Casuarina equisetifolia

The tree Casuarina equisetifolia has been introduced and used as a wind curtain and to stabilize foredunes, although there are many native species—grasses, forbs, and even trees—that can and should be used for dune stabilization.

From: Coastal Plant Communities of Latin America , 1992

Bioshield: An Answer to Climate Change Impact and Natural Calamities?

Iyyappan Jaisankar , ... T.P. Swarnam , in Biodiversity and Climate Change Adaptation in Tropical Islands, 2018

6.3.2 Non-Mangrove-Based Species

Non-mangrove species can also be used as bioshield along the coastal zone which is popularly known as shelterbelts. In general, shelterbelts are strips of vegetation composed of trees and shrubs grown along the coasts to protect coastal areas from high velocity winds and also from devastations like the ones caused by tsunami. They also serve the purpose of sand binders and prevent sand erosion. Some of the important species suitable for coastal bioshield are Casuarina equisetifolia Forst., Manilkara littoralis, Ficus hispida, Thespesia populneoides (Roxb.) Kostel., Hibiscus tiliaceous L., Baringtonia asiatica, Pongamia pinnata L., Azadirachta indica A. Juss., Morinda citrifoia, Cassia fistula L., Cocos nucifera L., Anacardium occidentale L., Syzygium spp. and Pandanus tectorius.

Monoculture plantations generally favour fast growing coastal non-mangrove species such as C. equisetifolia. Such monocultures are often not optimal from a biodiversity perspective and may hinder natural regeneration of native species. For instance, C. equisetifolia, a commonly used exotic species for bioshields in India, has a native range extending from Myanmar to Australia and was shown to be invasive in several countries, for example the United Sates, Cuba, Ecuador and Mexico (Global Invasive Species Database, 2005). If bioshield is to be established, then it must be effective against extreme events at the planned site, it should cause no damage to native ecosystems and it should not to be used to justify the absence of emergency procedures for extreme events.

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Carambola (Averrhoa carambola L.)

O. Warren , S.A. Sargent , in Postharvest Biology and Technology of Tropical and Subtropical Fruits: Açai to Citrus, 2011

18.4 Preharvest factors affecting fruit quality

Carambolas are very susceptible to mechanical damage. Movement from wind results in considerable scarring and damage to fruit that swing and rub against other fruit and branches (Fig. 18.2 and Plate XXXIV: see colour section between pages 244 and 245).

Fig. 18.2. Wind damage of carambola fruit due to swinging against a branch.

Slight scratching of the fruit while on the tree leads to unattractive fruit at the retail level as scars darken and become more pronounced during storage. Production in Florida requires windbreaks and wind screens that prevent wind from disturbing fruit while on the trees. Windbreaks usually consist of mature Australian pine ( Casuarina equisetifolia ), while windscreens are constructed of poles with cables that support shade cloth. Windbreak techniques for production in other regions include; rows of palm trees, and intercropping with other fruit trees. As described above, harvesting the fruit later than the one-quarter yellow stage yields sweeter fruit. However, this would require the fruit to remain on the tree up to 10 days longer, increasing the likelihood of wind damage.

One drawback of harvesting carambolas at later maturity is that the extended harvest season delays flowing and new fruit set for the succeeding crop. However, selective pruning of branches lessens wind scarring, and thinning the young fruit stimulates the trees to produce in the off-season. Nunez-Elisa and Crane (2000) found that pruning in July and September increased panicles of flowers by 14 and 20% respectively, and that pruning in other months also proved successful. These practices could add significant value to the crop since there are no Florida-grown carambolas from March to July.

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ENDOPHYTIC FUNGI

JEFFREY K. STONE , ... JAMES F. WHITEJR., in Biodiversity of Fungi, 2004

HOST COLONIZATION PATTERNS: SYSTEMIC VERSUS LIMITED DOMAINS

The infection domain of endophytes has a profound effect on sampling efficiency for species diversity. Clavicipitaceous endophytes of grasses form systemic associations with their hosts; their fungal hyphae colonize virtually all plant tissues and are found both in the seed coat and in close association with the embryo in certain species. Nonsystemic infections of "P-endophytes" of grasses, mainly Phialophora species and Gliocladium species, are more limited but also can be seed-borne (An et al. 1993). There also are scattered reports of systemic, seed-borne endophytes in nongrass hosts. Bose (1947) reported that hyphae of Phomopsis casuarinae permeated the tissues, including the seed coat of every Casuarina equisetifolia plant he examined. Boursnell (1950) documented an unidentified systemic fungus in Helianthemum chamaecistus, and Rayner (1915, 1929) found unidentified fungi infecting Ericaceae. Histological studies detailing endophyte infection patterns of endophytes that colonize mostly nongrass hosts are available for only a few host species (Stone 1987; Suske and Acker 1987; Cabral et al. 1993; Viret and Petrini 1994). In those cases, however, the domain of the endophyte colonization in healthy tissue often is restricted, usually limited to no more than a few cells (Figs. 12.1 to 12.4, Rhabdocline parkeri infections and Phyllosticta infections). The differences between systemic infections and those of limited domain dictate that sampling strategies take patterns of host colonization into account if recovery of greater diversity of species or if precise estimation of relative species importance in specific tissues or organs is the objective. Where sample units are not appropriate to the microscopic scale of infections, undue bias will be introduced. Unfortunately, in the majority of published studies selection of sample units was apparently arbitrary and is highly variable (Carroll 1995); inferences regarding species dominance and diversity drawn from those may be suspect as a consequence.

FIGURE 12.1. Intracellular Rhabdocline parkeri hyphae (arrows) in Douglas fir (Pseudotsuga taxifolia) needles (×500).

FIGURE 12.2. Intracellular Phyllosticta abietis hyphae (arrows) in Giant fir (Abies grandis) needles (×500).

FIGURE 12.3. Hypha of an unidentified endophyte in epidermal cells of Picea pungens. Needles were cleared in 10% KOH and stained with 0.05% trypan blue in lactoglycerol.

FIGURE 12.4. Hypha of Stagonospora innumerosa in an epidermal cell of Juncus effuses var pacificus. The epidermis was excised with a razor blade, cleared by boiling in lactophenol-ethanol (1:2 v/v), and stained in acid fuchsin-malachite green (Cabral et al. 1993).

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BEACH FORESTS

Friedhelm Göltenboth , ... Peter Widmann , in Ecology of Insular Southeast Asia, 2006

Producers

Beach forests exhibit a low tree species diversity. Most of the trees are widespread within the Indopacific Region and are easily recognized by their typical structure. Dominating tree species are Barringtonia asiatica, Calophyllum inophyllum, Terminalia catappa, Pongamia pinnata, Pandanus tectorius and Hibiscus tiliaceus. Fruiting trees and especially the flowers of Erythrina orientalis are important feeding sources for an array of wildlife.

Casuarina equisetifolia is able to establish on barren sand. Its leaves are widely reduced and the green twigs took over the task of photosynthesis (Fig. 15.4). The tree is able to fix atmospheric nitrogen with the help of symbiotic bacteria living in close contact with the root system. The latter and litterfall create favorable soil conditions for other beach forest species which subsequently replace the Casuarinas, since it is not able to establish under closed canopy conditions. Members of the family Fabaceae are also able to fix nitrogen and are relatively common in beach forest. Common examples are Pongamia pinnata and Erythrina orientalis. The latter exhibits scarlet red inflorescences which are pollinated not only by bees but also by birds, particularly sunbirds and flowerpeckers. Others may steal nectar without pollinating the flowers or even destroy complete flowers (Table 15.1).

FIGURE 15.4. Characteristic parts of Casuarina equisetifolia (Fam. Casuarinaceae).

TABLE 15.1. Birds that were observed to visit flowers of Erythrina orientalis and their likely interrelationship.

