Open access peer-reviewed chapter
Abstract
Forests cover nearly one-third of the terrestrial surface and support life with energy, raw materials, and food and offer a range of services ranging from biodiversity conservation to climate regulation. The realization of this goods and services depends on the health of these pristine ecosystems. Forest degradation diminishes the utilitarian and ecosystem potentials of the forest and assessing this at local and global scales is draught with complexities and challenges. Recently, climate change has been identified as a major factor of forest degradation across the globe. Although native forests may be adapted to disturbances to a critical threshold level, the intensification of the stress will move the forests in a new trajectory. Evaluating the cause-effect relationship of forests and climate also play determinable roles in the forest-climate loop. Such analysis is critical in identifying the factors of degradation and would be crucial in developing strategies for restoring and conserving the forest ecosystems.
Keywords
- forest degradation
- climate tolerance
- biophysical responses
- plasticity responses
- biological invasions
1. Introduction
Forests cover thirty-one percent of the total global land area and nearly half of these forests are relatively intact with more than one-third remaining as naturally regenerated forests of native species (primary forests), with no visible indications of disturbances. The total area under forests across the globe is estimated to be 4.06 billion hectares, and this ecosystem provides habitat for a vast variety of terrestrial flora and faunal species [1]. Besides biodiversity, forests provide a plethora of ecosystem services ranging from sociocultural benefits, to nature experiences and climate regulation. Unfortunately, these pristine natural resources are under tremendous threat both from natural and anthropogenic stresses.
The conventional forest management targeted only a minor subset of the accrued benefits from forests and specifically concentrated on harnessing their potential for timber production or recreation [2, 3]. The structure and composition of a large extend of the world’s present forest systems are a direct or indirect result of such manipulations. With time, there was an increasing realization that forests provide services much beyond their traditional uses and have to be viewed from multiple dimensions to realize their full potential. One of the most important among these benefits is that forests are the most viable option for combating global climate change.
Forests exert regulations on the global climate in at least two ways: (i) forest ecosystems remove approximately 3 Pg C annually emitted to the atmosphere by anthropogenic activities and (ii) act as the major terrestrial sink holding more than two times the carbon in the atmosphere [4]. Though the climate mitigation role of forests is beyond doubt, a complex situation emerges on a reverse evaluation of the influence of climate on forests and their concomitant effects on the carbon cycle. Hence, evaluating the cause-effect relationship of forests and climate solely on carbon stocks and sequestration potential may not be sufficient. Forest structure, cover, compositional changes, and biophysical shifts (water and energy balances) play determinable roles in the forest-climate loop. Forest fires, pest outbreaks, invasive alien species, pollution, forest fragmentation, and soil erosion are degradative factors that hamper the functions and productivity of forests, thereby adding to atmospheric carbon. In the present chapter, we intend to analyze (i) biophysical responses of forests to climate change and (ii) the climate-change-induced impacts on forests.
2. Defining forest degradation
The concept of health applied to individual trees would appear quite simple and easily quantifiable by measures such as absence of disease or physiological stress. However, shifts in the monitoring scales from trees to forest as a system make the assessment very complex. Stand productivity is commonly treated as a measure of the health of natural and planted forests. Though this provides a good proximate estimation for utilitarian purposes, it neglects several other important features of forest ecosystems such as vegetation structure, species assemblage, carbon storage, nutrient cycling, and hydrological functions. This deficiency necessitates a more holistic definition of forest health with easily quantifiable attributes. Though giant leaps have been made in technologies and scientific techniques in forestry studies, researchers have struggled for decades with operational definitions of ecosystem degradation. Lanly and Jean-Paul [5] state that “The situation with respect to forest degradation is unsatisfactory particularly because of the imprecision and multiple, and very often subjective, interpretations of the term.” Lund [6] could identify more than 50 definitions for forest degradation showcasing the inconsistencies and vagueness associated with the concept.
Ghazoul et al. [7] derived a concept of forest degradation by combining the theories and analogies of resilience and basins of attraction. The proposed basin of attraction represented the different ecosystem states, which continuously modify toward a single or multiple stable steady states. It should be noted that the term steady state does not mean a static state per se, but would be highly dynamic and with interactions between the abiotic and biotic elements that would continuously produce small changes in structure and composition at local levels, even without any disturbance. Even slight disturbances, however, would displace the ecosystems from their present stable steady state to an unstable state and will initiate changes that would enable the system to either return to their earlier state or achieve another stable state. The level of displacement of the system depends on the type, intensity, scale, and frequency of disturbance [8]. The system’s ability to return to the earlier stable state (i.e., resilience) would depend on the intensity, frequency, and novelty of the disturbance causing degradation.
A robust approach to assess forest health has been put forth by FAO (The Food and Agriculture Organization of the United Nations), which combines the perspectives of “forest health and vitality” by considering biotic (e.g., weeds, insects and pathogens) and abiotic (e.g., pollution and drought) stresses and their effects on tree growth, survival, wood yield, wildlife habitat, non-timber forest products, cultural, esthetic, and recreation values. As such, a healthy forest system should be a balanced ecosystem that sustains complexity while providing ecosystem services. Such healthy systems would be recalcitrant to change and exhibit an excellent ability to recover from natural and anthropogenic stressors. Declining forest health or degradation is a global issue, but there exist problems in making realistic assessments because of difficulties in fixing appropriate timescales, reference states, thresholds, and ecosystem values.
