1. Introduction
Weeds are adventitious plants that grow in crops without being sown intentionally but can play a crucial role in these systems [
1]. These plants have short life cycles, produce abundant seeds, and form seed banks in the soil that ensure their persistence over time in various ecosystems [
2,
3]. Due to their nature, they can positively or negatively affect agricultural environments, either through soil conservation [
4], associated beneficial fauna and allelopathic effects on crops [
5], or due to the intense competition exerted by some species for resources such as nutrients, water, and sunlight [
6,
7]. Some studies suggest a high correlation between severe soil disturbances, with an increase in annual weed communities [
8,
9]. However, although tillage stimulates the germination of weed seeds dormant in the soil, the effect caused by this and other cultural practices on seed banks depends on the weed species and the interactions with the environment [
10,
11,
12]. Thus, the diversity of weed species that comprise the seed banks could fluctuate over time and with different crop rotation systems [
13]. In this way, understanding the dynamics of weed communities subjected to different anthropic pressures in different agricultural systems could help design more efficient and environmentally friendly management strategies.
Biodiversity and ecological dynamics of weed communities in agricultural production systems have been the subject of recent studies due to the negative impact that human activities have on these highly modified environments [
10]. Authors have suggested that the composition of weed communities in agriculture shows a wide variation related to the different types of crops and the historical uses of the soil [
2]. For example, in a study that evaluated seed bank dynamics for five years under a corn-soybean rotation system, seed density in the soil decreased by almost 90% during the first year under a productive system based on corn, and the trend was maintained by rotating with soybeans during the following years [
2]. Thus, understanding the diversity variability of weed communities in areas under different anthropogenic pressures, including various crops and associated tasks, is essential to identify problematic species in agricultural production systems and developing more efficient and sustainable management strategies [
14]. However, even though in recent years there has been a growing interest in understanding the ecology and diversity of weed communities in agricultural areas with high anthropogenic pressure, little has been studied in the northern region of the Andes, where urban and agricultural expansion have generated highly disturbed scenarios [
15].
In the northern part of the Colombian Andes, agriculture, livestock, and urbanization have historically caused significant impacts on plant cover, generating drastic changes in soils and promoting the colonization of weeds, many of these invasive [
15,
16]. For example, a study carried out in a production system of roses under greenhouse conditions in the Sabana de Bogotá area to evaluate the diversity of weed species in cultivated fields registered 46 species, of which two,
Cardamine hirsuta and
Pennisetum clandestinum, showed a marked dominance with 67% of the total plant cover [
17]. Similarly, in a peach orchard in the same region, a low species diversity was found, with a high dominance of
Oxalis corniculata reaching 68% coverage [
18]. However, some weed species in this Andean area have become a serious problem in forested areas without agricultural pressure, as is the case of the invasive species
Thunbergia alata, in which an average density of 493 seeds/m
2 has been documented, with a viability of 100% stored in the soil [
19]. This suggests that the various aspects of the life histories of weeds could be related to the structuring of communities, according to anthropogenic dynamics that alter natural ecosystems, both in cover and in seed banks in the soil.
Understanding the diversity of species that comprise seed banks can provide valuable information on the relationships of weeds with their environment [
20] and the effect of transforming natural areas into different agricultural contexts. Such information could help minimize the use of herbicides and agricultural inputs, contributing to the conservation and health of ecosystems [
21]. In this sense, the aim of this study was to analyze the diversity of vegetation and weed seed banks in four areas of the northern Andes of Colombia under different anthropogenic pressures (little intervened forest, and vegetable, avocado, and livestock farming), with the hypothesis that species diversity changes according to the type of intervention, and that some dominant species can be identified as specific indicators of each system. Consistent with this, the following questions will be answered: (a) Can differences in the diversity (Alpha) of the weed communities of the seed banks between the different agricultural production systems and the forest ecosystem be observed? (b) Are there differences in weed species composition in the soil seed banks between the agricultural production systems and the forest ecosystem (Beta diversity)? (c) Which weed species in the seed banks of the soil manage to manifest themselves in its surface vegetation and can potentially be considered "weeds"? (d) Will a higher dominance of weed species be observed in the ecosystems most affected by human activity? (e) Which weed species could be considered indicators of each evaluated system?