Common name Scientific name Interrelationship
Cockatoo Cacatua sp. destroys flowers
Spangled drongo Dicrurus hottentottus pollinator or nectar thief
Black-winged iora Aegithina tiphia pollinator or nectar thief
Asian glossy starling Aplonis panayensis pollinator or nectar thief
Olive-backed sunbird Nectarinia jugularis pollinator
Plain-throated sunbird Anthreptes malacensis pollinator
Flowerpecker Prionochilus sp. pollinator

In sandy beaches as well as on top of cliffs two members of the Fabaceae family with valuable timber are found: Pterocarpus indicus and Intsia bijuga. Terminalia catappa is a tree very easily recognized because of its pagoda-like structure (Fig. 15.5). It is still widespread throughout South East Asia, since it is a valued ornamental. Its almond-shaped fruits can withstand sea water for weeks and are dispersed by currents. They are consumed by fruit bats which act as seed dispersers, too. The pulpy fruits of Calophyllum inophyllum are also dispersed by bats (Fig. 15.6). These trees often develop extensive crowns. Trunks are usually short and branches are massive. Even when the root system gets exposed through wave action, the branches still can support the weight of the tree.

FIGURE 15.5. Structure of Terminalia catappa (Fam. Combretaceae).

1

Pagoda-like structurer of the mature tree

2

Single leaf

3

Fruits showing their boat-shaped structure

FIGURE 15.6. Calophyllum inophyllum (Fam. Guttiferae)

1

Structure of the massive tree

2

Single leaf with its characteristic parallel veins

3

Single fruit

The Barringtonia asiatica shows a very similar architecture, supposedly also as an adaptation of not getting uprooted during storms. A special adaptation to this rare but catastrophic events is the fact that the leaves all sit on weak stalk-like branches as in the case of Calophyllum inophyllum. They are easily blown away during storms thereby reducing the wind pressure substantially.

Barringtonia asiatica exhibits large white and pinkish brush-like flowers which only open during nighttime and are pollinated by bats and bees and are shed the following morning. The fruits are large and quadrangular and are dispersed by sea currents. The fruits are light like a cork and glazed over as with a line of varnish. They are poisonous to fish which prevents them from being eaten while floating (Fig. 15.7). The fruits of Heritiera littoralis even have developed 'sails' in form of protrusions along the joints. Consequently, their dispersal is not only influenced by currents, but also by wind.

FIGURE 15.7. Seagoing fruits of various beach forest trees (not to scale).

The coconut palm Cocos nucifera develops a fruit or nut which can withstand sea water for months. The leathery exocarp and the fibrous mesocarp are water resistant. The woody endocarp also protects the embryo against mechanical damage. The hollowed center contains the coconut water in younger nuts and the white endosperm which is rich in fat, carbohydrates and sufficient proteins to support the young plant for some time after fertile soil layers shall have been reached after germination. The coconut palm does now occur along all tropical coasts and is cultivated far inland. The origin of the plant is not definitely known, but the Westpacific Region is suspected to be the original area of distribution. However, in natural stands of beach forest, coconuts are widely lacking for unknown reasons (Fig. 15.8).

FIGURE 15.8. Coconut palm Cocos nucifera (Fam. Palmae).

1

Structure

2

Cross section through fruit

Several species of screw pines or Pandanus sp. can be found in beach forests. Some species are adapted to thrive in small crevices of coastal cliffs. The most common species is Pandanus tectorius whose dried and split leaves provide an important raw material for all kinds of weaving (Fig. 15.9).

FIGURE 15.9. Screw pine Pandanus tectorius (Fam. Pandanaceae).

1

Structure

2

Branch with fruits

Despite its palm-like appearance, the common Cycas circinalis is not related to this group at all. It belongs to the very old family Cycadaceae which was most abundant about 200 million years ago during the Triassic era. A list of woody species recorded from South East Asia beach forests is given in Table 15.2.

TABLE 15.2. Selection of woody species recorded from South East Asia beach forests.

Scientific name Family
Cycas circinalis Cycadaceae
Pongamia pinnata Fabaceae
Erythrina orientalis Fabaceae
Pterocarpus indicus Fabaceae
Intsia bijuga Fabaceae
Calopyllum inophyllum Guttiferae
Casuarina equisetifolia Casuarinaceae
Ficus sp. Moraceae
Terminalia catappa Combretaceae
Osbornia octodonta Myrtaceae
Barringtonia asiatica Lecythidaceae
Pemphis acidula Lythraceae
Hibiscus tiliaceus Malvaceae
Thespesia populnea Malvaceae
Heritiera littoralis Sterculiaceae
Melia dubia Meliaceae
Xylocarpus granatum Meliaceae
Xylocarpus moluccensis Meliaceae
Mimusops parviflora Sapotaceae
Morinda citrifolia Rubiaceae
Scaevola taccada Goodeniaceae
Premna odorata Verbenaceae
Cocos nucifera Palmae
Pandanus tectorius Pandanaceae

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TROPICAL FORESTS | Tropical Dry Forests

S.J. Van Bloem , ... A.E. Lugo , in Encyclopedia of Forest Sciences, 2004

Plants

Seasonally dry forest communities worldwide contain a variety of important plant species. Trees valued for lumber include teak (Tectona), mahogany (Swietenia), sal (Shorea robusta), and African mahogany (Khaya). Commercially important fruit trees include tamarind (Tamarindus indica), mango (Mangifera indica), and cashew (Anacardium occidentale). Agroforestry projects have planted Leucaena leucocephala and Prosopis juliflora (mesquite) to improve soils via nitrogen fixation. Casuarina equisetifolia (Australian pine) and Eucalyptus camaldulensis are native to Australian dry forest and have been introduced in many areas for soil stabilization and wood production. In addition to these species, many others are used for firewood, construction wood, food, and medicinal purposes.

Deciduous trees are usually most common in dry forests, but evergreen species become more important at both the upper and lower limits of the rainfall gradient (Figure 2). The frequency of growth forms depends on climate and disturbance. Cacti and euphorbs frequent drier locations while the diversity of lianas and other vines increases with greater rainfall and following disturbances that open canopy gaps. Dry forests have more understory species than tree species but their abundance and biomass is quite low, except in open woodlands.

The high variety of growth forms and numerous physiological adaptations provide tolerance to drought conditions. Dry forest species can maintain metabolism under lower soil and leaf water potentials than temperate or moist tropical species. Dry forests average higher ratios of root to shoot biomass than moist or temperate forests. Though data on root biomass are scarce, 35–49% of root mass is below 10   cm depth as compared to 5–21% in wet forests. In dry forests, maximum root: shoot ratios range from 0.4 to 1.0. In moist forests they rarely exceed 0.25. Cacti and some deciduous tree species store water in succulent stems. The amount of water stored cannot maintain leaves, but supports flower and fruit development prior to the onset of the rainy season.

Water use is influenced by leaf habit (evergreen vs. deciduous), leaf morphology, and wood density. Compared to wetter forests, more dry tropical trees have wood specific gravity greater than 1.0. Dense-wooded and evergreen species have narrow xylem that resists cavitation under dry conditions but transports water less efficiently. Light wooded and deciduous species have wider xylem that is more prone to cavitation and greatly reduces water conductance as the dry season progresses, but transports water more efficiently and responds faster to light rains at the onset of the rainy season. Thus, the ability to reduce cavitation during drought is traded for more efficient water conductance. Deciduous species avoid dry season water loss by shedding leaves, usually at the onset of the dry season, while the sclerophyllous leaves of evergreen species have thick cuticles and smaller internal air pockets that resist desiccation. Sclerophylly may increase in plant populations growing under drier conditions, or experiencing nutrient limitation caused by insufficient soil moisture for nutrient uptake and transport. Sclerophyllous trees frequently exhibit high nutrient use efficiency, suggesting nutrient limitation, even when soil nutrient pools are relatively high. Thus, the leaf habit of evergreen species aids in drought tolerance, while deciduousness leads to drought avoidance.

