Acorn production by oaks in central coastal California: influence of weather at three levels

Abstract

Mean annual acorn crop size of oaks in central coastal California correlated with weather for four of five species. For the deciduous Quercuslobata and Quercusdouglasii, larger crops were produced in years when April temperatures were warmest, while for the evergreen Quercusagrifalia and Quercuschrysolepis, crops were larger when there was more rain one and two years prior to the year when acorns were produced. No correlations were found between weather and mean annual acorn production by Quercuskelloggii. Within years, individual Q. douglasii that flowered during periods of greater solar radiation produced more acorns, and during 1 of 5 years individual Q. lobata and Q. agrifolia produced larger crops when they flowered during warm, dry periods. These results indicate that conditions favorable for pollination and fertilization strongly enhance mean annual acorn production in Q. lobata and Q. douglasii and may have an effect on differences in acorn crop size among individual Q. lobata, Q. douglasii, and Q. agrifolia. Mean annual acorn crops of these three species were significantly concordant among three sites in central coastal California 300 km apart. Weather conditions were also significantly correlated, especially annual rainfall and mean April temperatures. Thus, the environmental factors that have the strongest influence on mean annual acorn production within a site are also those that are the most geographically concordant. However, we found no relationship between environmental factors and differences in mean annual acorn production by these same three species at the three sites.

Patterns and sources of variation in flowering, seed supply and seedling recruitment in surfgrass Phyllospadix torreyi

“…Such was found to be the case for 4 out of 5 species of oaks in central coastal California, where variation in weather during floral and seed development explained up to 78% of the variation in acorn crop size (Koenig et al 1996). In the present study, the absence of surfgrass seedlings in winter 1999 can be traced to the pervasive failure of fruits to mature in fall 1998 when high levels of aborted fruits were observed.…”

Tree growing space and acorn production of Quercus robur

“…Climatic factors influencing the fructification of oak include unfavourable temperature and precipitation conditions in the time of flowering and the occurrence of stress caused by drought or frost periods during previous years (Harapin et al 1996;Koenig et al 1996 and2010;Askeyev et al 2005). Several hypotheses and causes were generally discussed by Kelly (1994) and Koenig et al (1994) when explaining the occurrence of strong mast years in oak stands.…”

Modeled regional climate change and California endemic oak ranges

“…It is highly sensitive at both seedling and adult stages to water stress (9). Higher acorn production by both species is correlated to warmer April temperatures (10), probably a result of greater pollen advection and therefore greater fertilization under warmer, less humid spring conditions (11).…”