Throughfall In A Mature Oak-Beech Forest Ecosystem


Özhan S., Hızal A., YURTSEVEN İ.

Istanbul University Journal of the Faculty of Forestry, cilt.61, ss.33-40, 2011 (Hakemli Üniversite Dergisi)

  • Cilt numarası: 61 Konu: 1
  • Basım Tarihi: 2011
  • Dergi Adı: Istanbul University Journal of the Faculty of Forestry
  • Sayfa Sayıları: ss.33-40

Özet

Bu araştırmada yaşlı meşe-kayın karışık orman ekosisteminde ormanaltı yağışın belirlenmesi ve yağış-ormanaltı yağış ilişkisinin ortaya konması amaç edinilmiştir. Ormanaltı yağış ölçümü, Belgrad Ormanı Ortadere Yağış Havzasındaki karışık meşcereleri temsil etmek üzere tesis edilen bir deneme alanında 5 ayrı standart yağış ölçer ile yapılmış, toplam yağış ölçümü ise deneme alanına yakın bir yerde traşlama kesimi ile oluşturulan açık alanda gerçekleştirilmiştir. 
Yapraklı ve yapraksız dönem ölçmeleri olarak iki periyoda ayrılan ormanaltı yağış değerleri açık alana düşen yağışın yüzdesi olarak hesaplanmıştır. Araştırma bulgularına göre ormanaltı yağış, yapraklı dönemde % 75,4 ve yapraksız dönemde ise % 82,7 bulunmuştur. Bu iki ortalama arasında istatistiksel anlamda önemli fark saptanmıştır (P =0,004). Mevsim ayırımı olmaksızın yapılan değerlendirmede de yağışın % 80.1 inin ormanaltı yağış şeklinde toprağa ulaştığı belirlenmiştir. Regresyon analizlerine göre yağış miktarı (mm.) ile ormanaltı yağış (mm. ve %) arasında her iki periyot için önemli düzeyde ilişkiler saptanmıştır. Bu ilişkiler yağış (mm.) ile ormanaltı yağışın mm. değeri için doğrusal (yapraklı dönemde R2= 0,969, yapraksız dönemde R2=0,987) ve yağış (mm.) ile ormanaltı yağışın % değeri için logaritmik 
olarak tanımlanmıştır (yapraklı dönemde R2= 0,523, yapraksız dönemde R2=0, 551)

It is important to know the processes of precipitation in forest ecosystems due to their effects on hydrological cycle and watershed hydrology. One of these processes is throughfall. The throughfall is the portion of precipitation that falls directly to the ground or drips from the forest canopy. Although numerous studies concerning throughfall have been made in different forest ecosystems in Europe and USA, there are only five researches in Turkey. In other words, limited data are available concerning throughfall in our country.

The objectives of this paper were: 1) to determine the throughfall of old oak-beach mixed forest ecosystem which is dominated in Belgrad Forest near İstanbul, and 2) to reveal relations between throughfall and precipitation in growing and dormant seasons.

The study was undertaken within the Ortadere Watershed of Belgrad Forest, near İstanbul. A forest stand which represents the vegetation of watershed was selected as a study plot that comprised of

old growth oak (Quercus frainetto ten.) and beech trees (Fagus orientalis Lips.), The average canopy cover was 80 %.

Mean temperature is 12.3 oC and mean annual precipitation is 1129.4 mm. Mean daily temperature is 21.7 °C during August, the warmest month, and 4.2°C during January, the coldest month.

In order to determine amount and variation in throughfall, two transects with 10 m. in length intersecting vertically each another were set up under forest canopy and 5 standard rain gauges were placed on the junction and endpoints of these transects. Amount of the throughfall was measured after each precipitation event. Total rainfall was recorded with a standard rain gauge placed in a clear-cut forested area nearby the study plot. Since stemflow was not measured, interception loss was not calculated.

The results summarized in Table 1 show that throughfalls are 75.4 % and 82.7 % in growing and dormant seasons, respectively. Coefficients of variation of these averages are very high. This can be explained by great differences among precipitation events. The difference between throughfall of two seasons is statistically significant (=0.004). It means that greater portion of precipitation reaches the ground in dormant season than that of growing season. Significant differences were not found among averages in sampling points of throughfall measurements. In other words, study plot has a so homogenous canopy cover that distribution of throughfall was not affected significantly.

There are statistically highly significant correlations between precipitation and throughfall. Therefore, linear and curvilinear regression equations for growing and dormant seasons were developed where precipitation (mm) was the independent variable and throughfall (mm and %) was the dependent variable (fig. 3,4,5,6). Linear correlations belong to relations between precipitation in mm. and throughfall in mm. (R2= 0.969, Y=0.806X ; R2=0.987, Y=0.860X for growing and dormant season respectively) and curvilinear correlations between precipitation in mm. and throughfall in per cent (R2= 0.523 , Y=12.75ln(X)+33.15 for growing season and R2=0.551, Y=8.705ln(X)+51.19 for dormant season)