Understanding Secondary Forests: From Definitions to Regional Case

Studies in China

Yuyang Su

School of Environmental and Natural Sciences, Bangor University, Bangor, LL57 2DG, U.K.

Keywords: Secondary Forests, Forest Restoration, Chinese Forest Ecosystems, Forest Degradation.

Abstract: Forests are essential for maintaining environmental health and supporting human well-being. However,

human activities and natural disturbances have greatly altered primary forests, forming secondary forests.

This study examines the distribution and types of secondary forests in China, analyses the causes of their

degradation, and discusses measures for their restoration. Secondary forests in China can be classified

according to four criteria: age, location, natural characteristics and management measures. These

classifications help to develop effective management strategies for secondary forests. The degradation of

secondary forests in northeastern China is mainly caused by anthropogenic activities such as logging and

natural disturbances. In addition, the total nitrogen and phosphorus contents of the surface soil of secondary

forests were significantly reduced. Degraded secondary forests can be restored through natural succession and

managed restoration practices. Natural succession, including secondary forest succession, refers to the gradual

recovery and re-establishment of primary forests after disturbance. However, this process is slow and often

requires human intervention to be effective. Managed restoration practices include dynamic management,

conserving valuable tree seedlings, introducing ecologically critical species, and establishing mixed and

multi-layered natural forests. Active human interventions, such as engineering and biological methods, are

recommended for severely degraded forests to rapidly restore the natural landscape of secondary forests.

Therefore, effective management and restoration practices that are tailored to the degree of degradation and

successional processes are essential for the sustainability of these important ecosystems.

1 INTRODUCTION

Forests encompass one-third of the world’s land mass.

Humans depend on forests for food, shelter and

energy. Forests are home to most terrestrial species

and absorb carbon from the atmosphere, which helps

regulate the global carbon cycle and mitigate climate

change. Forest ecosystems can protect soil, stabilize

river flow and water runoff, prevent land degradation

and desertification, and reduce the risk of natural

disasters such as droughts, floods and landslides. In

addition, rivers near forests provide freshwater

resources for human life, agriculture, industry and the

environment. Forests are essential for climate

regulation and biodiversity, but the world still faces

the challenge of deforestation. Deforestation is

mainly driven by agriculture, forestry and other land-

use activities. This is one of the important factors

leading to global greenhouse gas emissions. These

https://orcid.org/ 0009-0006-5155-1250

can reduce the forest’s ability to adapt to threats such

as climate change and habitat degradation, thus

forming a negative feedback loop that ultimately

leads to more biodiversity loss. Humans need to

strengthen forest protection and conduct sustainable

resource management to reduce damage to forests

(UNEP, 2024).

Forest land refers to natural forests, secondary

forests and artificial forests, including timber forests,

economic forests, firewood forests, shelter forests and

other types of forests, young forests and nurseries.

Forest land resources are the land used to produce and

reproduce forest resources and the most basic means

of production for forestry production, including

forested land, suitable forest land, sparse forest land,

unforested afforestation land, shrub land and nursery

land.

Secondary forests are naturally regenerating

woodlands that arise after primary forests have

Su, Y.

Understanding Secondary Forests: From Deﬁnitions to Regional Case Studies in China.

DOI: 10.5220/0013001900004601

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Innovations in Applied Mathematics, Physics and Astronomy (IAMPA 2024), pages 145-150

ISBN: 978-989-758-722-1

145

undergone repeated unsustainable logging or

extensive damage (Zhao et al., 2006; CATIE, 2016).

These forests develop after the original environment

has been significantly altered due to unsustainable

logging, fuelwood collection, wildfires, agriculture,

and excessive grazing. Secondary forests, although

classified as natural forests alongside primary forests,

replace the original forest communities and exhibit

significant differences in structure composition,

productivity, and ecological functions compared to

primary forests. Additionally, forests that regenerate

on sites where plantations have been harvested,

including those with sprouting of planted species and

mixed forests formed by invasive species, are also

categorized as secondary forests (Zhao et al., 2006;

CATIE, 2016). This paper introduces the distribution

and types of secondary forests in China, the causes of

secondary forest degradation and restoration

measures.

2 IMPORTANCE OF

SECONDARY FORESTS

With the continuous expansion of human activities

and the intensification of environmental damage, the

survival of secondary forests faces great threats.