This work will provide novel information related to the composition of the weed communities in the seed banks of little-studied areas with different anthropic impacts. It will also provide basic knowledge on patterns of diversity and ecology of different weed species associated with anthropized ecosystems in one of the most diverse regions in the world and with high rates of endemism, as is the northern area of the Andean mountain range in Colombia [
22]. These findings may contribute significantly to integrated weed management plans, prioritizing those that show a marked dominance and that could be considered specific to each productive system evaluated.
4. Discussion
Human activities exerted on ecosystems can have an impact on the ecological dynamics of weed communities, as well as on the composition and dominance of species [
44,
45,
46,
47,
48]. Among these activities, agriculture and deforestation have been identified as the leading causes of impacts on natural areas [
47,
48]. Although several studies have documented variations in the diversity of weed communities related to disturbances [
10,
14,
47,
49,
50], in the Andes, there is a shortage of research that evaluates the effect of anthropogenic disturbance associated with different agricultural practices on weed vegetation cover [
17,
51]. In this work, the taxonomic diversity of weed communities in one of the areas of greatest anthropogenic pressure, the northern Andes in Colombia, was studied by comparing the surface cover and the soil seed banks in three intensive agricultural production systems and a slightly intervened forest ecosystem.
Our results indicate that, despite finding no significant differences in weed richness between the compared areas (Alpha q0), variations were observed in the composition of the communities, mainly reflected in the high turnover values (βC-bal) and minor nesting (βC-gra). In addition, the diversity profiles were less equitable in the agricultural production systems compared to the forested area, suggesting a higher dominance of species considered "weeds," which have a negative economic impact on these production systems. Additionally, the second order Beta diversity (β2) for the seed banks [0.15; 0.91] suggests that weed communities under different anthropic pressures have similar structuring patterns in which dominance increases, but differences in dominant species are probably the result of contrasting life histories that allow them to respond in different ways to selection pressures generated by human activity.
Several studies have documented the differences in the composition and abundance of weed species between production systems and forest ecosystems and attribute these changes to variations in the growth habits of the species and the agricultural management supplied to the weeds to control their growth [
10,
45,
52,
53,
54]. Likewise, previous studies have shown that the composition of weed communities in soil seed banks is influenced by human activities [
2,
47]. Similarly, recent research suggests that differences in weed species composition between natural ecosystems and agricultural production system areas are subject to constant anthropogenic disturbances caused by tillage, with higher dominance of weed species in agricultural systems that have experienced major interventions [
10,
45,
47,
55,
56]. Thus, the disturbance frequencies governed by tillage in production systems generate notorious changes in the weed community, where highly disturbed environments tend to be simpler and less stable in the abundance of weed populations [
10,
45,
47,
55,
56]. For example, as a disturbance in soil seed banks increases in corn, soybean, and oat cropping, the dominance of weed species capable of adapting to these areas tends to increase [
57,
58]. Similarly, it has been observed that the weed communities in the forest cover do not reflect dominance in the most conserved areas, in contrast to the most intervened areas, such as cropping fields, being the species of the conserved ecosystems less abundant and competitive. [
48].
However, cases have also been reported where, in agricultural production system areas, the abundance, diversity, and uniformity of the weed community in the seed banks tend to increase as the disturbances caused by soil tillage decrease [
55]. Gurber & Claupein [
60] recorded a higher abundance of weed species in more conserved areas compared to those highly disturbed. These authors relate their results to the high capacity of weeds to produce a large number of seeds that persist in the soil forming seed banks, also suggesting that the physical and chemical characteristics of the soil can influence the diversity of weeds in less disturbed ecosystems.
