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Indicator Assessment
Vegetation productivity indicates the spatial distribution and change of the vegetation cover - a key characteristic of ecosystem condition.
Vegetation productivity in Europe on average has a regional pattern of increase and decline. Increase was observed most in South Eastern Europe, over croplands and wetlands in the Steppic region and grasslands and sparsely vegetated lands and in the Black Sea and Anatolian regions. Decline happened most over croplands and grasslands in the Atlantic region as well as over wetlands in the Alpine region.
Climate has important influence on vegetation productivity in Europe. Strongest driver is precipitation, especially in the South Eastern regions. Decreasing number of frost days increased productivity in the Pannonian region but decreased productivity in the Atlantic region.
Climatic variations are important drivers of vegetation productivity, but land use changes are even stronger. Productivity was most increased by agricultural land management and converting other lands to agriculture, whereas largest decrease was caused by sprawling urban areas.
Linear trend in yearly vegetation productivity
Note:
Change of vegetation productivity during the years 2000-2016. Vegetation productivity was calculated for each 500m grid cell from a remote sensing derived vegetation index (PPI). The layer shows the changes expressed in % of 2000 calculated from the fitted line of the linear trend model.
Significant vegetation productivity trends per ecosystems.
Note: The chart shows significant trends of vegetation productivity, expressed in % change. The % change values were derived from the fitted linear trend line.
In order to concentrate on strong productivity change signals, a linear trend was fitted over the yearly productivity values and significant (p<0.1) slopes were selected. For significant pixels productivity change was calculated from the fitted regression line with „Yfit,start“ and „Yfit,end“ as the start and end points, respectively. Changes between „Yfit,start“ and „Yfit,end“ were expressed in percentage of the „Yfit,start“ value in order to ensure comparability of change values.
Vegetation productivity changes were significantly different between ecosystems and biographical regions as well as between their combinations (two-way unbalanced ANOVA, p < 0.0001; F=8.821). Decreasing and increasing productivity showed strongest significant differences between biographical regions (F=30.020) than between ecosystems and between their combinations (F=6.331 respectively F=2.408).
Both climatic variations and land use changes had a significant effect on vegetation productivity dynamics (analysis of covariance (ANCOVA), F=124.5, p<0.001) in Europe. Land use change had stronger effect on productivity changes than climatic trends (Type III Sun-of-Squares, F=147.1, p<0.001). To a lesser extent precipitation variations and changes in the number of frost days had significant influence on how productivity change (F=145.4 and F=28.1, respectively). Standardized model parameters indicated that converting other land covers to agriculture (LCF5) resulted in highest productivity increase and that increasing urbanisation resulted in most productivity decrease.
Climatic and land use change effects on vegetation productivity are analysed in subsequent sections.
On average, vegetation productivity increased most in South Eastern Europe. Highest increase was seen in Steppic croplands and grasslands (over 90% increase). Vegetation productivity increased over 80% in grasslands of the Black Sea and Anatolian regions, in sparsely vegetated lands of the Black Sea region and in wetlands of the Steppic regions. In the northern latitudes productivity increased with 70% in Arctic woodlands and forests. The observed increasing trends in the Arctic region is probably due to the shorter periods of snow cover rather than more productivity. The Atlantic biogeographical regions was the only region where on average vegetation productivity decreased especially over grasslands (11% decrease) and croplands (10% decrease). The Alpine and Boreal regions showed low productivity increase (9% and 15%, respectively) compared to other regions, although productivity of alpine wetlands decreased with as much as 11%.
Significant productivity changes during 2000-2016 show distinct and local spatial patterns in Europe (Figure 1):
Observed increase in vegetation productivity was confirmed also by other studies published in scientific papers. Guay et al. (2014) used global NDVI datasets GIMMSg and GIMMS3g together with NDVI extracted from SeaWiFS, SPOT-VGT and MODIS datasets showing that about 40 % of the studied areas exhibited similar changes in vegetation productivity regardless the used NDVI dataset. Significant increase in vegetation productivity was detected for over 15 % of the study area whereas opposite trend was found for only 3 % of the area. Huang at al. (2017) studied long term productivity shifts for the high northern latitude areas (above +50°). On the other hand, Pan et al. (2018) highlights the possibility that increasing vegetation “browning” (i.e. productivity decline) may be in fact masked by overall vegetation greening (i.e. productivity increase). This is demonstrated by using the GIMMS3g NDVI dataset for the period between 1982 and 2013. More than 60% increase of the browning area accelerated after 1994 is reported by the authors. Increase browning trends are then reported for all latitudes of the northern hemisphere. The authors then conclude that although most of the vegetated areas exhibited overall greening trend, greening-to-browning reversal occurred on all continents and affected much larger area then browning-to-greening reversal.
