Resilience and Decline: The Impact of Climatic Variability on Temperate Oak Forests

Abstract

Oak forests are an important part of temperate European ecosystems, where they are actively improving biodiversity, carbon storage, and ecological stability. However, current concerns such as climatic changes, and especially rising temperatures and changing precipitation patterns, are impacting their resilience. In this context, our study intends to evaluate the impact of climatic variability on temperate oak forests, focusing on the influence of temperature and precipitation. This covers different sites that have different environmental conditions. By using both a bibliometric approach and a systematic analysis of publications that have studied the influence of climate change on oak forests, our study has identified specific species and site responses to climate stressors. Furthermore, we have also evaluated trends in drought sensitivity. All these aspects have allowed us to understand and suggest improvements for the impact of climate change on the resilience and productivity of oak ecosystems. We have analyzed a total number of 346 publications that target the impact of climate change on oak forests. The articles were published between 1976 and 2024, with the majority originating from the USA, Spain, Germany, and France. These studies were published in leading journals from Forestry, Environmental Sciences, and Plant Sciences, among which the most cited journals were Forest Ecology and Management, the Journal of Biogeography, and Global Change Biology. As for the keywords, the most frequent ones were climate change, drought, growth, forest, and oak. However, we have observed a trend towards drought sensitivity, which indicates the intensification of climate changes on oak ecosystems. Moreover, this trend was more present in central and southern regions, which further highlights the impact of regional conditions. As such, certain local factors (soil properties, microclimate) were also taken into account in our study. Our literature review focused on the following aspects: Oak species affected by climate change; Impact of drought on oak forests; Influence of climate change on mixed forests containing oaks; Effects of climate change on other components of oak ecosystems; Radial growth of oaks in response to climate change; Decline of oak forests due to climate change. Our results indicate that oak forests decline in a process caused by multiple factors, with climate change being both a stressor and a catalyst. Across the globe, increasing temperatures and declining precipitation affect these ecosystems in their growth, functions, and resistance to pathogens. This can only lead to an increased forest decline. As such, our results indicate the need to implement forest management plans that take into account local conditions, species, and climate sensitivity. This approach is crucial in improving the adaptivity of oak forests and mitigating the impact of future climate extremes.

1. Introduction

Climate change is a widely acknowledged phenomenon, though it continues to generate debate in some circles. It remains a central focus of scientific discourse, with many questions still unresolved. Among the most frequently explored areas is the relationship between climate change and forest ecosystems. As of 20 February 2025, a search revealed 68,736 scholarly articles addressing this broad topic.

Oaks, belonging to the genus Quercus in the beech family (Fagaceae), comprise approximately 500 to 600 species globally. They are particularly abundant in parts of Europe (e.g., Bulgaria, Portugal, Italy, Spain, and Romania), North America (Canada, the United States, and Mexico), and Asia (including Afghanistan, China, Mongolia, Nepal, Russia, Japan, India, and Pakistan) [1,2,3,4]. In the United States, 93 oak species are distributed across nearly the entire country [5]. In Mexico, oaks (Quercus spp.) are prominent in both lowland and montane forests, where they often represent the tallest tree species [6].

Recent studies and observations regarding climate changes have emphasized clear regional variability patterns. These are crucial in analyzing the response of oak forests located in temperate areas [7].

In Europe, climate variability has evidently increased, with a focus on precipitation patterns. Greater annual precipitations are recorder in high altitude areas from Northern Europe, while drying phenomena are prevalent in Southern and Eastern Europe. SPI studies have showcased fewer and less severe droughts in Northeastern Europe, with an opposite pattern in Southern Europe, namely severe droughts during spring and summer. The north-south difference is also proved by SPEI (which includes both temperature and precipitation). The past three decades have showcased wetter conditions in Northern Europe and increased droughts in Central and Southern Europe [8,9,10].

In North America, divergent regional trends were indicated by many climate studies and projections. For example, warming and droughts are projected to decrease soil moisture and affect ecosystem processes in areas such as the southern Great Plains, the Southwest, and northern Mexico. On the other hand, warmer and wetter conditions are projected to positively impact northern areas such as the northern Plains and southern Canada. Increased temperatures will also appear in the Pacific Northwest, but with no significant changes in annual precipitation. However, it is expected that summer precipitations will decline sharply. Rising temperatures are expected to cause more frequent and extreme hydrological events and droughts. This proves the suggestion of some others that temperatures will become more important than precipitation in affecting future drought risks [11,12].

In Asia, an increased drought was recorded in Northern East Asia (NEA). This was mainly caused by rising temperatures. Compared with precipitation trends (that recorded no significant changes), warming indicators are directly linked with drought intensification. Some studies (1902–2018) have shown that extreme droughts are predominantly increasing during the growth seasons. China and Mongolia have shown the highest number and duration of droughts, becoming the driest parts of East Asia. On the other hand, Japan, South Korea, and North Korea have wetter summers, which lead to fewer droughts [13,14].

In this context of regions affected by regional climate conditions (increased precipitations, increased droughts caused by higher temperatures, consistent dryings in southern areas), it is essential to understand how oak forests are adapting and responding to these climate influences.

In the Central Himalayas, oak forests constitute the climax evergreen vegetation between 1000 and 3600 m elevation [15]. Holm oak (Quercus ilex L.) is a dominant species in the Mediterranean, occupying transition zones between temperate forests and shrublands [16]. English oak (Quercus robur L.) is a foundational species in mixed and broadleaved forests across Eastern Europe [17,18]. In Asia, the Mongolian oak (Quercus mongolica) is widespread [19], while in Pakistan, seven oak species have been recorded [1].

Despite their adaptability, oaks often face strong competition from more competitive species, such as European beech (Fagus sylvatica L.), particularly in optimal growing sites [20]. Conversely, oaks are more successful under challenging ecological conditions—such as arid environments, clay soils, or floodplains—where they can establish natural stands and occupy specific ecological niches [21,22]. Nonetheless, monospecific oak stands growing under ideal conditions remain rare.

Bibliometrics—a method that uses statistical analysis to evaluate the impact and structure of the academic literature—has become an essential tool in scientific research. It allows researchers to systematically examine large bodies of literature, revealing historical trends, knowledge gaps, and emerging areas of interest. In recent years, the development of advanced software tools has greatly enhanced the efficiency and accuracy of bibliometric analysis [23,24]. Unlike traditional literature reviews, bibliometric methods enable rapid mapping of a research field and the identification of key publications and research directions.

By utilizing citation and content analysis, bibliometric techniques have gained increasing prominence, supported by the growth of digital databases and computational tools. Their effectiveness depends on the availability of large datasets, making them especially suitable for analyzing well-established research areas [25].

Although numerous reviews have addressed the broader implications of climate change [26,27,28,29,30] and forestry-related topics [31,32,33,34,35], no comprehensive review has specifically examined the intersection of climate change and oak forests.

To fill this gap, we conducted an in-depth review of the ISI-indexed literature using both traditional and bibliometric approaches. The results offer an integrated overview of current knowledge, highlight research trends, and provide a valuable foundation for future studies exploring how climate change affects oak-dominated ecosystems.

