Ecological thinning is a

silvicultural Silviculture is the practice of controlling the growth, composition/structure, as well as quality of forests to meet values and needs, specifically timber production. The name comes from the Latin ('forest') and ('growing'). The study of forests ...

technique used in

forest management Forest management is a branch of forestry concerned with overall administrative, legal, economic, and social aspects, as well as scientific and technical aspects, such as silviculture, forest protection, and forest regulation. This includes man ...

that involves cutting trees to improve functions of a forest other than timber production. Although

thinning In agricultural sciences, thinning is the removal of some plants, or parts of plants, to make room for the growth of others. Selective removal of parts of a plant such as branches, buds, or roots is typically known as '' pruning''. In forestry ...

originated as a man-made

tool, aimed at increasing

timber Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). ...

yields, the shift from production forests to multifunctional forests brought with it the cutting of trees to manipulate an

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

for various reasons, ranging from removing

non-native species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...

from a plot to removing poplars growing on a riverside beach aimed at recreational use. Since the 1970s, leaving the thinned trees on the forest floor has become an increasingly common policy: wood can be decomposed in a more natural fashion, playing an important role in increasing

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

by providing habitat to various

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

and small

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

. Many

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

(e.g. '' Calocera viscosa'') and

mosses Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta ('' sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and ho ...

are saproxylic or epixylic as well (e.g. ''

Marchantiophyta Liverworts are a group of non-vascular plant, non-vascular embryophyte, land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in wh ...

'') – some moss species completing their entire life-cycle on a single log. Where trees are managed under a commercial regime, competition is reduced by removing adjacent stems that exhibit less favourable timber quality potential. When left in a natural state trees will "self-thin", but this process can be unreliable in some circumstances. Examples of this can be found in the

Buxus ''Buxus'' is a genus of about seventy species in the family Buxaceae. Common names include box and boxwood. The boxes are native to western and southern Europe, southwest, southern and eastern Asia, Africa, Madagascar, northernmost So ...

– Ironbark forests and

woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...

s of Victoria (Australia) where a large proportion of trees are

coppice Coppicing is the traditional method in woodland management of cutting down a tree to a tree stump, stump, which in many species encourages new Shoot (botany), shoots to grow from the stump or roots, thus ultimately regrowing the tree. A forest ...

, resultant from timber cutting in decades gone by.

Ecophysiological repercussions

Thinning decreases

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

closure and increases the penetration of solar radiation into the canopy. The

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

efficiency of this energy is improved, and needle retention is prolonged, especially in the lower parts of the

crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, parti ...

. The root system, crown length, crown diameter, and crown area all increase after thinning.Misson, L.; Vincke, C.; Devillez, F. 2003. Frequency responses of radial growth series after different thinning intensities in Norway spruce (''Picea abies'' .Karst.) stands. For. Ecol. Manage. 177(1–3):51–63. Even if soil evaporation and individual tree transpiration increases after thinning, total evapo-transpiration at stand level tends to decrease;Whitehead, D.; Jarvis, P.G.; Waring, R.H. 1984. Stomatal conductance, transpiration, and resistance to water uptake in a ''Pinus sylvestris'' spacing experiment. Can. J. For. Res. 14:692–700. canopy water interception is reduced and throughfall increased, so that tree-water status usually improves after thinning. Radial annual growth is an integrative index of tree physiological response to environmental variation. Working with

Norway spruce ''Picea abies'', the Norway spruce or European spruce, is a species of spruce native to Northern, Central and Eastern Europe. It has branchlets that typically hang downwards, and the largest cones of any spruce, 9–17 cm long. It is very clo ...

, which can be expected to behave in some respects similarly to white spruce, Misson et al. showed that a reduction in stand density alters the classical climate–growth relationship. At individual tree level, thinning could be used to increase tree resistance to drought stress. Nevertheless, this effect is limited when site conditions are limiting. Misson et al. concluded that heavy thinning should be applied when forest decline is expected from drought stress. Furthermore, stands on dry sites should be thinned more heavily because such sites cannot support high-density stands. Aussenac,Aussenac, G. 1987. Effets de l'éclaircie sur l'écophysiologie des peuplements forestiers. Schweiz. Z. Forst. 138:685–700. also working with Norway spruce, investigated the response to thinning. Thinning altered the temporal evolution of radial growth at all frequencies in radial growth chronologies. Previous studies had shown, not surprisingly, that thinning decreases the canopy closure and encourages solar radiation to penetrate the canopy.Habonimana, B. 2000. Effet de l'intensité d'éclaircie sur le microclimat et la croissance du pin larico de Corse (''Pinus nigra'' Arnold subsp. ''laricio'' Poir.). Thèse de Doctorat. Université Catholique de Louvain, Louvain-la-Neuve. Solar energy then becomes more important inside the crown.Law, B.E.; Riitters, K.H.; Ohmann, L.F. 1992. Growth in relation to canopy light interception in a red pine (''Pinus resinosa'') thinning study. For. Sci. 38:199–202. The improved photosynthetic efficiency of this energyFrançois, F.; André, P.; Devillez, F. 1985. Effet de l'intensité de l'éclaircie sur l'extinction du rayonnement solaires en jeunes futaies de ''Picea abies'' (L.) Karsten. ann. Sci. For. 42:323–338. influences the retention time of needles, especially in the lower part of the crown.Marek, M.V.; Markova, I.; Kalina, J.; Janous, D. 1997. Effect of thinning on parameters of photosynthetic characteristics of Norway spruce canopy. I. Light penetration and photosynthesis. Lesnictvi-Forestry 43:141–153. Furthermore, the length, diameter, and area, of the crown, and the size of the root system all increase after thinning.Lehtpere, R. 1960. The crown expansion of Japanese larch after heavy thinning. Forestry 33:140–148.Hamilton, G.J. 1969. The dependence of volume increment of individual trees on dominance, crown dimensions and competition. Forestry 62:133–144. These modifications at the crown level influence photosynthate production positively as long as water supply is not limiting. Even if soil evaporation and individual tree transpiration are more important after thinning, total evapo-transpiration at stand level tends to decrease.Morikawa, Y.; Hattori, S.; Kiyono, Y. 1986. Transpiration of a 3-year-old ''Chamaecyparis obtusa'' Endl. stand before and after thinning. Tree Physiol. 2:105–114. Furthermore, with the reduced importance of

