Planting the Seeds of Change: The Role of Plants in the Climate System

Introduction

Plants in the Climate System As they keep up with elevated atmospheric CO2 concentrations, a warming climate, and altered precipitation regimes, climate change is contributing to the rapid range shift and loss of plants and animals toward higher elevations. In order to function and survive within the temperature and precipitation ranges that they can tolerate, many species will need to relocate.

As plants are fixed, they are supposed to contrast broadly in their capacity to find climatic reaches they can endure, contingent upon their attributes and environment qualities. Quantifying species dispersal ability based on dispersal-related traits (such as vectors, seed mass, and seed/fruit types) is one way to explain how disperser species shift their range and track climate change.

Seed Dispersal: A Key Ecological Process

Seed dispersal, defined as the transport of seeds, spores, or propagules away from the mother plant, is one of the key processes in ecology and biodiversity conservation. Dispersion of seeds is the first spatial demographic process that can determine potential range shifts. It is also a critical factor driving plant ecological responses to global environmental changes.

Impact of Environmental Changes on Seed Dispersal

Environmental changes can disrupt the seed dispersal process, and such a disruption might either increase or decrease dispersal distance depending on the dispersal mode of the species. For example, anemochorous seeds (wind-dispersed) can travel much further in open or disturbed landscapes than in dense or undisturbed forests because of contrasting wind speed, direction, and intensity. Thus, any type of severe habitat disturbance will significantly alter the patterns in seed movement, recruitment, and establishment of plant populations.

Focus of Seed Dispersal Literature

However, the literature on seed dispersal is focused on the dispersal syndrome hypothesis (DSH) or co-adapted syndrome, which states that fruits and dispersal vectors co-evolved (mutualistic interactions) influencing the foraging strategies of dispersers.

A large amount of information focuses on only one environmental change driver (e.g., habitat fragmentation) affecting the seed dispersal processes. Although there are overwhelming theoretical studies on the enumeration or assessment of dispersal vectors of a particular group of plants , information on how the dispersal mechanisms of many plants evolve in a changing environment remains scarce.

Challenges in Studying Seed Dispersal in Changing Environments

While studies on how global environmental drivers and their interaction affect plant movement have considerably received much attention, the mechanisms by which changing environmental conditions affect seed transport between sites are still unclear because of contrasting results. These contrasting results are attributed to geographical locations, species life-history traits, variability in seed dispersal-related traits, habitat structure, and complex mutualistic interactions.

The seed dispersal capacities of many species are also not known, which limits our understanding of the seed dispersal disruption caused by global change drivers. Moreover, studying how plant populations track their niche through seed dispersal in a changing environment is also empirically difficult to study due to logistical and technical challenges.

Objectives of the Review

Consequently, a systematic review of the current state of the literature about seed dispersal mechanisms in a changing environment was conducted to help us understand how plants keep up with climate change as populations of dispersal vectors decline.

Geographical Distribution of Studies

The obtained literature was summarized and analyzed to give insight into the geographical distribution of studies about seed dispersal in a changing environment;how the changing environment affects seed dispersal;whether changing environment reduces or enhances plants dispersal abilities; seed/fruit dispersal-related traits, and  research directions. The present review is relevant to understanding plant seed movements in the face of anthropogenic climate change.

Importance of Seed Dispersal in Plant Ecology

Seed dispersal is critical for plant population recruitment, gene flow, long-term survival, and other ecological processes amid climate change. This has recently raised the priority of plant seed dispersal research in many countries. However, the present systematic review found very little to no data on seed dispersal research in several megadiverse and hotspot countries, suggesting that the reviewed topic has hardly been studied in many key biodiversity areas in the world.

Global Priorities in Seed Dispersal Research

As global climate change is predicted to have major effects on species’ distributions, seed dispersal research in megadiverse and hotspot countries should be enhanced to promote high species diversity. This is because the manner in how the seeds are dispersed from the mother plants determines the recruitment capacity, which is a prerequisite of plant community establishment and development. Knowledge of seed dispersal can benefit the development of effective management and conservation options for threatened species in megadiverse and hotspot countries.

Gaps in Seed Dispersal Research in Megadiverse and Hotspot Countries

Seed dispersal studies in these countries will help elucidate the temporal and spatial patterns of plant movements as well as behavioral mechanisms of dispersal agents in plant communities following global change. Field-based seed dispersal studies in megadiverse and hotspot countries will also be able to assess currently important biotic dispersal vectors for conservation as most plant species depend on animals and fungi to disperse their seeds.

The overhunting of ecologically important vertebrates, for instance, can cause vertebrate-mediated tree species to suffer from reduced seed dispersal and impoverished seedling communities in terms of diversity and seed size. Many of the hunted species are frugivores, which are major dispersers of tree and shrub seeds.

Impact of Habitat Degradation on Seed Deposition

A similar pattern was observed in a fragmented forest in Spain, such that the likelihood of seed deposition decreased significantly because there were fewer areas with trees for perches and fruit for bird dispersers. Even in an arid and semi-arid country, seed dispersal rates were significantly lower in disturbed forest habitats than in undisturbed ones, and the result was also attributed to a reduced abundance of frugivores or seed dispersers.

Comparison of Seed Dispersal in Protected vs. Unprotected Sites

A study conducted in a disturbed habitat in the Mediterranean Basin yielded a similar result, i.e., a reduction in habitat complexity negatively impacted bird abundance due to altered fruit movement and simplification of the seed shadows.

Seed dispersal was also two-fold higher at the protected than at the unprotected sites, even though both sites have been selectively logged in the past. The authors attributed the findings to changes in activity patterns, quantity, or population makeup of vertebrate seed eaters between sites, which had been subjected to the unsustainable hunting of terrestrial mammal dispersers.

Conclusions

This systematic review summarizes the existing understanding of the projected effects of changing environments on the complex processes of seed dispersal across regions. Results revealed that global climate changes, by means of altering air temperature, rainfall, wind speed, the biophysical environment (e.g., habitat quality, fruit availability) and plant/seed traits, may negatively affect the seed dispersal patterns of vertebrate-dispersed plants, thereby influencing the fate of local and global biodiversity.

The six groups of plants whose long-distance seed dispersal are seriously affected by changing environments include anemochorous, endozoochorous, epizoochorous, hydrochorous, myrmecochorous, and ornithochorous species. The present review also found that fruit/seed traits control the fate of seed dispersal depending on environmental conditions. Overall, the findings of the present systematic review provide a summary of evidence on how plants keep up with climate change as populations of seed dispersers decline.

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