The primary goal of our research was to assess the sensitivity of temperate oak forests to climatic variability, with a particular focus on the impacts of temperature and precipitation on these ecosystems. By analyzing published articles, we aimed to identify species-specific and site-specific growth responses to climate stressors, evaluate temporal trends in drought sensitivity, and improve our understanding of how ongoing climate change may affect the resilience and productivity of oak-dominated ecosystems.

2. Materials and Methods

The first part of this study involved a bibliometric analysis to assess global scientific research on the impact of climate change on oak forests from 1976 to 2024. We conducted our analysis using the Science Citation Index Expanded (SCI-Expanded) within the Web of Science database, as well as Scopus, to identify relevant publications.

After carefully evaluating different search strategies and using various keywords, the phrase “influence of climate change on oak forests” was selected as the primary search term. This search yielded 695 articles from Web of Science and 442 articles from Scopus. However, only research articles and review papers were included in our analysis. Following a thorough examination of each article, the final dataset was reduced to 346 articles after eliminating duplicates (articles appearing in both databases), publications unrelated to the topic, and those lacking abstracts.

The articles were filtered based on these criteria: (1) peer-reviewed article; (2) includes an abstract; (3) focuses on the influence of climate change on oak forests. On the other hand, the articles that were excluded were (1) publications that used keywords in unrelated contexts (for example, using the term “climate change” in forests in general); (2) the terms were used in non-scientific content (editorial notes, errata); and (3) non-English sources or the gray literature (technical reports, NGO publications).

The bibliometric analysis focused on ten key aspects: (1) publication types, (2) research areas, (3) publication years, (4) countries, (5) authors, (6) institutions, (7) language, (8) journals, (9) publishers, and (10) keywords.

Data processing was performed using the Web of Science Core Collection tools, Scopus, Excel, and Geochart [36,37,38,39]. To generate visual maps and conduct cluster analyses, we utilized VOSviewer (version 1.6.20) [40].

The second part of this study employed a traditional literature review approach, providing an in-depth analysis of the 346 selected articles. The findings were categorized into six main research areas: (1) Oak species affected by climate change; (2) Impact of drought on oak forests; (3) Influence of climate change on mixed forests containing oaks; (4) Effects of climate change on other components of oak ecosystems; (5) Radial growth of oaks in response to climate change; (6) Decline of oak forests due to climate change.

The first part of this study involved a bibliometric analysis from Web of Science as well as Scopus to identify relevant publications (Figure 1).

3. Results

3.1. Classical Review—Synthesis of the Literature

From the analysis of the types of publications (898) in which the articles on the impact of climate change on oak forests are classified, it is observed that the largest number are research articles (638 articles, 94% of the total publications), followed by 32 reviews (4%), while proceedings papers and book chapters represent 1% (Figure 2).

We have identified 36 research areas in which we can frame the published articles. The most representative areas are Forestry (41%), Environmental Sciences (29%), and Plant Sciences (12%) (Figure 3).

Starting from 1986 (when the first article on this topic was published), the number of publications has steadily increased, reaching 21 in 2020 and 41 in 2024 (Figure 4).

Authors from 77 countries have published articles on this topic. The most well-represented countries are the USA, Spain, Germany, France, and China (Figure 5).

Countries can be grouped into five clusters, two of which contain the most countries; the first cluster includes Croatia, Denmark, Estonia, Finland, Germany, Israel, Italy, the Netherlands, Poland, and Sweden; the second cluster includes Argentina, Brazil, Hungary, India, Mexico, Saudi Arabia, Spain, Tunisia, and the USA (Figure 6).

The vast majority of articles (95%) are written in English. However, we have also identified articles written in other languages, such as French and Spanish (three articles each), Croatian, German, and Russian (two articles each), and Slovak (one article).

The journals with the greatest number and most significant articles published on the impact of climate change on oak forests are Forest Ecology and Management, Forests, Science of the Total Environment, and Agricultural and Forest Meteorology (

Table 1. Leading journals publishing articles on the impact of climate change on oak forests.

Crt. No.	Journal	Documents	Citations	Total Link Strength
1	Forest Ecology and Management	75	2987	81
2	Forests	38	396	31
3	Science of the Total Environment	18	535	26
4	Global Change Biology	14	1514	25
5	Dendrochronologia	13	184	24
6	Agricultural and Forest Meteorology	19	359	22
7	Annals of Forest Science	9	133	18
8	European Journal of Forest Research	9	143	16
9	Journal of Ecology	9	308	12
10	Catena	13	275	9
11	Journal of Biogeography	10	2252	9
12	Ecosystems	6	186	8
13	Ecology and Evolution	7	138	5
14	Frontiers in Forest and Global Change	9	49	4
15	Ecosphere	8	164	1

and Figure 7).

The institutions to which the authors of these articles belong, ranked by importance, are as follows: Chinese Academy of Sciences (nine articles); United States Department of Agriculture (USDA) (nine articles); Centro de Investigacion Ecologica y Aplicaciones Forestales (CREAF-CERCA) (seven articles); Consejo Superior de Investigaciones Cientificas (CSIC) (seven articles); Swiss Federal Institutes of Technology (seven articles); Czech University of Life Sciences Prague (five articles).

Among the 93 publishers who have published articles on this subject, the most representative are Elsevier (219 articles), Springer Nature (104 articles), Wiley (101 articles), and MDPI (52 articles).

In these articles, the most frequently used keywords are climate change, drought, growth, forest, and oak (

Table 2. Most frequently used keywords in articles on the impact of climate change on oak forests.

Crt. No.	Keyword	Occurrences	Total Link Strength
1	climate-change	190	509
2	drought	140	508
3	growth	88	325
4	forest	87	258
5	climate	95	251
6	dynamics	63	229
7	oak	66	216
8	responses	61	213
9	diversity	56	167
10	biodiversity	50	263
11	temperature	46	161
12	vegetation	54	140
13	management	40	125
14	carbon	36	124
15	soil	37	113
16	variability	35	113

).

Based on their connections, keywords can be grouped into several clusters, the most important being the first cluster includes dendrochronology, drought, forest management, forests, oak, radial growth, stands, and tree mortality; the second cluster includes climate change, impacts, model, mortality, phenology, precipitation, responses, and trees (Figure 8).

Regarding the evolution over time of keyword usage, it can be observed that in the early period (2015–2016), the most commonly used words were vegetation, disturbance, carbon, and fire. In the middle period (2017–2018), the predominant keywords were climate change, oak, biodiversity, patterns, and tree. In the most recent period (2019–2024), the keywords used were temperature, precipitation, drought, radial growth, and soil (Figure 9).

3.2. Oak Species’ Climate Sensitivity Across Regions

A significant number of oak species are cited in studies concerning the impact of climate change on forests. The main of these species are presented in

Table 3. Oak species affected by climate change.

