# Presentation: 662085

## Plant Invasions in an Agricultural Frontier: The case of bracken fern invasion in southern Yucatán Peninsular region. 

**Plant Invasions in an Agricultural Frontier: The case of bracken fern invasion in southern Yucatán Peninsular region. **
**Laura C. Schneider**
**Department of Geography-SYPR Project**
**Rutgers University**

- Acknowledgements: This poster is supported by  the Southern Yucatán Peninsular Region (SYPR) project involving Clark University, University of Virginia, El Colegio de la Frontera Sur, and Harvard University. Its principal sponsors have been NASA-LCLUC (Land Cover and Land Use Change) program (NAG5-6046, NAG5-11134, and NNG06GD98G), Center for Integrated Studies of the Human Dimensions of Global Environmental Change, Carnegie Mellon University (NSF SBR 95-21914), and NSF-Biocomplexity (BCS-0410016).

**Land Change in Southern Yucatán Peninsular Region**

**Ejidos/Agricultural based community**

- Study Region (*Ejidos*)
- Calakmul Biosphere Reserve

- 40 km

**Calakmul Biosphere Reserve Archaeological tourism**

- (Adapted from Roy Chowdhury and Schneider, 2004)

- Deforestation hotspots from 1987-1997

- Landscape Mosaic

- Land Cover in SYPR

**Maize Cultivation**

**Cash Crop: Jalape****ño peppers.**

**Secondary Growth**

**Invasive species**

- Biological invasions are widely recognized as a serious threat to environments, economies and human welfare throughout the world. The large scale of some biotic invasions and the impact and ineffective policies and practices to prevent or control them, have made biological invasions one of the major factors that constitute global change. Research on biotic invasions, however, remains limited to trying to understand the human-environment relationships that give rise to those invasions, especially in tropical regions.

- Remote sensing analysis shows that approximately 3.8% of forest (mainly upland forest) has been lost from 1987 to 1997.  West and East regions where part of the oil boom sponsored “development programs” in the 1970s and early 1980s (e.g. cattle ranching and rice projects). Reforestation can be seen more conspicuity in those areas as well. South deforestation rates are the highest, mainly due to increase in cash crops (e.g. peppers)

- Currently, the dominant land tenure system is the *ejido*: communally managed land granted by the Mexican government. The main activity of farmers is subsistence agriculture, but recently there has been an increase in commercial cultivation of hot peppers. These and other land pressures pose various problems in concert with the needs of the conservation and archeo-tourism programs for maintenance of mature forest in the region and for lessened demands on remaining forest on* ejido* lands.

**Bracken Fern (*****Pteridium Aquilinium*****) Invasion**

- 1985  15 km2

- 1994  40 km2

- 2001  75 km2

- Regional  (years)

- Upland Forest
- Bracken Fern

**Ecological Impacts**
- “Arrested” succession (Patches up to 25 years old)
-  Increase of fire frequencies
-  Decrease in biodiversity
-  Changes on soil nutrients

- Bracken Fern in the region is usually located close to main roads and settlement areas, but  it could also be found in the areas more difficult to access and in areas surrounded by forest. The main strategies for bracken to flourish and disperse are: high resistance to diseases and pests, the presence of allelopathic substances, vegetative reproduction, the high density of the frond canopy and litter suppressing the ground flora, and tolerance to a broad range of climatic and edaphic conditions. Another factor contributing to bracken fern invasion is the resistance of the rhizome to fire and adverse weather conditions, allowing the colony to spread vegetatively. Swidden agriculture is the main type of land management in the region and fires are critical in the configuration of bracken fern distribution in the landscape.

**Patterns of bracken fern invasion**

**Linkages of Land Management Practices and Bracken Fern Invasion**

| 70% of 1, 80% of 2: attempt agriculture in fern areas | Ejido 1 w/ fern (n=24) | Ejido 1 w/o fern (n=8) | Ejido 2 w/ fern (n=10) | Ejido 2 w/o fern (n=10) |
| --- | --- | --- | --- | --- |
| Average fern plot (ha) | 19 | N/A | 4 | N/A |
| Average plot in agriculture (ha) | 3 | 5 | 2 | 4 |
| Maize yields in bracken area (kg/ha) | 250 | N/A | 120 | N/A |
| Maize yields in agricultural areas | 650 | 750 | 700 | 1100 |
| # days/ha weeding | 6 | 4 | 6 | 9 |
| Average fallow cycle | 2:6 | 2:5 | 2:4 | 2:4 |

