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Dieback on Drought-Prone Forest Ecosystems

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A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Forest Ecology and Management".

Deadline for manuscript submissions: closed (20 March 2020) | Viewed by 39002

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Dr. Raúl Sánchez-Salguero

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Dpt. Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km 1, 41013 Sevilla, Spain
Interests: forest management; dendroecology; biogeography, forest dynamics; tree decline; ecological models; global change
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Dr. Luis Matías

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Dpt. of Animal Biology, Plant Biology and Ecology, University of Jaén. Campus Las Lagunillas s/n, 23071 Jaén, Spain
Interests: forest ecology; plant–animal interactions; global change; tree physiology; woody plants; tree decline; species distributions

Dr. Jesús Julio Camarero

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Pyrenean Institute of Ecology, Spanish National Research Council (CSIC), Zaragoza, Spain
Interests: treeline ecotone; dendrochronology; wood anatomy; biodiversity & conservation; climate change
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The world is rapidly getting warmer, and mortality events rose over the past 30 years in forest ecosystems through growth decline, loss of vigour, and in many cases, death, revealing the high vulnerability of many forests in all biomes. These episodes have the potential to rapidly alter ecosystem services, with important implications for the carbon–water balance, nutrient cycling, and population and community dynamics. Besides the presence of inciting (e.g., heat and drought events) and contributing factors (e.g., opportunistic biotic agents), the predisposition of particular species, populations, or individuals of a given species is considered as central to understanding why some organisms survive while others succumb to climatic stress. There is also a knowledge gap about the role of intraspecific trait variability, which might be caused either by genetic or local environmental differences, on determining key mechanisms leading to mortality events such as the carbon starvation–hydraulic failure model for plants.

This Special Issue of Forests calls to join efforts to improve our understanding of how ecosystems respond to changes in climate and which functional or structural traits make some species more prone to dieback and mortality episodes. We propose multidisciplinary contributions using varied disciplines such as ecophysiology, functional ecology, forest pathology, dendroecology, remote sensing, and modelling. Authors should address ecological and management aspects, including mitigation and adaptation to the environmental risks faced by forests globally. Contributions including experimental, observational, and theoretical studies are welcome for any biomes or scale.

Dr. Raúl Sánchez-Salguero
Dr. Luis Matías
Dr. Jesús Julio Camarero
Guest Editors

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Keywords

forest dieback
extreme climatic events
disturbances
climate warming
climatic risks
forests vulnerability
forest pathogens
insect outbreaks
forest fires
regeneration
forest management

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Published Papers (8 papers)

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Research

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19 pages, 3579 KiB

Open AccessArticle

Shifts in Growth Responses to Climate and Exceeded Drought-Vulnerability Thresholds Characterize Dieback in Two Mediterranean Deciduous Oaks

by Raúl Sánchez-Salguero, Michele Colangelo, Luis Matías, Francesco Ripullone and J. Julio Camarero

Forests 2020, 11(7), 714; https://doi.org/10.3390/f11070714 - 27 Jun 2020

Cited by 11 | Viewed by 3404

Abstract

Drought stress has induced dieback episodes affecting many forest types and tree species worldwide. However, there is scarce information regarding drought-triggered growth decline and canopy dieback in Mediterranean deciduous oaks. These species face summer drought but have to form new foliage every spring which can make them vulnerable to hotter and drier conditions during that season. Here, we investigated two stands dominated by Quercus frainetto Ten. and Quercus canariensis Willd. and situated in southern Italy and Spain, respectively, showing drought-induced dieback since the 2000s. We analyzed how radial growth and its responses to climate differed between non-declining (ND) and declining (D) trees, showing different crown defoliation and coexisting in each stand by: (i) characterizing growth variability and its responsiveness to climate and drought through time, and (ii) simulating growth responses to soil moisture and temperature thresholds using the Vaganov–Shashkin VS-lite model. Our results show how growth responsiveness to climate and drought was higher in D trees for both oak species. Growth has become increasingly limited by warmer-drier climate and decreasing soil moisture availability since the 1990s. These conditions preceded growth drops in D trees indicating they were more vulnerable to warming and aridification trends. Extremely warm and dry conditions during the early growing season trigger dieback. Changes in the seasonal timing of water limitations caused contrasting effects on long-term growth trends of D trees after the 1980s in Q. frainetto and during the 1990s in Q. canariensis. Using growth models allows identifying early-warning signals of vulnerability, which can be compared with shifts in the growth responses to warmer and drier conditions. Our approach facilitates establishing drought-vulnerability thresholds by combining growth models with field records of dieback. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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18 pages, 2697 KiB