Crt. No.	Oak Species	Region	Citing Article	Key Risk/Characteristic	Vulnerability Level
1	Quercusa acutissima Carruth.	China	Chen et al., 2022 [41]	Moderate range; some drought exposure	Medium
2	Quercus quifolioides Rehder & Wilson	China	Liao et al., 2021 [42]	High elevation, narrow niche	Medium–High
3	Quercus alba L.	USA	Marquis et al., 2019 [43]	Moderate drought sensitivity	Medium
4	Quercus brandegeei Goldman	Mexico	Brinckwirth et al., 2023 [44]	Endemic, highly restricted range	High
5	Quercus brantii Lindl.	Iran	Jafarian et al., 2023; Mirhashemi et al., 2023 [45,46]	Semi-arid zone; recent dieback reported	High
6	Quercus canariensis Willd.	Spain	Gea-Izquierdo et al., 2012 [47]	Range contraction, low drought tolerance	High
7	Quercus castaneifolia C.A. Mey	Iran	Asadi et al., 2024 [48]	Localized, some decline reported	Medium–High
8	Quercus cerris L.	Italy; Hungary; Serbia; Bulgaria; Italy	Mazza et al., 2024; Mészáros et al., 2022; Kostić et al., 2022; Šimková et al., 2023 [49,50,51,52]	Mixed resilience, regional decline	Medium
9	Quercus chenii Nakai	China	Chen et al., 2022 [41]	Limited distribution	Medium
10	Quercus chungii F.P. Metcalf	China	Jiang et al., 2016 [53]	Local endemism	Medium–High
11	Quercus ciliaris C.C. Huang & Y.T. Chang	China	Zhang et al., 2022 [24]	Limited elevation band	Medium
12	Quercus crispula Blume	Japan	Onosato et al., 2021 [54]	High latitude, frost exposure	Medium
13	Quercus delgadoana S.Valencia, Nixon & L.M. Kelly	Mexico	Argüelles-Marrón et al., 2023 [55]	Endemic, vulnerable to drought	High
14	Quercus faginea Lam.	Spain	González-Rodríguez et al., 2011 [56]	Shrinking populations	Medium–High
15	Quercus floribunda Lindl. Ex A. Camus	India	Thapliyal et al., 2024 [57]	Montane, climate-sensitive	Medium–High
16	Quercus garryana Douglas ex Hook.	USA	Pellatt and Gedalof, 2014; Gedalof and Franks, 2019 [58,59]	Range contraction, fire regime shifts	High
17	Quercus guyavaefolia H.Lév.	China	Liao et al., 2021 [42]	Endemic, elevation-specific	Medium
18	Quercus humboldtii Bonpl.	Mexico	Zorrilla-Azcué et al., 2021 [60]	Regional endemic, climate-sensitive	Medium–High
19	Quercus ilex L.	United Kingdom; Spain; France; Italy	Brasier, 1996; Ruiz-Gómez et al., 2019; Le Roncé et al., 2021; Asensio et al., 2024 [61,62,63,64]	Resilient to drought	Low
20	Quercus infectoria Oliv.	Iraq	Hama and Khwarahm, 2023 [65]	Arid zones, fragmentation	High
21	Quercus ithaburensis Decne.	Turkey	Bayar, 2022 [66]	Limited range, land use pressure	High
22	Quercus liaotungensis Koidz.	China	Keyimu et al., 2022 [67]	Regional species, stable	Medium
23	Quercus libani G. Olivier	Iraq	Hama and Khwarahm, 2023 [65]	Endemic, dry conditions	High
24	Quercus lobata Née	USA	Koenig et al., 2020 [68]	Habitat loss, climate-sensitive	Medium–High
25	Quercus longinux hayata	Taiwan	Sun et al., 2024 [69]	Narrow endemic, montane	High
26	Quercus longispica Hand.-Mazz.	China	Liao et al., 2021 [42]	Rare species, vulnerable to shifts	Medium–High
27	Quercus macranthera Fisch & C.A. Mey, ex Hosen	Iran	Foroozan et al., 2017 [70]	Isolated populations	Medium
28	Quercus marilandica Muenchh.	USA	Rogers and Russell, 2014 [71]	Dry tolerance, some risk	Medium
29	Quercus meavei Valencia-A, Sabas & O.J. Soto	Mexico	Argüelles-Marrón et al., 2023 [55]	Narrow endemic	High
30	Quercus mongolica Fisch. Ex Ledeb.	South Korea	Altman et al., 2020 [72]	Expanding northward	Low–Medium
31	Quecus monimotricha Hand.-Mazz.	China	Liao et al., 2021 [42]	Rare, climate-sensitive	Medium–High
32	Quercus oleoides Schltdl. & Cham	Costa Rica	Center et al., 2016 [73]	Tropical dry forests, drought stress	Medium–High
33	Quercus oxyphylla Hand.-Mazz.	China	Zhang et al., 2022 [74]	Endemic, climate-limited range	Medium
34	Quercus pannosa Hand.-Mazz.	China	Liao et al., 2021 [42]	Narrow range	Medium–High
35	Quercus petraea (Matt.) Liebl.	Europe; Romania; Germany	Vospernik et al., 2023; Nölte et al., 2020; Friedrichs et al., 2009; Crisan et al., 2023 [18,75,76,77]	Core species, moderate resilience	Medium
36	Quercus pyrenaica Willd.	Spain	Moreno-Fernandez et al., 2021 [78]	Fire-sensitive, declining locally	Medium–High
37	Quercus pubescens Willd.	Spain; Russia; Croatia	Santonja et al., 2015; Safonova et al., 2023; Šestan, 2012 [79,80,81]	Mixed responses, some decline	Medium
38	Quercus robur L.	Romania; Belgium; Germany; Netherlands; Croatia; Russia	Nechita and Popa, 2012; Vranckx et al., 2014; Shupe et al., 2022; Bouwman et al., 2021; Ugarković et al., 2016; Askeyev et al., 2005 [82,83,84,85,86,87]	Heat and frost-sensitive	Medium–High
39	Quercus rubra L.	USA; Germany	Juice et al., 2016; Kormann et al., 2024 [88,89]	Widely planted, moderately resilient	Low–Medium
40	Quercus schottkyana Rehder & E.H. Wilson	China	Jiang et al., 2016 [53]	Endemic, at elevation limit	Medium
41	Quercus semecarpifolia Sm.	India	Saran et al., 2010; Shekhar et al., 2022 [90,91]	Alpine tree line exposure	Medium–High
42	Quercus senescens Hand.-Mazz.	China	Liao et al., 2021 [42]	Rare, narrow distribution	Medium
43	Quercus serrata Murray	Japan	Onosato et al., 2021 [54]	Broad range, some frost risk	Medium
44	Quercus spinosa David	China	Liao et al., 2021 [42]	Elevation specialist	Medium
45	Quercus stellata Wangenh.	USA	Rogers and Russell, 2014 [71]	Heat-tolerant, some resilience	Low–Medium
46	Quercus suber L.	Tunisia; Portugal	Bouzidi et al., 2020; Mechergui et al., 2021; Ribeiro et al., 2024 [92,93,94]	Dieback, drought/fungal stress	High
47	Quercus variabilis Blume	China	Yu et al., 2016 [95]	Expanding, moderate resilience	Low–Medium
48	Quercus velutina Lam.	USA	Keyser et al., 2016; Marquis et al., 2019 [43,96]	Eastern oak, some drought risk	Medium

.