leaf area index Leaf area index (LAI) is a dimensionless quantity that characterizes plant Canopy (forest), canopies. It is defined as the one-sided green leaf area per unit ground surface area (''LAI = leaf area / ground area, m2 / m2'') in Broad-leaved tree, bro ...

(LAI), thinning reduces canopy water interception and increases throughfall.François, F.; Mertens, P.; André, P.; Devillez, F. 1984. Egouttement en jeunes pessières et intensité de la première éclaircie. Ann. Sci. For. 41:439–448. This explains why the soil moisture content increases in a thinned stand.Della-Bianca, L.; Dills, R.E. 1960. Some effects of stand density in a red pine plantation on soil moisture, soil temperature, and radial growth. J. For. 58:373–377. Thus, during the vegetation period, tree-water status is usually better in a thinned stand than in a high-density stand.Ginn, S.E.; Seiler, J.R.; Cazell, B.H.; Kreh, R.E. 1991. Physiological and growth responses of eight-year-old loblolly pine stands to thinning. For. Sci. 37:1030–1040.Stoneman, G.L.; Crombie, D.S.; Whitford, K.; Hingston, F.J.; Giles, R.; Portlock, C.C.; Galbraith, J.H.; Dimmock, G.M. 1996. Growth and water relations of ''Eucalyptus marginata'' (jarrah) stands in response to thinning and fertilisation. Tree Physiol. 16:267–274. For semi-tolerant species such as Norway spruce and white spruce, solar energy is less limiting than for intolerant species. This can account for the exponential relationship found by Misson et al. between thinning intensity and mean radial growth. Only when thinning was relatively severe did important radial growth variation occur. Furthermore, the ecophysiological advantage of an improved water supply could be counterbalanced by limiting site conditions. For Norway spruce in the Belgian Ardennes, Misson et al. recommended that stand basal area should not exceed 26 m²/ha on a dry site, or 29 m²/ha on a moist site if the objective is to maintain high long-term radial growth. Misson et al. found that adaptations to thinning cover a continuous range of different time scales, with long-, medium-, and short-term growth variations being controlled by very different internal factors influenced by the environment. Misson et al. ascribed what they called long- and medium-term radial growth variation of individual trees mainly to structural adaptation, such as enlargement of the crown or the root system. Short-term radial growth variations, on the other hand, were considered to be due mainly to physiological

acclimatisation Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), ...

, with response to factors such as

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

tal conductance regulation, variation of photosynthetic capacity, and respiration. Nevertheless, it is clear that the adaptations are linked, and that radial growth is the integrative response of this mutual inter-relationship.Kahle, H.P.; Spiecker, H. 1996. Adaptability of radial growth of Norway spruce to climate variations: Results of a site-specific dendroecological study in high elevations of the Black Forest (Germany). pp. 785-801 In J.S. Dean, D.M. Meko and T.W. Setnam (eds.). Tree rings, environment and humanity. The University of Arizona, Tucson, AZ.

Research

Research programs under way in various parts of the world (e.g. United States and Australia) are aimed at providing an alternate approach in

where conservation objectives are a high priority. Methods of ecological thinning being developed on

techniques for local forest types. Ecological thinning is being developed using two principles: 1. appropriate stem reduction to reduce competition and 2. retention of trees (selection) that are more suitable for wildlife (i.e. not timber production). An example of ecological thinning research is the project in Victoria's Box-Ironbark forests, investigating various thinning and timber removal methods under an

adaptive management Adaptive management, also known as adaptive resource management or adaptive environmental assessment and management, is a structured, iterative process of robust decision making in the face of uncertainty, with an aim to reducing uncertainty ove ...

or AEM framework. The primary objective is to generate (over time) a number of forest habitat values (i.e.

tree hollows A tree hollow or tree hole is a semi-enclosed cavity which has naturally formed in the trunk or branch of a tree. They are found mainly in old trees, whether living or not. Hollows form in many species of trees. They are a prominent feature of n ...

) that are crucial for

wildlife conservation Wildlife conservation refers to the practice of protecting wild species and their habitats in order to maintain healthy wildlife species or populations and to restore, protect or enhance natural ecosystems. Major threats to wildlife include habita ...

References

External links

Parks Victoria Box-Ironbark Parks & Reserves
– follow link to thinning trial FAQ
Ecological Thinning Conference Poster
– Poster presented to ESA2004 in Adelaide, Australia
Review of Thinning Prescriptions
– Review of thinning in park management in Australia
Cedar River Watershed Habitat Conservation Plan
– Catchment project in Seattle, US {{Forestry Forest management Forest ecology Sustainable forest management Environmental terminology Habitat Sustainable agriculture

Ecophysiological repercussions

Research

See also

References

External links