Establishment and height development of naturally regenerated Scots pine near the timberline

Transcription

1 Establishment and height development of naturally regenerated Scots pine near the timberline Ville Hallikainen, Metla Mikko Hyppönen, Metla Juha Hyvönen, Metla Juhani Niemelä, Metsähallitus

2 1. Introduction Less than half of the present regeneration area of Scots pine in Finnish Lapland is regenerated using natural regeneration (seed-tree method). The proportion of natural regeneration increases towards the north: in Upper Lapland natural regeneration clearly dominates. In the north, and on the high altitudes there are met the biggest problems in seedling recruitment (low temperature sum, winter fungi etc.). There the time needed for the seedling establishment is usually long.

3 Introduction... continued Seedling establishment may take a long time in which case the seed trees highly restrict the development of the already existing seedlings. According to forest professionals seedling establishment and initial development of the seedlings may be slow and difficult also on dry sites, and especially on the sites dominated by Calluna vulgaris. Hypothesis: Heather (Calluna vulgaris) and crowberry (Empetrum nigrum) have allelopathic effects on seedling establishment and initial development of pine seedlings.

4 2. Materials and methods The study of North-East Lappland consisted of two data sets. Two cross-sectional inventory studies of naturally regenerated Scots pine stands owned by Metsähallitus. The age of the stands (time since seed-tree cutting) ranged from 2 to 13 years, the mean being 7 years. The size of the stands ranged from 1 to 101 hectares. The number of seed trees ranged from 4 to 175, mean was 31. Almost all the stands were classified as dry or sub-dry. Soil treatment: 33 untreated, 22 disk trenching, 6 scalping, 1 plouhing.

5 Materials and methods...continued: study area, forest stands and sample plots Thus, 62 seed- tree stands located in the municipality of Savukoski (data set 1), sampled randomly from the regeneration areas of Metsähallitus. The number of sample plots in the stands ranged from 2 to 13 (data set 1) Fifteen stands was randomly chosen for data set 2, each of them including 25 sample plots The size of the sample plots (data set 1): seedling plots 50 m 2, plots for matured trees 1000 m 2. Data set 2: 10 m 2.

6 Materials and methods...continued: additional description of the forest stands Temperature sum, d.d. (years ) mean 690, minimum 653, maximum 792. Altitude, m.a.s.l. mean 250, min. 170, max Thickness of humus layer, cm mean 3.3, min. 0.6, max Height of pine seedlings, cm mean 50, min. 7, max Age of pine seedlings, years mean 10, min. 2, max. 50. Number of pine seedlings, ha -1 alive: mean 1021, min. 0, max dead: mean 460, min. 0, max Total number of seedlings, ha -1 alive mean 1623, min. 0, max

7 Materials and methods...continued: additional description of the forest stands, number of seedlings by the stands 8000 Number of seedlings ha Scots pine Norway spruce Silver birch Pubescent birch Forest stand number

8 Materials and methods...continued: statistical analysis The data in the modelling was hierarchical, the levels being a forest stand and a sample plot level. Forest stand was considered as a random factor. The seedling number ditributions were highly skewed and zero-inflated. The generalized linear mixed model for seedling recruitment: nominal and ordered logistic regression models with a random factor were computed. The seedling height model was a linear mixed model. Hierarchical cluster analysis was used to reveal the relationships in the vegetation composition (data set 2). Used software: SAS, Systat, SPSS and MlwiN.

9 3. Results: Data set 1. Predicted seedling emergency : a multinomial logistic model Time needed for sufficient recruitment on dry sites is over ten years. Big difference between the site types. Residual trees restrict the recruitment. Temperature sum has a great influence on the recruitment.

10 Results...continued: Data set 1. The predicted height of the dominant seedlings on the sample plots The effect of time since seed-tree cutting: an increase in the average is a centimeter per year. The effect of paludification: seedlings averaged 17 centimeters smaller on the paludified sites. The intermediate birches near the seedlings increased seedling growth. The effect of the vicinity of the seed trees: if a seedling was under the seed tree, the average height was 35 cm, the corresponding heights in the distances of 10, 20 and 30 meters were 41, 49 and 60 centimeters respectively.

11 Results...continued: Data set 2. The relationships on the coverages of the ground vegetaion species.

12 Results...continued: Data set 2. A model for the seedling recruitment, the predicted effect of the ground vegetation on the recruitment. Humus If the humus layer s thickness is about 3 cm, the probability of at least 4 seedlings per plot is about 10 %, but at least 1 seedling 40 %.

13 Results...continued: Data set 2. A model for the seedling recruitment, the predicted effect of the ground vegetation on the recruitment. Heather Increasing coverage of hether increases the probability of seedling recruitment (or survival of the recruited seedlings?)

14 Results...continued: Data set 2. A model for the seedling recruitment, the predicted effect of the ground vegetation on the recruitment. Moss species Increasing coverage of moss species (mainly Pleurozium schreberi and Dicranum sp.) decreases stronly the probability of seedling recruitment.

15 4. Additional natural regeneration increasing the number of seedlings on artificially regenerated sites, an example A study made by Metsähallitus and Forest Research Institute in Northern Finland (the administrative countries of Oulu and Lapland). Hierarchical data of 133 randomly sampled forest stands (artificially regenerated areas), 2300 sample plots. 107 stands artificially regenerated using pine and 26 using Norway spruce. Study question: How a soil scarification affects the total number of recruited seedlings?

16 Additional natural regeneration... continued. The predictions of a model.

17 Additional natural regeneration... continued. The predictions of a model. The total number of seedlings (>= 10 cm) is at least seedlings / hectare if soil scarification has been carried out. There are differences between the scarification methods, depending on the site. Altitude has an effect on the number of seedlings, especially on the scalped sites.

18 5. Conclusions The results of natural regeneration varies very much in northern Finland (see also Hyppönen 2002). The combination of artificial and natural regeneration is recommended in the worst areas, near the timberline. Natural regeneration may need couple of decades. Thank you!