Auxological Research Of Virgin Forests In The Southern Carpathians

Auxological Research of Virgin Forests in the Southern Carpathians

Introduction

In the beginning all the forest ecosystems were represented by natural virgin forests stands with un-even age structure and obvious ecological, silvicultural and economic advantages (Giurgiu, 1988). Also, the virgin forests represent a model for their durability and high efficient eco-productivity that people strive to obtain (Bândiu, 2013). Therefore, a comparative analysis between these two types of structures is important for developing in-depth knowledge.

Regarding the forest ecosystems’ evolution and their natural dynamics virgin forests are considered inestimable sources of information (Motta et al., 2010) that can be used as scientific basis for improving the forest management economy (Giurgiu, 2013).

During the time various researches highlighted the structural and functional characteristics of the virgin forests. Although such studies failed to meet the requirements and to reveal their natural potential level, they are still a solid base for the next researches of primary ecosystems.

Preliminary research has highlighted the virgin forests’ characteristics in relation to the managed forests, and has referred, inter alia, to the stand structure relative to age, as well as to the correlation between DBH and DBH growth (Giurgiu, 1974).

Recent researches have focused on statistical-based knowledge of a natural forest’s spatial structure, concluding that these ecosystems are characterized by high amplitude of DBH (Popa, 2013).

For the reconstruction of the climate spanning the last centuries, as well as the analysis of the forest ecosystems’ dynamics, researches on dendrochronological series for fir, spruce (Popa, 2013) and beech (Roibu, 2013) had been carried out. The present research study is a continuation within the afore-mentioned topic.

The most important researches related to the structure, dynamics, cause of death and regeneration progress, for the studied area, had been carried out by Tomescu and Turcu between 2004 and 2006, and others from 2009 on. The purpose of these researches was to determine the trees’ age by tree sampling.

In Romania broadleaf forest covers 69,3 % of the afforested land, of which beech comprises 30,7%, oaks 18,2% and other broadleaf 20,4 %. The present investigations subject of this paper have a special importance and they aim, primarily, to develop in-depth knowledge on the peculiarities of the tree growth in the primary forests.

The objectives of the present research are twofold evolution and analysis of a virgin beech stand from the growth point of view and elaboration of a dendrochronological series for beech. The aims of the dendrochronological series are as follows: i) radial growth and DBH tree variability; ii) stand structure relative to tree radial growth; iii) dendrochronological aspects; iv) correlation between the tree radial growth and the environmental conditions; v) volume growth.

2. Materials and Methods

The permanent research plot is situated in the “Izvoarele Nerei” Natural Reserve which is located in the “Semenic-Cheile Carasului” National Park, administrative location in 22 compartment, III Negranita management unit from the Nera Forest District, the upper limit of the management unit, altitude 1352 m (fig. 1).

Fig.1 Semenic P20 research plot localization in the “ Semenic – Cheile Carasului” National Park.

The choice of this research plot is based on the consideration of the identification and delineation criteria established in OM 3397/2012 and the fact that the beech forests from the Banat Mountains have the largest and most compact century-old forest from Europe (Toader, 2004). In addition, the technological quality of this beech forest is acknowledged internationally.

From the climatic point of view, the “Semenic – Cheile Carasului” National Park is located in the continental temperate region, with high Mediterranean influences. Winters are long and cold, with snow cover range between 60 and 100 cm, and duration between 80 and 120 days (Tomescu, 2013), leading to a short vegetation season (3 mounts).

Tree growth varies from year to year depending on the vegetation conditions (Popa, 2004) on the one hand, and on competition relationships between trees on the other hand. The growth is materialized by the annual tree ring which holds/contains important information about the time evolution of the tree growth.

For the radial growth determination, 372 trees had been sampled with the Pressler driller, 1,3 m above the ground, by following the cardinal points (N, E, S, V), in order to reduce the influence of the transversal form section and the radial growth, respectively. For highlighting the annual tree rings structure, the samples had been mounted on special wood supports/props and ere ground with different abrasive belts. Samples had been measured by using CooRecorder 7.4., tree ring measure software based on image technical analyses.

The measurement quality had been addressed by the COFECHA application while the growth standardization series by ASTRAN application. Also for determine the pointer years was used Weiser software (Garcia- Gonzalez, 2001).

Volume growth had been determined by means of the method with one inventory method by using radial tree samples taken from the living trees (Giurgiu, 1979, Leahu, 1994, Badea, 2008).

This method allows to determine the volume growth by diameter classes based on the radial tree growth adjusted to the radial tree samples.

The following relation has been used :

(Giurgiu, 1979)

Where : – volume growth in volume percent by diameter classes;

– basal area growth percent by diameter classes;

– reduced average height growth percent.

The basal area growth percent by diameter classes has been determined with the following equation:

(Giurgiu, 1979)

where: average radial growth;

d – diameter class.

