The purpose of our study was to examine whether the degree of ectomycorrhizal (EM) colonization was associated with amount of shade for potted seedlings of five rain forest tree species. Seedlings ...were exposed to a range of shade treatments—from the open to that emulating the degree of shade beneath a deep-canopied forest. The experiment was carried out at the field station (580 m.a.s.l) of the Sinharaja World Heritage Site in southwestern Sri Lanka. We selected five species for the study:
Shorea affinis (Thw.) Ashton,
S. congestiflora (Thw.) Ashton,
S. cordifolia (Thw.) Ashton,
S. gardneri (Thw.) Ashton, and
S. zeylanica (Thw.) Ashton, all members of a sympatric clade of endemic canopy trees in the family dipterocarpaceae. Results show that the percentage EM colonization was significantly different among shade treatments, for all five species (
p < 0.05). However, EM root colonization was not significantly different among species. Highest percentages of EM colonization for all species, except for
S. congestiflora, were in treatments providing full open conditions. However, seedling growth of all species were best under partial shade conditions (
p < 0.05), intermediate between the deep shade of a forest understory and no shade of open environments. The non-linear relationship between seedling growth performance and EM colonization is discussed.
Resource allocation within trees is a zero-sum game. Unavoidable trade-offs dictate that allocation to growth-promoting functions curtails other functions, generating a gradient of investment in ...growth versus survival along which tree species align, known as the interspecific growth-mortality trade-off. This paradigm is widely accepted but not well established. Using demographic data for 1,111 tree species across ten tropical forests, we tested the generality of the growth-mortality trade-off and evaluated its underlying drivers using two species-specific parameters describing resource allocation strategies: tolerance of resource limitation and responsiveness of allocation to resource access. Globally, a canonical growth-mortality trade-off emerged, but the trade-off was strongly observed only in less disturbance-prone forests, which contained diverse resource allocation strategies. Only half of disturbance-prone forests, which lacked tolerant species, exhibited the trade-off. Supported by a theoretical model, our findings raise questions about whether the growth-mortality trade-off is a universally applicable organizing framework for understanding tropical forest community structure.
The pollination biology of two sympatric species, Polyalthia coffeoides and Polyalthia korinti (Annonaceae), is described in detail. An Endaeus species (Coleoptera: Curculionidae) is shown to be the ...major pollinator of both species, with Carpophilus plagiatipennis (Coleoptera: Nitidulidae) as the secondary pollinator of P. coffeoides. Both Polyalthia species show intrafloral dichogamy (protogyny) with a reproductively inactive phase between the pistillate and staminate phases, although there is no evidence of interfloral dichogamy. A pollination chamber is formed by the inner petals throughout the reproductively active phases. Thermogenesis occurs in P. korinti, with internal floral temperatures up to 6°C above ambient levels. The heat is presumably an energy reward for the beetles. Although most pollination systems are regarded as diversified and opportunistic, specialized pollination systems are typical of the Annonaceae. Although P. coffeoides and P. korinti have overlapping distributions, habitats, and flowering seasons and share the same pollinators, the extent of competition for pollinators is likely to be lessened due to the abundance and nonspecificity of the beetles. PUBLICATION ABSTRACT
Our study tested the potential for establishing shade-tolerant tree species within different canopy removal treatments of an 18-year-old
Pinus caribaea (Caribbean pine) plantation. We investigated ...whether planting within a
Pinus plantation can be a solution to the dispersal, weed competition, and pathogen/insect problems rain forest tree species have during their initial establishment on sites previously cleared of forest. The plantation was originally established on abandoned swidden adjacent to the Sinharaja Man and the Biosphere rain forest reserve in southwestern Sri Lanka. The five species selected for the study were
Caryota urens,
Dipterocarpus zeylanicus,
Pericopsis mooniana,
Shorea stipularis, and
Swietenia macrophylla. Seedlings were monitored over two years for survival, root collar diameter and height growth along transects that were in seven different environmental treatments within the
Pinus plantation. Environmental treatments comprised: (i) under plantings beneath a closed canopy of
Pinus that were unaffected by any row removal; (ii) the centres of clearcut strips of
Pinus that were 6 m width; (iii–vii) and five treatments across clearcut strips within closed canopy
Pinus that were 12 m wide. The five treatments within the 12 m wide clearcut strip included inside edges beneath the
Pinus canopy on the eastern (iii) and western (iv) sides of the strip; outside edges on the eastern (v) and western (vi) sides of the strip; and the centre (vii) of the strip opening. At the end of two years, a sample of the seedlings growing within each environmental treatment were taken and measured for dry masses and leaf areas. Results demonstrate that all species grew poorly and had higher mortality in the
Pinus understorey than the other environmental treatments. The dipterocarp species (
D. zeylanicus,
S. stipularis) were slower growing and more site-sensitive to changes in environmental treatment than the non-dipterocarp species.
