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Variations in forest vegetation are effected by several factors, one of the most important of which being the crown canopy. This study aims to survey the effect of close and open crown canopy on the herbaceous diversity in Nav-e Asalem forests in Guilan province. To this aim, 15 canopy gaps of small (100-200 m2), medium (200-300 m2) and large (300-400 m2) sizes were selected with 5 replications each. Moreover, control plots of the same sizes were selected under the tree canopy. Along small and large diagonals in each gap microplots of 2×2 m each were measured in a randomized systematic design. The percentage of herbaceous cover was estimated using Domin scale. To assess plant diversity in each plot, diversity indices of Simpson, Shannon-Wiener, Smith-Wilson Evenness Index and herbaceous richness were derived. Results showed that increasing the gaps area resulted in a significant increase of diversity and richness. Furthermore, no significant difference was observed between diversity and richness indices between small area gaps and control areas.

Gaps within forest canopy cause changes in the received amount (intensity) and quality (PAR) of incoming light on forest ground. This research was performed in natural gaps of a reserve control compartment at Kelardasht region in Mazandaran, northern Iran and aimed to determine the role of gap size and relative light intensity on soil enzyme activity. Hence, 14 gaps at four size class (2- 200-300 m2- 300-400 m2 and >400 m2) and four light classes (25 %) were selected. Soil was sampled at 0-20 cm of top soil in the center of each gap. The results showed significantly different dehydrogenase activity in classes of gap size and light intensity, where its maximum amount was observed in the large gap size (300-400 m2) and at low light intensity (< 8%), respectively. Urease activity did not show significant difference within the classes. In addition, relative soil moisture was significantly different across the gap size and light intensity classes, whereas organic matter and Nitrogen did not show to be significant different.

This paper aims to study the spatial pattern of marked trees in compartments 513 and 514 of district five of Safarood Ramsar which is located between 1200 and 1300 m.a.s.l. in the watershed management unit 30. For this purpose, twenty, 1ha sample plots were selected based on two independent communities, 16 plots in managed and 4 plots in unmanaged (control) stands, and the data on 2000 and 2012 were compared. Results showed that the structure of the 20 plots on 2000 was irregular and the selection cuttings within 12 years have made ​​some effects on the structure in 2012 which is now a bit far from irregular form. The number of trees in small, large and extra large diameter classes is reduced. The spatial pattern of marked trees in the compartment 512 showed cluster pattern (located around large and extra large timber), whereas in the compartment 513 was random (located around small and medium timber) which is directly related to the typology of the stands. Moreover, the results indicated that the mean area of gaps in the managed and control stands was 414m2 and 284m2, respectively. Mean total height of seedlings was 1.4m and 1.2m in the managed and control stands, respectively. Mean seedlings number in the managed and control stands was 603 and 512 in 100 m2, respectively. None of the differences of above mentioned data were statistical significant.

