Ecological and Biological Properties of Holm Oak (Quercus ilex L.) on the Island of Rab

Na otoku Rabu, u šumama hrasta crnike, u proljeće 2006. godine osnovane su četiri pokusne plohe (2 × 2 m) od čega jedna u šumi srednjega uzgojnoga oblika, a tri u panjačama različite dobi i strukture. U šumskim su ekosustavima praćene mikroklimatske prilike. Obavljene su morfološke analize korijenskoga sustava ponika i pomlatka hrasta crnike. Tijekom 2006, 2007. i 2008. godine brojen je ponik i pomladak hrasta crnike na pokusnim plohama radi utvrđivanja prirodnoga mortaliteta. Mikroklimatske su prilike u panjačama nepovoljnije za rast i razvoj vegetacije u odnosu na mikroklimatske prilike u sastojini srednjega uzgojnoga oblika. U panjači je temperatura zraka viša, a relativna vlaga zraka niža u odnosu na mikroklimu sastojine srednjega uzgojnoga oblika. Na svim četirima pokusnim plohama zabilježen je izuzetno velik broj prirodnoga ponika i pomlatka hrasta crnike. Veća brojnost ponika dobivena je u panjačama (480 000 – 1 190 000 kom./ha) za razliku od sastojine srednjega uzgojnoga oblika (465 000 kom./ha). Utvrđena je velika varijabilnost u završetku klijanja ponika hrasta crnike. Klijavost ponika u sastojini srednjega uzgojnoga oblika kulminirala je ranije nego u panjačama, što razumijeva i postojanje boljih mikroklimatskih uvjeta na staništu. Dobivene su statistički značajno veće visine ponika hrasta crnike u sastojini srednjega uzgojnoga oblika u odnosu na sastojine panjača. Mortalitet je mladih biljaka hrasta crnike za 8,98 % također veći u sastojini srednjega uzgojnoga oblika u odnosu na sastojine panjača. Prosječan mortalitet ponika i pomlatka hrasta crnike iznosio je 52,35 %. Dokazano je podjednako odumiranje ponika i pomlatka s obzirom na pokusne plohe. Dobivena je negativna i visoka korelacija između duljine korijena i prosječnoga promjera korijena ponika i pomlatka hrasta crnike. Kod volumena korijena nije dokazana statistički značajna razlika između datuma mjerenja.This paper deals with ecological and biological properties of Holm Oak trees (Quercus ilex L.) on the Island of Rab. Forest ecosystems are influenced by numerous local meteorological and climatic conditions. In spring 2006 four experimental plots (2x2 m), one in the middle forest (both seed and coppiced trees) and three in coppices of different age and structure, were established on the Island of Rab. Rotronic hygromers for measuring air temperature (°C), relative air humidity (%), wet bulb temperature (°C) and dewpoint/frostpoint (ºC) were placed on two sites (middle forest and coppice). The values were measured from May 2006 to May 2007. Lux-meter was used for measuring relative light intensity. In 2006 soil humidity (%) was measured five times with Theta Probes model ML2x at the average depth of Holm Oak seedling rooting. On three occasions 30 Holm Oak seedlings were samples for root analysis. The scanner Epson Expression 10000XL and software WinRHIZO ProLA2400 for the analysis of washed roots were used to determine the total root length (cm), average root diameter (mm), volume (cm3), number of tips (pcs), forks (pcs) and crossings (pcs). In order to determine the natural mortality, the seedlings and young plants of Holm Oak were counted on ten occasions during the three years of research (in 2006, 2007 and 2008). The seedling heights were measured at the end of the germination phase and at the end of the first growing season. Minimum air temperature in coppice was lower compared to the middle forest. Microclimatic conditions in coppice are less favorable for the growth and development of vegetation than those in the middle forest. Coppice has higher air temperature and lower relative air humidity compared to the microclimate in the middle forest. Large numbers of natural Holm Oak seedlings and young plants were recorded on all the four experimental plots, which can be attributed to favorable climatic factors influencing the yield on the Island of Rab. A large number of seedlings was obtained in coppice (480,000 – 1,190,000 pcs/ha) compared to the middle forest (465,000 pcs), which can be attributed to the age of the stand, i.e. the size of the fructifying trees and the shrub cover. There is a great variability between the four experimental plots with respect to the end of germination (4/7 – 3/10). The germination of Holm Oak seedlings in the middle forest reached its peak earlier (4 July 2006) than in the coppice (31 July 3 October), which implies the presence of better microclimatic site conditions. On some experimental plots Holm Oak acorns were germinating throughout 2006, which is an indicator of poor germination conditions. The key factor responsible for seed dormancy in this case was the lack of moisture in the soil. Statistically significant larger heights of Holm Oak seedlings were measured in the middle forest compared to the heights in the coppice. The mortality of young Holm Oak plants was also by 8.98% higher in the middle forest than in the coppice. The mortality of Holm Oak seedlings and young plants between 3 October 2006 and 30 January 2008 was 52.35%. The same trend of seedling and young plant mortality was recorded on all the experimental plots. After 27 months a large number of natural young plants of very good vitality survived on all the plots. A negative and very high correlation between the root length and average root diameter was obtained for Holm Oak seedlings and young plants (r=–0.7884). With respect to the measurement date there was no significant difference in root volume, which means that in the 20 months of research there was no significant increase in root volume of Holm Oak seedlings and young plants in the soi