The importance of having a proper definition for forest degradation would be crucial in properly defining the type of disturbance (natural or anthropogenic) that has led to a diminished status of the system. Forests are very complex and dynamic systems that constantly shift their structure and composition. Disturbance regimes and their subsequent interactions change forest structure and composition and are usually more expressed at the local to regional scales [9]. However, disturbances by climate change usually have wider ramifications that reverberate across the entire planet. Paleontological records of charcoal and pollen have attributed the rises in fire frequency and resultant degradation in boreal and temperate forest systems to changes in human management and climate [9].
3. Biophysical responses of forests to climate change
There has been an increasing concern on the potential impacts of climate change on forests [10, 11, 12, 13, 14, 15]. Due to the comparatively larger size and life span of forests with respect to most agricultural systems, the former systems respond relatively slowly to changes compared with agroecosystems. In agriculture there remains an option to breed climate-resilient varieties or to shift entirely to a new landscape within a few decades. However, such quick fix solutions may not be available for most forested systems.
3.1 Climate tolerance by forest systems
Tree species in the forests have life spans of more than 200 years and, in most cases, would be able to tolerate a reasonable range of weather fluctuations [16]. However, extreme climatic events such as floods, drought, and wind throws can result in widespread tree mortality and species decline. Tree ring data have been used extensively to quantify the degree to which the growth was suppressed before the tree survival gets affected and to establish the relationship between tree growth decline and climate [17]. Loehle [16] reported that trees in Pacific Northwest are aged between 400 and 500 years, hence would have germinated alongside the Little Ice Age (approximately 550 years ago) and survived a complete cycle of cooling and warming. Studies by Stahle and Cleaveland [18] on Taxodium distichum (bald cypress press) and Scuderi [19] in Pinus balfouriana (foxtail pine) in North America also show that over the life span (several hundred years) of many trees, multiple cycles of weather extremes would have been a rule rather than an exception, and it can be safely expected that trees, to a large extend, can tolerate such fluctuations.
3.2 Plasticity response by trees to climate change
Trees adopt a conservative growth strategy by adjusting their growth rates with weather. Frequent adverse weather conditions projected in most climate models may not always lead to complete tree mortality, but may rather try to balance with the developing average climatic conditions over a period. This means that trees with long life spans would adopt conservative strategies to avoid rapid growth in short runs of good conditions and thereby death in adverse conditions [16]. Such strategies, however, have been less reported in short-lived and early successional species.
Physiological and morphological acclimation responses by plants also help them to adapt to changing climate. Herbaceous plants have been known to alter their shoot-root ratio to acclimate to growing conditions. However, there are serious gaps in research data with respect to such responses in larger trees. Drought and high intensity rains eroding the fertile topsoil are two prominent effects predicted in most climate change assessments. Trees have been reported to reduce shoot-root ratio and energy demands to decrease stresses due to water deficiency during drought [20, 21]. Such size and biomass adjustments are usually developed at young ages. On the other hand, mature trees usually get locked into the already established biomass partitioning patterns that they would have developed at young age. Such developed functionalities restrict their ability to alter resource demands, hence more likely to succumb to rapidly changing climatic conditions [22]. Under persisting severe climate conditions, trees that die are usually replaced by the same species (i.e., no change in forest composition), but with a more adaptive body organization to tolerate the changing climate situations. However, such adaptations would affect aboveground productivity and would have serious ramifications for the functioning of ecosystem. Species replacement in forest systems would occur only if better adapted species to new and changing climate conditions are present in the regeneration pool and if they are competent enough to outpace the inferior species [15].
3.3 Genetic responses by trees to climate change
Tree species have physiological ecotypes, each with very distinct limits of tolerance and adaptation to variation in climate. In other words, within each species there would be a broad range of climate optima facilitating wider adaptations to changing climate. Bonan and Sirois [23] observed that the eco-physiological responses did not vary much under a wide range of temperatures.
3.4 Forest soils under climate change
Soil provides the base matrix for ecosystems to grow and flourish providing all essential growth inputs. The vegetation that develops on a soil in turn supports the base matrix by way of nourishing, protecting, and cycling the resources. A disruption in this cycle would eventually add to the disruptive forces accentuating degradation. The degradation of surface soils of forests by natural or anthropogenic stressors can accelerate soil nutrient leaching especially in tropical humid regions [24, 25]. Thick root mats on sandy soils in the Amazon tropical rainforest have been found to retain up to 99% of the available nutrients, thereby preventing nutrient leaching losses [26, 27]. In forests affected by fire, concentrations of most primary (P, K) and secondary nutrients (Ca, Mg and S) increase rapidly immediately after burning, which promote root development, chlorophyll content, and reproduction in surviving plants [28]. However, most of these nutrients are lost within a short time through leaching and runoff, thereby furthering degradation and supporting ecosystems with lesser diversity and ecological potentials [29, 30, 31]. The degradative effects will be faster in coarse texture soils than in clayey soils due to the higher negative charges in clay that strongly bind and retain the nutrients from leaching losses [32] Topography also has a profound influence on soil nutrients with chances of nutrient losses higher on the upper slopes under high-intensity rains [30].
