Forests: Temperate Evergreen and Deciduous Lindsay M. Dreiss John C. Volin Department of Natural Resources and the Environment, University of Connecticut, Storrs, Connecticut, U.S.A.

Ecotone— Fragmentation

Abstract Temperate forests represent one of the major biomes on Earth. They are most common in eastern North America, western and central Europe, and northeastern Asia, where the climate is defined by warm summers, cold winters, and intermediate levels of precipitation. To a lesser extent, they are also present in this same climate in Australia, New Zealand, South America, and South Africa. Temperate forests are dominated by either deciduous or evergreen canopies. In temperate deciduous forests, more commonly found in the Northern Hemisphere, plants drop their leaves in autumn, allowing for high seasonal variation in light availability to the understory. By contrast, in temperate evergreen forests, which are more commonly found in the Southern Hemisphere, plants keep their leaves year round. The temperate forest biome is rich in geologic and anthropocentric history, with much of the land shaped by glacial and human activity. Located in some of the most industrialized places in the world, temperate forests have been instrumental to socioeconomic development in these regions. As a consequence, these forests have been heavily impacted by expanding human populations, which remain the primary continuous threat to the structure and function of these forests.

INTRODUCTION Temperate forests represent one of the major biomes on Earth, covering ~14% of Earth’s terrestrial land surface[1] (Fig. 1). Along with boreal and subtropical/tropical wet and dry forests, temperate forests are one of the Earth’s dominant forest types. In comparison to other types, temperate forests are intermediate in latitude, temperature, and precipitation. By contrast, they generally exhibit much stronger seasonality, favoring those plant and animal species that were able to adapt to short-term climatic variation. Environmental stresses from seasonal change include extreme temperatures and variable access to moisture (in the form of rain and/or snow), light, and nutrients (due to the deciduous nature of some canopies). As a result, significant changes in microclimates and growing conditions throughout the year are common, creating adaptive opportunities and resulting in unique structure and composition of ecosystems.[2–4] Temperate forests are located in some of the most heavily populated and developed regions on Earth, including much of eastern North America, western and central Europe, northeastern Asia and, to a lesser extent, Australia, New Zealand, South America, and South Africa[5–7] (Fig. 1). Temperate forests are an established part of the history and culture of these regions and continue to play an important role in providing ecosystem services to human populations, including timber products, carbon storage, clean

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drinking water, erosion prevention, recreation, tourism, aesthetics, property value security, and others. On the other hand, the unsustainable use of such services has led to negative consequences for temperate forest ecosystems worldwide. In this entry, we provide an overview of temperate forests from both an ecological and societal perspective. We describe the unique characteristics of temperate deciduous and evergreen forests, the major anthropogenic agents that have impacted them in the past and some of the emerging threats they face today. CLIMATE Climate is a fundamental factor in defining the temperate forest biome. Generally, a forest is considered temperate if it is located in a region with hot summers and cold winters. The annual range in temperature can be ±30°C, and the mean annual temperature is between 3 and 18°C, with mean midwinter temperature below 8°C and mean midsummer temperature about 18°C.[8] In the Northern Hemisphere, the length of the frost-free period ranges from 120 to over 250 days, with growing season and temperature increasing closer to the equator. As a result of less land mass in the Southern Hemisphere, the climate is milder than at similar latitudes in the Northern Hemisphere. Temperatures in the Southern Hemisphere can be cold, but typically far less than 1% of the hours of the year are

Encyclopedia of Natural Resources DOI: 10.1081/E-ENRL-120047447 Copyright © 2014 by Taylor & Francis. All rights reserved.

