Estimating acorn crops using visual surveys

Abstract

We describe a visual survey technique for evaluating acorn production. In contrast with previously proposed methods, our technique yields ratio-level data on annual productivity that are analyzable with standard statistics and, by sampling the same trees each year, data on the reproductive patterns of individual trees. We compared this technique with two independent sets of acorn-trap data acquired on oaks of three species at Hastings Reservation in central coastal California. Correlations between acorns counted by the visual surveys and collected from acorn traps under the same trees were significant for all three species. Most scatter in the data appeared to be attributable to three causes: (1) sampling error, especially among trees with very small crops, (2) finite counting speed, leading to a lack of discrimination among trees with very large crops by the visual surveys, and (3) arboreal acorn removal by animals. This latter factor can be particularly large, rendering visual surveys more reliable than the use of traps. Furthermore, only the high efficiency of visual surveys allows for the practical assessment of samples large enough to accommodate high within-population variation and detect widespread geographic variation in acorn production. Visual surveys offer a method of assessing the fruit or cone crops of many hardwood and conifer species that is not only more efficient but also more accurate than the use of traps.

Acorn production in Spanish holm oak woodlands

“…The counts are made during a f ixed time period, in sectors of the crown, or in quadrats (Koenig et al, 1994;Garrison et al, 1998;Perry and Thill, 1999). A variation of this method has been extensively applied in [dehesas] (Vázquez et al, 1999), and the traditional way of estimating acorn crops are subjective estimations called «aforos».…”

The role of ecophysiological studies in the genus Prosopis: implications for the conservation of drought-prone species

“…Thus some species living in drought-prone climates tend to suppress their growth to enhance seed production, such as Quercus ilex, which suffers from water stress during very dry years, This strategy is reflected in the negative correlations observed between these two parameters (Sánchez-Humanes et al, 2011). In contrast, years with high humidity show positive correlations between these parameters, indicating a balanced strategy that allows growth and seed production simultaneously (Koenig et al, 1994). This behavior has not yet been observed in species living in desert climates.…”

Variation of early reproductive allocation in multi-site genetic trials of Maritime pine and Aleppo pine

“…Since Aleppo pine cones remain attached to the branches, either opened or as serotinous cones, we used an alternative method to estimate accumulated cone production trough the tree life. Cones counted in 15 seconds were taken as a surrogate of reproduction (Koenig et al, 1994). According to a preliminary sub-sample, counting cones during 15 seconds was considered to provide a reliable estimation of the total cone number per tree, comparing estimations in trees with different cone loads.…”