Protected area (PA), usually built to address the potential ecological pressure from different sources, aims to sustain, protect, and maintain the wilderness of nature for ecological, economic, and scenic purposes. Establishing, maintaining, and expanding the monitor network of PAs helps to enhance the ecological and biological value of these areas, especially in the light of species decline and habitat degradation. Intensively monitored and regulated through various administrative agencies, California keeps one of the best maintained network of PAs in the world, which supports various studies to address the significant threats to the preservation of wilderness from the projected warming climate and pressure from human development, including water deficit and prolonged drought, abnormality in wildfires, urban sprawl, and light pollution.
With the help of satellite remote sensing technologies and geospatial analysis, we can overcome the limitation of data availability in traditional ecological studies and expand the study of PAs to a continuous gradient both in time and space. This dissertation aims to develop a comprehensive understanding through remote sensing technologies on three signiﬁcant and linked ecological disturbance in California PAs, including the change of land cover, the dynamic of wildfire, and the extent and intensity of human activity reflected by stable nighttime light. Exploiting various of remote sensing observation and its derivatives, this study investigated the three topics through trend, seasonality, abnormality, spatial distribution, and hotspot of change to provide a cost-effective and repeatable studying paradigm for PA managers to better understand the past and present situation, as well as the ecological challenges of PAs. In addition, it also supplemented the study of PAs as a case study focusing on a non-tropic ecosystem, which usually involves greater interaction with human thus faces ecological pressure at a higher level.
The analysis on land cover dynamics and change from 2000 to 2015 found that many protected areas in California have experienced an increase of brownness since 2000. PAs with a higher coverage of greenness are associated with a higher temporal variability, mostly because of the more complex life cycle of green vegetation and the sensitivity to the disturbance, possibly due to a drying climate regime. Partly linked to the gradual influence from the drying climate, the change in the regime of wildfire may cause a more drastic change in land cover, through the removal of aboveground biomass and its inﬂuence on the post-wildﬁre regrowth. In the study focusing on California PAs from 2000 to 2013, a shift in wildfire-prone land cover and season was observed starting from 2008, while the wildfires southern California shrubland during the fall season became nearly extinct and the northern California evergreen forest wildfires in the late spring increased, partly explained by the recent loss of available fuel in biomass and the increase of potential of ignition in evergreen forest as a result of prolonged drought. Most burned areas experienced a signiﬁcant weakening of the immediate growing season, although the inﬂuence from ﬁre on local landscape decayed over time, which became irrelevant after ﬁve years on average. The lower fuel moisture and a more intensive removal of aboveground biomass makes shrubs more sensitive in time, with a shorter period for biomass removal by ﬁre and a greater delay in the start and peak of post-ﬁre growing season.
The long-enduring and sometimes intensive disturbance from human activity, especially from the development can be even more disastrous than wildﬁre in damaging the aboveground biomass by interrupting the natural nutrient and mass circulation,thus brings more fundamental and sometimes irreversible consequences to ecosystems. However, after decades of protection, especially the removal of settlements in side PAs, land management strategies may have bored beneficial fruits to reduce the negative effects from historical human disturbance. As a good proxy of human activity and development, the historical records of stable nighttime light from 1992 to 2012 tracked the temporal change and spatial migration of hotspot of human activity inside California PAs. A decrease of lit area at night inside PAs occurred from 1992 to 2012, with a turning point around 2004 when the relatively sharp decrease started from became more gradual thereafter. Besides, area covered by higher stable nighttime light not only shrank, but also retreated from the area with high wilderness. If solidly conﬁrmed by other socioeconomic variable, the above ﬁnding demonstrated the eﬀectiveness of PA establishment and the fruits of multiple conservation strategies kept for decades.
The investigation of three major disturbances to the wilderness of California PAs provided an example of exploiting the cost-eﬀective and continuously available observation of the Earth surface at a regional level to understand the ecological challenges of PAs. The findings can help the National Park Service and other related agencies of PA administration in the review, adjustment, and proposal of regulations and policies regarding to PAs. Future work and analysis can be focused on improving the accuracy of predictive models involved the analysis, either by concentrating on the diﬀerence between categories of protection, or through a better understanding on the related ecological process and mechanisms to identify or develop better explanatory variables. In addition, when conducting analysis on PAs, the buﬀer area adjacent to PAs cannot be ignored, which is an important source of disturbance to PAs as well as an ecological corridor that links nearby PAs into clusters. Considering the great diversity in the landscape of PAs, the analytical results can be aggregated and interpreted by different ecoregions to derive more accessible guidance to local policy makers.