GERMINATION OF PINE SEEDS UNDER CANOPY AND ON CUTTINGS OF MOSSY AND BILBERRY PINE FORESTS

 

Sudnik A.V. (IEB NASB, Minsk, Belarus)

 

В результате проведения эксперимента по определению грунтовой всхожести семян сосны обыкновенной в различные условия микросреды под пологом и на вырубках сосняков мшистых и черничных можно сделать вывод, что субстрат, в который попадают семена, оказывает решающее влияние на прорастание семян и укоренение всходов.

 

The studying of laws of development and growth of seedlings from the seeds, which have got in various conditions of a microenvironment, was carried out in the experiment on definition of ground germination of pine seeds under tree canopy and on cuttings of mossy and bilberry pine forests (Pinetum pleurozoisum and P. myrtillosum). The purpose of research is to reveal a regulation role of shrubs, grasses, mosses and floor covering in appearance and development of seedlings. The experimental sowing of pine seeds was carried out under tree canopy and on cuttings in similar associations of mossy and bilberry pine forests in Borisov and Puchovichi forest enterprises.

Seeds under tree canopy were sowed in the following variants: 1) the control; 2) removal of grassy-shrubby layer; 3) removal of a moss cover; 4) removal of a moss cover and grassy-shrubby layer; 5) the mineral soil (removal of floor covering, moss cover and plants of grassy-shrubby layer); 6) imitation of a surface fire of weak intensity. On cuttings the sowing of seeds was carried out on 1, 4 and 5 variants.

The sowing was carried out in the beginning of a vegetative season (April – May) on quadrates by dimension 1х1m in 3-fold frequency (for each variant) on 100 seeds without samara without embedding (imitation of a self-sown crop). In total 108 experimental quadrates were sowed. In June and July the quantity of viable seedlings was counted up. Only part of all crop of pine seeds representing reproductive potential of pine populations is realized in renewal: from 0-1 to 68%, i.e. already at a stage of a germination 32-100% of individuals are lost (table 1).

For germination of seeds the heat, moisture and oxygen are necessary, and for rooting and growth of seedlings – also presence of light and a mineral or organic substratum with elements of feeds. More favorable climatic conditions for germination of seeds such as amount of deposits, mean daily temperature, relative moisture of air in May were marked during experiment in Puchovichi forest enterprise. Therefore the received parameters of germination of seeds were higher than in Borisov forest enterprise (table 1).

As a result of the studying of germination of pine seeds under tree canopy and on cuttings it is possible to draw a following conclusion, that substratum, in which seeds get, has deciding influence on a germination of seeds and rootage of seedlings.

 

 

Table 1 - Germination of pine seeds in various variants under canopy and on cuttings of mossy and bilberry pine forests

Variants	Borisov forest enterprise				Puchovichi forest enterprise
	under canopy		on cutting		under canopy		on cutting
	mossy	bilberry	mossy	bilberry	Mossy	bilberry	mossy	bilberry
Technical germination	81	81	81	81	93	93	93	93
Earth germination on quadrates:
1) control;	1	0	6	5	2	2	1	0
2) removal of plants of a grassy-shrubby layer;	3	3	–	–	5	3	–	–
3) removal of a moss cover;	8	10	–	–	19	14	–	–
4) removal of a moss cover and a grassy-shrubby layer;	13	12	17	7	25	21	14	7
5) mineral soil;	22	24	13	15	68	36	15	12
6) imitation of a surface fire of weak intensity.	20	18	–	–	38	29	–	–

 

The greatest quantity of seedlings has appeared on quadrates, where the moss cover, grassy-shrubby layer and floor covering were removed up to a mineral ground. The top part of a mineral layer has higher moisture and lower fluctuation of temperature then moss cover and floor covering. This explains the best germination of pine seeds and successful rooting of seedlings in these conditions. Germination of pine seeds in these conditions reached 68 and 36% accordingly under canopy of mossy and bilberry pine forests (table 1). On the other hand mineralized ground is comparatively poor by humus, cindery elements and microflora, is condensed on surface quickly and is subjected to frost heave that causes mass squeezing of annual seedlings (Sannikov and Sannikova, 1985). Decrease of germination up to 15% on cuttings is possible to explain by fast drying of top 5 sm layer of ground, that is adverse not only for appearance but also for growth of pine seedlings.

Germination under canopy of mossy and bilberry pine forests on quadrates, where plants of grassy-shrubby layer and moss cover were removed, reached 25 and 21% accordingly (Table 1). The floor covering in depending on its thickness, density, structure, degree of decomposition and degree of a ground covering renders influence on germination of seeds and rooting of seedlings (Sundkvist 1993). Roughly-humus weakly decomposed floor covering with its adverse physical properties such as high air permeability, bad water-capillary connection with mineral horizon of ground and unstable hydrothermal regime is main obstacle for renewal of a pine under canopy and on clear cuttings. First of all the negative role of floor covering is explained by them, that its moisture strongly varies. In droughty days the floor covering can dry up before full loss of moisture. Small roots of seedlings are compelled to repeatedly bent between fallen needles, leaves and branches while they do not achieve mineral layer of ground. On this way roots frequently are retarded in floor covering and at drought die off. Consequently, the more think layer of floor covering, the better seedlings root in ground and survive. Therefore germination of seeds in this variant is smaller than at full removal of floor covering. Germination of seeds on cuttings of mossy and bilberry pine forests reached 17 and 7% accordingly. As a result of felling the degree of decomposition of floor covering has increased, and thickness has decreased. Presence of floor covering by thickness up to 1-2 sm on clear cuttings reduces evaporability from a surface of ground and protects seedlings from sun.

The delay of seeds by shrubs, grasses and especially mosses influences negatively on seed reproduction of a pine. The powerful moss cover not only prevents penetration of seeds to soil, but also frequently causes loss of vitality or death of seedlings. This is connected with fluctuations of moisture of mosses, and also because the storage of compounds keeping in seeds before achievement of soil by seedling root is exhausted. Removal of a moss cover has resulted to increasing of germination in 8-10 times. The species composition, power and degree of development of grassy-shrubby cover render certain influence on penetration of seeds to soil, but especially on subsequent growth and development of seedlings. Removal of plants of this layer raises germination in 1,5-3 times.

Comparatively high germination was marked on quadrates after imitation of surface fires (Table 1). Germination was lower, than on quadrates with a mineral ground, and higher, than on quadrates with other variants. The "burn" substratum is optimal for growth and development of seedlings on the majority of chemical properties (рН, the content of cindery elements, mineral forms of nitrogen, etc.) and also on heat-provision, microbiological activity and other conditions (Sannikov and Sannikova 1985, Richter 1996, Volkov et al. 1997 etc). The best conditions for appearance of pine seedlings are provided, when removal of the top undecomposed layer of floor covering and moss cover with adverse physical and chemical properties takes place as a result of a fire. In a case of “underburning” underfired layer of floor covering and mosses interferes to appearance and survival of seedlings. Therefore germination of pine seeds on quadrates after imitation of surface fire is lower, than on quadrates with mineral ground, despite of increase of provision of substratum by moisture, heat, accessible elements of a mineral feeds, destruction or suppression of lower layer plants competing with pine seedlings.

Conditions for appearance of seedlings from seeds under canopy and on cuttings of mossy pine forests are more favorable in comparison with conditions of bilberry pine forests. Germination of seeds in similar conditions of a microenvironment under forest canopy is much higher, than on clear cuttings. It is possible to explain by fast drying of soil layer. It is unfavorable not only for appearance, but also for growth of pine seedlings on clear cuttings.