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Review
Nurse plant theory and its application in ecological restoration
in lower subtropics of China
Hai Ren
*
, Long Yang, Nan Liu
Heshan National Field Research Station of Forest Ecosystem, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
Received 28 May 2007; received in revised form 13 July 2007; accepted 13 July 2007
Abstract
Nurse plants are those that facilitate the growth and development of other plant species (target species) beneath their canopy because
they offer benign microhabitats that are more favorable for seed germination and/or seedling recruitment than their surrounding envi-
ronment. Nurse plants have been mainly used to restore vegetation in arid and sub-arid zones in recent years. Based on summarizing the
definition of nurse plant and target plant, we review the nursing effect mechanisms, ecological factors that influence nursing effect, rela-
tionships between nurse plant and ecological restoration. This review also brings forward possible pairs of nurse and target species at
lower subtropical areas. Furthermore, we provide the potential tendency in nurse plant research and application.
Ó2007 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in
China Press. All rights reserved.
Keywords: Nurse plant; Target species; Forest restoration; Nursing effect
1. Introduction
The relationship between plants, mainly including com-
petition (negative effect), neutral, and facilitation (positive
effect), is an important driving force of plant community
succession or vegetation restoration. Ecological research
has been focused on competition. Research on positive
interaction between plants is still ignored [1] although it
is gradually known as competition and facilitation (at
least one side benefit) in the plant communities of the
main biome of the world in the past 15 years. Nurse
plants are those which facilitate the growth and develop-
ment of other plant species (target species) beneath their
canopy because they offer benign microhabitats that are
more favorable for seed germination and/or seedling
recruitment than their surrounding environment, for
adjusting light, temperature, soil humidity and nutrient,
as well as avoiding grazing [2,3]. Nurse plants can also
establish the seedlings of target species through positive
interaction between plants. Nursing effect is mainly
accomplished by the interactions between plants, which
influence community structure and dynamic performance
intensively and the appearance or absence of specific spe-
cies [2,3]. So the research on nurse plant can validate,
consummate and enrich the theory that interactions
among plant species drive the natural succession, which
also provides the meaning of ecological restoration. In
this paper we review the application of nurse plant in res-
toration ecology and the future development of this
research field and especially discuss the possible pairs of
nurse and target species at lower subtropical areas and
its applications in forest restoration.
2. Nurse plant and target species
2.1. Nurse plant
Nurse plant plays an important role in recovering the
structures and functions of primary ecosystem and is
1002-0071/$ - see front matter Ó2007 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited
and Science in China Press. All rights reserved.
doi:10.1016/j.pnsc.2007.07.008
*
Corresponding author. Tel.: +86 20 37252916; fax: +86 20 37252831.
E-mail address: renhai@scib.ac.cn (H. Ren).
Available online at www.sciencedirect.com
Progress in Natural Science 18 (2008) 137–142
thought to be a driving force in the succession of certain
environments, especially in extremely degraded ones. In
recent years, the phenomenon of nurse plant has been
investigated in degraded habitats, including Mediterranean
mountain, alpine habitat, arid desert, semi-arid shrub-land,
northern dry forest, savanna, ecotone between farmland
and pasture, swamp, tropical sub-humid forest, marshes,
and so on [2,4–9].
The selection of nurse plants determines the success of
the ecological restoration project. Some nurse plant and
target species pairs have been confirmed in the study of
the world’s main biomes in the past few years. In the
extremely degraded environment, the best nurse plants
are the native species that offer microhabitat for target
plant establishment or recruitment. Although some exotic
species (e.g. Robinia pseudoacacia in southern England)
are successfully used as nurse plant, the biological invasion
of those species should also be prevented. Unpalatable
species can be used in heavily grazed sites, because these
nurse plants can provide refuges for small animals and tar-
get species [2,10,11]. It has been found that acervate plants
evidently facilitate target plant seedling survival in rainless
years. Legumes species are potential nurse plants which can
improve the survival and growth of target species in desert
and Mediterranean semi-arid habitat for their amelioration
in soil nitrogen and overshadow function. However, the
effect is undesirable when both nurse and target plants
are legumes [12]. In desert, shrubs usually act as nurse
plants for other seedlings, especially cacti. In forest, seed-
ling establishment may be enhanced in the vicinity of adult
plants that improve some extreme ecological factors [7].