Trees exert direct influence on the availability and quality of water in forest ecosystems [33, 34, 35] and play an important role in regulating soil erosion and runoff rates, which gets offset by degradation. Accordingly, climate factors that affect degradation and vegetative cover modification will have substantial impacts on the water-related provisioning services. Interaction of forest systems with water and energy cycles provides the basic foundation for water resource distribution, carbon storage, and terrestrial temperature balances. Studies by Rodrigues et al. [35] showed that climate change could lead to a 24–46% rise in annual soil erosion in managed forest systems and that the losses were consistently higher in systems with lower site qualities. The projected increments in the mean annual temperatures and annual rainfalls under the different climate change scenarios are expected to aggravate erosion risks in forest systems. Apart from high-intensity rains, increased fire incidences by enhanced drought conditions would also open up canopy leading to soil erosion, thereby furthering forest degradation.
Besides a store house of nutrients, forest soil also contains a complex microbial community with diverse metabolic capabilities that regulate all biogeochemical transformations in these systems. These biogeochemical cycles control the nutrient transformation and maintain fertility of soil [36, 37]. Though degradation causes significant decline in beneficial microbial population, studies have also shown that the diversity of certain adaptable microbial groups may increase in some forest systems [38, 39]. Theoretical models predict that soil fungal communities may be more resistant to forest degradation than bacteria in tropical forests [40, 41].
3.5 Fire responses of forests under climate change
Forests are highly vulnerable to wildfires and such fire-induced changes are considered an important part of the landscape dynamics. Wildfires are responsible for degradation in about 4.8 million hectares of forest worldwide, and this accounts for nearly 23% of forest degradation by all factors [42]. Low, moderate, and high-intensity fires occur under a wide set of environmental and climatic variables such as very low humidity, high wind speeds, high temperature, and high dry biomass (fuel) load, all of which are accentuated under changing climate. Once initiated the propagation of forest fire usually follows three mechanisms, which degrade the existing forest systems:
crawling fire: the fire that spreads through low-level vegetation;
crown fire: the fire that spreads through the top of the forest at an incredible speed. They can be extremely dangerous particularly on windy days;
jumping or spotting fire: the burning fuel (branches and leaves) is carried by wind and likely to cause distant fires. Thus the fire can jump over a road, river, or even a firebreak.
Forest fires, besides effecting the vegetation dynamics, cause prominent disturbances in the system and act as an agent of environmental change with local to regional impacts on land use, productivity, carrying capacity, biodiversity, and regional to global impacts on hydrological, biogeochemical, and atmospheric processes. About 55% of the forest systems in India are affected annually by fires, which result in degradation and exacerbation of carbon dioxide levels in the atmosphere. Besides flora, forest fires affect the forest habitat and population and distribution of short range faunal species. Tropical wild fires produce high organic carbon emissions, trace gases, black carbon, and release almost 100 million tonnes of smoke aerosols into the atmosphere. These submicrometer smoke aerosols emitted in large quantities to the atmosphere play a major role on the radiation balance of the earth-atmospheric system. Further, fires also destroy the organic matter, which would be needed to maintain an optimum level of humus in forest soils. Frequent fires may also decrease the growth of grasses, herbs, and shrubs, which may result in increased soil erosion.
3.6 Biological invasions in forests under climate change
Invasive alien species (IAS) negatively impact forest ecosystems by extirpating native species, altering ecosystem functions, changing species composition, reducing food and cover for wildlife, and posing threats to biodiversity [43, 44]. Invasive alien plants can affect water availability to native species, increase forest fire hazards, and affect productivity of natural and planted forests. Although a comparison of the number of IAS and their extent of invasion in tropical and temperate forests is impeded due to data deficiency from the former, available information indicates that the number of IAS is increasing rapidly in temperate forests, and this may increase as high latitude areas get warmer with climate change [45].
Climate change (changes in global temperatures, precipitation, fire regimes, and occurrence of climate extremes) is reported to be a major driver of biological invasions by increasing susceptibility of all ecosystems to IAS [46, 47]. Climate change may also increase chances of introduction of new alien species, promote their spread by altering historical biogeographic limits, and enhancing probability of establishment and colonization [48]. If unsuitability of climate had previously prevented a species from establishing in a new biome, a change in climate may help its establishment, invasion, and spread [46, 49].
Climate change is thus a major driver of forest degradation since it promotes invasion by alien species in these ecosystems and causes a multitude of negative impacts. The damages due to climate-change-induced biological invasions can be more severe in forests, which are already degraded and fragmented due to human interventions or other causes. The interactions between climate change, land-use change, forest disturbance, and invasive alien plants may facilitate evolution of novel communities (assemblages of native and alien species) in natural forests [50]. Such interactions can also create new pathways of invasion and enhance vector efficacy [46]. On the other hand, deforestation, which leads to a local rise in atmospheric temperature, light availability, and increased supply of soil nutrients, can promote invasion by alien plants affecting natural regeneration of native tree species in forest ecosystems [51]. In short, the consequences of climate change on invasion by alien species and their impacts on forests are complex.
