Large‐scale disturbance legacies and the climate sensitivity of primary Picea abies forests

Abstract

Determining the drivers of shifting forest disturbance rates remains a pressing global change issue. Large-scale forest dynamics are commonly assumed to be climate driven, but appropriately scaled disturbance histories are rarely available to assess how disturbance legacies alter subsequent disturbance rates and the climate sensitivity of disturbance. We compiled multiple tree ring-based disturbance histories from primary Picea abies forest fragments distributed throughout five European landscapes spanning the Bohemian Forest and the Carpathian Mountains. The regional chronology includes 11,595 tree cores, with ring dates spanning the years 1750-2000, collected from 560 inventory plots in 37 stands distributed across a 1,000 km geographic gradient, amounting to the largest disturbance chronology yet constructed in Europe. Decadal disturbance rates varied significantly through time and declined after 1920, resulting in widespread increases in canopy tree age. Approximately 75% of current canopy area recruited prior to 1900. Long-term disturbance patterns were compared to an historical drought reconstruction, and further linked to spatial variation in stand structure and contemporary disturbance patterns derived from LANDSAT imagery. Historically, decadal Palmer drought severity index minima corresponded to higher rates of canopy removal. The severity of contemporary disturbances increased with each stand's estimated time since last major disturbance, increased with mean diameter, and declined with increasing within-stand structural variability. Reconstructed spatial patterns suggest that high small-scale structural variability has historically acted to reduce large-scale susceptibility and climate sensitivity of disturbance. Reduced disturbance rates since 1920, a potential legacy of high 19th century disturbance rates, have contributed to a recent region-wide increase in disturbance susceptibility. Increasingly common high-severity disturbances throughout primary Picea forests of Central Europe should be reinterpreted in light of both legacy effects (resulting in increased susceptibility) and climate change (resulting in increased exposure to extreme events).

Trade‐offs between temporal stability and level of forest ecosystem services provisioning under climate change

“…S17 and Temperli et al 2013) and influence the future stability of ecosystems (Schurman et al 2018). Our results indicate that increasing the level of service provisioning might at the same time reduce its temporal stability.…”

The climatic drivers of primary Picea forest growth along the Carpathian arc are changing under rising temperatures

“…After correcting for age effects, growth rate fluctuations in Southern Romania appear more closely linked to known disturbances (asterisked on Figure 5; see also Schurman et al, 2018) and After correcting for age effects, growth rate fluctuations in Southern Romania appear more closely linked to known disturbances (asterisked on Figure 5; see also Schurman et al, 2018) and…”

“…Tree age effects on BAI can confound growth trend analyses (Bowman, Brienen, Gloor, Phillips, & Prior, 2013) and known variability in the disturbance histories of each landscape implied the potential for age differences among landscapes (Schurman et al, 2018).…”

Redefining temperate forest responses to climate and disturbance in the eastern United States: New insights at the mesoscale

“…Gravel, Beaudet, and Messier () reported synchronous understorey dynamics across southern Quebec since 1975 and postulated that it might have been triggered by an extreme climate event. Using the largest reported disturbance chronology in Europe (> 11,000 tree cores), Schurman et al () found that decadal disturbance rates varied unexpectedly for Picea abies forests and were likely to be driven by drought extremes. At time‐scales approaching a century, past disturbance events in European forests have also led to either an increase (Schurman et al, ) or a decrease in the susceptibility of a forest landscape to subsequent disturbance (Thom, Rammer, Garstenauer, & Seidl, ).…”

“…Using the largest reported disturbance chronology in Europe (> 11,000 tree cores), Schurman et al () found that decadal disturbance rates varied unexpectedly for Picea abies forests and were likely to be driven by drought extremes. At time‐scales approaching a century, past disturbance events in European forests have also led to either an increase (Schurman et al, ) or a decrease in the susceptibility of a forest landscape to subsequent disturbance (Thom, Rammer, Garstenauer, & Seidl, ). A fire‐scar network in the western USA elucidated the first link between Pacific Ocean sea surface temperature variability and wildfire variation caused by drought (Swetnam & Betancourt, ).…”