- Can Forest Restoration Affect the Genetic Diversity of Plants?
Restoration efforts are not merely beneficial for conserving remaining forests, but may also be the only opportunity to ensure biodiversity conservation and environmental stability over time. For example, addressing reforestation and reducing deforestation rates can lead to positive effects such as decreasing the isolation of remaining fragments (Taubert et al. 2018), while reforested areas can serve as biological corridors between conservation areas (Chazdon et al. 2017). The restoration of priority areas—especially those with high potential for regeneration—can facilitate gene flow and mitigate the decreased gene flow that inevitably follows the loss of extensive forest cover (Santos et al. 2016).
Restoration can be active or passive, or a combination of both. Active restoration involves human interventions such as planting the restoration area with native tree species by direct seeding or planting seedlings, a strategy particularly valuable on sites where propagules are missing either because of a depleted soil seed bank or lack of trees for seed dispersal (Brancalion et al. 2016). Passive restoration, on the other hand, mainly involves natural regeneration by isolating the area from further anthropogenic disturbance and encouraging spontaneous seedling regeneration (Brancalion et al. 2016, Vergara et al. 2016). Both restoration approaches can yield favorable outcomes, and their complementarity can produce ecosystem values like those found in native forests (Zeng and Fischer 2021, Crouzeilles and Curran 2016). The restoration methods used depend on many factors including availability of source populations and suitable conditions (Gastauer et al. 2021), and they can affect long-term genetic diversity.
Genetic diversity studies are crucial to identify new and better strategies for genetic enrichment (Santini et al. 2018), and to prevent negative outcomes such as genetic bottlenecks and the founder effect due to genetic drift. These studies are essential for measuring the success of environmental restoration not only during or after restoration, but also before the project is even undertaken (Granado et al. 2018). Over time, inbreeding rates and genetic bottlenecks in reintroduced populations may lead to a reduction in the quantity and quality of seeds. These deleterious effects can be substantially aggravated under severe environmental conditions, resulting in reduced population fitness. Currently, research suggests incorporating genetic connectivity into restoration planning to increase the likelihood of success (Zeng and Fischer 2021, Proft et al. 2018). Enhancing connectivity through gene flow potentially increases the effective population size (NE) (Proft et al. 2018).
To support conservation and restoration goals, understanding genetic parameters of conserved forest remnants and the influence of various restoration approaches on these parameters is essential (Mutegi et al. 2014). Many studies have emphasized the importance of genetic diversity, although most of them have found similar values for heterozygosity in restored and native areas (Sujii et al. 2019, Zucchi et al. 2018, DeWald and Kolanoski 2017, Céspedes et al. 2003). In recent years, many studies have compared the genetic diversity of restored populations to [End Page 152] natural populations. The results have been inconclusive due to differing factors such as the target species evaluated and restoration methods used. Generally, the genetic characteristics of the first-generation trees (planted seeds or seedlings) will determine the population's potential to adapt and reproduce for long-term survival (Aavik and Helm 2018). Thus, restoration practioners need to ask whether using sources from different locations is advisable or whether using local seed sources yields plants that are more resilient to the conditions of these habitats. In this review, we summarize studies that have evaluated the genetic diversity of restored areas compared to natural forest remnants, and discuss the effectiveness of forest restoration in maintaining genetic diversity, depending on the restoration strategy chosen.
We searched for published papers indexed in Scopus, Web of Science, Google Scholar and Scielo from 2000 to 2022. For the search, we built strings composed by the following keywords: Forest restoration, Genetic diversity, Gene flow, and their variations (i.e., "genetic variability" OR "genetic diversity" OR "genetic variation" AND "Forest restoration" OR "landscape restoration" OR "ecosystem restoration"). When our searches returned over...