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Forests: Temperate Evergreen and Deciduous

Fig. 1

Global temperate deciduous and evergreen forest biomes.

subject to frost, while in the Northern Hemisphere subfreezing temperatures are typically reached many days during the winter.[6] Temperate forests receive even precipitation year round averaging 750–1500 mm/yr. Snowfall can range from nonexistent in southern regions to extremely heavy in northern regions. In the Northern Hemisphere, temperate forests are geographically located between the boreal forest/tundra and the tropical/subtropical forests while in the Southern Hemisphere they are found south of the tropical/subtropical forests up to tree line in some areas (Fig. 1). Correspondingly, the climate, productivity and species diversity of temperate forests are intermediate in relation to other biomes.[9] The seasonal climatic regime in the temperate forest regions has changed very little in the past 1000–2000 years. This is reflected in the structure and ecosystem dynamics of the forests.[10] Winter deciduous trees or coniferous evergreen species that are physiologically dormant during winter months dominate the majority of the forests. Genera differ between Northern and Southern hemispheres. Examples include Acer, Fagus, Tilia, Quercus, Carya, Populus, Ulnus, Betula, Fraxinus, Magnolia, Cornus, Robinia, and Juglans in the Northern Hemisphere and Eucalyptus, Acacia, Quercus, and Nothofagus in the Southern Hemisphere. At higher latitudes and altitudes, where temperatures range from –30 to 20°C annually, temperate forests become more dominated by coniferous evergreen tree species. These regions are generally drier, with annual precipitation from 300 to 900 mm. Seasons are defined by cold, long snowy winters and warm, humid summers with at least

four to six frost-free months.[11] Evergreen temperate forests may also occur in regions with a stronger maritime climatic influence. Precipitation can be very high (typically 700–1000 mm) and snow is uncommon.[12,13] Summer fog is often an important contributor to moisture uptake, reducing stresses from evapo-transpiration. In addition, the growing season is much longer and sometimes continuous in forests closer to the equator. In the midst of global climate change, however, a shift is occurring in the location of ecotone and temperate forest species. Climate-linked range shifts have been observed in the northern hardwood–boreal forest ecotone where there has been a decrease in boreal and an increase in northern hardwood basal area.[14] The velocity of temperature change is projected to be much faster in temperate broadleaf and mixed forests than in temperate coniferous forests.[15] Temperature being considered the primary control on treeline formation and maintenance, global warming is also facilitating treeline advances to greater altitudes and latitudes.[16,17] The synergistic effects of warming temperatures and intensifying droughts have also triggered concerns. The sensitivity of tree mortality and range shifts can result from extreme water stress and lead to other ecological consequences including changes in carbon stores and dynamics, changes in microclimate, and changes in future production of important habitat and food sources.[18,19]

LAND FORMATION AND HISTORY On the geological time scale, climate has shaped the land on which temperate forests now grow. Between 110,000

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and 10,000 years ago, during the Late Pleistocene age, glacial ice sheets left large parts of the Eurasian and North American continents as treeless, frozen tundra.[20,21] Below the tundra stretched the temperate forests, and beyond these, temperate, grassy plains. As the glaciers retreated, they left behind glacial till and lake-bottom sediments. As the zones of tundra followed the shrinking glaciers, the boreal and temperate forests encroached on the tundra belt until the matrix of ecoregions looked much like it does today. Since the end of the last ice age, human activity has become a primary factor in shaping temperate forests. The three largest temperate forest regions, eastern North America, western and central Europe, and northeastern Asia, have played an important role in the development of human society. In North America, temperate forests were heavily impacted by the spread of European settlements in the 1700s. Much of the temperate forest was cleared, logged, and/or burned to make way for agricultural needs and human settlements.[22,23] In the 18th century, the temperate forests of Europe were the birthplace of new lines of scientific study and management, becoming what is now modern forestry.[24,25] These practices were applied in Europe and North America, where temperate forests provided the wood for fuel, building materials, and raw material in industrial processing during the Industrial Revolution of the 19th and 20th centuries.[26,27] With the spread and development of forestry practices, large amounts of temperate forest were logged for the production of timber, pulp, paper goods, and other forest products. During the 19th and into the 20th century, much of the agricultural land in the temperate forest range in North America was abandoned and the temperate forest grew back, peaking in its coverage in the mid-twentieth century.[28] Today it is once again under threat from continuous loss and fragmentation primarily through human developments. In Europe, many native temperate deciduous forests have been extirpated and replaced with planted monocultures, many of which are not representative of the native vegetation.[29] Most of the remaining European temperate forests display a simplified structure and composition resulting from centuries of tree harvesting and forest grazing. In other places, land use change and conversion still continue to affect forest ecosystems. For example, the temperate forests of Asia, which cover parts of China, Japan, and Korea, were largely unaffected by glaciation through the Pleistocene.[30,31] Because of this, Asian temperate forests have higher levels of biodiversity than their counterparts in Europe or North America and are home to species with ancestries that extend much further back in geologic history. However, more recent heavy logging and fires have reduced forested land area and caused species such as the red-crowned crane (Grus japonensis) and the red panda (Ailurus fulgens) to be listed as endangered.[32] Collectively, temperate forests across the globe may have experienced more severe impacts over broader areas than any other large forest biome.[33]