3.3. Physiological and Growth Responses of Oak Forests to Drought and Temperature

Our analysis has shown that drought can reduce carbon sequestration rates (CSR) in oak forests. This happened even in areas that recorded modest temperature raises. An example is the northeastern range limits of Quercus robur [84], which is relatively sensitive to climatic changes, making it susceptible to climate proxy. Growth rates were mostly correlated with precipitation and water balances in both Q. robur and Q. petraea. This happened especially during summer months [87]. We did not observe any significant latitudinal, longitudinal, or elevation patterns, with the exception of a decreased water balance during summer months in the case of Q. petraea with increasing latitude. In addition, both species did not maintain their pre-drought growth during drought years, although they did show a fast recovery after summer droughts. This contrasted specifically with sluggish or incomplete recoveries recorded after spring droughts [97].

Q. cerris showcased a higher drought tolerance and a stronger climate-related growth when compared with Q. robur from the lowland mixed forests of Serbia and Bulgaria [51,52,98]. In Hungary, Q. petraea and Q. cerris were limited in their growth because of precipitation [50]. Q. robur growths were correlated with climatic changes in floodplains, including scPDSI, groundwater levels, and river discharge [99].

In North America, chestnut and white oaks were the species that recorded the best resilience towards drought in comparison with black and northern red oaks. For example, the stem size and density of black oaks has caused a negative influence on their resistance to drought [96]. A similar situation was recorded in Tunisia, where Q. suber recorded higher mortality rates (up to 63,622 trees) during the prolonged droughts recorded between 1988 and 1995 [100].

In Central Europe, radial growth was the factor most positively associated with spring and summer temperatures, although it was moderated by groundwater [101]. In East Asia, Quercus spp. was more resilient to warming temperatures compared with Pinus densiflora. Some projections suggest possible compositional shifts in the future [102,103].

Q. liaotungensis and Q. robur were very influenced by the hydroclimate conditions recorded during late summers and autumns [67,82]. Negative correlations between radial growth and potential evapotranspiration were also recorded for Q. robur and Q. petraea in June [75]. Growths were mainly caused by prolonged droughts that lasted more than two years in the Moldavian Plateau [104].

3.4. Mixed and Transitional Forest Dynamics Under Climate Stress

In the transition zone between oak and beech forests, where drought is the most limiting factor, oaks with less favorable stem diameter position (Weisse’s middle stems) show slower radial growth, have less pronounced climatic precipitation signals, and have milder responses to extreme climatic events [105].

In oak–beech forests in the Swiss lowlands, at most sites, the relative importance of oak decreased gradually compared to beech. Mortality increased over time for both oak and beech, but the increase was stronger for oak. Oak and beech mortality decreased with increasing DBH. Additionally, oak mortality increased with stand basal area, whereas no such trend was found for beech [106]. Also for oak–beech, in Italy: After the 1990s, beech trees showed a climate-driven decrease in growth compared to oak, especially after 2003 (−20% of basal area increment), with a significant growth trend reversal between the species. Q. cerris trees showed a significantly higher ability to recover their growth levels after extreme droughts [49].

A currently warmer and drier climate seemed to favor the height growth superiority of European beech, whereas it decreased the superiority of Scots pine. The results indicated that even if the climate changes as predicted, the growth of oak will depend upon silvicultural promotion [107].

Dendrochronological studies on mixed stands of Oregon white oak and Douglas-fir on Southern Vancouver Island revealed species-specific differences in radial growth sensitivity to drought. Oregon white oak trees, particularly those growing at high densities or competing with Douglas-fir for moisture, were found to be more sensitive to drought and more sensitive to growing conditions during the prior year. The response of Douglas-fir to drought was less variable, possibly due to the relatively low conifer densities at the study site, as well as the species’ ability to root graft, its higher shade tolerance than Oregon white oak, and its rapid growth rates that allow it to achieve a more dominant canopy position. The non-stationary response to climate exhibited by Oregon white oak provides insights into the mechanisms by which Oregon white oak savannas are being converted to coniferous woodland but also suggests that tree-ring reconstructions of climate need to explicitly address changes in stand dynamics that could influence the growth–climate relationship [59].

Examined species interactions in mixtures of Scots pine (Pinus sylvestris) and pedunculate oak (Quercus robur) for varying soil conditions in the Netherlands over a period of 30 years, showing lower productivity of oak and higher productivity of Scots pine under climate change [85].

Both species, broadleaf Quercus mongolica (QUMO) and coniferous Abies koreana (ABKO), grow at the southern end of their distributional range, and they have adjacent altitudinal ranges in South Korea. This suggests an upward migration potential for QUMO due to warming-enhanced growth at higher elevations. In the elevational zone where ABKO and QUMO coexist, warming plays a primary role in ABKO growth reduction, while QUMO growth increases and thus induces a potential upward migration of QUMO. This combined effect can lead to population decline of ABKO [72].

3.5. Ecosystem-Level Effects and Structural Shifts of Oak Forests

In oak–beech forests of the Swiss lowlands, oak has gradually lost its relative dominance compared to beech at most sites. While mortality rates have increased for both species over time, the increase has been more pronounced in oak. The mortality of both species decreased with increasing diameter at breast height (DBH) but tended to rise with higher precipitation levels. Additionally, oak mortality increased with stand basal area, whereas no such correlation was observed for beech [106]. A similar trend was observed in oak–beech forests in Italy, where beech trees experienced a climate-driven reduction in growth compared to oak after the 1990s, especially after 2003 (−20% basal area increment). A significant growth trend reversal was noted between the species, with Quercus cerris displaying a significantly higher ability to recover growth levels after extreme droughts [49].

A warmer and drier climate appears to favor the height growth superiority of European beech while reducing the growth dominance of Scots pine. These findings suggest that even if climate projections materialize, oak growth will be strongly influenced by silvicultural management [107].

Dendrochronological studies on mixed stands of Oregon white oak and Douglas-fir on Southern Vancouver Island revealed species-specific differences in radial growth sensitivity to drought. Oregon white oak, particularly in high-density stands or when competing with Douglas-fir for moisture, showed heightened sensitivity to drought and growing conditions from the prior year. In contrast, Douglas-fir exhibited a more stable response to drought, likely due to its lower density, root grafting capabilities, higher shade tolerance, and rapid growth rate, allowing it to attain canopy dominance. The non-stationary climate response of Oregon white oak provides insights into its transition from savanna to coniferous woodland and suggests that tree-ring-based climate reconstructions should consider stand dynamics that influence growth–climate relationships [59].

A study on Scots pine (Pinus sylvestris) and pedunculate oak (Quercus robur) mixtures in the Netherlands over a 30-year period showed that climate change and varying soil conditions resulted in reduced oak productivity while increasing Scots pine productivity compared to current climatic conditions [85].

