Successional-Categorization of Forest-Tree-Species in Lithuania: History
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Subjects: Plant Sciences

Developing forest harvesting regimes that mimic natural forest dynamics requires knowledge on typical species behaviors and how they respond to environmental conditions. Species regeneration and survival after disturbance depends on a species’ life history traits. The four types of ecologically invariant life-history trajectories of species turnover are a core component to evaluate if the development of the forest community is progressing towards the restoration of the climatic climax.

  • life history
  • species turnover
  • successional strategy
  • disturbance generalist
  • disturbance specialist
  • succession generalist
  • succession specialist
  • forest dynamics

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Definition

Developing forest harvesting regimes that mimic natural forest dynamics requires knowledge on typical species behaviors and how they respond to environmental conditions. Species regeneration and survival after disturbance depends on a species’ life history traits. The four types of ecologically invariant life-history trajectories of species turnover are a core component to evaluate if the development of the forest community is progressing towards the restoration of the climatic climax.

1. Introduction 

Forests are complex systems of interacting organisms; to manage them for tree species composition and production we need thorough knowledge of the variety of tree species’ life histories and how they interact. Within the hemi-boreal forest climatic zone there are three main forest disturbance regimes that host a variety of successional characteristics: (i) stand succession (large or stand replacing disturbance such as severe fire, windthrows, or current clear felling), (ii) cohort dynamics (related to partial disturbances of a stand such as a low intensity ground fire or forest thinning), and (iii) gap dynamics (such as small patch or a fallen tree) [1]. Succession is a sequential shift of patterns and processes in terms of the relative abundance of dominant species [2]. The succession of forest stands and patches largely determines the extent to which forest communities are able to cope with changes in environmental conditions and forest loss due to natural disturbances or human activity [3,4,5,6]. Forest disturbances trigger successional events that lead to climatically determined end communities or climatic climax, generally regarded as a position of stability in the development of vegetation [7,8,9].

The first definition of climax was described by Clements [10] as the ability of species composition to remains stable for more than one tree generation (i.e., the tree species replace themselves) in the absence of disturbance other than tree deaths due to old age. Thus, a forest that can regenerate naturally with the same composition over time can qualify as natural climax. In reality, however, the difference between a successional forest and a climax forest is subjective, as a forest ecosystem is dynamic, where succession is a continual process [32]. Although Clements’ [10] dynamic ecology concept is still valid [11], it does not represent the boundless factors impacting ecological succession. For example, the role and importance of both biotic and abiotic factors in predicting species distributions remains unclear [12,13,14,15,16]. Therefore, no clear conclusion can be drawn as to the successional position of tree species [10]. The probability of species survival and succession after disturbance depends on a species’ genetic profile to deal with a variety of environmental characteristics [17]. In other words, a tree’s life history traits define its position along its successional pathway that includes functional strategies for reproduction or resource capture [18].

The fundamental principle underlying the theory of invariance is that the laws of nature always have the same form for all observers [19]. This implies that all the elements of any developing living system interact, and thus all elements are ecologically equivalent, as the essence of ecological law and processes lies in invariance by which a living system following a disturbance returns to its stable state [20,21]. From a wildlife perspective, each organism, population, and community have different environmental scales in both time and space [22], and individual species may impact another species’ life history traits [23,24]. Thus, there are different perceptions about the interactions among species (that otherwise can survive virtually the same for millions of years), which proceed towards the ecological equivalence of climatically determined end communities [25]. Primary forests exist in a delicate but stable climax with all other components of the ecosystem; not one component can change without compensating changes in the others. For example, harvesting or thinning a forest stand will inevitably be followed by changes in the soil profile, vegetation, and life occurrence [9]. Generally, the dynamics of forest communities can be controlled by a set of ecologically invariant life-history traits of tree species turnovers [9,26,27,28,29]. Thus, a variety of tree species' life histories and how they are integrated into the forest system need to be summarized as a continuum of ecologically invariant life-history trajectories of species turnover [77].

The natural tendency of forest succession is towards climatic climax, whereas the succession of forests after human activity (e.g., fire, grazing, and soil deterioration due to over-cultivation) can result in adaptation of biotic climaxes [9]. Therefore, forest restoration that aids the recovery of forest structure, ecological functioning, and biodiversity towards those typical of a climax forest by the re-instatement of ecological processes is needed [30]. From an organism-centered perspective, developing forest management and exploitation regimes that mimic the natural conditions as closely as possible requires the determination of the degree to which typical species behaviors are responsible for the emergence of climatic climax [31,32,33,34,35,36].

2. Successional Categorization of Forest Tree Species in Lithuania

Lithuania (62,000 km2) is situated in the hemi-boreal climatic zone (i.e., the transitional zone from temperate to boreal forests) and is affected by the humid marine climate of the Baltic Sea [37]. The natural potential forest cover of Lithuania is predominantly composed of five main forest types: (i) hemi-boreal spruce forest with mixed broadleaved trees (55%), (ii) mixed oak–hornbeam forests (22%), (iii) boreal and hemi-boreal pine forests with partial broadleaved trees (18%), (iv) lime-pedunculate oak forests (4%), and (v) species-poor oak and mixed oak forests (1%) [38]. Thus, the natural climatic climax of the region for tree species consisted of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) Karst), birch (Betula pendula Roth and B. pubescens Ehrh), alder (Alnus glutinosa L. Gaertn. and A. incana L. Moench), English oak (Quercus robur L.), small-leaved lime (Tilia cordata Mill.), and European hornbeam (Carpinus betulus L.) [39]. Currently approximately 33% of Lithuania is forested with Scots pine, Norway spruce, and birch forming the dominating forest stand types [40]. The full range of hemi-boreal forest species found in Lithuania and their life history dynamics can be found in Table 1.