- امان‌زاده، ب.، امانی، م.، امین‌املشی، م. و صالحی، م.، 1385. بررسی زادآوری راش در روشنه‌های طبیعی جنگلهای اسالم. پژوهش وسازندگی، 71: 25-19. - حبیب‌پور گتابی، ک. و صفری شالی، ر.، 1388. راهنمای جامع کاربرد SPSS در تحقیقات پیمایشی. انتشارات متفکران، چاپ دوم، 860 صفحه. - حجتی، س.م.، 1378. بررسی نحوه پراکنش و ساختار سنی تجدید حیات طبیعی گونه راش در راشستان‌های بخش گرازبن جنگل خیرودکنار- نوشهر. پایان‌نامه کارشناسی ارشد، دانشکده منابع طبیعی دانشگاه تهران، 67 صفحه. - دلفان اباذری، ب.، ثاقب‌طالبی، خ. و نمیرانیان، م.، 1383. بررسی سطوح روشنه‌های زادآوری بر وضعیت کمی نهالهای استقرار یافته در قطعه شاهد جنگلهای کلاردشت طرح لنگا. فصلنامه تحقیقات جنگل و صنوبر ایران، 12 (2): 266-251. - زبیری، م.، 1384. آمار و اندازه‌گیری جنگل. انتشارات دانشگاه تهران، چاپ دوم، 400 صفحه. - گودرزی، غ.، 1375. بررسی وضعیت زادآوری راش در بخش 2 طرح جنگلداری لیوان و بنفشه‌تپه. پایان‌نامه کارشناسی ارشد، گروه جنگل‌داری و اقتصاد جنگل، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، 78 صفحه. - مرتضی‌پور، ص.، مهاجر، م.ر.، ثاقب‌طالبی، خ. و زاهدی، ق.، 1384. بررسی رابطه زادآوری درخت راش با شکل زمین. تحقیقات جنگل و صنوبر ایران، 13 (4): 474-447. - مروی مهاجر، م.ر.، 1376. جزوه جنگل‌شناسی تکمیلی. دانشکده منابع طبیعی دانشگاه تهران، 55 صفحه. - مروی مهاجر، م.ر، 1385. جنگل‌شناسی و پرورش جنگل. انتشارات دانشگاه تهران، چاپ دوم، 387 صفحه. - موسوی میرکلایی، س.ر، ثاقب‌طالبی، خ.، طبری، م. و پورمجیدیان، م.ر.، 1382. تعیین اندازه سطح حفره تاج‌پوشش برای بهبود زادآوری راش. مجله منابع طبیعی ایران، نشریه دانشکده منابع طبیعی دانشگاه تهران، 56 (1و2): 46-39. - مهربان‌فر، ز.، 1388. مقایسه غنا و نوع گونه‌های درختی با ابعاد مختلف قطعه نمونه (مطالعه موردی: بخش گرازبن جنگل آموزشی و پژوهشی خیرود). سمینار کارشناسی ارشد، دانشکده منابع طبیعی دانشگاه تهران، 35 صفحه. - Adeniji, B.A., Kahissai, K.T. and Kisingo, A.W. 2004. Impact of gap size on tree species regeneration in different location in Kibale forest. Plant and Forest Ecology, 86: 217-227. - Brokaw, N.V.L., 1982. The definition of treefall gap and its effect on measures of forest dynamics. Biotropica, 11: 158-162. - Diaci, J., Pisek, R. and Boncina, A., 2005. Regeneration in experimental gaps of subalpine Picea abies forest in the Slovenian Alps. European Journal of Forest Research, 124: 29-36. - Dobrowolska, D. and Veblen, T.T., 2008. Treefall-gap structure and regeneration in mixed Abies alba stands in central Poland. Forest Ecology and Management, 255: 3469-3476. - Gagnon, J.L., Jokela, E.J., Moser, W.K. and Huber, D.A., 2004. Characteristic of gaps and natural regeneration in mature longleaf pine flatwood ecosystems. Forest Ecology and Management, 187: 373-380. - Huth, F. and Wagner, S., 2006. Gap structure and establishment of Silver birch regeneration (Betula pendula Roth.) in Norway spruce stands (Picea abies L. Karst.). Forest Ecology and Management, 229: 314-324. - Lertzman, K.P. and Krebs, C.J., 1991. Gap-phase structure of a subalpine old growth forest,Canadian Journal of Forest Research, 21: 1730-1741. - Liu, Q. and Hytteborn, H., 1991. Gap structure, disturbance and regeneration in a primeval Picea abies forest. Journal of Vegeteation Science, 2: 391-402. - Martins, S.V. and Rodrigues, R.R., 2002. Gap-phase regeneration in a semideciduous mesophytic forest, south-eastern Brazil.Plant Ecology, 3: 1-12. - Myers, G.P., Newton, A.C. and Melgarejo, O., 2000. The influence of canopy size on natural regeneration of Brazil nut (Bertholletia excelsa) in Bolivia. Forest Ecology and Management, 127: 119-128. - Pedersen, B.S. and Howard, J.L., 2004. The influence of canopy gaps on overstory tree and forest growth rates in a mature mixed-age, mixed-species forest. Forest Ecology and Management, 196: 351-366. - Runkle, J.R., 1981. Gap regeneration in some old-growth forests of the eastern United States. Ecology, 62: 1041-1051. - Yamamoto, S., 2000. Forest gap dynamic and tree regeneration. Journal of Forest Research, 5: 223-229. Nowadays the investigation and identification of natural process such as succession and gaps existence in forest ecosystems have been considered extently in forests management programs. This study examined the regeneration of tree species in relation to size, shape, slope gradient and direction of gaps in a Fagetum community in Gorazbon district of Kheyrud Forest, northern Iran. Three sample area, each 25 ha, were selected and after field study, all gaps within the compartments 317, 318 and 319 were identified. Regeneration of all tree species were record in the gaps, using 100% inventory. Beech, maple, hornbeam and elm tree, were observed in all of the studied gaps, but no significant differences were observed between regeneration frequencies of the species in different gap sizes. The most frequent species were observed in elliptical-shaped gaps. The most frequency of regenerations of beech and maple were observed in slop classes of 11-20%. Also, regeneration of beech, maple, hornbeam and elm showed more frequency in southwest-facing gaps rather than the other directions. According to total number of regeneration in gaps located on the slopes, beech regeneration showed the best establishment rather than another species. Maple and hornbeam followed beech in next ranks.

Identifying regeneration characteristics is a decisive prerequisite in forest stands management. Therefore, the objective of this research was to 1) present the most appropriate tree species for reforestation within stand gaps and 2) study the effect of relative light intensity on regeneration characteristics. Quantitative characteristics were measured in 10 gaps at district one of Loveh forest in Golestan province. Results showed differing frequencies of species depending on gap positions and relative light intensities. Except checker (Sorbus torminalis) regenerations, no significant difference was observed between mean of spring shoot length within gap positions. Annual height growth of checker was maximum for 40% relative light intensity, while the annual diameter growth of hornbeam (Carpinus betulus) and wild cherry (Prunus avium) were maximum for relative light intensity ranging between 30 and 40%, respectively. No significant difference for relative light intensities was observed between other spices characteristics. Therefore, the study concludes that the highest attention should be paid to species mixtures and their ecological requirements for reforestation within the gaps.

