This was one study i looked at that had the most pertinent information on rainforest regrowth. Generally, a very hard thing to accomplish, regrowth from cleared land is an object we as a group would like to see. Then, not only could we protect the rainforest and fight a battle of attrition, but we might actually replace the lost territory. That means we can create the richness, the full flavor of the forest. So, no matter how slim a chance, any type of regrowth effort or study could be put to very good use. This coupled with the study on planting of shoots and other regenerative properties of some flora, we might be able to succesfully enact a proactive rainforest growth project.

   The study highlights the main biotic and abiotic factors that influence the patterns of Neotropical secondary forest successions, referred as the woody vegetation that regrows after complete forest clearance due to human activities. It focuses on both patterns of species replacement and various processes that occur during succession, and suggest that the sequence of processes may be predictable even if species composition is not.
    Tropical secondary forests are important as timber sources ,providers of environmental services such as protection from erosion and atmospheric carbon fixation templates for forest rehabilitation , refugia of plant biodiversity in fragmented landscapes, and as local providers of medicinal and useful plants . In addition, the area of tropical secondary forest is predicted to increase in the next century due to industrialization and urbanization processes, which often lead to an
abandonment of agricultural activities . Because of fast-growing properties of secondary forests and the current pressures on old-growth forests in many Neotropical locations, they hold
enormous but yet untapped management potential. Although we recognize that legal aspects  as well as technical and political interventions play a key role in influencing
secondary forest utilization in the Neotropics, there is still a tremendous need to understand and further refine our knowledge of ecological processes involved in secondary succession, so that such processes can be
adequately considered in the management of this resource.

    Secondary forest succession has been extensively described throughout the lowland Neotropics for many decades  and understanding how forests recover after clearance is still a current research topic both for basic and applied purposes  Most commonly, the structural characteristics of thedeveloping forest 9e.g., basal area, biomass, species richness, and species composition) are studied, and occasionally functional characteristics are measured. This bias has allowed secondary forests to be relatively well defined from a structural perspective, relative to old growth conditions . Despite the theoreticalframework, there has been little scientific integration of the structural and functional characteristics and processes that occur during secondary succession. Much of the emphasis in secondary succession has focused onwhich species or group of species dominate which stages of succession . From a functional perspective, however, ecosystems may recover functions long before they recover, if any, floristic similarity to previous conditions. For example, growth of roots, regardless of species, may serve to reduce soil erosion and allow plants to uptake nutrients that might otherwise be leached. In addition, recovery of leaf area through the growth of the forest canopy casts shade, reducing soil temperature and soil water evaporation. This functional perspective to examining succession stems from the hypothesis that there is ecological redundancy among plant species, i.e., from an ecosystem standpoint many plant species can perform similar functions. Thus another way to approach secondary forest succession is to ask when ecosystem function returns to pre-disturbance levels.

    In general terms, secondary forest succession is influenced by stochasticity, a species' biology, and its interaction with other species (either between plants, or between plant and animals), and by the interplay of biotic and abiotic components (vegetation and climate). All these factors ultimately determine a particular floristic composition at a given age (stage) and also influence the degree of structural and functional recovery of the original vegetation. Therefore, secondary forest succession can be visualized as a continuum from an early stage where the factors that govern colonization are most important (i.e., substrate conditions for germination, timing of seed arrival via off-site dispersal, presence of soil-stored seeds and resprouts), to later stages where competitive ability and tolerance of environmental conditions among species (determined primarily by species-specific growth rates, longevity, maximum size at maturity, and degree of shade tolerance) largely dictate patterns of species replacement over time (Walker and Chapin, 1987).
 
 
 
 
 

Regerative factors and sections.
 
 
 

Buried seeds in the soil, as well as recently dispersed seeds, contribute to the development of secondary vegetation. However, the share of soil-stored seeds to forest regrowth appears more important , especially when land use intensity before abandonment has been low-to-moderate. Even though the density of soil-stored seeds is reduced when the site has been burned its contribution to immediate post-disturbance regrowth is usually much more than that of recently dispersed seeds for most species ( Young et al., 1987). Increased levels of incident light or temperature stimulate seed germination  of early colonizing species  Although there is large variation in seed longevity in the soil in those tree species that dominate secondary stands, it usually does not exceed 1 year after dispersal.  Thus, canopy dominance of light-demanding tree species during secondary succession is largely dependent on recent seed dispersal following site abandonment. Therefore, the probability of site colonization may be low for those tree species that either do not reproduce annually, or that are located at a critical distance, as spatial limitations to seed dispersal into open areas may be very strong only a few meters beyond the forest¯non-forest interface. This causes for extrodinairily slow regrowth rates.

