پایش تغییرات یکپارچگی مانگروهای ذخیره گاه زیست کره حرا در مواجهه با تغییرات بارندگی و وقوع خشکسالی

بررسی تغییرات یکپارچگی یا روند تکه‌تکه‌شدگی مانگروها در بلندمدت در اثر تغییر اقلیم می‌تواند سبب شناخت دقیق‌تر تغییرات ساختاری در مانگروها و ارتباط آن با پیامدهای ناشی از تغییر اقلیم شود. پژوهش پیش‌رو به بررسی تغییرات رخ داده در وضعیت یکپارچگی مانگروهای ذخیره گاه زیست‌کره حرای قشم در مواجهه با تغییر بارندگی و وقوع خشکسالی در طول یک دوره 31 ساله (1986-2017) پرداخته است. بدین منظور از سری زمانی 31 ساله تصاویر ماهواره‌ای و داده‌های بارندگی استفاده شد و مقادیر سنجه‌های تعداد لکه (np) و نمایه بزرگترین لکه (lpi) و نیز مقادیر spi در طول دوره تهیه شد. نتایج تغییرات تعداد لکه و نمایه بزرگترین لکه مانگروها در دوره های وقوع ترسالی (پیش از سال 1998) و خشکسالی (پس از سال 1998) نشان داد که با افزایش مقادیر spi (مقادیر مثبت) در دوره پیش از سال 1998، از تعداد لکه ها و نمایه بزرگترین لکه کاسته شده بود و در دوره پس از سال 1998 و با منفی بودن مقادیر spi، تعداد لکه و نمایه بزرگترین لکه افزایش یافت. در واقع، نتایج نشان‌دهنده افزایش وسعت هسته های اصلی و لکه های رویشی بزرگ (افزایش یکپارچگی ساختاری) ذخیره گاه در دوره زمانی ترسالی و روند معکوس آن در دوره خشکسالی بود. بر اساس اصول بوم شناسی سرزمین، افزایش تعداد لکه ها و نیز افزایش مقدار نمایه بزرگترین لکه (به دلیل کاهش گستره مجموع رویشگاه) در دوره زمانی پس از سال 1998، نشان‌دهنده تخریب این رویشگاه در سال‌های اخیر است. نتایج این پژوهش می تواند در ارزیابی آسیب پذیری این رویشگاه‌ها نسبت به پیامدهای حاصل از تغییر اقلیم استفاده شوند.

monitoring changes in the integrity of mangroves of the hara biosphere reserve in the face of rainfall changes and drought occurrence