In South Korea, both broadleaf Quercus mongolica and coniferous Abies koreana (ABKO) occupy the southernmost part of their range with adjacent altitudinal distributions. Warming has enhanced Quercus mongolica growth at higher elevations, suggesting an upward migration potential for the species. In areas where Abies koreana and Quercus mongolica coexist, warming has primarily led to a reduction in Abies koreana growth while promoting Quercus mongolica growth, potentially leading to a population decline of Abies koreana in the future.

3.6. Drivers and Patterns of Decline in Oak Forests

The decline of oak forests is a multifaceted process influenced by a combination of biotic and abiotic stressors, with climate change playing a central and increasingly prominent role. Recent studies have emphasized the synergistic effects of environmental stressors and biological agents in accelerating oak decline across diverse biogeographical regions.

In Mediterranean-type climate regions, a review by Marques et al. [108] identified pathogens (48%) and climate factors (17%) as the most frequently studied drivers of oak decline. Notably, interactions between multiple stressors—particularly those involving climatic variables—were often reported, suggesting that combined effects may exacerbate decline symptoms more severely than isolated stressors.

Phytophthora cinnamomi, a soil-borne oomycete, has been strongly associated with the widespread decline and mortality of Quercus suber and Q. ilex across the Mediterranean. Its impact is particularly pronounced when coupled with prolonged drought conditions, which are believed to act as predisposing factors in the Iberian Peninsula’s oak decline [61]. Similarly, Ruiz-Gómez et al. [62] identified extreme climatic events and the incursion of alien invasive species as primary drivers of Q. ilex loss in Mediterranean open woodlands.

In North Africa, particularly Tunisia, cork oak (Q. suber) forests have experienced marked reductions over the past century. Historical analyses report a decline of 40,000 hectares between 1952 and 1992 [109] and a 45% decrease in forest area between 1920 and 2005—from 148,000 to 70,000 hectares [110]. Modeling studies predict that up to 40% of climatically suitable habitat for cork oak could be lost by 2070, with the most pronounced impacts expected in northern Africa and the southern Iberian Peninsula [93]. The decline is closely linked to reduced precipitation, which is the key positive driver of cork productivity, while rising temperatures enhance evaporative demand, exacerbating water stress. Moreover, the encroachment of drought-tolerant species such as Aleppo pine into cork oak habitats indicates a broader ecological shift likely driven by climate change.

Despite cork oak’s adaptation to the Mediterranean climate—characterized by wet winters and hot, dry summers—this species remains vulnerable to long-term climate variability. Extended periods of high temperature and/or low precipitation can reduce soil water availability, triggering physiological stress and increasing susceptibility to pathogen attacks [111].

In Central and Eastern Europe, similar patterns of climate-induced decline have been documented. In Poland, oak decline (Q. robur) is attributed to the synergistic effects of biotic and abiotic stressors, with a notable increase in drought frequency—especially in May and June—contributing significantly to reduced vigor and increased mortality [112]. Long-term comparisons using Walter’s climate diagrams and dendrochronological data confirm the major role of climatic variability in driving these trends.

In Romania, the decline of oak species has been substantiated through a combination of historical reports and interdisciplinary research from intensive monitoring plots (Level II), where climatic stress was identified as the primary causal factor [113].

Northern latitudes are not exempt from these patterns. In Finland, long-term monitoring of oak populations revealed that trees affected by dieback had ceased growth during a sequence of dry summers between 2005 and 2007. These declining or dead trees exhibited reduced radial growth beginning as early as the 1990s, indicating a lagged response to prolonged drought conditions. In contrast, healthy individuals showed greater adaptive capacity and resilience to climatic fluctuations [114].

Overall, the accumulated evidence highlights that climate change—especially increasing temperatures and decreasing precipitation—interacts with biotic stressors to accelerate the decline of oak forests. This phenomenon is regionally variable but globally consistent in its attribution to climate-induced physiological stress, reduced growth, and heightened vulnerability to secondary agents such as pathogens and invasive species.

4. Discussion

4.1. Classical Review—Synthesis of the Literature

Most of the studied articles are scientific articles (94%), with 4% review articles. This indicates a maturity of this topic, reaching a point where meta- and synthesis studies are in place. This is also a reflection of climate change and its impact on oak forests. The fact that this has reached a research levels only indicates the need to evaluate and integrate studies and methodologies.

The articles covered 36 research areas, highlighting the interdisciplinary aspect of this study. Most of the articles covered Forestry (41%), Environmental Sciences (29%), and Plant Sciences (12%), reflecting the primary approach of oak forests from an ecological and environmental point of view. However, the numerous disciplines that have tackled oak forests also imply the large impact of this topic. This ranges from biodiversity conservation, land-use change, and ecosystem services to social, climatic, and biological domains.

The number of publications has grown significantly, with a notable rise of 41 in 2024. This again highlights the international concern caused by climate change and its impact on forest ecosystems. This fact consolidates the growing number of policies and public concerns raised by climate resilience, carbon sequestration, and biodiversity preservation. Furthermore, this indicates a future expansion and even diversification of sub-topics (assisted migration, genomic adaptation, and socio-ecological resilience).

Our research shows a larger input from countries such as the USA, Spain, Germany, France, and China. We can attribute this fact to a series of factors. The first one is that these countries possess significant oak forests, followed by established research and funding mechanisms in the climate and environmental areas. However, this can also reflect regional vulnerabilities, such as the particularly sensitive nature of Mediterranean countries (France, Spain), especially under drought conditions, while temperate areas (the USA and Germany) are affected by growth and mortality in the context of warming and seasonal variations. In addition, these are the countries that are usually very active in international forest monitoring networks and research programs, which fuels their need for studies and consistent data gathering.

International collaborations and themes are further enriched by identifying research clusters among these countries. For example, Cluster 1 (e.g., Germany, Sweden, and the Netherlands) focuses on temperate countries and boreal forests with strong environmental research agendas. On the other hand, Cluster 2 (e.g., USA, Spain, and India) includes countries that must deal with complex ecological situations and regional concerns caused by climate change, which makes them interested in adopting and implementing resilience strategies. This clustering can also reflect different research priorities—from the decline of temperate European forests to resilience toward drought from subtropical areas.

Our language analysis also showcased a larger number of English articles. This is expected in a global scientific community, but articles in other languages (Spanish, French, and German) can suggest a second layer of articles that can reveal studies that are more focused or niched. This aspect can be further studied in future reviews and comparative articles.

Our article’s subject is of high academic importance, proven by the high number of renowned journals that tackle this topic at a global research level (e.g., Forest Ecology and Management and Science of the Total Environment). These publications are known for providing studies that are relevant and rigorous while tackling high ecological concerns. This only highlights even more our concern towards the decline of oak forests.

The same importance can also be found in the institutions that promote monitoring programs (e.g., Chinese Academy of Sciences, USDA, and CREAF). This can come from their access to large forest plots, experimental infrastructure, or modeling capabilities. More importantly, institutions such as CREAF and CSIC are focused on Mediterranean forest ecology, while USDA and the Chinese Academy of Sciences cover more ecologically diverse regions.

