Background: Coastal ecosystems in Mexico remain understudied in spite of their ecological, economic and conservation value and are being impacted by human activities along the coast. Knowledge on spatial patterns of plant species distribution that helps preserve these fragile ecosystems is crucial. Aims: We evaluated differences in species richness, species diversity and species dominance patterns in 16 plant communities as well as the degree to which differences were driven by climatic conditions in sandy dunes in Yucatán. We evaluated the importance of invasive species in mediating patterns of species diversity and species dominance patterns. Results: We found wide variation in plant species richness, species diversity and species dominance patterns among communities that stems from broad climatic differences along dune systems. Invasive plants represent almost one-third of total species richness and seem to be drastically changing the species dominance patterns in these communities. Conclusions: Regional climatic differences along the Yucatán north coast seems to be a major driver of plant diversity and species composition. Our findings suggest that invasive plants have successfully colonised and spread along the coast over the past 30 years. Even though invasive species do not alter spatial patterns of species diversity, they are becoming more dominant with potential detrimental consequences for native plants.

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The aim of this study was to assess how the plant community and its species diversity are affected by establishment methods and warming. Priority effects, i.e., the order of species arrival in plant establishment, are an important subject when invasive species become more common, and the biodiversity decreases as the global temperature continues to increase. A field experiment was carried out to investigate the effect of establishment methods and temperature on plant communities by using four different establishment methods. The plants were divided into two groups (fast and slow germinating) and sown at two occasions, one earlier than the other. Half of the study plots were then treated with OTC (Open Top Chambers) and the other half were used as control. There was a difference in temperature between the OTC blocks and the control blocks. OTC had no effect on the number of species or the Shannon diversity index but affected the proportion fast germinating, slow germinating, and naturally established species. There was a significant effect of the establishment events on the plant community. There was also a significant interaction between OTC treatment and establishment, only present for the proportion of fast germinating species. The temperature differences can provide information on plant responses to global warming and the results can mostly be explained by priority effects such as numerical superiority and competition in combination with germination rate are. The results of this study can be used to better understand how warming and priority effects may affect plant communities in the future.

Interest in renewable energy and governmental mandates has motivated land managers to consider cellulosic feedstocks for bioenergy. I investigated plant community response to a system including switchgrass (Panicum virgatum) as a feedstock intercropped with loblolly pine (Pinus taeda). I estimated plant species evenness, richness, and diversity and biomass production, with emphasis on white-tailed deer (Odocoileus virginianus) forages. I detected 225 species in 2,220 1-m2 quadrats, and 7,495 biomass samples (96.4 kg dry weight) from 960 quadrats. Intercropping reduced plant species diversity, total non-pine tree biomass, and biomass of deer forages during switchgrass establishment. These effects were no longer apparent at treatment level two years after switchgrass establishment, except that deer browse and total deer forage biomass remained less in intercropped interbeds. Intercropping in managed pines may temporarily effect plant communities but further studies are needed to examine longer term effects and to quantify effects on nutritional carrying capacity for deer.

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The relations between environmental resources and biodiversity are crucial in the proper management and conservation of grasslands. Three nature reserves were chosen around the Gauteng Province, namely Roodeplaat Nature Reserve (RNR) in Tshwane, Suikerbosrand Nature Reserve (SNR) in Heidelberg, and Abe Bailey Nature Reserve (ANR) in Carletonville. We selected three sites within RNR, SNR and ANR, and paired these with adjacent sites in private farming/grazing areas adjacent to the nature reserves. At each site, species composition, species richness and plant diversity were determined with the use of 50m x 20m Modified-Whittaker plots (MWP), making a total of eighteen plots (MWP) at the nine paired sites. Two paired sites had high Shannon-Wiener Index (H’) average values at the adjacent grazing area as compared to the nature reserve area at ANR. Roodeplaat Nature Reserve (RNR) and Suikerbosrand Nature Reserve (SNR) had two paired sites with high H’ average values in the nature reserve as compared to the adjacent grazing area. The vegetation structure was similar for the three study locations, consisting of graminoids, herbs and isolated patches of shrubs. The species composition showed similarities between ANR and SNR sites, while RNR showed different species composition. SNR soils had the highest organic carbon (OC), total Carbon (C), total Nitrogen (N), Calcium (Ca), Potassium (K), Magnesium (Mg) and Sodium (Na) as compared to both ANR and RNR. Species richness had a significantly positive relationship with Organic Carbon and Total Nitrogen. Species diversity difference was detected between the nature reserves and adjacent grazing areas and the difference are likely due to a number of factors including soil properties, land disturbance and land use and management. More research is necessary to further understand the aspects impacting species richness, species diversity and species composition in grasslands. / School of Agriculture and Life Sciences / M. Sc.