This kind of positive effect by adult plants on their sur-
rounding seedlings is called Nurse Plant Syndrome. The
selection of nurse plants should avoid those species that
release allelopathic compound. It is reported by Sanchez-
Velasquez et al. [10] that different shaded levels formed
by the nurse plant in the tropical sub-humid forest are
significantly related to seedling establishment of target
species.
Field survey is the foundation of nurse plant research.
Generally, the species richness under nurse plant is higher
than that in the open sites. Therefore, the nursing
relationship between plants can be approximately esti-
mated by interspecific association. Furthermore, the influ-
ence of nurse plant on seed germination of target species
is examined by sowing seeds under nurse plant [13].
Seedling inseminations are mostly introduced in the
confirmation of nurse plant and nursing effect between
plants. In these experiments, the differences of seedlings
of target species under the nurse plant and on the open
(or between two crowns) are usually compared by analyz-
ing survival rate and growth rate between them, combin-
ing observation of microhabitat. However, it should be
indicated that the differences of soil physiochemical prop-
erties and microhabitat between under nurse plant and in
the open are not obvious in some cases of facilitation
[14,15].
2.2. Target species
The effect between plants is dependent on characteristics
of each species, which means the selection of target species
(regenerated ones) would also influence the restoration
effect. Furthermore, the balance of the interaction is
decided by the ecological requirement of target species
and capability of dealing with incompatible habitat [16].
The positive effects of nurse plant on the shaded-tolerant
pine and shrubs in late succession period are more than
those on pioneer species and shaded-intolerant species
[12]. The survival rate of Ambrosia dumosa in the open of
arid environment is higher than that under shrubs because
of its better adaptation in the open habitat, wherein, the
interaction between A. dumosa and the nurse plant is com-
petition, so that this species is not suitable as a target spe-
cies. If the tolerance of target species is poor in abiotic
habitat or the environment is extremely serious (such as
dry year), nurse plant cannot increase the seedling estab-
lishment [17].
The age and size of target species should also be consid-
ered for the balance of facilitation and competition accord-
ing to different life periods. The nurse plant has a stronger
positive effect when the target species is young, whereas,
competitive interaction is dominant when there are older
or bigger target plants. When the age and size of the nurse
plant is similar to that of the target species, the negative
effect of tussock plants will be enhanced [18].
2.3. Positive and negative nursing effect
Only when the intraspecific competition exceeds inter-
specific competition, can plant species coexist in a commu-
nity. Most interactions among species are represented
through some intermediary, for example, light, nutrition,
pollinator, herbivore and microbe. Competition actualizes
by competing resources directly, but facilitation is realized
by intermediary (such as soil) among species interaction
[1,19,20].
Higher recruitment success near the nurse plant cannot
eliminate the negative effect on target species, but it is
sure that positive effects exceed negative ones, which
result in the higher survival rate of target species under
the nurse plant than that in the open [21,22]. When arti-
ficial methods such as shading or watering are used, the
survival rate of target species may be lower than that
under the nurse plants. For example, Neobuxbaumia tet-
etzo, a cactus in Mexico, is nursed by Mimosa luisana,a
leguminous shrub, but the former species restricted the
growth of the nurse plant and consequentially substituted
it. Further research indicated that the survival rate under
the nurse plant was higher than that on the artificial mea-
sures such as shading. In addition, it is shown by the
experiment on Savanna in south Texas that nurse plants
grew better by clearing the target species under the nurse
plants, which can be described as the interaction of the
parasite/host [23,24].
138 H. Ren et al. / Progress in Natural Science 18 (2008) 137–142
Plants, when growing closely, compete directly for lim-
ited resources (such as light, water, nutrition and space)
if negative effect predominates. However, if positive effect
predominates, the neighboring plants will show this inter-
action by increasing survival, growth and fitness. Both
effects would take place simultaneously and change accord-
ing to time and places, which are balanced by expression of
the positive and negative ones. Some factors (such as phys-
iological and developmental characteristics) may influence
the balance [18], wherein the abiotic factors are mostly
important for increasing the importance of positive effect
in stressful habitats [4].