Sharp [
61] argues that the differences in the life cycles of the weed species (annual vs. perennial) may influence the dominance of the species. It has been documented that environments with high anthropogenic disturbances favor the growth of weeds with annual cycles, which have the capacity to grow rapidly when tillage is interrupted, reaching reproductive maturity in a short time [
8,
9,
10]. This allows the species to produce a large number of seeds in a single season, increasing their ability to disperse and colonize open areas [
10,
62,
63,
64]. In addition, it has been indicated that the notable abundance of weed species in cultivated areas and pastures may be related to reproductive strategies and seed dispersal mechanisms, allowing the species to expand to new habitats and quickly colonize those disturbed areas [
10,
48]. These studies support the current results since, in the agricultural production systems, there was a marked dominance and abundance of weed species with annual cycles, including
Trixella arvensis, Verbena litoralis, Cardamine hirsuta, Polygonum nepalense, and
Gnaphalium Americanum. The only exception was
Oxalis corniculata. The species found in the current study as dominant, which could be considered weeds in agricultural production systems, show certain characteristics that allow them to dominate agricultural areas. For example, it has been reported that the high abundance of the species
Cardamine hirsuta in horticultural crops could be related to its ability to easily adapt to disturbed environments and grow in open habitats with higher availability of direct light [
17]. Likewise, its reproductive capacity gives it advantages to dominate, since it is a species with a short cycle (annual) and a high germination potential; it has been recorded to produce approximately 5,000 seeds with germination percentages higher than 90% [
65,
66]. In addition, this species has self-dispersal mechanisms, favoring its dominance in anthropized environments [
17,
65,
67]. Similarly, it is argued that the dominance of
Oxalis corniculata in crop fields is related to its polymorphic reproduction since it is a species capable of easily reproducing both by seeds and vegetatively [
68,
69]. Conversely,
Polygonum nepalense has been reported as a weed in productive systems of the Colombian Andes, and its dominance is due to its reproductive traits through the production of a large number of seeds (approximately 27,900/m
2), having the ability to survive for long periods in the soil and form seed banks, in addition to having a wide range of adaptation to disturbed ecosystems [
17,
70,
71].
Other findings correspond to the fact that the diversity of soil seed banks was higher in the less disturbed ecosystem. These findings are reflected in high values of first- and second-order Alpha diversity (q
1 and q
2) in the forest ecosystem, presenting a more equitable and homogeneous behavior in terms of its species, and are supported by previous research. For example, Mitja & Miranda [
48] found similar results, indicating that forest covers with some degree of conservation may show a higher diversity of weed species, and the diversity in this type of habitat may be related to the stability dynamics of forest ecosystems [
45]. In line with these findings, in the current study, the weed community in the soil seed banks and the surface vegetation of the forested area were found not to show competitiveness characteristics. These results support the idea that less intervened ecosystems offer favorable conditions for the coexistence of multiple weed species in an equilibrium [
45,
46].
On the other hand, the weed communities in the soil seed banks in the agricultural production systems showed a lower first- and second-order Alpha diversity compared to the forest ecosystem. These results agree with previous investigations, indicating that the low diversity of weeds in soil seed banks is a consequence of the high disturbance pressure exerted by man on agricultural systems for their control [
45,
72], where intensive management practices can favor the growth and establishment of some weed species while restricting the development of others [
45,
46,
72]. Therefore, agricultural management, including selection pressures in production systems, could be a contributing factor to the low weed diversity observed in these environments [
10,
44,
45,
46,
56,
62].
The agricultural production systems assessed have historically experienced various types of agricultural management to control weed populations. Among these management practices, the application of herbicides and overgrazing stand out in livestock areas. In avocado and vegetable production systems, soil tillage practices are highlighted. Some studies have reported that the diversity of weeds in soil seed banks and their surface vegetation is influenced by the type of management used in each production system, suggesting that the use of herbicides, soil tillage, or grazing result in communities of different weeds [
8,
10,
44,
45,
46,
47,
57,
73]. However, although agricultural management practices in production systems can reduce the diversity of weeds, it has been observed that the abundance of these species does not always decrease and may even tend to increase the dominance of a few species that have the capacity to easily compete with other weed species [
47,
49,
50,
74], agreeing with the results found in the current study.
The results suggest that understanding the variability of the diversity of weed communities in soil seed banks and their surface vegetation in areas under different anthropogenic pressures in the northern Colombian Andes provides valuable information on the ecological dynamics of weeds species, which could facilitate the identification of those that really represent a problem in agricultural production systems. In addition, a clear understanding of how different agricultural management practices interact to condition weed communities is a key component in the development of integrated weed management programs focused on agricultural efficiency and environmental sustainability based on ecological approaches that promote the biodiversity of ecosystems [
48,
50,
52,
59,
75,
76,
77,
78,
79].
Figure 1.
Study area. (A). Geographical location of the northern Andes, Colombia. (B). Location of the department of Antioquia, indicating the highlands of the Oriente antioqueño area. (C). Spatial location of the agricultural production systems sampled. VC= low secondary vegetation area, L=livestock production system area, A= avocado production system area, and FV= vegetable production system area.
Figure 1.