During the rainy season, dry forest trees, regardless of their particular responses to drought, exhibit many physiological similarities. For example, both drought-deciduous and evergreen dry forest species have similar values for carbon assimilation and stomatal conductance. These values equal those found in moist forest trees. When scaled by growing-season days, both dry and wetter forests have similar growth rates, suggesting they all have equally efficient productivity during favorable seasons. This may be expected because trees (with the exceptions of bamboo, arborescent cacti, and some euphorbs) all use C3 photosynthesis, regardless of their habitat.

Phenology is closely related to the dry season in many cases, but there is a variety of patterns. Most deciduous species lose leaves at the onset of the dry season, but a few are wet-season deciduous (e.g., Faidherbia albida and Jacquinia pungens). Some species flower and fruit just before the rainy season commences, before leafing out, while others wait until after the rains have begun. Dry forest species generally flower and fruit for shorter periods than moist forest species. Often plants flower for less than 6 weeks – frequently for only the first few days following an isolated rain event or the first significant rain breaking a drought period. As annual rainfall increases on either a regional or local scale, the prevalence of species with wind-dispersed seeds decreases. In general, most species exhibit some pattern of seasonality.

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Role of Prosopis in reclamation of salt-affected soils and soil fertility improvement

Gurbachan Singh , in Prosopis as a Heat Tolerant Nitrogen Fixing Desert Food Legume, 2022

Survival, growth and biomass production of Prosopis and other tree species

The performance of different tree species was evaluated for 10   years on the basis of survival % and growth (height, diameter at breast height, crown diameter, and basal area) in a highly sodic soil at Sivri Experimental Farm near Lucknow in Uttar Pradesh State. All the species had over 95% survival except Cassia siamea (94%) and Acacia indica (90%) and P. alba (50%). Maximum plant height was recorded with Eucalyptus tereticornis followed by Casurina equisetifolia and P. juliflora. Acacia nilotica performed better than the other species in terms of diameter at breast height (DBH) with a basal area of 13.04   m2  ha−     1, followed by P. juliflora and Casurina equisetifolia, with a basal area of 9.92 and 9.64   m2 ha−     1, respectively (Table 3.5). These results are in agreement with those of Yadav and Singh (1970), Gill and Abrol (1987), Singh, Singh, and Sharma (2011), and Singh and Singh (1993b). All other species had a basal area of below 8.5   m2 ha−     1. Correlation coefficients (r) calculated for height and diameter were strongly positive in P. juliflora, Pongamia pinnata, Pithecellobium dulce, A. nilotica, Casuarina equisetifolia , Terminalia arjuna, E. tereticornis, and A. indica, whereas C. siamea (0.43), E. tereticornis (0.48), P. alba (0.56), T. arjuna (0.63), and A. nilotica (0.67) were having lower r values. P. juliflora recorded the highest crown diameter (8.87   m) followed by C. equisetifolia (8.75   m), A. indica (7.53   m), and A. nilotica (7.20   m). The overall growth of P. juliflora was much better compared to other species.

Table 3.5. Establishment and growth of multipurpose tree species aged 10 years on sodic soils.

Species Survival (%) Height (m) DBH (cm) r Crown diameter (m) Basal area (m2 ha−     1)
T. arjuna 100 4.96 9.20 0.63 2.40 5.53
A. indica 90 5.01 8.46 0.82 7.53 4.68
Prosopis juliflora 100 8.14 12.32 0.98 8.87 9.92
P. pinnata 100 5.87 9.27 0.98 5.42 5.61
Casuarina equisetifolia 97 8.25 12.24 0.85 8.75 9.64
P. alba 50 5.85 8.46 0.56 3.00 4.68
A. nilotica 96 6.83 14.12 0.67 7.20 13.04
Eucalyptus tereticornis 99 9.31 11.10 0.48 4.80 8.05
P. dulce 100 6.39 10.15 0.96 5.80 6.73
Cassia siamea 94 4.10 5.63 0.43 4.18 2.06
CD (P  =   0.05) – 0.96 6.50 – 1.12 1.6

Source: Singh, Y.P., Singh, G., & Sharma, D.K. (2010). Biomass and bio-energy production of ten multipurpose tree species planted in sodic soils of indo-gangetic plains. Journal of Forestry Research, 21, 19–24

P. juliflora is one of the highest biomass-producing tree species in arid and semi-arid regions/salt-affected soils (Felker, Cannell, Clark, Osborn, & Nash, 1983). However, the biomass production potential is governed by the factors like average rainfall of the area, quality of planting material, planting geometry, and cultural practices used for raising and maintaining the plantation. Growth performance and biomass production by 10   years old P. juliflora in comparison with other tree species in the soil of 10.4 pH is reported in Table 3.6. These growth and biomass figures are from a sodic land (village community land) near Panipat, Haryana. These plantations received irrigation during the first 2 years of establishment. Later on, the trees grew with the rainfall which was about 650   mm   year−     1; 80% of which was received between July and September.

Table 3.6. Growth performance and biomass production by Prosopis juliflora and other salt-tolerant trees in soil of 10.4 pH2, 10   years after planting.

Growth parameter Tree plantations
Prosopis juliflora Acacia nilotica Casuarina equisetifolia Eucalyptus tereticornis
Height (m) 12.9 11.6 14.5 14.9
DSH (cm) 15.9 15.4 15.6 13.6
DBH (cm) 12.5 13.6 12.0 11.0
Bole weight (kg/tree) 112.6 85.4 84.2 65.6
Branches   +   Leaves weight (kg/tree) 43.2 43.8 28.4 23.5

DSH, diameter at stump height (5   cm above the ground level); DBH, diameter at breast height (137   cm above the ground level).

Similarly, a comparison of biomass production of P. juliflora in relation to nine other commonly grown species at Shivri farm near Lucknow is given in Table 3.7.

Table 3.7. Biomass production and litterfall of Prosopis juliflora and other trees in a highly sodic soil (pH2 10.2–10.6), near Lucknow 10   years after planting.

Species Lopped biomass (kg/tree/year) Litterfall (t/ha/year)
Terminalia arjuna 6.15 5.1
Azadirachta indica 2.40 2.8
P. juliflora 11.30 6.1
Pongamia pinnata 6.10 5.0
Casuarina equisetifolia 6.34 5.7
Prosopis alba 9.25 2.0
Acacia nilotica 4.10 5.4
Eucalyptus tereticornis 3.50 1.3
Pithecellobium dulce 5.50 2.4
Cassia siamea 1.30 1.3
CD (P  =   0.05) 1.12 –

Source: Singh, Y. P., Singh, G., & Sharma, D. K. (2010). Biomass and bio-energy production of ten multipurpose tree species planted in sodic soils of indo-Gangetic plains. Journal of Forestry Research, 21, 19–24.