3. Reasons and mechanism of nursing effect
The nursing effect may not be attributed to single factor,
but to the ultimate performance of some compound fac-
tors, including the crown architecture effect (influencing
extinction coefficient, photosynthetic availability radiation,
and temperature buffering), shading increment, buffering
extreme temperature in microhabitat, increasing water,
nutrition availability (litter of nurse plants), protection
against herbivores, impact epiphyte and azotobacter in
soil, and so on. However, among the above environmental
factors, key factors should be explored in finding out the
reasons of nursing effect [2,25].
Nurse plants facilitate target species by shading from
crown architecture. Dewpoint temperature in winter under
nurse plant Cercidium microphyllum was higher than that in
the open of Sonoran Desert. Shading can protect plants
under the nurse plant from strong radiation. Kulheim
et al. [26] reported that light influences plant physiological
process directly and indirectly, and interspecific differences
are found in response to illumination in forest plants.
Strong irradiation may destroy reaction centers of photo-
systems and produce oxidative damages. Shade-tolerant
species under abundant sunlight will suffer from photoinhi-
bition. Shading can avoid higher temperature, maintain
higher soil humidity and lower transpiration of target spe-
cies, moreover, it increases rhizosperic nutritious availabil-
ity and circulation. All the processes above will improve
physical and chemical property of soil and increase survival
rate of target species [2,27,28].
Establishment of target species is affected by rainfall
redistribution of nurse plant canopy. Shrubs constrain
available understory water by rainfall redistribution at a
lower intensity of rainfall, whereas, when there is a heavy
rainfall, its redistribution by shrub crown arrives at under-
story through stem flow, which will influence the develop-
ment of target species [29]. The distance between target
species and nurse plant is another important factor and
the stressful condition is ameliorated gradually from the
center to the edge of canopy [30]. Castro et al. [29] planted
two pine species (Pinus sylvestris and Pinus nigra) in the
open, under the crown of sage (Salvia lavandulifolia) and
beneath the crown of thorny shrubs (north and south direc-
tions), thus finding out that the survival rate was much
higher under the north aspect of thorny shrubs. Nurse
plants influence mainly target species on germination and
seedling stage, wherein, positive effect may be showed evi-
dently on seedling stage. It is believed that, nurse plant of
predominant species in one successional stage will facilitate
plants in the next successional stage by allelopathy.
Changes of physiological balance between shading and
drought were discussed by graph model [2]. In addition,
some factors such as competition, consumption of
resources by the nurse plant and superposition of root
space between the nurse plant and target species should
also be considered. Competition or disturbance of non-tar-
get species under the crown of the nurse plant (i.e. herba-
ceous plants) will play positive roles [1–4].
4. Ecological factors that influence positive effect
Even if positive effect takes place between nurse plant
and target species, ambient condition (such as rainfall, soil
humidity, grazing intensity and microhabitat) influences
the radiation, soil, temperature and moisture under the
crown of nurse plant, thereby changing the nursing effect.
Positive effect of nurse plant increased with stressful abiotic
conditions which was obviously stronger in higher moun-
tains and on earlier restoration stage of degraded ecosys-
tem [4].
In the overexploited area of Mediterranean Basin, 11
woody species were planted under 16 pioneer shrubs, which
could aid in the establishment of woody species on later
successional stage. The successful rate was improved in dif-
ferent habitats by using meta-analysis to analyze survival
and growth among those species [31].
In a relatively nice habitat, spatial association among
plants may be negative, but not positive. In a fertile habitat
it was not positive by using nurse plant for its exhausting of
soil resources. However, in an unfertile habitat, crops with
small crown and poor growth facilitated the survival of syc-
amore seedlings [1,2].
In dry areas, changes in precipitation may alter the
interactions among plants from competition to facilitation
and vice versa. Ibanez and Schupp [32] conducted an exper-
iment in Logan Canyon. They found that when the seed-
lings of curl-leaf mountain mahogany (Cercocarpus
ledifolius) were placed under big sagebrush, facilitation
was apparent in a dry year whereas negative effects were
obvious during a wet year.