Study area. (A). Geographical location of the northern Andes, Colombia. (B). Location of the department of Antioquia, indicating the highlands of the Oriente antioqueño area. (C). Spatial location of the agricultural production systems sampled. VC= low secondary vegetation area, L=livestock production system area, A= avocado production system area, and FV= vegetable production system area.
Figure 2.
Alpha diversity profiles based on the number of equivalent species from the soil seed banks of weeds from the four production systems sampled in the Oriente antioqueño region, northern Andes, Colombia. VC= low secondary vegetation area, L=livestock production system area, A= avocado production system area, and FV= vegetables production system area.
Figure 2.
Alpha diversity profiles based on the number of equivalent species from the soil seed banks of weeds from the four production systems sampled in the Oriente antioqueño region, northern Andes, Colombia. VC= low secondary vegetation area, L=livestock production system area, A= avocado production system area, and FV= vegetables production system area.
Figure 3.
Weed species range-abundance curves in the seed banks of the sampled production systems. The names of species with abundances higher than 100 individuals are provided. VC= low secondary vegetation area, L=livestock production system area, A= avocado production system area, and FV= vegetable production system area.
Figure 3.
Weed species range-abundance curves in the seed banks of the sampled production systems. The names of species with abundances higher than 100 individuals are provided. VC= low secondary vegetation area, L=livestock production system area, A= avocado production system area, and FV= vegetable production system area.
Figure 4.
Indicator analysis of weed species of the four production systems sampled in the Oriente antioqueño region, northern Andes, Colombia. VC= low secondary vegetation area, A= avocado production system area, L= livestock productive system area, and FV= vegetables productive system area. Yellow, orange, and red colors correspond to InVal values higher than 60%.
Figure 4.
Indicator analysis of weed species of the four production systems sampled in the Oriente antioqueño region, northern Andes, Colombia. VC= low secondary vegetation area, A= avocado production system area, L= livestock productive system area, and FV= vegetables productive system area. Yellow, orange, and red colors correspond to InVal values higher than 60%.
Table 1.
Weed species abundance found in the soil seed banks of four productive systems evaluated in the Oriente antioqueño region, northern Andes, Colombia.
Table 1.
Weed species abundance found in the soil seed banks of four productive systems evaluated in the Oriente antioqueño region, northern Andes, Colombia.
Family |
Species |
VC |
L |
A |
FV |
Amaranthaceae |
Amaranthus viridis L. |
|
|
|
3* |
Apiaceae Araliaceae
|
Centella asiatica (L.) Urb |
7* |
6 |
|
|
Hydrocotyle umbellata L. |
6* |
|
|
|
Asteraceae |
Ageratum conyzoides L. |
20* |
|
12* |
|
|
Erechtites valerianaefolia C.E.C. Fisch |
5* |
22* |
1* |
|
|
Porcellites radicata (L.) Cass. |
15* |
7* |
48* |
|
|
Jaegeria hirta (Lag.) Less. |
3* |
6* |
5* |
|
|
Gnaphalium americanum Mill. |
|
110* |
60* |
9* |
|
Sonchus oleraceus L. |
|
18* |
|
|
|
Artemisia vulgaris L. |
|
5 |
|
20* |
|
Conyza bonariensis (L.) Cronquist |
|
1* |
9* |
|
|
Emilia sonchifolia (L.) DC. |
|
|
6* |
|
|
Galinsoga quadriradiata Ruiz & Pav. |
|
|
|
13* |
|
Senecio vulgaris L. |
|
|
|
3* |
|
Acmella oppositifolia (Lam.) R.K. Jansen |
|
|
|
1* |
Brassicaceae |
Cardamine hirsuta L. |
2 |
263 |
176 |
282 |
Caryophyllaceae |
Stellaria media (L.) Vill. |
46 |
1 |
8* |
2* |
|
Drymaria villosa Schltdl. & Cham |
|
|
15* |
|
Commelinaceae |
Commelina diffusa Burm. f. |
12* |
2* |
|
1* |
Convolvulaceae |
Ipomoea purpurea (L.) Roth |
|
|
|
1* |
Cyperaceae |
Cyperus odoratus L. |
67 |
83 |
48* |
12* |
|
Cyperus rotundus L. |
51 |
2 |
14* |
|
|
Kyllinga erecta Schumach. |
42 |
3 |
|
|
Fabaceae |
Mimosa albida Humb. & Bonpl. ex Willd |
3* |
|
|
|
Melastomataceae |
Chaetogastra kingii (Wurdack) P.J.F. Guim. & Michelang. |
14* |
|
|
3* |
Lythraceae |
Cuphea carthagenensis (Jacq.) J.F. Macbr. |
20* |
4* |
|
|
Iridaceae |
Sisyrinchium micranthum Cav. |
27* |
10* |
4* |
|
Lamiaceae |
Trixella arvensis (L.) Fourr. |
1 |
605* |
4* |
26* |
Phyllanthaceae |
Phyllanthus niruri L. |
2* |
|
|
|
Rubiaceae |
Richardia scabra L. |
32* |
5 |
20* |
|
Oxalidaceae |
Oxalis corniculata L. |
1 |
152* |
39* |
8* |
Poaceae |
Bromus sp. L. |
16* |
|
|
|
|
Paspalum paniculatum L. |
|
11* |
50* |
5* |
Polygonaceae |
Polygonum nepalense Meisn. |
4* |
125* |
9* |
136* |
|
Polygonum segetum Kunth |
|
1* |
|
|
|
Rumex crispus L. |
|
49* |
|
|
Plantaginaceae |
Plantago major L. |
5* |
1* |
6* |
|
Verbenaceae |
Verbena litoralis Kunth |
|
380* |
|
|
Table 2.