The yearly lopped biomass reported in Table 3.7 was maximum in P. juliflora and P. alba. The pruned/lopped biomass estimates indicate that the trees have enough potential to meet periodic fuelwood/energy needs. Periodic pruning/lopping of P. juliflora also helps the tree to grow straight and ensures the cultivation of inter-crops between tree rows. The trees also yield high-quality litter in terms of leaf and small twigs which fall on the ground and increases humus content in otherwise organic matter deficient soils. The 10 years observations on litterfall showed maximum litter production (6.1   t/ha/year) under P. juliflora canopies. The biomass production potential of this versatile tree can be regulated by adjusting spacing and management techniques (Singh, Abrol, & Cheema, 1989a, 1989b; Singh, Cheema, & Abrol, 1989). In case, the trees are raised for energy/electricity generation, closer planting may be preferred in the initial years to generate periodic biomass for the gasifier. These closely raised plantations can be thinned through lopping after 3–4   years of planting to generate sufficient biomass for energy and at the same time maintaining 50% of the trees for future harvest. This way, a cycle of biomass production can be achieved to meet biomass needs for energy generation. Several experiments were conducted at CSSRI experimental farms to study the biomass production potential of P. juliflora under different spacings and other cultural practices. For example, biomass accumulation in 5 years was 39   kg/tree when 5000 plants were grown/ha as compared to 32.2   kg/tree when the planting density was 10,000 plants/ha. To meet fodder requirements, salt-tolerant grasses like Kallar grass (Leptochloa fusca) can also be cultivated in the inter-spaces between tree rows. Biomass production in 6   years by Prosopis and Leptocloa grass under different spacing is given in Table 3.8.

Table 3.8. Biomass production in 6   years by Prosopis juliflora and Leptochloa fusca under different spacing in alkali soil.

Biomass (t/ha)
Prosopis Leptochloa Total
Spacings Lopped Harvested Total Prosopis   +   Leptochloa
2   ×   2   m 49.1 112.2 161.3 55.6 216.9
3   ×   3   m 31.6 55.2 86.8 68.7 155.5
4   ×   4   m 25.0 36.1 61.1 80.9 142.0

Source: Singh, G., & Singh, N. T. (1993). Mesquite for the revegetation of salt lands. Technical bulletin no. 18, CSSRI, Karnal, India, 24 p.

The data reported in Table 3.9 indicated that P. juliflora recorded the maximum (140.0   kg tree−     1) biomass followed by A. nilotica (123.6   kg tree−     1) and C. equisetifolia (105.6   kg tree−     1) harvested at 10 years of age. Singh and Singh (1993b) also reported similar results. Lopped biomass partially removed in different years was significantly higher in P. juliflora over the remaining species. The share of lopped biomass to total biomass was maximum (29.09%) in P. alba followed by P. pinnata (27.50%), whereas minimum in C. siamea (11.12%). Maximum root length was recorded with P. dulce (2.36   m) followed by A. nilotica (2.25   m) and P. juliflora (2.14   m) (Table 3.9). Total shoot, as well as root biomass tree−     1 was higher in P. juliflora, indicating its highest tolerance to sodium salts and inherent mechanisms to cope with salt stress environments. Maximum shoot: root ratio was recorded in A. nilotica (4.5:1) followed by P. juliflora (4.2:1) and C. equisetifolia (4.1:1) indicating that root development in general in sodic soils was impeded because of hard concretion layer at the lower level (Table 3.9).

Table 3.9. Dry biomass production by Prosopis juliflora and other species and allocation into the root and shoot components during 10   years.

Tree species Biomass (kg   tree−     1) Shoot:root ratio Lopped biomass (Mg   ha−     1) Biomass at harvest (Mg   ha−     1) Total biomass (Mg   ha−     1)
Shoot Root Total
T. arjuna 83.25 24.48 90.75 3.40 11.33 41.62 52.95
A. indica 38.45 9.80 48.25 3.51 6.40 19.22 26.62
P. juliflora 113.00 27.03 140.03 4.18 13.77 56.50 70.27
P. pinnata 53.20 14.73 67.93 3.61 10.09 26.60 36.69
Casuarina equisetifolia 84.20 20.28 104.48 4.15 11.01 42.10 53.11
P. alba 55.50 13.65 69.15 4.06 11.37 27.75 39.12
A. nilotica 101.50 22.14 123.64 4.50 12.34 50.75 63.09
Eucalyptus tereticornis 63.54 16.60 80.14 3.82 7.90 31.77 39.67
P. dulce 64.50 19.65 84.15 3.28 8.20 32.25 40.45
Cassia siamea 43.30 14.80 58.10 2.92 2.71 21.65 24.36
LSD (P  =   0.05) 6.34 2.36 – 0.54 1.12 5.42 7.52

LSD, least significant difference.

Source: Singh, Y.P., Singh, G., & Sharma, D.K. (2011). Ameliorative effect of multipurpose tree species grown on sodic soils of indo-Gangetic alluvial plains of India. Arid Land Research and Management, 25, 55–74.

Total nitrogen accumulation in aboveground standing trees varied from 108.79 to 320.37   kg   ha−     1 corresponding to biomass and nutrient concentrations in plant parts. Branches contributed more N in P. juliflora than the stem and leaves. Similarly, total P and K accumulation was greater in P. juliflora followed by A. nilotica. The highest nutrient accumulation in P. juliflora and A. nilotica may be because of more number and vigorous branches and it was in the order of branches   >   stem   >   leaves whereas, in other species the order of nutrient accumulation changed as stem   >   branch   >   leaf. Nitrogen accumulation in P. juliflora, P. pinnata, C. equisetifolia, P. alba, A. nilotica, P. dulce, and C. siamea was greater than P, K, Ca, and Mg. However, Ca storage in T. arjuna and A. indica was greater than N due to slow growth. P. juliflora, A. nilotica and P. pinnata contributed the greatest amount of N transfer through litterfall compared to other species. This may be due to more number of branches and high litter biomass as compared to other species. However, maximum P, K, Ca, and Mg were transferred through the litterfall of C. equisetifolia, P. juliflora, and T. arjuna, respectively (Table 3.10).

Table 3.10. Total nutrient accumulations in different plant components and leaf litter of 10 tree species planted on sodic soil.

Tree species Components Nutrient accumulation (kg   ha−     1)
N P K Ca Mg
T. arjuna Total* 254.26 30.31 224.2 329.19 73.10
Litter 42.84 6.63 7.65 34.17 26.52
A. indica Total 108.79 19.32 91.89 119.28 20.63
Litter 30.81 3.92 8.96 15.12 7.84
Prosopis juliflora Total 320.37 71.65 335.05 275.78 42.74
Litter 94.55 6.12 52.46 37.82 21.96
P. pinnata Total 210.13 29.26 179.99 208.07 28.30
Litter 85.10 7.52 31.52 23.12 16.21
Casuarina equisetifolia Total 274.81 46.58 194.50 256.56 41.17
Litter 48.45 9.12 23.94 29.07 17.10
P. alba Total 146.73 32.97 157.23 135.99 26.04
Litter 22.12 2.40 11.80 10.61 6.42
A. nilotica Total 291.49 62.27 222.36 284.94 38.08
Litter 90.72 5.41 15.12 23.22 14.04
Eucalyptus tereticornis Total 141.44 24.88 161.90 203.81 29.86
Litter 11.44 1.82 2.08 9.49 4.68
P. dulce Total 206.44 29.10 143.93 198.98 27.89
Litter 29.04 3.84 10.32 12.48 8.64
Cassia siamea Total 174.32 20.77 118.43 167.10 24.37
Litter 10.14 1.82 5.22 11.18 10.92
a
Total uptake includes Stem   +   Branch   +   Leaf.

Source: Singh, Y.P., Singh, G., Mishra, V.K., Arora, S., Singh, B., & Gupta, R.K. (2019b). Restoration of ecosystem services through afforestation on degraded sodic lands in indo-Gangetic plains. Indian Journal of Agricultural Sciences, 89(9), 1492–1497.

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Agroforestry: Hydrological Impacts☆

C. Ong , ... N.A. Jackson , in Reference Module in Food Science, 2017

Why Tree Root Distribution Matters

Historically, much research has focused on the more visible above-ground competition between trees and crops, and in understanding the effects of tree canopies on crops resulting from shading and rainfall interception. However, below-ground competition, determined primarily by the distribution and activity of tree and crop roots, is at least as important, but much less well understood, because the required research is more difficult. Below-ground aspects of competition are invisible to farmers, who often attribute competition to shade rather than for water and nutrients. In practice, crop yield is determined by the balance between the above-and below-ground elements of competition, depending on the prevailing limiting factors for growth. Disentangling these issues is challenging.

