Stand and cohort structures of old‐growthPinus resinosa‐dominated forests of northernMinnesota,USA

Abstract

Questions: What is the natural range of variability in stand and age structure of old-growth Pinus resinosa-dominated forests? Does the spatial pattern of tree ages provide insights into past disturbances that structured these forests?Location: Old-growth P. resinosa forests at seven sites in Minnesota, USA. Methods:We applied detailed dendrochronological methods to living and dead material to reconstruct stand and age structures prior to European settlement of the region. We linked dendrochronological data to mapped stem locations to shed light on spatial patterns of past disturbance.Results: Data pooled across sites revealed a mean living tree basal area of 34.8 m 2 ·ha À1 , snag basal area of 6.9 m 2 ·ha À1 and down woody debris (DWD) volume of 100 m 3 ·ha À1 . Living tree diameter distributions varied between sites; however, at all sites, smaller diameter classes were dominated by nonpines, many pre-dating the onset of fire suppression in the 1920s. There were a variety of P. resinosa age structures, including one-cohort, two-cohort (at times with additional sporadic recruitment) and three-cohort stands. For multicohort stands, the spatial pattern of cohorts shows considerable within-stand patchiness. Conclusions:The wide range of stand and age-cohort structures in these oldgrowth P. resinosa stands depicts pre-settlement forests more complex than those of the single-cohort, post-stand-replacing-fire model that has guided regional forest management. Within-stand patchiness of cohort age structures implies disturbances operating at scales smaller than typically associated with this regional forest type. Presence of non-pine 'ingrowth' on all sites might suggest that P. resinosa stands supporting these species lie within the natural range of variability for this community type, representing situations in which surface fires did not occur for extended periods or were spatially patchy at the stand scale. The diversity of reference conditions documented here suggests targets that might guide ecological restoration prescriptions for these ecosystems, with the goal of reintroducing structural and compositional complexity reflecting natural disturbance and stand development.

Long‐term impacts of variable retention harvesting on ground‐layer plant communities in Pinus resinosa forests

“…This retention level was chosen to allow comparison with other VRH experiments, such as the DEMO study (Halpern et al . ), in addition to being consistent with the disturbance dynamics and resultant structure of red pine forests in Minnesota (Fraver & Palik ). The large gap‐aggregated and small gap‐aggregated treatments created 0·3 ha and 0·1 ha gaps, respectively.…”

A reconceptualization of open oak and pine ecosystems of eastern North America using a forest structure spectrum

“…Indeed, very few managed landscapes remain dominated by open forests, having transitioned during the last century to increasingly dense stands comprised of fire-intolerant species in all strata (thus, many vertical layers) and a woody rather than herbaceous understory (Goebel and Hix 1996, McCarthy et al 2001, Bragg 2004, Fraver and Palik 2012, Dey et al 2017, Hanberry and Abrams 2018. Indeed, very few managed landscapes remain dominated by open forests, having transitioned during the last century to increasingly dense stands comprised of fire-intolerant species in all strata (thus, many vertical layers) and a woody rather than herbaceous understory (Goebel and Hix 1996, McCarthy et al 2001, Bragg 2004, Fraver and Palik 2012, Dey et al 2017, Hanberry and Abrams 2018.…”

Succession, climate and neighbourhood dynamics influence tree growth over time: an 87‐year record of change in aPinus resinosa‐dominated forest, Minnesota,USA

“…Although P. banksiana trees can survive to 250 yrs (Heinselman ), the average lifespan is much shorter, with death commonly occurring between 105 yrs (Cayford & McRae ) and 160 yrs (Bergeron & Dubuc ). P. resinosa trees live much longer, with the oldest individuals known to persist up to 400 yrs (Burns & Honkala ; Fraver & Palik ). It is generally accepted that N is the most limiting nutrient for forests in this region, but both N and P content (but not cations) in the upper 25 cm of soil correlate strongly with the site index for red pine, suggesting both nutrients could be limiting to growth (Alban ).…”