Thesis (MTech (Applied Sciences))--Cape Peninsula University of Technology, 2007 / Changes in plant specIes richness and diversity were investigated in Rocherpan Nature Reserve across a fence (or old fence line) separating 34 years of conservation management, conservation management for 11 years south and north, natural veld grazed by cattle and goats, natural veld grazed by sheep, and strip-ploughed veld grazed by sheep. Vegetation surveys were conducted in September 2001. The modified 20 m x 50 m Whittaker plot design with its attractive features of long-thin plots and the original Whittaker plot design were used. Number of species (as richness data) and the numbers of individual recordings per species per land use (as abundance data) were used in calculations in the 20 m x 50 m (1000 m2 ) plots. The species richness index showed significantly smaller numbers of species in the conservation management 11 years south land. The results also showed an increase in species numbers under the grazing land use systems. The data from the comparative study of the five different species diversity indices showed no significant differences. As a result, the Shannon-Wiener index was selected for further assessing the species diversity index and the species diversity significance of different land uses in the West Coast Strandveld. In this particular study, the species that showed an increase in vegetation cover in response to grazing land use regimes were Hemimeris racemosa (annual herb) and Ehrharta brevifolia (annual grass).

Recent management efforts in the Smith and Bybee Lakes Wildlife Area (SBL), a 700-ha preserve in north Portland, Oregon, have included using a water control structure to suppress invasive reed canarygrass (Phalaris arundinacea L.) by flooding during spring and early summer growth periods. For the first year of managed flooding, I sought to determine: (a) the extent and distribution of reed canarygrass at SBL; (b) the effectiveness of the change in water level at suppressing reed canarygrass; and ( c) the effects of the change in water level on other plant species. I established 30 vegetation transects throughout SBL before completion of the water control structure. These transects were randomly distributed, placed perpendicularly to the shorelines of the wetlands, and had a cumulative length of 3.1 km. I measured vegetation on the transects in autumn 2003 and autumn 2004 using the line intercept method at 10-cm intervals. I surveyed the transects to generate elevation profiles, accurate to 0.15 cm, to determine depth and duration of flooding, which I correlated with vegetative changes. I also monitored inundation depth, growth, and phenological response of individual stands of reed canarygrass during the 2004 growing season.

Tree clearing is practised for greater beef production and hence monetary gains from grazing systems of central Queensland. The high rates of clearing in the past and even recently (577, 000 ha/yr during 1999-2001) were mainly to develop land for pastures. The sustainability of cleared pasture systems over the long-term is questioned. Three major types of tree communities i.e. Eucalyptus populnea F. Muell., E. melanophloia F. Muell. and Acacia harpophylla F. Muell. ex. Benth. were selected on one property in central Queensland to quantify the impacts of clearing on pasture production and composition, and soil properties. The impacts were measured over time-since-clearing (recent (&lt5 years), medium (11-13years) and old (&gt30 years)) in unreplicated cleared pastures in comparison to their replicated uncleared/intact woodland pastures of each tree community. Measures of pasture above-ground biomass production on a single property over time-sinceclearing in cleared systems showed that gains were not sustained over the long-term. The difference in response to clearing between tree communities was evident and important to support the future policy decisions. The impact of clearing on soil properties (physicochemical and biological) was confirmed, and explained the lesser availability of nutrients with time of clearing in cleared pastures. The changes in some soil properties underscored the associated risks and changes in ecosystem functions due to clearing. Less litter was produced at cleared than uncleared pastures, but nutrient release was faster at cleared compared to uncleared systems. The overall effect of clearing in terms of pasture and litter production, and major soil parameters were analysed using multivariate analyses.