The use of soil water by trees and crops in AF systems depends on many factors, but is optimized when use of below-ground space is maximized both spatially and temporally. This involves consideration of both the architecture and activity of tree and crop roots at different developmental stages. Annual crops and perennial grasses are relatively shallow-rooted, occupying the surface horizons where soil water content is most variable and responds rapidly to rainfall. In contrast, tree roots can extend deep below the soil surface and laterally into the crop rooting zone, well beyond the edge of the tree canopy (Stone and Kalisz, 1991; Schroth, 1998). The main structural roots of trees are long lived and provide the framework on which the fine roots (<2   mm diameter), which are active in water and nutrient acquisition, are deployed; these are short lived and their turnover makes a considerable contribution to soil carbon accumulation. Although deep tree roots can tap into ground water, evidence from sap flow studies (Brooksbank et al., 2011c) indicates that trees preferentially access water from surface zones when this is available. Thus, trees usually compete with crops during the rainy season as their preexisting rooting framework provides a competitive advantage over the emerging roots of germinating crops. Though tree species vary in rooting architecture and root biomass, this is not necessarily reflected by their growth or competitiveness (Wajja-Musukwe et al., 2008). An evaluation of the ratio of root number in the top 1.8   m of soil to trunk volume has shown that Casuarina equisetifolia and Markhamia lutea had significantly higher ratios than A. acuminata, Maesopsis eminii, and Grevillea robusta; Casuarina and Maesopsis were most competitive with crops, whereas Markhamia and Grevillea were least competitive. Tree propagation method also affects root architecture, and hence, potentially, competition (Mulatya et al., 2002; Asaah et al., 2010, 2012).

Several options are available to farmers to manage below-ground water resources (Schroth, 1998; Rao et al., 2004). Their decisions depend on the relative value of products from trees and crops, labor supplies, and availability of soil resources. In some situations, trees and crops may be temporally segregated using rotational fallows, but in simultaneous AF systems competition can be controlled using appropriate tree/crop combinations and planting configurations, or tree management practices involving root and/or crown pruning to control water demand and zones of water uptake. An agronomic approach to achieve temporal complementarity is to use trees with complementary leafing phenology; for example, species that are fully or partly deciduous are less competitive with crops than the evergreen species that capture resources throughout the year (Fig. 1; Broadhead et al., 2003a,b; Muthuri et al., 2005).

Figure 1. Time courses for (A) leaf cover, (B) leaf flush, and (C) leaf fall in Grevillea robusta, A. acuminata, and Paulownia fortunei trees at Thika, Kenya, between January 2001 and July 2001. Vertical bars show double standard errors of the mean. Scores were ascribed using a four-point scale ranging from 0 (absent), 1 (low), 2 (intermediate) to 3 (high).

 Adapted from Muthuri, C.W., Ong, C.K., Mati, B.M., van Noordwijk, M., 2005. Modeling the effects of leafing phenology on growth and water use by selected agroforestry tree species in semi-arid Kenya. Land and Water Resources Research 4, 1–11.

Pruning offers a direct and adaptable method of controlling competition and has been the focus of several studies in East Africa (Tefera, 2003; Rao et al., 2004; Wajja-Musukwe et al., 2008; Namirembe et al., 2009; Siriri et al., 2010, 2012). This practice enables farmers to grow the tree species they prefer by managing their growth. Crown pruning varies in intensity and ranges from removing the lower branches to raise the tree canopy to the removal of almost all branches of trees or hedgerows (pollarding). Crown pruning has the added advantage of yielding animal fodder, fuel, and small wood and provides an ongoing and flexible source of nontimber products and income before the trees are harvested. Root pruning may be achieved by tillage as the normal process of land preparation disrupts the fine roots of trees in the surface soil horizons. As these rapidly regrow, longer lasting effects can be achieved by severing all lateral roots close to the trunk with a machete or hoe at the start of the cropping season. This enforces spatial separation of tree and crop roots, but yields no direct product unless farmers are sufficiently fuel-hungry to excavate cut roots. The ease of the first cut depends on the age of the trees but, if repeated annually, the cutting of root regrowth requires little effort and is easily integrated into land preparation. Although root pruning is an attractive option in some circumstances, practitioners must be aware that, if this is incomplete, the activity of the remaining uncut lateral roots is increased so that no overall improvement in crop yield is obtained (Wajja-Musukwe et al., 2008). Fig. 2 illustrates the potentially substantial beneficial effect of root pruning on crop growth: maize has attained full height adjacent to the tree on the pruned side, but in this situation of 'incomplete' pruning, the competition effect is exaggerated on the unpruned side.

Figure 2. Influence of root pruning on one side of the Grevillea robusta tree row 2   years previously (far side of the tree row) on the growth of maize in Western Kenya. Note that growth was greatly reduced by competition for below-ground resources on the unpruned side of the tree row (foreground).

The influence of pruning trees on associated crops varies between species. In the study of bench terraces in Uganda, mentioned earlier (Siriri et al., 2010), in which three tree species were grown on the infertile upper third of terraces and annual crops were planted on the lower terrace, shoot pruning of trees <2   years old was sufficient to maintain crop yield, but a combination of crown and root pruning was required as trees grew larger. Calliandra calothyrsus was more competitive than A. acuminata and S. sesban, whereas beans (Phaseolus vulgaris) were more sensitive to competition than maize (Zea mays). Measurements of sap flow through the trunks of trees can be used to determine diurnal and longer term patterns of water use and the impact of pruning. Such studies revealed that root pruning greatly reduced diurnal water use in G. robusta in Kenya (Fig. 3A; Anyango, 2005), and that shoot or root pruning both reduced sap flow in Alnus and Sesbania, whereas only root pruning was effective in reducing water use by Calliandra in Uganda (Fig. 3B; Siriri et al., 2013).

Figure 3. (A) Diurnal time courses of sap flow in unpruned and root-pruned Grevillea robusta trees shortly after root pruning was completed; vertical bar shows standard error of the difference (SED) (Anyango, 2005) and (B) influence of tree species and pruning treatment on mean daily sap flow rates for A. acuminata, C. calothyrsus, and S. sesban; vertical bars 1, 2, and 3 show SED values for species, pruning treatment, and tree-pruning treatment interaction. ∗∗∗Denotes significance at p  &lt;   .001 (Siriri et al., 2013).

Tefera (2003), working on boundary-planted trees (C. equisetifolia, G. robusta, M. lutea, and Eucalyptus grandis) in Kenya, observed that pruning (pollarding, root pruning, and pollarding plus root pruning) increased the survival and productivity of intercropped maize compared with unpruned control plots, although effects varied between species (Fig. 4). Two years after pruning, sap flow was lowest in pollarded C. equisetifolia and G. robusta trees and highest in root-pruned trees (Fig. 5), indicating that these were using alternative deep sources of soil water to support the transpirational demand of the canopy. These data indicate that root pruning can redirect water uptake by trees to deeper soil layers, thereby avoiding stomatal closure and enabling them to continue to grow; however, if the canopy is not pruned, it will continue to compete with crops through shading and rainfall interception. Such effects are likely to vary with site, tree species, and planting density.

Figure 4. Effects of shoot, root, or shoot plus root pruning on maize yield relative to sole maize crops for four tree species. Data are for the first three cropping seasons after pruning at Siaya, Western Kenya. LR and SR represent long and short rains (Tefera, 2003).

 Reproduced with permission from Rao, M.R., Schroth, G., Williams, S.E., et al., 2004. Managing below-ground interactions in agroecosystems. In: van Noordwijk, M., Cadisch, G., Ong, C.K. (Eds.), Below–Ground Interactions in Tropical Agroecosystems: Concepts and Models with Multiple Plant Components. CABI Publishing, Wallingford, UK, pp. 309–328.

