Climate Change and Plant Community | Term Paper | Geography

Here is a term paper on ‘Climate Change and Plant Community’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short term papers on ‘Climate Change and Plant Community’ especially written for school and college students.

Climate Change and Plant Community

---

There is unequivocal evidence that the earth’s climate is warming at an unprecedented rate. Temperature increases are geographically inequitable. Some regions, particularly at high altitudes and latitudes, are warming more than other areas. Other climatic effects, including prolonged drought in arid and semi-arid regions, increased flooding in mid to high latitudes and more extreme weather events are also increasing. Sea levels are rising. Climates are changing more rapidly than species can adapt and there is high risk of mass extinctions of biodiversity as the planet warms.

Term Paper # 1. Ecosystems at Risk:

An ecosystem is an array of living things (plants, animals and microbes) and the physical and chemical environment in which they interact. Healthy ecosystems provide the conditions that sustain human life through the provision of a diverse range of ecosystem services. Plant diversity underpins terrestrial ecosystems and they are often described according to the major vegetation type they consist of. Many ecosystems will be highly vulnerable to projected rates and magnitudes of climate change and the services lost through the appearance or fragmentation of ecosystems will be costly or impossible to replace.

Forest ecosystems are particularly important, containing as much as two thirds of all known terrestrial species and storing about 80 per cent of above-ground and 40 per cent of below-ground carbon. Deforestation is a major source of greenhouse gas emissions and contributes to loss of species as well as changes in regional and global climate.

Reducing deforestation is therefore one of the most effective ways of reducing greenhouse gas emissions. Ecosystem responses to climate change will be complex and varied. Climatic changes will essentially affect all ecosystem processes but at different rates, magnitudes and directions.

Responses will vary from the very short-term response of leaf-level photosynthesis to the long-term changes in storage and turnover of soil carbon and nitrogen stocks. All living organisms in terrestrial ecosystems ultimately depend directly or indirectly on photosynthesis for their energy requirements.

Solar radiation, temperature, precipitation, air humidity and atmospheric CO₂ are the key ambient forces that drive ecosystem processes. Of these, changes in temperature, water availability and CO₂ levels are subject to change in the next 100 years.

Impact of Temperature Change on Plant Growth and Ecosystems:

Plant growth and health may benefit from increased temperatures of global warming in that some regions will experience reduced incidence of damage from freezing and chilling. Plants in other regions may suffer from stress due to elevated temperatures. There is some evidence that extreme events (droughts, floods, high winds, etc.) may accompany global warming, in which circumstances plants may experience isolated highly damaging events.

Net primary production (NPP) will generally be increased by moderate increases in temperature estimated to occur in the next 60 years, especially in boreal and mid-latitude regions. Estimates are that NPP will increase 1 per cent per degree centigrade in regions where the mean annual temperature is 30°C and 10 per cent in regions where the mean annual temperature is 0°C.

Global warming is dramatically revamping not only the ice but also tundra and forests at the top of the world, greening some parts and browning others. The alterations could exacerbate climate change. The satellite records revealed a startling result in the vast boreal forests south of and ringing the tundra.

Although studies confirmed that the tree line was continuing to move northward and to higher elevations, in many places the satellites indicated that behind this advancing front the forests were losing biomass and becoming less productive.

The forests were browning – drying and dying – while the tundra was greening, a fact that seems to contradict the conventional wisdom concerning the forest response to climate warming. Since about a decade gone by, Wilmking et al. (2004) started collecting a set of tree ring samples from near Fairbanks and south of the Brooks Range that have helped unravel the apparent contradiction.

Instead of the customary positive correlation – higher temperatures in summer produced better growth and wide rings – they began to find stands in which higher temperatures had produced smaller rings and more slowly growing trees. In western Alaska, where it was wetter, they found the trees grew more vigorously as it warmed, but as they moved east into drier country, they discovered smaller rings, distressed trees and struggling, even dying, tree stands. The warmer summers were just too dry.

Dendrochronologists, Lloyd and Bunn (2007), using every boreal tree ring record they could uncover, confirmed that the browning of the boreal forests was a pan- arctic phenomenon and that although it predominated in spruce trees, it occurred in all boreal tree species. The exact causes of the declining tree growth are still being worked out, but drought and heat stress are two primary suspects, because browning has been observed more commonly in dry continental sites and in the southern part of each species’ range.

