Differences in nutrient-use efficiency have been attributed to differences in leaf habit. It has been suggested that evergreens, with their longer-lived leaves, and therefore longer nutrient retention, are more efficient than deciduous species in their use of nutrients. In tropical trees, however, leaf life span is not always a function of whole-tree deciduousness, leading to the proposal that nutrient-use efficiency is better related to leaf life span than to leaf habit. It was predicted that potential photosynthetic nutrient-use efficiency (maximum potential photosynthesis/leaf nutrient content) would decrease with increasing leaf life span, whereas cumulative photosynthetic nutrient-use efficiency (carbon assimilated over a leaf's life span/total nutrients invested in a leaf) would increase with increasing leaf life span. Potential and cumulative photosynthetic nutrient-use efficiencies (with respect to nitrogen and phosphorus) were measured for three fast-growing tropical trees: Cedrela odorata L. (Meliaceae), Cordia alliodora (R. & P.) Cham. (Boraginaceae), and Hyeronima alchorneoides Allemão (Euphorbiaceae). Mean leaf life spans of the three species varied about threefold and ranged from 50 to 176 days. The predictions were partially supported: Cedrela odorata had the shortest-lived leaves and the highest potential nitrogen-use efficiency, whereas Hyeronima alchorneoides had the longest-lived leaves and the highest cumulative nitrogen- and phosphorus-use efficiencies. Potential phosphorus-use efficiency, however, was invariant among species. It is suggested that there are potential tradeoffs between leaf characteristics that lead to high potential and cumulative nutrient-use efficiencies. High potential nutrient-use efficiency may be beneficial in high-nutrient environments, whereas high cumulative nutrient-use efficiency may be of greater benefit to species in low-nutrient environments.

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The effects of invasive species on community structure remain under-investigated due to the lack of long-term data. Our objectives were to examine the correlation between Lantana camara L. invasion and native species abundance, distribution, diversity, and population structure, across different forest types in a heterogeneous landscape. We examined changes in native vegetation and L. camara between 1997 and 2008. We used existing vegetation data from 134 plots spread across the 540 km 2 landscape from 1997 and re-censused these plots in 2008. We then examined the change in species richness, Shannon's diversity, evenness, and population structure of native species from 1997 to 2008. We also examined the relationship between L. camara density and species richness, diversity, evenness, and population structure. The presence and abundance of L. camara increased dramatically from 1997 to 2008. L. camara occurred in 81% of plots by 2008, compared with only 41% of plots in 1997. Similarly, the mean density of L. camara increased almost fourfold from 1997 to 2008. This was accompanied by a change in native community structure. Species richness, diversity and evenness declined significantly in some forest types, and at the landscape scale. There were also changes in the population structure of native tree species, with reductions in the density of tree saplings, possibly due to competition with L. camara. We demonstrate the pervasive threat posed by L. camara to native vegetation at the scale of individual forest types, and at the larger landscape scale, in our study area. These changes have long-term consequences for forest structure and composition.

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Invasive plant species in Indian protected areas have received relatively little attention until recently. This may partly be due to a historical emphasis on wildlife protection, rather than on a broader science-based approach to conservation of biodiversity and ecosystem functioning. A literature review of invasive plant species in India showed that nearly 60 % of all studies have been done since 2000, and only about 20 % of all studies are from protected areas. Studies from protected areas have largely focused on a small subset of invasive alien plants, and almost half these studies are on a single species, Lantana camara, probably reflecting the species' ubiquitous distribution. The spread of alien plants in India has been both ecologically and human mediated. Efforts to manage plant invasions have, in the past, been diluted by the ambivalence of managers attempting to find beneficial uses for these species. Despite growing knowledge about the harmful impacts of certain invasive plants on native species and ecosystems, their deliberate spread has continued, even till quite recently. And, despite the successful implementation of management initiatives in some protected areas, these efforts have not expanded to other areas. The lack of a national coordinated effort for invasive species monitoring, research, and management largely underlies this.

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Abstract:Forest recovery in abandoned pastures and agricultural fields is often impeded, therefore it is important to understand the factors limiting regeneration. Patterns of seed arrival and regeneration in five abandoned agricultural clearings nested within a seasonally dry tropical forest in India were examined along five transects radiating from the forest edge into the clearings. Wind-dispersed seeds dominated the seed arrival in clearings compared with vertebrate-dispersed seeds: 5563 wind-dispersed seeds and 1094 vertebrate-dispersed seeds of 14 and 13 tree species, respectively, were recorded. Numbers of the former declined steeply with increasing distance from the forest, whereas the latter showed no evident pattern with distance. Seeds of the invasive herb, Chromolaena odorata, were abundant in clearings. Although wind-dispersed seeds greatly outnumbered vertebrate-dispersed seeds, seedlings and saplings of vertebrate-dispersed species were three times more abundant than those of wind-dispersed species, indicating distinct differences in patterns of actual and effective seed dispersal. This points to recruitment limitation, and suggests that seed arrival may not be the principal barrier to regeneration in these clearings. Nonetheless, the clearings are likely to revert to forest over time.