**EJIDO 2**

**EJIDO 1**

- (a) Above ground biomass

- (b)  Biomass floor (litter)

|  | Less than 15 years  (n=8) | More  than 15 years (n=10) | p-value |
| --- | --- | --- | --- |
| pH | 7.81 ± 0.08 | 7.88 ± 0.16 | 0.263 |
| Organic Matter | 8.95 ± 1.30 | 9.08 ± 1.53 | 0.846 |
| Est. Nitrogen Release | 118 ± 4.95 | 119  ± 6.86 | 0.744 |
| P_ppm | 19.31 ± 10.6 | 11.8 ± 4.65 | 0.0610* |
| Ca_ppm | 13495 ± 2576 | 11521 ± 3481 | 0.201 |
| Mg_ppm | 330 ± 59 | 290 ± 74 | 0.231 |
| K_ppm | 577 ± 229 | 515 ± 132 | 0.484 |
| Na_ppm | 28.44 ± 3.32 | 25.7 ± 2.64 | 0.0690* |
| B_ppm | 1.56 ± 0.22 | 1.24 ± 0.14 | 0.0016* |
| Fe_ppm | 17.06 ± 5.51 | 21.1 ± 8.73 | 0.273 |
| Mn_ppm | 86.2 ±47.8 | 98.5 ± 84.5 | 0.719 |
| Cu_ppm | 4.80 ± 1.26 | 4.25 ± 2.11 | 0.531 |
| Zn_ppm | 2.15 ± 0.38 | 1.74 ± 0.81 | 0.219 |
| Al_ppm | 106.7 ±61 | 179.7 ± 115 | 0.126 |

**Conceptual Model of Bracken Fern Invasion in the Southern Yucatán**

- Weeding, fire control
- (unstable)

- Smaller plots, shadow, lack fire, closer distance to forested areas,
- cutting and weeding

**Land clearing: human or environmentally driven**** **

**Upland Forest-**
**Secondary Vegetation**

**Agriculture (milpa), pasture, agro-forestry, hot peppers**

**Succession**

- Abandonment/areas closer to bracken fern plots; northeast facing slopes

**Bracken Fern**

**Fire**

- Increase in Bracken Fern biomass, size of plots, and flammability. Decrease
- in P, increase in Al.

- Land clearing, change soil nutrients: short term increases in fertility

- Eradication of bracken by manual labor

**Land Tenure**

- At least four types of land tenure exist in the region: *ejido* land (largely usufruct), private land (largely ranches), forest extensions (*ampliaciones*) and National Land, the latter assigned exclusively to the Calakmul Biosphere Reserve. Private lands have the highest density and largest increase of bracken fern areas, followed by *ejido* land; bracken fern is almost absent in forest extensions and in the Calakmul Biosphere Reserve. This result is expected because the invasive species requires land clearing and frequent fires to establish itself; those disturbances are mainly driven by human activities taking place in *ejidos* and on ranches.

- The two *ejidos* examined here were selected using information on fern density derived from 1997 satellite data. The selected *ejidos* represent high density (ejido 1) and low density (ejido 2) of fern invasion respectively. A stratified random sample of 46 farmers in the two villages was selected for interview; the interviews were conducted between January and June 2002. The land-use history and current land conditions of these two case-study *ejidos* may be contrasted. One, a relatively new *ejido* characterized by high land pressures, strong involvement in cropping, has the highest percentage of forest and lowest percentage of bracken fern areas. The oldest *ejido* characterized by low land pressures and a more recent disinvestment in cropping, has the highest percentage of bracken fern invasion.

- (Adapted from Schneider and Geoghegan, 2006)

- Results of modeling suggest that farmers with smaller land holdings, specifically with smaller amounts of remaining forest, were less likely to abandon invaded areas. Also, the influence on the wage rate, proxied via the education variable, demonstrated that farmers with greater off-farm labor options were more likely to abandon an invaded plot. Finally, potentially important policy-relevant results from this study indicate that farmers who keep their agricultural plots in continuous production for longer periods are less likely to abandon these plots after invasion.

**Modeling land abandonment and bracken fern invasion**

- As many governmental and non-governmental organizations are involved with trying to reduce deforestation in the region to help protect biodiversity and other ecological goods associated with the Calakmul Biosphere Reserve, any policy designed to affect land use decisions in the region must take into consideration the impact on the spread of bracken fern and the response of farmers to the invasion.

**Ecological mechanisms of bracken fern invasion**

- Fire regime

- Fire regime

**Soil Nutrients in bracken fern fields of different length (years) of invasion**

- Above ground biomass and biomass floor for bracken fern in plots of eastern *ejidos *differentiated by the last time they burnt. Also, the same values are shown for 2-5 year secondary growth and Mature forest in the region (data taken from Lawrence and Foster, 2002)

- The above results indicate an increase in floor biomass by bracken fern individuals the longer the period without fires. Bracken fern floor biomass is prone to fires, and, through this strategy of promoting fire, it is very rare that a large invaded parcel (more than 10 ha) does not burn on a yearly basis. It is also important to notice that allelopathic substances are produced by bracken fern litter, which could limit the growth of other colonizers.

- To evaluate the effect of length of bracken fern establishment on soils, the samples were divided in two groups: plots that have been established for 15 years or more, and plots established between 5 and 15 years. The nutrient showing the highest statistically significant difference between the two groups is P. The result indicates a lower concentration of P in soils that have supported bracken fern for longer periods of time. There is also a lower concentration of B and K but higher levels of Al.
- The results indicate some of the long-term effects of invaded areas on soil nutrients: decrease in P, Na and B. Nitrogen levels do not seem to be affected by the invasion. A nutrient that limits growth in the vegetation in the region is P — a decrease in P could make it more difficult for secondary vegetation to compete successfully with bracken fern. The increase of toxic elements such as Al and Cu could have similar impacts.

- 5 km

- 2 km

- (Schneider, 2006; JLAG)

- Contact Information:
- Laura C.Schneider
- laschnei@rci.rutgers.edu