Next, our keyword clustering offers important data about the evolution and focus of methodologies. Terms such as “drought”, “radial growth”, “mortality”, and “phenology” suggest that the majority of studies are focused on the functional aspects of oak trees under climate change. On the other hand, the presence of modeling-related keywords (e.g., “model”, “responses”, and “impacts”) suggests a growth towards predictive tools needed to simulate future scenarios. If we consider the time spectrum, we can see that descriptive ecological studies have been replaced by process-based and predictive approaches, integrating physiological, meteorological, and management data.

The exponential growth of published articles over the years has been observed in other topics as well [24,115].

In conclusion, our bibliometric analysis highlights a research field that is continuously expanding. This area is shifting towards a more integrative and predictive approach, mainly caused by climate change and the need to conserve these forests. Future research will definitely benefit from a collaboration that exceeds borders and by integrating social, economic, and genomic concerns in order to address the resilience of oak forests under these climatic pressures.

4.2. Oak Species’ Climate Sensitivity Across Regions

From the total number of Quercus species (estimated at 500–600 globally), our review identified 48 species explicitly cited in the scientific literature as being affected by climate change (Table 1). These species span five continents and are reported in 29 countries, reflecting both the wide distribution of oaks and the global concern regarding their vulnerability to climatic shifts.

A notable pattern emerging from the reviewed literature is the geographic and taxonomic concentration of research efforts. For instance, a significant number of studies focus on East Asia—particularly China and Japan—where numerous endemic oak species, such as Quercus guyavaefolia, Quercus spinosa, and Quercus schottkyana, are located in climatically sensitive mountainous regions. These regions are especially vulnerable to climate-induced habitat shifts, as shown by Sun et al. [69], who found that oak species richness in southwestern China is predicted to contract under intensified climate scenarios. High-elevation ecosystems may serve as temporary refugia; however, upward or poleward migration is limited by topography and habitat fragmentation.

In Europe, Mediterranean and temperate oak species such as Quercus ilex, Q. suber, and Q. robur have been extensively studied, with mixed responses to climate stressors. Q. ilex, for example, has demonstrated resilience to drought conditions [62], yet there are also concerns about declining productivity and increased vulnerability to pests in certain Mediterranean regions. Meanwhile, Q. cerris (Turkey oak) appears to exhibit better drought tolerance than Q. robur (pedunculate oak), as shown by Kostić et al. [51], suggesting a potential shift in species composition in mixed oak forests under future drought regimes.

In North America, multiple oak species, such as Q. alba, Q. garryana, Q. rubra, and Q. stellata, have been analyzed in relation to temperature increase, altered precipitation patterns, and fire regimes. For example, Q. garryana in the Pacific Northwest shows signs of expansion potential in response to warming, although dependent on fire dynamics and land use [58]. Conversely, Q. rubra, though widely distributed, has shown growth reductions under extreme drought [89].

The Neotropical and Mesoamerican oaks, such as Q. brandegeei and Q. meavei, are also highlighted in recent studies [44,55], yet data remain limited. These regions are recognized as biodiversity hotspots with high endemism but low resilience due to restricted ranges and limited altitudinal migration options.

In the Middle East and Central Asia, species such as Q. brantii, Q. castaneifolia, and Q. libani face increasing aridification and extreme heat events, with studies from Iran and Iraq indicating significant physiological stress responses [45,65]. These regions are expected to become increasingly inhospitable for current oak populations, raising concerns about their long-term persistence without conservation intervention.

Taken together, the evidence underscores that while some oak species may adapt, persist, or even expand under changing climatic conditions, many others—especially those with narrow ecological niches or restricted geographic distributions—are likely to face habitat loss, demographic decline, or local extinction.

4.3. Physiological and Growth Responses to Drought and Temperature

Drought is the most important climatic stress factor that impacts both the health and productivity of oak forests [116,117]. This can lead to accelerated decline and increased mortality [118,119] and biotic stress caused by pest and pathogen interactions [120,121]. Many Quercus species have drought-adaptive traits such as deep rooting and efficient water use [47,122]. However, their response to stress is dependent on the species and the local context.

Q. robur and Q. petraea did not manage to maintain their growth after drought periods, which emphasized the importance of phenological timing. Mixed stress effects are recorded during early season droughts, which are connected with leaf expansion and cambial activities [97]. However, post-summer-drought recoveries show a more flexible response, as these periods are less phenologically constrained.

Q. cerris showed an increased tolerance to droughts, especially in southeastern Europe. This supports our view that precipitation has a more important role than temperature in oak growths [51,52]. This suggests the resilience to future precipitation changes, which is important in our climate-changing context.

The sensitivity of species to drought did not record any consistent geographic trends, meaning that local conditions (soil moisture, microclimates, groundwater availability) are more important than climatic conditions. This only reinforces the need to implement monitoring and management strategies, especially in the context of extreme climatic events [101,104].

Hydroclimatic conditions from previous years had a carryover effect on the growth of oak species, emphasizing a physiological memory mechanism. Late-summer and autumn climates have a direct influence on the storage of carbohydrates and the development of buds. This emphasizes the long-term influence of seasonal variability [67,82,123,124].

Growth trends from Germany and France indicate an increased productivity [125,126]. This was likely caused by CO₂ fertilization, nitrogen deposition, and longer growing seasons. However, these might also indicate latent vulnerabilities to heatwaves and droughts. Despite their adaptive growth patterns, Mediterranean species (Q. ilex) face reproductive challenges under chronic aridity [63,127].

In the context of warming scenarios from East Asia, Quercus spp. showed an advantage over P. densiflora. This suggests a future need for reconsidering forest composition and favoring oak species [102,103]. This not only impacts the local context but also biodiversity, ecosystem services, and the need for climate change-adapted forest management.

Overall, our findings prove that oak resilience is not uniform and not guaranteed in climatic contexts. Future silviculture strategies should take into account both the traits of species as well as climatic conditions and the ecohydrological conditions of the sites. This is needed to maintain both the stability and productivity of oak forests and mixed-oak forests under modern climatic conditions.

4.4. Mixed and Transitional Forest Dynamics Under Climate Stress

Oak species frequently coexist with other tree species, particularly European beech, Scots pine, Douglas-fir, and various conifers, forming complex mixed forest stands. The response of oaks within these ecologically and structurally diverse communities to climate change is often species-specific and highly context-dependent, reflecting both biotic competition and abiotic stressors such as drought and temperature extremes.

In transition zones between oak- and beech-dominated forests, such as those described by Sedmakova et al. [105], drought emerges as the primary limiting factor for oak performance. Middle-stemmed oaks (per Weisse’s classification), with less favorable stem diameter positions, exhibit reduced radial growth and a diminished response to both precipitation signals and extreme climatic events. This suggests that in mixed stands under drought stress, competitive position within the canopy structure significantly affects oak resilience.

Studies from the Swiss lowlands [106] further indicate a gradual decline in oak dominance relative to beech, with oak experiencing higher mortality rates over time—especially in denser stands and wetter conditions. The increased mortality with precipitation may seem counterintuitive, but it likely reflects associated pathogen or competitive stress under humid conditions, highlighting the complexity of oak response when biotic pressures are intensified by climatic variability.