abstractexamining long-term changes in the integrity or fragmentation trends of mangroves due to climate change can lead to a more precise understanding of structural changes in mangroves and their connection to the impacts of climate change. this study investigates the changes in the integrity status of the hara biosphere reserve mangroves in qeshm in response to variations in rainfall and drought over a 31-year period (1986-2017). for this purpose, a 31-year time series of satellite images and rainfall data were used, and values for the number of patches (np) and largest patch index (lpi) metrics, as well as spi values, were prepared over the period. the results of changes in the number of patches and the largest patch index of mangroves during periods of wet years (before 1998) and drought years (after 1998) showed that with the increase in spi values (positive values) before 1998, the number of patches and the largest patch index decreased, while in the period after 1998, with negative spi values, the number of patches and the largest patch index increased. in fact, the results indicated an increase in the extent of core areas and large vegetative patches (increased structural integrity) of the reserve during the wet period and the reverse trend during the drought period. based on landscape ecology principles, the increase in the number of patches and the largest patch index (due to the reduction in the total area of vegetation) in the period after 1998 indicates the degradation of this habitat in recent years. the results of this study can be used to assess the vulnerability of these habitats to the impacts of climate change.1. introduction:analyzing changes in mangroves and examining their relationship with drought can provide valuable information about the adverse effects of climate change on mangroves. specifically, investigating long-term changes in the integrity or fragmentation trends of mangroves in response to climatic changes can lead to a more precise understanding of the structural changes in mangroves and their connection to climate change impacts. the results can serve as a decision-support tool, playing a crucial role in developing climate change adaptation programs for these habitats (reddy et al., 2018). in fact, examining the relationship between changes in mangrove integrity over time can play a significant role in identifying sensitive and vulnerablehabitats and enhancing the effectiveness and success of restoration programs, thereby increasing their adaptability and resilience to multiple environmental hazards (hauser et al., 2017). therefore, the aim of this study is to investigate changes in the integrity (fragmentation) status of the hara biosphere reserve mangroves in qeshm in response to variations in rainfall and drought over a 31-year period (1986-2017). for this purpose, a 31-year time series of satellite images and rainfall data were utilized.2. materials and methodsin this study, the relationship between drought occurrence and changes in mangrove integrity was investigated by calculating annual spi values. for this purpose, a 31-year dataset (1986 to 2017) of monthly rainfall from the khomir synoptic station, located near the hara biosphere reserve, was used. after performing geometric and radiometric corrections on the 31-year time series (1986-2017) of landsat images, the time series of mangrove extent maps for the hara biosphere reserve was prepared. then, the time series of changes in the integrity or fragmentation of the hara biosphere reserve mangroves was prepared using two landscape metrics: the number of patches (np) and the largest patch index (lpi). these metrics are the best indicators of changes in the degree of fragmentation of these ecosystems. finally, the relationship between changes in landscape metrics and the severity of drought over the 31-year period was analyzed, and the changes in metric values before and after 1998 (the change point in drought occurrence trends in southern iran) were examined.3. resultsthe results showed that from 1986 to 1998, the spi values increased (positive spi values indicating a wet period), and then, over the 19-year period following 1998, the spi values decreased and consistently exhibited negative values (drought period). analysis of the obtained results indicated that the values of the np and lpi metrics in the hara biosphere reserve fluctuated over the 31-year period (1986-2017). specifically, the changes in the largest patch area in the hara biosphere reserve showed an increase during the pre-1998 period (wet period) and a gradual decrease thereafter until the end of the 31-year period. the results demonstrated that the trend of changes in the lp over the 31-year period (1986-2017) was opposite to the trend in the largest patch area. the lpi value gradually decreased from 1986 to 1998 (wet period) and then increased until the end of the 31-year period (drought period). the np decreased during the 12-year period (1986-1998), with the number of patches in the reserve being 1281 in 1986 and 911 in 1998. as the results show, the number of patches in the reserve increased during the period following 1998 (drought period), reaching 1639 by the end of the 31-year period.4. conclusionthe study showed that between 1986 and 1998 (wet period), as the number of patches in the reserve decreased, the area of the largest patch increased. this increase in the largest patch area, along with a decrease in the number of patches, indicates an increase in the reserve's integrity through the expansion of core areas and large vegetative patches in this habitat during the pre-1998 period (wet period). this increase in integrity could have a significant impact on the distribution and higher diversity of animal species dependent on mangroves (li et al., 2013). conversely, an increase in the number of patches, a decrease in the size of large patches, and the presence of gaps between patches disrupt biological exchanges and biodiversity at the habitat level, as well as reduce gene flow among subpopulations within the patches (li et al., 2013). these changes were observed in the mangroves of the reserve during the drought period after 1998.the study by mafi-gholami et al. (2017) showed that the area of mangroves in the hara biosphere reserve decreased during the long-term drought period after 1998. the results of this study also indicated that alongside an increase in the number of patches (increased fragmentation of large vegetative patches) during the post-1998 period, the largest patch index in this habitat increased. since the largest patch index is derived from the ratio of the largest patch area to the total habitat area, the increase in the largest patch index results from the decrease in the total habitat area during the long-term drought period post-1998. according to landscape ecology principles, an increase in the number of patches along with a decrease in the size of large patches and the total area of an ecosystem over time indicates degradation (riitters et al., 2002). the decrease in area and the increase in the number of patches in the hara biosphere reserve also indicate the degradation of this habitat during the recent long-term drought periods.referenceshauser, l.t., vu, g.n., nguyen, b.a., dade, e., nguyen, h.m., nguyen, t.t.q., le, t.q., vu, l.h., tong, a.t.h. and pham, h.v., 2017. uncovering the spatio-temporal dynamics of land cover change and fragmentation of mangroves in the ca mau peninsula, vietnam using multi-temporal spot satellite imagery (2004–2013). applied geography, 86, pp.197-207. doi: 10.1016/j.apgeog.2017.06.019li, m.s., mao, l.j., shen, w.j., liu, s.q. and wei, a.s., 2013. change and fragmentation trends of zhanjiang mangrove forests in southern china using multi-temporal landsat imagery (1977–2010). estuarine, coastal and shelf science, 130, pp.111-120. doi: 10.1016/j.ecss.2013.03.023mafi-gholami, d., mahmoudi, b., and zenner, e. k., 2017. an analysis of the relationship between drought events and mangrove changes along the northern coasts of the persian gulf and oman sea. estuarine, coastal and shelf science, 199, 141-151. doi: 10.1016/j.ecss.2017.10.008reddy, c.s., saranya, k.r.l., pasha, s.v., satish, k.v., jha, c.s., diwakar, p.g., dadhwal, v.k., rao, p.v.n. and murthy, y.k., 2018. assessment and monitoring of deforestation and forest fragmentation in south asia since the 1930s. global and planetary change, 161, pp.132-148. doi: 10.1016/j.gloplacha.2017.10.007riitters, k.h., wickham, j.d., o'neill, r.v., jones, k.b., smith, e.r., coulston, j.w., wade, t.g. and smith, j.h., 2002. fragmentation of continental united states forests. ecosystems, 5, pp.0815-0822. doi: 10.1007/s10021-002-0209-2