Questions

How do fire frequency and fire size affect the long-term population dynamics of Mulinum spinosum? Which demographic parameters contribute most to the overall effect of fire on population growth? What is the relative importance of resprouting in sustaining population increase?

Location

Grass-shrub northwestern Patagonian steppe, Argentina.

Methods

We monitored five permanent plots excluded from grazing for 6 years. We measured shrub abundance, dimensions, reproductive status, seedling emergence, and the size structure of M. spinosum, a resprouting native shrub inhabiting the northwest Patagonian steppe. Data were used to parametrize a stochastic matrix model developed to explore the influence of fire frequency and fire size on long-term population dynamics. We analyzed hypothetical scenarios that included fire frequencies ranging from one per year up to exclusion.

Results

Except for annual fires, projections show growing populations regardless of fire frequency. For fire return intervals greater than 50 years, the population becomes independent of fires, with an annual population growth rate of 5.6%. The results suggest two relevant aspects of the population dynamics of this species: M. spinosum is well adapted to the current fire frequency and its resprouting capability will allow M. spinosum to survive and persist in the community, even under frequent fires.

Conclusions

Climate change models forecast an increase in summer temperature in NW Patagonia and, consequently, an enhanced fire frequency. Fire is a driver of M. spinosum encroachment that gets worse in overgrazed grasslands. Mulinum spinosum encroachment derivate in a relative replacement of palatable grasses by shrubs changes the ecosystem functionality and reduces productivity. Controlling this process is highly difficult and we suggest a change in the land use for the areas already deteriorated.

中文翻译：

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生活在火海中：西北巴塔哥尼亚草原上的刺桐的种群动态

问题

火的频率和火的大小如何影响桑树的长期种群动态？哪些人口统计参数对火灾对人口增长的总体影响最大？在维持人口增长方面，重新发芽的相对重要性是什么？

位置

草灌木西北巴塔哥尼亚草原，阿根廷。

方法

我们对5个永久性地块进行了监测，排除了6年的放牧。我们测量了灌木丰度，大小，繁殖状况，幼苗出苗和M. spinosum的大小结构，M。spinosum是居住在巴塔哥尼亚西北部西北地区的一种重生的天然灌木。数据被用于参数化随机矩阵模型，该模型被开发来探究火灾频率和火灾规模对长期种群动态的影响。我们分析了假设情景，其中包括每年一次至排除的火灾发生频率。

结果

除每年发生火灾外，预测显示无论火灾发生频率如何，人口在增加。如果返回间隔大于50年，则人口不受火灾影响，人口年增长率为5.6％。结果表明，该物种的种群动态有两个相关方面：棘孢梭菌非常适应当前的火灾频率，其重生能力将使棘孢梭菌即使在频繁的火灾下也能够生存并在社区中生存。

结论

气候变化模型预测西北巴塔哥尼亚的夏季温度将会升高，因此火灾频率会增加。火灾是多刺梭状芽孢杆菌侵害的驱动力，在过度放牧的草原上情况更加严重。刺果木的侵蚀以灌木相对替代可口草的方法改变了生态系统的功能并降低了生产力。控制这一过程非常困难，我们建议对已经恶化的地区改变土地用途。