Human activities such as excessive logging, clearing

and grazing have reduced the area of secondary

forests and damaged the ecological environment (Yu

et al., 2011). Secondary forests occupy a dominant

position in China’s forest resources, so their

protection is vital. Secondary forests are crucial for

soil and water conservation and play a key role in

nourishing water, regulating climate, protecting the

ecological environment and creating economic

benefits. Their dense vegetation cover can effectively

reduce soil erosion and protect soil quality while

stabilizing regional water supply by storing water and

regulating the hydrological cycle through forests. In

addition, secondary forests can absorb carbon dioxide

from the atmosphere and reduce greenhouse gas

emissions, which helps regulate the climate and

improve air quality. The conservation and restoration

of ecosystem diversity also benefit from secondary

forests, supporting the habitats of many rare and

endangered species. From an economic perspective,

secondary forests provide abundant timber resources

and non-timber forest products, which provide

employment opportunities and economic gains for

local people and promote a virtuous cycle of

sustainable development and ecological conservation.

Therefore, effective management and conservation

measures can ensure that secondary forests continue

to fulfill their ecological and economic functions,

providing wide-ranging benefits and long-term

sustainable development for all sectors of society (Liu,

2007).

3 DISTRIBUTION AND TYPES OF

SECONDARY FORESTS IN

CHINA

Secondary forests in China are widespread,

constituting most of the country’s forest resources.

Excluding natural reserves, forest parks, undeveloped

regions in Tibet, protected tropical rainforests, and

scattered primary forests, all other forest areas are

secondary forests (Figure 1). These secondary forests

form the backbone of China’s forest resources and are

crucial for forest resource management.

Figure 1: Distribution and types of secondary forests in

China (Lei, 2011).

3.1 Types of Secondary Forests

Secondary forests in China can be classified based on

different criteria for effective management (Liu et al.,

2022):

Secondary forests in China can be classified based

on various criteria to ensure proper management.

These criteria include age, location, natural

characteristics, and management practices. Firstly,

secondary forests can be categorized by age into

early-stage, mid-stage, and late-stage forests. Early-

stage secondary forests are typically characterized by

young, fast-growing pioneer species that quickly

colonize disturbed areas. Mid-stage secondary forests

represent an intermediate phase where a mix of

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pioneer and climax species coexist with increasing

structural complexity. Late-stage secondary forests

are more mature, with a higher proportion of climax

species and greater biodiversity, resembling primary

forests more closely in structure and function.

Secondly, secondary forests can be classified by

location, distinguishing between remote and near-

urban secondary forests. Remote secondary forests

are situated far from human settlements and are often

less disturbed by human activities, allowing for more

natural ecological processes. In contrast, near-urban

secondary forests are located close to urban areas and

often face higher levels of human impact, such as

pollution, recreational use, and land-use changes,

which can affect their structure and ecological

function.

Thirdly, natural characteristics also serve as a

basis for classification. This includes dominant

species and species composition, ecological factors,

and topographical and site conditions. Dominant

species and species composition refer to the main tree

species that define the forest type, which can vary

widely depending on local climate and soil conditions.

Ecological factors influence the forest's growth and

development, including climate, soil type, and

hydrology. Topographical conditions encompass the

forest’s location on slopes, valleys, or flat areas,

affecting water drainage and sunlight exposure. Site

conditions and dominant species highlight the

interaction between the physical environment and the

species that thrive there, providing a detailed

understanding of the forest’s ecological dynamics.

Lastly, management practices are crucial for the

classification of secondary forests. These practices

include thinning and tending, regeneration and

rehabilitation, and utilization and protection.

Thinning and tending involve selectively removing

trees to reduce competition and promote the growth

of remaining trees. Regeneration and rehabilitation

efforts aim to restore degraded forests through natural

or assisted regeneration, enhancing biodiversity and

ecosystem services. Utilization and protection

encompass sustainable harvesting practices and

conservation measures to balance economic benefits

with ecological integrity. By using these

classification criteria, effective management

strategies can be developed to enhance the

sustainability and ecological function of secondary

forests in China.

3.2 Distribution

Figure 1 shows China’s forests are mainly located in

the Northeast, a region with unique characteristics

and great research potential. Therefore, this section

will focus on the distribution and types of forests, and

specific tree species in the Northeast.

3.2.1 Northeast Region

The Northeast region includes the provinces of

Heilongjiang, Jilin, and Liaoning, as well as the

eastern parts of Inner Mongolia. The primary forest

resources are concentrated in the Da Xing’anling,

Xiao Xing’anling, and the Changbai Mountains

(Figure 1).

The Da Xing’anling Mountain is located in the

northwestern part of Heilongjiang Province and the

northeastern part of the Inner Mongolia Autonomous

Region. It is dominated by cold temperate coniferous

forest and deciduous broad-leaved forests, with the

main tree species being Dahuirian larch and White

birch (Betula platyphylla Suk.).

The Xiao Xing’anling Mountain is located in the

northeastern part of Heilongjiang Province and is

mainly a temperate mixed coniferous and broad-

broad forest, with the main tree species including

Korean pine and Yeddo spruce.