Forests: Temperate Evergreen and Deciduous

STRUCTURE AND COMPOSITION In contrast to grasslands or desert ecosystems, temperate forests have a more complex structure composed of different layers of vegetation. Temperate forest layers typically include a layer of mosses and lichens on the forest floor (and often on tree trunks and limbs), herbaceous and shrub layers, a subcanopy of trees, and a taller dominant canopy tree layer.[34] The complexity of the subcanopy and canopy layers can vary and often depend on the light requirements of the dominant tree species. Trees are the dominant life form of these ecosystems and can be either deciduous or evergreen. Temperate forests undergo different stages in ecosystem succession, allowing for the coexistence of plant species with different life history strategies. These adaptations are often linked to specific growing conditions associated with different stages of forest growth. As a result, gradual transitions in plant community composition and forest structure change over time.[35,36] A classic example of succession in northeastern temperate forests in North America is when pioneer tree/shrub species such as birch (Betula spp.) and poplar (Populus spp.), which are fast growing and require high light availability, are often the first to establish following a disturbance. As trees grow and the canopy begins to close, conditions become more favorable for more longlived, shade-tolerant species such as maple (Acer spp.), oak (Quercus spp.), beech (Fagus spp.), and hemlock (Tsuga spp.). These later-successional trees become dominant or codominant and eventually out-compete early successional species, reaching heights of 35–40 m.[37] This process takes place over hundreds of years and can be reset at any time by a disturbance of natural or human origin. Indeed, within a relatively large and healthy naturally occurring forest area, all of these successional stages are present at once. Disturbance regimes, which refer to the type, intensity, and frequency of disturbances in a particular region, have a substantial impact on the composition and age structure of vegetation.[38–40] In temperate forests, eolic events such as hurricanes, tornadoes, and thunderstorm downbursts are a major contributor to forest dynamics. Fire was once also an important natural regulator, but with land use changes and suppression of fire by humans, many temperate forests have become increasingly dominated by late successional species.[41] Other natural disturbances include pest/disease outbreaks, flood or drought, and snow and landslides. Temperate Deciduous Forest The temperate deciduous forest canopy is composed mostly of broadleaved angiosperm tree species with the inclusion of some coniferous tree species. Temperate deciduous broadleaved forests are often defined by the associations of species. Association names are most useful for distinguishing broad differences in forest type and are often representative of variation in soils, topography, and climate. For example, in eastern North America, some common associations are