Contrastingly, in southern Europe, a different pattern emerges. In Italy, beech experienced a more pronounced decline in growth than oak after the 1990s, with Q. cerris showing strong recovery capabilities post-drought, especially after 2003 [49]. This reversal of growth trends suggests that in warmer, drier climates, oaks—particularly drought-tolerant species like Q. cerris—may gain a competitive advantage over mesic species such as beech. These findings align with broader trends pointing to potential species composition shifts in mixed forests under progressive warming.

Silvicultural management appears to be a critical factor influencing oak performance in mixed stands. As Stimm et al. [107] noted, even under climate scenarios that predict warmer and drier conditions, oak growth is highly dependent on human intervention and promotion. This reinforces the idea that natural resilience alone may not be sufficient to ensure oak persistence or dominance in changing climates—management practices will likely determine future forest composition.

Outside Europe, dynamics within North American mixed forests reveal additional complexities. In British Columbia, Oregon white oak exhibits heightened drought sensitivity in competitive conditions, particularly when in proximity to Douglas-fir [59]. The dominance of Douglas-fir, with its higher shade tolerance and rooting strategies, contributes to the gradual replacement of oak savannas by coniferous woodland. These changes underscore how interspecific interactions and shifting forest structure—not just climate—can drive species declines or range shifts.

This notion is echoed in long-term simulation studies from the Netherlands, where mixed stands of Scots pine and Q. robur under climate change conditions resulted in reduced oak productivity and increased Scots pine growth [85]. These results suggest that in the absence of targeted silviculture or natural disturbance that favors broadleaf regeneration, oaks may lose ground to faster-growing or more drought-adapted conifers.

At the biogeographic edges of their distributions, climate-driven shifts are also becoming more apparent. In Korea, Quercus mongolica shows upward migration potential due to enhanced growth at higher elevations, while its coniferous neighbor, Abies koreana, experiences reduced growth in the same zones (ABKO). This suggests that climate warming may drive oak expansion into higher altitudes while displacing less tolerant species, potentially altering entire forest zones over time.

Collectively, these studies highlight the increasingly dynamic nature of mixed oak forests in a changing climate. The interaction between climate stressors, interspecific competition, and forest structure determines not only the growth and survival of oaks but also their ability to retain or gain dominance within mixed stands. These interactions are further modulated by site-specific conditions such as soil moisture availability, elevation, and stand density.

Importantly, oak resilience in mixed stands cannot be considered in isolation. Competitive interactions with co-occurring species, historical land-use patterns, and the intensity of management practices all play crucial roles in mediating the effects of climate change. Going forward, forest managers and conservationists must recognize these complex interdependencies when developing adaptive strategies for maintaining biodiversity, ecosystem function, and the long-term sustainability of mixed oak forests.

4.5. Ecosystem-Level Effects and Structural Shifts

It is important to note that climate change affects all components of an ecosystem, not just trees. A wide range of examples highlighting these effects can be found throughout the published literature. The results compiled in this review indicate that oak ecosystems, particularly those located in ecotonal zones or mixed-species stands, are experiencing complex and sometimes contradictory responses to changing climate variables such as temperature, precipitation, and drought frequency.

In transition zones between oak and beech forests, such as the one examined by Sedmakova et al. [105], the interaction between topography, species composition, and climate-induced stress reveals the vulnerability of oaks with less favorable stem positions. These trees show not only slower growth but also reduced sensitivity to climatic signals, possibly due to chronic stress or reduced vigor. This highlights how microhabitat conditions and intra-stand competition can modulate species’ climate responses.

The comparative mortality data from Swiss oak–beech forests [106] further emphasize the species-specific vulnerabilities under climate stress. The finding that oak mortality is more sensitive to stand basal area and precipitation patterns than beech suggests that oak may be at a competitive disadvantage in increasingly dense or wetter sites. Beech’s ability to maintain stable mortality rates regardless of basal area might be indicative of its greater competitive or physiological resilience in those contexts.

Conversely, in some regions like Italy [49], oak appears to outperform beech under warmer and drier conditions, particularly following extreme drought events. The significant recovery of Quercus cerris after 2003 points to inherent drought-adaptive traits, such as deep rooting or efficient water use, which may become more advantageous under future climates. These contrasting patterns between northern and southern Europe underline the importance of regional context and species composition when interpreting climate impacts.

The study by Stimm et al. [107] reinforces this context dependency by showing how forest management continues to play a pivotal role. Despite climatic pressures, silvicultural practices can influence growth outcomes—either mitigating or exacerbating the effects of climate change. This supports the idea that forest resilience is not solely determined by climate factors but also by anthropogenic interventions.

Evidence from North America also illustrates species-specific responses, particularly in mixed stands. Gedalof and Franks [59] reported that Oregon white oak shows heightened drought sensitivity compared to Douglas-fir. This finding highlights the importance of interspecific competition and site history in shaping growth dynamics. Douglas-fir’s physiological traits give it a competitive edge, while Oregon white oak’s response varies with density and previous-year conditions, emphasizing the need to consider legacy effects and stand dynamics in ecological forecasting.

Similar dynamics are observed in the Netherlands, where Bouwman et al. [85] found that Scots pine benefits more from changing climate conditions than oak, especially on certain soil types. This again illustrates the shifting competitive balance among co-occurring species and the strong modulating influence of edaphic factors.

In East Asia, the case of Quercus mongolica and Abies koreana reveals a clear elevational response to warming (South Korea). As Quercus mongolica expands upward and Abies koreana declines, this suggests a long-term risk of local extinction for the latter species, especially in areas with limited elevational range. Such changes not only alter forest structure and composition but may also affect biodiversity, microclimate regulation, and other ecosystem services.

Taken together, these studies provide a compelling picture of how climate change is reconfiguring oak forest ecosystems across biogeographic regions. Key themes include the importance of species-specific traits, competition dynamics, microenvironmental factors, and human management. The cumulative effect of these interacting drivers may lead to significant shifts in forest composition, structure, and function, with potentially cascading impacts on associated flora and fauna.

4.6. Drivers and Patterns of Decline in Oak Forests

The large-scale decline of Quercus species across temperate and Mediterranean regions has emerged as one of the most striking ecological symptoms of ongoing climate change. Numerous studies have documented this pattern in both Europe [112,128,129] and North America [130,131], underscoring a global phenomenon that transcends ecological and geographical boundaries.

As shown in this review, drought—both as a chronic stressor and an acute disturbance event—plays a pivotal role in oak decline. Experimental studies confirm that drought reduces stem and shoot growth and overall leaf area [132], which in turn limits photosynthetic capacity and carbon assimilation. Although moderate climate warming may not directly impact leaf nitrogen or carbohydrate storage [133], prolonged or intense drought significantly disrupts water uptake and physiological function, contributing to tree decline and mortality [112].

The Mediterranean region provides a particularly vivid example of how climate-induced stress and biotic agents interact to drive oak decline. According to Marques et al. [108], although pathogens like Phytophthora cinnamomi are frequently identified as direct causes of mortality, their effects are often potentiated by climatic stressors, especially prolonged droughts. In the Iberian Peninsula and North Africa, where cork oak (Quercus suber) and holm oak (Quercus ilex) dominate, the decline has become both spatially widespread and temporally persistent. The sharp reduction in cork oak area—up to 45% in Tunisia over the past century [110]—signals not just the loss of individual trees but a broader ecological shift, including species replacement by drought-tolerant competitors such as Aleppo pine.

