European beech, silver fir, and Norway spruce differ in establishment, height growth, and mortality rates on coarse woody debris and forest floor—a study from a mixed beech forest in the Western Carpathians

Abstract

Abstract& Key message In mixed forests, coarse woody debris promotes the successful establishment and growth of conifers and beech. In contrast to beech and fir, older spruce seedlings were only present on coarse woody debris and not on the forest floor. & Context Coarse woody debris (CWD) is considered a suitable seedbed for small-seeded and light-demanding species. Its role in enhancing tree regeneration is well reported in boreal or subalpine spruce forests. Less is known about its role in the establishment, growth, and survival of other species, particularly in mixed forests. & Aims We analyzed the role of CWD in seedling establishment, growth, and survival for European beech, silver fir, and Norway spruce. & Methods We tracked the growth and survival of all germinants and seedlings over 5 years. & Results Conifers were relatively more successful than beech at colonizing on CWD. The density of seedlings was variable in all CWD decay classes but was the highest on welldecomposed CWD. CWD supported the growth of all species. Beech cohorts and older seedlings had similar mortality rates on both microsites. Spruce germinants did not survive on the forest floor for more than a year, and older seedlings were only observed on CWD. Fir cohorts had similar mortality rates on both microsites, but older seedlings survived better on the forest floor. & Conclusion Although the three species differed in their preferred microsite for establishment, CWD can be considered a suitable regeneration microsite for all three species by enhancing their growth and, in the case of spruce, both short-and long-term survival.

Regeneration processes on coarse woody debris in mixed forests: do tree germinants and seedlings have species‐specific responses when grown on coarse woody debris?

“…The differences in germinant and seedling counts can be explained by differences in the masting interval between the two sites and by differences in the species share of the mature stands. In 2006 and 2007, we observed many fir germinants in GNP (Orman & Szewczyk ) which boosted the number of fir seedlings in consecutive years. However, we should not underestimate the differences in CWD structure between the plots.…”

“…Moreover, we observed fewer differences in fir seedling densities growing on different CWD species than in the case of beech and spruce seedlings. Interestingly, a similar study, focused on the same three species in the Western Carpathians, also showed that among all species, fir exhibited minimal substrate preference when comparing CWD with the forest floor (Orman & Szewczyk ). In general, seedling and germinant densities for all species were higher on beech CWD compared with fir and spruce CWD.…”

“…). Fir did not respond to CWD species in its height growth, which is not surprising given that fir is a very shade‐tolerant species and grows slowly under closed canopies (Stancioiu & O'Hara ; Orman & Szewczyk ), and therefore, the difference in the height growth relative to CWD properties might be difficult to discern. These differences in substrate preferences for seedling establishment and survival vs. height growth of beech and spruce may indicate possible trade‐offs.…”

“…Thus, enhanced height growth of beech and spruce seedlings on spruce CWD may be partially caused by the presence of taller seedling populations found on this substrate, as the growth is size-dependent (Iida et al 2014). Fir did not respond to CWD species in its height growth, which is not surprising given that fir is a very shade-tolerant species and grows slowly under closed canopies (Stancioiu & O'Hara 2006;Orman & Szewczyk 2015), and therefore, the difference in the height growth relative to CWD properties might be difficult to discern. These differences in substrate preferences for seedling establishment and survival vs. height growth of beech and spruce may indicate possible trade-offs.…”

“…). Small‐seeded species benefit the most from CWD; however, large‐seeded broadleaved species, such as Fagus sp., in mixed forests can establish on CWD as well (Szewczyk & Szwagrzyk ; Orman & Szewczyk ).…”