Figure 5. Effect of pruning treatment on mean daily time courses of sap flow for Casuarina equisetifolia and Grevillea robusta trees 2   years after tree pruning (Tefera, 2003).

It is important to recognize that management for complementarity of water use by root pruning may detract from other potential advantages of tree–crop combinations, such as N fixation in root nodules by rhizobial bacteria and nutrient uptake by symbiotic mycorrhizal fungi associated with roots and proteoid roots, as these functions are more closely associated with surface than with deep roots.

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Conservation

In Cyclura, 2012

Threats

Habitat Loss and Degradation

The primary threats to the long-term survival of rock iguana populations continue to be habitat loss and degradation caused by people and domestic livestock. These effects are ubiquitous throughout the range of rock iguanas, although some good quality iguana habitat has been spared, particularly in parts of Cuba and the Bahamas that are remote, sparsely populated, and lack natural fresh water sources (Ehrig, 2000). Habitat loss takes a variety of forms, including limestone mining, which has destroyed large tracts of habitat on Cuba, Puerto Rico, and Jamaica. Even when the areas directly impacted by mining are limited, the roads that are cut to facilitate mining operations allow further incursion into forest habitats. Other direct sources of habitat loss include agriculture, especially in the Dominican Republic and on Grand Cayman, as well as land clearing for tourist resorts and housing developments (Figure 7.2). In the Dominican Republic, it has been estimated that 35% of Rhinoceros iguana habitat has been lost, and that 75% of that which remains is highly disturbed (Ottenwalder, 2000a).

FIGURE 7.2. Core iguana habitat in the British Virgin Islands (a) which was cleared for development that never occurred (b).

Although less direct than the impacts of land clearing, habitat fragmentation and disturbance are equally devastating to rock iguana populations. Hardwood timber extraction, especially prevalent on the larger islands such as Cuba and Hispaniola, has disturbed the forest canopy and impacted local watersheds. Wood cutting for the production of charcoal, a cheap cooking fuel, has significantly degraded iguana habitat in Jamaica and the Dominican Republic. Harvest methods traditionally involving machetes have been replaced with chainsaws, greatly increasing the pace of destruction (Wilson et al., 2004b). The Hellshire Hills, last stronghold of the Jamaican iguana, has been severely impacted by charcoal burning activities in the northeast, where today only barren ground remains (Vogel, 2000).

Finally, the feral livestock that invariably accompany human settlement have had serious negative consequences for rock iguana populations (Figure 7.3). Goats, burros, donkeys, sheep, and cattle compete with iguanas for food, alter local vegetation composition, and prevent the regeneration of native plants (Mitchell, 1999). Goats, introduced to the Caribbean in the sixteenth century as a food source for shipwrecked sailors, are particularly destructive, removing high quality iguana food plants through over-browsing. As a result of the disturbance caused by grazing, many iguana habitats have been invaded by invasive plant species such as Australian pine ( Casuarina equisetifolia ), which dominates degraded dry forests throughout the Caribbean. Feral livestock not only cause a shift in plant species composition toward toxic, non-palatable species, but also trample iguana nests and burrows, causing either direct collapse or compaction of soils such that they are unsuitable for future nesting.

FIGURE 7.3. Cattle and other livestock degrade iguana habitat by browsing on native vegetation and trampling suitable nesting habitat.

Predation by Introduced Mammals

In addition to habitat loss and degradation, predation by introduced mammals is decimating many rock iguana populations. Although the introduced Indian mongoose is currently only known to be a significant problem for one species, the Jamaican iguana, its impact has been devastating (Figure 7.4). Mongooses were first introduced to Jamaica in 1872 in a futile attempt to control black rats (Tolson, 2000). Iguana populations plummeted to the point where the species was believed extinct when it disappeared from the Goat Islands in the mid-1940s. Although a tiny remnant population was rediscovered in Jamaica's Hellshire Hills in 1990, it has taken years of intensive mongoose trapping and removal for the population to show the beginnings of recovery (Wilson et al., 2004a, 2004b; Lewis et al., 2011).

FIGURE 7.4. The Indian mongoose is known to be a significant predator of the Jamaican iguana.

Feral cats and domestic dogs are also a major threat to iguana populations throughout the region (Figure 7.5). While dogs are capable of predating adults of even the largest species, feral cats are more likely to threaten hatchlings and juveniles. However, for iguana species in the Bahamas and Turks and Caicos Islands, feral cats have been shown to kill and consume all age classes. On Pine Cay, a thriving population of more than 5,000 Turks and Caicos iguanas was driven nearly to extinction in less than five years after a few cats and dogs were brought to the island during hotel construction (Iverson, 1978). The population of iguanas on Anegada island is currently far below carrying capacity, likely largely due to the very large and uncontrolled population of feral cats (Bradley and Gerber, 2005). The natural range of the Turks and Caicos iguana has been reduced by 95%, and its current area of occupancy is inversely correlated with the presence of introduced mammals (Gerber and Iverson, 2000). Because rock iguanas evolved in the absence of any mammalian predators, they have no natural defenses against these enemies.

FIGURE 7.5. Ferals cats prey heavily on juvenile iguanas and can kill adult iguanas of smaller species.

While less destructive to adult iguanas, rats and feral pigs can still have devastating effects on iguana nests, especially immediately following egg deposition when olfactory cues can be strong (Wiewandt and Garcia, 2000). The impact of feral pigs has been especially problematic on Mona Island, Andros Island, and parts of Cuba. There is some evidence that rats may also depress adult iguana densities for smaller species such as the San Salvador iguana (Hayes et al., 2004). In 1996, a single introduced raccoon decimated the breeding population of iguanas on White Cay in the Bahamas (Hayes, 2000a). It was hypothesized that females were disproportionately impacted because of their greater visibility and the energetic demands placed on them during the nesting season (Hayes et al., 2004).

Hunting and Poaching

Hunting is a less severe threat to rock iguanas than habitat loss or predation by introduced mammals, but it is still a serious danger for some taxa. The hunting that does occur takes two very different forms: local subsistence hunting for food and deliberate poaching for the illegal pet trade. In rural areas of both Haiti and the Dominican Republic, Rhinoceros and Ricord's iguanas are hunted locally for food (Ottenwalder, 2000a, 2000b). In addition, iguana remains have been found in abandoned fishing camps on Andros Island in the Bahamas (Knapp, 2005b) (Figure 7.6). For two taxa of Bahamian iguanas, the Allen's Cay iguana and the White Cay iguana, incidences of in-country poaching and illegal smuggling to the United States for the pet trade have been reported, respectively (Iverson, 2000; Hayes, 2000a).

FIGURE 7.6. Remains of an iguana discovered at a hunting camp on the West Side of Andros Island, Bahamas.

 Photo by Chuck Knapp.

In 2008, a senseless tragedy at the Queen Elizabeth II Botanic Park iguana breeding facility on Grand Cayman illustrated the most serious single incidence of illegal loss of life on record (Binns, 2008). Vandals broke into the facility under cover of night and deliberately killed seven adult Grand Cayman Blue iguanas, representing 17.5% of the captive population, including several important genetic founders (Figure 7.7). Two of the animals that were attacked managed to survive, and the incident resulted in an outpouring of local, national, and international support for the program. Nevertheless, humans clearly remain some of the most potent predators of rock iguanas today.

FIGURE 7.7. Digger, a large and friendly Grand Cayman Blue iguana, was one of the unfortunate victims of a brutal and deliberate slaughter of captive blue iguanas at the Blue Iguana Recovery Program facility on Grand Cayman.