As intensity of land use increases, the potential of secondary forests to regenerate from soil-stored seeds  diminishes. For example, Aide and Cavelier (1994) suggest that in severely degraded grasslands in the Sierra Nevada de Santa Marta, Colombia, forest regeneration from the seed bank is of minimal importance .  Usually, the vegetation that develops right after clearing of old-growth forest tends to be poorer both in terms of species richness and abundance than that arising from cleared sites previously supporting successional vegetation. Because most of their component canopy species are unable to regenerate in the understory, drastic canopy removal seems necessary for sustained tree regeneration after timber harvesting; but at the same time, there is a high potential for competing vegetation that arises from the seed bank to interfere with tree seedling establishment and growth once the canopy has been opened. This scenario is likely to occur in secondary stands as a rule, as they are usually located within agricultural land.

 Post-dispersal seed fate

After seeds are dispersed, another important obstacle to tree establishment can be seed predation. Seed removal (a surrogate of predation) was higher in abandoned slash-and-burn farms than in adjacent forest in the upper Río Negro, Venezuela  also reported in Paragominas, Brazil, higher rates of seed removal by ants and rodents (>80% removal within 20 days for six out of 11 tree species examined) in abandoned pasture than in adjacent forest. In their study, the probability of seed arrival into pastures was higher for smaller-seeded species, but the probability of seed predation in the pasture was lower for larger-seeded species. Therefore, small-seeded species were not as dispersal limited as large-seeded species, but these on the contrary, had a greater chance of getting established. In contrast, Holl and Lulow (1997) observed no obvious correlation between seed size and seed removal rates in an abandoned pasture in Costa Rica. This discrepancy is perhaps due both to differences in community composition of seed predators between localities, and to differences in the extent of site degradation and type of plant cover. Thus, the net effect in predation rates between pasture and adjacent forest microhabitats appears site-specific: for a suite of tree species in each of the following studies, Aide and Cavelier (1994) found higher seed removal in forest, Nepstad et al. (1996) found the opposite trend, while Holl and Lulow (1997) detected no major differences between both microhabitats. At any rate, it seems that most studies carried out so far in the Neotropics on early forest succession have focused mostly at the seed level.
 
 

Light environments and forest succession

Light availability is a crucial abiotic resource that affects plant establishment and growth in moist and wet tropical forests.  Light may not be a limiting factor for early plant establishment in recently abandoned areas but in young stands, light limitation in the understory is expected to be high due to the formation of a dense canopy. At intermediate stages, and because secondary stands generally are even-aged, one would expect their canopies to be fairly homogeneous with few, small-sized gaps. In fact, the canopies of secondary forest stands in Costa Rica and Panamá had a higher frequency of understory microsites at intermediate light levels than old-growth stands which in turn, showed relatively more both low- and high-light microsites , although average light availability was similar among stand types.

It appears that after a few decades after site abandonment, rates of treefall gap formation greatly increase in neotropical secondary forests due to canopy senescence of early colonizing tree species. At the time the observations were initiated, the forest was 60 years old and no gaps were present in their 1.5 ha study plot. However, rates of gap formation and gap size had increased consistently over time. If similar patterns are found in other Neotropical locations, it would suggest that invasion of later plant colonists could be indeed suppressed or at least slowed down for many years probably due to light limitation. Gaps, however, also create soil disturbances and affect belowground processes (Ostertag, 1998) and thus the potential effects of these changes on species replacement also needs to be considered.  The species that dominate the canopies of secondary forests may also affect light availability and further affect successional trajectories.

Development and maintenance of soil properties

While light has been demonstrated to be extremely important to plant establishment in closed-canopy tropical forests, soil properties are also likely to affect the growth and species composition of colonists on deforested land. Many dramatic changes in soil properties occur after deforestation and the burning that often accompanies it . One of the most significant impacts is the loss of soil structure, as evidenced by increases in bulk density and decreases in soil porosity. A variety of chemical changes also occur after land conversion, but it is more difficult to generalize about the directionality of these processes. The loss of soil organic matter (SOM) can be particularly detrimental because SOM stabilizes soil aggregates, increases the water-holding capacity of soils, and serves as an energy source for soil decomposers; SOM alsoinfluences soil fertility by (1) holding onto organic forms of nutrients and (2) its high cation exchange capacity (CEC). A high CEC facilitates nutrient uptake by allowing cations adsorbed to the soil or SOM to be easily replaced by other cations in solution  Thus, in the long-term, deforestation can increase soil acidity and reduce soil fertility.

