## 5 Discussion
### Land Cover Changes Relative to Drought and Wildfire
#### 5.2.2 Breakpoints and Drought  
The sc-PSDI for NM and the detected significant breakpoints with decreasing and increasing trends were shown in Figure 10. A weighted average of the sc-PDSI was calculated over the breakpoints with decreasing and decreasing trends separately to evaluate their timing against drought events. Some previous findings suggested that extended periods of drought (or relatively dry conditions) can introduce lasting negative impacts (degradation) on rangelands and other ecosystems [8; 79]. Based on Figure 10, it was noticed that from all the detected breakpoints during the study period (1982-2015), 67.9% were observed only in 2000s from which 38.2% exhibited decreased trend in productivity (Figure 10a). Coincidently, these breakpoints overlapped with frequent and extended periods of drought events in NM that were also observed regionally in the southwest USA during 2000s. The impact of this regional drought had resulted in a decrease in productivity in more than 30% of the coterminous USA, out of which ~15% (equivalent to more than 41 million ha) was rangelands [37]. The increased number of breakpoints after 2000 suggested a permanent degradation or damage to ecosystems which mechanistically can occur when these ecosystems have little to no time to recover from a previous consecutive drought event. A recovery period from a drought event as defined by [79] is the return of an ecosystem to pre-drought values of GPP and can vary from immediate to multiple years depending on vegetation, climate, disturbance, and drought. It was indicated that dryland ecosystems such as those in NM, had experienced increased recovery periods that were highly sensitive to precipitation and temperature [79]. With the expected future projections of rising temperature and drier conditions, the drought recovery of dry ecosystems would even be longer. When droughs have shorter return period (or more frequent) this makes ecosystems more susceptible to drought or ecosystem degradation continues and builds up until a threshold is reached and the degradation become irreversible (or permanent), a condition that was referred to in [79] as a tipping point. This study suggested that these thresholds may have been reached as represented by the detected breakpoints. This explains, to some extent, the appearance of breakpoints compared to drought events. The timing of these breakpoints suggested the accumulation of dry conditions that impact ecosystem functions until reaching tipping points. Further analysis is needed to understand the timing or emergence of the breakpoints and drought accumulation periods and the response of ecosystems relative to vegetation type and climate. Moreover, these recent exceptionally drought conditions in NM (during 2000-2015) also varied in spatial extent, duration, and intensity [80]. These variations may have contributed to the occurrence of 38% breakpoints with decreasing trends (i.e., initiation and irreversible degradation) in southeastern (Eddy, Lea, Chaves, and Otero counties); northeastern (Colfax, De Bacca, and San Miguel counties); and northwestern NM (San Juan county). From all pixels that experienced significant decrease in productivity, 35% were observed in De bacca, San Miguel, San Juan, and Otero counties as drought might have a profound influence in reducing vegetation productivity (e.g., plant mortality) [81; 82]. On the other hand, reversal from degradation and significant increase in productivity was dominantly observed in the northwestern, southeastern, and southwestern NM (Figure 8). In NM, wetter years were observed from 1986 to the end of 1990s, followed by drier years from 1999-2003 and 2005 (Figure 10). Significant breakpoints with increase in productivity were identified during 2000s dry years in Otero, Dona Anna, Luna, San Juan and Socorro counties. About 13.5% of these breakpoints were observed in the first four of counties.