Oak–Hickory and Beech–Maple.[42] The temperate deciduous broadleaved forest that extends across East Asia (from 30° to 60°N) displays the greatest diversity of vegetation. The greater diversity in Asian temperate deciduous forests is likely the result of being less severely glaciated during the last ice age. This was largely a result of the more connected landmass, which allowed temperate forests to retreat from the advancing glaciers. For instance, in North America, the Florida peninsula and Gulf of Mexico coastal region was the southern limit for temperate forest refuge, while in Europe the east to west mountain range of the Alps limited southern migration. Other locations of deciduous broadleaved forests include areas around the eastern Black Sea, mountainous regions in Iran and Caspian Sea, and a narrow strip of South America including southern Chile and Argentina.[34,43–45] The composition of deciduous temperate forest depends on latitude. In North America, birches (Betula spp.), aspen (Populus spp.), and maples (Acer spp.) are common, along with needle-leaved conifers such as pines (Pinus spp.). Coniferous species tend to decline in abundance further south, but they remain in localized areas that exhibit drier, more nutrient-poor conditions and higher altitudes. In Europe, forests at higher elevations are composed mainly of conifers (Picea spp. and Abies spp.) and Fagus spp., as well as larch (Larix decidua). In central temperate deciduous forests, broadleaved deciduous species in Europe include oaks (Quercus spp.), European beech (Fagus sylvatica), and hornbeam (Carpinus betulus) [with Fraxinus spp. and Castanea spp. often just as common as Carpinus]. Common trees in North America include sugar maple (Acer saccharum), American beech (Fagus grandifolia), basswoods (Tilia spp.), oaks, and hickories (Carya spp.). In Asia, Japanese beech (Fagus crenata), oaks, maples, ashes (Fraxinus spp.) and basswoods are most common. At lower latitudes, broadleaved deciduous species are joined by broadleaved evergreen angiosperm trees, such as oaks, beeches (Northofagus spp.), eucalyptus (Eucalyptus spp.), and pines (Podocarpus spp.). Plant life Deciduous leaves are the most distinctive feature of temperate deciduous broadleaved forests. Autumn changes in leaf color and senescence have become very important to these regions both economically and ecologically. “Leafpeeping” tourists travel to deciduous forest destinations to view displays of reds, oranges, and yellows and invest in local markets.[46,47] The dropping of leaves in the fall is also a phenological event or recurring biological cycle that changes the seasonal microhabitat, creating unique understory conditions for other plants and animals. The onset of plant phenophases such as spring leaf flush and autumn leaf senescence are controlled by two major environmental signals: photoperiod (relative length of days/nights) and total degree days (relative measure of

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heating/cooling). However, with the onset of global climate change, recent studies recognize that temperature plays a more important role in many phenological events.[48,49] Plant hormonal signals to leaves cause chlorophyll, the compound that absorbs light for photosynthesis and makes the leaves look green, to degrade. Some nutrients from the leaves are partially recovered and moved (i.e., retranslocated) to stem and trunk tissues before the leaves fall off.[50–53] Buds are formed and go into dormancy until the following spring, when the accumulation of degree days over a temperature threshold triggers leaf growth. Canopy tree species differ in their timing of bud break and leaf expansion, with the development of the forest canopy taking place over a period of a month or more.[54] Once intact canopies are in full leaf flush and the growing season is underway, typically only 1–5% of sunlight reaches the forest floor.[55–57] Therefore, the portion of the year when canopy trees are leafless creates a unique opportunity of increased light availability for understory vegetation. With the beginning of the warm season, herbaceous plants, shrubs and small trees begin growth before the canopy does. Because maximum incident solar radiation flux and zenith angle of the sun are larger in the spring months, there is greater transmission of light and a greater likelihood for understory plants to reach photosynthetic capacity before canopy leaf flushing.[58,59] In an evolutionary adaptation designed to maximize the amount of light received, some plants, known as spring ephemerals, complete most of their annual growth cycle in the few weeks between snowmelt and the closure of the tree canopy. Other more shade-tolerant species begin or continue to grow after canopy closure.[60] Animal life Many animals in temperate deciduous forests are masteaters (nuts and acorns) or omnivores. Herbivores (e.g., deer, hare, and rodents) perform important tasks in the ecosystem, such as aiding in plant seed dispersal, but may cause stress when their populations are overly abundant. Small rodents, such as squirrels and chipmunks (Tamias spp.), and some birds, such as blue jays (Cyanocitta cristata), cache large seeds/nuts in the autumn for sustenance in the winter.[61] Seeds that animals fail to recover may grow in their buried location. Omnivores include raccoon, opossum, skunk, fox, and black bear in North America and badger, mink, and marten in Europe. Asian forest fauna also include primates such as macaques. In temperate forests around the world, humans have drastically reduced the populations of many large carnivores such as wolves in North America and Europe and tigers in Asia, and now smaller carnivores such as coyote (Canis latrans) and lynx (Lynx spp.) fulfill part of this niche.[62,63] Some animals have adapted unique behaviors to better suit them for the varied seasons. For example, some