In this study, in order to investigate regeneration success and determine the best gap area, the quantitative characteristics of the regeneration groups were evaluated at different gap area classes. For this purpose, 15 regeneration gaps were selected at three area classes with five replications at each class, including: 50-150 (small), 150-300 (medium) and 300-600 m2 (large). Four square meter plots at two meter intervals were used to measure some quantitative characteristics of the regeneration groups by a simple systematic design on north-south (N-S) and east-west (E-W) transects. The data was analyzed, using the completely randomized statistical design and one way variance analysis and Duncan test methods. The Results showed that the total height and the height growth of the saplings were significantly higher in the large gaps in comparison to the small gaps. In addition, the frequency of seedlings and the density of sapling were the greatest in the medium sized gaps. For this reason seedling frequency of Carpinus betulus and Parrotia persica was found in the medium sized gaps. Overall, it can be concluded that in the selection cutting method, the medium sized gaps (150-300 m2) are the most suitable ones.

Hornbeam is the most frequent species in forests of northern Iran. This paper aims to study the relationship between gap size and some quantitative and qualitative characteristics of hornbeam seedlings. For this purpose Khanikan district in Korkrood forest was selected in northern Iran. Four sizes of gap were selected based on silvicultural definitions including: area with less than 200 m², 200 to 500 m², 500 to 1000 m², and larger than 1000 m² and in each gap, 4 subplots each 2 m² were laid out. The current study was made in 2 phases: 1) study on light intensity using fish-eye camera, and 2) quantitative (including collar diameter and height) and qualitative characteristics of hornbeam seedlings. The obtained result showed that the intensity of light changed between 2 and 70 percent in different gaps and different locations of the gaps. The number of hornbeam seedlings increased with a relative increase in the light intensity initially and then decreased. Collar diameter and height of seedlings didn’t show significant differences among different light intensities. The number of seedlings was reduced significantly in the gaps larger than 500 m2. The best qualitative condition and the maximum number of hornbeam seedlings were observed in the gaps smaller than 200 m2.

In temperate forests, disturbances are regarded as processes of great importance to forest vegetation. For the better perception of biodiversity, different indices were used in mountain forests of Lalis located in Chalous. Line transect method used for sampling, and plant abundances were recorded, as well. Forest gaps areas were divided into four classes including smaller than 200 m2,200 - 400 m2, 400 - 600 m2 and larger than 600 m2 areas. In order to analyze of biodiversity, Simpson, Shannon and Wiener, Margalef, Menhenick, Peet and Camargo indices were used. Using analysis of variance, statistical difference between biodiversity indices in respect to gap sizes was found. The maximum and minimum of divers species and richness species indices were related to very large and small gaps, respectively. The highest evenness indices were related to medium and large gaps, whereas the least of evenness indices were related to small and very large gaps.

In this research typology of seedlings composition and density of Fagus orientalis stands in Caspian forests of Iran (Ramsar area), at altitude of 1200-1300 m.a.s.l. within 43 gaps were studied. The gaps were created after marking and cutting the trees. The gaps area varied between 67 and 617 m2. The trial was conducted under the fully randomized design. Based on gap size and homogeneity, 1 to 3 microplots (1m2) were established in each gap. Seedling frequency was counted in each microplot, according to their species and age range (1 and 2-4 years old). The statistical methods of chi-squareand ANOVA (analysis of variance) were used to analyze the data. There was no significant difference of seedling frequency and species diversity among the gap sizes. However, the number of the defined seedlings composition and density types were four and six, respectively. Beech showed the highest frequency among the species. The maximum and average densities of beech seedling were 60 and 15 per m2, respectively. 57% of gaps showed a number of 10/m2 with 1 to 4 years old seedlings.

The main objective of this study which was conducted in an intact stand of the experimental Kheiroudkenar forest (Chelir district), was to examine the ecological importance of dead trees followed by it’s impact on natural regeneration of the forest. In this study the seedlings around dead trees were recorded in a 50 ha stand, where the dead trees were divided into four decay classes. Considering the decay classes, results indicated that; there were different kinds of establishment of regeneration. The highest numbers of seedlings were accounted around dead trees classified in 3rd decay class, while 4, 2 and 1 decay classes were in the next orders. Gap opening related to dead trees had important effects on establishment of the regeneration. Results showed that with increasing of decay classes, size of gaps decreased. In this study gaps were divided into five groups, including close gap (closed canopy), very small (0-12.5 m2), small (12.5-50 m2), medium size gap (50-113 m2) and large size or open canopy (>113 m2). Abundance of seedlings under the closed gaps of stand crown was maximum, while the numbers of seedlings were reduced under the medium gap size, very small, small and large size, respectively. One way analysis of variance showed that there was no significant difference (at 5% significant level) among the number of seedlings around dead trees with different decay classes, however there was a significant difference among abundance of seedlings under different gap sizes, produced by dead trees. Therefore, gap opening caused by dead trees, had higher effect on establishment of regeneration than decay classes.