Additionally, the role of nitrogen in secondary succession deserves special attention because of its potential for loss in tropical ecosystems (. During land clearing, N is lost mainly through biomass removal, volatilization during burning, denitrification, and leaching ( Robertson, 1984; Keller et al., 1993). However, N levels in the soil can be increased after deforestation. For example, after felling and burning Costa Rican pre-montane wet forest, NO3 and NH4 levels increased and persisted for 6 months at levels much higher than adjacent secondary forest .


 
 
 
 

Regrowth rates and types

    Under light-to-moderate land use intensity, and when seed sources are nearby, (woody) plant species richness rapidly increases during the first years of secondary forest succession, and it takes no more than a few decades after abandonment to reach values comparable to old-growth forest . However, as intensity of past land use increases, slower recovery of species richness is expected due to soil compaction, propagule dispersal limitation, and fire occurrence.
    Plant size class needs to be taken into account when examining recovery of species richness during succession, because richness and abundance are positively correlated.  Thus, species richness in secondary stands tends to be more similar to old-growth forest when dealing with smaller (i.e., more abundant per unit area) than larger size classes. In slash-and-burn sites in the upper Rio Negro basin of Venezuela and Colombia, at least 40 years were required for species richness of stems 10 cm DBH to attain similar values to that of mature forest, although species richness recovered much more rapidly (between 10 and 20 years) in smaller (>1 cm DBH) individuals. Similarly, in 16¯18-year-old secondary forests that regrew in moderately used pastures in Costa Rica, plant species richness was much lower than that of old-growth forest for stems 10 cm DBH, but comparable in smaller-sized stems (Guariguata et al., 1997). In a replicated forest chronosequence in central Panamá, also reported no obvious variation in species richness of woody seedlings as a function of stand age compared to old-growth levels. In subtropical Puerto Rico, plant species richness of woody stems 1 cm DBH in abandoned pastures was similar to that of old-growth forest but not before 40 years after abandonment (Aide et al., 1996), an estimate slightly higher than those mentioned above. The fact that plant species richness in small size classes rapidly reaches old-growth forest values in all these studies mentioned, also suggests unlimited propagule dispersal from nearby sources.

While plant species richness in secondary forests can approach old-growth values within a few decades after site abandonment, returning to a species composition similar to old-growth forest will be a much longer process, particularly for canopy trees due to their slow turnover time
 

Accumulation of biomass

Typically, secondary forest succession is characterized by shifts in the biomass allocation of the plant community . In early succession, relatively more biomass is allocated to resource acquiring tissues (leaves and fine roots) and in later stages more is allocated towards structural materials (woody stems and coarse roots). Fine root (<2 mm diameter) biomass accumulates at a slower rate than leaf biomass, but its recovery can still be quite rapid. Secondary forests can have greater fine root biomass than plantations of similar age (Cuevas et al., 1991). Secondary forests can also have similar or higher fine root biomass than old-growth forest. Fine root length densities (cm root/cm3 of soil) in 15 year secondary forest can be higher than in old-growth forest in eastern Amazonia .

The regenerative power of Neotropical forest vegetation is clearly high, if propagule sources and land use intensity before abandonment has not been severe. Nonetheless, the recovery of biophysical properties and vegetation is heavily dependent on the interactions between site-specific factors and land use, which makes it extremely difficult to predict successional trajectories in anthropogenic settings. Considerations of site history have provided many useful insights into how Neotropical forest structure and function is influenced by human activity (e.g., Garcia-Montiel and Scatena, 1994; Foster et al., 1999), but as yet we are unable to develop a deterministic model of how land use history and intensity affects tropical forests.

Despite the difficulty in predicting species replacement patterns, the study hypothesizes that there is a sequence of events and processes that occurs during secondary succession, regardless of the species composition. This sequence begins with initial site colonization, progresses through canopy closure, recovery of species richness, increases in basal area and biomass, and ends with a return to a species composition similar to old-growth conditions. During early stages of succession, factors governing site colonization (e.g., seed dispersal, biophysical characteristics, remnant vegetation) are very important. After canopy closure, nutrient cycling rates and productivity tend to be high, until biomass and basal area begin to level off, but not reach old-growth conditions. After natural gap formation starts in the forest, long-lived pioneers dominate the canopy, the appearance of very large trees leads to aboveground biomass values similar to old-growth conditions, and productivity tends to asymptote. It hypothesizes that this sequence of events occurs in all successions, and suggest that many forest functions and characteristics may resemble old-growth conditions long before species composition does. This hypothesis raises many questions such as the length of time it takes for a forest to return to previous rates of desired ecosystem services, and how these rates are affected by past land use history, environmental conditions, and present management practices. These questions are important not only for those trying to restore tropical forests but also for those interested in production purposes.