Reviving Forests amidst Climate Change: A Scientific Perspective

Reviving Forests amidst Climate Change: A Scientific Perspective


Climate change “refers to a change in the state of the climate that can be identified by changes in the mean and/or variability of its properties, and that persists for an extended period, typically decades or longer” (Pachauri & Reisinger, 2007). The Intergovernmental Panel on Climate Change (IPCC, 2007), in its Fourth Assessment Report, concluded with more certainty that global climate change is unequivocal and it is widely believed to result primarily from the effects of emissions of carbon dioxide (CO2) and other greenhouse gases (GHGs) such as methane (CH4) and nitrous oxide (N2O), from human activities such that excessive burning of fossil fuels, unplanned and overexploitation of natural resources, degradation of marine and terrestrial ecosystems and so on. The world’s climate is changing. While there are natural climate variations, the climate change we are most concerned about is in regards to the modifications to the greenhouse effect that human activities have caused. Numerous observations about the Earth’s climate conclude:
That the global surface temperature has increased by an estimated 0.74 degrees Celsius (°C) over the past century. Over a 50 year period from 1956 to 2005 , the warming trend was nearly twice that for the 100 years from 1906 to 2005. Eleven of the 12 years from 1995 to 2006 rank among hottest years on record, since 1850, when sufficient worldwide temperature measurements began. Increases are widespread globally and are greater at higher northern latitudes.
Consistent with warming, the extent of snow and ice has decreased. Mountain glaciers and snow cover have also declined on average worldwide. The maximum area of seasonally frozen ground in the Northern Hemisphere has decreased by about 7 percent since 1900.
Since 1961, the world’s oceans have been absorbing more than 80 percent of the heat added to the climate, causing ocean water to expand thereby contributing to rising sea levels. This expansion was the largest contributor to sea level rise between 1993 and 2003.
Climate change is impacting the world’s ecosystems and it is expected that the magnitude of these impacts will increase along with temperatures over this century. If the global average temperature increases more than 1.5-2.5 °C, it is believed that approximately 20-30 percent of plant and animal species assessed so far will be at an increased risk of extinction (IPCC, 2007). Major changes in ecosystem structure and function, species, ecological interactions and geographical ranges, with predominantly negative consequences for biodiversity and ecosystem goods and services are also projected.

Impacts of climate change on forest insects and diseases
Climate, temperature and precipitation in particular, have a very strong influence on the development, reproduction, survival, distribution and spread of insects, pests and pathogens and as a result it is highly likely that these organisms will be affected by any changes in climate.
Temperature is considered to be the more important factor of climate change influencing the physiology of insect pests (Bale et al., 2002). Precipitation however can be a very important factor in the epidemiology of many pathogens, such as Mycosphaerella pini, that depend on moisture for dispersal.
The magnitude of the impacts of temperature on forest pests will differ among species depending on their environment, life history, and ability to adapt.

Climate plays a major role in defining the distribution limits of a species. With changes in climate, these limits are shifting as species expand into higher latitudes and altitudes and disappear from areas that have become climatically unsuitable (Parmesan, 2006; Menéndez, 2007). Such shifts are occurring in species whose distributions are limited by temperature such as many temperate and northern species.
For examples a major epidemic of the mountain pine beetle (Dendroctonus ponderosae) has been spreading northwards and upwards in altitude for several years. The pine processionary caterpillar (Thaumetopoea pityocampa) has significantly expanded its latitudinal and altitudinal distribution in Europe. Range restricted species, particularly polar and montane species, show more severe range contractions than other groups and are considered most at risk of extinction due to recent climate change. Parmesan and Yohe (2003) reported that more than 1 700 Northern Hemisphere species have exhibited significant range shifts averaging 6.1 km per decade towards the poles.

Phenology is one of the easiest impacts of climate change to monitor including earlier breeding or first singing of birds, earlier arrival of migrant birds, earlier appearance of butterflies, earlier choruses and spawning in amphibians and earlier shooting and flowering of plants (Walther et al., 2002).
Where life cycle events are temperature-dependent, they may be expected to occur earlier and increased temperatures are likely to facilitate extended periods of activity at both ends of the season, provided that there are no other constraints present (Harrington, Fleming and Woiwod, 2001). With increased temperatures, it is expected that insects will pass through their larval stages faster and become adults earlier. Therefore, expected responses in insects could include an advance in the timing of larval and adult emergence and an increase in the length of the flight period (Menéndez, 2007). Changes in butterfly phenology have been reported from the United Kingdom, where 26 of 35 species have advanced their first appearance (Roy and Sparks, 2000). First appearance for 17 species in Spain has advanced by 1-7 weeks in just 15 years (Stefanescu et al., 2003).

Drought is one of the most important climate-related events through which rapid ecosystem changes can occur as it affects the very survival of existing tree populations. Long-term drought can result in reduced tree growth and health thereby increasing their susceptibility to insect pests and pathogens. A number of insect pests and diseases are associated with stressed trees, such as Agrilus beetles and the common and widespread Armillaria species which have been linked to oak decline (FAO, 2008). Others are limited by host defences in healthy trees, such as the European spruce bark beetle (Ips typographus) (FAO, 2008).
Sugar concentrations in foliage can increase under drought conditions. Increases in the sugar content in drought-stressed balsam fir for example have been known to stimulate the feeding of certain stages of spruce budworm (Choristoneura fumiferana) and accelerate their growth (Mortsch, 2006).