Open AccessArticle

Differences in Near Isohydric and Anisohydric Behavior of Contrasting Poplar Hybrids (I-101 (Populus alba L.) × 84K (Populus alba L. × Populus glandulosa Uyeki)) under Drought-Rehydration Treatments

by Li Zhang, Li Liu, Han Zhao, Zaimin Jiang and Jing Cai

Forests 2020, 11(4), 402; https://doi.org/10.3390/f11040402 - 3 Apr 2020

Cited by 11 | Viewed by 3352

Abstract

Carbon starvation and hydraulic failure are considered important factors in determining the mechanisms associated with tree mortality. In this study, iso/anisohydric classification was used to assess drought resistance and mortality mechanisms in two contrasting poplar species, as it is generally believed that isohydric species are more susceptible to carbon starvation, while anisohydric species are more susceptible to hydraulic failure. However, these assumptions are rarely tested in poplar genotypes with contrasting growth strategies. Thus, we subjected potted poplar genotypes (I-101 (Populus alba L.) × 84K (Populus alba L. × Populus glandulosa Uyeki)) with fast and slow growth rates to drought–rehydration treatments. The slow-growing genotype maintained higher stomatal conductance and lower predawn leaf water potential than the fast-growing genotype, thus exhibiting a near-anisohydric stomatal behavior throughout the treatment period. The nonstructural carbohydrate (NSC) content indicated that the two genotypes had the same trend of carbon change (e.g., the NSC content in the leaves increased with drought and then decreased). However, when NSC content data were combined with the growth and photosynthetic data, it was observed that the slow-growing genotype mobilized carbon to maintain hydraulic safety, while the NSC content of the fast-growing genotype among tissues was static. The percent loss of hydraulic conductivity in the branches during treatments indicated that the fast-growing genotype could recover more quickly from xylem embolism than the slow-growing genotype. The slow-growing genotype with a slow growth recovery after rehydration showed a significant increase in carbon consumption, combined with a significant increase in the hydraulic safety threshold value, indicating that there may be drought tolerance. In comparison, the fast-growing genotype showed a faster hydraulic recovery ability that had no effect on the NSC content in the leaves and roots. Our findings demonstrate intraspecific isohydric behavior in poplar; however, the trade-off between carbon distribution and stomatal regulation should be considered separately within genotypes of the same species. In addition, NSC plays an important role in water–carbon balance in the drought–rehydration cycle. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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18 pages, 5511 KiB

Open AccessArticle

Tree-Rings Reveal Accelerated Yellow-Cedar Decline with Changes to Winter Climate after 1980

by Vanessa M. Comeau, Lori D. Daniels, Garrett Knochenmus, Raphaël D. Chavardès and Stefan Zeglen