The trees have been getting hammered in two other ways as well, both thought to be linked to the warming climate – increased insect outbreaks and a rise in the frequency and size of forest fires. In Alaska, big forest-fire seasons seem to be coming about every five years rather than every 10, and infestations of insects such as the spruce bark beetle, which have ravaged more than 5,00,000 hectares of prime forest in Alaska so far, appear to be intensifying.

The changes taking place on the tundra and in the boreal forests present an ironical symmetry. The boreal forests have encroached on an estimated 11,600 sq km of the southern edge of the Alaskan tundra in 50 years, yet over the same period they have been drying out, burning up and suffering insect damage behind their advancing front.

The outcome is going to be a conversion from forest to grassland. At the same time, the tundra is becoming increasingly shrubby and jungle-like. Does the future have in store a switch, where the forest will begin to look a lot like tundra, and the tundra looks more and more like forest?

The problem with answering this question is our limited ability to understand the linked processes that are driving the vegetation changes, let alone predict their future course. Even though the arctic sea ice is a simple system of just water and ice that responds in principle to physical rules that can be coded into models, the ice has been declining at a rate that is twice as fast as that predicted by 13 of the scientific community’s best large-scale models.

Current predictions are for an ice-free arctic ocean in 40 years, but these predictions are more extrapolations of observed changes than model results. For the tundra, the boreal forests, with their great biological complexity and competing feedback mechanisms – some that dampen growth and some that accelerate it – the existing models are still too simplistic to produce accurate predictions.

Impact of Precipitation and Water Availability on Plant Growth and Ecosystems:

Plant leaves have small openings called stomata that can be adjusted to regulate the exchange of water vapour and CO₂ with the atmosphere. Plants not under water stress keep their stomata open for optimum CO₂ exchange. Under stress, however, plants close their stomata to restrict water loss. They also may allow their leaves to droop to reduce light absorption or they may even shed leaves to reduce water loss.

C₄ plants have higher water use efficiency (WUE) than C₃ plants. Higher atmospheric CO₂ levels will cause stomata to close slightly, increase WUE, and increase carbon gain for plants with limited water supply. Higher temperatures may lead to higher differences in water-vapour concentration inside and outside the stomata, however, and thereby lead to reduced WUE.

Term Paper # 2. The Physiological Responses of Plants to Climate Change:

The diversity and distribution of the world’s terrestrial vegetation is the product of a complex suite of interactions between individual plants and a multitude of climatic and environmental variables. Plants are major regulators of the global climate, and their collective responses to increased atmospheric CO₂ concentrations have clearly played an important role in mitigating climate change up to this point.

In looking to the future, it is increasingly critical to understand how plants respond on a basic level to the changes imposed upon them by continued increases in atmospheric CO₂, as well as the cascade of climatic and environmental changes triggered due to this increase.

Observing and Predicting Plant Responses:

Understanding the effects of climate change on plant species and communities is a fairly recent conservation concern, but requires long-term data sets. Few such data sets exist, viz. long-term phonological records for a few plant species, but analysis can be hampered because data collection protocols and species selection generally were not set up to answer contemporary questions.

Similarly, experimental approaches can be prohibitively expensive and lengthy, so research in this field relies heavily on modeling. Models can be used for predicting responses of single species, multi- species assemblages, global vegetation patterns and climate or hardiness zones. Models are only as good as the data and assumptions on which they are built and are continually improving as we refine and test them using data from past climate changes.

While it remains important to scrutinize climate change predictions adequately, the scientific debate must not divert us from taking timely and appropriate action on both mitigation and adaptation. The extent of global change is still in our hands and scientific rigour should not replace action.

It is clear that different plant species will respond differently to climate change. Some species will stay in place and adapt to new climate conditions through selection or plasticity. Other species will move to higher latitudes or altitudes. Some species may become extinct. Because of this, plant community composition will be reorganized, new communities will emerge and others will be lost.

One of the biggest concern of this community reshuffling is the disruption of food webs and coevolved mutualisms, such as the relationships between a plant and its pollinator or seed disperser. If species that rely on each other no longer co-occur in the same time or space, both may be driven to extinction. Diseases, pests and invasive species may spread into new ranges putting more pressure on fragile communities. Maintaining bio-diverse communities will become an even greater conservation priority.

In an era of rapid climate change, species have three basic alternatives. They can migrate to appropriate environmental conditions, adapt to the new environmental conditions, or become extinct. In a changing environment, ‘woody’ species with fast generation times and wide ecological tolerances are more likely to adapt or migrate quickly and are more likely to flourish. Conservative species with specific habitat requirements or long generation times are more prone to the threat of extinction. At present an estimated one-quarter of vascular plant species are under threat in the wild.

