Understanding the factors influencing the growth of Zelkova abelicea in browsing exclosures

The growth of Zelkova abelicea (Lam.) Boiss. (Ulmaceae), a tree species endemic to the island of Crete (Greece), was studied within 31 fenced plots protected from browsing during three years after fencing across the entire distribution range of the species. Potential geographic, edaphic, climatic and physiognomic factors that could influence shoot elongation and height increase were investigated for each plot. We found that trees grew twice as much within the same period of time in western and central Crete compared to trees from eastern Crete. In addition, taller trees grew more than shorter individuals. Although some variation was found within the soil parameters, and particularly sites situated on slopes were distinguishable from sites situated in flat dolines, none of the soil parameters was found to be significant in explaining growth differences amongst Z. abelicea trees of different mountain ranges. Precipitation and temperature were interpolated for each plot from an existing network of 49 weather stations on Crete. Our analyses showed that the plots were distributed along a longitudinal, westwards increasing gradient in precipitation as well as along an altitudinal gradient in temperature. Our analyses revealed that geographical position on the island, precipitation in June and initial tree height were significant in explaining spatial differences in Z. abelicea growth. Our results underline the importance of spring and early summer climatic conditions in determining Z. abelicea growth and highlight differences throughout the island.