The Changbai Mountains are located in the

eastern part of Heilongjiang, Jilin and Liaoning

provinces. It covers from mixed coniferous forests in

the north to broad-leaved mixed forests in the south

(Yu et al., 2011). White birch is a deciduous broad-

leaved tree that grows in high-altitude areas. It likes

sunlight and can grow in cold places. It has low soil

requirements and can survive in weak acid and weak

alkaline soils (Chen et al., 2021). White birch is one

of the dominant tree species in secondary forests of

temperate regions.

The study shows that natural secondary forests of

birch in the Da Xing’anling Mountain have

significant roles in water conservation, soil

conservation, carbon sequestration and oxygen

release, accumulation of nutrients, purification of the

atmospheric environment, and biodiversity

conservation, especially in soil conservation

functions. Near-mature forests in the southern part of

the Da Xing’anling occupy an important position in

the total value of ecosystem services. Near-mature

forests are incompletely mature forests that usually

have high productivity and ecological functions, but

need to be developed in terms of wood quality,

canopy structure and ecological functions. Although

the value of ecological services per unit area was

similar for trees in all age groups, the overall value of

near-mature forests was significantly higher than that

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147

of other age groups, highlighting the key role of near-

mature forests in ecosystem services (Zhou et al.,

2014). Since 1998, the Government of China has

transformed the focus of forest management from

timber production to ecological sustainability.

Natural forest protection projects and a categorised

management system have been introduced. These

measures have included reducing the amount of

timber harvested and increasing the area and stock of

forests. They conducted a series of policies and

regulations, scientific management methods, social

participation and economic incentives. The

management of secondary forests has made some

progress in ecological conservation and sustainable

development.

3.2.2 Southwest Region

Southwest China includes Sichuan, Chongqing,

Yunnan and Tibet. The region has a varied

topography, including lowlands, plateaus and

mountains. Differences in altitude and climate create

a wide range of forest types. In Sichuan and

Chongqing, subtropical areas usually have secondary

forests. In Yunnan, the forests contain both

subtropical and temperate species. Tibet is

characterised by high-altitude coniferous forests

adapted to cold and dry conditions. These forests are

important for watershed protection, biodiversity

conservation and carbon sequestration. However,

they also face pressures from agricultural expansion,

logging and infrastructure development.

3.2.3 Southern Region

The southern region includes Zhejiang, Anhui,

Jiangxi, Fujian, Hubei, Hunan, Guangdong, Guangxi,

Hainan and Guizhou. The region has a subtropical

climate with dense forest cover. Most of the

secondary forests here consist of fast-growing, hardy

tree species. Many areas have been replanted with

economically valuable tree species. However, human

activities such as logging, urbanisation and

agricultural encroachment often threaten them. These

activities have led to habitat fragmentation and loss

of biodiversity.

4 SECONDARY FOREST

DEGRADATION AND

RESTORATION MEASURES

4.1 Impacts of Secondary Forest

Degradation

Degradation of secondary forests is common,

resulting in significant ecological issues. For instance,

in the Northeast region of China, there are significant

differences between secondary forests and the

original Korean pine forests. The productivity of

forest stands, species composition, and community

biodiversity have changed obviously. The stock of

large-diameter trees has decreased significantly, and

the proportion of precious tree species has decreased

significantly. The biodiversity and uniformity of the

tree layer in secondary forests were also significantly

lower than those in primary forests, with differences

increasing significantly after moderate and severe

disturbances. The total nitrogen and phosphorus

content of the surface soil in secondary forests was

reduced considerably.

4.2 Causes of Secondary Forest

Degradation

The degradation of secondary forests is the

decomposition of primary forests caused by human or

natural disturbances.

Human disturbances include felling, grazing, and

burning. These activities reduce competing plants and

increase light and space to promote the growth of

target tree species. However, they may destroy the

ecological balance and lead to reverse succession if

they are unreasonable. In history, the Northeast

region has experienced a number of large-scale over-

harvests, particularly during the Russian and Japanese

occupations from 1896 to 1945 and large-scale timber

production from 1950 to 1977. These activities

seriously damaged the forest structure and ecological

functions. Large-scale population movements and

agricultural exploitation resulted in clearing large

tracts of forest for cultivation (Yu et al., 2011).

Natural disturbances include storms and fires.

These natural events change the vegetation structure,

affect the competitive relationship of plant

populations, and promote the formation of new plant

communities. In general, disturbances cause

significant changes in the species composition, spatial

structure, and function of secondary forests,

manifested in reduced biological productivity,

deterioration of soil microenvironment, decreased

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forest vitality, and disordered ecological processes.