Table 1. A simplified framework for the life history dynamics for hemi-boreal tree species in Lithuania.

                             

Tree species

Life history traits

Dominant Stand Proportion [40]

Soil Moisture A [41,42]

Soil Fertility B [41,42]

Shade Tolerance

Hardiness C [43]

Life Expectancy [42]

(Harvesting age)[44]

Successional

Strategy

Dominant Forest Tree Species

Scots pine (Pinus sylvestris L.)

34.6%

1–3 and 5

1–3 and 5

Intolerant

9

300–400 (110)

Disturbance generalist

Norway spruce (Picea abies L. Karst)

20.9%

3–4

3–4

Intermediate

7

200–300 (71)

Succession generalist

Silver birch (Betula pendula Roth)

22.0%

2–5

2–4

Intolerant

9–10

150 (61)

Disturbance generalist

Black alder (Alnus glutinosa L. Gaertn)

7.6%

4–5

3–4

Intermediate

7

180–200 (61)

Disturbance generalist

Grey alder (Alnus incana L. Moench)

5.9%

2–5

3–4

Intermediate

9

50–70 (31)

Disturbance generalist

Eurasian aspen (Populus tremula)

4.6%

3–4

3–4

Intolerant

9

80–100 (41)

Disturbance generalist

English oak (Quercus robur L.)

2.2%

3–4

3–4

Intolerant

6–7

500–600 (121)

Disturbance specialist

European ash (Fraxinus excelsior L.)

0.9%

3–5

4–5

Intermediate

7–8

> 300 (101)

Succession specialist

Other Secondary Native Forest Species

Small-leaved lime (Tilia cordata Mill.)

0.4%

3

3–4

Intermediate

7

500–600 (61)

Succession specialist

Downy birch (Betula pubescens Ehrh)

0.4%

3–5

2–5

Intolerant

9

100D

Disturbance generalist

European hornbeam (Carpinus betulus L.)

0.2%

3

3–4

Tolerant

5

200–300 (61)

Disturbance generalist

Norway maple (Acer platanoides L.)

0.2%

3–4

3–5

Tolerant

8

150–300 (101)

Disturbance specialist

White willow (Salix alba L.)

<0.2%

4

4–5

Intolerant

8

>100 (31)

Disturbance generalist

Bird cherry (Prunus padus L.)

<0.2%

4–5

3–5

Intermediate

9

150D

Disturbance specialist

Crack willow (Salix fragilis L)

<0.2%

4

4–5

Intolerant

8

75 (31)

Disturbance generalist

Field elm (Ulmus minor Mill.)

<0.2%

2–4

4

Intermediate

5

300 (101)

Succession specialist

European white elm (Ulmus laevis Pall.)

<0.2%

3–4

3–4

Tolerant

6–7

250–300 (101)

Succession specialist

Wych elm (Ulmus. glabra Huds.)

<0.2%

3–4

4–5

Tolerant

6

300 (101)

Succession specialist

Wild apple (Malus sylvestris L. Mill.)

<0.2%

4–5

3–5

Intolerant

8

300D

Disturbance specialist

Wild pear (Pyrus pyraster L. Burgsd.)

<0.2%

3–4

3–4

Intermediate

6

200–300D

Disturbance specialist

 

 

 

 

 

 

 

 

Introduced Species

European beech (Fagus sylvatica L.)

<0.2%

3 [37]

3–4

Tolerant

5

500 (101)

Succession generalist

Sessile oak (Quercus petraea Matt. Liebl.)

<0.2%

3

2–3

Intermediate

6–7

500–600D

Disturbance specialist

Large-leaved lime (Tilia platyphyllos Scop.)

<0.2%

3–4

4–5

Intermediate

7

500–600D

Succession specialist

Wild cherry (Prunus avium L.)

<0.02%

3–4

3–4

Tolerant

8

100D

Disturbance generalist

3. Conclution

Each hemi-boreal forest tree species can be represented by one of the four types of ecologically invariant life-history trajectories of species turnover: disturbance generalists, disturbance specialists, succession generalists, succession specialists. Here, we touch on their importance of these four types of forest successional groups, their absence and presence in the community, and how they could be used as a core component to evaluate if the development of the community is progressing towards the restoration of the climatic climax. However, further research in needed to develop the concept of forest succession. This could be undertaken through the inclusion of other biotic components, such as, ground vegetation, wildlife and microorganisms, and their impacts on forest succession as an ecosystem. In closing, we suggest that forests should be managed to maintain environmental conditions that support their natural variety and the sequence of tree species’ life histories.

This entry is adapted from 10.3390/plants9101381

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