The Average height growth percent has been determined by means of the following equation:

(Giurgiu, 1979)

where: number of years spanning the period on which the the radial growth sampled had been averaged;

– annual percent of tree reduced height growth.

The annual percent of tree reduced height growth is determined / established from the production tables depending on the species, index class and in relation to the stand age (Giurgiu, 2004). In the next stage the volume growth had been determined by using the following formula :

(Giurgiu, 1979)

Where: is the volume of the diameter category.

The volume was established with the following regression equation:

log v = a0+a1logd+a2log2d+ a3logh +a4log2h (Giurgiu, 2004)

3. Results and discussion

3.1. Tree radial and diameter growths variability

Based on the information obtained by measuring the radial tree ring samples the chart showing the variability of the radial tree ring samples in relation to their diameters had been recorded (Fig. 2). One may observe that the field spread generated by the experimental values is grouped along a curve shaped as a second degree parabola, specific to uneven- age stand and by default, to virgin stands (Giurgiu, 1979).

Fig. 2 Variation of the radial tree growth average in relation to the tree diameter time period recorded 2003-2013.

An important characteristic pertaining the virgin stands is the variation of the radial tree growth average in relation to the tree diameter, that is to say that the correlation coefficient has lower values (r<0,4) in case of the virgin stands as compared to the managed stands (Giurgiu, 1979). In the case study the correlation coefficient is 0,40. Due to this power of self-regulation, for these types of ecosystems the radial tree growth decreases for bigger trees, correlation field is recorded by a second-degree parabola shaped curve.

3.2. Distribution of values of the radial growth variation coefficient in relation to the tree diameter

The radial growth variation coefficient in relation to diameter for the Semenic P20 virgin stand has a descending trend line (Fig. 3), high values for the lower diameter classes being recorded, and is gradually reduced to the superior diameter classes.

Fig. 3 Distribution of values of radial growth variation coefficient in relation to the tree diameter.

The radial tree growth, as well the diameter variation are influenced by the stand structure in relation to their age, vegetation conditions, trees health and the presence of gaps in the stand caused by windfall, snowfall or tree fall due to tree physiological death, issue specific to the virgin stands.

3.3. Virgin beech stands structure from the Semenic P20 in relation to their radial growth

Similar to the trees diameter distribution, in the virgin stand the Semenic P20, the tree distributions relative to their radial growth is an exponential descending type (Fig.4), with “J” shaped allure, where trees from the lower diameter classes record the highest radial growths.

The experimental radial growth distributions were adjusted by using the theoretical frequency functions: Beta, Gamma 3P and Weibull 3P.

Fig. 4 Tree distribution in relationship with their radial growth.

The goodness of fit was tested using χ2, Anderson – Darling (AD) și Kolmogorov – Smirnov (KS) tests (Table 1).

Table 1. Experimental values ​​of specific goodness-of-fitness

As the results of the Komogorov – Smirnov test , show (Table 1) one may observe that the theoretical distributions laws Beta and Gamma 3P are adjusting the Semenic P20 virgin stand while the Anderson – Darlig test shows no significant differences between the experimental and theoretical values of the distributions Beta and Weibull 3P. In addition, the χ2 criterion showed that no studied theoretical laws adjust the stand.

These differences, between the experimental and the theoretical values, are both explained by the development stages of the stand and by the environmental factors (competition relationships) of the stand and natural factors (windfall, snowfall, drought, insects attack), showing once again that the primeval ecosystems have a higher structural complexity.

3.4. Dendrochronological aspects in the Semenic P20 stand

For the dendrochronological series 36 samples had been used. These samples were taken with the Pressler driller, this method being less destructive as compared to the tree cutting and sample analyses method. The graph representation of the dendrochronological series (fig. 5) shows the stand evolution in time revealing the main life events as stages with high and low radial growth, influenced by other factors such as competitional relationships and multi-annual variation of the environmental conditions.

Fig. 5 Standardization of polynomial model growth series

The Allure of the average radial growth curve is specific to the virgin stands, featuring a unimodal character, with an ascending growth until 1970 (initial and optimal development stages), followed by an auxological regress induced by the decay development stage, issue characteristic to the virgin stands. The average span is 361 years, time period covered is 1651-2013, mean growth is 0,999, with a standard deviation of 0,482 and mean sensibility of 0,390 (Table 2).

Table 2. Statistical parameters off the dendrocronological series (Semenic beech stand)

First-degree autocorrelation is 0,465 and mean correlation coefficient is 0,068.

Positive characteristic years are: 1811, 2006, 2012.

Negative characteristic years are: 1805, 1836, 2010 (year characterized by drought.

Further the growth had been correlated with the climatic data such as temperatures and precipitations (fig. 6), by using CRU TS3.22 climatic database for the time period 1901-2013 (CEDA, 2014).