Intensity and frequency of fire in forests are facilitated by highly inflammable invasive alien plants especially where climate change causes extreme drought and rise in atmospheric temperature [52]. A shift in fire regimes may result from such fire events. And, forest fires may help quick regeneration of alien plants compared with native species and may alter carbon cycling in these ecosystems. Climate change is predicted to intensify the fire regimes in the future, which will help spread and establishment of invasive alien plants [53].
It is reported that warmer and extended autumns promote plant invasions in the understory of boreal forests and a fast-growing invasive herb interrupt regeneration of fir trees in forest gaps in balsam-fir-dominated boreal forests in Canada [54, 55]. Both are examples of climate-change-induced alien plant invasions in boreal forests. Climate warming is reported to promote the rapid spread of alien plants into higher altitude areas where they failed to colonize earlier due to unsuitable cold conditions [56]. This is an impending threat to mountain forests. Extreme climate events such as heavy winds, hurricanes, storms, and floods can help long-distance spread especially of propagules of alien plants, pests, and pathogens [57] causing forest health issues even in continents far-off from the source.
It is predicted that the current sources of IAS may change in the future due to shifts in geospatial matched climates worldwide. This will further impede management measures of IAS including preparedness and prevention. Also, there are indications that the distribution of invasive alien plants in terrestrial ecosystems may expand in the future under different climatic scenarios. The hotspots of these invasions are predicted to be located in South America, Europe, New Zealand, and northern and southern Africa [58]. Chances of invasion of woody and herbaceous alien plants in endangered ecoregions in these invasion hotspots in the changing climate scenarios are also projected.
It is well known that climate change may increase the susceptibility of forest flora and fauna to invasion by alien pests and pathogens by enhancing host susceptibility and range expansion [59]. All these factors will contribute to forest degradation significantly. With tree campaigns promoted across the world, there is a serious risk of fast-growing alien tree species, which are planted to sequester carbon in order to mitigate impacts of climate change, becoming invasive [60]. Adequate attention is yet to be paid on this emerging threat. In the near future, one of the major challenges for land managers and conservationists is that climate-change-induced impacts on forest and other ecosystems will make management actions against IAS a greater challenge [46].
4. Climate-degradation interactions in forest ecosystems
The effect of climate on forest systems can be both negative and positive. Climate change could force forests to periodic stresses such as droughts, intense rains, fires, and wind throws, which would adversely affect the tree resilience in these systems. Such stressors in an intense or frequent form can lead to large-scale mortality in susceptible forest systems and produce patches of dried forest. On the other hand, such climate-mediated stressors can facilitate a wide range of essential ecological process such as nutrient cycling, regeneration, and subsequently creation of new habitats at larger spatial scales. In short, climate stressors could modify the forest landscapes to encompass a diversity of mosaic of successional patches representing different stages of disturbance, recovery, biogeochemical cycles, stand structures, and new habitat niche for fauna [61, 62, 63].
Studies by Baccini et al. [64] showed that forest disturbance and degradation accounted for 46, 81, and 70%, of carbon losses from tropical forests in Asia, Africa, and America, respectively. The enhanced emissions from forest disturbance and degradation initiate a feeder breeder reaction wherein greenhouse gas content in the atmosphere gets accentuated, and this in turn would increase the extend and severity of degradation in terrestrial systems. On the other hand, increased CO2 in the atmosphere is also increasingly viewed as a factor for improving net primary productivity of forests. Elevated atmospheric CO2 content has been reported to increase photosynthesis, a process known as CO2 fertilization [65]. The magnitude of the CO2 fertilization effect would however depend on the carboxylation efficiency and leaf area index of plants to rising atmospheric CO2 concentrations [66]. The forest responses to changing climate would also depend in part on whether the plant photosynthesis from elevated CO
Under a changing climate scenario, the capacity of forests to sustain its productivity and ward of degradation would depend on whether the ratio of elevated CO2 (∆Ca) to enhanced temperature (∆T) exceeds the physiological thresholds. In a changing climate, plants would be forced to acclimatize over time, especially in plastic traits (e.g., leaf area), photosynthetic capacity (carboxylation capacity and electron transport capacity), and leaf responses to ΔCa and ΔT [68, 69, 70]. The tree density (basal area per ground area), forest leaf area per ground area, and rooting depth in combination would determine the competition for resources and ecosystems response to the ΔCa or ΔT. For forests that do not acclimate, the threshold ∆Ca/∆T must be >89 ppm°C − 1 and for systems that adapt to changing climate, a threshold ∆Ca/∆T of >67 ppm °C − 1 would be required to avoid chronic stress and subsequent degradation. A lower minimum of 55% of existing forest systems without acclimation and 71% of the forests with acclimation are expected to meet the physiological thresholds and negate degradation.
