Primary Forest Remnants Research Articles

A Simulation of Landscape-Level Stand Dynamics in the Northern Hardwood Region

(1) The STORM simulation was developed to predict the response of regional stand age structure to a given disturbance regime. The outcome of STORM depends upon rotation periods of canopy disturbance, diameter growth rates of trees, and the relative susceptibility of pole, mature and large trees to windthrow. (2) The simulation was run using data on disturbance frequencies from remnants of primary forest in western Upper Michigan. Rotation periods ranged from 69 years for > 10% canopy removal to 3734 years for > 70% canopy removal. Stands were classified into eight structural types, ranging from even-aged sapling stands to steadystate stands, which reflect the state of recovery from recent disturbances. (3) The model suggests that most (87-4%) stands in the primeval hardwood forest were multi-aged, with several major and many minor age classes. Quasi-even-aged stands resulting from catastrophic disturbance occupied 9-2% of the landscape, and steady-state stands about 3-6%. The low frequency of steady-state stands on the landscape appears to be determined primarily by the high frequency of disturbances removing part of the canopy, rather than the interval between catastrophes. (4) Sensitivity analyses indicate that changes in disturbance rates result in disproportionately large changes in the proportion of even-aged stands on the landscape, while mean canopy residence time for trees shows a damped effect.

Effects of Alien Plant Invasions on Native Vegetation Remnants on La Réunion (Mascarene Islands, Indian Ocean)

Although most of the lowland endemic forests of the mountainous Indian Ocean island of La Réunion have been converted by Man to other land-uses, relatively intact ecosystems still survive at higher elevations. Given the particular conservational value of these remnants of primary forest, detailed knowledge of the threats faced by these native ecosystems was urgently needed. Accordingly we conducted field surveys through the various plant communities on the island in order to answer particular questions regarding the vulnerability of native vegetation remnants to invasive, introduced plant species.Our results indicated that most invaders colonize human-disturbed sites most successfully. However, such alien plants are also frequent in the Réunion primary forest remnants, with at least 62 species penetrating into areas which have experienced no or little human disturbance. Nevertheless, the forest remnants were still mainly dominated by indigenous or endemic plant species and maintain what is, presumably, their original vegetational structure.The most threatening plant invaders are the trees Psidium cattleianum and Ligustrum robustwn, the bramble Rubus alceifolius, the shrubs Fuchsia magellanica and Lantana camara, and the herbaceous Hedychium gardnerianum, Boehmeria macrophylla, and Boehmeria penduliflora.We found the early stages of primary succession on young volcanic sites to be dominated by aggressively expanding populations of alien species. It appears very unlikely that native species will replace the invaders as the succession proceeds, and furthermore the survival of many indigenous species probably hinges on the active control of alien species.In order for alien plant management efforts to be successful, we propose a priority ranking based on the current and potential future extent of specific infestation, the rate of spread, the difficulty with which a species can be controlled, and its ecological impact on the areas invaded.Finally, the long-term survival of the Réunion ecosystems depends largely upon the drawing up and implementation of an adequate overall conservation policy regarding human-caused invasions by alien plants in the native vegetation.

Habitat and Seasonal Relationships of Some Cicadas (Homoptera: Cicadidae) in Central Costa Rica

The peak emergence periods and habitats of cicadas (Homoptera: Cicadidae) were examined in the central highlands of Costa Rica for several years. The region included remnants of primary forest along streams, various types of secondary habitats, and had a 4-month dry season. If cicada species have similar ecological requirements, it was predicted that some species would occupy different habitats and others would have allochronic peak emergence periods, perhaps synchronized with the wet and dry season cycle. Of the five species occurring here three {Fidicina pronoe (Walker) F. amoena Distant and Conibosa sp.) occupy secondary habitats including mixed plantings of coffee and bananas, while Quesada gigas (Olivier) and Zammara smaragdula Walker occupy forest remnants. The three secondary-forest species exhibit allochronic emergences: F. amoena emerges during the dry season, F. pronoe near the end of it and Conibosa in the wet season, Extensive censuses of nymphal casts of Q. gigas and Z. smaragdula along a stream revealed allochronic peak emergence periods, in the dry season for the former and in the wet season for the latter. Both cicadas emerge from the same patches of habitat, lending further support to the hypothesis that these species are ecologically similar. Because there is a relatively small amount of original forest cover remaining in this region today, some cicadas are adapting to secondary habitats. Habitat preferences in cicadas are probably determined, at least in part, by the feeding associations of nymphs with the root crowns of certain plants.