Quantifying natural disturbances using a large‐scale dendrochronological reconstruction to guide forest management

Abstract

Estimates of historical disturbance patterns are essential to guide forest management aimed at ensuring the sustainability of ecosystem functions and biodiversity. However, quantitative estimates of various disturbance characteristics required in management applications are rare in longer-term historical studies. Thus, our objectives were to (1) quantify past disturbance severity, patch size, and stand proportion disturbed and (2) test for temporal and subregional differences in these characteristics. We developed a comprehensive dendrochronological method to evaluate an approximately two-century-long disturbance record in the remaining Central and Eastern European primary mountain spruce forests, where wind and bark beetles are the predominant disturbance agents. We used an unprecedented large-scale nested design data set of 541 plots located within 44 stands and 6 subregions. To quantify individual disturbance events, we used tree-ring proxies, which were aggregated at plot and stand levels by smoothing and detecting peaks in their distributions. The spatial aggregation of disturbance events was used to estimate patch sizes. Data exhibited continuous gradients from low-to high-severity and small-to large-size disturbance events. In addition to the importance of small disturbance events, moderate-scale (25-75% of the stand disturbed, >10 ha patch size) and moderate-severity (25-75% of canopy disturbed) events were also common. Moderate disturbances represented more than 50% of the total disturbed area and their rotation periods ranged from one to several hundred years, which is within the lifespan of local tree species. Disturbance severities differed among subregions, whereas the stand proportion disturbed varied significantly over time. This indicates partially independent variations among disturbance characteristics. Our quantitative estimates of disturbance severity, patch size, stand proportion disturbed, and associated rotation periods provide rigorous baseline data for future ecological research, decisions within biodiversity conservation, and silviculture intended to maintain native biodiversity and ecosystem functions. These results highlight a need for sufficiently large and adequately connected networks of strict reserves, more complex silvicultural treatments

Disturbance history is a key driver of tree life span in temperate primary forests

“…There was a higher probability of finding old trees on plots with a lower maximum severity of plot-level disturbance, or where the maximum severity event occurred further back in time. These findings are not at all surprising given that both the beech-and spruce-dominated primary forests studied here experience a disturbance regime characterized by relatively frequent moderate-severity, partial canopy disturbances that are likely to remove susceptible individuals (i.e., large, old trees) in the canopy layer (Nagel et al, 2014;Čada et al, 2020;Frankovič et al, 2020).…”

“…Radial growth patterns of increment cores were analyzed for evidence of past disturbance events within each plot. Quantitative reconstructions of disturbance histories for different regions of the larger data set used here have been published previously (Standovár & Kenderes, 2003;Svoboda et al, 2014;Trotsiuk et al, 2014;Janda et al, 2017;Meigs et al, 2017;Nagel et al, 2017;Schurman et al, 2018;Janda et al, 2019;Schurman, Babst, Björklund, et al, 2019;Čada et al, 2020;Frankovič et al, 2020), and provide detailed descriptions of dendroecological methods. We therefore only briefly summarize the methods used to reconstruct disturbance below.…”

“…Although these exceptionally old trees are rare, 26 out of the 68 stands had more than 10 trees ha −1 that reached the species-specific 90th percentile age. Moreover, the remarkable variation in the density of these trees across the stands likely highlights how tree longevity is strongly influenced by local disturbance histories, which cover a gradient from low-intensity gap dynamics, to partial canopy disturbance, to severe stand replacement in the study region (Svoboda et al, 2014;Trotsiuk et al, 2014;Janda et al, 2017;Schurman et al, 2018;Čada et al, 2020;Frankovič et al, 2020).…”

Both Cyclone‐induced and Convective Storms Drive Disturbance Patterns in European Primary Beech Forests

“…These two drivers of wind form a cline of disturbance size across Europe with large‐scale disturbance being common in Western Europe (e.g., France and Germany) and smaller‐scale disturbance more common in Southeastern Europe (e.g., Slovenia to Montenegro) coincident with the prevalence of intense windstorms in the west (Bett et al., 2017) and intense convective instability in the southeast (Brooks et al., 2003; Taszarek et al., 2019). Based on disturbance reconstructions from the Carpathian Mountains at the border of Central and Eastern Europe, most disturbances are smaller scale (<10 ha; Čada et al., 2020) and thus, if large‐scale cyclones are driving windthrow dynamics in these forests, some moderator of wind is increasing forest resistance to large‐scale disturbance. Otherwise, it may be that small‐scale convective instability is at least partially responsible for the smaller disturbance patch size there, just as it is in Southeastern Europe.…”

“…The recent increase in strength of cyclones, usually in winter, has led some researchers to suggests that cyclone‐induced windstorms are increasing the frequency and severity of windthrow disturbance events (Schelhaas et al., 2003; Usbeck et al., 2010). However, although intense wind prevalence has increased (Figure 1), an increasing disturbance trend is not apparent in disturbance reconstructions from primary and old‐growth forests of Central or Eastern Europe (Čada et al., 2020; Firm et al., 2009; Schurman et al., 2018; Zielonka et al., 2010).…”