Extreme events associated with climate change can also put enormous pressures on forested systems, degrade them with respect to their ecological functions, and more importantly reduce their capacity to store carbon. Ciais et al., [71] estimated ca. 30% reduction in the gross primary productivity of forests and a strong anomalous net source of carbon dioxide amounting to 0.5 Pg C yr−1 in Europe following heat waves. The increase in future drought could turn forest systems into carbon sources accentuating carbon-climate feedbacks, particularly in the tropics and at higher latitudes [72, 73]. Several studies have reported forest degradation [74, 75] as a major factor responsible for the upward trend in carbon concentrations in the atmosphere. However, quantifying carbon losses due to forest degradation as opposed to estimating carbon stored in a stand replacing the lost forest is often challenging, hence ignored in most global estimation of carbon emissions.
In general, climate change enhances forest degradation by way of enhanced physiological stresses (e.g., under floods and droughts), incidence and spread of invasive alien species, insect pests and pathogens, increased fire incidences, and related degradation. Stressors for degradation can be placed under the broad categories of climate, biotic, and anthropogenic, which interact to produce combined effects on forest systems. For example, climate regulates the intensity and spread of forest fires even if they result from human activities. Similarly, plants stressed by extreme drought conditions would have lesser resources to resist disease or insect outbreak. Such instances would invariably decline the forest health, open up canopy, and give way for invasion by alien plants.
Projected climate changes in all likelihoods have been predicted to have profound influences on disturbance regimes and ensuing species demography [76]. The tolerance ability of species to variation in moisture and temperature regimes will be undoubtedly confounded by the alterations caused by disturbances [76]. For instance, climate-change-induced drought enhanced widespread insect pest outbreak leading to massive die-back of different tree species in the Colorado Plateau [77].
Besides the effect of climate on ecosystems, forests also regulate a large array of biophysical properties, which have a direct or indirect impact on the global climate change. Forests absorb a large proportion of sunlight incident on them, thereby having an effectively lower surface albedo than other land uses [78]. In regions with boreal forests, this could produce a cooling effect on deforestation, a reverse of that in the tropical regions. Forests also directly regulate climate by modifying the surface roughness and evapotranspiration. These forest-regulated biophysical factors in turn influence the exchanges of mass, energy, and water between the atmosphere and land surface [79]. These forest-determined surface changes can counteract perceived climate benefits from forest carbon sequestration and may have a negative pressure on the carbon stocks [80, 81].
5. Conclusions
The possibility of a future without healthy forests is a question that looms large and uncertain given the ambiguities in assessing and tracking the changes in forest systems. Deciphering the causes, predicted recovery trajectories and understanding the consequences of forest degradation would be crucial in restoring the lost services of forest systems. As the climate predictions indicate that most of the world forest systems will have to experience CO
Acknowledgments
We are thankful to KSCSTE – Kerala Forest Research Institute for providing support for developing the manuscript.
References
- 1.
FAO and UNEP. The State of the World’s Forests 2020. Forests, Biodiversity and People. Rome: The Food and Agriculture Organization of the United Nations; 2020 - 2.
Puettmann KJ, McG Wilson S, Baker SC, Donoso PJ, et al. Silvicultural alternatives to conventional even-aged forest management-what limits global adoption? Forest Ecosystems. 2015; 2 :1-16 - 3.
Felipe-Lucia MR, Soliveres S, Penone C, et al. Multiple forest attributes underpin the supply of multiple ecosystem services. Nature Communications. 2018; 9 :4839 - 4.
Canadell JG, Raupach MR. Managing forests for climate change mitigation. Science. 2008; 30 :1456-1457 - 5.
Lanly J-P. Deforestation and forest degradation factors. Proceedings of the XII World Forestry Congress. 2003 - 6.
Lund HG. What is a degraded forest? White paper prepared for FAO. Forest Information Services, Gainesville, Virginia, USA. 2009. p. 39. Available from: http://home.comcast.net/~gyde/2009forest_degrade.doc - 7.
Ghazoul J, Burivalova Z, Garcia-Ulloa IJ, King LA. Conceptualizing forest degradation. Trends in Ecology and Evolution. 2015; 30 :622-631 - 8.
Folke C, Carpenter S, Walker B, Scheffer M, Elmqvist T, Gunderson L, et al. Regime shifts, resilience, and biodiversity in ecosystem management. Annual Review of Ecology, Evolution, and Systematics. 2004; 35 :557-581 - 9.
Messier C, Puettmann KJ, Coates KD. Managing Forests as Complex Adaptive Systems. Routledge; 2013. p. 37 - 10.
Ritchie JC. Climate change and vegetation response. Vegetatio. 1986; 67 :65-74 - 11.
Roberts L. How fast can trees migrate? Science. 1989; 243 :735-737 - 12.
Gates DM. Climate Change and its Biological Consequences. Sunderland, MA: Sinauer Associates; 1993 - 13.
Solomon AM. In: Shugart HH, editor. Vegetation Dynamics and Global Change. New York: Chapman and Hall; 1993 - 14.
Solomon AM, Webb T. Computer-aided reconstruction of late-quaternary landscape dynamics. Annual Review of Ecology and Systematics. 1985; 16 :63-84 - 15.
