THE RELATIONSHIP BETWEEN PLANT DIVERSITY AND PRODUCTIVITY IN NATURAL AND IN MANAGED GRASSLANDS
Plant species richness-productivity relationship (SRPR) is crucial to the This report explains the diverse forms of the SRPR, clarifies the. How does biodiversity affect ecosystem function (or vice versa)? Found positive relationship between species richness and productivity in US and across . can be major determinants of the diversity–productivity relationship in presence of soil microbes, plant disease decreased with increasing diversity, and .
This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract We aimed to study relationships between plant biodiversity and soil chemical fertility in a mature tropical forest of Costa Rica. Simple linear regression analyses were conducted. Therefore, higher tree species richness tended to be found on sites with lower soil fertility, which is the complete opposite of temperate forests.
As a result, tropical and temperate forest ecology should be considered separately. Herb structural richness was positively correlated with soil fertility index and P concentration. Therefore, herb structural richness may be a good indicator of soil fertility.
This study gives important insights on ecological relationships between plant biodiversity and soil chemical fertility in a primary tropical forest. Introduction Tropical forest ecosystems are known for having the highest plant biodiversity on the planet.
Amazonian tropical forests can support life for up to and even more than tree species per hectare [ 1 ]. In Ecuador, 1, tree species were found living in an area of 25 ha [ 1 ]. This high plant biodiversity is essential for the survival of several living organisms that thrive in tropical ecosystems. It is thought that high plant biodiversity in tropical forest stands is mainly caused by factors such as high stable temperature low seasonalityhigh humidity high precipitationand high solar radiation all year round which favour the growth of a large number of species [ 2 ].
Although the main causal factors of plant biodiversity are related to climate and topography, it is important to understand what is happening at the microhabitat level. Does soil fertility have any effects on plant biodiversity in a mature tropical forest? Conversely, does plant biodiversity have any effects on soil fertility in tropical ecosystems?
Is there a relationship between the two? They concluded that trends are variable and the relationship between plant biodiversity and productivity may vary according to different habitats and can also be influenced by other abiotic and biotic factors [ 3 ]. The unimodal relationship in which productivity is low at low and very high diversity and is high at medium diversity seemed to dominate the temperate regions [ 4 ].
In a more specific study, Janssens et al. They found a positive relationship between plant biodiversity richness and diversity and the concentration of extractable P and K in soil [ 5 ].
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- Ecological effects of biodiversity
- International Journal of Forestry Research
No relationship was found between plant biodiversity and other factors such as total N and Ca concentrations, pH, and organic matter content [ 5 ]. In temperate regions, Tilman et al.
They found that nitrogen was more available to plant roots in plots with higher species richness and diversity due to the reduction of N leaching loss in soil, thereby increasing ecosystem productivity at the same time [ 6 ]. Using a different approach, Holl [ 7 ] compared plant biodiversity and soil chemical fertility in an abandoned pasture versus a near primary tropical forest of southern Costa Rica.
He found that the levels of most soil nutrients N, Ca, Mg, and especially P were usually lower in the pasture compared to the forest containing higher plant biodiversity [ 7 ]. Recently, Dybzinski et al. They found that soil from the higher plant species diversity plots was producing more biomass than soil from lower diversity plots and this phenomenon was caused by greater soil N availability, inputs, and retention [ 8 ].
THE RELATIONSHIP BETWEEN PLANT DIVERSITY AND PRODUCTIVITY IN NATURAL AND IN MANAGED GRASSLANDS
Then, Nirmal Kumar et al. They found a strong positive correlation between tree species richness and the concentrations of N, P, and C [ 9 ]. Much research has been done on the relationships of plant biodiversity with productivity and soil fertility in grassland ecosystems, temperate forest stands, and agroecosystems. On the other hand, there is a lack of research and data available about this correlation in tropical forest ecosystems.
In this study, we aimed to investigate the relationship between plant biodiversity and soil chemical fertility in a mature tropical forest of Costa Rica.
This is the first study that has looked at both plant species and structural diversities in relation to soil chemical fertility in a tropical forest.
Study Area and Methods 2. It is a biological reserve of 7, ha consisting of mature tropical forests with elevation varying between m and 1, m above sea level. This kind of climate and variable topography results in the presence of three types of forest called Premontane Moist Forest, Premontane Wet Forest, and Premontane Rain Forest. The forest types were identified using the life zone system created by Holdridge [ 10 ]. This reserve is located in an area known for its soils classified mainly as Inceptisols which tend to be moderately acid and contain low concentration levels of Ca, Mg, K, and Zn.
The relief tends to be abrupt. Furthermore, the reserve shelters high plant species richness in which 1, species of angiosperms have been identified in the past [ 11 ]. Inventory of Plant Composition and Abundance and Biodiversity Calculations Three sampling plots of 5 m by 25 m area were randomly selected in each of the three life zones [ 12 ]. Life zones are defined by the variation of temperature and precipitation in a given area which leads to the formation of different vegetation communities [ 10 ].
Life zones were identified based on elevation and presence of mosses and ferns on tree trunks. Premontane Moist Forest was located in elevations between m and 1, m and neither moss nor fern was present on tree trunks. Premontane Wet Forest was found in elevations between 1, m and 1, m and trees had low to moderate abundance of mosses and ferns on their bark.
Premontane Rain Forest was located in elevations between 1, m and 1, m and had high abundance of mosses and ferns on tree trunks. Sampling was done by randomly selecting, on a map, three sampling plots at least m apart located close but at least 25 m from a trail in order to avoid forest edge effect in each of the three life zones.