Human Interactions

Human recreational activities tend to be concentrated on beaches, which is often where iguanas nest communally. Walking through nest clearings can cause nest chambers to collapse and damage developing eggs. An emerging threat comes from well-meaning visitors who feed iguanas on tourist beaches, leading to high levels of intraspecific aggression and disruption of natural social systems. In a study of Cuban iguanas on the US Naval Base at Guantanamo Bay, Lacy and Martins (2003) found that iguanas inhabiting areas with high human interference showed increased levels of male–male aggression and fewer males interacting with females, both of which could significantly impact the natural mating system of this species (Figure 7.8).

FIGURE 7.8. At Guantanamo Bay, Cuba, iguanas with high human interference show increased levels of intraspecific aggression, with fewer males interacting with females.

In the Bahamas, powerboat tours advertising the opportunity to feed wild iguanas often visit the same cays multiple times in a single day. In a study designed to assess the impact of this practice, iguanas were compared on two islands without visiting tourists and three islands where tourists visit regularly and feed iguanas, often with inappropriate food items such as bread, cake, and potato chips. Blood samples collected immediately after capture showed differences in glucose, sodium, hemoglobin, packed cell volume, total solids, and overall body condition (K. Hines and C. Knapp, unpublished data). These data still remain to be analyzed, but it is clear that artificial feeding can result in detectable changes in the physiology of wild iguanas that potentially have a significant impact on their survival.

If they are carefully designed and monitored, human–iguana interactions may be managed in a manner that benefits the conservation of wild iguana populations. On Little Water Cay in the Turks and Caicos Islands, visitation is regulated and controlled by the Turks and Caicos National Trust. The Trust oversaw construction of a boardwalk that ensures that visitors do not inadvertently walk over iguana burrows or trample vegetation. Signage highlights aspects of the biology of Turks and Caicos iguanas, provides information on their conservation status, and gives details of appropriate iguana etiquette. Iguana-appropriate food items are provided for tourists to offer, and each visitor is charged a modest fee that is used to help fund iguana conservation and education programs.

Because rock iguanas are large, photogenic, and charismatic, they can play a role as important flagship species that promote conservation of their threatened dry forest habitats. Ecotourism, if carefully and appropriately managed, can be a valuable means to engage the public in conservation efforts. In particular, citizen science programs such as that managed by the John G. Shedd Aquarium in the Bahamas have strong potential to successfully engage volunteers and garner long-term support (Knapp, 2004).

Every year, many iguanas are killed on roads by vehicular traffic (Figure 7.9), especially in the Cayman Islands, where tourism is rapidly accelerating and few untouched natural areas remain (Burton, 2004b, 2010). Coastal roads can be especially hazardous for species that must successfully navigate across these roads in order to reach the sandy beach habitat required for nesting. Iguana-crossing signage and bumper stickers ("Give Iguanas a Brake") are being explored as a potential deterrent to this problem at key sites, but the effectiveness of this approach remains to be quantified (C. Knapp, personal communication).

FIGURE 7.9. This Cuban iguana met an unfortunate end when it was killed by a car.

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Plant Morphology

Michael G. Simpson , in Plant Systematics (Third Edition), 2019

Stem Branching Models (Figure 9.6)

Aside from the general stem branching patterns, more specific models of tree branching pattern have been described (Hallé et al. 1978). These are used almost exclusively for trees, but may be used with herbs as well. The models are based first on whether the tree is monoaxial, unbranched with a single (vegetative) apical meristem, or polyaxial, branched with more than one vegetative apical meristem. Additional considerations are whether the shoots are orthotropic, erect and essentially radially symmetric, the branching three-dimensional, or plagiotropic, more or less horizontal with dorsiventral symmetry, the branching two -dimensional and leaves generally in one plane (either distichous or secund). Plagiotropy may occur in two general ways. Plagiotropy by apposition is that in which extension growth of the branch is taken over by an axillary meristem, but with the original branch terminal meristem continuing growth, usually as a short shoot. Plagiotropy by substitution is that in which the original branch terminal meristem aborts or converts into a terminal inflorescence or flower, extension growth of the branch being taken over by an axillary meristem. In addition, the timing of development of a shoot can be important in plant growth. Syllepsis (or sylleptic growth) is growth of an axillary bud into a shoot without a period of rest. Prolepsis (or proleptic growth) is growth of an axillary bud into a shoot only after a period of rest.

Figure 9.6

Figure 9.6

Figure 9.6. Stem branching pattern models, after Hallé et al. (1978). See text for explanation.

Other, related terms have to do with flowering. An indeterminate shoot that bears lateral flowers but that continues vegetative growth is termed pleonanthic. A plant with a determinate shoot that completely transforms into a flower or inflorescence is called hapaxanthic. If the entire plant flowers and fruits only once, and then dies, it is termed monocarpic; the plant itself can be an annual or perennial, but the term is usually used only for perennials, given that all annuals are monocarpic.

The following are tree growth models (after Hallé et al., 1978, illustrated in Figure 9.6), each of which is named after a botanist who contributed to our knowledge of that model. Only a very few examples of the models are listed, ones that might be familiar to the reader; see Hallé et al. (1978) for elaboration of the models and considerably more examples. An important concept, however, is that of reiteration, the growth of shoots not conforming to the parameters of the model, e.g., due to environmental stress, such as mechanical or animal damage, obscuring its normal expression. Although these models are rather specialized, they are useful in the study of tree architecture (and a challenging and intriguing exercise for the student to decipher). A given model may represent the end product of evolutionary adaptations to a given environment or life strategy and their elucidation may have taxonomic, ecological, or biomechanical significance.

Attim's Model. Polyaxial; with a monopodial trunk with continuous growth, bearing equivalent branches, flowers always lateral. E.g., Avicennia germinans, black mangrove (Acanthaceae), Alnus incana (Betulaceae), Casuarina equisetifolia (Casuarinaceae), Euphorbia spp. (Euphorbiaceae), Eucalyptus spp. (Myrtaceae), Rhizophora mangle, red mangrove (Rhizophoraceae).

Aubréville's Model. Polyaxial; rhythmically growing and branching, with rhythmic growth, having a monopodial trunk bearing modular whorls or pseudo-whorls of branch tiers, plagiotropic by apposition, all with a similar phyllotaxis, the inflorescences lateral E.g., Terminalia spp. (Combretaceae), Manilkara zapota (Sapotaceae).

Chamberlain's Model. Polyaxial; having regular, sympodial branching, the modules usually orthotropic, each hypaxanthic by producing a terminal flower or inflorescence, linear growth continued by distal, lateral meristems E.g., many cycads (such as male Cycas spp.), Jatropha spp. (Euphorbiaceae), Dieffenbachia spp., Philodendron selloum (Araceae).

Champagnat's Model. Polyaxial; with successive modular orthotropic axes with spiral leaf arrangement, each curving and becoming pendulous by its own weight, a new modular unit arising from the upper part of the curved axis E.g., Sambucus spp. (Adoxaceae), Crescentia cujete, calabash tree (Bignoniaceae), Caesalpinia pulcherrima (Fabaceae), Lagerstroemia indica, crepe myrtle (Lythraceae), Bougainvillea spectabilis (Nyctaginaceae).

Corner's Model. Monoaxial, in which the inflorescences or sporophylls are lateral, the single stem capable of growth after flowering, not monocarpic E.g., many tree ferns, cycads (such as female Cycas spp.), many palms (Arecaceae).

Fagerlind's Model. Polyaxial; with a monopodial, orthotropic trunk producing tiers of modular branches, each branch sympodial and plagiotropic by apposition, with spiral or decussate leaves. E.g., Hymenosporum flavum (Pittosporaceae); Magnolia grandiflora, flowering magnolia (Magnoliaceae).

Holttum's Model. Monoaxial, with the terminal meristem developing entirely into an inflorescence, the tree dying after fruit maturation, therefore monocarpic E.g., many Agave spp. (Agavaceae), many palms (Arecaceae).