Forests 2019, 10(12), 1085; https://doi.org/10.3390/f10121085 - 29 Nov 2019

Cited by 17 | Viewed by 4358

Abstract

Research Highlights: Yellow-cedar decline on the island archipelago of Haida Gwaii is driven by warm winter temperatures and low winter precipitation, which is caused by anthropogenic climate change and exacerbated by the positive phase of the Pacific Decadal Oscillation (PDO). Background and Objectives: Declining yellow-cedars are limited by physiological drought during the growing season, caused by freezing damage to fine roots through a complex pathway identified by research in Alaska. Given this, we hypothesized: (1) yellow-cedars on Haida Gwaii were limited by the winter climate. (2) Trees of different health classes were responding differently to climatic variation. (3) Changing climate-growth relations would vary among phases of the PDO. Materials and Methods: We sampled 15 stands exhibiting crown symptoms and developed three regional chronologies from trees that were healthy, had crown or tree-ring symptoms of decline, and trees that had died. We tested for growth responses to inter-annual and multi-decadal variation in climate among trees of different health statuses using correlation functions and wavelet analyses. Results: The three chronologies had similar patterns from the early 1500s to 1900s and responded to climate in the same way, with multi-decadal variability, and common narrow marker years. Climate-growth responses among trees of different health statuses diverged after the 1976/1977 switch in the PDO. Warm growing season temperatures facilitated the growth of trees in the healthy chronology. By contrast, growth of trees that showed symptoms of decline or had died was negatively associated with low winter precipitation. After 1986, growth of trees in the declining chronology decreased sharply and mortality increased, which is concurrent with the warmest winter temperatures and consistent with the root-freezing hypothesis from Alaska. Conclusions: Yellow-cedar decline is driven by climate change, exacerbated by the PDO. Warming winter temperatures, accelerated by anthropogenic climate change, have led to dieback and death of yellow-cedars, even with the temperate ocean-moderated climate of Haida Gwaii. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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20 pages, 6766 KiB

Open AccessArticle

Use of MODIS NDVI Products to Map Tree Mortality Levels in Forests Affected by Mountain Pine Beetle Outbreaks

by Joseph P. Spruce, Jeffrey A. Hicke, William W. Hargrove, Nancy E. Grulke and Arjan J. H. Meddens

Forests 2019, 10(9), 811; https://doi.org/10.3390/f10090811 - 17 Sep 2019

Cited by 27 | Viewed by 4810

Abstract

Extensive bark beetle outbreaks have recently occurred in western North American forests, resulting in overstory tree mortality across millions of hectares. Annual aerial surveys are currently used to operationally monitor bark beetle induced tree mortality, though this method is subjective and can exclude some forest areas. Daily Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data offer a potential alternative means to develop regional tree mortality maps. Accurate methods using such data could aid natural resource managers in surveys of forests with frequent overstory mortality, helping to prioritize forest treatment and restoration activities. This paper discusses a study to test the potential of using MODIS data to detect tree mortality. We developed and tested an approach to use 250-m resolution MODIS Normalized Difference Vegetation Index (NDVI) data products collected during a mountain pine beetle (MPB) outbreak and related tree mortality event in the northern Rocky Mountains of Colorado, USA. The 94 km² study area is predominantly lodgepole pine forest with most of the MPB-caused mortality occurring between 2003 and 2008. We used a 2.4-m forest conditions map from 2008 aerial multispectral imagery to calculate percentage of mortality within 240-m pixels for use as reference data. Using either daily or 16-day products, MODIS NDVI change products were calculated for 2008 versus either 2000 or 2003 baselines. MODIS change products were used as predictors in linear regression analysis to assess correlation between MODIS data and the aerial percent forest mortality map. Depending on the MODIS product, linear regression analyses yielded r² values ranging from 0.362 to 0.544 without outliers removed and from 0.406 to 0.570 with extreme outliers removed. Daily MODIS NDVI products from 2003 and 2008 were used with exponential regression to improve the r² to 0.593. The project showed some MODIS NDVI data potential for mapping percent tree mortality in forests subjected to regional bark beetle outbreaks and severe drought. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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18 pages, 3918 KiB

Open AccessArticle

Regeneration in the Understory of Declining Overstory Trees Contributes to Soil Respiration Homeostasis along Succession in a Sub-Mediterranean Beech Forest

by Jesús Rodríguez-Calcerrada, Roberto Salomón, Josep Barba, Guillermo G. Gordaliza, Jorge Curiel Yuste, Carlos Magro and Luis Gil