With predicted temperature increases, changing hydrological cycles and other factors of climate change, as many as half of all plant species may be lost over the next century. This is a catastrophic scenario given the fundamental importance of plants to life on earth.

As yet there is a lack of published information on plant extinctions directly due to climate change but with baseline information now being collected on the distribution, threat and ecology of various plant groups, monitoring schemes can be established. Plant species restricted to high-risk habitats, including montane, island or coastal habitats are likely to be the first casualties of climate change. Plant conservation action needs to be increased now to ensure that options are available for the future.

Direct Effects of CO₂:

Photosynthetic rates in C₃ plants increase by 25-75 per cent for a doubling of CO₂. For C₄ plants the data are less conclusive and range from no response to an increase of 10-25 per cent. Results likely are temperature dependent. Increases in CO₂ with accompanying increment in photosynthetic rate and decreased water requirement, translate into increased growth and crop yield in C₃ plants, increased growth in C₄ plants, and increased tree seedling growth.

The response to elevated CO₂ will be most pronounced in regions where water availability is a limiting factor. The actual growth enhancements expected in response to gradually increasing CO₂ concentrations are likely to have only a small and gradual impact on terrestrial ecosystems globally.

Term Paper # 3. Climate Change, Plants and Livelihoods:

The growth rates of terrestrial and aquatic plants are temperature dependent, with species (and genotypes) having optimal growth and competitive ability at particular temperatures, and thus in particular climates. This is likely the greatest cause of the geographic separation of species along continental climatic gradients, such as north-south gradients and elevation gradients.

In addition, the geographic ranges and abundance of many terrestrial plants are limited by temperature extremes, especially by tissue damage associated with freezing or subfreezing temperatures. Moreover, within a region, differences in temperature-dependent growth could cause different plant species to be specialized on different portions of the growing season. In essence, plants may be limited by nutrients and other resources, by pathogens and herbivores, by disturbances, by dispersal abilities and by the physical environment including its climate.

Plant abundance in both terrestrial and aquatic ecosystems is also limited by the densities and species identities of pathogens and herbivores, which in turn can be limited both by their predators and by dispersal. Thus, top-down forces can greatly constrain both terrestrial and aquatic ecosystems. Physical disturbances also limit terrestrial plant communities and sessile (benthic) freshwater and marine plant communities.

For many terrestrial ecosystems, fire frequency has been a major constraint, as have been such physical disturbances as wind storms, landslides, mudslides, avalanches, clearings caused by gophers or other fossorial animals, disturbances caused by hooves, wallows, etc.

Term Paper # 4. Anthropogenic Global Change and Plant Constraints:

Many of the constraints are undergoing large, rapid changes because of human actions. Recent human activities have more than doubled the preindustrial rate of supply of nitrogen (N) to terrestrial ecosystems. Nitrogen had a preindustrial terrestrial cycle that involved the annual fixation of about 90 to 140 Tg (teragrams) of N/yr, with an additional 10 Tg of N/yr provided by atmospheric N fixation via lightening. Industrial N fixation for fertilizer currently totals about 88 Tg/yr.

About 20 Tg/yr of N is fixed during the combustion of fossil fuels and about 40 Tg/yr of N is fixed by legume crops. In addition, land clearing, biomass burning and other human activities mobilize and release about an additional 70 Tg of N/yr. The projected expansion of global population to about 9 × 10⁹ people by the year 2050 and shifts to diets higher in animal protein suggest that, by2050, global food production will be double its current rate.

If so, anthropogenic terrestrial N inputs in 2050 would be about 3 to 4 times the pre-industrial rate. Much of this N would enter rivers and be carried to near-shore marine ecosystems. N would also be deposited atmospherically on non-agricultural terrestrial ecosystems.

Nitrate is readily leached from soil, carrying with it positively charged ions such as Calcium (Ca). Atmospheric N deposition may be depleting Ca and other cations in hardwood forests of the eastern United States. This depletion of base cations could cause elements that had not been limiting in a region to become limiting. Plant species often have distributions constrained by soil pH and Ca.

Phosphorus (P) is a commonly applied agricultural fertilizer and current P application is a doubling of the natural global rate for terrestrial ecosystems. Projections to year 2050 are that agricultural P fertilization will be more than double. Much of this P may enter aquatic ecosystems, which can be P-limited. The accumulation of such greenhouse gases as CO₂ and methane may lead to global climate change, with the greatest changes, especially warmer winter temperatures.