Effect on vegetation productivity: number of frost days
Note: The chart shows the effect of frost frequency variations on vegetation productivity, expressed in standard deviation units of vegetation productivity.
Effect on vegetation productivity: precipitation
Note: The chart shows the effect of precipitation variations on vegetation productivity, expressed in standard deviation units of vegetation productivity.
Effect on vegetation productivity: temperature
Note: The chart shows the effect of temperature variations on vegetation productivity, expressed in standard deviation units of vegetation productivity.
Vegetation productivity was correlated to climatic drivers, such as the number of frost days, precipitation and temperature, in a multivariate linear regression. Using the Corine Land Cover (CLC) 2000-2018 series, only those grid cells were considered in this analysis where the CLC layers indicated no land use change between 2000-2018. Furthermore, only those grid cells were selected for the analysis where the trend in vegetation productivity was significant (p<0.1).
The climatic drivers and the dependent variable were standardised so that the variances of the dependent and independent variables are 1 and their mean is 0. All variables were detrended before the regression runs. Detrending and standardisation were performed to avoid spurious regression results as well as to obtain normalised slopes, which enable the direct comparison of productivity change as a result of variations in the diverse climatic drivers. Significance of the regression coefficient was measured as p<0.1. Due to standardizing all variables results are presented in standardized regression coefficients that show the change in the dependent variable measured in standard deviations.
In absolute terms, rainfall variations were the strongest driver of increasing vegetation productivity in Europe (Figure 3), especially in south Easter regions: affects were strongest in the Steppic and Pannonian regions and strong in the Black Sea and Anatolian regions. Productivity increase in these regions despite the observed decreasing precipitation (CLIM 002) may be attributed to increasing irrigation, which sustains productivity on the short term but decreases land functions on the long term.
While variations in the number of frost days were relatively important in the Pannonian and Atlantic regions, the effect of temperature variations on vegetation productivity was comparably lower all over Europe.
Regionally, precipitation was strongest driver of vegetation productivity in Pannonian and Steppic croplands, grasslands and sparse vegetation. Decreasing number of frost days resulted in increasing vegetation productivity in most parts of Europe. Strongest frost-productivity association was observed in the Pannonian region with increasing productivity over croplands, grasslands sparsely vegetated lands and woodlands.
Regarding the influence of temperature, the found patterns are supported by scientific results for grasslands. A lengthening of the growing season due to increased temperatures is found to possibly promote productivity while higher temperatures in summer might reduce productivity (Angert et al. 2005, Hufkens et al. 2016, Petri et al. 2012, in Petri et al. 2018). The role of ground temperatures in spring for productivity of grasslands is mentioned by Wingler et al. (2017) and spring as well as early summer are identified to be the most important season for grassland productivity in Ireland by Hurtado-Uria et al. (2013, in Wingler et al. 2017). The role of frost during spring for forest productivity is evident from historic events where severe temperature declines lead to only partial recovery of deciduous trees coverage in Europe and North America (Guh et al. 2008, Augspurger 2009, Hufkens 2012, Ningre et al 2009, Keyling et al 2012). Comparably fast de-acclimation in winter and spring (Kalberer et al. 2006, in Vitasse et al. 2014) implies high reactivity to sudden warm swells and comparably high frost vulnerability, peaking at leave emergence (Neuner et al 2007, in Vitasse et al. 2014). Regarding precipitation, the availability of water is recognized to be an important driver of productivity across the globe (Nemani et al. 2003, Garbulsky et al. 2010, Alström et al 2015, Seddon et al. 2016, in Knapp et al. 2016). Temperate grasslands - which exist in environments with a wide range of precipitation ranging from 150 to 1000mm/year - are sensitive to small changes in water availability (Knapp et al. 2016).
Effect of land use change on vegetation productivity
Note: The chart shows the vegetation productivity changes (%) over areas with land use change in the period 2000-2018. The values are broken down by major land use change drivers.
In order to address how vegetation productivity changed during 2000-2016 due to land use change, only those pixels were retained in the analysis where the Corine Land Cover 2000-2018 dataset indicated land cover change. Furthermore, only pixels with significant (p<0.1) productivity change were selected.
