# Exploring Ecosystem Functioning in Spain with Gross and Net Primary Production Time Series
## 6 Discussion
### Change Detection Analysis
For instance, _La Mancha_ wetlands (area 7) has been widely recognized to suffer from the depletion of the groundwater due to an excessive water extraction from the aquifers [62] and an intense use of agricultural exploitation practices. At local scale, the strong correlation between GPP (\(r_{\text{SPI-GPP}}>0.59\)) and NPP (\(r_{\text{SPI-GPP}}>0.53\)) with SPI found for almost all sites (Table 3) reinforces the statement that precipitation is a key factor of vegetation dynamics in temperate regions [57]. A remarkable reduction in photosynthetic activity and carbon assimilation (\(Q_{\text{GPP}}(10^{-2})<-0.02\) d\({}^{-1}\); \(Q_{\text{DPP}}(10^{-2})<-0.23\) d\({}^{-1}\)) was observed on interannual scale at sites C (shrublands), D (rainfed crops), F (evergreen broadleaved forest), and I (low-altitude evergreen needle-leaved forest). In these cases, a negative correlation with temperature may possibly be a determinant factor. Increasing temperatures can cause high evaporation and larger vapor pressure deficit, which in turn creates water deficit and, subsequently, a negative impact on optimum plant growth which seems to more directly affect carbon fluxes [63]. Particularly, site F (Mediterranean evergreen cork oak) was reported to experience a considerable increase of mean annual air temperature and rainfall extremes during recent decades, projecting a higher frequency of droughs and intense rain events. Productivity losses reported in this study are supported by a generalized decline of the cork oak in the Mediterranean basin found in different studies [64]. Site F shows a severe reduction in annual GPP in 2005, 2012, 2013, and 2017. As reported by the Spanish Meteorological Agency (www.aemet.es, accessed on 13 January 2022), 2005 has been recognized as the driest year, followed by 2017 and 2012 with 40%, 27%, and 15% less annual precipitation than the mean value, respectively. In this regard, [63] reported that drought is the driving factor of global NPP diminution. Moreover, different causes, such as the increase in the outbreaks of tree disease due to more favorable conditions for pathogen development, extreme overgrazing by livestock leading to a reduced regeneration rate, and an excessive development of forest resources [64] may also explain these findings. For site I (conifer forest species, mainly _Pinus nigra_ ssp. ), a reduction in productivity was observed (\(Q_{\text{GPP}}(10^{-2})=-0.021\pm 0.015\) d\({}^{-1}\); \(Q_{\text{DPP}}(10^{-2})=-0.23\pm 0.04\) d\({}^{-1}\)), which was more important in the production of new biomass. The large positive correlation with SPI and the large negative correlation with air temperature may indicate that this ecosystem is particularly vulnerable to climate variations. Vulnerability of zonal ecosystems, particularly forests, over the MLE is very high given its significant role in carbon and hydrological cycling studies [65]. Evidence of major changes for Mediterranean conifer species located at low elevations was also found in [66]. Site A (sparse vegetation) presented the largest negative GPP trend (\(Q_{\text{GPP}}(10^{-2})=-0.93\pm 0.09\) d\({}^{-1}\)) and a poor correlation with air temperature. The trend is supported by the land arity observed in recent decades due to water scarcity, temperature, and radiation factors [8]. The small correlation between GPP and air temperature (\(r_{\text{GPP-}T}=0.12\)evidences the precipitation (\(r_{\text{GPP-SPI}}\) = 0.59) as a limiting growth factor compared to air temperature. In sparse vegetation areas, vegetation conduces to the expansion of root system for the increasing absorption of minerals and water in an attempt to increase resilience. Figure 6a revealed that a very advanced degradation process may be explained by the severely decreased precipitation in the studied period. As reported by [67], less precipitation in aridity areas is compensated in the long term by a proportional loss of density in vegetation cover.