5. Case studies of nurse plants in vegetation restoration in
lower subtropical areas of China
The nurse plant should be used in ecological restoration,
mainly because the establishment of target species is greatly
influenced by abiotic habitat and disturbance. Natural
nurse plants were firstly put into ecological restoration in
southeast Spain, where Castro et al. [29] found that native
shrubs did not restrain the growth of two pine species
but decreased their death rate. They comprehensively
H. Ren et al. / Progress in Natural Science 18 (2008) 137–142 139
considered some ecological and biological characteristics,
such as rainfall, nurse species and target species, when
applying nurse plants to improve seed germination and
seedling establishment in ecological restoration.
Through extensive field investigation, interspecific asso-
ciation studies and field experiments, possible correspond-
ing nurse and target species pairs were found in lower
subtropics in China (Table 1).
Tussock plant Evolvulus alsinoides L. with 20 cm root
system and only 3 cm high above ground is the unique nurse
plant grown on a bare land of extremely degraded ecosys-
tem at Xiaoliang, Guangdong Province. We found that E.
alsinoides’s target species Phyllanthus cochinchinensis can
grow with 60 cm root length and 42 cm root spread range
with 27 cm height above ground. In severely degraded eco-
system, there exist two kinds of thresholds during ecosystem
restoration, which are the initial threshold characterized by
extremely harsh physical environmental conditions (includ-
ing high temperature, aridity and poor soil) and the second-
ary threshold controlled mainly by biodiversity level and
landscape context to seed provenance and establishment.
In this circumstance, nurse plants are grass clustered with
deep root, and so are target species. The formed tussock
community is not only propitious to themselves but also
advantageous in their resistance to poor environmental
conditions. Enlightened by the above field phenomenon,
exotic leguminous species, Acacia auriculaeformis, with fast
growth rate and better resistance to infertility, was intro-
duced as nurse plants at the severely degraded bare land
of Xiaoliang. We planted several A. auriculaeformis individ-
uals clusterly, then removed 1–2 individuals of 2-year-old
plants from the fascicular A. auriculaeformis and some
native species were planted under its canopy, including Psy-
chotria rubra,Pithecellobium clypearia,Syzygium hancei,
etc., whose survival rate could reach 80%. The survival rate
is about 0% if those native plants are directly planted in bare
lands. Similar experiment was also successful when carried
out at Nan’ao island [33–35].
It was found that a pioneer grass Neyraudia montana,as
the nurse plant of pioneer shrub Rhodomyrtus tomentosa,
provided better microhabitat at grasslands of Heshan Sta-
tion and Dinghushan Station, Guangdong Province, which
were considered to be mild degraded ecosystem. Pinus mas-
soniana, for its amelioration in light environment and soil
property, was the nurse plant of Schima superba at Heshan
Station, Dinhushan Station and Nan’ao Island. Castanop-
sis chinensis can facilitate Schima superba and Cryptocarya
concinna at Dinghushan Station, probably because of the
effects on shading, moist increment and enhancing avail-
able nutrient in soil [33].
Exotic species Sonneratia apetala has nursing effect on
native mangrove plants Rhizophora stylosa and Kandelia
candel at the coastal mudflat in the tideland area of Zhanji-
ang [36]. We had found that the survival rate of planted
native mangrove species was very low at the severely
degraded mudflat, however, the survival rate of S. apetala
reached 95%. S. apetala grew fast and became a closed
artifical forest within four years which could efficiently pre-
vent the swashing of tidal wave, and increase soil nutrient
therefore facilitating the invasion of some native mangrove
species. The number of species and intensity of native spe-
cies came to a peak in the artificial forests after six years of
growing.
From these nurse plants and target species, the pattern
[36–40] is found as follows. (1) The phenomenon of nurse
plants takes place mostly on the early stages of restoration
in degraded ecosystem or succession in plant community.