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mammals store fat and hibernate or go into torpor during the cold months. Some birds take shelter in the trees by becoming cavity-nesters, while others are migratory and avoid the cold winters by flying to more southerly climes. Soils and nutrients

Ecotone— Fragmentation

Temperate deciduous forest soils show variation with latitude and altitude, as well as with moisture. At the northern or higher extent of the range, where there is a greater presence of needle-leaf evergreen tree species, soils tend to be relatively acidic and nutrient poor. By contrast, soils are strongly leached and less productive in the southern or lower ranges. Temperate deciduous forest soils, however, tend to be deep and fertile and do not freeze year-round. Brown forest soils (alfisols, in the American soil taxonomy) develop under the nutrient-demanding broadleaf trees whose leaves bind the major nutrient bases.[64,65] This causes leaf litter to be less acidic and provide a rich humus layer. Along with the favorable summer growing season, this is one of the reasons why this biome has historically been popular for agricultural use. Temperate Evergreen Forest Temperate broadleaved evergreen forests occur at the warm, moist end of the latitudinal gradient of temperate forests and are characterized by long, hot, humid growing seasons, and relatively milder winters. Precipitation is high (1000–1750 mm) and the forest is dominated by broadleaved evergreen angiosperms. These forests occur in eastern Asia, coastal regions of New Zealand and Australia, western coastal regions of North America and parts of Chile, South Africa, and warmer European regions.[34, 43–45] There are several forest variants that occur in regions of maritime and dry-season climates. Maritime broadleaved forests are dominated by tall, broadleaved evergreen angiosperms and narrow- to broadleaved conifers and exhibit very high precipitation (2000–3000 mm). Maritime needle-leaved forests occur only in a narrow band along the coastline of North America from California to Alaska and throughout coastal southern Europe and are known for needle- and scale-leaved evergreen conifers such as giant sequoias in North America or angiosperms such as evergreen oaks in Europe. Dryseason broad-sclerophyll forests occur in areas with periodic drought, exhibiting more of a Mediterranean climate, with hot dry summer and cool wet winters. Needle-leaved conifers can be interspersed within deciduous canopies or occur in patches. They tend to grow at higher altitudes near treeline or in drier regions. Conditions can be highly seasonal, with severe winters and warm, humid summers. Conifer tree species include fir (Abies spp.), spruce (Picea spp.), pine (Pinus spp.), cedar (Thuja spp.), hemlock (Tsuga spp.), and larch (Larix decidua) among others.

Forests: Temperate Evergreen and Deciduous

Plant life While broadleaved trees in the Northern Hemisphere are exposed to variable environmental stress, broadleaved trees in the Southern Hemisphere are under weaker seasonal forces. Because of milder climates and less extreme variability in the Southern Hemisphere, it is more advantageous for trees to expose leaves all year round in order to maximize photosynthesis and carbon gain.[66,67] Temperate broadleaved evergreen tree leaves are generally thick with smooth margins as opposed to deciduous leaves, which by comparison are generally thin and lobed. These differences are in part due to higher levels of rainfall and humidity. Southern Hemisphere species maintain a waxy outer layer on leaves to repel water. In these mild temperate evergreen forests, species compositions are mainly from the families of Lauraceae, Fagaceae, Theaceae, Magnoliaceae, and Hamamelidaceae, all of which have a relatively low resistance to cold and freezing temperatures.[68,69] In the Southern Hemisphere, the very dry-adapted forests of Australia are also found. Fire disturbance in this dry region has allowed for the domination of Eucalyptus spp. which have thick bark for fire-resistance.[70,71] Also relatively common in many temperate evergreen forests are narrow-leaved evergreen trees. These species produce their seeds in compact structures called cones, which allow for greater protection of reproductive material from predation as well as some unique adaptations to environmental conditions.[72] Some evergreen conifers have flat, triangular scale-like leaves, such as found in the Cupressaceae and some Podocarpaceae, while many evergreen trees also produce needle-like leaves, which increase the leaf area for photosynthesis and are thicker and smaller to avoid desiccation.[73,74] Rates of area- or massed-based leaf photosynthesis in temperate needle-liked evergreen trees are typically much lower than for leaves of temperate deciduous tree species, except when amortized over the life of the leaf.[75] Temperate deciduous trees only keep their leaves for one growing season, while temperate evergreen forests keep their leaves for much longer. The moist temperate coniferous forests dominated by tree species such as giant sequoias (Sequoiadendron giganteum), coastal redwoods (Sequoia sempervirens), Douglas firs (Pseudotsuga menziesii), and kauris (Agathis australis) sustain the highest levels of biomass in any terrestrial ecosystem.[76] These forests are rare and known for a rich variety of plant and animal species. Typically, two or more tree layers of large broadleaved, dome-shaped evergreen angiosperms are present. These forests, which grow in moist regions, are also known for higher abundance and diversity of epiphytes and vines. In maritime climates, fog can provide a significant amount of the annual water available to vegetation.[77] Forming over adjacent oceans and water bodies, the moist air travels with both humidity and nutrients that can be