Rather, we merely note that rainfall patterns, the frequency and severity of droughts and other aspects of climatic mean and variance, which all constrain plant communities, are also forecast to change. In addition, CO₂ is a plant nutrient, and elevated levels of CO₂ represent atmospheric eutrophication with a limiting plant resource.

In total, human actions are modifying many environmental constraints that, in combination with intraspecific and interspecific trade-off, led to the evolution of extant plant species and thus influenced the composition, diversity and functioning of terrestrial and aquatic plant communities.

If current trends continue, within 50 to 100 years the suites of factors constraining the structure of many plant communities may fall outside the envelope of values that existed both before the industrial revolution and when many of the plant species evolved.

Term Paper # 5. Dynamics of Climate Change:

Like all biological systems, plant communities are temporarily and spatially dynamic as they change at all possible scales. Dynamism in vegetation is defined primarily as changes in species composition and/or vegetation structure.

i. Temporal Dynamics:

Temporally, a large number of processes or events can cause change, but for sake of simplicity they can be categorized roughly as either abrupt or gradual. Abrupt changes are generally referred to as disturbances; these include things like wildfires, high winds, landslides, floods, avalanches etc.

Their causes are usually external (exogenous) to the community – they are natural processes, occurring (mostly) independently of the natural processes of the community (such as germination, growth, death, etc.). Such events can change vegetation structure and species composition very quickly and for long time periods, and they can do so over large areas. Very few ecosystems are without some type of disturbance as a regular and recurring part of the long-term system dynamic.

Fire and wind disturbances are particularly common throughout many vegetation types worldwide. Fire is particularly potent because of its ability to destroy not only living plants, but also the seeds, spores, and living meristems representing the potential next generation, and because of fire’s impact on faunal populations, soil characteristics and other ecosystem elements and processes.

Temporal change at a slower pace is ubiquitous; it comprises the field of ecological succession. Succession is the relatively gradual change in structure and taxonomic composition that arises as the vegetation itself modifies various environmental variables over time, including light, water and nutrient levels. These modifications change the suite of species most adapted to grow, survive and reproduce in an area, causing floristic changes.

These floristic changes contribute to structural changes that are inherent in plant growth even in the absence of species changes (especially where plants have a large maximum size, i.e. trees), causing slow and broadly predictable changes in the vegetation. Succession can be interrupted at any time by disturbance, setting the system either back to a previous state, or off on another trajectory altogether.

Because of this, successional processes may or may not lead to some static, final state. Moreover, accurately predicting the characteristics of such a state, even if it does arise, is not always possible. In short, vegetative communities are subject to many variables that together set limits on the predictability of future conditions.

ii. Spatial Dynamics:

As a general rule, the larger an area under consideration, the more likely the vegetation will be heterogeneous across it. Two main factors are at work. First, the temporal dynamics of disturbance and succession are increasingly unlikely to be in synchrony across any area as the size of that area increases. That is, different areas will be at different developmental stages due to different local histories, particularly their times since last major disturbance.

This fact interacts with inherent environmental variability (e.g. in soils, climate, topography, etc.), which is also a function of area. Environmental variability constrains the suite of species that can occupy a given area, and the two factors together interact to create a mosaic of vegetation conditions across the landscape.

Only in agricultural or horticultural systems does vegetation ever approach perfect uniformity. In natural systems, there is always heterogeneity, although its scale and intensity will vary widely. Natural grassland may be homogeneous when compared to the same area of partially burned forest, but highly diverse and heterogeneous when compared to the wheat field next to it.

At regional and global scales there is predictability of certain vegetation characteristics, especially physiognomic ones, which are related to the predictability in certain environmental characteristics. Much of the variation in these global patterns is directly explainable by corresponding patterns of temperature and precipitation (sometimes referred to as the energy and moisture balances). These two factors are highly interactive in their effect on plant growth, and their relationship to each other throughout the year is critical.

iii. Soil Processes and Carbon Dynamics:

Temperature changes will have only minimal effects on reaction rates for inorganic processes in soils, but changes in soil moisture could have significant effects on rates of diffusion and supply of nutrients to plants. Both NPP and organic matter decomposition will increase likely under increasing temperature. If moisture is readily available, decomposition of organic matter is likely to be enhanced more than NPP under global warming, thereby adding more CO₂ to the atmosphere.