Alpha diversity values for the weed species registered in four productive systems sampled in the Oriente antioqueño region, northern Andes, Colombia.
Table 2.
Alpha diversity values for the weed species registered in four productive systems sampled in the Oriente antioqueño region, northern Andes, Colombia.
Diversity |
VC |
L |
A |
FV |
Total |
Observed |
q0 |
23 [18.89;27.11] |
25 [19.16;30.84] |
19 [17.59;20.41] |
16 [8.37;23.63] |
38 [32;43] |
q1 |
14.11 [13.03;15.19] |
7.75 [7.37;8.13] |
9.89 [9.10;10.68] |
4.30 [3.84;4.76] |
13.40 [12.87;13.94] |
q2 |
11.07 [9.80;12.35] |
5.47 [5.16;5.77] |
6.40 [5.48;7.33] |
2.77 [2.50;3.04] |
8.58 [8.18;8.97] |
Estimated |
q0 |
23.86 [18.42;29.30] |
27.53 [18.54;36.51] |
19.00 [17.78; 20.22] |
18.19 [8.52;27.86] |
40.19 [32.80;47.58] |
q1 |
14.39 [13.28;15.49] |
7.79 [7.40;8.18] |
10.01 [9.13;10.88] |
4.35 [3.88;4.81] |
13.46 [12.92;14.00] |
q2 |
11.21 [9.89;12.54] |
5.47 [5.17;5.78] |
6.44 [5.55;7.33] |
2.77 [2.50;3.04] |
8.59 [8.19;8.98] |
Sample coverage |
0.995 |
0.998 |
1 |
0.994 |
0.9991 |
Table 3.
Beta diversity of the soil seed banks of weeds in multiplicative partition among the four productive systems evaluated in the Oriente antioqueño region, northern Andes, Colombia.
Table 3.
Beta diversity of the soil seed banks of weeds in multiplicative partition among the four productive systems evaluated in the Oriente antioqueño region, northern Andes, Colombia.
|
VC x L |
VC x A |
VC x FV |
L x A |
L x FV |
A x FV |
β 0 |
0.29 |
0.33 |
0.58 |
0.27 |
0.51 |
0.54 |
β 1 |
0.41 |
0.46 |
0.79 |
0.24 |
0.21 |
0.30 |
β 2 |
0.84 |
0.60 |
0.91 |
0.43 |
0.41 |
0.15 |
Table 4.
Beta partitioned diversity of the soil seed banks of weeds among the four productive systems evaluated in the Oriente antioqueño region, northern Andes, Colombia.
Table 4.
Beta partitioned diversity of the soil seed banks of weeds among the four productive systems evaluated in the Oriente antioqueño region, northern Andes, Colombia.
|
β.bray.bal (turnover) |
β.bray.gra (nesting) |
|
VC |
L |
A |
FV |
VC |
0 |
0.69 |
0.655 |
0.935 |
L |
0.2 |
0 |
0.299 |
0.133 |
CA |
0.048 |
0.389 |
0 |
0.571 |
FV |
0.008 |
0.487 |
0.003 |
0 |