The Impact of Olive Orchard Abandonment and Rehabilitation on Pollen Signature: An Experimental Approach to Evaluating Fossil Pollen Data

Abstract

For millennia the olive was an important cultivated tree in the southern Levant, as evidenced by numerous archaeological finds and Holocene pollen assemblages. However, the impact of abandonment and rehabilitation of olive orchards (a recurrent historical process) on the fossil pollen record has not been studied. We documented quantitative differences in the olive pollen signature in a well-managed traditional olive orchard, an abandoned orchard, and an orchard rehabilitated after decades of abandonment, establishing the biological basis for understanding the olive pollen signature. The results indicate a strong decline in flowering and pollen production for decades following the cessation of cultivation and a rapid increase following rehabilitation. This strong response suggests that the fossil pollen curves are a reliable marker for determining the extent of olive oil production in ancient times. In terms of agricultural/economic efficiency, rehabilitation of an orchard takes much less time than establishing a new orchard. This could have been one of the reasons why the same sites were reoccupied during peaks of settlement activity in antiquity. The recent field results are compared to fossil pollen data from the Sea of Galilee during the Bronze and Iron Ages.

Keywords:

• Olive pollen
• Olea europaea
• olive domestication
• olive orchard
• orchards abandonment
• pollen signature
• Bronze Age
• Iron Age
• Levant

Acknowledgments

This study was funded by the European Research Council under the European Community’s Seventh Framework Program (FP7/2007–2013)/ERC grant agreement no. 229418. We thank Mr. A. Straus of Ramot Menashe Park and Mr. B. Mouassi of Baqa al Gharbiyye for their permission to conduct our research in their orchards. We would also like to acknowledge S. Ben-Dor Evian and M. Pollak for their technical help and especially T. Langgut for all his assistance in the field. M. Stein from the Israel Geological Survey and T. Litt and his team from the Bonn Palynological Laboratory are gratefully thanked for their help in the extraction of the Sea of Galilee core.

Notes

1 Today, wild olive trees are very rare in Israel. Most of the olives that grow in natural habitats are feral. We sampled a wild olive population located on the Carmiya range on Mount Carmel. Results of pollen grain ornamentation and size measurements (with the use of the software of ImageJ) showed no distinct differences in pollen surface ornamentation between wild and domesticated taxa. Only minor differences in average pollen size based on length and width measurements were documented, which unfortunately are not sufficiently pronounced. Further research on this wild population is impossible today since it was burnt during the conflagration on Mount Carmel in December 2010.

2 Aguilera and Valenzuela (2012) showed that olive trees tend to increase their pollen production rate as altitude increases (probably as a reproductive strategy to ensure fertilization). Flowering and pollen production are also influenced by meteorological and other environmental factors (e.g. Galán et al. 2004; Ribeiro et al. 2006). We therefore conducted our research in orchards which share similar ecology, altitude, and climatic conditions.

3 For pollen identification a reference collection of Israel pollen flora was used (Steinhardt Museum of Natural History, Tel Aviv University) as well as regional pollen atlases.