Loehle C, LeBlanc DC. Model-based assessments of climate change effects on forests: A critical review. Ecological Modelling. 1996; 90 :1-31 - 16.
Loehle C. Tree life history strategies: The role of defenses. Canadian Journal of Forest Research. 1988; 18 :209-222 - 17.
LeBlanc DC, Foster JR. Predicting effects of global warming on growth and mortality of upland oak species in the midwestern United States: A physiologically based dendroecological approach. Canadian Journal of Forest Research. 1992; 22 :1739-1752 - 18.
Stahle DW, Cleaveland MK. Reconstruction and analysis of spring rainfall over the southeastern U.S. for the past 1000 yr. Bulletin of the American Meteorological Society. 1992; 73 :1947-1961 - 19.
Scuderi LA. A 2000-year tree ring record of annual temperatures in the Sierra Nevada mountains. Science. 1993; 259 :1433-1436 - 20.
Keyes MR, Grier CC. Above- and belowground net production in 40-year-old Douglas-fir stands on low and high productivity sites. Canadian Journal of Forest Research. 1981; 11 :599-605 - 21.
Vogt KA, Vogt DJ, Moore EE, Fatuga BA, Redlin MR, Edmonds RL. Conifer and angiosperm fine-root biomass in relation to stand age and site productivity in Douglas-fir forests. Journal of Ecology. 1987; 75 :857-870 - 22.
Manion PD. Tree Disease Concepts. 2nd ed. Englewood Cliffs, NJ: Prentice Hall; 1991 - 23.
Bonan GB, Sirois L. Air temperature, tree growth, and the northern and southern range limits of Picea mariana. Journal of Vegetation Science. 1992; 3 :495-506 - 24.
Ishizuka S, Tanaka S, Sakurai K, Hirai H, Hirotani H, Ogino K, et al. Characterization and distribution of soils at Lambir Hills National Park in Sarawak, Malaysia, with special reference to soil hardness and soil texture. Tropics. 1998; 8 :31-44 - 25.
Kendawang JJ, Tanaka S, Ishihara J, Shibata K, Sabang J, Ninomiya I, et al. Effects of shifting cultivation on soil ecosystems in Sarawak, Malaysia. I. Slash and burning at Balai Ringin and Sabal experimental sites and effect on soil organic matter. Soil Science & Plant Nutrition. 2004; 50 :677-687 - 26.
Kenzo T, Furutani R, Hattori D, Tanaka S, Sakurai K, Ninomiya I, et al. Aboveground and belowground biomass in logged-over tropical rain forests under different soil conditions in Borneo. Journal of Forest Research. 2015; 20 :197-205 - 27.
Giardina CP, Sanford RL Jr, Døckersmith IC, Jaramillo VJ. The effects of slash burning on ecosystem nutrients during the land preparation phase of shifting cultivation. Plant and Soil. 2000; 220 :247-260 - 28.
Thomaz EL, Antoneli V, Doerr SH. Effects of fire on the physicochemical properties of soil in a slash-and-burn agriculture. Catena. 2014; 122 :209-215 - 29.
Kleinman PJA, Pimentel D, Bryant RB. The ecological sustainability of slashand-burn agriculture. Agriculture, Ecosystems and Environment. 1995; 52 :235-249 - 30.
Hattori D, Kenzo T, Yamauchi N, Irino KO, Kendawang JJ, Ninomiya I, et al. Effects of environmental factors on growth and mortality of Parashorea macrophylla (Dipterocarpaceae) planted on slopes and valleys in a degraded tropical secondary forest in Sarawak, Malaysia. Soil Science and Plant Nutrition. 2013; 59 :218-228 - 31.
Villa PM, Martins SV, de Oliveira Neto SN, Rodrigues AC, Martorano LG, Monsanto LD, et al. Intensification of shifting cultivation reduces forest resilience in the northern Amazon. Forest Ecology and Management. 2018; 430 :312-320 - 32.
Jordan CF. Nutrient Cycling in Tropical Forest Ecosystems. Chichester: John Wiley and Sons; 1985 - 33.
Brown T, Binkley D. Effect of management on water quality in north American forests, general Technical Report RM-248. USDA Forest Services, Fort Collins. 1994 - 34.
Carvalho-Santos C, Honrado JP, Hein L. Hydrological services and the role of forests: Conceptualization and indicator-based analysis with an illustration at a regional scale. Ecological Complexity. 2014; 20 :69-80. DOI: 10.1016/j.ecocom.2014.09.001 - 35.
Rodrigues AR, Botequim B, Tavares C, Pécurto P, Borges JG. Addressing soil protection concerns in forest ecosystem management under climate change, Forest Ecosystems. 2021; 7 :34. DOI: 10.1186/s40663-020-00247-y - 36.
Marin-Spiotta E, Silver WI, Swanston CW, Ostertag R. Soil organic matter dynamics during 80 years of reforestation of tropical pastures. Global Change Biology. 2009; 15 :1584-1597. DOI: 10.1111/j.1365-2486.2008.01805.x - 37.