Koriba's Model. Polyaxial; having orthotropic modules, each of which is sympodial and aborts or produces a terminal inflorescence, the modules initially equivalent, but later one becoming dominant and erect as a trunk, the others developing into branches E.g., Ochrosia spp. (Apocynaceae), Catalpa spp. (Bignoniaceae), Phytolacca dioica (Phytolaccaceae).

Leeuwenberg's Model. Polyaxial; having equivalent, orthotropic modules, each of which is sympodial and produces a terminal inflorescence, with two or more new modules arising below it. E.g., tree Aloë spp. (Asphodelaceae), Dracaena draco (Ruscaceae), Nerium oleander, Pachypodium spp. (Apocynaceae), Pandanus spp. (Pandanaceae).

Mangenot's Model. Polyaxial; with axes composed of modular units from a single apical meristem composed of an orthotropic proximal part (leaves often spiral), abruptly recurving into a plagiotropic distal part (the leaves often distichous), a new module orthotropically arising from the bend of the recurved section E.g., Vaccinium corymbosum, blueberry (Ericaceae), Strychnos sp., strychnine (Loganiaceae), Eugenia sp. (Myrtaceae).

Massart's Model. Polyaxial; rhythmically growing and branching, with an orthotropic, monopodial trunk having rhythmic growth, producing regular tiers of lateral branches that are plagiotropic by leaf arrangement or symmetry, never by apposition, reproductive structure position variable E.g., Agathis spp., Araucaria spp. (Araucariaceae), Sequoia sempervirens. redwood (Cupressaceae), Diospyros spp. (Ebenaceae), Myristica fragrans (Myristicaceae), Abies spp. (Pinaceae).

Nozeran's Model. Polyaxial; rhythmically growing and branching, with an orthotropic, sympodial trunk, each sympodial unit bearing a distal tier of monopodial or sympodial plagiotropic branches, the leaf arrangement of trunk and branches different E.g., Theobroma cacao, chocolate (Malvaceae).

Petit's Model. Polyaxial; continuously growing and branching, with a monopodial, orthotropic trunk producing tiers of modular branches, each branch sympodial and plagiotropic by substitution (thus branch modules hapaxanthic), with spiral or decussate leaves E.g., Gossypium spp., cotton (Malvaceae); Morinda citrifolia (Rubiaceae).

Prévost's Model. Polyaxial; rhythmically growing and branching, having two types of orthotropic modules forming trunk and branches from inception, the branch modules plagiotropic by apposition, arising sylleptically from subapical region of the trunk module, successive trunk modules proleptic and arising well below the tier of branch modules E.g., Cordia spp. (Cordiaceae), Euphorbia pulcherrima, crucifixion thorn (Euphorbiaceae).

Rauh's Model. Polyaxial; with a monopodial trunk, rhythmically producing tiers of branches, each branch identical to trunk; flowers always lateral E.g., Ilex spp. (Aquifoliaceae), Araucaria spp. (Araucariaceae); Kalanchoe beharensis (Crassulaceae), Euphorbia spp. (Euphorbiaceae), Quercus spp. (Fagaceae), Cecropia spp./Ficus spp. (Moraceae), Fraxinus spp. (Oleaceae), most Pinus spp. (Pinaceae); Acer spp. (Sapindaceae).

Roux's Model. Polyaxial; continuously growing and branching, with a monopodial, orthotropic trunk having spiral leaf arrangement, bearing lateral branches that are plagiotropic, but never by apposition, usually with distichous leaf arrangement, the branches inserted continuously on the trunk, reproductive structure position variable, but usually lateral on branches. E.g., Polyalthia spp. (Annonaceae), Dipterocarpus spp. (Dipterocarpaceae), Bertholletia excelsa, Brazil nut (Lecythidaceae), Durio zibethinus, durio (Malvaceae), Coffea arabica (Rubiaceae).

Scarrone's Model. Polyaxial; rhythmically growing and branching, with a monopodial trunk bearing tiers of branches, each branch sympodial by terminal flowering, but becoming orthotropic E.g., Anacardium occidentale, cashew, Mangifera indica, mango (Anacardiaceae), Jacaranda mimosifolia (Bignoniaceae), Echium spp. (Boraginaceae), Aeonium spp. (Crassulaceae), Arbutus unedo (Ericaceae), Aesculus spp., horse-chestnut (Sapindaceae).

Schoute's Model. Polyaxial; growth from meristems that produce orthotropic or plagiotropic trunks forking at regular, distinct intervals by equal dichotomy, otherwise with no lateral branches; inflorescences lateral. E.g., Hyphaene thebaica, Nypa fruticans (Arecaceae); Flagellaria indica (Flagellariaceae).

Stone's Model. Polyaxial; continuously growing and branching, with a orthotropic trunk that may flower terminally, bearing orthotropic branches, with additional branching occurring sympodially below terminal inflorescences E.g., Mikania cordata (Asteraceae), Pandanus spp. (Pandanceae).

Tomlinson's Model. Polyaxial; vegetative axes all equivalent, orthotropic, with equivalent orthotopic modules developing from basal nodes in subsequent axes. E.g., many monocots (Bromeliaceae, Cyperaceae, Poaceae, Zingiberales), Euphorbia spp. (Euphorbiaceae), Kalanchoë spp. (Crassulaceae).

Troll's Model. Polyaxial; with all axes plagiotropic, the modules superposed upon one another, the proximal part of each module becoming erect in development, the distal part a branch. E.g., Psidium guineense (Myrtaceae), Erythroxylum coca (Erythroxylaceae), Albizzia julibrissin, Bauhinia spp. (Fabaceae), Fagus grandifolia, beech (Fagaceae), Averrhoa carambola, star-apple (Oxalidaceae).

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Perspectives on reviving waterlogged and saline soils through plantation forestry

P.S. Minhas , ... Aradhana Bali , in Agricultural Water Management, 2020

3.3 Intercepting seepage along irrigation canals

The tree belts are usually established along the irrigation canals with the aim of halting their lateral seepage under Indian conditions. Such plantations consisting of different tree species were evaluated for a saline Vertisol site falling under TBP (Tung-Bhadra Project) command (Manjunatha et al., 2005). The average water-table depth was 0.6–1.4 m lower under plantations than the outside area. The plantations of A. nilotica, Dalbergia sissoo, Casuarina equisetifolia intercepted 72–90 % of the seepage occurring from canal while the interception was < 50 % by Hardiwickia binata and A. indica. Similarly, consistent draw down of 0.8–1.08 m in water table was recorded (Fig. 3) in the adjoining areas of a Eucalyptus plantation to a distance of 0.73 km both towards the canal side (contributing lateral flows) and even in the opposite direction (Jeet-Ram et al., 2007). However, the drawdown was lesser during monsoon rains e.g. water-table averaged 0.84-0.92 m deeper than at distance of 0.5 km from plantation, respectively in July-August when the trees extracted more water from rain-recharged soil profiles. It averaged 1.19–1.25 m in September –October when growth rate of trees was high and also during summer (e.g. 1.25 m in April) when atmospheric demand was high and tree roots extracted more water from the capillarity zone above water-table. The impacts are expected to further increase in areas with lower rainfall and higher evaporative demands e.g. the water-table declined by 15.7 m in about 6 years under a Eucalyptus plantation mixed with A. nilotica along the main canal of IGNP Phase II in arid Rajasthan (Kapoor and Denecke, 2001).

Fig. 3

Fig. 3. Water-table depths monitored across Eucalyptus plantations (rainfed and 20-year old) on a clayey soil at Keybram, Australia (A) and a sandy loam soil in Dhobwali, India (B).

 Source: Heuperman et al. (2002); Jeet-Ram et al. (2007)

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