Forests: Temperate Evergreen and Deciduous

Animal life The fauna of the temperate evergreen forest is similar to that of the deciduous forest ecosystems, with many smaller mammals, large ungulates and a few larger omnivorous mammals contributing to biological interactions. Many of these species, mostly birds and small rodents, have adapted skills to compensate for the scarcity of food in these nutrient poor systems. The red squirrel (Sciurus vulgaris) removes cone scales to reach the nutrient rich seeds of the coniferous trees.[88,89] They often hoard these seeds, many of which they do not recover, resulting in seed dispersal. In dry forests at higher latitudes, large ungulates such as moose (Alces alces) browse nutritious spring vegetation and wetland foliage in warmer seasons and on young tree shoots when the ground is frozen and covered with snow.[90,91] Some fauna in the coniferous evergreen forests located at higher latitudes have also adapted to the cold, snowy winters. For example, bears (Ursus spp.) are able to go into long periods of dormancy, maintaining both body

temperature and metabolism without eating, drinking, defecating, or urinating.[92] In austral regions, temperate evergreen forests are also home to many endemic species such as Leadbeater’s possum (Gymnobelideus leadbeaten), Parma wallaby (Marcopus parma) and Albert’s lyrebird (Menura alberti). Soil and nutrients Soils of temperate evergreen forests are well leached and low in productivity. Ultisols represent older, unglaciated soils that have been weathered to a much greater degree than those of temperate deciduous forests. Ultisols are generally less fertile than most temperate deciduous forest soils and were further degraded under plantation and subsistence agriculture in both the colonial and postcolonial periods.[65,93]

THREATS Threats to the temperate forest biome stem from direct or indirect human activity. Historically, farming has been one of the main reasons for deforestation in temperate biomes. Today, an increasing number of roads, residential and other developments have left forests highly fragmented, raising concerns over the healthy functioning of these ecosystems.[94] Many of the plant species living in temperate forests are well-adapted and function optimally in soils with fairly low nutrient availability. However, more impervious surfaces as well as modern agricultural and industrial practices can alter nutrient availability and contribute to a decline in forest health. Atmospheric deposition of nitrogen, acid deposition and fertilizer applications are changing the rate of input of nutrients along with the growth and dynamics of temperate forest communities.[95–97] This also leads to alterations in soil properties, nutrient cycling and microbial community composition as well as nutrient imbalances in plants and increases in forest mortality. These nutrient imbalances in plants make them more vulnerable to other outside stressors such as diseases and introduced invasive species.[98–100] Human activities are also altering global climate, a foundation for the characterization and distribution of temperate forests. For deciduous canopies, observational evidence has linked global climate change to differences in the timing of spring leaf growth and autumn leaf drop. Warm springs cause leaves to grow earlier, sometimes by up to one month (http://www.usanpn.org), lengthening the duration of the growing season in some temperate forests.[101–103] Climate variation may also result in a shift in flowering periods, potentially causing disruption in timing with pollinators/dispersers. In Japan, cherry blossom (Prunus serrulata) trees are blooming earlier than they did historically, causing concerns regarding the traditional festivals and tourism that surround the annual event.[104] Evidence of

