented in this article supports the use of the Envisat MTCI for monitoring vegetation phenology, principally due to its sensitivity to canopy chlorophyll content, a vegetation property that is a useful proxy for the canopy physical and chemical alterations associated with phenological change.
Highlights
Vegetation productivity is coupled closely with interactions between the terrestrial biosphere and the climate system
One aspect of vegetation dynamics that has received increasing attention recently is that of phenology, which refers to the timing of plant development phases, such as leaf onset, flowering, leaf senescence and leaf offset, so-called phenological events (Menzel and Fabian 1999, Morisette et al 2009)
An extension in the growing season leading to increased canopy longevity and carbon gain may provide an increased sink for atmospheric carbon (Lucht et al 2002), an extended growing season may contribute to warming due to a decrease in surface albedo (Betts 2000)
Summary
Vegetation productivity is coupled closely with interactions between the terrestrial biosphere and the climate system. Recent radiative (e.g. by atmospheric CO2) and non-radiative forcing (e.g. land cover change) of the climate system has led to a rise in the global mean temperature. The timing of vegetative phenological events indicates the impact of both short- and long-term climatic changes on the terrestrial biosphere (Reed et al 1994, Chuine and Beaubien 2001, Brügger et al 2003). Phenological events have implications for competition between plant species and interactions with heterotrophic organisms. In addition to these direct effects, alteration in the timing of phenological events is implicit in ecosystem services to humans, such as the production of food, fibre and extractable chemical substances, as well as the seasonal suitability of landscapes for recreational activities (Badeck et al 2004). Links have been postulated between changing vegetation phenology and disease transmission (Barrios et al 2010)
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