There were nine sampling plots analysed in this study. Table 1 shows the corresponding elevation and life zone for each sampling plot. Each plot was divided into five units of 5 m by 5 m and the abundance and height class of the different tree species were measured in each of these units [ 12 ]. The abundance and height class of the different shrub species were measured from a 3 m by 3 m area within each 5 m by 5 m unit [ 12 ]. Furthermore, the abundance and height class of the different herb species were measured from a 1 m by 1 m area within each 3 m by 3 m sampling unit [ 12 ].
Figure 2 shows how the sampling plots were laid out. The identification of plant species was done using plant identification guides and our knowledge of Costa Rica flora. When it was not possible to identify species in the field, a sample was collected and brought to Carlos Morales, a specialist in Botany at the University of Costa Rica.
Epiphytes, vines, and lianas were not included in this study. Table 2 shows the number of species of herbs, shrubs, and trees for each plant family encountered in the field. Life zone, elevation, and graphic dot for each sampling plot. Number of species of herbs, shrubs, and trees identified for each family encountered in the field.
Sampling plot in which abundance and height class of herbs, shrubs, and trees species were measured. In each sampling plot, the abundance was measured by visually estimating the percentage of ground that was covered by the crown of a plant species. The area covered m2 by a plant species per hectare was calculated by multiplying the percentage of ground cover, the area of the plot, and the number of plots that fits in one hectare.
The height class was measured using a stick which indicates six different height classes 0—10 cm, 11—30 cm, 0. Once the area covered and the height class of plant species had been measured, the mean crown volume index for each sampling plot was calculated by multiplying the area covered by the height and then averaging the crown volume index of the five subplots.
This mean crown volume index represents space occupied by each species in a specific sampling plot per 0.
Ecological effects of biodiversity - Wikipedia
These biodiversity indices were chosen because they were the most appropriate for the sampling techniques we used in this study [ 13 ]. Species richness is the number of plant species in a given area.
Species richness was calculated by counting the number of species that was recorded in each sampling plot. Shannon-Wiener species diversity is a measure of evenness and is affected by both the number of species and evenness of the community [ 14 ].
Higher evenness in the abundance of species leads to higher diversity in a community [ 14 ]. Higher values mean higher diversity. Specifically, a diversity in the functional roles of the species may be a more important quality for predicting productivity than the diversity in species number.
Some models have indicated the importance of disturbance rates and spatial heterogeneity of the environment,  others have indicated that the time since disturbance and the habitat's carrying capacity can cause differing relationships. The current consensus holds at least that certain combinations of species provide increased community productivity. First, it is imperative that scientists stop looking for a single relationship. It is obvious now from the models, the data, and the theory that there is no one overarching effect of diversity on productivity[ citation needed ].
Scientists must try to quantify the differences between composition effect and diversity effects, as many experiments never quantify the final realized species diversity instead only counting numbers of species of seeds planted and confound a sampling effect for facilitators a compositional factor with diversity effects. Relative amounts of overyielding or how much more a species grows when grown with other species than it does in monoculture should be used rather than absolute amounts as relative overyielding can give clues as to the mechanism by which diversity is influencing productivity, however if experimental protocols are incomplete, one may be able to indicate the existence of a complementary or facilitative effect in the experiment, but not be able to recognize its cause.
Experimenters should know what the goal of their experiment is, that is, whether it is meant to inform natural or managed ecosystems, as the sampling effect may only be a real effect of diversity in natural ecosystems managed ecosystems are composed to maximize complementarity and facilitation regardless of species number.
By knowing this, they should be able to choose spatial and temporal scales that are appropriate for their experiment. Lastly, to resolve the diversity-function debate, it is advisable that experiments be done with large amounts of spatial and resource heterogeneity and environmental fluctuation over time, as these types of experiments should be able to demonstrate the diversity-function relationship more easily. Negative Covariance Effect If some species do better when other species are not doing well, then when there are more species in the ecosystem, their overall variance will be lower than if there were fewer species in the system.
This lower variance indicates higher stability. Insurance Effect If an ecosystem contains more species then it will have a greater likelihood of having redundant stabilizing species, and it will have a greater number of species that respond to perturbations in different ways.
This will enhance an ecosystem's ability to buffer perturbations. Thus invaders may have reduced success in diverse ecosystems, or there may be a reduced likelihood that an invading species will introduce a new property or process to a diverse ecosystem.
Some temporal stability data can be almost completely explained by the averaging effect by constructing null models to test the data against.
Review of resistance and resilience stability data[ edit ] This area is more contentious than the area of temporal stability, mostly because some have tried generalizing the findings of the temporal stability models and theory to stability in general. Some experimenters have seen a correlation between diversity and reduced invasibility, though many have also seen the opposite.
By constructing null models to test the data against as in Doak et al. Finding these contexts would allow for mechanistic studies into why these ecosystems are more stable, which may allow for applications in conservation management. More importantly more complete experiments into whether diverse ecosystems actually resist invasion and disease better than their less diverse equivalents as invasion and disease are two important factors that lead to species extinctions in the present day.
Theory and preliminary effects from examining food webs[ edit ] One major problem with both the diversity-productivity and diversity-stability debates discussed up to this point is that both focus on interactions at just a single trophic level. That is, they are concerned with only one level of the food webnamely plants.
Other research, unconcerned with the effects of diversity, has demonstrated strong top-down forcing of ecosystems see keystone species. There is very little actual data available regarding the effects of different food webs, but theory helps us in this area. First, if a food web in an ecosystem has a lot of weak interactions between different species, then it should have more stable populations and the community as a whole should be more stable.