Powers JS, Corre MD, Twine TE, Veldkamp E. Geographic bias of field observations of soil carbon stocks with tropical land-use changes precludes spatial extrapolation. Proceedings of the National Academy of Sciences of the United States of America. 2011; 108 (15):6318-6322 - 38.
Bastida F, Selevsek N, Torres IF, Hernández T, García C. Soil restoration with organic amendments: Linking cellular functionality and ecosystem processes. Scientific Reports. 2015; 5 :15550 - 39.
Navarrete AA, Tsai SM, Mendes LW, Faust K, de Hollander M, Cassman NA, et al. Soil microbiome responses to the short-term effects of Amazonian deforestation. Ecology. 2015; 24 (10):2433-2448. DOI: 10.1111/mec.13172 - 40.
Zhang X, Chen Q , Han X. Soil bacterial communities respond to mowing and nutrient addition in a steppe ecosystem. PLoS One. 2013; 8 :e84210 - 41.
de Vries F, Liiri M, Bjørnlund L, Bowker MA, Christensen S, Setälä HM, et al. Land use alters the resistance and resilience of soil food webs to drought. Nature Climate Change. 2012; 2 :276-280. DOI: 10.1038/nclimate1368 - 42.
Curtis PG, Slay CM, Harris NL, Tyukavina A, Hansen MC. Classifying drivers of global forest loss. Science. 2018; 361 (6407):1108-1111. DOI: 10.1126/science.aau3445 - 43.
Liebhold AM, Brockerhoff EG, Kalisz S, Nuñez MA, Wardle DA, Wingfield MJ. Biological invasions in forest ecosystems. Biological Invasions. 2017; 19 (11):3437-3458. DOI: 10.1007/s10530-017-1458-5 - 44.
Moore AB. Alien invasive species: Impacts on forests and forestry – A review. Forest Health & Biosecurity Working Paper 8. Food and Agriculture Organization, Rome. 2005 - 45.
Pauchard A, Milbau A, Albihn A, Alexander J, et al. Non-native and native organisms moving into high elevation and high latitude ecosystems in an era of climate change: New challenges for ecology and conservation. Biological Invasions. 2016; 18 (2):345-353. DOI: 10.1007/s10530-015-1025-x - 46.
Walther GR, Roques A, Hulme PE, Sykes MT, et al. Alien species in a warmer world: Risks and opportunities. Trends in Ecology & Evolution. 2009; 24 (12):686-693. DOI: 10.1016/j.tree.2009.06.008 - 47.
Diez JM, D’Antonio CM, Dukes JS, Grosholz ED, Olden JD, Sorte CJ, et al. Will extreme climatic events facilitate biological invasions? Frontiers in Ecology and the Environment. 2012; 10 (5):249-257. DOI: 10.1890/110137 - 48.
Hellmann JJ, Byers JE, Bierwagen BG, Dukes JS. Five potential consequences of climate change for invasive species. Conservation Biology. 2008; 22 (3):534-543. DOI: 10.1111/j.1523-1739.2008.00951.x - 49.
Chown SL, Huiskes AHL, Gremmen NJM, Lee JE, Terauds A, Crosbie K, et al. Continent-wide risk assessment for the establishment of non-indigenous species in Antarctica. Proceedings of the National Academy of Sciences of the United States of America. 2012; 109 (13):4938-4943. DOI: 10.1073/pnas.1119787109 - 50.
Chmura D. The spread and role of the invasive alien tree Quercus rubra (L.) in novel forest ecosystems in Central Europe. Forests. 2020; 11 (5):586. DOI: 10.3390/f11050586 - 51.
Langmaier M, Lapin K. A systematic review of the impact of invasive alien plants on forest regeneration in European temperate forests. Frontiers in Plant Science. 2020; 11 :524969. DOI: 10.3389/fpls.2020.524969 - 52.
Bowman DMJS, Kolden CA, Abatzoglou JT, Johnston FH, van der Werf GR, Flannigan M. Vegetation fires in the Anthropocene. Nature Reviews Earth & Environment. 2020; 1 (10):500-515. DOI: 10.1038/s43017-020-0085-3 - 53.
Balch JK, Bradley BA, D’Antonio CM, Gómez-Dans J. Introduced annual grass increases regional fire activity across the arid western USA (1980-2009). Global Change Biology. 2013; 19 (1):173-183. DOI: 10.1111/gcb.12046 - 54.
Humber JM, Hermanutz L. Impacts of non-native plant and animal invaders on gap regeneration in a protected boreal forest. Biological Invasions. 2011; 13 (10):2361-2377. DOI: 10.1007/s10530-011-0048-1 - 55.
Mulder CPH, Spellman KV. Do longer growing seasons give introduced plants an advantage over native plants in Interior Alaska? Botany. 2019; 97 (6):347-362. DOI: 10.1139/cjb-2018-0209 - 56.
Dainese M, Aikio S, Hulme PE, Bertolli A, Prosser F, Marini L. Human disturbance and upward expansion of plants in a warming climate. Nature Climate Change. 2017; 7 (8):577-580. DOI: 10.1038/nclimate3337 - 57.
Masters G, Norgrove L. Climate change and invasive alien species. CABI Working Paper 1. 2010. p. 30. Available from: https://www.cabi.org/Uploads/CABI/expertise/invasive-alien-species-working-paper.pdf - 58.
