Current and future conifer seed production in the Alps: testing weather factors as cues behind masting

Abstract

Temporal patterns of masting in conifer species are intriguing phenomena that have cascading effects on different trophic levels in ecosystems. Many studies suggest that meteorological cues (changes in temperature and precipitation) affect variation in seed-crop size over years. We monitored cone crops of six conifer species in the Italian Alps (1999–2013) and analysed which seasonal weather factors affected annual variation in cone production at forest community level. Larch, Norway spruce and silver fir showed masting while temporal patterns in Pinus\ud sp. were less pronounced. We found limited support for the temperature difference model proposed by Kelly et al. Both seasonal (mainly spring and summer) temperatures and precipitations of 1 and 2 years prior to seed maturation affected cone-crop size, with no significant effect of\ud previous year’s cone crop. Next, we estimated future forest cone production until 2100, applying climate projection (using RCP 8.5 scenario) to the weather model that best predicted variation in measured cone crops. We found no evidence of long-term changes in average cone production\ud over the twenty-first century, despite increase in average temperature and decrease in precipitation. The amplitude of predicted annual fluctuations in cone production varies over time, depending on study area. The opposite signs of temperature effects 1 and 2 years prior to seed set show that temperature differences are indeed a relevant cue. Hence, predicted patterns of masting followed by 1 or more\ud years of poor-medium cone production suggest a high degree of resilience of alpine conifer forests under global warming scenario

Environmental effects on fine‐scale spatial genetic structure in four Alpine keystone forest tree species

“…Bisi et al. () showed that spring and summer temperatures and precipitations of one and two years prior to seed maturation influence cone‐crop size in Alpine conifer species. Based on their model and taking into account climate change scenarios, they do not expect marked changes in masting patterns in Alpine forests.…”

“…Bisi et al. () found marked interannual variation in cone production, with years resembling masting events in P. abies , A. alba and L. decidua , whereas P. cembra had less interannual variation in cone‐crop size. All species are wind‐pollinated, and seeds are exclusively dispersed by wind in A. alba , L. decidua and P. abies , whereas in P. cembra, seed dispersal is tightly associated with a bird, the European nutcracker ( Nucifraga caryocatactes ), and establishment is strongly affected by biotic interactions (Neuschulz, Merges, Bollmann, Gugerli, & Böhning‐Gaese, ).…”

“…Sites with more favourable years for growth and reproduction (e.g., cool years with high spring precipitation; see, e.g., Oberhuber, for Pinus cembra ), with few or no late frosts, may reduce the variance of reproductive success, and in turn FSGS, by allowing most trees to contribute to reproduction, while in sites experiencing hotter, drier years, many trees might be effectively sterile, increasing FSGS. Third, masting events (i.e., the interindividual synchronization of seed crops in particular years) are driven by climate factors, in particular spring/summer temperatures and rainfall (Bisi et al., ; Kelly et al., ). Climate could then affect the variance of reproductive success, and thus FSGS, in forest trees with marked masting, such as Larix decidua, Picea abies or Abies alba .…”

Reproduction as a bottleneck to treeline advance across the circumarctic forest tundra ecotone

“…Favourable climate conditions driven by synoptic weather patterns have been identified as triggers of regionally synchronous pulses of high seed production (e.g., 'mast' years; Koenig and Knops 1998). All seven species in this study exhibit masting dynamics that are hypothesized to be the result of some combination of warm, dry conditions in the growing seasons up to two years prior to cone development (see examples for our study species in Woodward et al 1994, Houle 1999, Sirois 2000, Krebs et al 2012, Bisi et al 2016, Gallego Zamorano et al 2018. However, documentation of seed production in mast years requires long time series and our study design was insufficient to assess controls over mast years.…”

Red squirrels decline in abundance in the boreal forests of Finland and NW Russia

“…We also aim to assess the impacts of climate change and deforestation on trends in red squirrel abundance, while taking into account predator abundance. The summer temperature of the previous year, on the other hand, is one of the most important determinants of the cone crop (Pukkala et al 2010, see also Bisi et al 2016 for the effects of climate on conifer seed production). Due to global warming, when several species shift their area of distribution polewards (Parmesan 2006), we expect to see the more northern populations of red squirrels remain stable or increase as a result of milder winters and increased overwinter survival, which is a critical phase especially for subadults (Selonen et al 2015).…”