Journal of

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Undoubtedly, identifying and introducing drought resistant species for reforestation of the Zagros forests should be considered by forest specialists.,the current research identified mechanisms of drought tolerance in Hawthorn (CrataegusaroniaL.) and Mahaleb (Prunusmahaleb L.) seedlings in a greenhouse experiment using a completely randomized design. The experiment contained 3 stress treatments with 5 replications each. The treatments were soil moisture as control (based on field capacity), moderate stress (based on 50% field capacity) and severe stress (water withholding). Our findings showed that relative water content and stem water potential decreased in both species with increasing of drought severity. Although the total chlorophyll content was no affected by drought stress, carotenoid content was declined in response to the stress. Proline and total soluble carbohydrate concentration, as osmotic adjustments, increased in both species. According to electrolyte leakage and malondialdehyde results, we concluded that Hawthorn can tolerate moderate and gradual drought stress by the means of some adaptations but accidental water withholding stress leads to oxidative stress in this species. On the other hand, although moderate and gradual drought stress leads to oxidative stress on the Mahaleb, but accidental water withholding stress did not have the same course of negative effect as it had on Hawthorn.

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Considering the importance of forest structure and interaction among different tree species, this study conducted aimed to determine and compare spatial pattern, heterogeneity, and dimensions of Hawthorn and Maple trees with other neighbor trees. For determining Hawthorn and Maple trees structure, 30 individual of each trees were identified and studied. Based on the results, uniform angle index for Hawthorn and Maple trees were 0/744, and 0/733 respectively, which would propose a clumped pattern for these two species. Computed mingling index values for Hawthorn and Maple were 0/877 and 0/955 respectively that show a high tree species mixture. Also, the average of crown canopy differentiation and crown canopy dimension were 0/582 and 0/322 respectively, for Hawthorn tee and it was 0/42 and 0/656 respectively for Maple tree. Based on mean values, these results show that Hawthorn had high level of differentiation but was inferior in comparing to its neighbors whereas Maple has intermediate differentiation and is dominant to the other neighbors. The average distance to nearest neighbors for Hawthorn and Maple were calculated 7/374 and 6/278 respectively. The results of an absolute discrepancy algorithm (AD) showed a high differentiation of Hawthorn and Maple mixture in comparing to the other indices. It is concluded that maple is superior to hawthorn in dimension and because of low frequency of these two species, they hold high values of mingling indices.