Forests 2019, 10(9), 727; https://doi.org/10.3390/f10090727 - 24 Aug 2019

Cited by 7 | Viewed by 3547

Abstract

Research Highlights: Tree decline can alter soil carbon cycling, given the close relationship between primary production and the activity of roots and soil microbes. Background and Objectives: We studied how tree decline associated to old age and accelerated by land-use change and increased drought in the last decades, affects soil properties and soil respiration (R_s). Materials and Methods: We measured R_s over two years around centennial European beech (Fagus sylvatica L.) trees representing a gradient of decline in a sub-Mediterranean forest stand, where the number of centennial beech trees has decreased by 54% in the last century. Four replicate plots were established around trees (i) with no apparent crown dieback, (ii) less than 40% crown dieback, (iii) more than 50% crown dieback, and (iv) dead. Results: Temporal variations in R_s were controlled by soil temperature (T_s) and soil water content (SWC). The increase in R_s with T_s depended on SWC. The temperature-normalized R_s exhibited a parabolic relationship with SWC, suggesting a reduced root and microbial respiration associated to drought and waterlogging. The response of R_s to SWC did not vary among tree-decline classes. However, the sensitivity of R_s to T_s was higher around vigorous trees than around those with early symptoms of decline. Spatial variations in R_s were governed by soil carbon to nitrogen ratio, which had a negative effect on R_s, and SWC during summer, when drier plots had lower R_s than wetter plots. These variations were independent of the tree vigor. The basal area of recruits, which was three times (although non-significantly) higher under declining and dead trees than under vigorous trees, had a positive effect on R_s. However, the mean R_s did not change among tree-decline classes. These results indicate that R_s and related soil physico-chemical variables are resilient to the decline and death of dominant centennial trees. Conclusions: The development of advanced regeneration as overstory beech trees decline and die contribute to the R_s homeostasis along forest succession. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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18 pages, 3049 KiB

Open AccessArticle

Radial Growth Patterns Associated with Tree Mortality in Nothofagus pumilio Forest

by Milagros Rodríguez-Catón, Ricardo Villalba, Ana Srur and A. Park Williams

Forests 2019, 10(6), 489; https://doi.org/10.3390/f10060489 - 6 Jun 2019

Cited by 19 | Viewed by 3739

Abstract

Tree mortality is a key process in forest dynamics. Despite decades of effort to understand this process, many uncertainties remain. South American broadleaf species are particularly under-represented in global studies on mortality and forest dynamics. We sampled monospecific broadleaf Nothofagus pumilio forests in northern Patagonia to predict tree mortality based on stem growth. Live or dead conditions in N. pumilio trees can be predicted with high accuracy using growth rate as an explanatory variable in logistic models. In Paso Córdova (CO), Argentina, where the models were calibrated, the probability of death was a strong negative function of radial growth, particularly during the six years prior to death. In addition, negative growth trends during 30 to 45 years prior to death increased the accuracy of the models. The CO site was affected by an extreme drought during the summer 1978–1979, triggering negative trends in radial growth of many trees. Individuals showing below-average and persistent negative trends in radial growth are more likely to die than those showing high growth rates and positive growth trends in recent decades, indicating the key role of droughts in inducing mortality. The models calibrated at the CO site showed high verification skill by accurately predicting tree mortality at two independent sites 76 and 141 km away. Models based on relative growth rates showed the highest and most balanced accuracy for both live and dead individuals. Thus, the death of individuals across different N. pumilio sites was largely determined by the growth rate relative to the total size of the individuals. Our findings highlight episodic severe drought as a triggering mechanism for growth decline and eventual death for N. pumilio, similar to results found previously for several other species around the globe. In the coming decades, many forests globally will be exposed to more frequent and/or severe episodes of reduced warm-season soil moisture. Tree-ring studies such as this one can aid prediction of future changes in forest productivity, mortality, and composition. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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16 pages, 5079 KiB

Open AccessArticle

Effect of Drought on Outbreaks of Major Forest Pests, Pine Caterpillars (Dendrolimus spp.), in Shandong Province, China

by Yongbin Bao, Fei Wang, Siqin Tong, Li Na, Aru Han, Jiquan Zhang, Yuhai Bao, Yunchi Han and Qiumei Zhang

