Estimating acorn crops using visual surveys

Titre

Estimating acorn crops using visual surveys

Canadian Journal of Forest Research

Créateur

Walter D. Koenig

Johannes M.H. Knops

William J. Carmen

Mark T. Stanback

Ronald L. Mumme

Sujet

Acorn

Acorn production

Productivity

Visual survey

Date

1994-10-01

doi

10.1139/x94-270

uri

http://www.nrcresearchpress.com/doi/10.1139/x94-270

Résumé

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.

volume

24

numéro

10

pages

2105-2112

Titre abrégé

Can. J. For. Res.

Langue

en

issn

0045-5067, 1208-6037