(2) The phenomenon of nursing effect on the earlier stage
of restoration or succession is mostly carried out as shrubs
nursed by grasses and trees nursed by shrubs. (3) Nursing
phenomenon usually happens among the native species in
corresponding pairs. (4) Exotic leguminous species, Acacia
auriculaeformis and Acacia mangium, are considered as
good nurse plants for ameliorating N condition in soil
and providing shade for target species including shrubs
and trees. (5) Nurse plants have better characteristics than
Table 1
Possible nurse and target species pairs at south subtropical areas in China
Places Nurse plants Target species
Bare land at Xiaoliang Evolvulus
alsinoides
Phyllanthus
cochinchinensis
Artificial forest at Xiaoliang Acacia
auriculaeformis
Psychotria
rubra
Acacia
auriculaeformis
Pithecellobium
clypearia
Acacia
auriculaeformis
Syzygium
hancei
Hillyland at Heshan Neyraudia
montana
Rhodomyrtus
tomentosa
Rhodomyrtus
tomentosa
Pinus
massoniana
Artificial forest at Heshan Acacia
auriculaeformis
Psychotria
rubra
Acacia
mangium
Michelia
macclurel
Hillyland at Dinhushan Neyraudia
montana
Rhodomyrtus
tomentosa
Coniferous and broad-leaved mixed
forest at Dinghushan
Pinus
massoniana
Schima superba
Castanopsis
chinensis
Schima superba
Broad-leaved forest Castanopsis
chinensis
Cryptocarya
concinna
Artificial forest at Nan’ao Island Pinus
massoniana
Schima superba
Acacia
auriculaeformis
Psychotria
rubra
Acacia
auriculaeformis
Pithecellobium
clypearia
Acacia
auriculaeformis
Schima superba
Artificial mangrove in National
Natural Reserve of Zhanjiang
Sonneratia
apetala
Rhizophora
stylosa
Sonneratia
apetala
Kandelia candel
140 H. Ren et al. / Progress in Natural Science 18 (2008) 137–142
those of target species, including being light-dependent,
fast-growing, infertility resistant and drought tolerant. (6)
The individuals of target species are generally smaller than
those of nurse plants in the early stage. (7) Seedlings can
successfully establish around the adult plants in forests
for the amelioration of some extreme ecological factors.
(8) Nurse plants are considered not only to play a key role
in recovering the properties and functions of the primary
ecosystem, but also to drive succession in poor environ-
ments on the early stage of restoration.
6. Perspective in the study and application of nurse plants
Recently, most researches are focused on seedling sur-
vival of the target species, but less on the research of seed
germination, seedling growth and fitness. Most researches
rest on describing the phenomenon of the nurse effect, less
on the structural and functional mechanisms of positive
effects towards ecophysiological and morphological aspect.
With the purpose of ecological restoration, most researches
concern about the influence of nurse plants on target spe-
cies, but less on the feedbacks of target plants and without
long-term observation in their interactions. Most species
studied are native ones due to easy manipulation and pre-
diction, lacking studies in exotic species. Nurse plants are
mostly tussock shrubs, but not herbaceous or woody spe-
cies, and fewer studies combine nurse plant with target spe-
cies representing different successional stages. Nurse plants
were less investigated in degraded ecosystem, especially in
China, therefore, further tests are needed to find out the
potentials of nurse plants in reforestation.
Currently, the main forest recovery methods include
closing hillsides to facilitate afforestation (natural succes-
sion), artificial reforestation (rebuilding artificial pure for-
ests or mixed forests directly), rebuilding forest
construction (planting native species after picked logging)
and Miyawaki’s method (growing seedlings of native spe-
cies directly). All of these methods have both strong or
weak points. Some reforestation technologies, such as
nutritive cup, water retaining agent, nodules, and shading,
were developed to match the above methods [38–42].
The nurse plant technique is different from the above
reforestation methods. Due to the functions of nurse plant
in ameliorating microhabitat (such as shading and water
increment, extreme temperature buffering in microhabitat,
and so on) suitable target species were grown under the
crown of nurse plants. Even more, positive effects among
plants make target species establish successfully and short-
ened restoration course. The successful utilization of nurse
plants may become a novel reforestation method which will
explore excellent native species, accelerate natural recovery
and enrich species diversity.
Acknowledgements
This work was supported by National Natural Science
Foundation of China (Grant Nos. 30200035, 30670370),
the Chinese Academy of Sciences and the Guangdong &
Guangzhou Sci-Tech Planning Project (07118249,
2005B60301001, 2007J1-C0471). We are grateful to Dr.
Huang Changzhi in CDFG/OSPR/Scientific Division of
Sacramento in USA and Dr. Lu Hongfang in EPA of
USA for the assistance in English writing of this
manuscript.
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