Urban sprawl was the major driver of productivity decrease in Europe (-24%). In the Netherlands urban sprawl resulted in as much as 72% productivity decline and it was 50% in Bulgaria. However, urban sprawl induced significantly higher productivity of some previously not urbanized areas, for example in Slovakia (153% increase), and in Greece and Portugal (>70% increase). Sprawl of other artificial areas such as industrial and commercial sites, transport networks, airports, mines and dumpsites had also induced productivity loss in Europe (-19%). In Slovenia and Kosovo productivity declined up to 67% and up 45% in Belgium and Estonia. City planning (urban land management) also resulted in decreasing productivity in general (4%), being strongest in Serbia and Montenegro (70%). On the other hand productivity increased in many urban areas indicating greening cities, for example in Greece, Hungary or Finland (up to 60% increase) as a results of developing green urban areas.
Agricultural management practices showed a 59% productivity increase during 2000-2016. Extension of set aside fallow lands and pastures reached a 140% increase in North Macedonia and 110% increase in Greece. Crop rotation increased agriculture productivity by 115% in Turkey whereas in Hungary crop rotation caused a 54% productivity decrease. Rotating permanent crops increased agricultural productivity the most, with the most pronounced increase in Spain (132%) and Romania (120%). On the other hand, the management of agricultural land decrease productivity by 43% in Belgium, and around 30% in Cyprus, France and Ireland.
Converting land into agriculture resulted in the largest productivity increase in Europe with an average of 63%. In Czechia productivity increased by 180% in areas where developed land was converted to agriculture. In Lithuania, Germany and Serbia where wetlands were converted to agricultural areas productivity increased with 160%. On the contrary, converting wetlands to agriculture in Croatia and North Macedonia resulted in 45-48% productivity decline. In Luxembourg converting developed land and in Kosovo converting semi-natural areas to agriculture caused productivity decline over 50%.
Managing forested areas resulted in 51% forest productivity increase in Europe. On the upper end of the scale are Bulgaria with forest creation and afforestation processes and Slovakia with forest internal conversions and (200% and 180% increase, respectively). On the contrary, forest internal conversions in Bulgaria resulted in 78% decrease whereas productivity decreased with 66% in Cyprus where forest creation and afforestation took place. In Switzerland recent feeling, new plantations and other forest transitional activities caused a 47% decrease in productivity.
The indicator addresses trends in land surface productivity derived from remote sensing observed time series of vegetation indices. The vegetation index used in the indicator is the Plant Phenology Index (PPI, Jin and Eklundh, 2014). PPI is based on the MODIS Nadir BRDF-Adjusted Reflectance product (MODIS MCD43 NBAR. The product provides reflectance data for the MODIS “land” bands (1 - 7) adjusted using a bi-directional reflectance distribution function. This function models values as if they were collected from a nadir-view to remove so called cross-track illumination effects. The Plant Phenology Index (PPI) is a new vegetation index optimized for efficient monitoring of vegetation phenology. It is derived from radiative transfer solution using reflectance in visible-red (RED) and near-infrared (NIR) spectral domains. PPI is defined to have a linear relationship to the canopy green leaf area index (LAI) and its temporal pattern is strongly similar to the temporal pattern of gross primary productivity (GPP) estimated by flux towers at ground reference stations. PPI is less affected by presence of snow compared to commonly used vegetation indices such as Normalized Difference Vegetation Index (NDVI) or Enhanced Vegetation Index (EVI).
The product is distributed with 500 m pixel size (MODIS Sinusoidal Grid) with 8-days compositing period.
References:
Jönsson P., Eklundh L., 2004. TIMESAT—a program for analyzing time-series of satellite sensor data. Computers & Geosciences 30 (2004) 833–845.
Eklundh L., Jönsson P., 2015. TIMESAT: A Software Package for Time-Series Processing and Assessment of Vegetation Dynamics. In: Kuenzer C., Dech S., Wagner W. (eds) Remote Sensing Time Series. Remote Sensing and Digital Image Processing, vol 22. Springer, Cham
Jin, H., Eklundh, L. 2014. A physically based vegetation index for improved monitoring of plant phenology, Remote Sensing of Environment, 152, 512 – 525.
Karkauskaite, P., Tagesson, T., Fensholt, R., 2017. Evaluation of the Plant Phenology Index (PPI), NDVI and EVI for Start-of-Season Trend Analysis of the Northern Hemisphere Boreal Zone, Remote Sensing, 9 (485), 21 pp.
Jin, H.X.; Jönsson, A.M.; Bolmgren, K.; Langvall, O.; Eklundh, L., 2017. Disentangling remotely-sensed plant phenology and snow seasonality at northern Europe using MODIS and the plant phenology index. Remote Sensing of Environment 2017,198, 203-212.