Elevated levels of atmospheric carbon dioxide
Higher atmospheric CO2 levels result in improved growth rates and water use efficiency of plants and trees. This increased productivity leads to lower nitrogen concentrations in trees and plants as carbon-nitrogen (C:N) ratios rise and thus reduces the nutritional value of vegetation to insects (Kopper and Lindroth, 2003; Mortsch, 2006). In response, insects may increase their feeding and consequently tree damage in an attempt to compensate for the reduced quality and gain the necessary nitrogen.

Forest pest species influenced by climate change
Information on forest insect pests, diseases and other pests which have been impacted by climate change is provided to better understand the potential impacts of climate change on forest health.

Agrilus pannonicus.
A number of Buprestid beetles of the genus Agrilus have been linked to oak decline. Incidences of these species have increased worldwide (both in their countries of origin and by international movement) and their impacts are being linked to host tree stress potentially caused by climate change (FAO, 2008). For example, Agrilus pannonicus (=A. biguttatus (Fabricius)) has recently been associated with a European oak decline throughout its natural range. (Ciesla, 2003). Infestations can result in extensive tree mortality which, combined with other factors involved in the decline, can drastically alter the species composition of oak forests.

Dendroctonus ponderosae
The mountain pine beetle (Dendroctonus ponderosae) is the most destructive pest of mature pines in North America, particularly lodge pole pine (Pinus contorta). A major epidemic of this pest has also been going on in western Canada (British Columbia), and more recently, (Alberta) for several years and even with large-scale efforts to mitigate the impacts of the pest, millions of trees have been killed. A record of over 10 million hectares of pines was recorded as infested during 2007 aerial overview surveys in British Columbia.
The problem has been exacerbated by successive years of mild winters, resulting in decreases of mortality of overwintering stages and generation time. Their life cycle is generally completed in one year; warmer temperatures can result in two generations per year while cooler ones may results in one generation every two years (Amman, McGregor and Dolph, 1990).

Aphids are a group of insects that can be expected to be strongly influenced by environmental and climatic changes. In general, it has been predicted that aphids will appear at least eight days earlier in the spring within 50 years, though the rate of advance will vary depending on location and species (Harrington et al., 2007). This could potentially result in greater damage to host plants depending on the phenology of host plants and natural enemies.
Zhou et al. (1995), for example, investigated the timing of migration in Great Britain for five aphid species (Brachycaudus helichrysi, Elatobium abietinum, Metopolophium dirhodum, Myzus persicae, Sitobion avenae) over a period of almost 30 years and concluded that temperature, especially winter temperature, is the dominant factor affecting aphid phenology for all species. They found that a one degree Celsius increase in average winter temperature advanced the migration phenology by 4-19 days depending on species.

While only a few species of butterflies are considered to be serious forest pests. The geographic ranges of many species have shifted northward and upwards in elevation associated with climate warming, leading to increases in species richness at high latitudes and elevations and in some cases possible local extinction at lower altitudes.
The spruce budworm, Choristoneura fumiferana, is a major defoliator of coniferous forests across North America. Balsam fir (Abies balsamea) is the preferred host but they readily attack white, red and black spruce (Picea glauca, P. rubens, P. mariana respectively) and may even be feed on tamarack (Larix spp.) and hemlock (Tsuga spp.)
The gypsy moth, Lymantria dispar, is a significant defoliator of a wide range of broadleaf and even conifer trees. While low population levels can exist for many years without causing significant damage, severe outbreaks can occur resulting in severe defoliation, growth loss, dieback and sometimes tree mortality.

Mycosphaerella pini is a fungus that infects and kills the needles of Pinus spp. resulting in significant defoliation, stunted growth and eventually death of host trees although susceptibility among pine species does vary. Unlike many other pests, changes in precipitation patterns may be more important than changes in temperature for predicting the spread and impact of M. pini.

Climate change evidences in Jammu and Kashmir Forests
Vegetation patterns (distribution, structure, composition, density, and ecology of forests) across the globe are controlled mainly by climate. Climate change impacts have been observed in the forests of Jammu and Kashmir since last few decades. It is likely that the marked expansion of 11 percent in temperate deciduous, cool mixed and conifer forests at the cost of alpine pastures likely to shrink has been demonstrated. The unusual trends of winter migration of birds in the wetlands of Jammu, Kashmir and Ladakh have been visualised. It has been observed that there is a decline in socio-economic species like deodar, fir and spruce and increase in blue-pine in Kashmir valley and chir-pine in the Jammu region. Increased incidences of forest fires have been noticed. The spread of invasive alien species like Lantana, Parthenium, Ageratum and so on has been taking place. Inevitably any change in the forest (distribution, density, composition etc) under climate change scenario would immensely influence economies like forestry, agriculture, livestock husbandry, non-timber forest products, medicinal plants based livelihood.

The evidence presented from this desk review shows that climate change is having considerable and widespread impacts on forest health worldwide. Clearly, if such climatic and ecological changes are now being detected when the globe has warmed by an estimated average of only 0.74 °C, it can be expected that many more impacts on species and ecosystems will occur in response to changes in temperature to levels predicted by IPCC. The forest sector needs effective monitoring, forecasting, and detection activities to allow for quick action in the face of changing or increasing pest outbreaks including continual pest risk assessments. There is also a need for alternative practices to reduce subsequent vulnerability of forests, such as planting pest tolerant trees identified through breeding programmes, increasing species and age class diversity to promote growth and resilience to mortality, rehabilitate degraded forests on war footing, in-situ conservation of rare, endangered and threatened species, using appropriate silvicultural interventions to increase tree vigour and lower pathogen and insect pest impacts under predicted climate scenarios, carefully and judiciously using facilitated tree species migration and comprehensive risk assessments as well as enhanced knowledge management systems using a variety of information technologies such as simulation models, geographic information systems (GIS) and remote sensing could also play a role in protecting forests from the impacts of climate change.

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