THE EFFECT OF LANDSCAPE PATTERN ON THE 2010 WILDFIRE SPREAD IN THE MORDOVIA STATE NATURE RESERVE, RUSSIA
This study was aimed to identify natural complexes, which, after the wildfire of 2010, served as natural barriers to the fire spread in the Mordovia State Nature Reserve (Russia), and to assess the role of landscape surroundings in reducing the fire severity. The paper investigates the properties, size and pattern of landscape complexes at the local scale in 200-m boundary zones where a fire stops or changes its severity. Three fire severity classes were associated with field and spectral diagnostic features. The high-severity class is detected on satellite images by a sharp reduction in phytomass from June to September in the year of the wildfire impact. Classes of medium and low severity fire are detected by a gradual decrease in phytomass within four years after the wildfire. In the Mordovia State Nature Reserve, the area affected by the fire is estimated at 151 km2. Based on the landscape map of the Mordovia State Nature Reserve, the proportion of various types of landscape complexes was calculated within the border zones, adjacent to the front side: 1) to the general fire perimeter, 2) to the boundaries of the inner non-burned islands, 3) to the boundaries dividing a high-severity fire from a medium and low fire severity. We found that the occurrence of hydromorphic complexes is 1.5-10.0 times higher on the side of the considered boundaries where the fire energy decreases. Within the fire perimeter, hydromorphic complexes either become hotbeds of high fire severity due to the high amount of available fuel, or form islands of unburned forest. The success of hydromorphic complexes in stopping or slowing a fire depends more on their size than on the level of wetness. The width of swampy and damp river channels was measured along the entire length with a 1-km interval. Diameter measurements were made for swampy depressions. We found that narrow swampy river channels of 150-160-m wide do not present a fire barrier and completely burn out in a high-severity fire. River segments, where the channel width increases up to 170-180 m, present a barrier for a low-severity fire, but do not slow down the spread of medium or high-severity fire. River valleys of 200-250-m width mostly do not burn, but also do not present a barrier because a high-severity fire jumps to other sides of the valley and spreads further. A low-severity fire dies down, and a stronger fire subsides when it meets a river channel 250-300 m wide. River valleys, over 700 m wide, act as a barrier to any wildfire type. Swampy depressions do not act as fire breaks, but their clusters increase landscape heterogeneity and slow down the fire. The average diameter of mires in the perimeter of a high fire severity is 32 m; their area proportion is 0.07%. The diameter of mires in the perimeter of medium and low fire severity increases on average up to 63-77 m. And their area proportion increases up to 0.40-0.59%.