Abdi, A. M., N. Boke-Olén, H. Jin, L. Eklundh, T. Tagesson, V. Lehsten and J. Ardö (2019). First assessment of the plant phenology index (PPI) for estimating gross primary productivity in African semi-arid ecosystems. International Journal of Applied Earth Observation and Geoinformation 78: 249-260.
Jin, H., A. M. Jönsson, C. Olsson, J. Lindström, P. Jönsson and L. Eklundh (2019). New satellite-based estimates show significant trends in spring phenology and complex sensitivities to temperature and precipitation at northern European latitudes. International Journal of Biometeorology 63(6): 763-775.
Measurement unit: The land productivity metrics is a dimensionless measure. It is calculated as the integral area under the yearly phenological curve, the function describing the growing season from the season start to the season end.
Spatial units: the proposed indicator is delivered as a set of raster data layers with cell size of 500 m by 500 m.
Addressing ecosystem services and their complex interactions call for a coherent approach to understand the coupled human-environment system.
In November 2013, the European Parliament and the European Council adopted the 7th EU Environment Action Programme (7th EAP) to 2020, ‘Living well, within the limits of our planet’. Degradation of ecosystems is recognized as one of the major threats to the provision of ecosystem services, biodiversity and Europe’s resilience to climate change and natural disasters within the 7th Environmental Action Plan, priority objective 1, paragraph 23. Priority objective 5, paragraph 66 stats that environmental monitoring is one cornerstones of the Unions environmental policy and within Priority objective 5, paragraph 71 mapping and assessment of ecosystem services are recognized as a necessary basis for developing the most appropriate responses to environmental change.
The 7th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7th EAP refer to climate change adaptation.
In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change(COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe. One of the objectives of the EU Adaptation Strategy is better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and sub-national adaptation strategies and plans, and (4) adaptation case studies.
In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.
Biodiversity and ecosystem stability are tightly intertwined as “biodiversity loss reduces the efficiency by which ecological communities capture biologically essential resources, produce biomass, decompose and recycle biologically essential nutrients”. To halt the loss of Biodiversity and manage related ecosystem dynamics and degradation the EU states maintenance and restoration of ecosystems as target 2 of the Biodiversity Strategy to 2020.
The Millennium Ecosystem Assessment and Action 5 of the EU Biodiversity Strategy to 2020 calls Member States to map and assess the state of ecosystems and their services in their national territory.
No specific target.
The PPI time-series is affected by noise due to e.g. atmosphere and remaining cloud influence, resulting in some spikes and outlier values. Since large spikes and outliers might significantly affect the further function fitting, they first have to be removed from the data. This is done in an initial filtering process, further described in the TIMESAT software manual.
After the outlier removal the next step in the analysis is the determination of the number of growing seasons. This is based on a harmonic function fit (sine-cosine functions) to the data. The presence of a second season is established by evaluating the amplitudes of the first and second components of the harmonic fit. Presence of noise in the data complicates the decision on whether the given secondary maximum represents a true growing season or not. Therefore, an amplitude threshold is used to remove seasons that are smaller than the given threshold. A detailed description of the determination of the number of growing season is found in the TIMESAT software manual.
After the number of growing seasons have been determined double logistic functions are fitted to the data from each pixel. This is done to generate smooth continuous functions that well describe each individual growing season. It is assumed that most of the noise included in PPI (or any other vegetation index) results in negative bias of the values. Therefore, iterative adaptation of the logistic functions to the upper envelope of the data is applied in the following step. The function fit is performed on the PPI data. Values less than the first function fit are then considered as influenced by noise and thus less important, so their weights are decreased for the next iteration of the function fitting.
Phenological metrics (and other parameters describing character of the given growing season) are finally extracted from the fitted function data. The following parameters are extracted for each detected growing season to determine productivity:
Seasonal amplitude is calculated as a difference of the fitted curve maximum and the base level. The SOS and EOS points on the curve are then given as the fraction of the amplitude, i.e. the date when the fitted curve reaches/drops below the defined percent fraction of the seasonal amplitude. For this indicator 20% of the seasonal PPI amplitude was used as the SOS and EOS detection threshold.
The output of the process is a productivity metrics for each year of the time series 2000-2016 (17 years) covering the EEA39 territory. The spatial resolution of the productivity dataset is 500mx500m pixel size. In order to address change in productivity, a linear regression was fit to the productivity time series of each grid cell of the dataset. As PPI, and consequently also productivity, is a dimensionless measure, the change was expressed in the r value of the linear regression model instead of the slope of the fitted model. The r value, i.e. the coefficient of determination, is expressed between -1 and 1. It shows how close the data are to the fitted regression line. In general, the higher the value the better the model fits the data. The advantage of the R value is that unlike the slope of the linear regression model the r value can be compared across bioclimatic regions and between various ecosystems. The change was also expressed as the relative growth. The relative growth is expressed in percentage and is calculated as the change between the first and the last year of the time series in proportion of the first year`s productivity value.