Fig. 6. Correlation between the radial tree growth and the temperatures, precipitations

This correlation spanned 112 years and highlights the fact that the radial growth is more influenced by precipitations than the temperature. Therefore is demonstrated the high stability of virgin forests.

The age record (363 years has been found in the virgin stand the Semenic P20 and refers to a beech tree featuring DBH 68 cm and 32,10 m height, dating back to 1651 (fig. 7).

Fig. 7 Radial growth for a tree aged 363 years from the Semenic P20 virgin stand

The chronology study of individual tree is important for the growth dynamic analysis. Our analysis findings show that the tree had a lower growth rate in the first 220 years (probably the competitional relationships were the main cause, being shadowed by another tree). After words, when the competition was released the growth increased up- to-date, proving the high growth capacity of trees in the virgin forests at an advanced age.

3.5. Volume growth

To determine the volume growth of the stand, the first step was to determine the volume for each tree (v) and the growth volume percent (piv).After the volume growth for each tree had been determined, then by summing the values the volume growth for entire stand (Iv) had been calculated for the time period 2003 – 2013 (63,32 m3/ha). The average of the annual growth is 6,33 m3/year/ha.

In comparison with the managed beech stands from the selection forests, where the volume growth is between 4,2 and 6,7 m2/year/ha (Guiman, 2007),the Semenic P20 virgin stand has the characteristics of a stand with high volume growth (even for the virgin forests).

Despite the influences of the environmental and climatic factors (the stand is situated at 1532 m altitude, above the beech altitudinal limit, where the vegetation season is short and strong winds occur) and the age influence ( there had been found trees aged over 200 years) on the volume growth, the Semenic P20 stand proves high eco-productive characteristics of virgin stands.

The volume growth distribution in relation to DBH (Fig. 8) is a unimodal , the highest volume growth concentrate in the average DBH area, around the d50, the maximum stability area, specific to uneven aged stands, and to virgin stands, respectively.

Fig. 8 Semenic P20 volume growth between 2003-2013

Thanks to their high adaptive and survival capacity in varied and heavy (even extreme) conditions, the virgin forests, which are complex ecosystems, are net superior to the managed forests, proving once again/time and again the high stability they offer to the ecosystem to which they belong, regardless of the culture system.

5. Conclusions

The virgin forests represent a model for their durability and high efficient eco-productivity. Regarding the forest ecosystems’ evolution and their natural dynamics virgin forests are considered inestimable sources of information (Motta et al., 2010) that can be used as scientific basis for improving the forest management economy (Giurgiu, 2013);

The choice Semenic P20 research plot is based on the consideration of the identification and delineation criteria established in OM 3397/2012 and the fact that the beech forests from the Banat Mountains have the largest and most compact century-old forest from Europe (Toader, 2004). In addition, the technological quality of this beech forest is acknowledged internationally;

About graphical representation of tree radial and diameter growths variability has a shape of a second degree parabola, specific to uneven- age stand and by default, to virgin stands;

The radial growth variation coefficient in relation to diameter for the Semenic P20 virgin stand has a descending trend line with high values for the lower diameter classes being recorded, and is gradually reduced to the superior diameter classes;

As the results of the Komogorov – Smirnov test , show that the theoretical distributions laws Beta and Gamma 3P are adjusting the Semenic P20 virgin stand while the Anderson – Darlig test shows no significant differences between the experimental and theoretical values of the distributions Beta and Weibull 3P. In addition, the χ2 criterion showed that no studied theoretical laws adjust the stand;

For the dendrochronological series 36 samples has been used and the graphical representation showed the stand evolution in time. The length of this series has 361 years, first dated year is 1631. The average radial growth is 0.999 and standard deviation is 0.482. Also the first degree autocorrelation is 0.465 and average R bar is 0.068;

Climatic data as temperatures and precipitations, for the time period 1901 – 2013, in correlation with radial growth shows that the stand is not major influenced by precipitations and temperatures (with small exceptions generated by precipitations). Also demonstrate the high stability of virgin forests;

By analyzing the chronology of individual trees has been shown the high growth capacity of trees in the virgin forests at an advanced age;

The volume growth of Semenic P20 stand, for the period 2003 – 2013, is 63,32 m3ha-1 and the annual growth is 6,33 m3 year -1 ha-1. In comparison with the managed beech stands from the selection forests, where the volume growth is between 4,2 and 6,7 m3 year -1 ha-1 (Guiman, 2007),the Semenic P20 virgin stand has the characteristics of a stand with high volume growth (even for the virgin forests);

The volume growth distribution in relation to DBH) is a unimodal , the highest volume growth concentrate in the average DBH area, around the d50, the maximum stability area, specific to uneven aged stands, and to virgin stands, respectively.

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