title: A meta-analysis of cambium phenology and growth: linear and non-linear patterns in conifers of the northern hemisphere.
abstract: OBJECTIVE
  Ongoing global warming has been implicated in shifting phenological patterns such as the timing and duration of the growing season across a wide variety of ecosystems. Linear models are routinely used to extrapolate these observed shifts in phenology into the future and to estimate changes in associated ecosystem properties such as net primary productivity. Yet, in nature, linear relationships may be special cases. Biological processes frequently follow more complex, non-linear patterns according to limiting factors that generate shifts and discontinuities, or contain thresholds beyond which responses change abruptly. This study investigates to what extent cambium phenology is associated with xylem growth and differentiation across conifer species of the northern hemisphere.
  
  
  METHODS
  Xylem cell production is compared with the periods of cambial activity and cell differentiation assessed on a weekly time scale on histological sections of cambium and wood tissue collected from the stems of nine species in Canada and Europe over 1-9 years per site from 1998 to 2011.
  
  
  RESULTS
  The dynamics of xylogenesis were surprisingly homogeneous among conifer species, although dispersions from the average were obviously observed. Within the range analysed, the relationships between the phenological timings were linear, with several slopes showing values close to or not statistically different from 1. The relationships between the phenological timings and cell production were distinctly non-linear, and involved an exponential pattern.
  
  
  CONCLUSIONS
  The trees adjust their phenological timings according to linear patterns. Thus, shifts of one phenological phase are associated with synchronous and comparable shifts of the successive phases. However, small increases in the duration of xylogenesis could correspond to a substantial increase in cell production. The findings suggest that the length of the growing season and the resulting amount of growth could respond differently to changes in environmental conditions.
authors.affiliation: Département des Sciences Fondamentales, Université du Québec à Chicoutimi, Chicoutimi (QC), Canada.
authors.forename: Sergio
authors.initials: S
authors.lastname: Rossi
authors.forename: Tommaso
authors.initials: T
authors.lastname: Anfodillo
authors.forename: Katarina
authors.initials: K
authors.lastname: Cufar
authors.forename: Henri E
authors.initials: HE
authors.lastname: Cuny
authors.forename: Annie
authors.initials: A
authors.lastname: Deslauriers
authors.forename: Patrick
authors.initials: P
authors.lastname: Fonti
authors.forename: David
authors.initials: D
authors.lastname: Frank
authors.forename: Jozica
authors.initials: J
authors.lastname: Gricar
authors.forename: Andreas
authors.initials: A
authors.lastname: Gruber
authors.forename: Gregory M
authors.initials: GM
authors.lastname: King
authors.forename: Cornelia
authors.initials: C
authors.lastname: Krause
authors.forename: Hubert
authors.initials: H
authors.lastname: Morin
authors.forename: Walter
authors.initials: W
authors.lastname: Oberhuber
authors.forename: Peter
authors.initials: P
authors.lastname: Prislan
authors.forename: Cyrille B K
authors.initials: CB
authors.lastname: Rathgeber
mesh_terms: D058506:Cambium / Q000254:growth & development*; D002170:Canada; D002454:Cell Differentiation; D057231:Climate Change; D005060:Europe; D064028:Tracheophyta / Q000254:growth & development*; D052584:Xylem / Q000166:cytology / Q000254:growth & development*
keywords: Cambium; cell differentiation; cell production; climate change; conifers; growth; meristem; phenology; productivity; secondary wall formation; xylogenesis