However, if moisture becomes more limiting then decomposition will be reduced. Models that take both temperature and moisture into account suggest that increased NPP would lead to increases in soil carbon under increasing atmospheric CO₂. Land use is a much more important factor than changes in NPP for determining soil carbon. Typically about half of the native carbon is lost from soils when they are put under cultivation over a period of 50-100 years. Minimum tillage practices reduce carbon loss from soils.

Climate change, specifically changes in temperature and water availability, could change soil microbial and faunal populations, but changes in land-use practices are likely to have much greater impact. However, another element of global change, namely increased deposition of nitrogen from industrial NO_x emissions, is being more widely associated with major losses of fungi in the root zone in some (particularly forest) biomes.

iv. Ecological Processes and Community Dynamics:

Organisms interact with their physical environment and with other organisms to form a complex set of dependencies and interrelationships sometimes called the “web of life”. This interconnectedness makes the study of impacts of changes in external factors on ecosystems very difficult.

The combinations of all environmental facts and interactions with other organisms determine the preferred places for each organism to live, i.e., its “niche”. Some niches are more vulnerable to climate change than others. Interactions within ecosystems include competition, herb-ivory and actions of parasites, disease and mutualists (ecosystem components that provide mutual benefit such as pollinating bees and flowering plants).

The collection of different species that interact in a variety of ways in a defined patch of land is called a community. Communities are always changing and are subject to “succession”, which may be a complete changeover to another collection of plants or a more incremental series of species losses and gains.

Loss of one species may provide opportunities for changes in populations of existing species or gain of new species. Communities may migrate and disperse as their environmental conditions change. The rate of change compared to the ability of the community to move determines whether the community will survive under such changing conditions.

Losses of diversity and shifts in species composition have, at their core, a conceptually simple basis. The plant species that coexist in the unfertilized control plots do so for a variety of reasons, including interspecific trade-off in their ability to compete for limiting resources, or trade-off between competitive ability versus local dispersal ability or a trade-off between competitive ability versus resistance to herb-ivory or disease.

Term Paper # 6. The High Dimensionality of Environmental Change:

The greater the dimensionality of a habitat is (i.e., the greater its number of constraints), the more its diversity and composition would be impacted by a given amount of environmental change in each variable. Human actions are changing many environmental constraints simultaneously, including N, P, Ca, CO₂, pH, fire frequency, trophic structure and climate. The high dimensionality of these changes may lead to much greater impacts on plant communities than anticipated from a consideration of only one or a few of these factors.

A simple example illustrates this. Consider a habitat in which there are three constraints, factors 1, 2 and 3. The low and high values of these factors might map into a cubic trait space for competitive coexistence. If the values of factor 1 were shifted up by 50 per cent, but nothing else changed, the old trait space and the new trait space would share 50 per cent of their volume, indicating that this change would eliminate about half of the original species and create vacant niches that could be colonized by a comparable number of species, should they exist regionally.

If both factor 1 and 2 were increased 50 per cent, the new trait space would overlap with only 25 per cent of the old (i.e., 1/2 × 1/2 = 1/4).If each of the three factors were shifted by 1/2, new trait space would overlap with only 1/8 of the original. In this case, 7/8 of the original species would be driven locally extinct. Comparably, if each of three variables were to be shifted by 2/3, the resultant trait space would overlap only 1/27 of its original volume, and 26/27 of the original species would be lost, on average.

In the short-term, such shifts in environmental constraints would eliminate many species and favour once-rare species. The longer-term dynamics of these terrestrial plant communities would depend on the dispersal rates of species both within a region and from other regions, if any, that formerly had characteristics similar to those that occur in the human-impacted region. They also would depend on the evolutionary responses of the species that remain in these habitats.

Term Paper # 7. Remarks on Climate Change and Plant Community:

Anthropogenic changes in environmental limiting factors are likely to cause significant loss of plant diversity, leaving many niches empty and creating plant communities dominated by weedier species (poor competitors but good dispersers).

The extent of this effect will depend both on the number of constraints that are changed (i.e., dimensionally) and on the magnitude of such changes. Because the impacts of multidimensional environmental changes are expected to be multiplicative, a series of relatively small changes may be as important as a single change.

The vacant niches of a region experiencing a major change in an environmental constraint, such as a high rate of N deposition, indicate several things about such habitats. First, species that have traits and which fall within the newly created vacant niches should be able to invade into, spread through and persist if propagules are regionally available. Secondly, any heritable variation within existing species that allowed individuals to fill the vacant niches would be favoured.