Forests 2019, 10(3), 264; https://doi.org/10.3390/f10030264 - 15 Mar 2019

Cited by 15 | Viewed by 4648

Abstract

As the main defoliators of coniferous forests in Shandong Province, China, pine caterpillars (including Dendrolimus suffuscus suffuscus Lajonquiere, D. spectabilis Butler, and D. tabulaeformis Tsai et Liu) have caused substantial forest damage, adverse economic impacts, and losses of ecosystem resources. Therefore, elucidating the effects of drought on the outbreak of these pests is important for promoting forestry production and ecological reconstruction. Accordingly, the aim of the present study was to analyse the spatiotemporal variation of drought in Shandong Province, using the Standard Precipitation Index, and to investigate the impact of drought on the outbreak of pine caterpillar infestations. Future trends in drought and pine caterpillar populations were then estimated using the Hurst exponent. The results showed that: (1) Drought decreased gradually and showed a wetting trend from 1981 to 2012, with frequency decreasing on a decadal scale as follows: 1980s > 1990s > 2000s > 2010s; (2) The total area of pine caterpillar occurrence decreased strongly from 1992 to 2012; (3) Long-term or prolonged drought had a greater positive impact on pine caterpillar outbreak than short-term drought; (4) In the future, a greater portion of the province’s area will experience increased wetting conditions (57%) than increased drought (43%), and the area of pine caterpillar outbreak is estimated to decrease overall. These findings help elucidate the relationship between drought and pine caterpillar outbreak in Shandong Province and, hence, provide a basis for developing preventive measures and plans. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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Review

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17 pages, 831 KiB

Open AccessReview

Sudden Aspen Decline: A Review of Pattern and Process in a Changing Climate

by Jack A. Singer, Rob Turnbull, Mark Foster, Charles Bettigole, Brent R. Frey, Michelle C. Downey, Kristofer R. Covey and Mark S. Ashton

Forests 2019, 10(8), 671; https://doi.org/10.3390/f10080671 - 9 Aug 2019

Cited by 18 | Viewed by 10020

Abstract

The American quaking aspen (Populus tremuloides Michx.) and its close relative, the Eurasian quaking aspen (Populus tremula L.), cover a realm that is perhaps the most expansive of all tree species in the world. In North America, sudden aspen decline (SAD) is a growing concern that marks the rapid decline of quaking aspen trees leading to mortality at the stand and landscape scale. Research suggests that drought and water stress are the primary causes of SAD. Predisposing factors (age, structure, and landscape position), as well as associated stressors (i.e., pests and pathogens), have been linked to mortality in affected stands. The conflation of multiple interacting factors across the aspen’s broad geographic range in North America has produced significant debate over the classification of SAD as a disease and the proper management of affected stands. Interestingly, no such effects have been reported for the Eurasian aspen. We here review and synthesize the growing body of literature for North America and suggest that SAD is a novel decline disease resulting from multiple inciting and interacting factors related to climate, land-use history, and successional dynamics. We suggest that the range of aspen observed at the onset of the 21st Century was bolstered by a wet period in western North America that coincided with widespread regional cutting and clearing of late-successional forests for timber and grazing. No comparable land-use history, successional status, or age-class structure is apparent or linked for Eurasian forests. Eurasian aspen is either absent or young in managed forests, or old and decadent in parks in Fenno-Scandinavia, or it grows more intimately with a more diverse mixture of tree species that have arisen from a longer period of frequent timber cutting in Russia. Based on these insights we provide recommendations for practical management techniques that can promote stand resilience and recovery across a range of stand conditions in North America. Managers should attempt to identify SAD-prone stands using the presence of predisposing conditions and focus treatments such as coppice or prescribed fire on stands with suitable topographies, elevations, and climates. We conclude that SAD will persist throughout the coming decades, given the enormity of past cutting history, fire exclusion, and current changes in climate until a more active restoration agenda is implemented. Full article

(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)

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