Вікова структура та збереженість природних дубових деревостанів Лівобережного Лісостепу

Abstract

Наведено результати аналізу вікової структури природних дубових деревостанів насіннєвого походження в Лівобережному Лісостепу. Показано низьке представництво природних насіннєвих деревостанів у молодняках. Доведено існування тренду щодо збільшення середнього віку природних дубових насіннєвих насаджень у міру збільшення географічної широти, а також меншої збереженості насіннєвих штучних насаджень порівняно з природними

Приведены результаты анализа возрастной структуры естественных дубовых древостоев семенного происхождения в Левобережной Лесостепи. Показано низкое представительство естественных семенных древостоев в молодняках. Доказано существование тренда увеличения среднего возраста естественных дубовых семенных насаждений с возрастанием географической широты, а также меньшей сохранности семенных искусственных насаждений по сравнению с естественными.

In the Left-bank Forest-Steppe the area of oak stands makes up 48 % of forest covered lands. They are represented by natural stands of seed origin, by coppices and by plantations of seed origin. Numerous studies in the permanent plots prove the highest stability of natural oak stands, and that the stands of seed origin are more long-lived, than coppices. However such conclusions were not yet proved in regional level. It is known, that tree mortality increases in certain critical periods of forest development. In result of it, survival of forest decreases. Therefore the graphs of survival (preservation) of stands of different species composition, condition or origin can be compared. Probability of stands to survive in certain age can be evaluated as cumulated proportion of stands, which survive up to such age. Such approach was successfully used by researchers in pine stands of different regions. The aim of our research was to reveal the peculiarities of age structure for natural oak stands of the Left-bank Forest-Steppe as well as survival of oak stands up to different age depending on their origin. The database of Production Association «Ukrderzhlisproekt» was analyzed concerning forest fund of thirteen Forest State Enterprises, located in the Left-bank Forest Steppe. There were five Forest State Enterprises from Kharkiv region, four Forest State Enterprises from Poltava region and three Forest State Enterprises from Sumy region. The forest plots with European oak (Quercus robur L.) as the main forest forming species were selected from database for each Forest Enterprise. These data were grouped by origin and ten-year age classes, and respective distribution of oak stands area was evaluated. Probability of oak stand survival up to certain age was evaluated by Yu. Demakov (2000). Percentage of oak stands area in each ten-year age class and cumulative percentage of stand area, which persists up to each age, was evaluated. It was shown, that natural oak stands of seed origin in the forest fund of analyzed State Forest Enterprises of the Left-bank Forest-Steppe survive up to age over 160 years, and some of them over 200 years. Natural middle-aged oak stands of seed origin are found in the forests of all analyzed forest enterprises, while such stands of the 1st age class (up to 10 years old) are found only in the State Enterprise «Kremenchukske Forest Economy». Mean age of natural oak stands of seed origin is 98 years old, it is the lowest in the State Enterprise «Kremenchukske Forest Economy» (72 years old), and the highest in the State Enterprise «Sumske Forest Economy» (127 years old). Increase of mean age of natural oak stands of seed origin with latitude has been proved (r=0.65; r0.05=0.58). The similar type of survival curve for oak stands has been proved in different forest enterprises of the region. Survival of plantations is always lower than origin forests. It supports the importance of promotion the natural oak stands of seed origin.