Wan JZ, Wang CJ, Yu FH. Risk hotspots for terrestrial plant invaders under climate change at the global scale. Environmental Earth Sciences. 2016; 75 (12):1012. DOI: 10.1007/s12665-016-5826-8 - 59.
Dudley JP, Hoberg EP, Jenkins EJ, Parkinson AJ. Climate change in the North American Arctic: A one health perspective. Eco Health. 2015; 12 :713-725. DOI: 10.1007/s10393-015-1036-1 - 60.
Dickie IA, Bennett BM, Burrows LE, Nuñez MA, et al. Conflicting values: Ecosystem services and invasive tree management. Biological Invasions. 2014; 16 (3):705-719. DOI: 10.1007/s10530-013-0609-6 - 61.
Kolb TE, Wagner MR, Covington WW. 1995. Forest health from different perspectives. In: Eskew LG. comp. Forest health through silviculture: Proceedings of the 1995 National Silviculture Workshop, Mescalero, New Mexico, May 8-11, 1995. Gen. Tech. Rep. RM-GTR-267. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 5-13. - 62.
Edmonds RL, Agee JK, Gara RI. Forest Health and Protection. New York: McGraw-Hill; 2000 - 63.
Raffa KF, Aukema B, Bentz BJ, Carroll A, et al. A literal use of “Forest Health” safeguards against misuse and misapplication. Journal of Forestry. 2009; 107 (5):276-277 - 64.
Baccini A, Walker W, Carvalho L, Farina M, Sulla-Menashe D, Houghton RA. Tropical forests are a net carbon source based on aboveground measurements of gain and loss. Science. 2017; 358 :230-234. DOI: 10.1126/science.aam5962 - 65.
Luo Y, Niu S. The fertilization effect of CO2 on a mature forest. Nature. 2020; 580 :191-192 - 66.
Li Q , Lu X, Wang Y, Huang X, Cox PM, Luo Y. Leaf area index identified as a major source of variability in modeled CO2 fertilization. Biogeosciences. 2018; 15 :6909-6925 - 67.
Sperry JS, Venturasa MD, Todda HN, Trugmana AT, Anderegga WRL, Wanga Y, et al. The impact of rising CO2 and acclimation on the response of US forests to global warming. PNAS. 2019; 116 :25735-25744 - 68.
Benomar L, Lamhamedi MS, Rainville A, Beaulieu J, Bousquet J, Margolis HA. Genetic adaptation vs. ecophysiological plasticity of photosynthetic related traits in young Picea glauca trees along a regional climatic gradient. Frontiers in Plant Science. 2016; 7 :48 - 69.
Dillon S, Quentin A, Ivkoví M, Furbank RT, Pinkard E. Photosynthetic variation and responsiveness to CO2 in a widespread riparian tree. PLoS One. 2018; 13 :e0189635 - 70.
Dusenge ME, Duarte AG, Way DA. Plant carbon metabolism and climate change: Elevated CO2 and temperature impacts on photosynthesis, photorespiration and respiration. The New Phytologist. 2019; 221 :32-49 - 71.
Ciais P, Reichstein M, Viovy N, Granier A, et al. Europe-wide reduction in primary productivity caused by the heat and drought in 2003. Nature. 2005; 437 :529-533 - 72.
Cox PM, Betts RA, Jones CD, Spal AS, Totterdell IJ. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature. 2000; 408 :184-187 - 73.
Dufresne JL, Fairhead L, Le Treut H, Berthelot ML, et al. On the magnitude of positive feedback between future climate change and the carbon cycle. Geophysical Research Letters. 2002; 29 (10):43-1-43-4. DOI: 10.1029/2001GL013777 - 74.
Hammond WM, Yu K, Wilson LA, Will RE, et al. Dead or dying? Quantifying the point of no return from hydraulic failure in drought-induced tree mortality. The New Phytologist. 2019; 223 :1834-1843 - 75.
Venturas MD, Sperry JS, Love DM, Frehner EH. A stomatal control model based on optimization of carbon gain versus hydraulic risk predicts aspen sapling responses to drought. The New Phytologist. 2018; 220 :836-850 - 76.
Burkett VR, Wilcox DA, Stottlemyer R, Barrow W, et al. Nonlinear dynamics in ecosystem response to climatic change: Case studies and management implications. Ecological Complexity. 2005; 2 :357-394 - 77.
Breshears DD, Cobb NS, Rich PM, Price KP. Regional vegetation die-off in response to global-change-type drought. PNAS. 2005; 102 :15144-15148 - 78.
Betts RA. Offset of the potential carbon sink from boreal afforestation by decreases in surface albedo. Nature. 2000; 408 :187-190 - 79.
Bonan GB. Effects of land use on the climate of the United States. Climatic Change. 1997; 37 :449-486 - 80.
Marland G, Pielke RA, Apps M, et al. The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy. Climate Policy. 2003; 3 :149-157 - 81.
Subak S. Forest certification eligibility as a screen for CDM sinks projects. Climate Policy. 2002; 2 :335-351