Some secondary forests have undergone serious

reverse succession.

4.3 Restoration of Secondary Forest

Degradation

4.3.1 Natural Restoration

Natural restoration includes secondary forest

succession, which refers to the process by which

primary forests gradually recover and rebuild after

being disturbed by human or natural factors. This

process involves the reorganization of ecosystems

and the successional changes of plant communities.

This usually starts with pioneer species and

eventually reaches a top community state similar to

that of primary forests. Secondary forests require

more than two hundred years of succession to regain

their primary forest function (Wu et al., 2023).

Secondary forest succession is generally divided into

three stages.

1) Initial stage: Pioneer species invade and

occupy open space.

2) Mid-term stage: Environmental conditions

gradually improve, and more adaptable species

gradually replace pioneer species.

3) Late stage: The community tends to be stable

and gradually forms a top community close to the

original forest.

4.3.2 Managed Restoration Practices

In recent years, China has implemented various

policies and management strategies to address these

challenges. Natural forest protection projects and a

shift in forest management towards ecologically

sustainable development have played a key role.

Ecological restoration, scientific management,

community participation and economic incentives

have facilitated the gradual recovery of secondary

forests. These efforts include disturbance control,

human intervention and near-natural management to

enhance forest resilience and biodiversity. Human

intervention in secondary forests varies according to

their degradation level and the concept of positive

succession, suggesting standards and measures for

restoration. Typically, interventions are classified

into two categories: addressing the degree of

degradation and promoting active succession.

According to the degree of degradation of the

secondary forest, there are three measures:

1) Slightly degraded secondary broadleaved

mixed forest: It is suggested for natural recovery,

providing a good external environment, and

promoting positive succession.

2) Moderately degraded secondary

miscellaneous wood forest: It is suggested to adopt

dynamic management, strengthen the protection of

precious tree seedlings, appropriately carry out

human intervention, introduce ecological key species,

establish mixed and multi-layer natural forests, and

promote positive succession.

3) Severely degraded closed-off tussah forest:

According to the characteristics of the forest stand, it

is suggested that active human intervention measures

be taken. For example, engineering and biology can

cultivate coniferous and broadleaved mixed forests

dominated by oaks and restore the natural landscape

of natural secondary forests as soon as possible.

According to positive succession of secondary

forests, there are four ways to promote:

1) Controlled disturbance: Through reasonable

felling and burning, it is suggested to reduce the shrub

layer, increase light and space, and promote the

growth of target tree species.

2) Artificial intervention: In the case of

insufficient natural regeneration, it is suggested that

artificial replanting be carried out to increase the

density and regeneration rate of target tree species.

3) Protection and management: It is suggested

that grazing and picking activities be reduced,

seedlings and seed banks protected, and retrograde

succession prevented.

4) Near-natural management: It is suggested that

scientific management models be adopted, such as

planting needles, protecting broadleaf trees, and

improving forests’ ecological stability and diversity

through selective felling and replanting.

Despite these advances, significant challenges

remain. Large areas of low-quality forests, high

demand for timber and inconsistent management

practices across regions pose a continuing threat to

sustainable forest management.

5 CONCLUSION

This study emphasises the importance of secondary

forests in Northeast China, focusing on the

distribution of secondary forests, causes of

degradation, and measures for revegetation.

The analyses showed that secondary forests in

China are widely distributed in the Da Xing’anling,

Xiao Xing’anling and Changbai Mountains, and play

a significant role in China’s forest ecosystems.

However, historical overexploitation, agricultural

expansion and natural disturbances have led to severe

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149

degradation, as evidenced by declining productivity,

biodiversity loss, and ecological imbalance.

Both natural and artificial restoration methods are

needed to address secondary forest degradation.

Natural restoration occurs through secondary forest

succession and relies on pioneer species to gradually

restore ecosystem functions, although this takes a

long time. Managed restoration practices requires

targeted human intervention. Mildly degraded forests

can recover naturally, while moderately degraded

areas benefit from dynamic management practices

that protect seedlings and introduce key species to

promote positive succession. Severe degradation

requires active measures, including engineering and

biological interventions, to restore mixed forests and

re-establish natural landscapes. Promoting positive

succession in secondary forests requires disturbance

control, artificial interventions to increase tree density,

conservation measures and near-natural management

practices. These efforts are aimed at improving forest

resilience and biodiversity.

Despite progress in restoration, challenges remain.

Large areas of low-quality forests, high demand for

timber resources and inconsistent management

practices pose a continuing threat to sustainable forest

management. Sustained ecological restoration,

supported by scientific management and government

involvement, remains critical to ensure the restoration

and long-term viability of China’s secondary forests.

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