Detailed description of the methodology for calculating the productivity metric can be found in the TIMESAT software manual (publically available)
Eklundh, L., Jönsson, P., 2017. TIMESAT 3.3 Software manual, Lund and Malmö University, Sweden, available at: http://web.nateko.lu.se/timesat/docs/TIMESAT33_SoftwareManual.pdf
Scientific references:
Jönsson, P., Eklundh, L., 2002. TIMESAT – A program for analysing time-series of satellite sensor data, Computers and Geosciences, 30, 883 – 845.
Jönsson, P., Eklundh, L., 2004. Seasonality extraction and noise removal by function fitting to time-series of satellite sensor data, IEEE Transactions of Geoscience and Remote Sensing, 40 (8), 1824 – 1832.
Jin, H.X., Jönsson, A.M., Bolmgren, K., Langvall, O., Eklundh, L., 2017. Disentangling remotely-sensed plant phenology and snow seasonality at northern Europe using MODIS and the plant phenology index. Remote Sens Environ 2017, 198, 203-212.
The PPI time-series is affected by noise due to e.g. atmosphere and remaining cloud influence, resulting in some spikes and outlier values. Since large spikes and outliers might significantly affect the further function fitting, they first have to be removed from the data. This is done in an initial filtering process, further described in the TIMESAT software manual.
The productivity metrics has no gaps.
One question is the choice of fitting function in TIMESAT. In the scientific literature, several fitting methods have been used and proposed. In this analyses logistic functions were chosen since they are well founded in the scientific literature (e.g. Zhang et al. 2003, Fisher et al. 2006, Beck et al. 2006), and in a recent study have been found to be one of the most robust methods for regional phenology estimation (Cai et al. 2017).
Another source of uncertainty is the detection of the SOS and EOS points om the seasonal vegetation profile. In order to address appropriate levels for SOS and EOS we analysed estimates of GPP (gross primary productivity) from ground-measured data from carbon flux towers from the international FLUXNET network. This was done to evaluate if there was any significant difference in the SOS and EOS estimated from these measurements between different land cover classes. The analysis did not indicate any clear separability between the classes. This was due to high variability in the GPP data, and hence there was no basis for making individual choices for different land cover classes or climate zones. Therefore, a fixed threshold of 20 % of the annual PPI amplitude was used in the indicator assessment process. The chosen level was based on analyses in Jin et al. (2017). It cannot be ruled out that the use of a single threshold across Europe may have introduced some uncertainty.
References:
Zhang, X., Friedl, M.A., Schaaf, C.B., Strahler, A.H., Hodges, J.C.F., Gao, F., Reed, B.C. and Huete, A., 2003. Monitoring vegetation phenology using MODIS, Remote Sensing of Environment, 84, 471-475.
Beck, P.S.A.; Atzberger, C.; HÞgda, K.A.; Johansen, B.; Skidmore, A.K., 2006. Improved monitoring of vegetation dynamics at very high latitudes: A new method using MODIS NDVI. Remote Sens Environ 2006, 100, 321-334.
Fisher, J.I., Mustard, J.F. and Vadeboncoeur, M.A., 2006. Green leaf phenology at Landsat resolution: Scaling from the field to the satellite, Remote Sensing of Environment, 100, 265-279
Cai, Z.Z.; Jönsson, P.; Jin, H.X.; Eklundh, L., 2017. Performance of Smoothing Methods for Reconstructing NDVI Time-Series and Estimating Vegetation Phenology from MODIS Data. Remote Sensing 2017 9.
Jin, H.X.; Jönsson, A.M.; Bolmgren, K.; Langvall, O.; Eklundh, L., 2017. Disentangling remotely-sensed plant phenology and snow seasonality at northern Europe using MODIS and the plant phenology index. Remote Sens of Environment 198, 203-212.
The dataset represents several plant functional types aggregated with 500 x 500 m pixels. Therefore, the dataset can only be used at the ecosystem level indicating productivity changes of main plant functional types. As opposed to filed measurement remote sensing products measure vegetation light absorption from a satellite at several hundred km height which might introduce bias due to atmospheric disturbances.
No uncertainty has been specified
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/land-productivity-dynamics/assessment or scan the QR code.
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