Ecotone— Fragmentation

intercepted by plants, reducing water stress caused by transpiration. Some studies suggest that some leaf shapes have evolved for more efficient collection of fog drip. It has also been hypothesized that fog in dry summer months is essential in supporting the sustained growth of large trees such as the redwoods of California.[78,79] Temperate coniferous forests at higher altitudes often have narrow tree morphologies which allow heavy snow to slough off branches before breaking them.[72,73] These forests are dense, with trees growing close together to minimize wind damage; wind minimization is important because conifers often have very shallow root systems due to higher allocation of nutrients in the top layers of soil.[80,81] Evergreen trees in higher, drier areas allocate carbon to thick bark for greater protection from low-heat summer fires. Some conifers have adapted to take advantage of fire events, producing serotinous cones in which seeds are maintained in a dormant state until a fire occurs, opening the cones and releasing the seeds for germination.[82,83] Because the canopy of these temperate forests is evergreen, the vegetation in the understory experiences low light availability. Understory plants have adapted to maximize their light/energy capture as well as their photosynthetic capacity under such conditions. Shaded plants tend to allocate more growth to leaves, displaying larger, thinner leaves which take up more horizontal area for light capture.[75,84] Physiologically, shade leaves saturate at lower light levels and have lower light compensation points, which allows them to maintain positive rates of net photosynthesis at low light levels. Understory plants also adapt to respond quickly to environmental changes in order to make use of sunflecks or brief, unpredictable periods of high sunlight usually lasting only seconds.[85–87] Instantaneous adjustments in photosynthetic rates allow plants to be efficient with the limited light they receive to put toward carbon gain.

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warming temperatures also suggests a shift in species distributions toward the poles, which could result in the extinction of some plant and animal species.[105,106] Rapid global climate change creates conditions less suitable for many species adapted to their particular environment, increasing the amount of stress put on individuals as well as their vulnerability to certain pathogens or pests.[107] Climate also has a strong influence on the success of certain fungi, bacteria, and viruses, affecting infection severity and spread. For example, in the northwestern United States, heavy rains and wet weather during warm periods are optimal conditions for sudden oak death infection.[108] In many cases, humans accidentally introduce these diseases. Chestnut blight (Cryphonectria parasitica), a fungus introduced to America from Europe in 1904, is one of the best-known examples. In four decades, the chestnut blight largely eliminated American chestnut (Castanea dentata) from the continent, one of the most important and widespread tree species across the eastern temperate forest of North America.[109,110] Other introductions to temperate forests include nonnative plant invaders that have, in some cases, taken over large portions of forested land, changing species, and nutrient compositions as well as the identity of the landscape.[111–113] In some cases, invasive species have the potential to reduce biodiversity, extirpate native species and negatively impact ecosystem structure and services, thereby negatively affecting the economy and human health and well-being. Species such as garlic mustard (Alliaria petiolata), native to Europe and introduced to forests of North America, exude chemicals that may disturb natural plant–plant and plant–soil processes and interactions.[114] Many invasives may be unpalatable to native fauna such as Japanese knotweed (Fallopia japonica)[115] which is nonnative to forests of Europe and North America or even poisonous like St. John’s Wort (Hypericum perforatum) in Australia.[116] Negative effects of invasive plants on human populations include economic losses[117] and even disease as in the case of Japanese barberry (Berberis thunbergii), a shrub introduced to North America that creates favorable habitat for vectors of Lyme disease (Borrelia burgdorferi).[118]

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sustainable use of these resources and proper protection and management of temperate forests will be important in ensuring the health and productivity of the biome. REFERENCES 1.

2.

3.

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5. 6. 7. 8. 9.

10. 11. 12. 13.

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CONCLUSION Temperate forests are ecologically distinct biomes and provide important regional and global ecosystem services. The species in these ecosystems have evolved unique physiological traits to function under a variety of seasonal stresses. Being closely related to variation in environmental conditions, temperate forests may act as an ecological indicator of global climate change, changes in nutrient cycling and other environmental alterations brought on by human activities. Temperate forests have been and are of important use to industry and tourism. As they continue to play an important role in regional cultures and economies,

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