S. macrophylla grew tallest in all environmental treatments as compared to the other species. Overall, the best environments for seedling establishment and growth for all species were in the centres of the canopy strips (6–12 m). This study contributes to investigations testing the feasibility of using
Pinus as a nurse for establishing more shade-tolerant species; and as a technique for forest restoration in south and southeast Asia.
1 Responses to the addition of P and Mg are described for eight species of Shorea section Doona (Dipterocarpaceae) which vary in their adult distribution across a topographic/soils gradient at ...Sinharaja Forest Reserve, Sri Lanka. 2 All combinations of the two nutrients resulted in increased dry mass yield, seedling height and leaf number after 24 months for seedlings of these species growing in pots of soil taken from a nearby Pinus plantation compared to a control which did not receive nutrients. In the presence of P, dry mass yield, leaf number and lateral root ratio declined in response to increasing Mg. In the presence of Mg, seedling height and stem mass ratio increased in response to increasing P. 3 After 24 months maximum dry mass yield in response to nutrient addition was greater for the four species which occur on more nutrient-rich soils in the field. Maximum percentage increase in dry mass in response to nutrient addition was negatively correlated with mean dry mass of unfertilized seedlings, but the relationship did not discriminate between species according to adult distribution across the catena. 4 There was no relation between seedling root mass ratio (RMR) or phenotypic plasticity in seedling RMR and adult distribution in relation to nutrient supply. 5 In Shorea section Doona, trade-offs between seedling `responsiveness' and `tolerance' to nutrient supply, in terms of either growth or dry mass allocation, are not powerful determinants of differences in adult distribution in relation to nutrient supply. Differential dry mass yield in response to nutrient addition was determined by differences in seed size and seedling relative growth rates under the experimental conditions, as well as the degree of response to nutrient addition. Response to nutrient addition may be constrained by seedling characteristics relating to variation in irradiance and water availability.
The breeding systems of two sympatric species, Polyalthia coffeoides and Polyalthia korinti (Annonaceae), are assessed using a range of approaches, including controlled pollination experiments and ...analysis of intersimple sequence repeat markers within and between populations. Natural (open) pollination resulted in similar levels of fruit formation as artificial cross-pollination, suggesting that pollinator availability is not a limiting factor in reproduction. Both species possess facultatively xenogamous breeding systems, with 33%-36% fruit formation in artificially crossed experiments and 17%-19% fruit formation following geitonogamy. Reduced fruit set following geitonogamy suggests partial self-incompatibility; this is supported by index of self-incompatibility values of ca. 0.5 in both species. Analysis of population genetic structure supports the hypothesis of a mixed but largely xenogamous mating system. Genetic diversity within populations was estimated to be ca. 80% and 66% of total genetic diversity for P. coffeoides and P. korinti, respectively. The levels of gene flow between populations were moderate (Nm = 2.033 for P. coffeoides and 0.970 for P. korinti), and genetic identity (I) values between populations within species were high. This possibly reflects the fragmentation of a previously more extensive population, correlated with the historical deforestation associated with crop cultivation and irrigation in Sri Lanka. PUBLICATION ABSTRACT
The angiosperm flora of Sri Lanka, which has been comparatively well studied by many eminent botanists for over two centuries, has a rich endemic component and also exhibits strong affinities to that ...of peninsular India. Some of the 15 floristic regions recognized in the island have exceptionally rich, highly localized floras. But increased forest disturbances over the years have taken a heavy toll. A plea is made to conserve at least one sufficiently large forest reserve in each floristic region. A meaningful conservation program has been launched in the Sinharaja MAB Reserve; similar programs are urgently needed for other protected areas of the island.
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