This replacement dynamic suggests that oak species, despite their traditional adaptation to Mediterranean climates, are reaching the limits of their tolerance under current climate trajectories. As demonstrated by Mechergui et al. [93], modeling projections predict a substantial reduction—up to 40%—in climatically suitable habitat for cork oak by 2070. These changes are tightly linked to precipitation decline and increasing evaporative demand, both of which elevate physiological stress and reduce resilience.

Central and Eastern Europe exhibit similar trends, although the specific stressors and timings differ. In Poland, the increase in late-spring droughts correlates with diminished tree vigor and elevated mortality [112]. In Romania, long-term monitoring has confirmed that climatic stress, rather than pollution or pathogens, is now the principal driver of oak decline [113]. These findings highlight a critical temporal dimension: even relatively moderate shifts in climate variables can produce cumulative stress over decades, eventually tipping stands into decline.

In northern Europe, oak populations are not immune. For instance, in Finland, the delayed growth response observed in declining trees—years before visible symptoms—points to the importance of long-term drought sequences and legacy effects [114]. This suggests that oak decline is not merely a reaction to present-day extremes but often the outcome of prolonged sublethal stress that weakens trees and predisposes them to eventual dieback.

Cork oak decline, in particular, warrants urgent attention due to its ecological, economic, and cultural significance. The widespread reduction in cork production—by 40–60% in severely defoliated stands in Italy [134] and up to 30% forest loss in northwest Morocco [135]—represents a major challenge for Mediterranean land use systems. This is compounded by a decline in stand density and regeneration capacity, which could undermine the long-term sustainability of cork-based industries and the habitats they support.

In summary, the decline of oak forests is a multifactorial process, but climate change serves as both a direct stressor and a catalyst for other biotic threats. Across biogeographical zones, increasing temperatures and declining precipitation reduce growth, impair physiological function, and weaken resistance to pathogens. This leads to a compounded vulnerability that accelerates forest decline. Importantly, while the specific expression of oak decline varies by region, the underlying mechanism—climate-induced stress combined with secondary biotic factors—is globally consistent. Future forest management strategies must therefore incorporate proactive adaptation measures, including species selection, stand thinning, assisted migration, and long-term monitoring, to preserve oak ecosystems in an era of accelerating climate change. A high level of genetic diversity and maximum caution in the transfer of forest reproductive materials are also needed [136,137,138].

Management of drought stress in forests consists of the following:

Modeling the drought risk and mapping the sensitive lands for the next rotation (20 ± 100 yr, according to local oak species, climate, and policy/silviculture) may offer basic information for forest planning and future management [139].

Promoting drought-resistant oak species is the most accepted silvicultural option in short-, medium-, or long-term forest policy [140].

Silvicultural measures, such as regeneration prior to regeneration cuts, planting oak seedlings from local germplasm, shortening the rotation period of coppice stands, and gradual conversion of coppice towards high forests, were recommended in the Mediterranean zone [141]. In high stand density, the oak root system and crown biomass are low, and the competition for water and nutrients is high; therefore, thinning and other silvicultural measures that strengthen the trees improve the oak’s resistance to drought [142].

Selection of oak ecotypes and resistant genotypes was a constant goal of worldwide research, proving significant differences in oak genotypes regarding drought [143,144].

Controlling (treating) the harmful organisms (defoliators, sucking insects, bark beetles, leaf, root, and sapwood pathogens, etc.) was used on a large scale (i.e., survey and control of defoliators) or in particular oak stages (young plantations, special cultures, urban forests) [145,146]. Many studies present the dangerous impact of the invasive pest and pathogens on oak forests [147,148].

5. Conclusions

Our study provides strong evidence that temperate oak forests have different degrees of sensitivity towards climatic actions, especially temperature and precipitation. Our analysis showcases specific species and sites that have shown growth responses, proving the impact of local climate conditions on forest dynamics.

Our study emphasizes the response of pedunculate oak (Quercus robur) to climatic conditions, especially in its northeastern range limits. This sustains its potential as a proxy climate indicator. Our findings show that climate variability and warmer temperatures (caused by changing winter and summer temperatures) can affect oak populations from Eastern Europe.

Oak species react differently towards drought and recovery. For example, some species can adapt, persist, and even grow under changing climatic conditions. On the other hand, other species, especially those with restricted geographic distributions and from narrow ecological niches, deal with habitat losses, declines, and even extinction.

The resilience of oaks from mixed stands should also consider larger aspects, such as competitive interactions between species, the historical usage of the land, and the usage of management practices. In order to move forward, forest managers and conservationists should take into account these interactions when initiating maintenance strategies.

Our research sustains that climate change (especially increased temperatures and decreased precipitation) acts together with biotic stressors in accelerating the decline of oak forests. Even though this aspect varies locally, it is globally consistent if we take into account the climate stress, reduced growth, and heightened vulnerability to pathogens and invasive species. As such, the decline of oaks depends on each region, but the underlying mechanism (climatic stress) is globally consistent.

As we have observed, the last decades have indicated an increase in drought sensitivity, which poses a great threat to oak forests. The consequences can be damaging, as they cover forest productivity, biodiversity, and carbon sequestration. Our findings sustain the need to implement adaptive forest management strategies that take into account both the composition of species and local conditions.

Our study can be complemented in the future by long-term monitoring and integrative models that can predict the response of forests towards different climate change scenarios. Oak ecosystems can be conserved only if we understand the connection between biotic and abiotic factors in a fast-changing climate.

In conclusion, our study provides a base for understanding the impact of different climatic events on temperate oak forests. Our results can be used especially in areas where oak species are under-represented both locally and in studies. Our findings have emphasized key vulnerabilities and adaptive traits that can be used by other researchers in management strategies and in conserving oak biodiversity and the overall forest resilience under our current climatic changes.

While this study provides valuable insights into the climate sensitivity of oak forests, several limitations should be acknowledged: while we examined recent climatic trends and their influence on growth patterns, the study did not account for other potentially interacting factors such as pest outbreaks, competition dynamics, or forest management history, all of which may confound the observed climate-growth relationships. Also, our temporal analysis may be limited by the relatively short span of high-resolution climate data available for some sites, constraining our ability to detect longer-term trends or legacy effects. Future research addressing these limitations through expanded spatial sampling, multi-proxy approaches, and integration of biotic stressors will enhance our understanding of the resilience and adaptability of oak forests in the face of ongoing climate change.

Future research should focus on long-term monitoring and integrative modeling approaches to better predict forest responses under various climate change scenarios. Understanding the interplay between biotic and abiotic stressors will be crucial for conserving oak-dominated ecosystems in a rapidly changing climate.

Future forest management strategies must therefore incorporate proactive adaptation measures, including species selection, stand thinning, assisted migration, and long-term monitoring, to preserve oak ecosystems in an era of accelerating climate change.